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Originally Posted by Rtech Maybe what was meant was the the car should not be left in the full lock position. This puts a lot of pressure on the seals in a hydraulic PS system, which, if left in that position for a length of time would cause some seals to give way, leading to a loss of PS. This is a fact though. I think... |
My, my, what Urban legends abound! Technology is based on logic not hearsay
1) Neither springs, nor Hydraulic pressure in the steering system, returns steered wheels to the straight ahead position. Steered wheels return to the straight ahead position only due to the "caster" (the British spell it as "castor") angle of the kingpin, leading the point of contact of the wheel on the road.
For this very reason, swiveling caster wheels on hospital-beds and airport baggage trolleys, straighten out when you push them straight ahead.
2) Power Steering
Case: Hydraulic Power Steering
When the engine is switched off, the power steering pump stops producing hydraulic pressure. Power steering systems are not designed with any pressure tank to hold the pressure for "next morning" steering assistance. There is no fear of any seal giving way due to imaginary pressure in the steering system when the engine is not running.
That being said, you can damage a power steering system by continuously holding the steering wheel against the travel locks at either extreme, with the engine driving the power-steering pump. When you do this, pressure applied to the steering-rack is maximized. All of the fluid output of the power-steering pump flows through the relief valve (that is the loud hum you hear). This heats up the power-steering fluid and it applies maximum pressure to the seals. The hot fluid and high pressure can damage a seal. But when you switch-off the engine in a parked car all of this no more applies!
Case: Electronic Power Steering
In a completely electric power-steering system. Sensors detect the motion and torque of the steering column and embedded software applies varying amounts of assistive power via electric motors, depending on driving conditions. Even in this case the pressure exerted disappears when the car is switched off.
3) In lands used to over a century of automobiles, (Europe and USA)
it is law, that cars parked on a hill
must have their wheels steered all the way to prevent rolling all the way downhill, should the parking brakes fail.