Parameter Steering
Parameter Steering (PML) is a speed-responsive power steering system. It incorporates conventional servo assistance into its basic function. Vehicle speed serves as the parameter. With the aid of electronics, the hydraulic steering force assistance is precisely adapted to the respective requirement in each defined speed range. Thus when parking, high steering force assistance is ensured which then decreases as speed increases.
The steering force assistance is no longer reduced at speeds above 50 MPH (80 km/h). The result is that parameter steering does not become excessively difficult to operate as speed increases further.
Speed is recorded via the PML control unit (located in combination control module box, in right rear corner of engine compartment) which receives the speed signals from the speed sensors.
By means of speed detection, a performance map stored in the PML control unit is used to control the PML "P" valve (Y10). An electronically controlled control orifice in the PML "P" valve (in the steering housing) controls the differential pressure at the end facing the spool valve, depending on the actual effective operating pressure and the respective speed.
The torque to be supplied by the driver at speeds above 50 MPH (80 km/h) is therefore approximately 3-4 ft. lbs. (5-6 N.m).
The components for controlling the PML are constantly monitored. If there is a fault in the electronic system, the parameter function is switched off and the basic steering is retained. At speeds below 50 MPH (80 km/h), the torque at the steering wheel is reduced in accordance with the stored performance map in the PML control unit so that it is approximately 1-2 ft. lbs. (2-3 N.m) during parking. See Fig 1 .