The Power Steering System & Steering Gear

There are several components in your vehicle’s power steering system that make it easier to turn and steer the vehicle accurately. Cars of old had huge steering wheels and required a lot of muscle to manage the manual steering system. Thanks to technology, modern vehicles are much easier to turn and steer.

The major power steering system components between the steering wheel and steering gear include the steering wheel itself, steering column, steering coupler, steering gear, power steering hoses, and power steering pump. Typically, the power steering system has been hydraulic, but electric power steering systems are becoming increasingly more common. Electric power steering systems consist of additional components including various sensors, wires, actuators, motors, and an electronic control unit.

There are three basic types of power steering systems found in vehicles: the hydraulic power steering (HPS), the electric power hydraulic steering (EPHS), and the fully electric power steering (EPS). Electric and electronic power steering both refer to the same system.

Hydraulic power steering (HPS) uses hydraulic pressure supplied by an engine-driven pump, known as the power steering pump, to assist the motion of turning the steering wheel. The power steering pump is turned by the accessory drive or serpentine belt and provides pressurized power steering fluid to the high side power steering hose which delivers it to the input side of the power steering control valve at the steering gear. Power steering fluid is drawn from the power steering fluid reservoir which is maintained at the appropriate level by a low side power steering hose that returns the fluid from the gear at a much lower pressure.

HPS provides many disadvantages. Since the power-steering pump equipped on most vehicles runs constantly and pumps fluid all the time, it wastes horsepower. This wasted power translates into wasted fuel and higher emissions. In addition, this system is susceptible to leaks and noises, and commonly results in failure due to a broken belt.

Electric power hydraulic steering (EPHS) is a hybrid of hydraulic and electric. In this system, a hydraulic pump gets its energy from an electric motor instead of a belt driven by the engine. In EPHS the customary drive belts and pulleys that drive a power steering pump are replaced by a brushless motor. The power steering is driven by this electric motor, which reduces the amount of power that needs to be taken from the engine.

In the electric power steering (EPS) system, an electric motor replaces the hydraulic pump and a fully electric power steering system is established. The electric motor is either attached to the steering rack or to the steering column. The electronic control unit controls the steering dynamics. EPS is often a preferred system since it results in better fuel economy and lower emissions.

EPS provides many additional advantages. The amount of assistance provided by EPS is easily tunable to the vehicle type, road speed, and even driver preference. Another benefit is the elimination of environmental hazards posed by leakage and disposal of hydraulic power steering fluid. In addition, electrical assistance is not lost when the engine fails or stalls, whereas hydraulic assistance stops working if the engine stops.

"Steer-by-wire" or "drive-by-wire" steering systems are also being designed and implemented. These systems eliminate the mechanical connection between the steering wheel and the steering system, replacing it with a purely electronic control system. This system frees up a lot of space in the dashboard that can be used for other things.

There are two main types of steering gears used for most modern vehicles: the rack and pinion steering gear and the recirculating ball steering gear. The rack and pinion style is by far the most common, but the recirculating ball is still used on some trucks and heavier vehicles, and always utilizes a Pitman arm to transfer movement to the steering linkage.

The rack and pinion steering gear translates driver steering input into movement of the front wheels for turning. In this system, a pinion gear is connected to the steering shaft which means that as the steering wheel is turned it turns the pinion gear in a circular motion, then moves the rack in a linear motion. It is basically using the rotational motion of the steering wheel, then converting that rotational motion into linear motion, which is required to turn the wheels. On either end of the steering rack are rubberized plastic bellows, which secure to the rack body and the moving part of the rack to keep dust and debris from entering the rack and pinion unit.

The recirculating ball steering gear also translates driver steering input into movement of the wheels for turning. In this system, a box is fastened over a worm drive that contains many ball bearings. These ball bearings loop around the worm drive and move into a recirculation channel, then back into the worm drive. When the steering wheel is turned, the worm drive turns and forces the balls to press against the channel inside the nut. The pressure from the balls forces the nut to move along the worm drive which rotates a Pitman arm, moves the steering linkage, and ultimately turns the wheels.

The steering column is the housing which holds the steering wheel and shaft secure. The steering coupler is located at the bottom of the steering shaft. This is a joint that allows the steering wheel to rotate without binding up in the column, due to the fact that the input shaft and steering column are not in perfect alignment and at a slight angle to one another. The steering coupler connects the steering wheel and shaft to the steering gear.

If your vehicle has hydraulic power steering, there are two main power steering hoses: the high side (high pressure) hose and the low side (low pressure) hose. Both are attached to the rack and pinion with threaded brass fittings. The high side hose is attached to the power steering pump with a threaded brass fitting, while the low side hose slides over a small pipe and is secured with a hose clamp. The high side hose carries pressurized power steering fluid to the steering gear to provide the power assist to the steering inputs. The low side hose carries low pressure fluid back to the pump and reservoir.

Because of the many components of the power steering and steering gear systems, and due to their cohesive nature, an inspection of these systems should be thorough. Hydraulic components, including the power steering pump and hoses, should be inspected for leaks. The power steering belt should be inspected for damage, cracking, wear, and tightness. The steering gear should be inspected for looseness and leaks. The bellows boots on a rack and pinion steering gear should be inspected for tears and damage. The steering wheel and column should be secure, and the steering coupler should be tight, but move freely with no noises. Electronic power steering components should be visually inspected for damage.

The power steering should be operated both left and right while driving to inspect for binding, noises, and ease of operation. The power steering system and steering gear greatly contribute to the safe operation of your vehicle. Have an ASE certified technician inspect all the components of your vehicle’s power steering and steering gear systems as outlined above at least once per year.