US3115066A - Piston valves - Google Patents

Description

Dec. 24, 1963 D. FIRTH ETAL 3,115,066

PISTON VALVES Filed April 29. 1960 Patented Dec. 2' 5, 1963 3,115,066 PESTGN VALVES Donald Firth and James Duncan Hamilton, East Kilhrx ie,

Glasgow, Scotland, assignors to Council For Scientific and industrial Research, London, England, a body corporate of the United Kingdom Filed Apr. 29, 1960, Ser. No. 25,743 Claims priority, application Great Britain May 4, 1959 4 Claims. (Cl. 1-250) This invention relates to piston valves and particularly, but not exclusively, piston valves for fluid pressure pumps or motors of the reciprocatory type and has for an object to improve the operation thereof.

In hydraulic pumps and motors especially of the kind in which the piston is always displaced on its outward stroke by fluid pressure and only positively displaced on its inward stroke, there is a risk of hammering or shock wave conditions being set up in the cylinder when the valve mechanism changes over to admit either the low pressure charging fluid-in the case of pumps-or the high pressure working fluid-in the case of motorsto the working cylinder. For example, in an eccentric-andslipper type of pump, the working cylinder contains a small volume of fluid at the high delivery pressure at the instant of cut-oil. of the outlet valve. It is then exposed to the relatively low pressure inlet circuit at the instant of opening of the inlet valve. This can cause hammering and shock waves in the inlet circuit and produces roughness in the pump particularly at high speeds. In the case of a motor which operates on the same principle, the same effect obtains at the instant when the piston has exhausted through the outlet valve and the inlet valve opens to admit high pressure fluid.

In order to avoid the recurrent shocks mentioned above, the present invention provides variable timing of one or both of the valves so as to ensure that the pressure conditions within the cylinder at the instant of changeover from one stroke to the next approximate to the new pressure conditions which will prevail at the commencement of the next stroke.

This is achieved, according to the present invention, by means of a piston valve which works in a ported sleeve, the port being permanently in communication with a port in the cylinder. The sleeve is adjustable relative to the piston so as to vary the instant of opening or of cut-off, according to the function of the valve (i.e., whether it is an inlet or exhaust valve). This may be effected manually or automatically, according to preference, and the sleeve may have more than one port whose events are controlled by the piston. To eficct said adjustment, the port or ports and the valve piston have helical operative edges and the sleeve and valve piston are angularly adjustable relative to one another.

In the case of an hydraulic motor where the piston drives an eccentric through a slipper, the timing of the outlet valve is conveniently adjusted to cause the valve to close a few degrees before T.D.C. so that the residual oil left in the cylinder from the exhaust stroke is compressed to approximately the inlet pressure. In the case of a pump, on the other hand, the timing of the inlet valve is preferably delayed by a few degrees after T.D.C. to allow the residual oil trapped in the cylinder after a delivery stroke to expand until its pressure approximates to the inlet pressure.

By the above arrangement a smooth transition can be achieved between one stroke and the next in the vicinity of T.D.C. with a consequent improvement in the smoothness of operation of the pump or motor.

In order to ensure that this smooth transition is effected under all conditions of operation, the valve timing is preferably arranged to be a function of the speed or load on the pump or motor.

A practical embodiment of the invention, as applied to a multi-cylinder hydraulic motor, will noW be particularly described with reference to the accompanying drawing which is a section through a cylinder and associated valve gear of a radial hydraulic motor or pump, the section being taken on a radial plane including the axis of the shaft.

In the drawing, the driven member of the motor is an eccentric l1 which is engaged by the slipper 2 of each piston rod 3. The little end 4 of the rod is part spherical and is held in a seating 5 within the piston 6. The piston works in a cylinder 7 in the main cylinder block 8 of the motor and is closed by a head 9. The piston 6 is shown in the drawings in the T.D.C. position and the clearance volume ill is open either to pressure or to exhaust through an inlet port 1111 or an outlet port 112 respectively. The inlet port 11 is controlled by an inlet valve 13 and the outlet port 112 is controlled by an outlet valve 14-.

Both valves 13, 14 are of generally identical construction and are operated by tappets 15 from respective inlet and exhaust cams 1 6, '17. Each tappet slides in a bush 21 pressed into a socket in the cylinder block 8.

The piston valves '13 and 14 are each of generally tubular form having spaced upper and lower external lands 23, 24. The reduced diameter stern portion 25 between the lands registers with an inlet 66 or an outlet 61 described in detail later. The lands -23, 24 form pressure fluid seals within a respective valve bore 28 or 29, the upper land 23 serving also to open and close the inlet or exhaust port 11, 12. The length of the stem 25 between lands is such as to ensure that the inlet or outlet 61 is never cut off during the valve stroke. Within each valve bore is a sleeve or liner 50 within which the piston 14 itself actually reciprocates.

In the upper end of each sleeve 50 is a series of ports 152, each symmetrically disposed, around the sleeve periphery, about an imaginary helical line 57. Each port 152, when developed on a plane tangential to the sleeve St has the shape of a parallelogram.

Each port 152 is permanently in register with an annular inlet port groove 53 (connected to the inlet port 11) or outlet port groove 59 (connected to the outlet port 12) in the respective valve bore 28 or 29 in the main block 8. Below the inlet port groove 53 a pressure fluid inlet groove 69 is machined around the internal wall of the inlet valve bore 2%, whilst a similar exhaust groove 61 is machined around the internal wall of the outlet valve bore 29. Radial ports 62 in each sleeve 5t? register with the respective grooves 6t 61.

The upper land 23 of each valve 13 or 14 has its operative or working edge 63 of helical form, the pitch of the helix being the same as that of the helical axis of symmetry 57 of each of the ports 152. (In the drawing, the upper land 23 of the valve 13 is shown in its upper position for convenience of illustrating the ports 152.) Each lower land 24 of each valve has a radial working edge opposed to the helical edge 63 of the upper land and the reduced stem section 25 in which is formed with a longitudinal slot 64. This slot is engaged by a peg or spigot 65 screwed into the block 8 and projecting through one of the sleeve ports 62 to prevent rotation of the valve about its axis.

Since the lower or working edge 63 of the upper land 23 of each valve has the same contour as the axis of symmetry 57 of the ports 152, the upper land controls the ports 152 in the same way as it would if it were radial and the ports were symmetrical about a circumference of the sleeve Sit, in the conventional manner of piston valves. However, for a fixed stroke of the valve 13 or 14 and a constant relation between the inlet or exhaust cam 16, 17 respectively and the piston 6, the valve timing will depend on the relative angular orientations of the land 23 and the sleeve 5t). Thus, by rotation of the latter within the valve bore 23 or 29 whilst the valve 13 or 1 is angularly locked by engagement of the peg 65 in the siot 6 opening or cut-ofi of the inlet or outlet ports 11 or 12 of the main cylinder 10 can be varied to occur at different points in the stroke of the valve 13 or 14.

For xarnple, let it be assumed that the valve 13 is in the position where the helical working edge 63 of its upper land 23 coincides with the position shown in the drawing of the axis of symmetry 57 of the ports 152. In this position, the ports are half closed by the land 23. If, now, the valve 13 remains stationary and the sleeve 50 is rotated clockwise, as seen from above, the upper Wall 1520 of each port will approach a position of coincidence with the working edge 63 of the land 2T=i.e. the ports will progressively open.

On the other hand, if the sleeve 50 is rotated counterclockwise, the lower wall 152]) of each port will approach a position of coincidence with the working edge 63 and the ports 152 will progressively close.

The instants of etfective closing and opening of the ports 11 and 12 can thus be adjusted to suit the working conditions of the motor, either manually or automatically. An automatic control would respond to the speed or load on the motor, or both, and can be of any preferred construction.

In order to allow for a suitable area of aperture of the ports 152 and a helix pitch which is sufiiciently coarse to give the necessary range of timing control without excessive angular adjustment of the sleeve 50, it is preferred to form each port 152 with the central axis of how of fluid therethrough inclined, in a plane containing the valve axis, to a radius of the sleeve 50 in that plane. The angle of this incliniation will be determined, in any particular case, by the angular spread of the ports 152, their height in the axial direction, and the desired or permissible height in the same direction of the annular groove 58, the latter consideration being dictated by the requirement that the aperture of each port 152 in the outer wall of the sleeve 50 must fully register with the groove. In the arrangement illustrated in FIG. 1, the generatrices of the upper and lower walls 152a, 1521) of each port have a constant inclination to the valve axis, so that the angle of inclination of the flow axis of the port is equal to the angle 5.

In order to facilitate the smooth action of the rotatable sleeve 50 during timing adjustment, it must be a sliding fit within the valve bore 23 or 29, and this may lead to the leakage of high pressure working fluid into the resultant clearance space which may, in turn, cause an undesirable build-up of pressure. To prevent this, radial drain grooves 70 are machined across each end of the sleeve 50. Each sleeve 5! is rotatable under the control of a cylindrical rack 55 engageable with pinion teeth 54- formed around part of the periphery of the sleeve 50. The rack is housed in a bore 56 in the cylinder block 3.

A spring 35 is housed in an axial counterbore 66 in the upper land 23 of the valve 13 or 14 and bears at its upper end against a shallow recessed screw cap 67 threaded into the top end of the valve bore 23 or 29. An internal shoulder 68 in the counterbore constitutes the lower abutment for the spring 35, and the counterbore is continued at 69 with reduced diameter to open through the lower end face of the valve 13 or 14 to provide a drainage and pressure relief passage for fluid which 4 may otherwise become trapped above the upper land 23.

We claim:

1. In a hydraulic positive displacement machine, a piston valve comprising a sleeve; a port in said sleeve adapted to communicate with a working cylinder of the machine and having a helical operative edge; a valve member reciprocable in said sleeve; a land on said valve member having a control edge of helical form to register with the helical operative edge of said port and having an angular extent greater than that of said operative edge of said port; and means for adjusting the angular displacement of said sleeve about its longitudinal axis.

2. In a hydraulic positive displacement machine, a piston valve according to claim 1 wherein said valve member is engageable with a coacting fixed formation for preventing rotation of said member about its axis.

3. In a fluid pressure machine, a closed work cylin der including at least one lateral port through which fluid will flow, a work piston reciprocably supported in said work cylinder for axial movement therein, means drivingly connected to said work piston, the improvement comprising, in combination, a piston valve including a control cylinder disposed parallel to said work cylinder and including a lateral port adjacent to and in alignment with said one lateral port of said work cylinder, :1 control sleeve supported in said control cylinder for adjustment in said control cylinder, said sleeve including a lateral port substantially alignable with said work and control cylinder ports, and a control piston reciprocably supported in said control cylinder and operatively connected to said means drivingly connected to said work piston for operation thereby, said control piston including a control edge traversable with respect to said lateral port in said sleeve for controlling the fluid flow between said cylinders in timed relation to operation of said means drivingly connected to said work piston, said control sleeve lateral port being adjustable for varying the effective axial position of said port in the control sleeve relative to the stroke of said control piston, said control sleeve lateral port having a helical operative edge, said control piston having a land including a control edge of helical form to register with the helical operative edgeof said port, the control edge of said control piston having an angular extent greater than that of said operative edge of said control sleeve port, and means for adjusting the angular displacement of said sleeve about its longitudinal axis.

4. A piston valve according to claim 2 wherein said co-acting fixed formation comprises fixed pin, said valve member including a longitudinal slot in which a terminal end portion of said fixed pin is disposed for preventing rotation of said valve member about its longitudinal axis.

References (liter! in the file of this patent UNITED STATES PATENTS 1,822,667 Proell Sept. 8, 1931 2,158,342 Trader May 16, 1939 2,322,518 Huber June 22, 1943 2,471,117 Orshansky May 24, 1949 2,930,402 Garnet Mar. 29, 1960 FOREIGN PATENTS 375,321 France May 24, 1907 635,023 Great Britain Mar. 29, 1950 780,191 Great Britain July 31, 1957

Claims (1)

1. 3. IN A FLUID PRESSURE MACHINE, A CLOSED WORK CYLINDER INCLUDING AT LEAST ONE LATERAL PORT THROUGH WHICH FLUID WILL FLOW, A WORK PISTON RECIPROCABLY SUPPORTED IN SAID WORK CYLINDER FOR AXIAL MOVEMENT THEREIN, MEANS DRIVINGLY CONNECTED TO SAID WORK PISTON, THE IMPROVEMENT COMPRISING, IN COMBINATION, A PISTON VALVE INCLUDING A CONTROL CYLINDER DISPOSED PARALLEL TO SAID WORK CYLINDER AND INCLUDING A LATERAL PORT ADJACENT TO AND IN ALIGNMENT WITH SAID ONE LATERAL PORT OF SAID WORK CYLINDER, A CONTROL SLEEVE SUPPORTED IN SAID CONTROL CYLINDER FOR ADJUSTMENT IN SAID CONTROL CYLINDER, SAID SLEEVE INCLUDING A LATERAL PORT SUBSTANTIALLY ALIGNABLE WITH SAID WORK AND CONTROL CYLINDER PORTS, AND A CONTROL PISTON RECIPROCABLY SUPPORTED IN SAID CONTROL CYLINDER AND OPERATIVELY CONNECTED TO SAID MEANS DRIVINGLY CONNECTED TO SAID WORK PISTON FOR OPERATION THEREBY, SAID CONTROL PISTON INCLUDING A CONTROL EDGE TRAVERSABLE WITH RESPECT TO SAID LATERAL PORT IN SAID SLEEVE FOR CONTROLLING THE FLUID FLOW BETWEEN SAID CYLINDERS IN TIMED RELATION TO OPERATION OF SAID MEANS DRIVINGLY CONNECTED TO SAID WORK PISTON, SAID CONTROL SLEEVE LATERAL PORT BEING ADJUSTABLE FOR VARYING THE EFFECTIVE AXIAL POSITION OF SAID PORT IN THE CONTROL SLEEVE RELATIVE TO THE STROKE OF SAID CONTROL PISTON, SAID CONTROL SLEEVE LATERAL PORT HAVING A HELICAL OPERATIVE EDGE, SAID CONTROL PISTON HAVING A LAND INCLUDING A CONTROL EDGE OF HELICAL FORM TO REGISTER WITH THE HELICAL OPERATIVE EDGE OF SAID PORT, THE CONTROL EDGE OF SAID CONTROL PISTON HAVING AN ANGULAR EXTENT GREATER THAN THAT OF SAID OPERATIVE EDGE OF SAID CONTROL SLEEVE PORT, AND MEANS FOR ADJUSTING THE ANGULAR DISPLACEMENT OF SAID SLEEVE ABOUT ITS LONGITUDINAL AXIS.

Images