GB1568685A

GB1568685A - Reciprocatory devices

Info

Publication number: GB1568685A
Application number: GB355676A
Authority: GB
Original assignee: UK Secretary of State for Industry
Current assignee: UK Secretary of State for Industry
Priority date: 1977-01-31
Filing date: 1977-01-31
Publication date: 1980-06-04

Description

(54) IMPROVEMENTS IN OR RELATING TO RECIPROCATORY DEVICES (71) 1, THE SECRETARY OF STATE FOR INDUSTRY, London, do hereby declare the invention, for which I pray that a patent may be granted to me, and the method by which it is to be performed, to be particularly described in and by the following statement: - This invention relates to reciprocatory devices and more particularly but not exclusively is concerned with fluid operated tools driven by the reciprocation of a driving piston within a cylinder housing in which the acceleration of the piston is controlled by the position of a control valve of the spool or shuttle type.

This invention has particular, though not exclusive, application to that type of such tools in which a bias force is maintained continuously by pressurised fluid acting against a face of the piston. The control valve connects a duct communicating with a piston face to either a high or low pressure fluid supply, so that as the spool or shuttle reciprocates within its bore, it applies to the piston face a driving force which is alternatively greater or less than the bias force and is in the opposite direction to the bias force.

The operation of the control valve may be controlled either directly or indirectly by the position of the driving piston within the cylinder housing, or by an external switching means.

According to the present invention there is provided a reciprocatory device comprising a first member reciprocable relative to a second member, biasing means to urge the first member to move in one direction along an axis, driving means to move the first member along the axis in the opposite direction against the biasing means by the action of fluid pressure, a control valve carried by the first member for controlling the driving means by connecting it alternatively to high and low pressure fluid, and a timing valve carried by the first member, wherein the control valve comprises a valve member reciprocable relative to the first member, a control valve biasing means which can provide a force acting be*v'een the valve member and the first member and a control valve driving means which can provide a force generated by the action of fluid pressure and acting between the valve member and the first member to move the valve member against the action of the control valve biasing means, and wherein the timing valve comprises a timing valve member reciprocable relative to the first member to supply either high or low pressure fluid to the control valve driving means, a timing valve biasing means which can provide a force acting between the timing valve member and the first member and a timing valve driving means which can provide a force generated by the action of fluid pressure and acting between the timing valve member and the first member to move the timing valve member against the action of the timing valve biasing means, the control and timing valves being arranged such that in use, when the timing valve member moves in a given direction, it causes the control valve member to move in the same direction and the control valve member in turn causes the first member to move in the opposite direction.

In a preferred embodiment of the device according to the invention the first member is a piston and the valve member is a spool reciprocable within a bore in the piston.

The location of the spool within its bore is controlled by the control valve driving means, itself actuated by the presence or absence of high pressure within a control duct which is in direct communication with the timing valve, preferably of the spool or shuttle type and preferably parallel to the axis of the piston and located within it.

Such a timing valve can be made to switch the control valve at an instant independent of the position of the piston.

By way of example, one embodiment of the invention will now be described with reference to the drawing filed with the provisional specification, in which: Figure I is a schematic transverse section of a reciprocatory tool according to the present invention illustrating the relative locations of a drive piston, control valve and timing valve incorporated in the tool; and Figure 2 is a developed section along the lines II-II of Figure 1 of the driving piston, its housing and associated fluid supply lines.

The tool shown in the drawings operates by the reciprocation of a driving piston 1 constituting a first member within a cylinder housing 2 constituting a second member, the driving piston at the forward end of its reciprocation being arranged to strike the rear of a tool bit (not shown).

The driving piston 1 has a cylindrical bore 3 which bore is closed by a rod 4 slidable within the bore 3. The rear end of the rod can be urged against an end wall 5 of the cylinder housing and the driving piston 1 can be driven forwardly by the action of pressurised fluid within the cylindrical bore 3, and the bore 3 and rod 4 constitute a driving means for the piston 1.

The pressure of the fluid within the bore 3 is switched by a control valve 6 to an alternatively high and low value, and the reaction force on the front end of bore 3 driving the piston 1 is made alternatively greater or less than a force on the piston 1 in the opposite direction produced by fluid maintained at a high pressure and arranged to act against a step 7 in the outer surface of the piston 1. The step 7 provides a biasing means for the piston 1. The area of the step 7 is arranged to be approximately one half of that of the front end of the bore 3 so that the piston is alternatively driven to the right and left hand sides of the drawing by approximately equal resultant forces.

The step 7 is constantly subjected to a high pressure fluid supply, smoothed by a hydraulic accumulator 8, by way of a peripheral recess 9 in the inner wall of the cylinder housing 2 and a duct 10 bored within the cylinder housing and interconnecting the recess 9 and an inlet port 11 at the rear of the housing 2.

The outer surface of the driving piston is provided with three ports: a forward signal. port 12 located in a forward posi ton so that it only communicates with the recess 9 when the piston 1 is-at or close to the rear of its stroke (to the left in the drawing);. a rearward signal port 13 located just forward of. the rear edge 14 of the outer surface of the piston, and which communicates with the recess 9 only when the driving piston is at our close to the forward end of its stroke (to the right of the draw ing); and a port 15.located at a position in termediate between ports 12 and 13 as to be. ptrmanently in communication with the recess 9.

A timing valve 16 is located within a bore drilled fnto-the rearof the driving piston 1 in an axial direction, and comprises a tim ing;,yakF member constituted by a spool 17 reciprocable between a front wall 18 of that bore and a cover plate 19 screwed to the rear face of the driving piston 1.

The bore of the timing valve is provided with two peripherical recesses 20 and 22.

The recess 20 is located towards the rear end of the bore and is connected to the port 15 by a duct 21. The recess 22 is located towards the front end of the bore and is permanently located to a low pressure fluid return line through a duct 23 and ports 42 and 43 located respectively in the cover plate 19 and the rear wall of the cylinder housing. The bore of the timing valve 16 is also provided with a port in its front wall 18 connected to the signal ports 12 and 13 by ducts 24. It is provided with a control port 25 between recesses 20 and 22 and connected through a control duct 26 to a signal recess 27 towards the front end of the control valve 6.

The spool 17 has an axial bore 28 maintained in communication with the recess 20 through ducts 29. Into the bore 28 extends a rod 46 which can be urged against the cover plate 19 by fluid pressure in the bore 28. The rod 46 and bore 28 constitute a timing biasing means. Reciprocation of the spool 17, by the force of alternating high and low pressure of fluid from the ducts 24 on the front end of the spool, i.e. on the timing valve driving means, switches the control duct 26 alternately to high or low pressure by way of the control port 25, a groove 47 in the spool 17, and the recesses 20 and 22 respectively.

The control valve 6 is constructed, and operates, similarly to the timing valve. It has a control valve member constituted by a spool 31. The control-valve spool 31 is subject to the reaction force of fluid acting on a rod 30 located in an axial bore at the rear of the spool 31 and maintained at high pressure to provide a biasing means bv communication with a peripheral recess 32 in the valve wall connected to duct 21. The spool 31 is also subject to the reaction force of fluid acting on a driving means including a rod 33 of diameter somewhat larger than that of rod 30, located in an axial bore, at the forward end of the spool 31, the axial bore communicating with the signal recess 27. The valve wall is further provided with a peripheral recess 34 located between the recesses 32 and 27 and connected to the fluid return line by duct 23. A port 35 is located between the recesses 32 and 34 and communicates via a duct 36 with the front end of the cylindrical bore 3.

The spool 31 is provided with a peripheral recess 37 so located around its central portion that on reciprocation of the spool 31.

by alternating high and low fluid pressure in the duct 26, the duct-36 is connected -alternately and respectively to high pressure by the recess 32 and duct 21 and to low pressure via recess 34 and duct 23.

In normal operation, high pressure fluid is supplied to the port 11 and hence to duct 10 and recess 9. If the piston 1 is not at the rear of its stroke, the port 12 does not communicate with the recess 9 but is sealed of by the wall of housing 2 and the spool 17 of the timing valve is thus free to move forward, under the action of high pressure fluid entering recess 20 and bore 28 via duct 21 and recess 9, and this forward movement connects the duct 26 and recess 27 to the recess 22 and hence the low pressure fluid.

The high pressure fluid which fills the narrow bore in the spool 31 of the control valve urges forward the spool 31 and thus connects the duct 36, and hence the bore 3, to low pressure via recess 34, duct 23 and port 43. With low reaction force on the front face of the bore 3 to urge the driving piston forward, the piston retracts under the force of high pressure fluid on the step 7.

As soon as the groove 12 comes into communication with the recess 9, however, the duct 24 and hence the forward end of the timing valve are connected to the high pressure supply. The spool 17 therefore retracts, switching the duct 26.to high pressure via the port 25 and recess 20, and so causing the spool 31 of the control valve to retract under the action of high pressure fluid acting between the spool 31 and the large diameter rod 33. The duct 36 and hence the bore 3 are therefore switched to high pressure by recesses 37 and 32 so that the piston begins to accelerate forward under the action of the force of the fluid on the forward face of the bore 3, which has a greater area than the step 7.It will be noted that forward acceleration of the piston tends to result in the spools 17 and 31 of the timing and control valves respectively taking up their most rearward position, i.e. that in which the spools have switched the piston to accelerate forward.

There ought therefore to be no danger of the acceleration of the piston causing mistimed or premature switching of the valves control and timing.

The piston moves forward until the rear edge 14 of the piston wall passes the rear wall of the deep portion 44 of the recess 9. At this position of the stroke the port 20 communicates with exhaust duct 43 round the edge 14 of the piston and the deep portion 44 is isolated from the high pressure fluid supple (duct lO) bv engagement of the step 7 of the piston with a shallower part of the groove 9. The duct 24 and hence the front portion of the timing valve 16 exhausts to low pressure via ports 13 and 43. The timing valve spool 17 thus moves forward, switching the control and duct 26 to low pressure via recess 22 and duct .23 whereupon the control valve spool 31 also moves forward.

The fluid in the bore 3 therefore exhausts to low pressure via duct 36, groove 37 and port 34, and the piston begins again to accelerate rearwards. At the same time the inertia of the valve spools confirms them in their forward position. Reciprocation in this manner continues until the driving power provided by the high pressure fluid supply is removed.

The tool is also provided with a facility for enabling the stroke length of the piston 1 to be varied, so that for example the initial stroke of the cycle may be made with the piston not retracting fully before commencement of the following advance.

This facility is effected by means of a recess 38 in the cylinder housing communicating via a duct 39 with a source of high pressure fluid which can supply a flow of fluid whose rate can be varied. A port 40 in the outer surface of the piston 1 communicates through a duct 41 with duct 24 and hence the forward end of the timing valve 16, and the port 40 is located so as to open into the recess 38 whatever the position of the piston 1 in its stroke.

If it is desired that the piston stroke be shortened, fluid can be fed at the required rate or instant into the duct 39. The timing valve 16 will switch the control valve as soon as the fluid fed to its forward end via recess 38, the ports 40 and ducts 41 and 24 has forced the spool 17 back to connect the port 25 with the recess 20.

Tt can be seen that the less rapidly fluid is fed to the duct 39, the later will switching take place and the longer will be the stroke.

If this metered supply is not used reciprocation of the piston 1 will be as described earlier.

It is further possible to vary the rate of reciprocation of the driving piston by providing a throttle 45 in the exhaust duct 23.

The throttle can be used as a restricter of fluid flow and, if it is a varaible throttle, it varies the speed of retraction of the piston 1 but does not affect its forward movement.

The biassing means of the piston, control valve and timing valve need not employ fluid pressure for its operation. They can be for example simple compression springs.

WHAT I CLAIM IS: - 1. A reciprocatory device comprising a first member reciprocable relative to a second member, biasing means to urge the first member to move in one direction along an axis, driving means to move the first member along the axis in the opposite direction against the biasing means bv the action of fluid pressure, a control valve carried

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. the recess 32 and duct 21 and to low pressure via recess 34 and duct 23. In normal operation, high pressure fluid is supplied to the port 11 and hence to duct 10 and recess 9. If the piston 1 is not at the rear of its stroke, the port 12 does not communicate with the recess 9 but is sealed of by the wall of housing 2 and the spool 17 of the timing valve is thus free to move forward, under the action of high pressure fluid entering recess 20 and bore 28 via duct 21 and recess 9, and this forward movement connects the duct 26 and recess 27 to the recess 22 and hence the low pressure fluid. The high pressure fluid which fills the narrow bore in the spool 31 of the control valve urges forward the spool 31 and thus connects the duct 36, and hence the bore 3, to low pressure via recess 34, duct 23 and port 43. With low reaction force on the front face of the bore 3 to urge the driving piston forward, the piston retracts under the force of high pressure fluid on the step 7. As soon as the groove 12 comes into communication with the recess 9, however, the duct 24 and hence the forward end of the timing valve are connected to the high pressure supply. The spool 17 therefore retracts, switching the duct 26.to high pressure via the port 25 and recess 20, and so causing the spool 31 of the control valve to retract under the action of high pressure fluid acting between the spool 31 and the large diameter rod 33. The duct 36 and hence the bore 3 are therefore switched to high pressure by recesses 37 and 32 so that the piston begins to accelerate forward under the action of the force of the fluid on the forward face of the bore 3, which has a greater area than the step 7.It will be noted that forward acceleration of the piston tends to result in the spools 17 and 31 of the timing and control valves respectively taking up their most rearward position, i.e. that in which the spools have switched the piston to accelerate forward. There ought therefore to be no danger of the acceleration of the piston causing mistimed or premature switching of the valves control and timing. The piston moves forward until the rear edge 14 of the piston wall passes the rear wall of the deep portion 44 of the recess 9. At this position of the stroke the port 20 communicates with exhaust duct 43 round the edge 14 of the piston and the deep portion 44 is isolated from the high pressure fluid supple (duct lO) bv engagement of the step 7 of the piston with a shallower part of the groove 9. The duct 24 and hence the front portion of the timing valve 16 exhausts to low pressure via ports 13 and 43. The timing valve spool 17 thus moves forward, switching the control and duct 26 to low pressure via recess 22 and duct .23 whereupon the control valve spool 31 also moves forward. The fluid in the bore 3 therefore exhausts to low pressure via duct 36, groove 37 and port 34, and the piston begins again to accelerate rearwards. At the same time the inertia of the valve spools confirms them in their forward position. Reciprocation in this manner continues until the driving power provided by the high pressure fluid supply is removed. The tool is also provided with a facility for enabling the stroke length of the piston 1 to be varied, so that for example the initial stroke of the cycle may be made with the piston not retracting fully before commencement of the following advance. This facility is effected by means of a recess 38 in the cylinder housing communicating via a duct 39 with a source of high pressure fluid which can supply a flow of fluid whose rate can be varied. A port 40 in the outer surface of the piston 1 communicates through a duct 41 with duct 24 and hence the forward end of the timing valve 16, and the port 40 is located so as to open into the recess 38 whatever the position of the piston 1 in its stroke. If it is desired that the piston stroke be shortened, fluid can be fed at the required rate or instant into the duct 39. The timing valve 16 will switch the control valve as soon as the fluid fed to its forward end via recess 38, the ports 40 and ducts 41 and 24 has forced the spool 17 back to connect the port 25 with the recess 20. Tt can be seen that the less rapidly fluid is fed to the duct 39, the later will switching take place and the longer will be the stroke. If this metered supply is not used reciprocation of the piston 1 will be as described earlier. It is further possible to vary the rate of reciprocation of the driving piston by providing a throttle 45 in the exhaust duct 23. The throttle can be used as a restricter of fluid flow and, if it is a varaible throttle, it varies the speed of retraction of the piston

1 but does not affect its forward movement.

by the first member for controlling the driving means by connecting it alternatively to high and low pressure fluid and a timing valve carried by the first member, wherein the control valve comprises a valve member reciprocable relative to the first member, a control valve biasing means which can provide a force acting between the valve member and the first member and a control valve driving means which can provide a force acting between the valve member and the first member and a control valve driving means which can provide a force generated by the action of fluid pressure and acting between the valve member and the first member to move the valve member against the action of the control valve biasing means, and wherein the timing valve comprises a timing valve member reciprocable relative to the first member to supply either high or low pressure fluid to the control valve driving means, a timing valve biasing means which can provide a force acting between the timing valve member and a timing valve driving means which can provide a force generated by the action of fluid pressure and acting between the timing valve member and the first member to move the timing valve member against the action of the timing valve biasing means, the control and timing valves being arranged such that in use, when the timing valve member moves in a given direction, it causes the control valve member to move in the same direction and the control valve member in turn causes the first member to move in the opposite direction.

2. A reciprocatory device as claimed in claim 1 wherein the first member is a piston and the second member is a housing have a bore in which the piston is reciprocable.

3. A reciprocatory device as claimed in claim 1 or claim 2 wherein the timing valve driving means is connected at all times to a source of high pressure fluid which can supply a flow of fluid whose rate can be varied.

4. A reciprocatory device as claimed in any of claims 1 to 3 wherein the low pressure fluid supply for connection to the driving means of the first member is supplied through a duct containing a throttle.

5. A reciprocatory device substantially as hereinbefore described with reference to the drawings filed with the provisional specification.