Patent GB-1280369-A (GB)
Title: Acceleration control for hydraulic transmissions
IPC: B60K17/10
Filed: 1969-10-30
Abstract: 1280369 Hydrostatic transmission control CESSNA AIRCRAFT CO 30 Oct 1969 [21 Nov 1968] 53089/69 Heading F2D [Also in Division G3] In a hydrostatic transmission wherein a make up pump 30 supplies pressure liquid to a pump displacement adjusting servo 17, a valve 50 throttles the supply to the servo 17 when the vehicle acceleration exceeds a predetermined value to limit the rate at which pump displacement is changed and thus vehicle acceleration. In Fig. 1 a pendulum 66 pivoted at 67 to the vehicle frame responds to a vehicle acceleration or deceleration and acts through a linkage 69 on the spool 60 of the valve 50. When the vehicle accelerates or decelerates the spool 60 is moved left or right to throttle the liquid flowing through the valve 50. A by-pass valve 81 provides a minimum flow to the servo 17 when the valve 50 blocks flow thereto under excessive acceleration or deceleration. A manual valve 20 is provided in the line 31 to the servo 17 to initiate ratio shift in the hydrostatic transmission. The hydrostatic transmission may as shown comprise an engine driven variable displacement swash-plate pump 13 in closed circuit with a fixed displacement swash-plate motor 18 which drives the vehicle wheels 39 through a change speed gear 36. In Fig. 2 (not shown) the pendulum (66) is spring centred. In Fig. 3 (not shown) the acceleration responsive means comprises a spring centred axially slidable mass (92) connected to the valve spool (60). In Fig. 4 (not shown) the acceleration responsive means comprises a quantity of liquid in a tank (100). When the vehicle accelerates or decelerates the differential in liquid level between the front and back of the tank produces different static pressures in conduits (102, 103) connected to a signal amplifier (105) which supplies pressures proportional to the differential static pressures to opposite ends of the spool of the valve (50). The valve (50) is thus moved to a position in which it restricts flow to the displacement adjusting servo. In Fig. 5 the acceleration responsive means comprises a float 135 which detects the change in level of a liquid in a tank 130 and positions the valve spool 60 accordingly. The displacement of both the pump and motor are variable and are adjusted by servos 120, 125. A pump 109 supplies pressure liquid through a forward-reverse valve 110 and a neutral valve 116. During forward acceleration the liquid is initially supplied through the valve 50 and servo 125 to the servo 120 to increase pump displacement. When the pump displacementis maximum the servo 120 opens a poppet valve 122 allowing fluid to drain from a motor servo chamber 124 thus permitting pressure in a chamber 125 to reduce motor displacement. On changeover of the valve 110 pressure liquid is supplied through the servo 120 to the motor servo chamber 124 to increase motor displacement. At maximum motor displacement the servo 125 opens a poppet valve 126 to permit fluid to drain from the pump servo chamber 120 and thus to permit pressure liquid in the pump servo chamber 121 to reduce pump displacement. By-pass valves 140, 141 provide minimum flow to or from the pump and motor servos when the valve spool 60 completely blocks flow thereto or therefrom.