Honda-The Power of Dreams
Electric Power Steering System with Variable Gear Ratio Development Objectives

Tokyo, July 2, 1997 --- The steering wheel is one of the most important tools in driving and as such should be little affected by external forces, yet faithfully respond to driver intentions.
In 1990 Honda introduced on the NSX its first electric power steering (EPS). This EPS system was developed to offer a steering feel worthy of a high performance mid-engined sports car.
The new electric power steering system we are introducing today is the culmination of our efforts in developing a high performance steering system meeting the particular demands of front wheel drive cars. This electric power system has a variable gear ratio, making it the first steering system of its type in the Japanese ordinary passenger car category.
This new steering system faithfully responds to driver expectations by providing just the necessary amount of steering assistance at all times. Being electrically powered, it also contributes toward reduced fuel consumption.

Construction and Technical Achievements

* Description of the Electric Power Steering (EPS) System
The EPS provides steering assistance through a co-axial electric motor. A micro-processor determines according to vehicle speed and driving conditions the amount of steering assistance required at any given moment. The system provides a linear steering response proportional to steering wheel rotational speed, allowing for a very smooth and responsive steering feel.

* Dramatically improved steering feel
  • Minute assistance control at high speed for increased feeling of safety.
  • Substantially reduced steering kickback.
  • Substantially reduced torque steer.
  • Reduced steering judder at high speeds and under braking.
  • Reduced tram lining on worn roads and/ or on slippery surfaces.
  • Smooth return of the steering wheel to the straight ahead position, and smooth handling even under acceleration coming out of a corner.

* Energy Conservation, Environmental Protection and Safety

  • The change to an electric-powered motor and elimination of the oil pump, allowed for a 3 to 5% improvement in fuel consumption (in house data).
  • Simpler configuration for substantial weight reduction.
  • Steering assistance maintained even with a stalled engine.
  • Improved cold start.
  • Built-in failure warning, self diagnosis and self protection functions.

* Programmable Assistance
The EPS can be programmed to offer a variety of different steering characteristics. It is thus possible to offer a number of different options in one single car, and let the driver choose depending on his/her taste and road conditions.

* Variable Gear Ratio (VGR)
The steering rack features a normal gear ratio near the straight ahead position with the steering ratio quickening as the steering wheel is turned farther. On the road this translates into smooth, confidence building high speed lane changes and increased maneuverability at lower speeds or when parking.

An EPS system does not have an oil pump nor does it use oil. Powered electrically, there is also no engine power drain. It is thus simpler, lighter and more fuel efficient.