Abstract

Conveyance loading ramp has its inner end pivotally supported adjacent a building structure and the other end mounted on a mobile undercarriage having a pair of ground engaging wheels mounted one on each side of the ramp for rotation about a common horizontal axis. The undercarriage is supported for pivotal movement about a vertical axis for steering and an improved hydraulic driving and steering system includes separate hydraulic motor connected in series to drive the wheels. A first reversible variable flow control valve connected in the hydraulic circuit is operable to control both the rate and direction of flow of hydraulic fluid to the series connected motors and a second reversible variable flow valve connected in the circuit between the first valve and the hydraulic motors is operable to bypass one only of the hydraulic motors with a portion of hydraulic fluid from the first valve whereby the series connected hydraulic motors can be driven at different rates to steer the outer end of the ramp during expansion and retraction movement. A single manually actuated control connected to the first and second valves simultaneously controls both steering of the undercarriage and the direction and rate of movement of the drive motors.

Other References

• "Basic Electrical Engineering", McGraw-Hill Book Co., Inc., 2nd ed. 1957