TABLE OF CONTENTS
PREAMBLE. ……..………………………...............................................................................................................................................v
SUMMARY OF THE PROJECT CONTENT.. ……..………………………............................................................................................vi
TABLE OF CONTENTS.……..………………………..............................................................................…..........................................vii
LIST OF FIGURES. ……..………………………..............................................................................…..................................................ix
CHAPTER I: INTRODUCTION..……..………………………..............................................................................…................................1
1.1. Motivation……..………………………..............................................................................…...........................................................1
1.2. Alternative power sources to ICE.……..………………………..............................................................................….......................3
1.2.1. Electric motor.……..………………………..............................................................................…..................................................3
1.2.2. Compressed-air engine (high pressured)……..………………………..........................................................................................4
1.2.3. Hybrid powertrain.……..………………………..............................................................................…............................................4
1.3. Classification of hybrid vehicle powertrain combinations.……..……………………….....................................................................5
1.3.1. Series HEV.……..………………………..............................................................................…......................................................6
1.3.2. Parallel HEV.……..………………………..............................................................................…....................................................7
1.3.3. Series - Parallel HEV……..………………………..............................................................................…........................................8
1.3.4. Mixed HEV.……..………………………..............................................................................….......................................................9
1.4. Design requirements.……..………………………..............................................................................….........................................10
1.4.1. Main components.……..………………………..........................................................…...............................................................10
1.4.2. Efficiency and fuel consumption.……..………………………..........................................................….........................................12
1.4.3. Battery and charging capability.……..………………………..........................................................…...........................................12
1.5. Hybrid vehicle models on the market……..………………………..........................................................….....................................12
1.6. Approach to the study.……..………………………..........................................................…............................................................15
1.7. Conclusion.……..………………………..........................................................….............................................................................15
CHAPTER II: THEORETICAL BASIS FOR CALCULATION AND DESIGN OF HYBRID VEHICLE POWERTRAIN SYSTEM........17
2.1. Perspectives about calculation and design of hybrid vehicle powertrain system……..………………………….............................17
2.1.1. Design perspectives of hybrid vehicle powertrain system.……..………………………..............................…..............................17
2.1.2. Developing the calculation and design process for the hybrid vehicle powertrain……..………………………............................18
2.2. Calculation and design basis for powertrain of hybrid vehicle.……..………………………..............................…...........................19
2.2.1. Powertrain coordination modes in HEV.……..………………………..............................…..........................................................19
2.2.2. Basis of determining the structure of the hybrid vehicle power source coordinator that uses power split device.......................22
2.2.3. Calculation basis of HEV power sources.……..………………………..........................................................…............................30
2.2.4. Powertrain energy management strategy.……..………………………..........................................................…............................41
2.3. Conclusion.……..………………………..........................................................….............................................................................44
CHAPTER III: DESIGN, CALCULATION AND SIMULATION OF HYBRID VEHICLE POWERTRAIN..............................................46
3.1. Design and calculation of HEV powertrain.……..………………………..........................................................…............................46
3.1.1. Design of HEV powertrain coordination system.……..………………………..........................................................….................46
3.1.2. Powertrain calculation for HEV.……..………………………..........................................................…...........................................47
3.2. Design of a planetary gear set for vehicle drivetrain.……..………………………..........................................................….............52
3.2.1. Calculation of gear ratios between gear pairs in the basic transmission system ......................................................................52
3.2.2. Calculation and design of gear parameters.……..………………………..........................................................….......................53
3.2.3. Analysis of forces acting on gear.……..………………………..........................................................….......................................59
3.2.4. Shaft design calculation.……..………………………..........................................................…....................................................62
3.3. Simulation in MATLAB/SIMULINK.……..………………………..........................................................…........................................65
3.3.1. Introduction to HEV series – parallel modelling in MATLABSIMULINK software.......................................................................65
3.3.2. Control algorithms.……..………………………..........................................................….............................................................76
3.3.3. Driving cycle used in MATLAB/SIMULINK……..………………………..........................................................…..........................82
3.3.4. Result of simulation.……..………………………..........................................................…............................................................87
CHAPTER IV: MAINTENANCE AND REPAIRING.............................................................................................................................99
4.1. Safety preparation before maintaining and repairing HEV.……..……………………….................................................................99
4.2. Precautions for high-voltage circuit inspection and service for HEV……………………………………….....................……..……100
4.3. Precautions to be observed when performing inspection or service in engine compartment for HEV .......................................103
4.4. Recommendation service actions for impact-damaged HEVs.……..………………………..........................................................104
4.5. Troubleshooting of HEV.……..………………………..........................................................….......................................................106
4.6. Master maintenance.....................................................................................................................................................................108
CONCLUSION..……..………………………..........................................................…...........................................................................110
REFERENCES.……..………………………..........................................................…............................................................................111
PREAMBLE
The graduation project in Automotive Engineering, titled "”Design and simulation of hybrid powertrain system characteristics for 5-seat vehicle"” is the result of our persistent efforts and the dedicated support of the faculty from the Department of Dynamic Mechanics, School of Mechanical Engineering.
I would like to express my sincere gratitude and respect to my supervisor, Dr. ……………….. for his invaluable guidance throughout the completion of this project.
I am also deeply thankful to all the lecturers at Hanoi University of Science and Technology for providing me with a strong foundation of knowledge and encouraging a spirit of creativity - essential tools as I begin my journey on a long professional path ahead.
Given my limited experience and understanding, there may be certain shortcomings in the project’s content and analysis. I sincerely welcome all feedback and suggestions from the faculty to help me improve and further refine this work.
Thank you very much!
SUMMARY OF THE PROJECT CONTENT
The graduation project titled "Design and simulation of hybrid powertrain system characteristics for 5-seat vehicle" aims to address the problem of improving fuel efficiency and reducing emissions in conventional internal combustion engine vehicles through the development of a hybrid powertrain system.
The methodology involves theoretical research, system design and calculation for a series-parallel hybrid configuration, simulation modeling using MATLAB Simulink, and performance evaluation based on standard driving cycles.
Key tools used in the project include MATLAB/Simulink for system simulation and performance analysis. The reference model is based on the specifications of the Toyota Corolla Cross HEV 1.8.
The simulation results demonstrate that the proposed hybrid powertrain system meets the original design objectives, achieving both improved efficiency and reduced emissions. The project shows high practical applicability and potential for future research and development in the field of hybrid vehicles in Vietnam.
Through this project, students have gained valuable knowledge in hybrid powertrain systems, as well as practical skills in simulation, technical analysis, and system design.
The overview of the project has 4 chapters:
Chapter 1: Introduction.
Chapter 2: Theoretical basis for calculation and design of hybrid vehicle powertrain system.
Chapter 3: Design, calculation and simulation of hybrid vehicle powertrain.
Chapter 4: Maintenance and repair.
Hanoi, July …, 20….
Student
(sign and specify your full name)
1./ ……………….
2./ ……………….
CHAPTER I: INTRODUCTION
1.1. Motivation
Environmental pollution has become an issue not only for a single country or region but also a global concern for all of humanity. The economic and social development processes of nations worldwide have caused severe impacts on the environment. These impacts have led to environmental degradation and significant changes in human living conditions. Notable consequences include climate change, global warming, ozone layer depletion, acid rain, and particularly air pollution caused by transportation activities.
In Vietnam, air pollution in major urban areas has become an urgent issue. This pollution originates from various sources, among which are the increasing number of vehicles in large cities, as shown in Figure 1. is considered one of the primary causes. This is because the level of air pollution is directly proportional to the number of vehicles on the road. According to data from the Vietnam Register, as of September 2022, there were 4,937,988 automobiles nationwide, doubling the number recorded in December 2016 (which stood at 2,516,144 vehicles).
Moreover, the technical condition of vehicles is also a critical issue. Figure 2. illustrates that most old automobiles and motorcycles, after prolonged operation, exhibit high emission levels. This is largely due to the fact that many road users in Vietnam have yet to develop the habit of performing periodic vehicle maintenance as recommended by manufacturers. Consequently, poor maintenance leads to inefficient combustion, increased fuel consumption, and a corresponding rise in pollutant emissions into the environment. Facing the severe environmental pollution caused by transportation activities, which negatively impacts human health and daily life, numerous measures have been implemented.
So, utilizing electric or hydrogen energy in transportation requires one of two solutions: either completely replacing the internal combustion engine - ICE (Battery electric vehicles - BEVs or Fuel cell vehicles - FCVs) or integrating ICE with electric motors (Hybrid electric vehicles - HEVs).
1.2 Alternative power sources to ICE
1.2.1 Electric motor
Based on the characteristic curve shown in Figure 3, it can be observed that the electric motor’s performance closely aligns with the ideal traction characteristics of an automobile. Typically, an electric motor starts from 0. As it reaches its base speed, the voltage increases while the current remains constant. When operating above the base speed, the voltage remains constant while the current decreases. This results in constant power output, while the torque follows a hyperbolic decrease as speed increases.
1.2.2 Hybrid powertrain
A 'gasoline-electric hybrid vehicle' is an automobile which relies not only on gasoline but also on electric power sources. In HEV, the battery alone provides power for low-speed driving conditions. During long highways or hill climbing, the gasoline engine drives the vehicle solely. Hybrid electric vehicles comprise of an electric motor, inverter, battery as electric drive and an internal combustion engine with transmission connected as gasoline-based drive. It is to achieve better fuel economy and reduce toxic emissions.
HEVs have been vehicles of numerous advantages. Hybrids do indeed get superior gas mileage. They use less gasoline and therefore emit less greenhouse gases. Thus, the problem of environmental pollution can be avoided to a certain extent. Apart from that they use less gasoline in comparison to the other vehicles of the same power that run only on gasoline.
=> Conclusion, in the current context, hybrid vehicles, which combine an ICE and an electric motor, are considered the most suitable solution in the transitional phase toward the development of “clean” automobiles. This approach aims to meet the strict environmental requirements of urban areas while addressing the risk of fossil fuel depletion. So, research on hybrid vehicles needs to be given greater attention and further promoted.
1.3 Classification of hybrid vehicle powertrain combinations
There are three basic hybrid powertrain diagrams:
- Series HEV - In this configuration, the ICE combined with a generator, supplies energy to charge the battery and provide electrical power to the electric motor (EM). The EM delivers torque directly to the wheels.
- Parallel HEV - This type of hybrid system allows the vehicle to be driven by either the ICE, the EM, or both. The EM also functions as a generator to recharge the battery during regenerative braking system (RBS) or when the ICE produces more energy than required for propulsion.
- Mixed HEV - This configuration integrates features from various hybrid architectures (such as series, parallel, and power-split systems) to optimize vehicle performance, fuel efficiency, and adaptability across different driving conditions. Mixed HEVs provide high flexibility in power flow management, allowing the vehicle to seamlessly switch between different operating modes depending on demand.
1.3.1 Series HEV
The series hybrid vehicle, as illustrated in Figure 6, shows that the EM serves as the primary power source driving the wheels, while the ICE functions solely to drive a generator, which supplies energy to the EM and charges the battery.
With the series hybrid configuration, the ICE can always operate within its optimal load and speed range, thereby improving its thermal efficiency. Additionally, since the torque delivered to the wheels is generated by the EM, vehicle speed control becomes relatively simple. Furthermore, the power flow structure is straightforward (linear), eliminating the need for a transmission system, which simplifies the overall vehicle design.
1.3.3 Series - Parallel HEV
In a series-parallel hybrid vehicle, the EM, generator, ICE, and wheels are interconnected through one or more planetary gear sets or other mechanical devices. Figure 8 illustrates the schematic of a series-parallel hybrid system, where the power generated by the ICE and EM is distributed and transmitted to the wheels via two pathways: series and parallel.
In the series pathway, energy flows from the ICE to the generator, converting mechanical energy into electrical energy. This electrical energy is then managed by the energy storage system (ESS), where part of it is used to charge the battery while the rest is sent to the EM to drive the wheels, or alternatively, the entire energy output may be used to power the EM directly.
1.4 Design requirements
1.4.1 Main components
In contrast to conventional vehicles, hybrid vehicles are equipped with a battery, an electric motor, a propulsion motor, and various power electronic modules, including a DC-DC converter and a DC-AC inverter.
a. Internal combustion engine
In the hybrid powertrain, the ICE acts as the main energy source, providing power for the entire system. Hybrid vehicle engines usually feature a higher compression ratio than traditional engines, leading to improved efficiency and higher specific power output.
b. Electric motor
The electric motor plays a vital role in hybrid vehicle technology. Depending on the hybrid vehicle's design, it may function as a peak power controller, a load-sharing component, or a low-torque source. To ensure optimal performance, the electric motor must operate efficiently in both standard and extended modes. Under normal conditions, the motor delivers consistent torque within its rated speed range. Once it exceeds this range, it transitions to traction mode, where torque gradually decreases as speed increases. In hybrid vehicles, the electric motor initially provides the necessary torque for full acceleration before shifting to an extended mode to maintain a steady driving speed. Additionally, the electric motor is responsible for recovering energy during braking.
c. Battery
The battery is a key component in hybrid vehicles, significantly affecting overall efficiency. Hybrid vehicle batteries are characterized by high energy density, limited internal durability, long charge-discharge cycles, and a relatively short lifespan. The choice of battery depends on the vehicle's design goals, with high-energy-density batteries being commonly used in traditional hybrids and plug-in hybrid electric vehicles (PHEVs).
1.4.3 Battery and charging capability
Battery type: Primarily Lithium-ion (Li-ion) or Nickel-metal hydride (Ni-MH).
Battery capacity from 1.0 kWh to 18 kWh, depending on the hybrid type (HEV, PHEV).
Charging capability: Plug-in Hybrid Electric Vehicles (PHEVs) require support for AC charging or DC fast charging.
1.5 Hybrid vehicle models on the market
Hybrid car technology started gaining popularity in the late 1990s. The first mass-produced hybrid vehicle was the Toyota Prius, which was launched in Japan in 1997, followed by the Honda Insight, introduced in 1999 in both the United States and Japan. The Prius later expanded to Europe, North America, and other global markets in 2000. Since then, hybrid vehicle technology has continuously evolved, leading to the introduction of numerous new hybrid models with increasingly advanced features and improved efficiency.
The Mercedes-Benz S400 BlueHybrid was introduced at the 2009 Chicago Auto Show, with sales beginning in the U.S. in October 2009. As a mild hybrid, it became the first hybrid vehicle to use a lithium-ion battery. The hybrid technology in the S400 was co-developed by Daimler AG and BMW. A similar system was later implemented in the BMW Active Hybrid 7, which was launched in the U.S. and Europe in mid-2010. Additionally, in December 2009, BMW introduced the BMW Active Hybrid X6, a full-hybrid SUV.
At the 2010 Geneva Motor Show, Volkswagen announced the 2012 Touareg Hybrid, which later entered the U.S. market in 2011. VW also revealed plans to launch diesel-electric hybrid versions of its most popular models, starting with the Jetta in 2012, followed by the Golf Hybrid in 2013, along with hybrid variants of the Passat. Several other gasoline-electric hybrids were released in the U.S. in 2011, including the Lexus CT 200h, Infiniti M35 Hybrid, Hyundai Sonata Hybrid, and Kia Optima Hybrid.
In Vietnam, around 2009, Vietnam saw its first hybrid cars imported by private dealers, though in limited quantities and mostly luxury models. Some of the most notable hybrids at the time included the Lexus RX400h and LS600hL, which were particularly popular among wealthy buyers. By 2010, the officially distributed Mercedes-Benz S400 Hybrid entered the Vietnamese market. However, hybrid vehicles only gained mainstream acceptance in recent years, as more affordable hybrid models emerged, such as the Toyota Corolla Cross 1.8HV, Nissan X-Trail Hybrid, and Toyota Prius Hybrid, Toyota Camry HEV, Honda Civic eHEV 2025. However, with increasingly stringent emission regulations, hybrid vehicles are expected to capture a larger market share in Vietnam's automotive industry in the near future.
1.6 Approach to the study
The increasing implementation of power-split hybrid systems in automotive applications is driven by their ability to merge the benefits of both series and parallel hybrid architectures, making them well-suited for use in both city traffic and highway driving conditions. Nonetheless, a significant engineering challenge associated with power-split hybrids is the design and control of the power-split mechanism, as well as the optimization of power distribution between the ICE and the electric propulsion system. Addressing these technical aspects forms the foundation of this research.
The research methodology follows a step-by-step approach, commencing with simulation-based analysis and later validated through experimental testing. Initially, key vehicle performance parameters such as speed, power demand, and operational efficiency are determined and integrated into the simulation framework. The obtained results will then be analyzed to evaluate energy efficiency, power output, fuel economy, and emission levels.
1.7 Conclusion
From the findings discussed earlier, the following key conclusions can be summarized:
- Hybrid vehicles offer superior environmental benefits compared to traditional ICE vehicles, as they enhance energy efficiency and significantly reduce emissions, contributing to lower environmental impact.
- Given the increasing depletion of fossil fuel reserves and the enforcement of strict emission control regulations on conventional vehicles, researchers have explored various solutions to mitigate transportation-related emissions. Among these solutions, alternative propulsion systems, particularly hybrid powertrains, have emerged as the most viable and effective approach. Hybrid vehicle technology has seen substantial advancements, with numerous hybrid models now mass-produced and achieving strong sales performance in highly regulated markets such as Europe, as well as in regions traditionally dominated by gasoline and diesel-powered vehicles, including Asia.
- This research is centered on the design and computational modeling of a two-seater hybrid vehicle, with a specific focus on optimizing the power distribution system between the ICE and the electric motor. Furthermore, it presents an optimized operational strategy for hybrid powertrains and validates theoretical design through controlled laboratory experiments.
CHAPTER II: THEORETICAL BASIS FOR CALCULATION AND DESIGN OF HYBRID VEHICLE POWERTRAIN SYSTEM
2.1. Perspectives about calculation and design of hybrid vehicle powertrain system
2.1.1.Design perspectives of hybrid vehicle powertrain system
A hybrid vehicle utilizes two power sources: an ICE and an EM. In this system, the ICE serves as the primary power source, while the EM acts as an auxiliary power source. Therefore, when designing and selecting the power sources and defining the power management strategy for a hybrid vehicle, it is crucial to ensure that the ICE operates within its most fuel-efficient range while maintaining high efficiency. This is a key factor in enhancing the overall performance of a hybrid powertrain compared to conventional vehicles. For instance, as illustrated in Figure 13, the fuel consumption characteristics of the ICE indicate that its optimal efficiency is achieved at a fuel consumption rate of approximately 250 g/kWh, corresponding to an efficiency of 34.3%
Due to varying driving conditions and user demands, vehicle speed fluctuates, requiring the power output from the energy sources to adjust accordingly. Typically, in hybrid vehicle power management strategies:
- At startup, idle mode, and low-speed operation, only the EM is active.
- When the vehicle reaches an optimal economic speed, only the ICE operates within its most efficient range.
- For high-power demands, both ICE and EM work together to supply the required energy.
2.1.2.Developing the calculation and design process for the hybrid vehicle powertrain
Effectively integrating hybrid power sources requires a clear and well-structured process framework. This framework should outline each step of implementation while also establishing evaluation criteria for assessing the results obtained. By following this structured approach, we can develop a solid foundation and direction for the project. The process has 9 steps that are detailed as follows:
- Step 1: Defining the design approach: In this study, the chosen approach considers the ICE as the main power source, while the EM as an auxiliary source because it is based on the driving condition, where speed and torque frequently change that require the ICE to be main power source to satisfy driving conditions.
- Step 2: Selecting a power distribution method of power sources from practiced method versus scientific research.
- Step 3: Designing and calculating the hybrid power coordination system based on specifications to ensure smooth power integration.
- Step 4: Developing a strategy for optimal energy use and management.
- Step 5: Calculating characteristic parameters and curves for both the ICE and EM.
- Step 8: If the conditions in step 7 are satisfied, the product manufacturing step will be carried out according to the simulation and refined parameters of the MATLAB/SIMULINK.
- Step 9: Testing and validation.
2.2. Calculation and design basis for powertrain of hybrid vehicle
2.2.1. Powertrain coordination modes in HEV
In this research project, we will only focus on the series - parallel coordination method because its outstanding advantages in both economy and efficiency are being researched and widely applied on commercialized HEVs.
Normally, a hybrid powertrain will consist of an ICE, an EM and a generator. The power sources are connected to each other through 1 or more mechanical connections, electrical connections or other devices. During vehicle operation, the hybrid powertrain must always ensure that the modes corresponding to the following cases are implemented:
a. Electric motor only mode
When the vehicle is running at low speed and the power lower than the power of ICE, ICE does not work, the clutch opens. As shown in Figure 15, the vehicle is pushed by the EM which takes electrical energy from the battery and transmits it to the wheels. This case is suitable when the vehicle is running in the city.
c. Engine only mode
In this case, the required speed and power of the vehicle is greater than the allowed speed in the city, then the EM is disconnected, the clutch is engaged, and the vehicle is pushed by the ICE as shown in Figure 17. This mode is also used when the battery charge is at a high level.
c. Regenerative braking mode
When the vehicle performs downhill movement or braking, the clutch opens the controller to control the EM to function as a generator to absorb braking energy into electrical energy, as shown in Figure 19
2.1.2 Basis of determining the structure of the hybrid vehicle power source coordinator that uses power split device
a. Construction of power split device
The power split device (PSD) in a HEV is essentially a planetary gear set, consisting of the following components
The power output of the ICE, which is transmitted via the planetary gear unit, is divided into the motive force directed to the drive wheels and the motive force to the generator (MG1) for generating electricity. Also, when MG1 rotates and the engine starts, MG1 functions as a starter.
As part of the power split planetary gear unit, the sun gear is connected to MG1, the ring gear is connected to the counter drive gear (output) and the carrier is connected to the engine.
b. Operation of PSD and nomographic
The nomographic below gives a visual representation of the planetary gear rotation direction, rotational speed and torque balance.
In the nomographic, a straight line is used to represent the relationship between the rotation directions and rotational speeds of the 3 gears in the planetary gear. The rotational speed of each gear is indicated by the distance from the 0-rpm point. Due to the structure of the planetary gear, the relationship between the rotational speeds of the 3 gears is always expressed by a straight line.
- READY-ON state
Current is sent to the MG1 which functions as a starter for ICE and starts the ICE via the sun gear.
If the SOC of the HV battery is low, it is charged by the MG1, which is driven by the engine.
The engine motive force, which is input by the carrier, is output to the sun gear. Thus, motive force is transmitted in order to operate the MG1 as a generator.
- Constant-speed cruising
When the vehicle is running under low load and constant-speed cruising conditions, the engine will be operated in its most efficient range to power the vehicle.
The engine motive force, which is input by the carrier, is output to the ring gear. The motive force of MG2 is output to the ring gear via the MG2 reduction gear. The combination of these 2 motive forces is transmitted by the compound gear in order to drive the front wheels.
- During full throttle acceleration
When the vehicle driving condition changes from low load cruising to full-throttle acceleration, this system supplements the motive force of MG2 with electrical power from the HV battery.
The engine motive force, which is input by the carrier, is output to the ring gear. The motive force of MG2 is output to the ring gear via the MG2 reduction gear. The combination of these 2 motive forces is transmitted by the compound gear in order to drive the front wheels.
2.2.3. Calculation basis of HEV power sources
2.2.3.1. Diagram of powertrain design
a. Vehicle speed and working condition regulations
The calculation of the HEV powertrain includes features of the vehicle, size and mass of the components that make up the powertrain, road conditions, driving habits, cost, ... The vehicle's dynamic features are chosen as constraints in the optimization problem posed above because they are closely related to the optimization goal in terms of technology. Road conditions and driving habits in Vietnam will be considered in the vehicle's dynamic performance criteria and in the operating cycle issued by Vietnamese agencies or organizations. In addition, driving habits in
Currently, in Vietnam, there is no specific regulation that standardizes the evaluation indicators for the dynamic performance of motor vehicles, particularly for specific types such as hybrid vehicles. However, three fundamental criteria for assessing the dynamic performance of motor vehicles can be indirectly identified through official documents issued by competent authorities in Vietnam.
c. Generator/Starter motor (MG1)
- Functions as a starter to crank the engine.
- Acts as a generator to convert mechanical energy from the engine into electrical energy.
- Supplies electricity to MG2 or charges the high-voltage battery.
- Freewheels when inactive to maintain gear synchronization.
e. HV Battery
- Stores high-voltage electrical energy.
- Supplies power to MG1 and MG2 during electric drive or boost mode.
- Receives recovered energy during regenerative braking and deceleration.
- Equipped with temperature sensors and a battery smart unit to monitor voltage, current, SOC, and thermal condition.
- Connected to other subsystems via high-voltage power cables.
2.2.3.2 Calculation basis for determining the capacity of the power source: EM, ICE and battery
While: v : Vehicle speed
Fw : Aerodynamic drag
hg : Center of gravity height coordinates
hw : Distance from road surface to air resistance point
Ff2 and Ff1 : Are rolling resistance at wheels 2 and 1 Z2 and Z1 are reaction forces at wheels 2 and 1 (normal)
Mf1 and Mf2 : Are rolling resistance moments at wheels 1 and 2
Fm : Is the hook force
Fk : Is the traction force at the driving wheel
Mk : Is the traction moment at the driving wheel
Fg :Is the uphill resistance
Fj : Is the inertial resistance L : Is the wheelbase of the vehicle a and b are the distance from the vehicle center of gravity to the front and rear axles
G0 : Is the total weight of the vehicle α : Is the tilt angle
hm : Is the distance from the road surface to the hook force point
lm : Is the distance from the rear axle to the hook force point
a. Calculating the power of HEV
According to the survey diagram in Figure 2.20, if we project the force components onto the X direction, we have the equation for the car's traction balance when the car goes uphill:
Fk=Ff+Fi+ FW+Fj+Fm (2.1)
Ff (N) is the rolling resistance force generated mainly due to elastic deformation of the wheel and partly due to friction in the wheel bearings, and is determined by the following equation:
Ff=m*G*f*cosw (2.2)
While: m: Vehicle mass (kg); G - total weight of the vehicle; α - slope angle of the road surface (degrees); f is the rolling resistance coefficient.
- Selection of the type of electric motor:
We have selected a 3-phase Permanent magnet synchronous motor (PMSM) because of several key advantages:
- It has very high energy conversion efficiency (typically over 90%), which helps reduce fuel consumption and extend electric driving range — critical for urban traffic in Vietnam's crowded cities.
- Compared with DC motors, it provides higher power density. This helps reduce the overall weight of the vehicle and improve performance, which is especially beneficial for small and mid-sized cars popular in Vietnam.
- Does not use brushes or commutators like traditional DC motors, which means less wear and tear, lower maintenance costs, and better reliability, important for Vietnamese users who often seek low operating costs.
- With modern inverters and control systems, PMSMs offer excellent torque control and smooth acceleration. This improves driving comfort and is ideal for stop-and-go traffic in Vietnamese cities.
- It generally has good thermal stability and operates efficiently in hot environments that suitable for Vietnam’s tropical climate.
e. Calculation of the ICE power
- Engine selection :
The type of engine is selected based on the vehicle category being designed. Typically, for passenger cars, a gasoline engine without speed limitation or a diesel engine can be chosen. For trucks and buses, diesel engines are generally preferred. In theory, gasoline engines with speed limitations can be considered; however, in practice, this type is no longer used in modern trucks and buses. Additionally, engine selection also depends on the requirements of the customer or end user.
In this research, we choose ICE using gasoline to design and calculation
- Selection of engine rated speed:
If a commercially available engine is used, its rated speed is predefined by the manufacturer. However, in the case where a vehicle manufacturer places a custom order for an engine, the rated speed (typically the speed at maximum power, denoted as at ) can be selected according to design requirements.
- Construction of the engine external characteristic curve:
The external characteristic curve of an engine is typically obtained through testing on an engine dynamometer. This curve may also be provided in the engine's technical documentation upon delivery from the manufacturer. However, in many cases, especially during theoretical calculations, the actual characteristic curve may not be available. In such cases, the external characteristic can be approximated using the Leidekman formula.
d. Calculation of total powertrain (ICE combined with EM) at Vmax
In the above formula, is the total weight of the vehicle and is calculated by the following formula:
G=Gt+G0= Gt+GICE+GEM+GBattery+Gother (2.19)
While: (unit – kg)
G0: Is the curb weight of the vehicle
GICE : Is the mass of the internal combustion engine
GEM : Is the mass of the electric motor
GBattery : Is the mass of the battery pack
Gother is the mass of other components
Gt=(m1+m2 )*n is the payload
m1 : Is the weight of one person
m2 : Is the weight of personal luggage per person n=5 : Is the designed number of occupants
The frontal area of the vehicle is calculated as: F=0.8*B0*H (B0 is the track width of the designed vehicle; H is the overall height of the vehicle).
2.2.4 Powertrain energy management strategy
2.2.4.1. Powertrain coordination strategy in HEV
a. Control rules
In hybrid vehicle control, the coordination between the ICE and the EM in a smooth and efficient manner is a key factor that determines the superiority of hybrid vehicles in terms of emissions and energy consumption compared to conventional powertrains. To satisfy the requirements for efficiency, emission reduction, and operational smoothness, the combination of power from the ICE and EM must comply with the following rules:
- Rule 1: When the EM is not operating, the ICE runs independently.
- Rule 2: The EM only operates within power and speed regions that offer low fuel consumption and low emission characteristics.
- Rule 3: The EM is the primary power source, while the ICE serves as an auxiliary source, taking advantage of its flexibility to compensate for the EM.
- Rule 4: In high-power demand situations, both the ICE and EM operate simultaneously.
Rule 5: The ICE is also used to drive the generator for charging the battery.
b. Overview about flowchart of powertrain coordination strategy in HEV
To coordinate the ICE and EM smoothly and efficiently, it is essential to consider the vehicle speed, the legal speed regulations for motor vehicles, and the real-time traffic conditions. Since vehicle speed directly relates to the power demand of the powertrain and the operating speeds of the power sources, the vehicle speed range is divided into smaller intervals based on relevant regulations and the operating characteristics of each power source. For each speed interval, a specific power source coordination strategy is defined to ensure accurate and optimal performance.
To coordinate the ICE and EM effectively and smoothly, vehicle speed, traffic regulations, and current traffic conditions must be considered. Because vehicle speed directly affects the required power output and the rotational speeds of the power sources, it is divided into appropriate segments. Each segment is associated with a specific coordination strategy to ensure optimal and precise operation.
In the no-load mode, the ICE will be supplied with electricity and ready to operate when the accelerator is pressed. The ICE will continue to operate independently until the speed threshold . From speed to , only the EM operates because this is the speed range where the EM has low fuel consumption and low emissions. For speeds from to since this is the range requiring high power, the power of both the EM and ICE will be combined.
2.2.4.3. Torque-based vehicle control strategy in HEV
In addition to the vehicle speed-based hybrid control method, to comprehensively cover all possible driving situations, it is also necessary to consider the vehicle's torque. Figure 36 illustrates the flowchart of the torque-based control strategy. The research uses torque variation (∆M) to determine the vehicle’s operating states, followed by evaluating parameters such as throttle signal and speed variation to identify the current mode of operation and the required power and speed. Based on this, the control of power sources of EM and ICE is carried out to meet the vehicle's various demands.
2.3. Conclusion
Based on the theory of powertrains and hybrid vehicle simulation, Chapter II has achieved the following results:
- Developed the procedure for implementing the research topic and evaluating a hybrid powertrain system.
- Established the theoretical basis for calculating the power source as well as the power split ratio between the power sources in a hybrid vehicle.
- Created a flowchart for the dissertation implementation and an overview flowchart of the hybrid powertrain control strategy, including battery charging for the hybrid vehicle, in preparation for the detailed strategies discussed in the next chapter.
- Built the theoretical foundation for calculating the power source and battery charging in the MATLAB/SIMULINK for hybrid vehicles.
- Investigated the calculation formulas for fuel consumption and emissions for the power source in a hybrid vehicle.
CHAPTER III: DESIGN, CALCULATION AND SIMULATION OF HYBRID VEHICLE POWERTRAIN
3.1. Design and calculation of HEV powertrain
3.1.1. Design of HEV powertrain coordination system
a. General requirements
In the process of designing conventional vehicles, the maximum engine power is determined based on several technical characteristics of the vehicle like dynamic performance, off-road capability, etc., which are set during the design phase. For HEV, different powertrains need to be coordinated so that the total power delivered to the driving wheels equals the maximum engine power of a conventional vehicle with equivalent technical performance. Additionally, the power of each source must be selected so that the entire system operates with the best possible economic, technical, and emission indicators.
To evaluate the feasibility of the powertrain coordination option between the EM and ICE, it is necessary to calculate the power sources.
The necessity of energy management for the power sources in HEV is identified as an important objective and is calculated based on a specific strategy to ensure continuous and efficient operation of the system.
b. Power split unit design
Currently, automobiles are the most used means of transportation and freight in Vietnam. However, they are also among the major sources of harmful pollutant emissions to the environment. Therefore, improving existing technologies and developing new powertrain solutions for automobiles have become a significant focus for manufacturers. Within the scope of this thesis, a solution for combining multiple power sources in a hybrid electric drivetrain will be presented.
Figure 3.1 illustrates the schematic diagram of the series-parallel hybrid drivetrain utilizing a planetary gear set for an automobile. The system consists of an ICE, an electric motor/generator (MG1), and a traction electric motor (MG2), all connected through a planetary gear set. The engine is connected to the carrier of the planetary gear set via a clutch; the motor/generator (MG1) is linked to the sun gear; and the traction motor (MG2) is connected to the ring gear through an intermediate gear.
3.1.2. Powertrain calculation for HEV
3.1.2.1. Calculation and determination of the power of the HEV’s powertrain system
When the vehicle operates at , the power of the vehicle’s powertrain is calculated according to equation 2.9. Here, m is the gross weight of the vehicle and is calculated by:
m=mt+m0=mt+mICE+mEM+mBattery+mother (3.1)
By design, m0=1410 kg is the vehicle's curb weight including mICE is the mass of the ICE; mEM is the mass of the EM; mBattery is the mass of the battery pack; mother is the mass of other components; and mt=(m1+m2 )*n is the payload.
Assumption: m1=75 kg is the weight of one person; m2=15 kg is the weight of luggage per one person; n = 5 is the number of people according to the design. With a 5-seat vehicle design, the total payload mt=450 kg.
The frontal area of the vehicle drags A is calculated as A=0.85*B0*H. The parameters are defined as follows: the vehicle’s design track width B0=1825 mm, the overall design height of the vehicle H=1620 mm. Substituting the values into the formula, we get: A=0.85*1825*1620=2513025 mm2.
However, the vehicle must also supply power for auxiliary systems, so the rated power of the propulsion system is typically selected to be 20–30% higher. Therefore, the maximum power of the selected powertrain is:
Pe(max))=113.11* 1.3=147 kW
3.1.2.3. Calculation to determine the power of the ICE
We have Pe(total)=147 kW and the power needed by electric motor PEM=53 kW. So, the power needed of the engine is PICE=Pe(total-P_(EM )=147-53=96 kW
HF=P(EM )/(P(EM )+P(ICE ))=P(EM )/P(e(total) ) = 53/147=0.36 (3.2
Based on the above calculation results, it is found that the 2ZR-FE engine of the 2025 Toyota Cross, with the specifications presented in Table 5, is suitable for selection and further research.
3.1.2.4. Calculation to determine the power of the generator
At a speed of V=60 (km/h)=16.67 (m/s) , which is the steady cruising speed of the vehicle on the road, the drivetrain efficiency is t=0.85 and the generator efficiency is m=0.9.
Pgenerator=16.67/(1000*0.85*0.9)*(1860*9.8*0.02+1/2*1.24*0.4*2.3652 *(6.672 )=12.29 (kW
We choose a PMSM motor with Pgenerator=13 kW with maximum speed 6000 rpm. The role of generator is to start the gasoline engine, generate electricity to charge the hybrid battery, and coordinates energy in the hybrid system.
3.1.2.5. Choosing the hybrid battery
A Nickel Metal Hydride (Ni-MH) battery pack is used, which offers the advantage of high energy density, thereby reducing the overall mass and size of the battery system. A battery pack with a rated voltage of 201.6 V is selected to supply power to the electric traction motor. The battery has a capacity of C = 19.5 Ah
3.2. Design of a planetary gear set for vehicle drivetrain
3.2.1. Calculation of gear ratios between gear pairs in the basic transmission system
By applying the Willis method, it is possible to calculate the gear ratio of different configurations of planetary gear trains, as well as the angular velocity of any individual member within the power split device.
Neglecting frictional losses, the relationship between the torques acting on the fundamental members of the planetary gear set can be determined:
T1*ω1+T2*ω2+T3*ω3 = 0
With the given input parameters: T3=172(Nm),ω3= 3600(rpm) (corresponding to the engine) and T1=163(Nm),ω1= 5600(rpm) (corresponding to the electric motor).
We have:
k1=0.485
k2=0.515
3.2.2. Calculation and design of gear parameters
3.2.2.1. Material selection
From the perspective of ensuring that the gears can be used throughout maintenance and overhaul cycles, and to facilitate mass production, the same material is selected for all gears. However, since the gears share the same module, the larger gears are subjected to lower loads when meshing. As a result, even when the smaller gears require replacement or overhaul, the larger gears remain serviceable. The selected material is 40CrNi alloy steel.
Large gear: Surface hardened to HRC 55–63
Ultimate tensile strength: δ=900(MPa). Yield strength: δy=700(MPa)
Substituting the values into the formula, we get:
NHE= NFE=60×1×4000×8000=192×107
We have: NHE>NHO1 so KHL1=1, similarly KHL2=1
When calculating helical gear transmissions, the allowable contact stress [σH] is taken as the average value of [σH ](1 )and [σH ]_(2 )but must not exceed (1.25*[σH )min
[σH ]=([σH ]1+[σH ]2)/2=(1150+1054)/2=1102 MPa<1.25[σ_H ]_min (Satisfied)
[σF ]1=(σFlim1 〖*KFL)/SF =(750×0.8×1)/1.55=387 MPa
[σF ]2=(σFlim2*KFL)/SF =(750×0.8×1)/1.55=387 MPa
Maximum allowable overload stress:
[σH ]max=2.8×δch2=2.8×700=1960 MPa
[σF ]1max=0.8×δch1=0.8×700=560 MPa
[σF ]2max=0.8×δch2=0.8×700=560 MPa
3.2.2.3. Recalculate the center distance and gear ratio
Center distance from the sun gear ZS to the planet gear ZP:
A=(0.5×m×(ZS+ZP))/(cos30°)=(0.5×1×(58+29))/(cos30°)=50.22 (mm)
Gear ratio:
Z=ZR/ZS =116/58=2
3.2.2.4. Geometric parameters of the gears
Normal module: m_n=1 mm
Pitch: t=π×mn=3.14 mm
Tilt angle of the gear: β=30°
Number of teeth of the ring gear: Z2=116 (teeth)
Number of teeth of the planet gear: ZP=29 (teeth)
Number of teeth of the sun gear: Z1=58 (teeth)
- Addendum diameter:
Addendum diameter is calculated:
da= dω±2mn
The minus sign (–) corresponds to internal meshing, and the plus sign (+) corresponds to external meshing
+ Ring gear ZR:daR=dωR±2m_n=133.94-2×1=131.94 (mm)
+ Planet gear ZP:daP=dωP±2mn=33.48+2×1=35.48 (mm)
+ Sun gear ZS:daS=dωS±2mn=66.97+2×1=68.97 (mm)
- Face width:
b=ψbd×dω
+ Ring gear ZR:bR=ψ_bd×dωR=0.3×133.94=40.18 (mm)
+ Planet gear ZP:bP=ψbd×dωP=0.3×33.48=10.04 (mm)
+ Sun gear ZS:bS=ψbd×dωS=0.3×66.97=20.09 (mm)
Choose bR=40 (mm); bP=10 (mm); bS=20 (mm)
3.2.3. Analysis of forces acting on gear
3.2.3.1 .Forces acting on gears
In the diagram, reaction forces from the driven member acting on the driving member are shown with dashed lines, while forces from driving members acting on driven members are represented by solid lines.
From the illustration, the planetary gear experiences opposing forces: radial force and axial force . Due to the identical fundamental geometric characteristics of the entire Wilson gearset, the forces acting on all planetary gears have equal magnitudes.
Consequently, along the centerline of the planetary gear shaft, the radial and axial forces cancel each other out. The force analysis diagram of the Wilson planetary gearset is shown in Figure 39.
- Tangential force:
The general formula is given by:
Pi=Fti= (2Mti)/di
In there:
Pi: Tangential force acting on the i-th gear
Mti: Torque of the i- th gear
di: Pitch diameter of the i-th gear
Tangential force acting on the front planetary gearset: PR=2569 (N)
- Axial force:
The general formula is given by: Fai=Pi×tgβ
With Fai: Axial force acting on the i-th gear
So: Fai=2569×tg30°=1483.21 (N)
3.2.3.2. Gear strength calculation
- Calculation based on bending strength
The bending stress acting on the gear is determined by the formula:
σH=Kd×Kms×Kc×Ktp×Kgc×P/(b×π×mntb×Y×Kβ)
In there:
P: Tangential force on gear teeth (MN)
b: Face width (m)
Y: tooth form factor. Determine from standard table
Kd: External dynamic factors. Kd=2.3
Kβ: Contact ratio factor
Kms: Friction coefficient. For driving gear: Kms=1.1, driven gear: Kms=0.9
- Calculate the bending stress of the sun gear
In this case, the sun gear Zs is the driving gear.
Friction factor: Kms=1.1 Working face width of the gear:bs=20mm=20×103 (m)
According to Table 6.18 [5], the tooth form factor is Y= 3.62
Tangential force acting on the planet gear ZS: PS=2569 (N)=2569×10-6 (MN)
With Kβ=1 substituting the calculated values into the formula, we have:
=> Substitute the numbers we get: σH1=34.31 (MN/m2)
With Kβ=1 substituting the calculated values into the formula, we have:
=> Substitute the numbers we get: σH2=54.14 (MN/m2)
So σH1 và σH2 < [σH ]=750 MPa=750 MN/m2, the gears satisfy the bending strength condition.
3.2.4 Shaft design calculation
3.2.4.1. Choose materials
Due to the characteristics of the vehicle design, which involves frequently changing operating modes, high-speed motion, and unstable loads, the material selected for the shaft is 20CrNi steel. The mechanical properties of 20CrNi steel are as follows:
- Hardness (HRC): 46–53
- Ultimate tensile strength: σb=1000 (Mpa)
- Yield strength: σch=750 (Mpa)
3.2.4.2. Preliminary determination of shaft diameter
Purpose: To determine the preliminary diameter of the shaft, which allows for the selection of appropriately sized bearings. This also helps define the thickness of each shaft segment, especially at load application points. Based on this, a preliminary shaft diameter profile can be sketched.
The shaft material is 20CrNi3A with carburizing treatment, and with a surface fatigue limit of σb=1000 (MPa), we have:
σ-1=0.46×1000=436 (MPa)
τ-1)=0.58×436=252.88 (MPa)
Value of the bending section modulus at the critical cross-section on the output shaft of the gearbox. This is the section where the sun gear (S) is mounted. According to the formula, the values of the bending section modulus at the selected cross-sections are summarized in the following table.
After calculating the values, the safety factors are summarized in the following table.
We have [S]=1.5 – 2.5 all shafts satisfy the fatigue safety requirements.
3.3. Simulation in MATLAB/SIMULINK
3.3.1. Introduction to HEV series - parallel modelling in MATLABSIMULINK software
MATLAB (short for MATrix LABoratory) is a numerical computing and technical programming software developed by MathWorks (USA). MATLAB is well known for its powerful matrix processing capabilities, high-precision numerical computation, data visualization, and system simulation.
This software is widely used in various fields such as engineering, mathematics, physics, finance, control systems, signal processing, image processing, machine learning, and artificial intelligence (AI). MATLAB provides an integrated programming environment with its own language that is easy to learn and use for both beginners and professionals.
With a user-friendly graphical interface and powerful simulation capabilities, MATLAB is an essential tool for students, lecturers, engineers, and researchers to solve complex technical problems quickly and effectively.
a. Internal combustion engine (ICE)
Based on input from control logic value, the engine produces torque and speed, and the values are sent back to the control logic as feedback. The engine is connected to the carrier and the same drives the generator via Carrier-Sun gear connection. During the drive cycle, when the power demand is low, only the motor is operated to meet the driver’s requirements, and the engine is shut off. This is advantageous because the motor operates on DC current from the battery and is agile, unlike that of the engine, under unsteady load conditions.
In contrast to SI engines of conventional vehicles operating on Diesel cycle, the IC engine in HEV operates on Atkinson cycle. This is because of the fact that the engine in HEV does not operate on its full load capacity as compared to that in conventional passenger vehicles but operates at part loads corresponding to maximum efficiency. Due to this phenomenon the engine cannot operate in Diesel cycle but on Atkinson cycle, which caters to the part load during engine operation in HEV, giving a 10% better fuel efficiency than SI engine.
However, the power density is reduced in operation of the Atkinson cycle due to reduction in input load. This is compensated by power input from the motor during cycle operation.
c. Motor generator 2 (MG2)
The motor generator 2 (MG2) plays a key role in delivering traction power and regenerative braking functionality. To simulate on MATLAB/SIMULINK software, the modeling of MG2 begins with high-voltage DC power supplied from the hybrid battery. This voltage is regulated through a DC-DC converter to provide the appropriate level for MG2 operation.
The motor control system receives a torque command signal from the ECU, which directs MG2 to produce a specific torque based on driver input, vehicle speed, and the current hybrid operation mode.
After that, the electrical measurement block is taken to monitor current, voltage, and power drawn by MG2.
The motor drive unit converts the electrical power into mechanical torque, controlling the rotor’s angular velocity. Moreover, it simulates the electromagnetic behavior of MG2 by incorporating critical performance parameters such as maximum rated torque, rated speed, rated power, and other loss and friction characteristics, including spring stiffness, viscous damping, and coulomb friction.
Output - Electrically, the MG2 model includes mechanical torque (Nm), rotational speed (rpm), and electrical losses, which electrical information from the electrical measurement block, along with mechanical information, is used to compute energy losses and evaluate motor efficiency.
d. Power split device and reducer
The power split device (PSD) and reducer are key mechanical subsystems in the hybrid powertrain that facilitate the combination and distribution of torque from the internal combustion engine (ICE), MG1, and MG2 to the vehicle’s driving wheels. Their design is based on a planetary gear set, providing seamless power blending and allowing the engine to operate independently from the vehicle speed.
The planetary gearset consists of three main components:
- The sun gear receives mechanical input from MG1.
- The planet carrier gear is driven by the ICE, delivering engine torque into the system.
- The ring gear is coupled to MG2, which functions as the main traction motor delivering torque directly to the wheels.
This configuration enables power flow management in both directions. MG1 can act as a generator to regulate engine speed or supply electric power, while MG2 provides propulsion torque or regenerative braking, depending on the driving mode.
The output torque from MG2 is transmitted through a reduction gear mechanism, comprising a reducer drive gear (F) and a counter-driven gear (G). This stage reduces the high-speed rotation of MG2 into a suitable speed and torque level for vehicle propulsion. After reduction, the power is delivered to the drive gear and subsequently to the differential gear, which distributes the mechanical power to the left and right axles.
f. DC- DC converter
The DC-DC converter is a crucial power electronic component in hybrid and electric vehicles, responsible for converting and regulating high-voltage direct current (DC) from the battery to the required voltage levels for various subsystems. It functions as an interface between the HV battery and the downstream electrical loads, such as the low-voltage (12V) system or motor control units.
In addition to standard numerical computation, MATLAB stands out thanks to its specialized toolboxes, such as: Simulink (for dynamic system simulation), control system toolbox (for analyzing and designing control systems), signal processing toolbox, and many others tailored for specific technical fields.
3.3.3. Driving cycle used in MATLAB/SIMULINK
a. Driving cycle NEDC (New European Driving Cycle) and EUDC (Extra-urban driving cycle)
The New European Driving Cycle (NEDC) was a driving cycle, last updated in 1997, designed to assess the emission levels of car engines and fuel economy in passenger cars (which excludes light trucks and commercial vehicles). It is also referred to as MVEG cycle (Motor Vehicle Emissions Group).
The NEDC, which is supposed to represent the typical usage of a car in Europe, is repeatedly criticized for delivering economy-figures which are unachievable in reality. It consists of four repeated ECE-15 urban driving cycles (UDC) and one Extra-Urban driving cycle (EUDC).
- For Urban driving cycle:
The Urban Driving Cycle ECE-15 (or just UDC) was introduced first in 1970 as part of ECE vehicle regulations; the recent version is defined by ECE R83, R84 and R101. The cycle has been designed to represent the typical driving conditions of busy European cities, and is characterized by low engine load, low exhaust gas temperature, and a maximum speed of 50 km/h.
When the engine starts, the car pauses for 11s - if equipped with a manual gearbox, 6 s in neutral (with clutch engaged) and 5 s in the 1st gear (with clutch disengaged) - then slowly accelerates to 15 km/h in 4 s, cruises at constant speed for 8 s, brakes to a full stop in 5 s (manual: last 3 s with clutch disengaged), then stops for 21 s (manual: 16 s in neutral, then 5 s in the 1st gear).
At 49 s, the car slowly accelerates to 32 km/h in 12 s (manual: 5 s in 1st gear, 2 s gear change, then 5 s in the 2nd gear), cruises for 24 s, slowly brakes to a full stop in 11 s (manual: last 3 s with clutch disengaged), then pauses for another 21 s (manual: 16 s in neutral, 5 s in the 1st gear).
- Extra-urban driving cycle:
The Extra-Urban Driving Cycle EUDC, introduced by ECE R101 in 1990, has been designed to represent more aggressive, high speed driving modes. The maximum speed of the EUDC cycle is 120 km/h; low-powered vehicles are limited to 90 km/h.
After a 20 s stop - if equipped with manual gearbox, in the 1st gear with clutch disengaged - the car slowly accelerates to 70 km/h in 41 s (manual: 5 s, 9 s, 8 s and 13 s in the 1st, 2nd, 3rd and 4th gears, with additional 3 × 2 s for gear changes), cruises for 50 s (manual: in the 5th gear), decelerates to 50 km/h in 8 s (manual: 4 s in the 5th and 4 s in the 4th gear) and cruises for 69 s, then slowly accelerates to 70 km/h in 13 s .
b. Driving cycle WLTP (Worldwide Harmonized Light Vehicles Test Procedure)
The Worldwide Harmonized Light Vehicles Test Procedure (WLTP) is a global driving cycle standard for determining the levels of pollutants, CO2 emission standards and fuel consumption of conventional ICE and hybrid automobiles, as well as the all-electric range of plug-in electric vehicles.
The key differences between the old NEDC and new WLTP test are that WLTP:
- Having higher average and maximum speeds
- Including a wider range of driving conditions (urban, suburban, main road, highway)
- Simulating a longer distance
- Having higher average and maximum drive power
- Looking at steeper accelerations and decelerations
- Testing optional equipment separately
In my test, we use WLTP class 3b:
The WLTP is divided into 4 different sub-parts, each one with a different maximum speed:
- Low - up to 56.5 km/h
- Medium - up to 76.6 km/h
- High - up to 97.4 km/h
- Extra-high - up to 131.3 km/h.
These driving phases simulate urban, suburban, rural and highway scenarios respectively, with an equal division between urban and non-urban paths (52% and 48%).
c. Driving cycle FTP-75:
The EPA Federal Test Procedure, commonly known as FTP-75 for the city driving cycle, are a series of tests defined by the US Environmental Protection Agency (EPA) to measure tailpipe emissions and fuel economy of passenger cars (excluding light trucks and heavy-duty vehicles).
It consists of 3 stages:
- Stage 1 with a duration of 505s (corresponding to a distance of 5.78km with an average speed of 41.2km/h).
- Stage 2 with a duration of 864s.
- Stage 3 segment lasts 505 s and begins after the 2nd stage end scompletely d cilantro and waits for 10min(600s). Stage 3 is the hot start phase.
And that's it with FTP-75:
- Phase 1 is cold start phase(0-505s)
- Phase 2 is intermediate phase(505-1369s)
- Phase 3 is the hot start phase(1969-2474s)
3.2.4.Result of simulation
3.3.4.1. The simulation of the vehicle's operating characteristics during acceleration from 0 to 100 km/h.
a. Vehicle speed
- Red line: Target/reference speed.
- Blue line: Actual vehicle speed.
- The vehicle reaches around 80 km/h in 30 seconds (fails to reach 100 km/h), indicating possible drivetrain or control limitations.
c. MG1 speed & MG1 mechanical power
- MG1 speed: Continuously decreases into the negative range → acts as a generator.
- A noticeable fluctuation occurs around 17 seconds.
- MG1 power: Remains low (~ -1 to -6 kW), indicating MG1 is charging the battery.
- MG1 mainly works as a generator, converting mechanical energy from the engine into electrical energy.
f. G force
- Initially about 0.11 g, gradually decreases to around 0.02 g → reflects decreasing acceleration force, likely due to traction limits or power management.
- The vehicle accelerates smoothly but with reduced force over time, characteristic of energy-efficient hybrid operation.
3.3.4.3. Result of NEDC driving cycle
This section presents a comprehensive analysis of a series-parallel HEV operating under the New European Driving Cycle (NEDC). Key performance indicators such as vehicle speed, motor speeds and powers, engine behavior, battery SOC, and longitudinal acceleration (G-force) are examined to assess the powertrain's response and energy flow characteristics.
a. Vehicle speed diagram
The vehicle speed varies from 0 to 120 km/h, consistent with the speed profile of the NEDC cycle. Several stop phases are observed (at t ≈ 200 s, 800 s, 1400 s, and 2100 s), interleaved with urban and extra-urban driving segments. The smooth acceleration and deceleration profiles reflect the moderate dynamic demand of NEDC.
=> The simulation accurately tracks the reference NEDC speed profile, indicating a well-calibrated vehicle model and control system.
c. MG2 mechanical power diagram
MG2 power fluctuates between -20 kW and +50 kW. Regenerative braking is visible through the negative power values, especially during deceleration phases (e.g., t ≈ 600 s, 1300 s). Peak power of approximately +50 kW occurs during rapid acceleration events in extra-urban driving.
=> MG2 provides efficient propulsion and regenerative braking, playing a central role in the energy recovery and power delivery strategy
f. MG1 mechanical power diagram
MG1 power ranges from approximately - 6 kW to over + 5 kW. Negative power peaks are associated with battery charging, while positive spikes coincide with ICE start-up demands. Frequent alternation between modes reflects the hybrid controller’s active role in managing energy flow.
=> MG1 contributes to both battery charging and ICE operation, supporting dynamic energy balancing in the system.
i. Engine power diagram
Engine power remains consistently in the negative range, from 0 to approximately -7 kW. This indicates that the ICE is not delivering positive torque but instead is being driven by MG1 for cranking or light-load rotation. No propulsion-related ICE activity is observed.
=> The ICE acts as a passive unit in this scenario, being spun by MG1 likely for warm-up, idling, or battery charging under low load.
CHAPTER IV: MAINTENANCE AND REPAIRING
4.1. Safety preparation before maintaining and repairing HEV
Ensuring safety during vehicle maintenance operations, particularly for HEVs, is of paramount importance due to the potential hazards associated with high-voltage systems, rotating components, and pressurized fluids. Inadequate safety measures not only pose serious risks to technicians but may also compromise vehicle integrity and operational reliability. Moreover, the condition and readiness of maintenance and repair equipment directly influence the effectiveness and safety of the repair process. Therefore, a comprehensive safety protocol that includes the proper selection and inspection of personal protective equipment and maintenance tools is essential before any maintenance task is undertaken.
* Caution: Be sure to perform these checks properly, not performing these checks properly after finishing work can lead to a serious accident or injury.
4.2. Precautions for high-voltage circuit inspection and service for HEV
HEVs equipped with Nickel-Metal Hydride (NiMH) batteries operate at high-voltage levels and utilize an electrolyte containing a strong alkaline solution, primarily potassium hydroxide. Given the potential risk of severe injury or electrocution, it is critical to adhere strictly to manufacturer-recommended procedures and safety protocols when inspecting or servicing the high-voltage electrical circuits in such systems:
- Technicians must undergo special training to be able to service and inspect the high-voltage system.
- All high-voltage wire harnesses and connectors are colored orange. The HEV battery and other high-voltage components have "High Voltage" caution labels. Do not carelessly touch these wires or components.
- When there is a problem with a wire harness or connector of a high-voltage circuit, repairs to the harness or connector should not be attempted. Replace damaged or malfunctioning high-voltage wire or connector.
* Notice:
+ After removing the service plug grip, do not turn the ignition switch ON (READY), unless instructed by the repair manual, as this may cause a malfunction.
+ After turning the ignition switch off, waiting time may be required before disconnecting the cable from the negative (-) auxiliary battery terminal. Therefore, make sure to read the disconnecting cable from the negative (-) auxiliary battery terminal notices before proceeding with work.
- Before using insulated gloves, be sure to check them for cracks, tears and other types of damage by performing the following procedure.
While:
1. Place the glove on its side.
2. Roll the opening up 2 or 3 times.
3. Fold the opening in half to close it.
4. Confirm that there are no air leaks.
- When servicing the vehicle, do not carry metal objects like mechanical pencils or rulers that can be dropped accidentally and cause a short circuit.
- Before touching a bare high-voltage terminal, put on insulated gloves and use an electrical tester to make sure that the terminal voltage is 0 V.
4.3. Precautions to be observed when performing inspection or service in engine compartment for HEV
HEVs are designed to automatically start and stop the internal combustion engine depending on system requirements, even when the vehicle appears to be stationary. This operation is indicated by the illumination of the READY light on the combination meter assembly. Accidental engine startup during service can lead to serious personal injury. Therefore, the following precautions must be observed when working in the engine compartment of these:
- Technicians must confirm that the READY light on the combination meter and the ignition indicator are both turned OFF before opening the hood or beginning any engine compartment work.
- Before starting service, ensure the vehicle is in the park (P) position, the parking brake is engaged, and the wheels are properly chocked to prevent unintended movement
- Be aware that certain components, such as the cooling fan or water pump, may operate automatically even after the engine is turned off. Wait a few minutes after switching off the READY mode before beginning work.
- After completing inspection or service, ensure that no tools, rags, or foreign objects remain in the engine compartment before closing the hood and reactivating the system.
- Use a "CAUTION: ENGINE MAY START AUTOMATICALLY" sign or tag to notify surrounding personnel that service is being conducted on a hybrid vehicle.
4.6. Master maintenance
To ensure optimal performance, reliability, and longevity of its powertrain and auxiliary systems, a structured and comprehensive maintenance schedule is essential. This section outlines the master maintenance plan and periodic service requirements based on manufacturer recommendations and operational best practices. The procedures presented herein are intended to support predictive and preventive maintenance strategies, minimize unexpected downtime, and maintain compliance with safety and environmental standards.
* Note: Unit (x1000 km). Example: Maintenance at column 10 is 10 x 1000 = 10,000 km
R : Perform, replace, maintain (maybe)
M : Disassemble, clean and measure
CONCLUSION
After four months of dedicated work, we have successfully completed my graduation project titled " Design and simulation of the hybrid powertrain system characteristics for a 5-seat vehicle". Throughout the project, we gained a solid understanding of the hybrid vehicle powertrain system and learned how to analyze, evaluate, and propose optimal design solutions.
The project allowed me to carry out in-depth research and perform simulations of hybrid drivetrains based on validated driving cycles. The results obtained reflect the performance standards of developed countries, ensuring safety and efficiency. This period also gave me the opportunity to approach real-world technical issues and apply theoretical knowledge, marking our first steps into the practical automotive industry, particularly in the field of hybrid vehicles in Vietnam.
Despite our efforts, due to limited time and knowledge, this project still has several shortcomings and does not cover all related aspects. we sincerely look forward to receiving feedback and suggestions from instructors and peers to further improve and complete the topic.
Once again, we would like to express our deep gratitude to :Dr. …………… and the faculty members of the Academic Group of Automotive Engineering for their valuable guidance and support throughout this project.
Sincerely thank you!
REFERENCES
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