All About Electric Power Steering

The evolution of power steering: HEPS, EPS, and steer-by-wire

Electric power steering took a long time to catch on, but the technology it's built on has been around for a very 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.

What Is Power Steering For?

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. This early form of electric power steering added additional assistance to traditional power steering with electric pumps.

That technology has been largely supplanted by electronic power steering, which ditches hydraulics altogether. Electric power steering is available in a wide variety of vehicles from virtually every manufacturer.

A closely related technology known as steer-by-wire is an important component in the 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. Just like traditional systems, it uses hydraulic power to reduce the amount of force that it takes to steer a car.

The difference between the two technologies lies in how hydraulic pressure is generated. Where traditional systems generate pressure with a belt-driven pump, electro-hydraulic power steering systems use electric pumps.

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. This is a great safety feature since it makes it easier to steer to safety in the event of an engine dying while driving down the road.

This feature has also been useful in electric vehicles and some fuel-efficient gas vehicles, in that it's able to provide power steering to vehicles that don't have a traditional gas or diesel engine, and hybrid vehicles that are designed to shut down the gas engine at highway speeds.

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 mounted to the steering gear or rack 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, the electric motor may be mounted either to the steering column or directly to the steering gear, or steering rack.

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 decide the amount of steering assistance that’s provided, and others work on a variable curve.

Most OEMs offer electric power steering on one or more of their models.

What Is Steer-by-Wire?

Electric power steering systems remove the hydraulic component while retaining traditional steering linkage, but true steer-by-wire systems 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 pioneered this concept with early drive-by-wire concept cars that eschewed traditional steering linkage, but industry and driver acceptance of this technology has been somewhat chilly.

Nissan announced in late 2012 that it would be the first automaker 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.

Introduced in the 2014 Infiniti Q50, the Independent Steering Control System was steer-by-wire but left traditional steering linkage in place. While they were decoupled during normal usage, they were still there.

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 autonomous cars.

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