Design Considerations for Hydraulic Powerbrake Systems 861200

The Hydraulic Powerbrake System (HPBS) is the hydraulic analogue to the Air Powerbrake System (APBS). The HPBS control element is the brake control valve which is a special design of the pressure reducing valve. The machine operator steps on the pedal mechanism and the valve discharges brake control pressure into the brake cylinder in proportion to his foot effort. The maximum brake line pressure is limited by the choice of measuring spring. Most off-highway machines travel at very low velocities and the HPBS may provide the benefit of anti-skid braking control if the system designer employs some fundamental mechanical princilpes.
The principle involved in anti-skid braking control is to keep the operator from over controlling the brake. The tire must always roll; the coefficient of friction between the tire and the road surface must remain in the static friction condition. One technique is to use a computer based control to modulate the brake line pressure by measuring the rate of wheel rotational deceleration and adjusting the brake line pressure so the wheel does not lock. The technique proposed in this paper is to limit the maximum brake line pressure by mechanical means so the vehicle stops within the prescribed distances without skidding on most surfaces.


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