Electric Power Steering for ATVs
New for 2007 is Honda’s revolutionary Electric Power Steering (EPS) system offered on the Foreman 500 4x4 ES. First announced on June 23 by Honda R&D Japan, the breakthrough represents the world’s first EPS system for ATVs.
As the world’s leader in engine, drivetrain and vehicle design, Honda has many products featuring technologies that cross divisional lines. For example, the 1983 CBR400F with revolution-modulated valve control (REV) represented the first-ever mass-production application of variable valve technology. REV was the precursor to Honda’s well-known VTEC (Variable Timing and Lift, Electronic Control) automotive engines, not to mention the 2002 VFR800FI VTEC Interceptor.
Honda first introduced EPS on the 1993 Acura NSX, and the system has since appeared on a number of Honda cars, including the 2006 Civic and 2007 Fit. Using a brush-type DC motor installed concentrically around the steering rack, the system combines torque and velocity information from the steering wheel with vehicle-speed information to calculate the optimum amount of steering assist to provide. Utilizing electronic sensors and a sophisticated electronic control unit (ECU) allowed engineers to decrease steering assist at higher speeds and increase it at lower speeds when it’s most needed.
As equipped on the 2007 Foreman 500 4x4, this latest EPS iteration employs Honda’s cutting-edge technology to minimize size and weight-important considerations for ATV design-while simultaneously taking advantage of today’s processing power and Honda engineering to custom-tailor the application to a workhorse ATV. The EPS system monitors steering torque and vehicle speed to adjust the levels of steering assist and feel. When stopped or at low speeds, it provides more assistance for a light steering effort. As speed increases, the amount of assistance is reduced to provide the appropriate level of feedback. Perhaps the most significant benefit is the system’s ability to provide light and consistent steering feel in both 2WD and 4WD operation. As a secondary benefit, the EPS system acts like a steering damper to greatly reduce undesirable kickback through the handlebars in rough or rocky terrain.
Honda’s ingenious design utilizes a torsion shaft inside the steering stem that moves a sensor up or down in response to steering torque applied by the rider. The sensor detects the core’s rate of movement and direction and sends the information to an ECU. The ECU, following the preprogrammed parameters of a digital control map, regulates current to the electric-assist motor. By providing more or less output assist torque to the output shaft, the motor effectively helps the rider by augmenting or minimizing the amount of steering assistance. The Honda EPS system also includes two maps-one for 2WD and one for 4WD so the rider’s feeling is more consistent regardless of mode.
To manage kickback and bump-steer, several measures are employed. First, the ECU "reads" countersteer torque that results when terrain-induced forces through the steering stem counteract rider input. In this instance, the motor’s electromagnetic force provides a stabilizing resistance. Even though EPS function may seem unnoticeable at higher speeds, the damping effect is available at all speeds. In addition, rubber dampers on the worm gear shaft, designed to reduce steering free-play, give the system a direct, natural steering feel at all speeds and provide additional cushioning when kickback occurs.
In practice, Honda’s EPS makes it easier to maneuver through rough terrain, rocks, washes and ruts. And because it reduces steering effort and significantly dampens bump-steer, EPS allows the Foreman 500 4x4 to avoid deflection and track straighter, which in turn dramatically reduces rider fatigue.
The Honda EPS system is mounted in line with the steering stem, and its 15-pound weight is carried low and close to the Foreman’s center of gravity so handling is not compromised. The lighter steering feel more than makes up for the extra weight. The self-contained ECU is carried in a tray just forward of the oil cooler. Adding icing to the cake, Honda’s EPS system is also self-contained, totally enclosed and watertight, eliminating the need for any maintenance whatsoever. For Foreman 500 4x4 owners, it truly is a case of having your cake and eating it too.