GB2529665A

GB2529665A - Drive train

Info

Publication number: GB2529665A
Application number: GB1415239.1A
Authority: GB
Inventors: Richard Kettle
Original assignee: Caterpillar Shrewsbury Ltd
Current assignee: Caterpillar Shrewsbury Ltd
Priority date: 2014-08-28
Filing date: 2014-08-28
Publication date: 2016-03-02
Anticipated expiration: 2034-08-28
Also published as: GB2529665B; GB201415239D0

Abstract

A drive train (10, fig 1), for a tracked vehicle, comprises a transmission (11) having a transmission output shaft (13) which is selectively engaged with a least one final drive assembly 12 via a final drive input shaft 17. A rotatable location shaft 26 is mounted for axial movement within a bore in the final drive assembly and is coupled with the input shaft 17. Manual rotation of a screw member 25 rotates location shaft 26 so that it moves in an axial direction, which moves the input shaft 17 axially into or out of engagement with the output shaft (13). The screw member 25 has a threaded portion 48 which engages with a threaded portion in an axial bore 29. A tool such as a spanner cooperates with a head portion 51 and may be used to rotate the screw member 25 which is rigidly attached to the location shaft 26. Attached to the screw member 25 is a flanged portion 47 which abuts a housing when the input shaft 17 is fully engaged with the output shaft 13.

Description

DRIVE TRAIN

TECHNICAL FIELD

This disclosure relates to a drive train for a vehicle, and more particularly to a drive train comprising a transmission system and a final drive assembly and aspects relating to the connection therebetween.

BACKGROUND

A working vehicle may have two principle modes of operation: high speed (e.g. for travelling); and low speed (e.g. for digging, loading etc.). It is therefore often necessary to provide further gearing between the engine and the wheels of a vehicle in addition to the main gearbox or the transmission system. A final drive assembly may be configured to provide multiple speed ranges to assist the vehicle during its various operations. The vehicle may have a gear selector to select one of the multiple speed ranges in the final drive assembly. For example, in a low speed range the vehicle may operate at a slow speed with high torque, which may be required during digging, earth moving, and the like. Alternatively, in a high speed range the vehicle may operate at a higher speed, whioh may be reguired for travel.

A final drive assembly nay be connected to the vehicle transmission system so that the rotational output of the transmission system provides rotational input to the final drive assembly. This may be achieved by engaging the transmission output shaft (also known as the driveshaft) with an input shaft of the final drive assembly. The engaging end of the final drive assembly input shaft may have external splines which rr.esh with internal splines (i.e. slots or spaces of a mating form to the external splines of the final drive assembly input shaft) inside the engaging end of the transmission output shaft. The spline connection provides an equally distributed load along the sides of the teeth.

There are, however, a number of general considerations relating to the engagement of the final drive assembly with the transmission system.

Firstly, when a vehicle is being towed, for example when the engine is keyed-off, components from the transmission system and final drive assembly may have limited lubrication due to a lack of hydraulic pressure to pump lubricant around the systems. In order to protect such components from wear, due to such limited lubrication, the final drive assembly and transmission system may be disconnected from one another during towing.

Secondly, it may be required to "pull out" the final drive input shaft so as to enable the vehicle's power pack (which includes the transmission system) to be either put into the vehicle hull, or rec.oved therefrom. Once the power pack is in place, the final drive input shaft may be placed into connection with the transmission output shaft.

Thirdly, when engaging the final drive input shaft with the transmission output shaft, the splines may initially be misaligned such that they are in an end-on-end abutment, thus causing a delay in the initial engagement of the splines.

SUMMARY

The present disclosure provides a drive train for a vehiole comprising: a transmission system comprising a rotatable transmission output shaft; and at least one final drive assembly, comprising a housing; a rotatable final drive input shaft configured to selectively and rotatably engage with the transmission output shaft; a rotatable location shaft mounted for axial movement within an axial bore in the housing and coupled with the final drive input shaft, wherein rotation of the location shaft moves it in an axial direction, which moves the final drive input shaft axially into or out of engagement with the transmission output shaft; and a screw member rotatably mounted to the housing and attached to an end of the location shaft, wherein rotation of the screw member in one direction relative to the housing moves the location shaft axially in a first direction and moves the final drive input shaft into engagement with the transmission output shaft and rotation of the screw member in an opposite direction relative to the housing moves the location shaft axially in a second direction and moves the final drive input shaft out of engagement with the transmission output shaft.

BRIEF DESCRIPTION OF THE DRAWINGS

The drive train of the present disclosure is described with reference to the accompanying drawings, in which:-Figure 1 is a side elevation of a drive train comprising a transmission system with a pair of final drive assemblies (shown separated from the transmission system) Figure 2 is pictorial representation of the transmission system of Figure 1; Figure 3 is a side elevation of one of the final drive assemblies of Figure 1; Figure 4 is a cross sectional side elevation of a part of the final drive assembly of Figure 3 with the final drive input shaft extended; Figure 5 is a cross sectional side elevation of the final drive assembly of Figure 4 with the final drive input shaft retracted; Figure 6 is an enlarged view of part of Figure 5 showing a latching mechanism between the final drive input shaft and a location shaft; Figure 7 is a pictorial representation of a retention cap for restraining axial movement of the final drive input shaft viewed from above the cap; Figure 8 is a pictorial representation of the retention cap of Figure 7 viewed from underneath the cap; Figure 9 is a cross sectional side elevation of a part of the final drive assembly of Figure 3 with the retention cap in a first position; and Figure 10 is a cross sectional side elevation of a part of the final drive assembly of Figure 3 with the retention cap in a second position.

DETAILED DESCRIPTION

The present disclosure describes three features of a drive train for a vehicle, which may be used in conjunction with each other or independently. The first feature is a mechanism for engaging and disengaging a final drive assembly and a transmission system of the drive train. The second feature is a mechanisn for assisting the alignment of an input shaft of the final drive assembly and an output shaft of the transmission system during engagement. The third feature is device for rraintaining the disengagement or engagement of the final drive assembly and a transmission system.

A drive train 10, an example of which is illustrated in Figure 1, may comprise a transmission system 11 and at least one final drive assembly 12. A typical final drive assembly 12 may inolude a compound gear set (not shown) comprising a pair of coupled epicyclic gear sets. A switching assembly (not shown) may be provided to switch between the speed ranges by engaging one or both of the epicyclic gear sets.

The example illustrated in Figure 1 has two final drive assemblies 12, one mounted on either side of the transmission system 11. However a drive train 10 may have just one or more than two final drive assemblies. The features described herein may be adapted for use with single or multiple final drive asserr.blies 12 and any references to the final drive assembly or speoific parts of an assembly should also be interpreted tc refer to each final drive assembly or specific parts of each final drive assembly as appropriate.

The transmission system 11 may be mounted within the hull of a vehicle (not shown), with the final drive assembly 12 attached to the outside of the hull. As shown in Figure 2, the transmission system 11 may have a transmission output shaft 13, an end 14 of which may be accessible through an aperture 15 in a transmission housing 16 which may house the various components of the transmission system 11. In the present example, which has two final drive assemblies 12, each end 14 of the transmission output shaft 13 may be accessible through an aperture 15 in each side of the transmission housing 16. The transmission output shaft end 14 may have an axial bore having an internal spiine arrangement 21 comprising a plurality of splines.

As shown in Figure 3, the final drive assembly 12 may comprise a final drive input shaft 17. A first end 18 of the final drive input shaft 17 may project from an aperture in a final drive assembly housing 19, which may house the various components of the final drive assembly 12. The first final drive input shaft end 18 may have an external spline arrangement 22 comprising a plurality of splines.

The transmission output shaft 13 and the final drive input shaft 17 may be rotatabiy coupled by means of engagement of the aforementioned spline arrangements 21,22 when the external splines of the first final drive input shaft end 18 engage with the internal splines inside the transmission output shaft end 14.

A mechanism may be provided for manually engaging and disengaging the final drive assembly 12 and the transmission system 11. The mechanism may comprise means for moving the final drive input shaft 17 in an axial direction, relative to the final drive assembly housing 19, which enables it to be engaged with, or disengaged from, the transmission output shaft 13. The means for moving the final drive input shaft 17 may comprise a manually rctatable screw member 25 and location shaft 26 arrangement which enables the final drive input shaft 17 to be moved axially by rotating the screw member 25, as illustrated with reference to Figures 4 to 6.

The final drive input shaft 17 may have a second end 27, which may be rotatably ccupled with a sun gear 28 of one of the epicyclic gear sets of the final drive assembly 12.

This may be achieved by means of an external spline arrangement (not shown) at the second final drive input shaft end 27 and an internal spline arrangement (not shown) within the sun gear 28.

The location shaft 26 and final drive input shaft 17 may be mounted in an axial bore 29 within the final drive assembly housing 19. The final drive input shaft 17 and location shaft 26 may be coupled such that axial movement of the location shaft 26 in either direction moves the final drive input shaft 17 in the same direction. The coupling may also may enable the location shaft 26 and final drive input shaft 17 to be free to rotate relative to each other.

However, under certain conditions, the coupling may enable the location shaft 26 and the final drive input shaft 17 to be rotatably coupled. The coupling may be effected by a latching mechanism 24, which may also provide the second of the afcre-mentioned features, which may assist the alignment of a final drive input shaft 17 and the transmission output shaft 13 during engagement. The latching mechanism may be a form of dog clutch.

The latching mechanIsm 24 may be provided at a first end 30 of the location shaft 26 (see Figure 6) . The location shaft first end 30 may comprise a radially extending flange portion 31 and an axially projecting spigot 32. The spigot 32 may have a narrower diameter than the flange portion 31. The latching mechanism 24 may comprise a engagement member 33 (i.e. a dog piece in a dog clutch) rigidly attached to the spigot 32. A bearing 34, which may be a ball journal bearing, may be mounted on the location shaft 26 adjacent the location shaft first end 30. A sleeve may be mounted on the location shaft 26, which may act as a spacer to keep the location shaft 26 centralised within the axial bore 29. The bearing 34 may be located between the flange portion 31 and the sleeve 35.

The second final drive input shaft end 27 may comprise an internal bore 36 which may receive the location shaft first end 30. The internal bore 36 may be stepped. In the example illustrated in Figure 6, the internal bore 36 has first, second and third bore sections 37,38,39. The second bore section 38 may have a smaller diameter than the first bore section 37, and the third bore section 39 may have a smaller diameter than the second bore section 38. The diameter of the first bore section 37 may be selected so as to be slightly larger than an external diameter of the bearing 34 to allow the bearing 34 to slide axially therein.

Inwardly projecting first and second shoulders 40,41 are formed between the first and second bore sections 37,38 and the second and third bore sections 38,39 respectively. The bearing 34 may ensure that rotation of the location shaft 26 does not force rotation of the final drive input shaft 17.

This may only occur when the latching mechanism 24 is engaged as described below.

The latching mechanism 24 may further comprise a spring 42, which may be a compression spring, located within the first and second bore sections 37, 38 of the internal bore 36. The spring 42 may extend between the second shoulder 41 (or another a supporting member located on, or forming a part of, an internal wall of the internal bore 36) and the bearing 34. The location shaft 26 may slide axially into the internal bore 36 until the bearing 34 abuts the first shoulder 40, which acts as a first stopping member.

A retaining member 44 may be mounted at the mouth of the internal bore 36. The retaining member 44 may have an axial bore 45 which has a diameter greater than that of the location shaft 26, but smaller than an external diameter of the bearing 34. The location shaft 26 may slide axially out of the internal bore 36 until the bearing 34 abuts the retaining member 44, which acts as a second stopping member.

The spring 42 may be arranged to normally bias the location shaft 26 into this position.

The latching mechanism 24 may further comprise one or more latch members 43, which may project inwardly from the wall of the axial bore 29. The latch member 43 may be configured to engage with the engagement member 33 when the location shaft 26 has moved to a position where the bearing 34 abuts the first shoulder 40 of the internal bore 36.

Engagement of the latch member 43 and engagement member 33 may rotatably couple the final drive input shaft 17 and location shaft 26.

-10 -The screw member 25 may be mounted on a second end 46 of the location shaft 26. The screw member 25 may be made from cast iron or another suitable material. The screw member 25 may have a flange portion 47 and a sleeve portion 48 extending from a first face of the flange portion 47. An external surface 49 of the sleeve portion 48 may be provided with a screw thread. An inner surface 50 of the axial bcre 29 may be provided with a screw thread which is complementary to, and may engage with, the screw thread of the sleeve portion 48. This may enable the screw member 25 to be screwed into, or out of, the axial bore 29 between a first and a second position. When the screw member 25 is in its first position, the final drive input shaft 17 and transmission output shaft 13 are engaged. When the screw member 25 is in its output second position, the final drive input shaft 17 and transmission output shaft 13 are disengaged. The flange portion 47 may have a diameter greater than that of the axial bore 29. Tn the first position, shown in Figure 4, the sleeve portion 48 may extend through the aperture 20 in the final drive assembly housing 19 into the axial bore 29. Tn this position the flange portion 47 may be seated against an outer surface of the final drive assembly housing 19.

The screw member 25 may further comprise a head portion 51 which may extend from a second face of the flange portion 47. The head portion 51 may have a blind bore having a base 52 in which is formed on aperture 53. A portion of the second end 46 of the location shaft 26 may extend through the aperture 53 into the head portion 51 and a nut 54 may be located thereon to secure the screw member 25 to the -11 -location shaft 26 and to prevent relative rotation between the screw member 25 and the location shaft 26. Thus, as the screw member 25 is rotated and moves axially, the location shaft 26 rotates and moves axially with it. Other means of securing the screw member 25 to the location shaft 26 may alternatively be used. Although not shown in the drawings, the external surface of the head portion 51 may be configured to enable a tool, such as a spanner or wrench, to be used to turn the screw mecher 25.

The drive train 10 may comprise a retention device for either maintaining a disengagement of the final drive assembly 12 and the transmission system 11 (see Figure 9) or engagement thereof (see Figure 10) The retention device may comprise a retention cap 60, which may be made of aluminium or another suitable material.

The retention cap 60 may comprise a flange 61 and a projecting cup-like body 62. A plurality of apertures 63 may be located around the flange 61. The final drive assembly housing 19 may be provided with a plurality of threaded apertures for receiving fixings 64, such as screws, passing through the apertures 63 in the cap flange 61, to enable the retention cap 60 to be removably attached to the final drive assembly housing 19. The retention cap 60 may be attached to the final drive assembly housing 19 in a first position (see Figure 9) with the body 62 projecting into the final drive assembly housing 19. The retention cap may also be reversed and attached to the final drive assembly housing 19 in a second position (see Figure 10) with the body 62 projecting away the final drive assembly housing 19.

-12 -The body 62 may be configured to provide a socket for receiving the screw member 25, when the locaticn shaft 26 and retention cap 60 are each in their respective second positions (see Figures 5 and 10) . The socket may have an internal locking surface 65, which may be configured to receive the screw member 25 (or a part thereof) and prevent it from rotating. This prevents the location shaft 26 from rotating and moving axially within the axial bore 29.

The body 62 may also be configured to provide an external abutment surface 66. When the location shaft 26 and retention cap 60 are each in their respective first positions (see Figures 4 and 9) , the external abutment surface 66 projects into the final drive assembly housing 19 and abuts an end of the location shaft 26.

Alternatively the retention cap 60 may have a different configuration. Instead of an internal locking surface 65 within a socket, it may have another locking arrangement which engages with the screw member 25 to prevent rotation of the location shaft 26.

INDUSTRIAL APPLICABILITY

The drive train of the present disclosure may be

particularly suitable for a tracked or other vehicle which must be able to operate at both low torgue/high speed and high torque/low speed conditions, for example in earth moving applications. The drive train may comprise a two speed final drive assembly that may be used for each of the tracks of a twin tracked vehicle, making possible the use of -13 -a conventional multi-speed transmission as the primary transmission.

The drive train may include some or all of the features described in this disclosure. To operate the first feature, for engaging and disengaging a final drive assembly and a transmission, the screw member 25 may be rotated manually by an operator. This may be done by engaging a tool with the head portion 51 and/or by hand. Rotation of the screw member 25 in one direction may enable it to be screwed into the axial bore 29, thereby axially moving the attached location shaft 26 in a first direction to a first position, as shown in Figure 4. This may push the final drive input shaft 17 along the axial bore 29. In this first position, the first final drive input shaft end 18 may project through the aperture 20 in the final drive assembly housing 19, to enable it to engage with the transmission output shaft 13.

As the flange portion 31 may have a diameter greater than that of the axial bore 29 it may seat against the final drive assembly housing 19 when the final drive input shaft 17 is engaged with the transmission output shaft 13 to prevent further rotation of the screw member 25.

Rotation of the screw member 25 in the opposite direction may enable it to be screwed out of the axial bore 29, thereby axially moving the attached location shaft 26 along the axial bore 29 in an opposing second direction to a second position, as shown in Figure 5. This may pull the final drive input shaft 17 along the axial bore 29. In this second position the final drive input shaft 17 may be withdrawn into the final drive assembly housing 19 and thereby disengaged from the transmission output shaft 13.

-14 -The withdrawal of the final drive input shaft 17 into the final drive assembly housing 19 may enable the removal and refitting of the transmission system 11, without the need to remove the final drive assembly 12 from the vehicle.

The second feature may automatically activate as and when required during engagement of the input shaft of the final drive assembly with the output shaft of the transmission during engagement. The latching mechanism 24 only comes into use when there is an end-on-end conflict between the splines of the final drive input shaft 17 and the splines of the transmission output shaft 13. The latching mechanism 24 may assist the alignment of the splines of the final drive input shaft 17 and the transmission output shaft 13 during engagement by enabling a small degree of rotary motion to be imparted to the final drive input shaft 17.

As the screw member 25 is rotated in the first direction, to engage the final drive input shaft 17 with the transmission output shaft 13, if the spiines of spline arrangements 21,22 are aligned correctly for engagement, the resilience of the spring 42 may enable the final drive input shaft 17 to be pushed by the location shaft 26 into engagement with the transmission output shaft 13.

However, if the splines are not aligned correctly (i.e. head-on abutment) , the final drive input shaft 17 is unable to continue to move in the first direction, and the spring 42 may compress as a result of the continuing axial movement of the location shaft 26 as the screw member 25 is rotated.

-15 -The spring 42 may compress until the engagement member 33, which turns with the location shaft 26, comes into connection with the latch merrber 43. This occurs when the bearing 34 abuts the first shoulder 40. Engagement between the engagement member 33 and the latch member 43 rotatably couples the location shaft 26 and the final drive input shaft 17. As a result, further rotation of the location shaft 26 imparts rotation to the final drive input shaft 17.

When the final drive input shaft 17 has rotated sufficiently, such that the splines are aligned correctly and start to engage, the compressed spring 42 may extend, thereby pushing the final drive input shaft 17 fully into connection with the transmission output shaft 13. This allows the engagement member 33 to disengage from the latch member 43. The location shaft 26 and final drive input shaft 17 are then able to rotate freely relative to each other.

To utilise the third feature, the retention cap 60 may be attached to the final drive assembly housing 19 in the appropriate orientation when it is desired to maintain engagement or disengagement between the final drive input shaft 17 and transmission output shaft 13. When the retention cap is attached in its second position (as shown in Figure 10) , it may prevent the location shaft 26 from rotating and moving axially. This, in turn, may prevent the final drive input shaft 17 from moving axially. Thus the final drive input shaft 17 is unable to move back into engagement with the transmission output shaft 13 and is retained in the disengaged position.

-16 -When the retention cap 60 is reversed, and secured to the final drive assembly housing 19 in its first position (see Figure 9) , the body 62 may project into the final drive assembly housing 19. In this position the body 62 may abut and exert a force on the location shaft 26, maintaining the final drive input shaft 17 in engagement with the transmission output shaft 13.

Claims

-17 -CLAIMS: 1. A drive train for a vehicle comprising: a transmission system comprising a rotatable transmission output shaft; and at least one final drive assembly, comprising a housing; a rotatable final drive input shaft configured to selectively and rotatably engage with the transmission output shaft; a rotatable location shaft mounted for axial movement within an axial bore in the housing and coupled with the final drive input shaft, wherein rotation of the location shaft moves it in an axial direction, which moves the final drive input shaft axially into or out of engagement with the transmission output shaft; and a screw member rotatably mounted to the housing and attached to an end of the location shaft, wherein rotation of the screw member in one direction relative to the housing moves the location shaft axially in a first direction and moves the final drive input shaft into engagement with the transmission output shaft and rotation of the screw member in an opposite direction relative to the housing moves the location shaft axially in a second direction and moves the final drive input shaft out of engagement with the transmission output shaft.
2. A drive train as claimed in claim 1 wherein the screw member comprises a threaded portion which engages with a threaded portion of the axial bore, such that rotation of -18 -the screw member relative to the housing causes the screw member to travel along the axial bore.
3. A drive train as claimed in claim 1 or claim 2 wherein the screw member is rigidly attached an end of the location shaft.
4. A drive train as claimed in any one of the preceding claims wherein the screw member comprises a flange portion which has a diameter greater than that of the axial bore, and which abuts the housing when the final drive input shaft is fully engaged with the transmission output shaft.
5. A drive train as claimed in any one of the preceding claims wherein the coupling between the location shaft and final drive input shaft allows rotation of the shafts relative to each other.
6. A drive train as claimed in any one of the preceding claims wherein the screw member comprises a head portion which is configured to engage with a tool to effect rotation thereof.Amendments to claims have been be filed as follows CLAIMS: 1. A drive train for a vehicle, said drive train comprising: a transmission system comprising a rotatable transmission output shaft; and at least one final drive assembly, comprising a housing; a rotatable final drive input shaft configured to selectively and rotatably engage with the transmission output shaft; a rotatable location shaft mounted for axial movement within an axial bore in the housing and LU coupled with the final drive input shaft, wherein rotation of the location shaft moves it in an axial direction, which moves the final drive input shaft axially into or out of engagement with the transmission output shaft; and r a screw member rctatably mounted to the housing and attached to an end of the location shaft, wherein rotation of the screw member in one direction relative to the housing moves the location shaft axially in a first direction and moves the final drive input shaft into engagement with the transmission output shaft and rotation of the screw member in an opposite direction relative to the housing moves the location shaft axially in a second direction and moves the final drive input shaft out of engagement with the transmission output shaft.2. A drive train as claimed in claim 1 wherein the screw member comprises a threaded portion which engages with a threaded portion of the axial bore, suoh that rotation of the screw member relative to the housing causes the screw member to travel along the axial bore.3. A drive train as claimed in claim 1 or claim 2 wherein the screw member is rigidly attached to an end of the location shaft.4. A drive train as claimed in any one of the preceding claims wherein the screw member comprises a flange portion which has a diameter greater than that of the axial bore, and which abuts the housing when the final drive input shaft is fully engaged with the transmission output shaft. IC)5. A drive train as claimed in any one of the preceding claims wherein the coupling between the location shaft and final drive input shaft allows rotation of the shafts relative to each other. r6. A drive train as claimed in any one of the preceding claims wherein the screw member comprises a head portion which is configured to engage with a tool to effect rotation thereof.