GB961060A - Vehicles with hydrostatic transmission - Google Patents

Abstract

961,060. Motor vehicle hydraulic transmissions. ELECTRO-HYDRAULICS Ltd. Nov. 16, 1962 [Nov. 23, 1961], No. 42006/61. Heading B7H. [Also in Division F2] The hydraulic system of a vehicle with hydrostatic transmission and at least one hydraulically-operated service such as a loadelevating ram 49 comprises a variable-speed prime mover driving a variable displacement first pump 1, which supplies fluid to a fixed displacement motor 4 coupled to the vehicle wheels, and a second pump 5 supplying hydraulic pressure for an hydraulic service, means 53 to vary the displacement of the first pump in response to a first manual control such as an accelerator pedal 81 and further means to override the influence of the first manual control under the control of a second manual control such as a brake pedal 88 or a service control valve 40 or 41. The arrangement is such that the prime mover speed may be increased to increase the hydraulic supply to a service without a corresponding increase in vehicle speed. In the embodiment, a fork lift truck, the hydraulic system, shown in the neutral condition, further comprises a reservoir 8, boost pump 7, relief valve and manual unloader valve 13, the latter permitting free-wheeling of motor 4, service control valves 40, 41 respectively for mast-lifting rams 47 and lift ram 49, differential area device 27 which either prevents stalling of the prime mover or limits the displacement of pump 1 and hence the vehicle speed when a service is being operated. For forward drive, for example, lever 76 is moved to the left, moving rod 84 and link 87 to the left and rod 75, link 80 and spring centralized lever 70 to the right. Depression of accelerator pedal 81 increases the prime mover speed through linkage 91, 92, 93 and rotates link 57 clockwise about pivot 58 to increase the displacement of pump 1 through linkage 56, 54, 53 and swash plate servo 51. When maximum pump displacement has been obtained increase in engine speed is provided by rotation of portion 81B of pedal 81 about pivot 81C. Depression of brake pedal 88 rotates link 66 anticlockwise, drawing rod 62, block 61 and rod 56 to the right, reducing the displacement of.pump 1 and compressing spring 60A. Simultaneous operation of both pedals 81 and 88 maintains the output of pump 1 constant. The differential area device 27 contains a piston 97, with a passage 100 through it, rigid with a smaller diameter spindle sliding in piston 102 and a larger diameter spindle 98 surrounded by spring 99, the spindle diameters and spring being such that when the motor inlet pressure communicated through line 21 or 22, shuttle valve 23 and line 25 rises sufficiently to stall the prime mover piston 97 moves down and spindle 98 contacts end 70F of lever 70 rotating it anticlockwise and hence reducing the motor displacement through linkage 68, 54, 53. The pressure delivered by pump 5 is communicated through line 37 to the upper end of piston 102 and when the pressure rises sufficiently depresses the piston 102 and hence spindle 98 to reduce the displacement of pump 1 and hence the vehicle speed. Fig. 2 shows a service selector valve arranged to move link 93 so as to increase the engine speed when control lever 103 is moved from the central neutral position by moving cam-plate 104 vertically, which pushes pin 106 to the right, rotating bell-cranks 107 and 109 clockwise so that stop 110 moves lever 111 and hence link 93.