Patent GB-454967-A (GB)
Title: Improved jack
IPC: B66F3/30
Filed: 1935-04-12
Abstract: 454,967. Lifting-jacks. THOMPSON, E. B., 1134, 25th Street, Des Moines, Iowa, U.S.A. April 12, 1935, No. 11366. [Class 78 (iii)] A vibratory jack, for use in oscillating motorvehicle frames so as to assist the lubrication of the vehicle springs &c., comprises a fluid-pressure cylinder and piston, an automatic valve actuated by the movement of the piston so as alternately to admit fluid to and exhaust it from below the piston, and manually-controlled means for rendering the automatic valve inoperative. In the construction shown the jack 16, Fig. 1, is shown in conjunction with a vehicle hoist 10 having nmways 12 for the vehicle wheels 14. The jack is provided with trunnions 70 for bars 69 hooked over bars 11 on the runways so as to support the jack. The jack is provided with a lower loose piston 17, Fig. 5, having its upward movement limited by a bolt 18, and an upper piston 19 having a hollow piston rod 20 in which slides a ratchet bar 21 engaged by a pawl 23 on the piston rod 20 and carrying a crutch or slipper 22 for engaging the vehicle frame 15. To use the jack a hand-wheel 57 is rotated and a valve is opened to supply air beneath the lower piston. This piston is raised and with it the upper piston and the slipper 22, so that the vehicle frame is raised relatively to the wheels and the vehicle springs are loosened. Further rotation of the handwheel 57 opens a valve supplying air to the space between the two pistons so that the upper piston is raised relatively to the lower piston, which keeps its raised position as limited by bolt 18. The upper piston 19 thus raises the frame 15 still more, but at the end of its upward stroke the piston 19 moves a valve 28 through linkage and this valve releases the air from the space between the pistons so that the upper piston sinks and lowers the frame 15. As the piston 19 sinks it operates the valve 28 so that compressed air is again admitted between the pistons and the cycle of operations is repeated, the vehicle frame thus being reciprocated up and down. The piston 19 is connected to the valve 28 by a snap-action linkage comprising arms 43 pivoted on a fixed shaft S and connected by links 47 to the piston, and arms 45 also pivoted at S and carrying a bar 46 engaging a recess 33 in the end of the valve. The downward movement of the valve is limited by a stop 34. The bar 46 and the shaft 44 connecting the arms 43 and the links 47 are connected by tension springs 49. In the position shown in Fig. 5, the piston and the valve are in their lowest positions and air can be admitted from a passage 35 through a part 29 in the valve to a passage 36 and pipe 37 leading to the space between the two pistons. As the piston 19 rises the shaft 44 also rises until it passes the dead centre of the bar 46 and the pivot shaft S ; the springs 49 then act and move the valve 28 upwards to a position in which the air passage 35 is closed and a port 30 communicates with a branch 38 of passage 36, so that air can pass from beneath the piston 19 through the port 30 and other ports 31, 32 in the valve to the space above the piston which is open to the atmosphere through an outlet 42. The piston 19 thus falls by gravity and when near its lowest position the shaft 44 passes the lower dead centre position and the springs 49 lower the valve 28 thus admitting air again beneath the piston 19. The valve 28 may be held in its lower position, so as to keep the piston 19 raised, by means of a hand-controlled knob 63, Fig. 2 carrying a lug (not shown), which when the knob is depressed rests on the bar 46 and prevents the valve being raised. The knob is normally raised by a spring 66 and may be locked in its lowest position by a pin 64 engaging the horizontal part of an L-shaped slot 61. In a modification the valve 28 is associated with a manually-controlled valve which is normally open but can be closed so that air cannot exhaust from beneath the piston 19 which is thus held in a raised position. Air is admitted to and exhausted from the space below the lower piston 17 by a valve 52, Fig. 4, and air is admitted to the space between the pistons by a valve 54, both valves being selectively controlled by the single handwheel 57 which carries a lever 55 pivoted to both valve stems and floating between collars 58 on the screwed spindle 56 of the handwheel. Air is supplied through a pipe 25 to the valve-box 26. In the position shown in Fig. 4 valve 54 is closed by a spring 59, the lower end of valve 52 is closed, and the upper end open, so that the space beneath the lower piston 17 is connected to the atmosphere through a pipe 40, passage 39, and valve port 51. If the hand wheel is rotated to raise the spindle 56 the lever 55 turns about its pivot on the valve 54 and raises the valve 52 thus closing the upper exhaust port 51 and opening the lower inlet port, so that air passes from the valve-box 26 through passages 50, 39 to the space beneath the lower piston 17 and raises the piston. Further rotation of the hand wheel in the same direction causes the lever 55 to turn about its pivot on valve 52 so that valve 54 is opened and air is admitted through passage 53 to passage 35 and the valve 28, and through the latter valve to the space between the pistons to cause the reciprocating motion of the upper piston. The jack cylinder is formed with a convex base and with three spring-loaded legs 72 so that it will stand on a sloping surface, the legs yielding when the jack is under load so as to enable the jack to set itself with the centre of the base firmly in contact with the ground surface.