All About Electric Power Steering

The Evolution of Power Steering: HEPS, EPS, and Steer-by-Wire

electronic power steering
Electronic power steering can take a number of different forms, some of which make steering easier, and others that are designed to replace traditional steering systems altogether. Marin Tomas / Moment / Getty

Electric power steering is pretty new, but the technology it's built on has been around for a long time. In fact, power steering has been around just about as long as the automobile, and large trucks were fitted with aftermarket systems as early as 1903, but it wasn’t offered as an OEM option until the 1950s. The technology is ubiquitous today due to its inclusion as standard equipment in nearly all new cars and trucks, but it remained optional in a number of lower-priced, entry-level cars throughout the 1980s and 1990s.

The purpose of power steering is to reduce the amount of effort that it takes for the driver to steer. This was traditionally accomplished through hydraulic power, which can be generated by a belt-driven pump that runs off the rotation of the engine. However, the technology has undergone a steady stream of innovations and upgrades since it first showed up as an OEM option in the 1950s.

The first major upgrade to traditional hydraulic power steering that saw any sort of wide uptake was electro-hydraulic power steering. However, that technology has been largely supplanted by electronic power steering. And while electronic power steering is offered by a number of automakers, some OEMs are also working with steer-by-wire systems as they push toward fully drive-by-wire cars.

Electro-Hydraulic Power Steering

Electro-hydraulic power steering (EHPS) is a hybrid technology that operates just like traditional hydraulic power steering. The difference between the two technologies lies in how the hydraulic pressure is generated. Where traditional systems generate pressure with a belt-driven pump, electro-hydraulic power steering systems use electric motors. One of the major benefits of electro-hydraulic power steering is that the electric pump doesn’t necessarily lose power when the engine is shut off, which is a feature that some fuel-efficient vehicles have taken advantage of.

Electric Power Steering

Unlike hydraulic and electro-hydraulic systems, electric power steering (EPS) doesn’t use any form of hydraulic pressure to provide steering assistance. The technology is fully electronic, so it uses an electric motor to provide direct assistance. Since there is no power lost generating and transmitting hydraulic power, these systems are typically more efficient than either hydraulic or electro-hydraulic steering.

Depending on the specific EPS system, an electric motor is mounted either to the steering column or directly to the steering gear. Sensors are used to determine how much steering force is required, and then it is applied so that the driver only has to exert a minimum amount of effort to turn the wheel. Some systems have discrete settings that vary the amount of steering assist that’s provided, and others work on a variable curve.

Most OEMs offer EPS on one or more of their models.

Steer-by-Wire

While electric power steering systems remove the hydraulic component while retaining traditional steering linkage, true steer-by-wire also do away with the steering linkage as well. These systems make use of electric motors to turn the wheels, sensors to determine how much steering force to apply, and steering-feel emulators to provide haptic feedback to the driver.

Steer-by-wire technology has been used in certain heavy-duty equipment, forklifts, front-end loaders, and other similar applications for a while, but it’s still relatively new to the automotive world. Automakers like GM and Mazda have made fully drive-by-wire concept cars in the past that eschewed traditional steering linkage, but most OEMs have kept the technology out of production models.

Nissan announced in late 2012 that it would be the first OEM to offer the technology in a production model, and its Independent Steering Control system was announced for the 2014 model year. However, even that system retained the vestiges of a traditional steering system. The linkage and column were still there, although they were decoupled during normal usage. The idea behind that type of system is that If the steer-by-wire system fails, the coupler can engage in order to provide the driver with the ability to use the mechanical linkage to steer.

Together with other drive-by-wire technologies, like brake-by-wire and electronic throttle controls, steer-by-wire is a key component in self-driving vehicles.