Integration of electric power steering motor and ECU power supply

EPS (Electric Power Steering), which was developed based on the energy conservation and emission reduction of automobiles and is widely used, has made new breakthroughs again. As the demand for space saving and lightweighting in the automobile market increases, the ECU and motor, which were separated from the previous steering drive motor, are integrated to further promote the development of small products.

The integration of the motor and ECU reduces the number of wire harnesses required for interconnection and omits the process of assembling the product, thus playing an important role in reducing costs. In addition, the wire harness connecting the motor and ECU has an antenna function, but after the motor and ECU are integrated, the antenna can be removed to get rid of the problem of noise interference.

Integrating the split EPS motor with the ECU not only reduces size and weight and reduces costs, but also solves the problem of noise interference caused by the wiring harness.

In order to improve the integration of the originally independent products, the technical obstacles are obvious.
The first is the heat problem. The motor itself generates heat, and the integrated EPS has no space for heat dissipation. These two problems become obstacles. In addition, the ECU must also be miniaturized and improved in combination with the motor, so the heat dissipation of high-density integrated circuits will be further reduced. In particular, electrolytic capacitors have problems such as large size, dry-out caused by heat, and evaporation of electrolyte. Since heat has a great impact on solder, tiny cracks may occur inside due to thermal fatigue.
In terms of capacitors, small, low-resistance capacitors are used to achieve miniaturization and high reliability, and a layout solution is found to solve the problems of heat effects and space occupation. Regarding solder problems, they are solved by improving the composition of the material and the shape of the pad.

Heat is a huge challenge to achieve power integration. By improving the selection of high-density integrated circuit components, circuit layout, circuit board type and pad design, we finally overcame the difficulties and achieved integration.

While integrating the motor and ECU, we also needed to challenge ourselves to improve controllability. In order to achieve a more natural torque generation when using the motor as an assist, we also established a control method that can minimize the cogging effect and torque fluctuation that hinder the steering control feeling and cause vibration and noise.
To establish this control method, we first installed the integrated EPS power supply unit on a test vehicle and repeated basic operations to collect data. While exploring the correlation between the motor torque generation method and the control feeling, we designed a logic program to make it a reality, evaluated it based on the test, and then implemented improvements, and continued this method.
In addition, in order to achieve a more natural control feeling, we minimized the torque fluctuation that causes noise and vibration, and made an EPS power supply unit with optimal control parameters that integrates the motor and ECU.

While integrating the two, we also attempted to establish control methods that could profoundly improve steering feel, noise, and vibration.