Patent GB-988913-A (GB)
Title: Improvements in and relating to hydraulic transmissions
IPC: B66B1/04
Filed: 1962-08-24
Abstract: 988,913. Hydraulic apparatus. HYDREL A.G. Aug. 24, 1962 [Aug. 26, 1961], No. 32567/62. Heading F1P. [Also in Division B8] Apparatus for smoothly accelerating and decelerating an hydraulic motor connected by a duct to a constant displacement hydraulic pump, comprises a control cylinder connected to the duct through a valve unit, the piston of the cylinder being displaced during acceleration or deceleration of the motor at a speed varying with time between zero and a maximum, the maximum being such that the corresponding rate of intake of the cylinder equals the constant output of the pump. In Fig. 1, a reversible pump 5 is connected by duct 6 and valve 12 to the motor 3, which has a plunger 2 operating a lift cage 1. The control cylinder 21 is fixed, and its piston 22 is joined by crank arm 25 to a pivot 28 on disc 26 rotatable within a ninety degree arc by a reversible motor 27. A spool valve 23 is operable by solenoids 30, 31, and can connect duct 6 through line 20 to lines 32, or 33 and 34, leading to the cylinder 21. A further spool valve 36 is operable by solenoids 37, 38, and can connect lines 40 and 41, from the valve 23, to reservoir line 42 or to line 35 connected to pump 5. The solenoids and motor 27 are operated by the lift cage or personnel to control the lift. While the lift is ascending pivot 28 is in position A. The pump 5 delivers fluid from reservoir 8 to duct 6, the pressure of the fluid opening valve 12 to allow the ram 3 to extend. To stop the lift, valve 23 is put into the position shown, and disc 26 is rotated so that pivot 28 travels from A to B at uniform angular speed. Piston 22 moves to the right, at increasing speed, and withdraws fluid from duct 6 through lines 32 and 20 at an increasing rate, and thus steadily decreases the amount of fluid flowing to the ram. At its extreme right-hand position, piston 22 clears ports in its cylinder to connect duct 6 to reservoir through lines 20, 32, and 29. The pressure in duct 6 thus drops, and valve 12 closes, and the lift is stopped. Motor 27 is also stopped, but pump 5 continues to run. When the lift is to go up again, valve 23 is changed over, and motor 27 drives pivot 28 from B to A at uniform speed. Piston 22 moves to the left, cutting off line 29. Initially, the whole of the pump delivery flows into cylinder 21 through ducts 20 and 33, but fluid flows to the ram 3 at an increasing rate as pivot 28 approaches point A. The left-hand side of cylinder 21 is connected to reservoir through lines 32, 40, and 42. Thus the lift is accelerated smoothly. If the lift is to go down, valve 36 is changed over, and pump 5 is driven to withdraw fluid from duct 6 (or from the reservoir through valve 45) and supply it to line 35. Motor 27 moves pivot 28 from B to A, and cylinder 21 discharges through lines 32 and 20 to duct 6, to supply the pump. Initially, cylinder 21 supplies all the pump intake, but as pivot 28 approaches point A, the supply from the cylinder drops, and fluid is taken from the ram at an increasing rate, to accelerate the lift smoothly. Fluid is supplied to the righthand side of cylinder 21 through lines 35, 41, and 33. To stop the descending lift, valve 23 is changed over, and pivot 28 is moved from A to B. Piston 22 moves to the right, and supplies fluid to duct 6 through lines 33 and 20, slowly at first, but eventually to supply the whole of the pump intake, so that the lift decelerates smoothly. When pivot 28 reaches point B, duct 6 is connected to reservoir through lines 29, 34, 33, and 20, and the lift stops. Motor 27 may be a fixed piston and moving cylinder driving disc 26 through a rack and pinion. Fig. 2 shows an embodiment in which a piston K1 reciprocates a machine tool. The pump P supplies pressure fluid to line 102, which is connected by valve 110 to lines 103, 104 alternately, to reciprocate the piston K1 The line 103 or 104 which is not under pressure, is normally connected to reservoir through valve 110, line 120a or 120b, internal passages (shown in broken lines) in the piston rod of piston K8, and line 120. At the ends of each stroke of piston Kl, however, fluid is taken from the pump delivery at an increasing rate by a control piston K7 in a cylinder 112, through line 102a, valve 111, and line 103a or 104a, so that the piston K1 is smoothly decelerated. At the beginning of each stroke of piston K1, fluid is taken from the pump delivery at a decreasing rate by piston K7, to accelerate the piston K1 smoothly. The appropriate valve movements are made by ganged crank drives Sil and Si2 which are moved by the flow of pressure fluid from pump P to alternate sides of piston K7, these movements being initiated by a crank Aw moved by piston K6 pperated by cams 137 driven by piston K1, controlling piston K6 by fluid pressure relays KT1, KT2, K2, and K3. Thus at the end of a stroke of piston K1 in either direction, a cam 137 operates relay KT1 or KT2 as appropriate, to move piston K6 and displace the crank drive Si2, which moves valve 111 to connect the appropriate side of piston K7 to the pump, piston K7 then being driven by the pump to complete a half revolution of the crank drives.