Toyota Electric Power Steering (EPS)Written by gary on February 7th, 2010
Electric Power Steering (EPS) is replacing hydraulic power steering in many new vehicles today.
One of the advantages of electric power steering is that it eliminates the power steering pump, which can use as much as 8 to 10 horsepower under load. This improves fuel economy while also eliminating the weight and bulk of the power steering pump and hoses. Getting rid of the hydraulics also does away with fluid leaks and the need to check the power steering fluid. Electric power steering is also quieter than hydraulic systems because there is no pump noise and no fluid flowing through hoses and valves. But the most noticeable difference is in handling and steering refinement.
Electric power steering can be fine tuned with a precision that is hard to match with hydraulic controls. By monitoring the driver’s steering inputs, vehicle speed, and other suspension dynamics, the system can provide just the right amount of steering feel and effort to match rapidly changing driving conditions. EPS can deliver extra effort when you need it, and reduce steering effort when you do not need it. It can even provide steering assist when the engine is off.
When the driver turns the wheel, a steering sensor detects the position and rate of rotation of the steering wheel. This information along with input from a steering torque sensor mounted in the steering shaft is fed to the power steering control module. Other inputs such as vehicle speed and inputs from the traction control or stability control systems are factored in to determine how much steering assist is required. The control module then commands the motor to rotate a certain amount, and a sensor on the motor provides feedback to the control module so it can monitor the motor’s position.
Better yet, because an EPS system is software driven, it is possible to tap into the steering module and modify steering effort and feel. This can be done with a factory scan tool on some applications, and with aftermarket “tuner” scan tools and software.