|
Electronic Rack and Pinion
Some cars may be equipped with an electronic rack and pinion power steering gear. Instead of using a flat rack with straight teeth as found in a conventional rack, this type of steering gear uses a helical-gear rack driven by a moving ball nut.
The ball nut is acted upon by a fast-acting electric motor. A magnet and a magnetic sensor mounted on the pinion shaft works as a torque sensor, which signals the ECU, telling the computer how much steering torque is being applied by the driver, and in what direction. As the magnetic sensor detects greater movement, the signal sent to the ECU becomes stronger. This causes the ECU to send a varying voltage to the electric motor inside the rack housing. The ball nut, which is directly attached to the electric motor, then runs over the helical grooves on the rack, causing the rack to move right or left as needed. An electric power steering rack does not use a hydraulic system, so there is no power steering pump, hoses, reservoir or fluid.
Power Rack and Pinion Diagnosis
If vibration is felt in the steering wheel and / or the dash during parking or low speed operation, it is possible that air is trapped in the power steering fluid. The vibration should go away after a few miles of operation. However, a loose or worn tie rod or tie rod end might also be the cause. If the steering catches, binds or sticks in certain positions, or is difficult to turn, there are a number of possibilities, including low power steering fluid, under-inflated tires, dry, non-lubricated front ball joints, worn lower ball joints, dry outer tie rod ends, a loose power steering drive belt, faulty power steering pump, excessive friction in the steering column, a binding lower ball joint, a worn front strut spring seat and bearing or excessive friction in the steering gear. If the steering is hard to turn, or if the driver experiences momentary increases in effort when turning the steering wheel, the power steering pressure switch might be bad, or the steering gear assembly might have a leak in the high pressure circuit. Other causes might include under-inflated tires, low power steering fluid level, dry ball joints, worn lower ball joints, or low power steering pump pressure. If the rack and pinion unit was damaged in a collision, the toothed rack might be bent or chipped.
|
