GB2170870A - Clutch with ball screw loading mechanism - Google Patents

Abstract

A power shift clutch includes a clutch loading mechanism between an input shaft 1 and an output shaft 2. The mechanism includes a ball screw mechanism 11 including ball bearings 11B which travel in a spiral raceway 11C, the spiral pitch of which is arranged so that the screw is self-releasing. The mechanism 11 may be used in a boat gearbox with multiple friction plate power drive clutches 7 and 9 at respective ends of the mechanism 11. <IMAGE>

Description

SPECIFICATION Power drive clutch The invention relates to a clutch, more particularly a mechanically operated, controllable power drive clutch for the transmission of rotary motion between power transmitting rotatable shafts. The shafts may be co-axial or axially offset. The invention is applicable to a clutch of the type which can be engaged and disengaged whilst power is being transmitted to and through the clutch; this practice is more commonly known as a power change or power shift.

Known mechanically operated loading mechanisms to engage the clutch usually suffer from disadvantages and limitations, and can require cumbersome and expensive refinements in order to operate successfully. For example, where the clutch clamping load is a product of the transmitted torque passing through the clutch, such that the torque acting on and passing through the clutch loading mechanism is in a series relationship with, and directly proportional to, the transmitted torque, the clutch loading mechanism is also responsive to any transient torques or shock loads that may be experienced by the drive line.Because the torque passing through the power drive clutch and the torque passing through the clutch loading mechanism are in a series relationship, the members are interactive with each other and, therefore, a regenerative torque relationship exists between them, which in certain known circumstances will produce undesirable results. For example, during a power change/shift clutch engagement, kinetic energy is transferred between the rotating bodies being synchronised by the clutch, and it is therefore possible for the drive line to be subjected to much higher torques than the maximum torque which can be developed by the prime mover of the drive line, the only limitation to the build up of the torque being the slip torque of the clutch. Therefore, if the described regenerative torque build up continues unchecked, extremely harsh clutch engagement results.To overcome this problem, torque limiting devices are necessary; these add complexity and cost to the clutch. Furthermore, a mechanical servo device is usually required to disengage the clutch whilst power is passing through it.

In the construction where a numerically high mechanical advantage clutch loading mechanism is used which is totally independant of the torque acting on and passing through the clutch, the clutch clamping mechanism usually has a very limited travel, and there are problems in accommodating the take up of the clearances and the wear allowance of the clutch. This restriction of limited travel is present because the ratio of the movement between the clutch operating member and the clutch clamping member is usually inversely proportional to the ratio of the mechanical advantage. Consequently, in-service adjustments or automatic wear compensators are required, which can add considerable cost to the clutch.

It is one object of the invention to provide a clutch which is substantially free of the disadvantages of known clutches. The invention is based upon the first realisation that if the clutch loading mechanism is positioned and powered in a parallel torque flow relationship with the torque being transmitted to and through the power drive clutch, the clutch will not be responsive to any transient torques or harmful shock loads that may be experienced by the drive line. The invention is based on a second realisation that by providing for the interference fit engagement of the engaging and engaged parts slippage can take place at a set torque limit.

According to one aspect of the invention there is provided a clutch including an input shaft to be connected to a prime mover and an output shaft to be connected to a driven member, the shafts being connectable together by one of a forward gear and a reverse gear mechanism, each gear including a friction driven plate, a clutch loading mechanism located between the gears and having a friction drive plate to engage the friction driven plate of the respective gear, the clutch loading mechanism comprising a ball screw connectable to the input shaft to form a parallel torque circuit with the driving torque, the ball screw being self releasing.

Because a parallel torque circuit is formed, the clamping load acting on the power drive clutch need not be responsive to any transient or shock torques experienced by the drive line and these harmful effects are eliminated if they exceed the slip torque setting of the clutch.

The clutch loading mechanism may be engagable with the input shaft in a number of ways. For low power applications a cone clutch may be present, and spring loaded by plungers in the body of the ball nut. Preferably a multiple coil spring clutch is present to connect drums housing the friction driven plates of each gear to a sleeve slidable along the ball nut and carrying at each end the friction drive plates. The spring clutch and the drums may be interference fitted so that slippage takes place at a set torque limit, and this in turn controls the slip torque of the power drive clutch. In addition such a multi coil spring clutch has an extremely good torque servo action.

According to another more specific aspect of the invention there is provided a mechanically operated, power drive clutch of the interleaved multiple friction plate type, comprising a self-releasing ball screw clutch loading mechanism, carried on and around one of the shafts to be coupled and positioned and pow ered in a parallel torque flow relationship with the torque being transmitted through the clutch, an axially extending drum rotating with the input drive and journalled on the shaft for relative rotation thereto, drive friction plates of the clutch attached within the bore of the drum for rotation therewith, an antifriction thrust bearing carried on the said shaft and positioned in between the clutch and the ball nut member of the ball screw clutch loading mechanism, a second low power clutch drive device having a set slip torque value, and which when selectively engaged, forms the parallel torque flow circuit by connecting together the drum member and the ball nut and the drive connection therebetween, and causes the ball nut to rotate relative to the shaft and simultaneous axial movement thereto, loads and clamps together the interleaved multiple friction plate clutch, and the slip torque of which is controlled to the corresponding level set by the slip torque of the second drive clutch device.

In a more specific aspect the invention provides a mechanically operated, power drive clutch for the transmission of rotary power between rotatable shafts, comprising a spiral ball raceway formed in and around the circumference of the shaft to be coupled, a number of loose individual spherical balls which circulate within the raceway, a cylindrical ball nut member having a spiral ball raceway formed within its bore and for rolling engagement with the spherical balls, and thereby producing a ball screw action with the shaft, the driven friction plates of the interleaved multiple friction plate clutch fixed to the shaft for rotation therewith and the drive friction plates of the interieaved multiple friction plate clutch fixed within the bore of an axially extending cylindrical drum integral with a gearwheel journalled on the shaft for relative rotation thereto, an anti-friction clutch thrust bearing carried on the shaft, and positioned in between the clamping face of the ball nut and the end friction clutch plate of the interleaved multiple friction plate clutch, a multiple coil spring clutch having a number of its coils carried on the outside diameter of the drum and with an interference fit therewith to produce a set slip torque at the interface with the drum, a sleeve mounted on the outside diameter of the ball nut for rotation therewith and relative axial movement thereto, and having a stepped down diameter at one end which fits freely and with a running clearance within the remaining coils of the spring clutch extending axially outwards from the end face of the cylindrical drum, a selector ring slidably mounted on the unstepped portion of the sleeve for selective engagement with the multiple coil spring clutch and by the relative rotaty motion therebetween, causes the spring clutch to wind radially inwards and around the stepped diameter of the sleeve, and the friction created therebetween causes the sleeve to rotate with the spring clutch rotating with the gearwheel, and thus imparting the same rotary motion to the ball nut, causing it to simultaneously move axially along the shaft, and after taking up clearance between the thrust bearing and the interleaved friction plates, clamps together the power drive clutch, and thereby, produces rotary motion of the shaft.

In a more specific aspect the invention also provides a mechanically operated, power drive clutch for the transmission of rotary power between rotatable shafts, comprising a spiral ball raceway formed in and around the circumference of the shaft to be coupled, a number of loose individual spherical balls which circulate within the raceway, a cylindrical ball nut member having a spiral ball raceway formed within its bore, and for rolling engagement with the spherical balls, and thereby, producing a ball screw action with the shaft, and the axial motion thereof, used to clamp together an interleaved multiple friction plate clutch, having the driven friction plates fixed to the shaft for rotation therewith, and the drive friction plates fixed within the bore of an axially extending cylindrical drum integral with a gearwheel journalled on the shaft for relative rotation thereto, an anti-friction thrust bearing carried on the shaft, and positioned in between the clamping face of the ball nut and the end friction clutch plate of the interleaved multiple friction plate clutch, a number of compression springs housed in radially formed holes within the body of the ball nut, and acting on radially slidable plungers, constrained against a slidably mounted selector ring carried on the outside diameter of the ball nut and for rotation therewith, a female conical friction surface formed in the end of the bore of the selector ring, and adjacent to a corresponding male conical friction surface formed on the outside of the drum and for selective engagement therewith, to activate the engagement of the power drive clutch, a circular groove formed in the bore of the selector ring for selective engagement with the plungers when positioned in the neutral drive mode, a sloping ramp profile formed in the bore of the selector ring, and for selective engagement with the plungers, and thereby producing an axial load to clamp together the conical friction surfaces, and the slip torque therebetween acting on the ball nut, controls and limits the slip torque of the interleaved multiple friction plate clutch.

The clutch of the invention is suitable for devices in which the input and output shafts are co-axial or axially offset.

In order that the invention may be well understood, it will now be described, by way of example, with reference to the accompanying drawings, in which Figure 1 A is a sectional view of one twin power drive clutch of the invention and Figure 1B is a sectional view taken on lines X-X of Figure 1 A; Figure 2A is a sectional view of another twin power drive clutch of the invention and Figure 2B is a sectional view taken on lines Y Y of Figure 2A.

In the embodiments there is shown a twin power drive clutch arranged back to back about a single ball screw clutch loading mechanism cooperative with both clutches, in the setting of a forward, neutral and reverse gearbox drive for a boat with the prime mover connecting to the input shaft and rotating in a clockwise direction when looking onto the input shaft, and the output shaft connecting to the propellor. Where possible the same reference numerals are used in the description of the embodiments.

The gearbox of Figures 1 A and 1B comprises a casing 3 in which are journalled for rotation and axial thrust, an input shaft 1 connected to the prime mover (not shown) and rotating in a clockwise direction when viewed on the input spline 1C, an output shaft 2 connected to the propellor, and an idler shaft 4 carrying an integral idler gear 4A. The input shaft 1 carries an integral pinion gear 1 A in constant mesh with a gearwheel 5 having an axially extending drum 5A and journalled on the output shaft 2 with an anti-friction bearing 5B. The drum 5A has axial cutouts along its diameter to accept and house drive friction plates 7A carrying corresponding projections around the outer diameter.The drum 5A carries around its outside diameter and with six thousandths of an inch interference fit, a right hand wound, multiple coil, reverse spring clutch 8, having two coils extending axially out from the drum. The input shaft carries another pinion gear 1B in constant mesh with the idler gear 4A which is also in constant mesh with a gearwheel 6 having an axially extending drum 6A and journalled on the output shaft with an anti-friction bearing 6B. The drum 6A has axial cutouts along its diameter to accept and house the drive friction plates 9A carrying corresponding projections around the outside diameter. The drum 6A also carries around its outside diameter and with six thousandths of an inch interference fit, a right hand wound, multiple coil, forward spring clutch 10, having two coils extending axially out from the drum.

The driven friction plates 7B and 9B of the respective interleaved multiple friction plate power drive clutches 7 and 9, are internally splined to and axially slidable along the output shaft 2. In between the power drive clutches is centrally positioned a ball screw clutch loading mechanism 11, comprising a ball nut 1 1 A with a right-hand formed inner spiral roller ball raceway, indidvidual loose spherical balls 11 B, and a right-hand formed spiral roller ball raceway 1 1C carried in and around the outside diameter of the output shaft 2.Therefore, any relative rotary motion between the ball nut and the output shaft will simultaneously result in axial movement of the ball nut along the output shaft, the direction of movement being determined by the resultant rotary motion of the ball nut relative to the output shaft. In other words, if the ball nut rotates clockwise relative to the output shaft, then the ball nut moves to the right, and vice versa if the ball nut rotates anticlockwise. The spiral pitch of the ball screw is selected so that the screw action is self releasing, and therefore, when the torque applied to the ball nut is released, the axial load produced by the torque is automatically and simultaneously released.The ball nut carries on its outside diameter, a slidably mounted sleeve 12 with both of its end portions stepped down in diameter so that they fit freely within the respective coils of the multiple coil spring clutches extending out from the drum.

The central portion of the sleeve carries a slidably mounted selector ring 13, having lugs 13A and 13B projecting from its side faces for engagement with the drive tags 8A and 10A respectively, and which are formed by bending radially outwards the end portion of the spring clutches. The two drive pins 14 locate in diametrically opposite radial holes passing through the sleeve 12, and are slidably mounted within axial slots formed in the outside diameter of the ball nut and in the bore of the selector ring, so that as the members rotate together, they can also simultaneously slide axially relative to each other.An external lever 17, operated by a flexible cable connected to a remote control unit (not shown), selectively moves the lever, which acts on an integral shaft 1 7A journalled through the casing 3, and positions a slidable selector fork 15 carried in the casing and located in a circumferential groove formed in the outside diameter of the selector ring for selective axial movement therewith.

In the neutral drive position selected by the remote control unit, the selector ring 13 is selectively positioned midway along the sleeve 12 and central to the drive tags 8A and 10A, so that the lugs 13A and 13B are respectively disengaged from the drive tags. Therefore, the multiple coil spring clutches are free to rotate clear of the end portions of the sleeve which will therefore remain at rest together with the ball screw clutch loading mechanism 11 and the output shaft 2, and hence a neutral drive is accomplished.When the remote control unit is selectively moved to the forward drive position, the selector ring 13 is moved until the lug 13B engages with the drive tag 10A, and the relative rotary motion therebetween winds the multiple coil forward spring clutch 10 down and around the right end portion of the sleeve 12, and the friction therebetween rotates the ball nut 11 A which simultaneously moves axially and clamps together the interleaved multiple friction plate forward power drive clutch 9, thus causing the output shaft 2 to start and rotate.Whilst a speed difference exists across the power clutch members, the axial load applied to the power clutch by the ball nut continues to increase, however, at the required torque level across the clutch, the controlled interference fit between the outside diameter of the drum 6A and the forward spring clutch 10 gives way to slippage therebetween, thus limiting the torque that can be transmitted to and through the ball nut, which in turn limits the end load acting on the power drive clutch, and so controls the amount of torque build up across the clutch. If the drive line should experience any kind of shock loads, for example, if the propeller hit an underwater obstacle, the clutch would still behave in the described manner, and by so doing, provide added protection to the complete drive line of the boat.

When the remote unit is moved from the forward drive position immediately into the reverse drive, thus requiring a power change from the gearbox to quickly make the boat go astern, the selector ring 13 disengages the lug 13B from the drive tag 10A, allowing the forward spring clutch 10 to spring back to its original free state, that is, clear of contact with the sleeve 12, and releasing the torque which was acting on and through the ball nut loading mechanism, and because the mechanism is self releasing, the corresponding axial load is automatically released, and the forward power drive clutch disengages the drive with the output shaft 2.The engagement of the lug 13A with the drive tag 8A, and the relative rotary motion therebetween winds the multiple coil reverse spring clutch 8 down and around the left end portion of the sleeve 12, and the controlled friction therebetween causes the sleeve to rotate in the opposite direction to the said input shaft drive. This motion is imparted via the drive pins 14 to the ball nut 11A, which then simultaneously moves axially along the output shaft 2, and after taking up the clearances between the thrust bearing 7C and the interleaved friction plates 7A and 7B, clamps the members together, and the friction therebetween causes the output shaft to stop rotating clockwise, come to rest and accelerate anti-clockwise until the synchronous speed is reached.The dynamic behaviour of the reverse power clutch 7 is controlled in exactly the same way as that previously described for the forward power drive clutch 9. Accordingly, the invention provides in this embodiment a marine gearbox drive capable of changing its mode of operation under any power conditions, and particularly whilst maximum torque is being delivered to and through the power drive clutches.

The embodiment of Figures 2A and 2B differs from that of Figures 1 A and 1B in that the ball nut 11 A carries within its body, equally spaced radial holes housing coil compression springs 18, acting on slidable plungers 19 which are forced by a known load against a selector ring 20, slidably mounted on the outside diameter of the ball nut. The selector ring 20 has formed at either end of its bore diameter, female conical friction surfaces 20A and 20B, respectively. The opposing axially extending drums 5A and 6A have corresponding male conical friction surfaces 5C and 6C, respectively. In the neutral drive position, the plungers 19 rest in a circular groove 20D, formed in the bore of the selector ring and so preventing it from moving axially relative thereto.Within the bore of the selector ring are also formed sloping ramp faces 20C and 20E, which selectively co-operate with the plungers 19, and forces the conical friction surfaces into engagement with their respective members and by so doing, brings about engagement of the interleaved multiple friction plate clutches.

In the neutral drive position selected by the remote control unit, the selector ring 20 is selectively positioned so that the plungers 19 rest in the circular grooves 20D, and therefore the rotating male conical friction surfaces are clear of their respective stationary female conical friction surfaces, so a neutral drive is accomplished.

When the remote control unit is selectively moved from the neutral drive position to the forward drive position, the selector ring 20 is selectively move towards the rotating drum 6A. During this movement, the lungers 19 spring out of the groove 20D, and engage with the ramp faces 20C, and the axial load therebetween forces the female conical friction surface 20B into engagement with its corresponding male friction surface 6C, and the friction therebetween rotates the selector ring, which in turn rotates the ball nut 11A, causing it to axially move into engagement with the power drive clutch 9, and the clamping thereof, rotates the output shaft 2. The slip torque of the power drive clutch is controlled and restricted by the slip torque of the said conical cone clutch, which is controlled by the load of the said plungers acting against the said ramp faces.

When the remote control unit is moved from the forward drive position immediately into reverse drive, the selector ring 20 disengages the conical clutch surfaces 20B and 6C, and moves across the neutral position and engages the conical friction surfaces 20A and 5C, loaded by the plungers 14 acting on the ramp faces 20E. Therefore, the selector ring and the ball nut will be brought to rest and rotated in the opposite direction, causing the ball nut to engage and clamp together the reverse power drive clutch 7, the slip torque of which is controlled and restricted as previously described for the power drive clutch 9.

In both of these embodiments of the invention, (i) the clutch mechanism is not responsive to any transient torque or shock load that may be experienced by the drive line and (ii) because the travel of the clutch is independent of each other there is no problem in obtaining sufficient travel of the clutch clamping member and (iii) the slip torque capacity is controlled to a set level to ensure a good clutch engagement during a power change.

Claims (12)

1. A clutch including an input shaft to be connected to a prime mover and an output shaft to be connected to a driven member, the shafts being connectable together by one of a forward gear and a reverse gear mechanism, each gear including a friction driven plate, a clutch loading mechanism located between the gears and having a friction drive plate to engage the friction driven plate of the respective gear, characterised in that the clutch loading mechanism comprises a ball screw system connectable to the input shaft to form a parallel torque circuit with the driving torque, the ball screw being self releasing.

2. A clutch according to Claim 1, characterised in that the ball screw system comprises a ball nut with a spiral roller ball raceway, the spiral pitch of which is selected so that the screw action is self-releasing.

3. A clutch according to Claim 1 or 2, characterised in that the ball nut includes an axially movable sleeve adapted so that each end can engage either the forward gear or the reverse gear.

4. A clutch according to Claim 3, characterised in that the sleeve includes a selector ring arranged to move the sleeve between a forward gear engaging position, an intermediate neutral position and a reverse gear engaging position.

5. A clutch according to Claim 3 or 4, characterised in that relative rotary motion between the selector ring and the sleeve is arranged to wind the respective clutch and rotate the ball nut to clamp the multiple plates of the respective clutch.

6. A clutch according to Claim 4 or 5 characterised in that the ends of the sleeve are arranged to be freely received in the coils of a coil spring clutch extending from a drum of each gear.

7. A clutch according to any preceding Claim, characterised in that the spring clutch and the drums are interference fitted so that slippage can take place at a set torque limit, which in turn controls the slip torque of the power drive clutch.

8. A clutch according to any preceding Claim, characterised in that the self-releasing ball screw is carried on and around one of the shafts, an axially extending drum is arranged to rotate with the input drive and is journalled on the shaft for relative rotation thereto, drive friction plates of the clutch-are attached within the bore of the drum for rotation therewith, an anti-friction thrust bearing is carried on the shaft and positioned in between the clutch and the ball nut member of the ball screw, and a second low power clutch drive device having a set slip torque value, is present and arranged to be selectively engaged to form the parallel torque flow circuit by connecting together the drum and the ball nut and the drive connection therebetween, and causes the ball nut to rotate relative to the shaft and undergo simultaneous axial movement thereto to load and clamp together the leaves of an interleaved multiple friction plate clutch, the slip torque of which is controlled to the corresponding level set by the slip torque of the second drive clutch device.

9. A mechanically operated, power drive clutch for the transmission of rotary power between rotatable shafts, comprising a spiral ball raceway formed in and around the circumference of the shaft to be coupled, a number of loose individual spherical balls which circulate within the raceway, a cylindrical ball nut member having a spiral ball raceway formed within its bore and for rolling engagement with the spherical balls, and thereby producing a ball screw action with the shaft, the driven friction plates of the interleaved multiple friction plate clutch fixed to the shaft for rotation therewith and the drive friction plates of the interleaved multiple friction plate clutch fixed within the bore of an axially extending cylindrical drum integral with a gearwheel journalled on the shaft for relative rotation thereto, an antifriction clutch thrust bearing carried on the shaft and positioned in between the clamping face of the ball nut and the end friction clutch plate of the interleaved multiple friction plate clutch, a multiple coil spring clutch having a number of its coils carried on the outside diameter of the drum and with an interference fit therewith to produce a set slip torque at the interface with the drum, a sleeve mounted on the outside diameter of the ball nut for rotation therewith and relative axial movement thereto, and having a stepped down diameter at one end which fits freely and with a running clearance within the remaining coils of the spring clutch extending axially outwards from the end face of the cylindrical drum, a selector ring slidably mounted on the unstepped portion of the sleeve for selective engagement with the multiple coil spring clutch and by the relative rotary motion therebetween. causes the spring clutch to wind radially inwards and around the stepped diameter of the sleeve, and the friction created therebetween causes the sleeve to rotate with the spring clutch rotating with the gearwheel, and thus impart the same rotary motion to the ball nut, causing it to simultaneously move axially along the shaft, and after taking up clearance between the thrust bearing and the interleaved friction plates, clamps together the power drive clutch, and thereby, produces rotary motion of the shaft.

10. A mechanically operated, power drive clutch for the transmission of rotary power between rotatable shafts, comprising a spiral ball raceway formed in and around the circumference of the shaft to be coupled, a number of loose individual spherical balls which circulate within the raceway, a cylindrical ball nut member having a spiral ball raceway formed within its bore, and for rolling engagement with the spherical balls, and thereby, producing a ball screw action with the shaft, and the axial motion thereof, used to clamp together an interleaved multiple friction plate clutch having the driven friction plates fixed to the shaft for rotation therewith, and the drive friction plates fixed within the bore of an axially extending cylindrical drum integral with a gearwheel journalled on the shaft for relative rotation thereto, an anti-friction thrust bearing carried on the shaft and positioned in between the clamping face of the ball nut and the end friction clutch plate of the interleaved multiple friction plate clutch, a number of compression springs housed in radially formed holes within the body of the ball nut, and acting on radially slidable plungers constrained against a slidably mounted selector ring carried on the outside diameter of the ball nut and for rotation therewith, a female conical friction surface formed in the end of the bore of the selector ring, and adjacent to a corresponding male conical friction surface formed on the outside of the drum and for selective engagement therewith, to activate the engagement of the power drive clutch, a circular groove formed in the bore of the selector ring for selective engagement with the plungers when positioned in the neutral drive mode, a sloping ramp profile formed in the bore of the selector ring, and for selective engagement with the plungers, and thereby producing an axial load to clamp together the conical friction surfaces, and the slip torque therebetween acting on the ball nut, controls and limits the slip torque of the interleaved multiple friction plate clutch.

11. An gearbox having co-axial or axially offset input and output shafts characterised by a clutch according to any preceding Claim.

12. A clutch substantially as described and with reference to the drawings.