Electric power steering is just one more way that auto manufacturers are increasing fuel efficiency. The main reason that car makers are switching to this style of system is to meet the government CAFE fuel efficiency standards. Switching a vehicle from a traditional hydraulic assisted power steering to an electric power steering adds about 1 MPG to the vehicles efficiency. Over 60% of all new vehicles sold in the US are now equipped with electric power steering and that number goes up every year.
The three main types of power steering
The Hydraulic Type
Hydraulic power steering is the type of steering assistance that all vehicles came with for decades. If a vehicle had power steering in the 50’s, 60’s, 70’s, or 80’s, it was almost certain to be a hydraulic power steering system. Hydraulic power steering systems use a hydraulic pump that is powered by a belt and pulley. The belt is attached to another pulley that is coupled to the crank shaft. When the steering wheel is turned, the hydraulic pump sends pressurized fluid to the steering rack. The pressure pushes the steering rack to one side or the other based on what direction you are turning the wheel.
The hydraulic power steering system is good in many ways. It is reliable and time tested. It is a system that has worked well for all types and sizes of vehicles for decades.
The Hydraulic system has a few drawbacks. Most automakers are switching to electric power steering because it is more efficient. A hydraulic system requires that a belt be coupled to the engine to turn a hydraulic pump the entire time the engine is running. These systems require belt and fluid changes. These systems also have rubber hoses that eventually leak or break. Bearings in the pumps go out, seals in the steering rack leak, and steering fluid leaks into the ground. If the engine is not turning there is no power assist on the steering. This means that if the vehicle stalls, you lose most of your steering ability.
The Electro-Hydraulic Type
The electric-hydraulic hybrid system is a half measure. It uses the same system and components as an all hydraulic system like described above, but instead of being powered by a pulley coupled to the engine, it is powered by an electric motor. An electric motor is powered by the battery or alternator. The spinning of this motor turns the power steering pump so it can generate pressure to send to the steering rack.
The only real advantage of this system is that it takes the burden of turning the power steering pump from the crank shaft pulley and puts it on the vehicle electrical system. Instead of the engine directly driving the pump, the pump is turned electrically, and the electricity is generated by the alternator. The alternator is of course driven by belt from the crank. There is a slight gain in efficiency in doing it this way.
This system has the ability to run the power steering electrically while the engine is not running. Most systems are not setup to do this though since you don’t do much steering while the engine is off, and it would drain your battery if you did.
All of the same disadvantages of a straight hydraulic system apply to this system except for the belt that drives the pump. Most of these units have the electric motor directly coupled to the pump and eliminate the belt. The disadvantages that this type has on top of all of the same hydraulic components are the electrical components. A standard hydraulic power steering system has zero electronics or electrical components to it. If the pulley is turning the pump, it’s running. This isn’t the case with the hybrid power steering. This type adds electrical wiring, an electric motor, fuses, grounding wires, relays, and switches. Any one of these added electrical components that goes bad can completely eliminate your power assisted steering.
Electric Power Steering
Electric power steering uses no hydraulic components. There is a small steering box like one used on a vehicle with no power steering. There is an electric motor attached to the steering wheel shaft. When sensors detect that you are exerting a certain amount of force on the wheel, the electric motor turns on and helps you turn the wheel the direction you are going. The electric motor is usually coupled directly to the steering column. There is no pump, reservoir, or hydraulic lines. This type of electric power steering consists solely of sensors, and a motor.
The electric power steering system is simple. It has minimal components, and has no fluid to leak or contaminate. There is no belt to wear out. Electric power steering is also the most efficient type of power steering. The reason it’s efficient is that it only runs when it’s needed. If you’re traveling in a straight line and you don’t require steering assistance, the system is using no power. In contrast, the other two types are running the entire time your engine is turning regardless of your need for steering assistance. When you’re sitting at a stop sign idling, the other two systems are using power from your engine. This system uses zero power until you need help turning.
Disadvantages of electric power steering
Electric power steering is a relatively new technology. Hydraulic power steering has been around for over 100 years. The first production car to have electric power steering was in 1988. That makes EPS the newest technology available for power steering systems. Many of these systems are computer controlled. Some people don’t like the settings that the computer is dialed in to. Computer controlled EPS means that there is an added component (the computer) that could go bad. Electric power steering has electrical components that a normal hydraulic system doesn’t. These added components add complexity and opportunity for component failure.
As more and more systems become electrically powered, the job of the alternator becomes increasingly difficult. Power brakes, water pumps, and power steering are all becoming electrically powered instead of being run by a pulley and belt. While these new systems are more fuel efficient, they all contribute to making the alternators job harder.
The Bottom Line
Electric power steering is now the most common type of power steering in new vehicles. This has almost certainly been driven by the need to increase fuel efficiency. All auto makers are now legally required to increase their MPG ratings and switching to EPS (Electric Power Steering) is one small step in that direction. As CAFE standards become stricter, we will see many more changes that are aimed at increasing vehicle efficiency. In the not too distant future, nearly all vehicles will be equipped with this technology.