CONTROL ARRANGEMENT FOR A POWER UNIT

摘要

1473204 Hydrostatic transmission control KLOCKNER - HUMBOLDT - DEUTZ AG 25 Sept 1974 [16 Nov 1973] 41680/74 Heading F2W In a hydrostatic transmission for a vehicle wherein an engine driven variable displacement pump 8 is in closed circuit with a variable displacement motor 12 and the pump and/or motor displacement is controlled by a servo 7, 13 to which control liquid is delivered by an engine driven constant displacement pump 15 through a line 17 at a pressure determined by a variable throttle valve 19 or 61, means are provided to prevent pressurization of the line 17 until the engine speed attains a predetermined value higher than engine idling speed. In Fig. 1, a valve 30 controlled by the pressure drop across a variable orifice 18 is spring biased to its open position in which it vents the line 17. The variable orifice 18 is connected by a lost motion linkage 22 to the engine fuel supply lever 3. The lost motion in the linkage 22 permits the lever 3 to increase engine speed to the predetermined value without adjusting the orifice 18. On further movement of the lever 3 the orifice 18 is closed to increase the pressure drop across the orifice to a value which is sufficient to change-over the valve 30. Thereafter the pressure in the line 17 increases to a value determined by the variable throttle 19 and is applied through a reversing valve 38 to the pump displacement adjusting servo 7 and through a line 43 to the motor displacement adjusting servo 13. If the load on the transmission is sufficient to slow the engine, the output from the pump 15 decreases and the pressure drop across the orifice 18 also decreases whereupon the valve 30 opens to effect an increase in transmission ratio and reduce the load on the engine. The resulting increase in engine speed causes the valve 30 to close and the original transmission ratio to be restored. In Fig. 2 the supply from the pump 15 to the line 17 is controlled by a valve 57 which remains closed until the engine speed attains the predetermined value whereupon an engine speed responsive governor 50 opens the valve 57 to pressurize the line 17 and thus permit adjustment of the transmission ratio. The governor loading spring 52 is connected through a lost motion linkage 22 with the engine fuel control lever 3. The lost motion in the linkage 22 is sufficient for the lever 3 to increase engine speed to the predetermined value without providing additional loading on the spring 52.