GB1598908A - Freewheel devices - Google Patents

Description

(54) IMPROVEMENTS IN FREEWHEEL DEVICES (71) We, BORECLIFF LIMITED, a British Company of Trow Way, Diglis Trading Estate, Worcester WR9 3DG, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to freewheel devices of the kind used in mechanical transmission systems for enabling overrun to take place between rotating drive transmitting parts of the systems. The invention is particularly, though not exclusively, applicable to mechanical transmissions such as are employed in driving agricultural implements from the power take-off shafts of tractors.

Freewheel devices are becoming increasingly necessary in the transmission systems for power take-off driven agricultural implements because of the higher and higher power requirements of the implements. A substantial amount of inertial energy can be stored in rotating parts of the implements which, without the provision of freewheel devices in the transmission, could continue propulsion of the tractors for a limited period when the throttle controls of the tractors are closed, or alternatively cause damage to some parts of the transmission system. The freewheel devices dissipate the stored inertial energy and allow the tractors to be stopped or slowed in a controlled manner.

The present invention consists in a freewheel device comprising concentric rotary inner and outer members connected, or adapted to be connected, respectively to two drive transmitting parts of a mechanical transmission system and being located in concentric relationship by a pair of axially spaced annular bearings fixed to one of the members for rotation therewith, a ratchet form on the other member adjacent to the said one mem ber and extending parallel to the rotational axis of the members, and at least one pawl of substantially strip form which extends between the bearings parallel to said rotational axis and is hingedly connected at its ends to the bearings for angular movement about an axis parallel to the said rotational axis between a drive position to which the pawl is normally urged by spring means and in which a longitudinal edge of the pawl engages with the ratchet form and the inner and outer members are thereby connected for rotation together, and a freewheel position in which the pawl overruns the ratchet form and relative rotation of the members is possible.

For use in transmitting drive, for example, from a power take-off shaft of a tractor to an implement the freewheel device is assembled so that the inner and outer members are driv ably connected together by the pawl when the power take-off shaft is rotating. When rotation of the shaft is stopped the member of the free wheel device associated with the shaft in the transmission system also ceases to rotate and the pawl immediately overruns the ratchet form, thus allowing the other member associa ted with the implement to continue to rotate until the stored inertial energy in the implement has been dissipated. This prevents the power take-off shaft and other Darts of the tractor's drive from being damaged by the continued rotation of the implement.

Because of its substantially strip form and its engagement with the ratchet form longitudinally of the rotational axis of the inner and outer members, a substantial area of driving engagement can be obtained between the pawl and the ratchet form. This extends the torque transmitting capacity of the device.

Furthermore the longitudinal arrangement of the pawl and ratchet form enables the enhanced torque transmission to be obtained within a size of the freewheel device which is comparable with known devices of smaller torque capacity.

The torque transmitting capacity of the device may be imoroved further by arranging that the pawl is in compression when it is transmitting torque and not in shear. This is possible by providing a longitudinal abutment surface on the said one member, and having on the pawl opposite to the longitudinal edge which engages with the ratchet form, a fur ther longitudinal edge which bears on the abutment surface when the pawl is in the drive position.

Preferably the pawl is disposed in a groove in the periphery of the said one member extending longitudinally of the member. The pawl protrudes from the groove when it is in the drive position and is contained within the groove when it is in the freewheel position.

The groove may have a longitudinal side sur face which forms the abovementioned abut ment surface.

The hinged connection between the pawl and the bearings may be formed by providing the pawl with longitudinal projections at its ends which engage in sockets in the bearings.

A plurality of pawls may be provided, pre ferably equiangularly spaced about the rota tional axis of the inner and outer members to avoid out of balance effects.

The freewheel device in accordance with the invention has been developed primarily for application to transmission systems for driving agricultural implements. However, it may have applications in other transmission systems as well, for example in transmission systems of some industrial machines and in clutch units.

An embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which, Figure 1 is a combined side elevation and longitudinal section on the rotational axis of a freewheel device in accordance with the invention, Figure 2 is a section on line 2-2 of Figure 1 showing pawls of the device in drive positions, Figure 3 is an exploded perspective view of part of the freewheel device, and Figure 4 is a fragmentary section on line 2-2 of Figure 1 showing one of the pawls in a freewheel position.

The freewheel device of this embodiment is intended for use in a transmission system for transmitting drive from a power take-off shaft of a tractor to an agricultural implement.

The device comprises a basically cylindrical inner rotary member 1 and a co-axial tubular outer rotary member 2 which extends over the inner member. The inner member 1 is adapted to be connected to a driving shaft 3 which couples in known manner to the power take-off shaft of a tractor, and the outer mem ber 2 is adapted to be connected to a driven shaft 4 which takes the drive to rotary parts of the implement. As illustrated, rhe inner member has a bore 5 with a radial keyway 6 by which the member is mounted on a keyed end of the driving shaft 3 for rotation with - shaft A bolt, not shown, carried by the inner member at a reduced diameter portion 7 of the member is tightened radially onto the driving shaft 3 to secure the inner mem ber to the shaft. The outer member 2 has an external annular end flange 8 with angularly spaced threaded holes 9 in its parallel to the axis of the member for receiving fixing bolts 10 by which the outer member is fixed to an end flange 11 of the driven shaft 4.

Two annular bearings 12, 13 locate the inner and outer members in the correct concentric relationship. One bearing 12 is mounted on the end portion 7 of the inner member, and the other bearing 13 is mounted on an opposite end portion 14 of the inner member of similarly reduced diameter to the end portion 7 but shorter than that end portion. The bearing 12 abuts against an annular radial face 15 of the inner member adjacent to the end portion 7 and the bearing 13 abuts against an annular radial face 16 of the inner member adjacent to the end portion 14. The bearings 12, 13 are received into counterbores 17, 18 respectively at opposite ends of the outer member. Next to the bearing 12 a washer 19 is fitted against which a circlip 20 abuts which is engaged in an annular recess 21 in the counterbore 17 and restrains the bearing from axial movement relative to the inner and outer members. The other bearing 13 is retained in the counterbore 18 by means of a washer 22 which is clamped in that counterbore against the bearing by the end flange 11 of the driven shaft 4 when that flange is fixed to the end flange 8 of the outer member.

As shown in Figure 3, dowel pins 23 are fixed to the inner member at the two radial faces 15 and 16. The dowel pins project perpendicularly from those faces and engage in complementary sockets 24 in the bearings so as to connect the bearings to the inner member for rotation with that member. The bearings are free to rotate relative to the outer member.

In the cylindrical surface of the inner member 1 there are four equi-angularly spaced grooves 25 which extend along the length of the inner member between the bearings. The grooves are all of similar form being of shallow, asymmetrical V-section, each having a narrow, abutment surface 26 which extends radially with respect to the longitudinal axis of the inner member, and a considerably wider bed surface 27 which extends at an obtuse angle to the abutment surface. The angle is preferably approximately 10SO. There are two longitudinally spaced blind holes 28 in the bed surface 27 of each groove 25 in which helical compression springs 29 are located which project from the bed surface but can be com- pressed to be fully received into the holes 28.

Each groove 25 has a pawl 30 located in it.

The pawl 30 is made from fiat metal plate of rectangular cross-section of a thickness slightly less than the wdith of the abutment surface 26 of the groove. It has an oblong rectangular body part 31 at each end of which there is a longitudinal projection 32 of about half the width of the body. The length of the body is slightly shorter than the length of the groove and the width of the body is appreciably less than the width of the bed surface 27 of the groove. The arrangement is such that, with one longitudinal side 33 of the pawl against the abutment surface of the groove, the pawl can lie flat against the bed surface and be contained within the notional arc of the cylindrical surface of the inner member over the groove. The projections 32 at the two ends of the pawl are aligned and they continue as extensions of the longitudinal side 33 of the pawl. They hingedly engage in oblong sockets 34 in the bearings which locate the pawl in the groove and allow the pawl to move angularly about the inner corner 35 of its rectangular cross-section at the longitudinal side 33. That corner engages in the angle between the side and base surfaces of the groove and the continuations of the corner at the projections 32 engage in adjacent angles of the sockets. The sockets 34 allow the pawl to move angularly between a drive position, as shown in Figure 2, to which it is normally urged by the springs 29 acting on the inner flat face of the pawl and in which its other longitudinal side 36 projects out of the groove, and a freewheel position in which it is contained within the groove. The longitudinal side 33 of the pawl abuts flush against the abutment surface 26 of the groove when the pawl is in the drive position, and the continuations of that side at the projections abut flush against end surfaces 37 of the sockets 34.

The outer member has four equi-angularly spaced ratchet forms 38 at its internal surface defined by grooves in the surface extending longitudinally of the member between the two bearings. The ratchet form grooves are similar, each being of V-section with a shallow abutment surface 39 which, when the ratchet form is opposite one of the grooves 25 in the inner member, faces towards the abutment surface 26 of that groove, and a wider bed surface 40 which extends at right angles to the abutment surface 39 and substantially tangentially to the cylindrical internal surface of the outer member. The pawls 30 engage at their longi tudinal sides 36 in the ratchet forms 38 in their drive positions, as shown in Figure 2.

The pawls occupy their drive positions for transmitting drive to an implement from the power take-off shaft of a tractor, the outer member being rotated with the inner member by the pawls so that drive is transferred from the driving shaft 3 to the driven shaft 4.

Whilst transmitting the drive from the inner member to the outer member the pawls are under compression. The compressive forces are imposed upon the pawls through the abutment surfaces 26 and 39 of the grooves 25 and ratchet forms 38 respectively. Furthermore torque is transmitted between the members along the entire lengths of the bodies of the pawls, and thus along a substantial part of the lengths of the members. Accordingly the freewheel device has a large torque transmitting capacity for its size. An additional advantage is that rubbing movement such as can occur between a pawl and its retaining pin in some known freewheel devices is eliminated.

When rotation of the power take-off shaft is stopped the inner member ceases to rotate but the outer member is able to continue to rotate about the inner member under the effects of stored energy in rotating parts of the implement. The rotation of the outer member relative to the inner member takes the abutment surfaces 39 of the ratchet forms 38 away from the pawls and the bed surfaces of the ratchet forms and subsequently the cylindrical internal surface of the outer member between the ratchet forms urge the pawls to pivot about their corners 35 into the grooves 25, against the loading of the springs 29, as shown in Figure 4. The pawls, of course, are automatically engaged in the ratchet forms again by the springs when the ratchet forms are opposite the grooves, so that drive can be transmitted from the inner member to the outer member when the power take-off shaft is rotated again.

It will be realised that the freewheel device described and illustrated is relatively easy to assemble, and that the pawls are located in place on the inner member simply by engaging their projections 32 in the sockets 34 of the bearings as the bearings are moved into position on the end portions 7 and 14 of the inner member. The dowel Dins 23 ensure that the bearings cannot be mounted in incorrect angular positions on the end portions.

WHAT WE CLAIM IS: 1. A freewheel device comprising concentric rotary inner and outer members connected, or adapted to be connected, respectively to two drive transmitting parts of a mechanical transmission system and being located in concentric relationship by a pair of axially spaced annular bearings fixed to one of the members for rotation therewith, a ratchet forms on the other member adjacent to the said one member and extending parallel to the rotational axis of the members, and at least one Dawl of substantially strip form which extends between the bearings parallel to said rotational axis and is hingedly connected at its ends to the bearings for angular mgvement about an axis parallel to the said rotational axis between a drive position to which the pawl is normally urged by spring means and in which a longitudinal edge of the pawl engages with the ratchet form and the inner and outer members are thereby connected for rotation together, and a freewheel position in which the pawl overruns the ratchet form and relative rotation

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

Claims (14)

**WARNING** start of CLMS field may overlap end of DESC **. half the width of the body. The length of the body is slightly shorter than the length of the groove and the width of the body is appreciably less than the width of the bed surface 27 of the groove. The arrangement is such that, with one longitudinal side 33 of the pawl against the abutment surface of the groove, the pawl can lie flat against the bed surface and be contained within the notional arc of the cylindrical surface of the inner member over the groove. The projections 32 at the two ends of the pawl are aligned and they continue as extensions of the longitudinal side 33 of the pawl. They hingedly engage in oblong sockets 34 in the bearings which locate the pawl in the groove and allow the pawl to move angularly about the inner corner 35 of its rectangular cross-section at the longitudinal side 33. That corner engages in the angle between the side and base surfaces of the groove and the continuations of the corner at the projections 32 engage in adjacent angles of the sockets. The sockets 34 allow the pawl to move angularly between a drive position, as shown in Figure 2, to which it is normally urged by the springs 29 acting on the inner flat face of the pawl and in which its other longitudinal side 36 projects out of the groove, and a freewheel position in which it is contained within the groove. The longitudinal side 33 of the pawl abuts flush against the abutment surface 26 of the groove when the pawl is in the drive position, and the continuations of that side at the projections abut flush against end surfaces 37 of the sockets 34. The outer member has four equi-angularly spaced ratchet forms 38 at its internal surface defined by grooves in the surface extending longitudinally of the member between the two bearings. The ratchet form grooves are similar, each being of V-section with a shallow abutment surface 39 which, when the ratchet form is opposite one of the grooves 25 in the inner member, faces towards the abutment surface 26 of that groove, and a wider bed surface 40 which extends at right angles to the abutment surface 39 and substantially tangentially to the cylindrical internal surface of the outer member. The pawls 30 engage at their longi tudinal sides 36 in the ratchet forms 38 in their drive positions, as shown in Figure 2. The pawls occupy their drive positions for transmitting drive to an implement from the power take-off shaft of a tractor, the outer member being rotated with the inner member by the pawls so that drive is transferred from the driving shaft 3 to the driven shaft 4. Whilst transmitting the drive from the inner member to the outer member the pawls are under compression. The compressive forces are imposed upon the pawls through the abutment surfaces 26 and 39 of the grooves 25 and ratchet forms 38 respectively. Furthermore torque is transmitted between the members along the entire lengths of the bodies of the pawls, and thus along a substantial part of the lengths of the members. Accordingly the freewheel device has a large torque transmitting capacity for its size. An additional advantage is that rubbing movement such as can occur between a pawl and its retaining pin in some known freewheel devices is eliminated. When rotation of the power take-off shaft is stopped the inner member ceases to rotate but the outer member is able to continue to rotate about the inner member under the effects of stored energy in rotating parts of the implement. The rotation of the outer member relative to the inner member takes the abutment surfaces 39 of the ratchet forms 38 away from the pawls and the bed surfaces of the ratchet forms and subsequently the cylindrical internal surface of the outer member between the ratchet forms urge the pawls to pivot about their corners 35 into the grooves 25, against the loading of the springs 29, as shown in Figure 4. The pawls, of course, are automatically engaged in the ratchet forms again by the springs when the ratchet forms are opposite the grooves, so that drive can be transmitted from the inner member to the outer member when the power take-off shaft is rotated again. It will be realised that the freewheel device described and illustrated is relatively easy to assemble, and that the pawls are located in place on the inner member simply by engaging their projections 32 in the sockets 34 of the bearings as the bearings are moved into position on the end portions 7 and 14 of the inner member. The dowel Dins 23 ensure that the bearings cannot be mounted in incorrect angular positions on the end portions. WHAT WE CLAIM IS:

1. A freewheel device comprising concentric rotary inner and outer members connected, or adapted to be connected, respectively to two drive transmitting parts of a mechanical transmission system and being located in concentric relationship by a pair of axially spaced annular bearings fixed to one of the members for rotation therewith, a ratchet forms on the other member adjacent to the said one member and extending parallel to the rotational axis of the members, and at least one Dawl of substantially strip form which extends between the bearings parallel to said rotational axis and is hingedly connected at its ends to the bearings for angular mgvement about an axis parallel to the said rotational axis between a drive position to which the pawl is normally urged by spring means and in which a longitudinal edge of the pawl engages with the ratchet form and the inner and outer members are thereby connected for rotation together, and a freewheel position in which the pawl overruns the ratchet form and relative rotation

of the members is possible.

2. A freewheel device according to Claim 1 wherein the pawl has longitudinal projections at its ends which engage in sockets in the bearings to provide the hinged connection of the pawl to the bearings.

3. A freewheel device according to Claim 2 wherein each projection is of rectangular cross section and the socket in which it engages has a cross-sectional shape which permits the projection to turn about a corner of the rectangular cross-section for the angular movement of the pawL

4. A freewheel device according to any preceding claim wherein the pawl is disposed in a groove in the periphery of the said one member extending longitudinally of the member, the pawl protruding from the groove when in the drive position and being contained within the groove when in the freewheel position.

5. A freewheel device according to any preceding claim wherein the said one member has a longitudinal abutment surface and the pawl has opposite to the longitudinal edge which engages with the ratchet form a further longitudinal edge which bears on the abutment surface when the pawl is in the drive position.

6. A freewheel device according to Claim 5 as dependent from Claim 4 wherein the groove has a longitudinal side surface which forms the abutment surface.

7. A freewheel device according to Claim 4 wherein the pawl has a longitudinally extending corner, and the groove has a longitudinal side surface and a bed surface which meet at an angle greater than the angle of the corner of the pawl, and the corner of the pawl engages in the angle of the groove between the side and bed surfaces and provides a fulcrum for the angular movement of the pawl.

8. A freewheel device according to any of claims 4 to 7 wherein the spring means comprises compression springs located in the bed of the groove and which bear on an adjacent surface of the pawl to urge the pawl to the drive position.

9. A freewheel device according to any preceding claim wherein the ratchet form comprises a groove in the said other member.

10. A freewheel device according to any preceding claim wherein the said one member to which the bearings are fixed for rotation therewith is the inner member.

11. A freewheel device according to Claim 10 wherein the inner member has reduced axial end portions on which the bearings seat, and the bearings are fixed to the inner member for rotation therewith by dowels extending between the inner member and the bearings parallel to the end portions.

12. A freewheel device according to any preceding Claim wherein there is a plurality of the pawls equi-angularly spaced about the rotational axis of the inner and outer members.

13. A mechanical transmission system including a freewheel device as claimed in any preceding Claim.

14. A freewheel device substantially as described herein with reference to and as illustrated by the accompanying drawings.