Patent GB-1193802-A (GB)
Title: Improvements in Hydraulic Transmissions
IPC: F16H61/46
Filed: 1968-07-15
Abstract: 1,193,802. Change-speed control. ROBERT BOSCH G.m.b.H. 15 July, 1968 [13 July, 1967], No. 33653/68. Heading F2D. [Also in Division F1] A vehicle has an engine fuel pump and hydrostatic transmission conjointly controlled, overriding means being provided to reduce the capacity of the transmission pump in order to limit the engine torque to a predetermined maximum which varies in accordance with the engine speed, and in order to limit the transmission pressure to a predetermined maximum. As shown a control lever 9 is fast with a shaft 11 carrying a cam 12 acting through a follower 22 on a control rod 25 of a servomotor 8 controlling the displacement of the transmission pump 1 which is driven by a diesel engine 2 and supplies an hydraulic motor 5. A cam 20 moving with the cam 12 but adjustable relative thereto, also acts on the control rod 25. The lever 9 is conected by links to a shaft 14 carrying cams 15, 16; the cam 15 controls an adjusting lever 27 of the injection pump 26 of the diesel engine. The servo-motor 8 controlling the stroke of the pump 1, which may be of the swash-plate type, comprises an annular servo-chamber 66 which is permanently connected to the high-pressure side of the transmission through a bore 73. The control rod 25 has a cranked end 76 accommodated in a bore 74 of a servo position 64, a valve piston 79 being biased by a spring 82 against the sloping surface 78 provided by the cranked end of the rod 25. Movement of the rod 25 to the right causes inward movement of the valve piston 79 which opens a servo chamber 65 to the chamber 66 through passages 85, 86 to shift the piston to the right to follow-up the movement of the rod 25. Leftwards movement of the control rod 25 moves the valve piston outwardly to open the chamber 65 to exhaust via passages 83, 84 and the piston moves leftwardly to follow-up movement of the control rod. The chamber 65 is connected by a line 48 to a control valve 38 which is operated to reduce the pump displacement in the event of excessive transmission pressure and of excessive torque being transmitted. The transmission pressure lines are connected through non-return valves 58, 59 to a line 57 leading to an actuator 56 acting through a lever 50 on the control valve 38 to shift it rightwardly in the event of excessive transmission pressure. Rightward movement of the valve opens the line 48 leading to the servochamber 65 to a line 45 which is connected to the transmission line 4 which is the return line for forward drive. Thus for forward drive the pressure in the servo chamber 65 is reduced so that the piston 64 moves leftwardly to reduce the forward displacement. Such leftwards displacement opens the chamber 65 to the chamber 66 but liquid leaves the chamber 65 via the valve 38 at a greater rate than that at which it enters so that the pump displacement is reduced until the transmission pressure falls. For reverse drive pressure in the chamber 65 is increased so that the piston 64 moves rightwardly to reduce the reverse displacement, the opening of the exhaust passages 83, 84 being insufficient to prevent his movement. The injection pump 26 has a regulating rod 29 which is drawn into the pump housing as the engine speed drops. The rod 29 has an abutment 30 co-operating with a lever 31 acting on the control valve 38 and fulcrummed at 32 to the end of the lever 33 which is fulcrummed at an intermediate point and carries at its other end a follower co-operating with the cam 16. Thus the engine speed at which the abutment 30 actuates the lever 31 is varied in accordance with the fuel pump setting and the valve 38 is actuated to reduce the pump displacement to prevent the engine torque rising above the optimum value corresponding to its speed. The cams are so shaped that for forward drive from the position shown to position A the engine speed is increased from its idling speed to 40% of its maximum speed while the transmission pump displacement remains at zero, from position A to position B the pump displacement is increased from zero to its maximum while the engine speed remains at 40% of its maximum value. From position B to position C pump displacement remains at its maximum value and the engine speed is increased to its maximum. For reverse drive the engine speed is increased to 40% of its maximum by the point E, both engine speed and pump displacement being increased up to point F. In order to operate a power take-off shaft 88 at engine speeds above 40% of the maximum without actuating the hydraulic transmission the servomotor 8 is not controlled by the cam 12 for forward drive, but by the cam 20 which is carried by a shaft 19 coaxially mounted within the shaft 10 and linked to a lever 17 pivoted to the control lever 9. When the lever 17 is positioned against a stop 21a forward drive occurs as described, if however the lever is moved against a stop 21, the cam 20 is shifted to its broken line position in which the transmission pump remains at its zero stroke position until the lever 9 reaches its position C and the engine speed is a maximum, and the pump displacement is thereafter increased by shifting the lever to a position D. Modifications.-In order to control the rate of which the servomotor 8 responds to movement of the control rod 25, the rod 25 may be adjustable by rotary movement about its own axis to alter the slope 78 engaged by the valve piston 79. Fig. 6 shows the modified part of an arrangement in which an injection pump without a regulating rod is employed; the ejection pump 100 has its displacement controlled by the cam 15 and is supplied by a feed pump 104, surplus liquid being returned to a reservoir through a throttle 115, The pressure of the liquid supplied to the injection pump acts in a chamber 106 on a piston 107 carrying an abutment 116 which co-operates with the valve actuating lever 31. The piston 107 is biased leftwardly by a spring 109 which is loaded by a cam 112 on the shaft 14.