Yuji Kozaki, Goro Hirose, Shozo Sekiya and Yasuhiko Miyaura Steering Technology Department, Automotive Technology Center 1. Introduction
The effects of global warming are becoming increasingly apparent. As a result, we product engineers are being asked to develop products that are more friendly to the earth’s environment. Electric power steering (EPS) is such aproduct. By using power only when the steering wheel is turned by the driver, it consumes approximately onetwentieth the energy of conventional hydraulic power steering systems and, as it does not contain any oil, it does not pollute the environment both when it is produced and discarded. While offering these environmental benefits now, in the future EPS is expected to facilitate automaticsteering—user-friendly technology that should ultimately reduce traffic accidents. Additionally, the software built into the EPS controller results in high performance and easy tuning during the development of prototypes of EPS systems. Because of these advantages, EPS has drawn the attention of automobile manufacturers all over the world. The EPS systems we produce have the highest market share not only inJapan but in Europe as well. This report outlines the construction of the column-type and piniontype EPS systems produced by our company, as well as gives a technical profile of their main components: electronic control unit (ECU), sensor and motor. two types: a column type in which the reduction gear is located directly under the steering wheel, and a pinion type in which the reduction gear isattached to the pinion of the rack and pinion assembly. Each type of EPS system is speed-sensitive—vehicle speed and engine rotation signals are input from the vehicle into the ECU. Fig. 1 shows a vehicle with column-type EPS.
3. General Description of Column-Type EPS System
3.1 Construction of column-type EPS
Fig. 2 shows the construction of the column-type EPS system. Collapsible safetycolumns are usually used. The unit is contained in the dashboard.
2. EPS System
The EPS system consists of a torque sensor, which senses the driver’s movements of the steering wheel as well as the movement of the vehicle; an ECU, which performs calculations on assisting force based on signals from the torque sensor; a motor, which produces turning forceaccording to output from the ECU; and a reduction gear, which increases the turning force from the motor and transfers it to the steering mechanism. EPS is available in
1. Motor 2. Worm gear 3. Worm wheel 4. Torque sensor mechanism 5. Potentiometer 6. Motor harness
7. Torque sensor harness 8. Energy-absorbing convoluted tube 9. Keylock assembly 10. Switch bracket 11. Lowerbracket 12. Rubber damper
Fig. 2 Construction of column-type EPS system
3.2 Column-type EPS series
Already ten years have passed since our column-type EPS systems were introduced in mini-cars ( 4.48 kN Stroke ratio Gear specifications Rack ratio Lock to lock Reduction gear Type Reduction ratio Type Motor Rated current Rated speed Rated torque Torque sensor Type Rated voltage Rated voltageControl range of motor current Controller Control items 39 mm/rev 126 mm 3.23 rev Plastic worm and worm wheel 17 DC brush motor 35A 1210 rpm 1.76 Nm Non-contact self-induction DC 12V DC 12V 0 – 35A 1) Differential compensation 2) Friction compensation 3) Astringent control
Fig. 4 Section of EPS system with rubber damper
3.7 Evaluation of rubber damper
Figs. 5 and 6 present frequency analysisresults from a bench test on the effectiveness of the rubber damper. In an endurance test of an EPS system without a rubber damper in an actual vehicle, the backlash naturally increased. When the backlash exceeded a certain level, the rattling noise began to be audible to the driver. However, in an endurance test of an EPS system with a rubber damper in an actual vehicle, the rubber damper...