GB1417699A - Hydraulic transmission systems - Google Patents

Abstract

1417699 Hydrostatic transmissions BROCKHOUSE ENG Ltd 22 Jan 1973 [22 Jan 1972] 3171/72 Heading F2W [Also in Division F1] In a hydrostatic transmission in which a prime mover (not shown) drives a variable displacement pump 20, 121 to supply pressure fluid to a motor 22, 122 a single control 25 (shown as a pedal) is provided common to both the pump and prime mover control means and allows pump displacement to be reduced when the output pressure thereof exceeds a predetermined value, and also allows this displacement to be reduced if the torque demanded of the prime mover is too great. In Fig. 1 a mechanical system is shown in which the pedal 25, when depressed moves the control member 21 of the pump away from its zero output position via a spring 30 and against the force of a piston 26 biased by the output 27 pressure of the pump, and also moves the fuel supply control 36 of the prime mover via linkage 42, a spring 40 and rods 33 and 35, against a force supplied by the prime mover speed governor 24, which has flyweights 45. Thus if the output pressure of the pump 20 increases beyond a value set by spring 30 by means of pedal 25 the piston 26 will be moved thereby to reduce pump output and so maintain this value, and if the engine speed increases beyond that set by the balanced position of rod 33 (due to the spring 40 acting against governor 24) the speed is reduced by the governor (or by the spring if the speed falls). If the engine is unable to meet the torque demanded of it by the pump 20, with pedal 25 fully depressed and the fuel supply at its maximum, the governor 24 will be unable to balance spring 40 and this spring will move rod 33 to the right against a light spring 37 and cause an extension 51 to abut control 21 and so reduce pump displacement, and the required torque. An alternative embodiment is shown in Fig. 2 in which hydraulic circuits are used in place of mechanical linkages. In this embodiment depression of pedal 25 causes pressure liquid to pass from a pump 110 via a valve 101 through conduits 111, 113 and 113a to the bottom of a governor valve 102 to move this to increase engine speed by the supply of pressure to the fuel supply control valve 104 from the pump 110 via lines 129 and 130, depression of pedal 25 also opening a valve 100 to supply pressure fluid to an actuator 118 or 117 for moving the swashplate of pump 121 for forward or reverse drive depending on the position of a reversing valve 114. The pressure supplied to adjust the pump 121 also actuates a valve 145 to cause the pressure in the high pressure line to motor 122 to be supplied to a piston 149 which acts on valve 100 via a lever 143, thus causing the pump displacement to be reduced if greater than a predetermined pressure (set by pedal 25 via spring 108) is being supplied to pump 122. The fuel supply is controlled by pressure supplied to behind a piston 132 to act on a lever 133, this piston having the head 134 of a rod 135 within it, which rod can move a valve body 136 against a spring 139, so that should the engine, with pedal 25 fully depressed, not produce the torque required by the pump 121 the resultant upward movement of valve 102 as the engine slows causes increased pressure to be supplied via line 130 to move piston 132 beyond the maximum fuel setting, thus moving valve body 136 through rod 135 and causing pressure fluid to pass through a line 141 to reduce pump displacement by moving a piston 142 to adjust valve 100. A line 151 is provided so that, with the system installed in a fork lift track, operation of a service through a separate hydraulic system causes pressure to be supplied to the bottom of valve 102 to increase the engine output. A charging pump 110a may be provided. Various throttle valves 165 may be provided for damping and a relief being the supply and return lines to motor 122 can be provided. A modified form of the embodiment shown in Fig. 2 (Fig. 9, not shown) has means to return the pump to neutral on release of pedal 25 to effect hydrostatic braking. The invention may be used with an hydraulic ram as motor instead of the rotary motors in the above embodiments. The control of fuel supply may involve the control of the electrical supply to an electric motor instead of the control of the fuel supply to an internal combustion engine. The motor 122 may have variable capacity to provide higher transmission ratios. The pump may be a vane type with adjustable eccentric instead of a swashplate type with axial pistons.