WO1996013399A1

WO1996013399A1 - Transmission

Info

Publication number: WO1996013399A1
Application number: PCT/GB1995/002455
Authority: WO
Inventors: Timothy Michael Howard
Original assignee: Ford Motor Company Limited; Ford Werke Ag; Ford France S.A.; Ford Motor Company
Priority date: 1994-11-01
Filing date: 1995-10-17
Publication date: 1996-05-09
Also published as: GB2294738A; GB9422002D0

Abstract

A transversely mounted vehicle gearbox has an input shaft (10) and an output shaft (12), the speed of which is stepped up from that of the input shaft (10). The output (12) from the gearbox, which is rotating fast, is then stepped down by an epicyclic gear (64) to wheel speed.

Description

TRANSMISSION

This invention relates to a transmission for a motor vehicle with a transversely mounted engine.

A vehicle transmission has gears which can be selectively engaged with one another to vary the ratio between the engine shaft speed and the gear box output shaft speed. The size and dimensions of the transmission components are related to the maximum torque which they have to transmit . Generally, the higher the rotational speed of the gear box shafts, the lower the torque. If the maximum torque to be transmitted through the transmission can be reduced, then the dimensions of the gear box components can also be reduced. This is advantageous.

The principle behind the invention is that the gearbox should be used merely for selecting different gear ratios, whilst other gearing downstream of the gearbox will be used for adapting the engine/gearbox output speed to road wheel speed.

According to the present invention, there is provided a transmission for a motor vehicle with a transversely mounted engine, the transmission including a transversely mounted gearbox output shaft and an epicyclic gearset arranged between the output shaft and a vehicle axle and offset from the output shaft axis, to transmit the rotation of the output shaft to the axle at a reduced rotational speed.

In this way the gearsets in the gearbox are used only for gear range changes and are independent of any desired wheel speed. The conversion (reduction) of the shaft rotational speed to axle speed is only carried out as a final stage of the transmission. The rotational speed experienced in the transmission can therefore be kept high, which implies relatively low torque loadings. As a result, the transmission components (including the transmission housing) can be downsized relative to prior art transmissions, with corresponding benefits in reduction of gear inertia.

The epicyclic gearset preferably has its sun wheel fixed so that it does not rotate. The pinion formed by the outer teeth of the annulus meshes with a final drive

10 pinion on the output shaft, and the planet wheels are carried by a planet carrier which is connected to a drive shaft. The drive shaft will normally be split in two, with relative motion between the two half shafts being controlled by a differential and each half shaft driving ⁵ one road wheel.

The differential is preferably another epicyclic gearset.

The transmission ratio in first gear between the input shaft and the output shaft can be between 2:1 and 3:1, preferably 2.5:1.

-.0 The step down ratio between the final drive of the output shaft and the epicyclic gearset is preferably between 2.5:1 and 3.5:1, preferably 3:1.

The invention also provides a transmission for a motor vehicle with a transversely mounted engine and rear driven 25 wheels, the transmission including a transversely mounted change-speed gearbox with a transversely mounted gearbox output shaft and a spiral bevel gear gearset arranged between the output shaft and a vehicle axle to transmit the rotation of the output shaft to the rear axle.

0 As a result of the fact that the output shaft rotates relatively fast and therefore experiences relatively low torque, it becomes possible to use the output gear of the output shaft as the input gear for a rear wheel drive layou . The output gear can be meshed with a combined spur gear and bevel gear mounted on an axis parallel to the output shaft and with the bevel gear meshing with a second bevel gear mounted on the rear wheel drive propshaft.

In this way, drive can be transmitted to rear wheels (which may be driven entirely conventionally through a differential) via a propshaft which rotates relatively fast and therefore is subjected to relatively low torque.

The invention will now be further described, by way of example, with reference to the accompanying drawings, in which:

Figure 1 is a schematic layout of a transmission in accordance with the invention;

Figure 2 is a section on the line II-II from Figure 1;

Figure 3 is a section on the line III-III from Figure 2; and

Figure 4 shows an alternative final drive arrangement.

The transmission shown in Figure 1 has an input shaft 10 and an output shaft 12. The input shaft has a splined end 14 which will be connected to the crankshaft of an internal combustion engine, to be driven by the engine. The output shaft 12 has a final drive gear 16 which will transmit drive to downstream parts of a drivetrain in a manner to be described.

The shafts 10 and 12 carry gear wheels 18 - 44 which are selectively brought into engagement with one another to provide different transmission ratios. The engagement and disengagement of selected gear wheels will be controlled in a known manner by synchro hubs 46, 48, 50 and 52. In Figure 1, all the gear wheels are shown in engagement with their counterparts on the other shaft, but this is for the sake of illustration only; in practice, none or only one set of gearwheels will be in engagement at any one time.

Typically, in a transmission of the type described here, first gear will be selected when the gear wheels 18 and

44 are in mesh, to give a ratio of about 2.5:1. Second, third, fourth and fifth gears will be selected when, respectively gear wheels 20 & 42, 22 & 40, 24 & 38 and 26

& 36 are in mesh. Sixth gear, with a transmission ratio of about 0.4:1 will be selected when gear wheels 28 & 34 are in mesh, and reverse gear will be selected when gear wheels 30 & 32 are in mesh. The synchro hub 52 controls selection of either first or second gear; the hub 46 controls selection of either third or fourth gear; the hub 50 controls selection of either fifth or sixth gear and the hub 48 is associated with the selection of reverse gear.

Although Figure 1 shows a six-speed gearbox, the principles of the invention can equally be applied to gearboxes having a greater or a lesser number of gear ratios.

In general, the gear ratios between the shafts 10 and 12 will be such that the output shaft rotates faster than the input shaft, ie the transmission will 'step up' the engine speed. The extent to which the speed can be stepped up will depend on many factors, but may in practice be limited by the performance of the bearings in which the shaft 12 is journalled, and or the lubrication of these bearings. For example, upper speed limits may be in the region of 12-15,000 rpm.

The fast-rotating final drive gear wheel 16 meshes with teeth on the external periphery of an annular gear 54 of an epicyclic gear set 56 (Figure 2) . In this gear set, the sun gear 58 is fixed at 60 and the planet carrier 62 transfers a stepped down rotation to a further gear set.

Figures 1, 2 and 3 show the drive being transferred to a linked planet spur epicyclic differential gear generally indicated at 64 which drives two half-shafts 66 and 68 of a front wheel drive transmission. It will be noted from the layout of the half shafts 66 and 68 that the transmission shafts 10 and 12 are arranged in a transverse layout .

The planet carrier 62 of the epicyclic 56 forms the annular gear 62a of the epicyclic 64. One half shaft 66 i_s connected to the sun gear 70 and the other half shaft 68 is connected to the planet carrier 72, the individual planet wheels being indicated by reference numerals 74 and 76. The planets 74 mesh with the internal gear of the annulus 62a and the planets 76 mesh with the external gear of the sun gear 70.

The speed reduction afforded by the reduction epicyclic 56 will be matched to the wheel speed requirement after the shaft gear ratios (18-44) have been optimised. The final drive may be constrained by centre distances and by the size of the output shaft drive gear (interference with input shaft bearing) . Figure 4 shows that the gearbox output shaft final gear 16 can be meshed with a spiral bevel gear set 78, with one of the bevel gears 80, 82 being fitted at the end of a propshaft 84. Using a layout like this, a transversely mounted gearbox arrangement can be utilised for both front wheel drive and rear wheel drive vehicles. The propshaft 82 will run to the rear axle offcentre along the length of the vehicle and can be supported against a body sidemember

Claims

1. A transmission for a motor vehicle with a transversely mounted engine, the transmission including a transversely mounted change-speed gearbox with a transversely mounted gearbox output shaf and an epicyclic gearset arranged between the output shaft and a vehicle axle and offset from the output shaft axis, to transmit the rotation of the output shaft to the axle at a reduced rotational speed.

2. A transmission for a motor vehicle as claimed in Claim 1, wherein the epicyclic gearset has its sun wheel fixed so that it does not rotate.

3 A transmission for a motor vehicle as claimed in Claim 1 or Claim 2 , wherein the pinion formed by the outer teeth of the annulus meshes with a final drive pinion on the output shaft, and the planet wheels are carried by a planet carrier which is connected to a drive shaft.

4 A transmission as claimed in any preceding claim, wherein the drive shaft is split in two, witn relative motion between the two half shafts oemg controlled by a differential and each half shaft driving one road wheel.

5. A transmission as claimed in Claim 4, wnerein the differential is another epicyclic gearset.

6. A transmission as claimed in any preceding claim, wherein the transmission ratio in first gear between the input shaft and the output shaft is between 2:1 and 3:1, preferably 2.5:1.

7. A transmission as claimed in any preceding claim, wherein the step down ratio between the final drive of the output shaft and the epicyclic gearset is between 2.5:1 and 3.5:1, preferably 3:1.

8. A transmission for a motor vehicle with a transversely mounted engine and rear driven wheels, the transmission including a transversely mounted change-speed gearbox with a transversely mounted gearbox output shaft and a spiral bevel gear gearset arranged between the output shaft and a vehicle axle to transmit the rotation of the output shaft to the rear axle.

9. A transmission as claimed in Claim 8, wherein an output gear on the output shaft is meshed with a combined spur gear and bevel gear mounted on an axis parallel to the output shaft and with the bevel gear meshing with a second bevel gear mounted on the rear wheel drive propshaft.

10. A transmission as claimed in Claim 8 or Claim 9, wherein the rear, driven axle is driven through a differential via a propshaft.