What is Power Steering?
Power steering is a system that helps a driver turn the steering wheel with less effort, pointing a car or truck's front wheels in the direction the driver intends to go.
Automakers utilize three systems in today's cars and trucks: hydraulic power steering, electric power steering, and electro-hydraulic power steering. These three systems each have benefits and drawbacks, but all serve the same function.
The first power steering system was patented just after the turn of the 20th century by Robert Twyford as part of a four-wheel-drive platform he was building. In 1926 Francis Davis invented a system closer to what is still in use today. Power steering did not make its way into a mass-produced automobile until the Chrysler Imperial in 1951.
Why Power Steering?
Power steering was first added to higher-end vehicles as a feature that made driving easier for affluent buyers. The less effort required to drive, the more luxurious the car felt.
Similar to the adoption of automatic transmissions, this feature trickled down into the mainstream over time. Power steering became more common as vehicles became heavier.
The wide adoption of front-wheel-drive meant the engine and transmission's weight were concentrated mainly on the front axle. It necessitated the addition of a mechanical aid. With vehicles consistently getting heavier, power steering is now ubiquitous.
The last car available in the United States without power steering was the 2020 Alfa Romeo 4C Roadster.
What is Hydraulic Power Steering?
Hydraulic systems use a power steering pump to apply hydraulic pressure to the steering system as the driver turns the wheel. The more the wheel turns, the more hydraulic fluid is allowed through the system, making it easier to turn.
Some systems use an electronic control valve to adjust the amount of fluid in the system to decrease the pressure at higher speeds and increase it at low speeds. This variable-assist power steering allows for less effort at lower speeds, like in a parking lot, and higher steering precision for faster speeds like highway driving.
A few downsides come with hydraulic systems. The main is the added maintenance of checking the hydraulic fluid level and periodically changing the power steering fluid.
As with all automotive fluids, there are also hydraulic lines and connections, which means possible leaks and replacement. Additionally, the hydraulic pump uses a belt and pulley directly powered by the engine, sapping fuel economy.
Hydraulic power steering systems are what most cars used until fairly recently. With the Chrysler Imperial in 1951, followed by Cadillac in 1952, these were the first mass-produced models fitted with hydraulic power steering.
What is Electric Power Steering?
Most modern cars use an electric power steering system or EPS. Today's EPS systems use an electric motor mounted on the steering rack or steering column to turn the steering shaft, move the rack and pinion, and thereby the front wheels. The electric motor gets its power from the vehicle's electrical system and only draws power when in use. If the steering wheel is held steady, the power steering system does not need to use any electricity.
Other benefits of electric power steering include increased fuel economy due to the electric motor only drawing power from the system when needed. The vehicle can also utilize the electric power steering components to move the steering wheel without any driver input, such as in modern lane-keeping assistance systems.
This technology is being used for semi-autonomous self-driving cars as well. The same system that assists the driver will eventually be able to control the vehicle entirely, based only on the car's sensors and computers.
Electric power steering allowed for another innovation, variable steering gear ratios. Honda debuted this technology in the Japanese market with the Honda S2000 Spec V. It has since made its way into other models worldwide. The system uses various inputs to determine the optimal steering input ratio for the steering system. It better mimics the steering feel of traditional hydraulic steering and even non-assisted steering setups.
Electric power steering made a rough entry into the American market. Automakers struggled to find the balance between assistance and effort that still allowed the road's feel to transmit to the driver through the steering wheel. It has, for the most part, been rectified, particularly in sports cars. Porsche's system stands out as being extraordinarily engaging and communicative.
What is Electro-Hydraulic Power Steering?
As the name indicates, electro-hydraulic power steering is a hybrid of two preexisting systems. An electric pump creates the hydraulic pressure to run a more traditional hydraulic system. It allows the power steering to be remote from the engine without running high-pressure hydraulic lines throughout the vehicle.
The other benefit is that the system can run off the battery when the engine is not on. Electro-hydraulic systems can still be found in many cars today, most commonly in heavy-duty trucks.
Toyota used an electro-hydraulic power steering system in its mid-engine MR2 sports car for this reason.
What is Steer-by-Wire?
Although not a power steering system, steer-by-wire deserves mention. All of the previously discussed setups operate differently. However, there is still a mechanical connection between the steering wheel and the turning wheels.
Drive-by-wire eliminates physical contact, meaning the driver turns the steering wheel, and a computer interprets that input to steer the vehicle. The car's computer also does the reverse, sensing the road and simulating that sensation through the wheel and back to the driver.
Infiniti was the first manufacturer to bring this to a mass-produced passenger car.
However, it has been used in aircraft for decades. Their systems still have a clutch-engaged mechanical connection and a traditional steering column, should the electronic systems fail.
Steer-by-wire control could someday spell the end for conventional steering wheels, opening the way for a joystick or other device to control a passenger car.