GB1023033A - Improvements in and relating to hydraulic transmissions - Google Patents

Abstract

1,023,033. Hydraulic transmissions. ETABLISSMENTS PAUL JACOTTET S.A., and G. ROUSSEL. Oct. 8, 1962 [Nov. 30, 1961], No. 37943/62. Headings F2C and F2D. In a vehicle hydrostatic transmission system comprising a variable-delivery and reversible pump supplying two or a multiple of two hydraulic motors of fixed or variable displacement, means is provided to tend to maintain the relative speeds of the motors constant. As shown in Fig. 1, a variable displacement pump 2 supplies liquid through pipes 7, 9, 10 to fixed displacement motors 3, 4 individually connected to the road wheels of the vehicle for forward drive, and the pump supplies through pipes 8, 11, 12 to the motors for reverse drive. Pumps 5, 6 are driven by the motors 3, 4 and, for forward travel, supply liquid through pipes 13, 14 to end chambers 36, 34 of a control valve 28 in the return lines 11, 12 from the motors 3, 4 to the pump 2. For reverse drive the pumps 5, 6 supply through pipes 15, 16 to end chambers 35, 33 of a control valve 27 in the return lines 9, 10 between the motors and the pump 2. The pressures in the valve chambers 33-36 are determined by restrictions 29-32 between these chambers and a reservoir 18 from which the pumps 5, 6 draw liquid through a line 17 and non-return valves. During forward drive the pump 2 supplies through the pipe 7 to the motors and, should, for example, the wheel coupled to the motor 4 slip, the output of pump 6 increases thereby increasing the pressure in the chamber 34 and moving the valve 28 downwards to restrict the discharge of liquid from the motor 4 through the line 12 thus reducing the speed of this motor and maintaining the speed of the motor 3. If slip occurs during reverse travel the valve 27 is actuated on slip to maintain the motor speeds constant. Should the wheel associated with motor 4 skid on overrunning in forward drive, the output of pump 6 is reduced and the valve 28 moves upwardly to restrict the discharge of liquid from the motor 3 through the pipe 11 to reduce the speed of the motor 3 and thus to increase the supply to the motor 4. In the modification shown in Fig. 2 the motors 3, 4 have a variable displacement controlled by servomotors 41, 40 and the pumps 5, 6 supply liquid through lines 13, 14 irrespective of the direction of drive. One side of the servomotor 41 is connected through non- return valves 43, 45 to whichever line 9, 11 is the supply line for the motor 3, and this side of the servomotor communicates through a restriction 47 in the servomotor piston with the opposite side of the servomotor and thence through a line 49 with a chamber of a control valve 52. One chamber of the servomotor 40 for the motor 4 is similarly connected to the supply line for the motor 4, and a restriction 46 in the piston intercommunicates the servomotor chambers, a line 48 from the second chamber leading to the control valve 52. The pumps 5, 6 discharge through the lines 13, 14 to chambers 55, 56 of the control valve 52 and the pressures in the chambers 55, 56 are determined by restrictions 53, 54 leading to exhaust. If for example the motor 3 slips during forward drive, the output of pump 5 increases and increases the pressure in chamber 55, thus moving the valve 52 upwardly to restrict exhaust of liquid from the servomotor 41 through the line 49 to set the servomotor to reduce the displacement of the motor 3. Thus a greater proportion of the output of the pump 2 is supplied to the motor 4, the speed of which is thus increased. If the wheel associated with motor 3 locks on overrun the output of the pump 6 falls and valve 52 is moved downwardly to restrict discharge from the servomotor 40 to reduce the displacement of the motor 4 so that more liquid is supplied to the motor 3 to increase its speed.