| 摘要 |
A vehicle speed control system includes a high speed/low speed selection switch and a speed control relay connected to a voltage source through a switched power line. The speed selection switch includes an input connected to the power line through the speed control relay. One output on the speed control switch is connected to an electrohydraulic valve which controls the speed range on a vehicle. The state of the electrohydraulic valve is dependent both on the switch position and on the state of the relay. The relay is deactivated when the power line is switched off and changes back to an activated state to allow high speed operation only if the speed selection switch is first placed in the low speed position after the vehicle power line is switched on. If the selection switch is in the high speed position when the power line is on, the speed control relay will remain inactivated until the selection switch is moved to the low speed position. Thereafter, movement of the selection switch to the high speed position with the switched power line on and the speed control relay activated activates the electrohydraulic valve to place the vehicle in the high speed condition. The operator therefore must change a switch position before high speed operation after start up, regardless of the position of the speed selection switch on start up. A similar circuit utilizing a three position switch provides hydraulic system flow control with high flow inhibited until the operator manually changes the position of the switch. |
