GB2231292A - Hydraulic impulse torque generator - Google Patents

Abstract

A hydraulic impulse torque generator comprises a central rotor 201 and a coaxial casing 202 defining a hydraulic fluid chamber 203. An expansion chamber 220, which is in fluid communication with hydraulic fluid chamber 203, contains a resiliently compressible cellular insert 222 of e.g. expanded polystyrene, polyurethane, polyethylene, or neoprene, in order to allow thermal expansion of the hydraulic fluid without leakage from the casing 202. <IMAGE>

Description

HYDRAULIC IMPULSE TORQUE GENERATOR This invention relates to a hydraulic impulse torque generator. e.g. for a power tool, such as a screwdriver or a wrench driven by an air motor or other motive source.

GB-1 002 262 and EP-A-0 235 102 both disclose hydraulic impulse torque generators comprising a central rotor and a coaxial rotatable casing defining a hydraulic fluid chamber which receives the rotor and which is to be filled with hydraulic fluid for transmitting torque between the casing and the rotor, each generator including an expansion chamber which is in two way fluid communication with the hydraulic fluid chamber, in order to compensate for thermal expansion of the hydraulic fluid in use. In each case, the expansion chamber is delimited by a spring-loaded piston. This arrangement is complicated and costly, and there is a risk of fluid leaking past the piston. Compression of the hydraulic fluid can also occur during adjustment of the output torque.

The present invention provides a hydraulic torque impulse generator in which the expansion chamber contains a resiliently compressible insert comprising one or more closed cells. preferably a multiplicity of closed cells.

The insert may consist of one or more separate parts. It is possible for the insert to comprise a single cell containing a compressible medium or to comprise separate cells or separated groups of cells or to comprise one or more aggregates of cells1 preferably in the form of a closed-cell foam, e.g. expanded polyurethane, polystyrene, or polyethylene, more preferably an elastomer, e.g. neoprene.

Preferred and optional features are set forth in claims 2 et seq.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is an axial section through a first hydraulic impulse torque generator; Figure 2 is an axial section through a second hydraulic impulse torque generator; Figures 3 to 6 are cross-sections through another hydraulic impulse torque generator at four different positions in the cycle of rotation of its casing; Figures 7 to 10 are cross-sections similar to Figures 1 to 4, but for the opposite direction of rotation: Figure 11 is an axial section through the hydraulic impulse torque generator of Figures 3 to 10; and Figure 12 is an axial section through another hydraulic impulse torque generator.

The impulse torque generators illustrated in Figures 1 and 2 generate impulse torque in substantially the same way as those described in GB-1 002 262 and EP-A-0 235 102. Therefore, their construction and operation do not need to be described in detail here. They each have a central rotor 201 mounted in a coaxial rotatable casing 202 defining a chamber 203 which receives the rotor 201 and which is filled with hydraulic fluid. The rotor 201 has a single spring-mounted blade 205 and the casing 202 and rotor 201 cooperate to generate torque impulses - applied to the rotor - in the known manner.

The rotor 201 extends between an end wall 204, which is detachable from the casing 202, and an end wall 206 integral with the casing. In Figure 1 the end wall 204 has a rim 207 screwed onto the casing 202. In Figure 2 the end wall 204 is fitted into the end of the casing 202 and retained by a member 209 screwed into the casing. At one end the rotor 201 has a shaft 214 which extends through the end wall 206 for connection to a tool bit (not shown). At the other end it has a journal 213 mounted in a bearing recess constituted by a blind bore 215 in the end wall 204. Beyond the free end of the journal 213, the bore constitutes an expansion chamber 220 containing a resiliently compressible insert 222 of closed-cell foam (expanded neoprene), which fills the chamber 220 when free of compression.

During use, the hydraulic fluid filling the chamber 203 undergoes thermal expansion and leaks past the journal 213 into the expansion chamber 220, compressing the foam insert 222. Leakage out of the casing 202 is prevented by O-ring seals 225. The narrow fluid path past the journal 215 acts as a restrictor and does not dissipate the hydraulic impulses or transmit them to the expansion chamber 220. After use, as the hydraulic fluid cools and contracts, the resilient insert 222 expands so as to assist in returning the fluid from the expansion chamber 220 to the main chamber 203, which is thereby kept full of hydraulic fluid.

The impulse torque generator illustrated in Figures 3 to 11 has a central rotor 1 which is mounted in a coaxial rotatable casing 2 which is filled with hydraulic fluid. The casing 2 comprises a cylindrical liner 3 extending between end walls 4, 6 which are retained in a cylindrical outer case 7 by an internal flange 8 formed at one end and a retainer 9 screwed into the other end. The end wall 4 has a hollow portion 11 which is accessible through the retainer 9 and which has splines 12 engageable by the output shaft (not shown) of the gear box of an air-motor-driven power tool having a housing in which the impulse torque generator is rotatably mounted. The speed of the output shaft may be 5000 to 10,000 rev/min, for example.

The rotor 1 extends between the end walls 4, 6. At one end it has a journal 13 mounted in the end plate 4 and at the other end a shaft 14 which extends through the end plate 6 and which is formed with a square end portion 16 adapted for connection to a tool bit (not shown). The rotor 1 has an axial bore 17 through which the casing 2 can be filled with hydraulic fluid via a radial bore 18, after which the bore 17 is closed by a ball 19 and a screw plug 21. The bore 17 communicates with an expansion chamber containing a foam pad 22 of closed cell structure for accommodating thermal expansion of the hydraulic fluid.

As seen in cross-section (Figures 3 to 10) the rotor 1 is formed with two lobes 31, 32 and has two-fold rotational symmetry: it is thus of generally oval cross-sectional shape. The extremities of the lobes are flattened to provide arcuate end portions 33 whose axis is the axis 34 of the rotor. The sides of the rotor (between the lobes) have respective localized recesses 36 which intercommunicate through transverse bores 37, 38 so that the fluid pressure on the two sides is equalized. A blind bore 39 communicates between the bore 37 and the end of the rotor adjacent the end wall 4.

Between the rotor 1 and the casing 2 there are two identical arcuate blades or shells 41, 42 partly encompassing the rotor 1 and extending between the end walls 4, 6 of the casing. The shells 41, 42 are cylindrical segments whose internal radius is less than the radius of the arcuate end portions 33 of the rotor and whose external radius is less than the internal radius of the liner 3. The shells 41, 42 are urged towards the rotor 1 (against the centrifugal force occurring during operation) by springs 43 mounted in the liner 3. Each shell 41 (42) has a first end 41a (42a), which is the leading end in the normal direction of rotation indicated by the arrow 44 in Figure 3 to 6, and a second end 41b (42b), which is the trailing end in the same direction of rotation and which in this case abuts against a corresponding elongate stop 46 formed inside the liner 3. The ends of the liner 3 have internal circumferential grooves 47 passing through the stops 46 and ensuring that the pressure outside the two shells 41, 42 is equalized. It will be appreciated that the stops 46 constrain the shells 41, 42 to rotate with the casing 2.

Referring now to Figures 3 to 6, the operating cycle of the hydraulic impulse torque generator will be explained, assuming that rotation of the rotor 1 is resisted by the engagement of a tool bit on the rotor shaft 17 with a screw element which has been tightened to an initial, low torque and which is to be tightened to a final, higher predetermined torque.

In the position shown in Figure 3, referred to as the transfer position, the trailing second ends 41b and 42b of the shells are in contact with the arcuate end portions 33 of the rotor 1 while the leading first ends 41a and 42a are in contact with the respective rising portion of the respective lobes 32 and 31 beyond the recesses 36. The result is that the leading first ends 41a, 42a are urged outwards, tending to increase the hydraulic fluid pressure outside the shells 41, 42 and to reduce the pressure inside. However, the pressure inside and outside the shells in the transfer position is equalized Vid the grooves 47, the gaps between the leading ends 41a, 42a and the stops 46, a transfer recess 48 in the end wall 4, the bore 39, and the transverse bore 37. As a consequence, no pressure differential acts on the rotor and no impulse torque is imparted to it.

In the following, first, intermediate position shown in Figure 4 the hydraulic fluid is free to rotate around the rotor 1 outside the shells 41, 42.

In the impact position shown in Figure 5 the trailing second ends 41b and 42b of the shells are again in contact with the arcuate end portions 33 of the rotor, while the leading first ends 41a and 42a are in contact with the respective rising portions of the respective lobes 31 and 32. Again the leading first ends 41a, 42a are urged outwards, tending to increase inside of the shells 41, 42, the pressure inside and outside the shells is not equalized, with the result that the abruptly increasing pressure differential acts on the rotor portions between the leading end 41a and the trailing end 42b and between the leading end 42a and the trailing end 41b, so that kinetic energy is transmitted from the casing 2 to the rotor 2, via the hydraulic fluid, as a torque impulse.

The magnitude of the peak torque depends on the resistance to rotation of the rotor and on the rate at which the pressure differential is dissipated. In order to provide adjustability of the latter parameter, and therefore of the final torque, a variable restrictor in the form of a needle valve 51 is arranged in a fluid path communicating between the inside and the outside of the shells 41, 42 in the impact position. In Figures 3 to 6 the fluid path is indicated diagrammatically as extending between two ports 52, 53 in one of the end walls 4, 6. In the specific embodiment shown in Figure 11 the high pressure inlet port 52 in the end wall 6 is restricted by the adjustable needle valve 51 and communicates with a recess 54 partly encircling the rotor shaft 14.At least in the impact position, the recess 54 communicates with a radial bore 56 leading to the rotor bore 17 and hence to the radial bore 18, which communicates with the interior of the shells 41, 42.

In the following, second, intermediate position shown in Figure 6 the hydraulic fluid is again free to rotate around the rotor 1 outside the shells 41, 42.

In the reverse direction of rotation, indicated by the arrow 57 in Figures 7 to 10, it is clear that Figure 5 shows the transfer position, Figure 8 the first intermediate position, Figure 9 the impact position, and Figure 10 the second intermediate position, as described above. However, it is to be noted that, in the impact position (Figure 9) the inlet port 52 to the fluid path including the needle valve 51 is closed by one of the shells, with the result that there is no adjustability of the peak torque, so that the maximum impact is applied. This is generally desirable when the tool incorporating the impulse torque generator is used for unscrewing.However, if the tool is to be used for tightening a screw element with a left-handed thread, the end wall 6 may be re-positioned so that the inlet 52 is open in the impact position in the reverse direction of rotation indicated by the arrow 57.

Figure 12 illustrates a hydraulic impulse torque generator which is similar to that just described above and which operates in the same way but which is designed to be interchangeable with a torque sensitive clutch.

In Figure 12 the same references are used as in Figure 11 for similar parts, and only the significant structural differences will be described below.

The rotor 1 has an enlarged axial bore 117 which receives a central bearing boss 113 integral with the end wall 4. Within the other end wall 6 the bore 117 is narrowed and receives a screw plug 121 which secures an end cap 101 on the rotor. Attached to the end cap 101 over the head of the plug 121 is an extension shaft 114 for receiving a tool bit. The bore 117 contains a hollow foam plug 122 of closed cell structure for accommodating thermal expansion.

In the transfer position the transfer recess 48 communicates with the blind bore 39, which in turn communicates via the bore 117 with a transverse bore 137 leading to the localized recesses 36 described above.

The torque sensitive clutch which the above-described device replaces has the same external shape and contains a conventional clutch mechanism which disengages when a given torque is exceeded and which need not be described here.

Various modifications may be made in the impulse torque generators described above. For example, if two impulses per cycle are desired, the transfer recess 48 and the bore 39 can be omitted. The needle valve 51 may be replaced by another form of variable restrictor or by a fixed restrictor or the fluid path 52-51-54-56 may be omitted if maximum impulse torque is required. The number of shells used may be fewer or more than two: in the latter case, if only one impulse per cycle is required, two or more transfer recesses 48 will have to be provided. Similarly the rotor may have fewer or more than two lobes.

The invention, as described above, also provides a hydraulic impulse torque generator comprising a central rotor, a coaxial rotatable casing which is to be filled with hydraulic fluid for transmitting torque from the casing to the rotor, the casing having end walls between which the rotor extends, one or more arcuate shells partly encompassing the rotor and extending between the end walls within the casing, and means for constraining the shell(s) to rotate with the casing, the rotor having one or more lobes, the or each shell having first and second ends in the circumferential direction, and the arrangement being such that, when the casing is rotated in a given direction relative to the rotor, at a given position in the cycle of rotation, the said ends of the shell(s) are in contact with the rotor along its whole length between the end walls while the first end of the or each shell is urged generally in a radial direction while in contact with the corresponding lobe, thereby causing a pressure differential between the inside and the outside of the shell(s), the pressure differential acting on the rotor in such a manner that kinetic energy is transmitted from the casing to the rotor as an impulse torque.

The constraining means may comprise one or more abutments on the internal surface of the casing, the or each abutment engaging against the second end of the corresponding shell when the casing is rotated in the said given direction. The or each abutment may extend between the end walls of the casing. A transverse groove may extend across the or each abutment.

Preferably, in the said given position, a fluid path including a restrictor communicates between the inside and the outside of the shell(s) in order to limit the impulse torque. The restrictor may be a variable restrictor. The rotor may have a plurality of lobes distributed around the circumference, and an equal number of shells. Transfer means may be provided for preventing the formation of a pressure differential acting on the rotor in all positions other than the said given position. Preferably, the transfer means includes at least one transfer recess in one of the end walls and at least one passage in the rotor having an inlet which can be brought into register with the transfer recess and communicating with the exterior of the rotor. The rotor may have at least one transverse passage for communicating between the regions inside the shells in the said given position.

Preferably, each lobe has an extreme surface portion which is arcuate and whose axis coincides with the rotor axis, and each shell is a cylindrical segment whose internal radius is less than the radius of the said arcuate surface portion of each lobe.

Preferably. when the casing is rotated in the opposite direction to the said given direction, an impulse torque is again generated at least once during each cycle of rotation.

The impulse torque generator may be removable and replaceable by a torque sensitive clutch.

Claims (14)

Claims:

1. A hydraulic impulse generator comprising a central rotor and a coaxial rotatable casing defining a hydraulic fluid chamber which receives the rotor and which is to be filled with hydraulic fluid for transmitting torque between the casing and the rotor, the generator including an expansion chamber which is in two-way fluid communication with the hydraulic fluid chamber, the expansion chamber containing a resiliently compressible insert comprising at least one closed cell.

2. An impulse torque generator as claimed in claim 1, in which the insert fills the expansion chamber when free of hydraulic fluid pressure.

3. An impulse torque generator as claimed in claim 1 or 2, in which the insert comprises at least one body of closed-cell foam.

4. An impulse torque generator as claimed in claim 3, in which the foam is of an elastomer.

5. An impulse torque generator as claimed in any preceding claim, in which the expansion chamber is closed except for an aperture through which it communicates with the hydraulic fluid chamber.

6. An impulse torque generator as claimed in any preceding claim, in which the expansion chamber occupies an end wall of the casing.

7. An impulse torque generator as claimed in claim 6, in which the rotor has a journal mounted in a bearing recess in the said end wall, the recess having a portion extending beyond the free end of the journal and constituting the expansion chamber.

8. An impulse torque generator as claimed in claim 7, in which the expansion chamber communicates with the hydraulic fluid chamber via a fluid path between the journal and the said end wall.

9. An impulse torque generator as claimed in claim 7, in which the expansion chamber communicates with the hydraulic fluid chamber via a fluid path passing through the rotor.

10. An impulse torque generator as claimed in any of claims 1 to 5, in which the expansion chamber occupies the rotor.

11. An impulse torque generator as claimed in claim 10, in which the expansion chamber is cylindrical and coaxial with the rotor.

12. An impulse torque generator as claimed in claim 11, in which the insert is annular and coaxial with the expansion chamber.

13. A hydraulic impulse torque generator substantially as described with reference to, and as shown in, Figure 1, Figure 2, Figures 3 to 11, or Figure 12 of the accompanying drawings.

14. A power tool incorporating a hydraulic impulse torque generator according to any preceding claim.