GB2051977A

GB2051977A - Power Transmission Mechanism

Info

Publication number: GB2051977A
Application number: GB8015345A
Authority: GB
Original assignee: BROWN GEAR IND; BROWN GEAR INDUSTRIES Ltd D
Current assignee: BROWN GEAR IND; BROWN GEAR INDUSTRIES Ltd D
Priority date: 1979-05-15
Filing date: 1980-05-09
Publication date: 1981-01-21
Also published as: GB2051977B

Abstract

A power transmission mechanism for a heavy vehicle includes a hydrodynamic torque converter 24,27 driven by a gear 22 and driveably connectible co-axially to epicyclic change-speed gearing 29 etc., an intermediate shaft 13 driven at 40,39 by said gearing and driveably connected at its ends to respective epicyclic gear units 42,43,45 for driving output shafts 15 at opposite sides of the vehicle, and a steering mechanism (not shown) e.g. of hydrostatic type so connected driveably at 56,59 to the epicyclic gear units as to be capable of varying the relative rotational speeds of the output shafts. To enable an important portion of the power transmission mechanism to be readily tested, replaced if the event of failure, or even used independently in a vehicle steered in more conventional fashion, the torque converter and the epicyclic change speed gearing are designed so as together to constitute a variable- speed gearbox incorporating all necessary clutches 31,32,33 and/or brakes 34,35,36,37 in a case 60 which is separable as an independently operable module from the remainder of the power transmission mechanism. <IMAGE>

Description

SPECIFICATION Power Transmission Mechanism The invention relates to a power transmission mechanism, particularly for a heavy duty wheeled or tracked vehicle, of the type including a hydrodyna mic torque converter driveably connectible coaxially to epicyclic change-speed gearing, and steering mechanism capable of varying the relative rotational speeds of two output shafts of the power transmission mechanism whichare disposed at opposite sides of the vehicle.

The object of the invention is to enable a portion of the power transmission mechanism to be readily tested, replaced in the event of failure, or even used independently in a vehicle steered otherwise than as aforesaid.

According to the invention, in a power transmission mechanism for a vehicle comprising a hydrodynamic torque converter driveably connectible co-axially to epicyclic change-speed gearing, an intermediate shaft driven by said gearing and driveably connected at its ends to respective epicyclic gear units for driving output shafts at opposite sides of the vehicle, and a steering mechanism so connected driveably to the epicyclic gear units as to be capable of varying the relative rotational speeds of the output shafts, the torque converter and the epicyclic changespeed gearing together constitute a variablespeed gearbox incorporating all necessary clutches and/or brakes which is separable as an independently operable module from the remainder of the power transmission mechanism.

A preferred embodiment of the invention will now be described, by way of example, with reference to the accompanying drawings of which: Fig. 1 is a diagrammatic plan view of the whole power transmission mechanism; and Fig. 2 is a part-sectional plan view principally of the variable-speed gearbox module showing how its housing is mounted within the power transmission mechanism.

Referriny now to Fig. 1, a power transmission mechanism for a heavy duty wheeled or tracked vehicle comprises drive gearing indicated generally at 10 adapted to be driven by the vehicle's engine (not shown), a hydrodynamic torque converter indicated generally at 11 driven by the drive gearing 10, epicyclic change-speed gearing indicated generally at 1 2 driven by the torque converter 11, an intermediate shaft 13 driven by the changespeed gearing 12, two epicyclic gear units indicated generally at 14 driven by the respective ends of the intermediate shaft 13, two output shafts 1 5 disposed at opposite sides of the vehicle and driven by the respective epicyclic gear units 14, and a steering mechanism indicated generally at 1 6 so connected driveably to the units 14 as to be capable of varying the relative rotational speeds of the output shafts 1 5.

The drive gearing 10 comprises a gear-type input coupling 1 7 adapted to be driveably connected to the engine, right-angled bevel gears 1 8, 19 driven by the input coupling 17, a train of cylindrical gears 20, 21, 22 for transmitting drive from the bevel gears 18, 19 to the torque converter 11, and a clutch 23 interposed between the bevel gears 18, 19 and said train for disconnecting the power transmission mechanism from the engine at start-up.

The torque converter 11 comprises an impeller 24 rigidly secured co-axially to the last gear 22 of the afore-mentioned train, a reaction member 25 held against rotation in one direction only in known manner by a freewheel 26, and a rotor 27.

A torque converter lock-up clutch 28 is provided for automatically connecting the impeller 24 to the rotor 27 without slip at a predetermined speed of rotation of any suitable component of the vehicle's drive means.

The epicyclic change-speed gearing 1 2 comprises three sets of epicyclic gearing having a common output member 29 which drives a set of epicyclic overdrive gearing indicated generally at 30, together with three hydraulically-engaged clutches 31, 32, 33 and four hydraulically-appiied brakes 34, 35, 36, 37 to enable the change-speed gearing 12 to provide five forward speed ratios and three reverse speed ratios.First (low) forward speed ratio is obtained by engaging the clutches 31,33 and applying the brake 36; second forward speed ratio is obtained by releasing the brake 36, applying the brake 35, and maintaining the clutches 31,33 engaged; third forward speed ratio is obtained by releasing the brake 35, applying the brake 34, and maintaining the clutches 31, 33 engaged; fourth forward speed ratio is obtained by releasing the brake 34, engaging the clutch 32, and maintaining the clutches 31, 33 engaged; and fifth (high) forward speed ratio is obtained by disengaging the clutch 33, applying the brake 37, and maintaining the clutches 31,32 engaged.First (low) reverse speed ratio is obtained by engaging the clutches 32, 33 and applying the brake 36; second reverse speed ratio is obtained by releasing the brake 36, applying the brake 35, and maintaining the clutches 32, 33 engaged; and third (high) reverse speed ratio is obtained by disengaging the clutch 33, applying the brake 37, and maintaining the clutch 32 engaged and the brake 35 applied. That is to say, only one clutch or brake need be deactuated and one other clutch or brake actuated in its place for every change of speed ratio in each direction. This has the advantage that the hydraulic clutch and brake control mechanism has no difficulty in rapidly filling the clutch or brake to be actuated in order promptly to effect any such change. The clutches 31,32 have a common driving member 38 rigidly secured co-axially to the rotor 27 of the torque converter 11.

The intermediate shaft 1 3 is disposed parallel to the principal axis of the epicyclic change-speed gearing 12 and transversely of the vehicle. Near that end of the shaft 13 remote from the torque converter 11 there is rigidly secured a gear 39 which meshes with a gear 40 driveably connected co-axially to an annular gear 41 constituting the output member of the epicyclic overdrive gearing 30.

Each of the epicyclic gear units 14 comprises an annular gear 42 rigidly secured co-axially to the associated end of the intermediate shaft 13, three or more planet pinions 43 rotateably mounted on a planet carrier 44 and meshing with the annular gear 42, and a sun gear 45 with which the planet pinions 43 also mesh.

Each of the output shafts 1 5 is integral with the planet carrier 44 of the associated epicyclic gear unit 14, and is thus co-axial with the intermediate shaft 13.

The steering mechanism 1 6 comprises a hydrostatic pump-and-motor system the pumps 46 of which are driven from the gear 22 rigidly secured to the impeller 24 of the torque converter 11 by way of a train 47 of cylindrical gears and a gear-type coupling 48. The motors 49 drive a composite null shaft which is disposed parallel to the intermediate shaft 13. The central part 50 of the null shaft, on which the motors 49 are mounted, is connected at its ends by gear-type couplings 51, 52 to the inner ends of respective outer parts 53, 54 of said shaft.The outer end of the part 53 has rigidly secured to or integral with it a gear 55 which meshes directly with a gear 56 rigidly secured co-axially to the sun gear 45 of the associated one of the epicyclic gear units 14, and the outer end of the part 54 has rigidly secured to or integral with it a gear 57 which meshes by way of an idler gear 58 with a gear 59 rigidly secured co-axially to the sun gear 45 of the other of the epicyclic gear units 14. This arrangement is knowm, and operates to rotate the respective sun gears 45 of the two epicyclic gear units 14 in opposite directions when the driver of the vehicle actuates control means for the hydrostatic pumpand-motor system, thereby varying the relative rotational speeds of the two output shafts 1 5 so as to steer the vehicle in the required direction.

The radius of turning is variable by the control means. When the vehicle is required to travel in a straight path, the control means are not actuated by the driver, the hydrostatic system is inoperative, the null shaft 50, 53, 54 does not rotate as its name implies, the sun gears 45 of the epicyclic gear units 14 act as non-rotating reaction members, and the two output shafts 1 5 rotate at the same speed as one another.

Referring now to Fig. 2, the torque converter 11, with its lockup clutch 28 and the gear 22 rigidly secured to its impeller 24, and the epicyclic change-speed gearing 12, with the gear 40 driveably connected to the annular gear 41 constituting the output member of the epicyclic gearing 30, are together contained in a common substantially cylindrical housing 60 and constitute a variable-speed gearbox module.A radial aperture 61 near that end of the housing 60 adjacent the torque converter 11 provides ingress for the gear 21 of the drive gearing 10 which meshes with the gear 22 rigidly secured to the impeller 24 of the torque converter 11, another radial aperture (not shown) near said end of the housing 60 provides ingress for that gear of the train 47 which meshes with the gear 22, and a radial aperture 62 near the other end of the housing 60 provides ingress for the gear 39 which is rigidly secured near the adjacent end of the intermediate shaft 13 and meshes with the gear 40 driveably connected to the annular gear 41 constituting the output member of the epicyclic overdrive gearing 30. The housing 60 is mounted within a casing 63 containing the whole of the power transmission mechanism.The mounting means at that end of the housing 60 adjacent the torque converter 11 comprise a short sleeve 64, rigidly secured to the casing 63, the periphery of which registers in a bore 74 in the housing 60, and the mounting means at the other end of the housing 60 comprise a short sleeve 65, also rigidly secured to the casing 63, having internal splines which engage at 72 with external splines on the housing 60 to hold it against rotation. Within the short sleeve 64 is a longer sleeve 66 which constitutes the reaction member of the freewheel 26 and is connected by splines at 79 to a flange 80 rigidly secured to the casing 63.A dead-shaft 67 secured to the casing 63 within the sleeve 66 contains oil delivery conduits 68, 69 for the torque converter lock-up clutch 28 and the clutch 31 respectively, and a dead-shaft 70 secured to the casing 63 within the sleeve 65 contains an oil delivery coriduit 71 for the clutch 33 and two lubricating oil conduits. The torque converter is filled by way of a connection 77 rigidly secured to the flange 80, and an annular space surrounding the sleeve 66; and emptied by way of an annular space between the bore of saidr sleeve and the dead-shaft 67, and a connection 78.That gear of the train 47 which meshes with the gear 22 is disposed above the plane containing the axes of the intermediate shaft 13 and the module, that is to say the plane of the sectional portion of the module in Fig. 2, and is rotateably mounted on a dead-shaft 76 so secured to the casing 63 as to be withdrawable axially to permit the removal of the gear thereof through an aperture (not shown) in said casing.

The casing 63 is so constructed that it can be split into two portions in a plane containing the common axis 75 of the intermediate and output shafts 13, 1 5 and perpendicular to the plane of the sectional portion of the module in Fig. 2. Thus, after draining the oil; removing a connection 73 for delivering oil to the clutch 32 and four similar connections (not shown) for delivering oil to the brakes 34, 35, 36, 37; withdrawing axially the deadshafts 76, 67, 70, the flange 80 and sleeve 66, and the sleeves 64, 65; removing that gear of the train 47 which meshes with the gear 22; and splitting the casing 63 and separating its portions as a result of which the gears 39, 40 move out of mesh; the module is readily separable from the power transmission mechanism by moving it in a direction away from the drive gearing 10 as a result of which the gears 21, 22 move out of mesh. Replacement of the module in the event of its failure is thus facilitated. Furthermore, as the module is operable independently of the remainder of the power transmission mechanism when its freewheel reaction member and oil delivery connections are restored, it can readily be tested prior to its installation in said mechanism, and it can even be used in a vehicle steered by means other than the steering mechanism herein before described. For example, in a fourwheeled vehicle, it can be used to drive the rear wheels by way of å differential gear unit whilst the front wheels can be angled relative to the longitudinal axis of the vehicle by a driveroperated steering wheel in well-known manner.

The invention includes within its scope epicyclic change-speed gearing other than that hereinbefore particularly described, for example as illustrated by any of Figs. 1, 2, 3 or 4 of our copending Application for Patent Number 7915572 (Serial Number 2023752A).

In a modification, the housing of the variablespeed gearbox module is mounted by means of respective splined connections at its ends within the casing containing the whole of the power transmission mechanism.

Claims

1. A power transmission mechanism for a vehicle comprising a hydro-dynamic torque converter driveably connectible co-axially to epicyclic change-speed gearing, an intermediate shaft driven by said gearing and driveably connected at its ends to respective epicyclic gear units for driving output shafts at opposite sides of the vehicle, and a steering mechanism so connected driveably to the epicyclic gear units as to be capable of varying the relative rotational speeds of the output shafts, wherein the torque converter and the epicyclic change-speed gearing together constitute a variable-speed gearbox incorporating all necessary clutches and/or brakes which is separable as an independently operable module from the remainder of the power transmission mechanism.

2. A power transmission mechanism according to claim 1, wherein the variable-speed gearbox module includes a housing which is mounted by means of a splined connection at one of its ends within a casing containing the whole of the power transmission mechanism.

3. A power transmission mechanism according to either of the preceding claims, including drive gearing on the input side of the variable-speed gearbox module.

4. A power transmission mechanism according to claim 3, wherein the drive gearing includes a clutch for disconnecting the power transmission mechanism from the vehicle's engine at start-up.

5. A power transmission mechanism according to claim 3 or claim 4, wherein radial apertures in the housing provide ingress respectively for a gear of the drive gearing, for a gear by way of which the steering mechanism is driven, and for a gear by way of which the intermediate shaft is driven.

6. A power transmission mechanism according to any one of the preceding claims, wherein the steering mechanism includes a null shaft.

7. A power transmission mechanism according to claim 6, wherein the null shaft is driveable by hydrostatic means.

8. A power transmission mechanism, for a vehicle, constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.

9. A variable-speed gearbox module, for a vehicle, constructed, arranged and adapted to operate substantially as hereinbefore described with reference to, and as illustrated by, the accompanying drawings.