Patent GB-1482947-A (GB)
Title: System for the combined control of an internal combustion engine and a hydrostatic transmission connected thereto
IPC: B60W10/10
Filed: 1974-08-13
Abstract: 1482947 Hydrostatic transmission control ROBERT BOSCH GmbH 13 Aug 1974 [13 Aug 1973] 35552/74 Heading F2W [Also in Division G3] A control system for a hydrostatic transmission comprising a variable displacement pump driven by a diesel engine, comprises electro-hydraulic means for varying pump and motor displacement, a signal derived from the position of an accelerator pedal 25, a signal responsive to the input torque of the transmission, a signal responsive to engine speed and signals responsive to the pressures in the main lines all effecting control of transmission ratio. The accelerator 25 may act directly on the fuel injection equipment 48 of the engine or it may control this via a transducer 26, demodulator 45 and voltage regulator 46. The output of demodulator 45 is also supplied to further, non-linear, regulators 62 and 91. Main-line pressure transducers 38, 39 supply signals to a device 84 which selects the greater signal to supply it through a circuit 85 (Fig. 12, not shown) to a multiplier 105. Multiplier 105 also receives a signal from a transducer 103 sensitive to pump swash-plate position and produces an output which is a measure of transmission input torque and supplies it to a control circuit 63. The circuit 63 also receives an input from a pressure-limiting circuit 86, this limiting the pressure in the higher pressure main-line in dependence on the accelerator position as represented by the output of non-linear regulator 91, and receives signals from the regulator 62 and from a transducer 33 responsive to engine speed. Circuit 63 compares the input torque, as indicated by multiplier 105 with desired torque (as indicated by accelerator position), the output of circuit 63 controlling pump and motor displacement operating devices 34, 41 through Schmitt triggers 65, 66 which have a dead zone to prevent hunting and through a driving direction control device 67. The engine speed responsive signal prevents the engine from being overloaded by being supplied through a voltage regulator 96 to the pressure limiter 86 to cause this limiter to supply a signal to circuit 63 which reduces the pressure in the transmission. A circuit 79 (Fig. 7, not shown) receives the pressure signals from transducers 38, 39 to detect when the vehicle is operated on overrun to alter the displacement to increase transmission pressure. For a vehicle in which the engine drives a power take-off, inching of the vehicle while the engine rotates at high speed is possible by use of a pedal 92 which supplies a signal to the pressure limiter 86, from transducer 93 via regulator 95 to reduce the transmission pressure. The electro-hydraulic pump displacement control is shown in Fig. 8, the swash-plate 114 being moved by a spring-biased double-acting piston 116 under pressure supplied to it from a pump 132, this continuously supplying pressure to a side of the piston with smaller area, due to the presence of piston-rod 117, and selectively supplying pressure to the other side through a solenoid operated valve 34a to move the piston 116 to the right. A further solenoid operated valve 34b vents the left side of the piston to move the piston to the left.