The first mass-production car with power steering was the 1951 Chrysler Imperial, and ever since then, the system used to reduce the force needed to turn vehicles has evolved. Today, there are three types of power-steering systems that counter pros may encounter: hydraulic power steering (HPS), electric power hydraulic steering (EPHS) and all-electric power steering (EPS).
HPS uses hydraulic fluid supplied by an engine-driven pump to assist in turning the steering wheel. An accessory drive belt provides pressurized fluid to the high-side power-steering hose and delivers it to the input side of the steering rack that drives the power-steering pump. Power-steering fluid is pulled from the reservoir, which is replenished to the appropriate level by a low-side power-steering hose that returns fluid from the gear at low pressure. This type of system has been used for decades until recently.
In the push for better fuel economy, manufacturers have introduced new electric systems to reduce the load on the engine. EPHS uses similar components as the traditional hydraulic units, but the pump is driven by an electric motor instead of the engine. This is more of a hybrid hydraulic-electric power-steering system.
In an all-electric EPS system, the electric motor reduces the load on the engine and is only active when the steering wheel is turned one way or the other, which improves fuel economy. Due to the increased drag on the alternator, a load is still applied to the engine when the steering wheel is rotated. However, the drag on the alternator is much less than the continuous drag from a belt-driven system.
In an EPS system, an electric motor is mounted on the steering column or steering rack. As torque is applied to the steering column, the motor kicks in the necessary amount of assist based on various conditions. Sensors detect input from the driver and the position of the wheel. If the wheel is held steady in the straight-ahead position, the EPS doesn’t provide assistance. But with any other movements or change of direction, the EPS will come on and decrease the force needed to turn the wheel.
With EPS, automakers can program variable assist for parking speeds using full assist to make it easier to maneuver around. The assist level also can be reduced at highway speeds to allow for more vehicle stability. Having some resistance built into the steering at higher speeds means the car will not dart around due to over-correcting. Think of a video game with a joystick instead of a feedback steering wheel. The lack of feedback usually makes steering impossible.
The Future of Power Steering
There is one other power-steering system that may be coming down the road sooner than we think. The system uses no direct mechanical connection to the steering linkage (except for emergency situations). The steering system is called “drive by wire” or “steer by wire.” Most technicians are already familiar with throttle by wire, which uses an electronic signal to operate the throttle instead of a cable. Steer by wire, which Infiniti introduced a few years ago on its Q50 sports sedan, uses electric wires to convey driver steering inputs to servo motors that steer the linkage. Remote-control cars have been using this technology for many years.
The advantage of this type of system is that it can be used for adaptive controls such as lane assist. While there have been a few hiccups with the original version from Infiniti, the new system is said to have addressed all of the issues and offer much better driver feedback.
We keep hearing about autonomous and electric vehicles taking over the roads in the next five or 10 years. For now, though, there’s a lot more we can squeeze out of the traditional package including the steering controls.