GB2111612A

GB2111612A - Change speed gear train and transmission incorporating same

Info

Publication number: GB2111612A
Application number: GB08137013A
Authority: GB
Inventors: Claude Peter Windsor-Smith; Raymond Alfred Tailby
Original assignee: Individual
Current assignee: Individual
Priority date: 1981-12-08
Filing date: 1981-12-08
Publication date: 1983-07-06

Abstract

A change speed gear train comprises an input shaft gear (18) and an output shaft gear (20). Three layshafts (28,30,32) have layshaft input gears (40,42,44) meshing with the input shaft gear and output gears (52,54,56) meshing with the output shaft gear and end clutches (58,60, 62) to control the transmission ratio. A constant drive input device (72) in the form of a torsionally damped mechanical input coupling is coupled between the gear train and an engine and drive take up is provided by progressive engagement of one of the layshaft clutches. A direct drive clutch (70) provides a direct drive connection between input shaft gear (18) and output shaft gear (20) whereby a direct top gear drive is provided. <IMAGE>

Description

SPECIFICATION Change speed gear train and transmission embodying same This invention relates to change speed gear trains, to drive transmissions embodying such gear trains and to vehicles incorporating such transmissions. The invention is particularly applicable to land vehicles such as highway vehicles including trucks, lorries, buses, other public service vehicles, and cars or automobiles.

However, the invention is also applicable to drive transmissions for locomotives and trains and other land vehicles.

The gear trains with which the present invention is concerned are of a kind comprising central (though not necessarily coaxial) input and output shafts carrying respective input and output gears, together with at least one and preferably two or more layshafts disposed around the input and output shaft assembly and carrying layshaft input and output gears meshing respectively with the input shaft and output shaft gears, the layshaft or layshafts being provided with end clutches for selective actuation to transmit drive through the layshaft from the input shaft to the output shaft.

Gear trains of this kind are disclosed in our published European patent applications 79 302732 and 79 302733, and in our unpublished European patent application No 81 301962.7. We hereby incorporate in the present application the entire disclosure of these prior European patent applications together with the disclosure of our two other UK patent applications filed herewith and entitled "Change Speed Gear Trains" and "Drive Couplings".

the gear trains and drive transmissions disclosed in our above-mentioned pending patent applications provide many advantages over the previous state of the art. However, the present invention is concerned with providing further refinements and/or versitility and/or convenience in relation to such gear trains and transmissions.

In our prior applications, most of the described embodiments of the gear trains comprise four clutch-controlled layshafts to transmit drive between the gearbox input and output gears, the four layshafts providing four corresponding drive transmission ratios.

A desirable refinement of the gear train would be the provision of the same number of transmission ratios with a simpler or smaller and less expensive construction, or the provision of an increased number of transmission ratios without very significant increase in the cost and complexity of the gear train.

A further desirable refinement would be the provision of means to reduce, or at the very least not to significantly increase, the masses of the components within the gear train which are rotating at engine speed, while providing the above refinements. This facilitates smooth and rapid gear changes.

A further factor arises in relation to the space requirements of the gear train. In the case of road vehicles such as lorries, having the conventional layout of a front engine driving the rear wheels of the vehicle, the engine is often mounted under the floor or loading space of the vehicle, and as a result there is a requirement that the gear box which is also mounted under the floor (and usually adjacent to the engine) should have a minimum height requirement so as not to significantly reduce the ground clearance of the vehicle.

Another requirement, which also applies particularly to lorries and trucks, is the need to provide a drive for certain vehicle accessories such as hydraulic pumps for operating various vehicle accessories such as doors and lift ramps and the like, and pneumatic pumps or compressors providing a source of pneumatic pressure for operating the vehicle brakes for example. It is obvious from the latter example that the drive to such accessories as braking system compressors should be uninterrupted during vehicle operation - even though it may be possible temporarily to store the vacuum by means of suitable reservoirs.

The drive to vehicle accessories such as air compressors is usually taken at some convenient point from a gear within the gear train of the vehicle. In this connection, it is to be noted that in most of the embodiments of our prior patent applications, the drive input to the gear train is through a fluid coupling and when the vehicle comes to rest it is the fluid coupling which interrupts the transmission of drive from the engine to the ground wheels, and a clutch on one of the ratio-providing layshafts is at all times engaged. Therefore, when the vehicle comes to rest, all gears within the gear train of the gear box likewise come to rest, and therefore the drive to (for example) an air compressor of the vehicle stops when the vehicle stops, whereas it is desirable that such drive should continue so as to maintain a satisfactory brake operating pressure at all times.

An object of the present invention is to provide a change speed gear train, together with a drive transmission and a vehicle incorporating such a gear train, of the kind mentioned above and providing improvements in relation to one or more of the technical requirements identified above.

According to the invention there is provided a gear train comprising central shaft means including drive input and drive output shafts having corresponding drive input and drive output gears, and at least one layshaft having layshaft input and output gears meshing respectively with the drive input and drive output gears of the central shaft means, the layshaft having clutch means at one end whereby drive transmission through the layshaft between the drive input and the drive output shafts can be selectively controlled. In said gear train, there is provided clutch means connected between the drive input and drive output shafts and selectively operable to transmit drive directly between said shafts. This provides a "straight-through" drive giving no speed reduction whereby the drive output shaft rotates at engine speed.

Said clutch means connected between said drive input and drive output shafts is arranged so that a major portion of the rotatable mass of the clutch means is connected to the output shaft.

Where the clutch means comprises an assembly of interleaved clutch plates forming two sets, one set being drivably connected at its inner periphery and the other set being drivably connected at its outer periphery, the output shaft is connected to said set of plates which are drivably connected at their outer peripheries.

Where said gear train is provided with only one layshaft for drivably connecting said drive input and drive output shafts, the clutch means providing a straight-through drive connection thereby provides a second transmission ratio. Two more transmission ratios can be provided by means of a range layshaft and the division of the output shaft (or indeed the input shaft) into two clutch-connectible portions each having its own gear and said gears constantly meshing with complementary gears on said clutch-controlled range layshaft. Such range layshaft arrangement is fully disclosed in our co-pending UK patent application entitled "Gear Trains" filed herewith.

Preferably, at least two clutch-controlled layshafts are provided to selectively transmit drive between said drive input and drive output shafts.

Said two layshafts may be provided, one on each side of said central input and output shaft assembly. A third layshaft may be provided above or below the input and output shaft assembly, whereby the profile of a gearbox casing housing the gear train can be generally triangular to correspond with the location of the layshaft axes.

The invention also provides a vehicle comprising a drive transmission incorporating such gearbox.

The vehicle preferably comprises a front-mounted engine or power plant and a drive transmission extending between the engine and driven rear wheels of the vehicle, said engine and drive transmission being mounted below a floor of the vehicle, said input and output shafts of the gear train extending through opposite ends of the gearbox, and the transmission further comprising a propellor shaft and a differential drive gear connected between said gearbox output shaft and the driven wheels of the vehicle.

Transfer gearing may be provided in the gear train to offset the gearbox output shaft with respect to the axis of the input shaft to suit particular vehicle layouts.

The invention also provides a drive transmission incorporating the gear train as defined above with a constant drive input device to transmit drive to the gear train from, for example, the engine or power plant of a vehicle, and control means for said layshaft clutch means whereby at least one of said clutch means can be progressively engaged for drive take-up purposes.

Said constant drive input device may comprise a mere mechanical drive input connection, with no facility for interrupting the drive, and preferably provided with torsional damping means (for example comprising resilient elements such as spriiigs or rubber blocks or bushes) to dampen cyclic torque variations. Other drive input devices may be provided, of the kind which provide an uninterrupted input of drive from an engine connected thereto, even when the engine is only ticking-over with the vehicle stationary.

The invention also provides a vehicle incorporating such constant drive input device to the gear train and having an accessory, such as a pneumatic compressor, drivably connected to a gear of said gear train which rotates at all times that the gear train input shaft rotates.

Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig 1 shows a diagrammatic representation of a gear train according to the invention; Fig 2 shows a plan view of a road vehicle incorporating the gear train of Fig 1; Figs 3 and 4 show side and end elevation views of a gear box incorporating the gear train of Fig 1; Figs 5 and 6 show views corresponding to Figs 3 and 4 showing the mounting of the gearbox of Fig 2 in relation to the floor of the vehicle; and Figs 7 and 8 show views corresponding to those of Figs 3 to 6 showing modification of the gearbox by the addition of an offset drive output shaft.

As shown in Fig 1 a gear train 10 comprises central shaft means 1 2 including a drive input shaft 14 and a drive output shaft 16, these shafts having respective drive input and drive output gears 1 8 and 20 respectively. Drive input gear 1 8 is a single gear whereas drive output gear 20 comprises a cluster of three gears 22, 24 and 26.

Three layshafts 28, 30 and 32 are provided to transmit drive between input gear 1 8 and output gear 20. Each of the three layshafts comprises an inner drive input shaft 34, 36, 38, having a layshaft drive input gear 40, 42, 44 meshing with the central drive input gear 18, and an outer tubular drive output shaft 46, 48, 50, arranged coaxially with and surrounding the inner shaft and carrying a layshaft drive output gear 52, 54, 56 meshing one with each of the cluster output gears 22, 24, 26 on output shaft 16.

Clutch means 58, 60 and 62 are provided, one on each layshaft at the end thereof to allow selective transmission of drive between the inner and outer portions of the layshaft and hence between drive input and drive output shafts 14 and 1 6. The clutch means are of the interleaved plate kind, arranged for actuation by pneumatic or hydraulic pressure through pressure lines 64, 66, 68.

Further details of the construction and arrangement of gear train 1 0 can be obtained from our pending European patent application No 81 301962.7.

Further clutch means 70 is provided to permit selective transmission of drive directly from drive input shaft 1 4 to drive output shaft 1 6 without any change of ratio so that a "straight-through" top gear is provided in addition to the three reduced ratios provided by layshafts 28, 30 and 32. Clutch means 70 is similar in construction to clutches 58, 60 and 62, comprising interleaved sets of clutch plates and a fluid pressure-operated annular actuating cylinder.A particular feature of the clutch 70 is that the interleaved sets of annular clutch plates or friction elements are splined to the drive input and drive output shafts 14 and 16 so as to be axially movable in the usual way, but it is the drive output clutch plates which are splined or keyed at their outer peripheries to an annular support or housing which is fast with the drive output shaft 1 6. Correspondingly, it is the clutch plates which are keyed or splined at their inner peripheries, which are connected to drive input shaft 14. Thus, the major portion of the rotating mass of the clutch is on the drive output side of it and therefore does not rotate at engine speed except when the clutch is engaged.

Drive input to gear train 10 is through a constant drive input device 72 in the form of a torsionally damped mechanical drive coupling device comprising springs, rubber elements or other resilient devices to cushion cyclic torque variations. Devices of this kind are known in the art and require no further description.

Referring to Fig 2, a road vehicle 74 has a front mounted engine 76 and a drive transmission 78 connecting the engine to rear wheels 80.

The transmission comprises a gearbox 82 containing gear train 10, together with a propellor shaft 84 having universal joints 86, 88 and connected to a differential drive unit 90 and hence to back axle 92. The direction of forward motion of the vehicle is indicated by Arrow F and the front wheels are designated by numeral 94.

Figs 3 and 4 show side and end elevation views of gearbox 82. Fig 4 shows how the triangular disposition of the axes 96, 98, 100 of layshafts 28, 30, 32 permits a generally triangular gearbox profile whereby its height 102 is significantly less than the height 104 of the generally square profile four layshaft gearbox 106 which is indicated for reference purposes. The axis of the drive input and drive output shafts is indicated by reference numeral 108.

Figs 5 and 6 show the mounting of gearbox 72 in vehicle 74 below the floor 110 thereof, whereby the reduced height requirement 102 of the gearbox significantly increases the ground clearance of the vehicle.

Figs 7 and 8 show a modified gearbox 112, otherwise similarto gearbox 72 but incorporating transfer gearing (not shown) within the gearbox and meshing with the drive output gear 20, whereby the final drive output shaft axis 114 is offset laterally from central input/output axis 1 6 to suit particular vehicle drive layout requirements.

The three layshafts are indicated as in Figs 4 and 6.

Though not shown in the above drawings, drive train 10 is provided with auxiliary drives for vehicle accessories such as hydraulic or pneumatic pumps and compressors. For this purpose, accessory drive gears are mounted on the gearboxes 72 and 112 for meshing engagement with one of the layshaft input gears 40, 42 or 44. Due to the use of the constant drive input device 72 and take-up of the drive by means of clutches 58, 60 and 62, the layshaft input gears are always rotating with the engine and therefore the accessory drive likewise operates throughout the time the engine runs.

In use, the drive train output shaft 1 6 is connected to propellor shaft 84 and vehicle 74 operates in the four transmission ratios provided by clutches 58, 60, 62 and 70, the transmission ratios being selected manually, semiautomatically of fully automatically as described in our prior application.

Pressure lines 64, 66, 68 are connected to a fluid pressure control system giving the necessary manual, semi-automatic or fully automatic control of ratio changing. In particular, the pressure line 68 to the bottom gear clutch 62 (used for taking the vehicle off from rest) incorporates particularly fine control to allow smooth engagement of drive from rest. For this purpose, hydraulic rather than pneumatic control of the clutches is preferred.

Among modifications which could be made in the above-described embodiments, while remaining within the scope of the invention are the following: 1. The provision of a freewheel assembly (i.e.

an assembly which permits the transmission of drive in one direction only) in place of the clutch plate assembly of at least one of the clutches of the gear train. Such a freewheel assembly serves to transmit torque when required for its particular transmission ratio, but when the other transmission ratios are engaged it freewheels and thus does not interfere which proper operation of the gear train. The freewheel assembly would normally be provided for the first gear ratio (i.e.

maximum torque and maximum transmission ratio step-down between engine and wheels). It will be understood that with such modification no engine braking will be provided in that particular transmission ratio. Moreover, the provision of additional clutch means between the engine and the ground wheels of a vehicle would normally be needed to prevent the transmission of drive on engine start-up. Nevertheless, the expression "clutch means" as used in this specification is to be interpreted, where appropriate, as covering the alternative provision of a freewheel assembly.

2. The provision of non-coaxial input and output shafts. These shafts though always generally central to the gear train need not necessarily be coaxial and the claims of this application, and related applications, are not to be interpreted as so-limited except where explicitly stated.

3. The use of a single gear, or only two gears on the output shaft (or the input shaft) of the gear train, in place of the cluster gear described above.

Claims

1. A drive transmission including a gear train comprising an input shaft having an input shaft gear, an output shaft having an output shaft gear, at least one layshaft having layshaft input and output gears in direct constant mesh with said input and output shaft gears, and clutch means at one end of said layshaft and operable to establish and interrupt the transmission of drive between the layshaft input and output gears, the drive transmission further comprising a constant drive input device connected to said input shaft to transmit drive to the gear train, and control means for said layshaft clutch means whereby said clutch means can be progressively engaged for drive take-up purposes.

2. A drive transmission according to claim 1 wherein said constant drive input device comprises a mechanical drive input connection.

3. A drive transmission according to claim 2 wherein said constant drive input device comprises torsional damping means.

4. A drive transmission according to any one of the preceding claims wherein said control means for the layshaft clutch means comprises hydraulic control means.

5. A drive transmission according to any one of the preceding claims having an accessory drive coupled to a gear of said gear train.

6. A drive transmission substantially as described herein with reference to the accompanying drawings.

7. A vehicle comprising a drive transmission according to any one of claims 1 to 6.

8. A gear train comprising an input shaft having an input shaft gear, an output shaft having an output shaft gear, at least one layshaft having layshaft input and output gears in direct constant mesh with said input and output shaft gears, and clutch means at one end of said layshaft and operable to establish and interrupt the transmission of drive between the layshaft input and output gears, wherein direct drive clutch means is connected between said input and output shafts and is selectively operable to transmit drive directly between said shafts, said direct drive clutch means being arranged so that a major portion of the rotatable mass of the clutch means is connected to the output shaft.

9. A gear train according to claim 8 wherein said direct drive clutch means comprises two sets of interleaved clutch plates, one set being drivably connected at its inner periphery and the other set being drivably connected at its outer periphery, the output shaft being connected to said set of plates which are drivably connected at their outer peripheries.

10. A gear train according to claim 8 or claim 9 wherein at least one further clutch-controlled layshaft is provided to selectively transmit drive between said input and output shafts, said two layshafts being provided on opposite sides of the input and output shaft assembly.

11. A gear train according to claim 10 wherein a third layshaft to selectively transmit drive between said input and output shafts is provided and a gearbox casing housing the gear train is of generally triangular profile to correspond with the location of the layshaft axes.

12. A vehicle comprising a gear train according to any of claims 8 to 11.

1 3. A vehicle according to claim 12 comprising a front-mounted engine and a drive transmission comprising said gear train, the drive transmission extending between the engine and driven rear wheels of the vehicle, the engine and drive transmission being mounted below a floor of the vehicle.

14. A vehicle according to claim 1 3 or claim 12 wherein said gear train comprises transfer gearing to offset the gearbox output shaft with respect to the axis of the gear train input shaft.