A diagnosis device is designed, which can diagnose vehicle state through standard port of the On-Board Diagnostics Ⅱ (OBD Ⅱ). Its software is designed based on STM32 single chip microcomputer, the physics layer communicates with vehicle gateway via CAN, the communication standard abides by the Unified Diagnostic Services (UDS) protocol and operates in three modes, i.e. communication with cell phone via Bluetooth, communication with computer via serial port connection, and operate offline via command memory. The embedded software is developed by hierarchical architecture based on C programming language.

For the estimation of road adhesion coefficient, a key parameter in vehicle active safety system, a three-degree-of-freedom vehicle dynamics model with Dugoff tire model was established, and the road adhesion coefficient estimator was designed based on Square root Cubature Kalman Filter (SCKF). This method introduced orthogonal trigonometric decomposition into Cubature Kalman Filter (CKF) algorithm, avoiding the root operation of covariance matrix in CKF, and improving the stability of the algorithm. MATLAB and CarSim co-simulation platform were used to carry out multi-condition simulation verification under different road conditions, and the proposed algorithm was compared with CKF algorithm. The results show that SCKF algorithm has high robustness and higher estimation accuracy than CKF algorithm, and can meet the requirements of vehicle active safety system.

The vehicle mass, which was estimated from longitudinal dynamics formula based on longitudinal acceleration, vehicle speed, motor torque, was used as input parameter to calculate energy recovery feedback torque, to make the vehicle has the same target deceleration under different loads. Test results indicate that the accuracy of vehicle mass falls in the range of ±10% in the real road test, and when vehicle mass is used to calculate energy recovery, the energy consumption is optimized by 5.5% in CRUISE simulation based on China-World Transient Vehicle Cycle (C-WTVC).

In order to study the influence of suspension time delay on the vehicle, the 1/4 semi-active suspension system with time delay was taken as the research object. The stability condition of the time-delay system was used to solve the stability interval of the adjustable damping. For the case outside the stability interval, the critical time delay point was solved, and the numerical simulation was carried out under the discrete impact road surface. The results show that when the time delay is reasonably selected in the stability interval, the ride comfort and handling stability can be improved. When the stability interval is outside, the time-frequency analysis of the suspension performance index is carried out by selecting the critical point of time delay and the nearby points. When the time delay is less than the critical time delay point, the system remains stable. When it is greater than the critical time delay point, the system diverges and is unstable, and the ride comfort and handling stability of the vehicle deteriorate. With the increase of time delay, the power of the suspension performance index gradually increases, and the power of the suspension performance index in the low frequency band is significantly greater than that in other frequency bands.

In order to realize the high performance and low cost development of lithium-ion batteries, this article explored the application of new battery materials in lithium-ion batteries, and introduced the application and research progress of Metal Organic Framework (MOF) in aspects of cathode materials, anode materials, electrolytes and separators, respectively. On this basis, the article revealed that construction of conductive MOF material, MOF composites and low-cost MOF material will be the focus of future research.

For the design of power unit electro thermal performance of EV inverter, a simulation modeling and analysis method of power unit electro thermal performance based on software Saber was proposed. Power module voltage stress, current capability, junction temperature and inverter efficiency were simulated and analyzed, the power loss of the power module was evaluated, the inverter efficiency map was plotted, and the overall efficiency of the inverter under special working conditions was obtained to evaluate the inverter performance. The simulation results show that the performance of the power module meets the system requirements, and the maximum efficiency of the inverter reaches 98.44%.

In order to solve the defects of hybrid-specific transmission including high power consumption of shift clutch pressure control system, complex pressure compensation algorithm and poor control accuracy, a wet clutch pressure control system and control method with characteristic of quick oil filling and substantial power consumption reduction was designed based on vehicle control strategy and one-dimension fluid flow equation, using pressure limited relief valve to replace fix orifice, using AMEsim to construct simulation model to obtain theoretical working characteristic of the system, and then electric pump control mode was studied and optimized with the oil filling speed of wet clutch as the optimization objective.

To accurately predict the lifetime of Insulated Gate Bipolar Transistor (IGBT), this paper proposed a model-based method for IGBT lifetime prediction. Based on simulated vehicle road spectrum, phase voltage, phase current and power factor were obtained. The switching frequency of the motor inverter was determined through table lookup, and IGBT losses were calculated accordingly. Combining the thermal network model, the junction temperature of the IGBT was calculated, allowing for the generation of the IGBT temperature variation curve. Using the rainflow counting method, characteristic parameters were extracted, and the corresponding IGBT damage rate was evaluated based on the IGBT lifetime model, this enables the assessment of whether the IGBT lifetime meets the design requirements.

In order to suppress the narrow pulse during the running process of Insulated Gate Bipolar Transistor (IGBT) module of Permanent Magnet Synchronous Motor (PMSM) inverter, this paper proposed a narrow pulse suppression method based on Pulse Width Modulation (PWM), analyzed the cause of the narrow pulse theoretically. Based on the premise of full consideration of PWM dead zone and narrow pulse, the paper proposed the segmented full-duty ratio PWM output scheme, and analyzed the PWM duty ratio segment that may generate narrow pulse, and the solution was given. Test results show that the above scheme can effectively suppress the generation of narrow pulse, achieve the effect of protecting the motor inverter, and improve the safety and stability of the control system.

To improve the correlation between reliability test condition and user actual driving behavior, this paper proposed a method of user condition classification and test condition construction based on user big data. In this method, the principal component analysis method was used to reduce the dimensionality of a large amount of data, and the K-means clustering method was used to classify the data and select representative segments, sort the data through the Markov method, and finally construct a reliability test condition conforming to the actual driving situation of the user. Driving data from twenty users under a big data platform was calculated according to this calculation process. Compared with the condition commonly used at present, the method from perspective of data source can describe user actual driving state more accurately.