GB2080747A - Motor vehicle driving axle - Google Patents

Abstract

A driving axle for a short-distance bus has its central portion displaced downwardly by a distance P to permit an advantageous vehicle-boarding height E, there being provided between two spur wheel reduction gearings 12 through which respective wheels 34 are driven an axle casing part 11 in the form of a smooth tubular member of small diameter with optimum ground clearance B. Differential gear 5 is combined in the casing with one of the spur wheel reduction gearings 12 so that neither the gangway width L nor the ground clearance B is reduced by a differential gear in the centre of the axle. The advantageous coordination of the distance P, boarding height E, ground clearance B, wheel track R and gangway width L is achieved by the use of reduction gearings each having a pinion 13 which acts on two intermediate gears 19 lying in the same plane 22 and which is mounted adjustably in relation to the output gear 23 of the reduction gearing 12 which is locked radially non-displaceably on the wheel driving shaft 25. In addition to the advantage of favourable transmission staging, accompanied by favourable use of the overall space due to small centre disturbances and small tooth widths, sensitivity to impacts is reduced and the noise level and extra costs are low in comparison with planetary gearings. <IMAGE>

Description

SPECIFICATION A driving axle for a motor vehicle This invention relates to a driving axle of a motor vehicle, in which individual reduction gearings disposed immediately preceding the vehicle wheels influence the floor height of the vehicle.

For many years arrangements of vehicle axles have been known which produce as low a loading surface or floor height as possible, even immediately between the driven wheels. For example, German Published Specification 2256121 discloses an axle arrangement for buses in which universal-joint shafts enable the differential of a bus axle to be located lower than the wheel driving shafts. This specification discloses that separate reduction gearing can also be arranged preceding the wheels. One advantage which is particularly emphasised is that the brakes can be arranged immediately at the differential.

In practice, constructions have also been disclosed in which the portal distance is obtained by using reduction gearings having vertically offset inputs and outputs. Since when a relatively small portal distance was maintained it was very rarely possible to obtain the required reductions when using a single-stage spur wheel reduction gearing, in many cases planetary gearings in the wheel hubs had also to be added to the reduction systems. The result was disadvantageous relative dimensions with considerable overall axial lengths and heavy costs. Other disadvantages were that the spur wheel reduction gearings were very sensitive to shocks during gear shift and that the planetary gearings operated very noisily.

Both the afore-mentioned constructions using universal-joint shafts and also the rigid axial constructions with conventional reduction gearings failed to meet the demands made by wide use in short-distance buses, since such systems are more particularly expensive, noisy, heavy and also lack advantageous axial and vertical mounting dimensions.

One essential reason for the mounting difficulties has hitherto been that the tooth width of the spur wheel reduction gearings used and the other associated constructional elements of the gearing required a considerable overall axial space particularly within the wheelbase between the two driven wheels.

Precisely in this respect emphasis was laid on adequate ground clearance, and an adequate gangway width has also to be provided above the axle without the vehicle floor height having to be raised by more than the usual single-step boarding height.

In the majority of conventional constructions, therefore, disadvantages accrued not only from the large axial distance of the normal spur wheel reduction gearings, but also from the overall radial and axial space required for the differential. The conventional arrangement of the differential at about the centre of the vehicle proved to be particularly disadvantageous in cases in which the engine and changespeed gear had to be accommodated transversely in relation to the vehicle axis at a short distance from the driving axle at one end of the vehicle, and the universal-joint shaft to the differential had to be accommodated as much as possible on one side of the vehicle.With these arrangements there was relatively sharp angles of bending of the universaljoint shaft in the direction of the differential and considerable universal-joint shaft lengths, resulting again in expensive constructions and heavy wear.

With the prior art constructions it was also difficult to adapt the portal distance and the given transmission ratio in such a way that only a few transmission stages were necessary. Often all that could be done was to discover a compromise between the overall height and transmission ratios by using multi-stage transmissions by means of, for example, planetary gearings in the wheel set. The relatively narrow vehicle profiles of short-distance buses then repeatedly gave difficulties as regards the incorporation of a wide enough gangway. The multi-stage reduction gearings also resulted in relatively unfavourable overall efficiencies, heavy weights and difficult conditions of mounting.

In contrast, in the case of city route buses, it is regarded as the optimum if the possibility is created of arranging the gangway of standard-gauge chassis even between the wheels as wide as over the whole length of the bus and at that height above the roadway which can be reached from the pavement by a maximum of one boarding step.

When devising the driving axle of the invention, therefore, the Inventors set themselves an object of providing, using only one spur wheel reduction gearing of narrow overall width per wheel to be driven, precisely that portal distance by which the gangway can also be made with constant floor height and floor width between the wheels themselves, whilst maintaining the largest possible ground clearance, more particularly in the centre of the vehicle. Another object of the invention is to improve on the prior art as regards the cost of construction and the reduction of noise and wear, including in the zone of the universal-joint shaft between the change-speed gear and the differential.

Accordingly, the present invention consists in a driving axle for a motor vehicle, comprising an axle casing having at each end a casing part which accommodates a spur wheel reduction gearing and an intermediate part which accommodates a layshaft interconnecting the two reduction gearings, a differential gear with a crown wheel and a meshing bevel pinion combined with the reduction gearing within one of the end parts of the casing, said crown wheel being connected rotationally fast to said layshaft and said bevel pinion being connectible via a cardan shaft to a change-speed gear and the engine of the vehicle, each said reduction gearing being constructed as a double reduction gearing having an input pinion carried by said layshaft and an output gear which is drivingly connected to said input pinion via two intermediate gears each meshing with the output gear and said input pinion to provide a power branching, each said output gear being mounted rotationally fast on a respective vehicle wheel driving shaft which is arranged in relation to the layshaft at a portal distance (P) which is determined by the transmission ratio of the reduction gearing, each wheel driving shaft having an input end carrying said output gear and an output end having a wheel hub cover which is connected rotationally fast to a wheel hub which is rotatably mounted by means of bearings on a wheel hub carrier which receives the wheel driving shaft and which is connected rotationally fast to the adjacent end part of the axle casing, further bearings being provided for the spur wheel reduction gearings, the differential gear and the layshaft, both end casing parts having mounting means for supporting a vehicle chassis, the layshaft being constructed in two parts of unequal length of which the longer part is mounted as a continuous shaft within the intermediate part of the axle casing which interconnects the two end parts of the casing.

The use of a known "double reduction gearing" for the deflection of force in the construction of a so-called inverted portal axle not only produces advantageous transmission stages, quieter running and gear wheels only about have as wide as in the prior art single reduction transmissions, but also results in the height of the portal distance readily being adaptable to the order of magnitude required in practice for an advantageous boarding height with full gangway width.

The construction of the driving axle of the invention also enables advantage to be taken of the distribution of power in the range of high tooth stressings in a very similar manner to that already known for many years (cf. for example, German Patent Specification 10 31 075) from other applications, for example, change-speed gears. Furthermore, a brake carrier and brake-actuating system can advantageously be accommodated on the hub carrier or the reduction gearing casing part. A known expanding wedge-type construction of brakes may be used, whose cylinders can advantageously be accommodated in a preferred contruction outside the wheel hub, at about the same level as the axle casing connecting tube, between the two wheel sets, without any adverse effect on either the gangway width or the ground clearance of the vehicle.The dividing up of forces by the intermediate gears can be used for the very quiet transmission of force, particularly with adjustment of the tooth clearance.

Although there is a large total transmission and relatively considerable transmitting powers, no extremely large portal distance need be provided.

The portal casing itself can be very narrow and also used directly for the attachment of the vehicle chassis without any extra overall length being required. Even between the wheels there is the full standard gangway width of the bus. In the important zone of the centre of the vehicle there is hardly any adverse effect on the ground clearance between the axle casing and the roadway. The extreme lateral arrangement of the differential, in combination with one reduction gearing casing part, facilitates the introduction of a universal-joint shaft from the change-speed gear, more particularly if, as is nowadays preferably the case with city bus routes, the drive unit of the vehicle is disposed transversely in relation to the direction of travel.The small angle of bending of the universal-joint shaft in the direction of the differential results in advantageous operational behaviour and long lives of the parts. It is also very advantageous to avoid universal-joint shafts between the reduction gearing and the differential and between the reduction gearings respectively, due to the lower costs and simpler methods of accommodating stub axles of known construction. The presence of strong layshaft casings, which are required in any case, and the sole attachment of the chassis tow such casings, results due to this double use in a saving in weight and the avoidance of the possible provision of further space-occupying attachment points on the central part of the axle casing.The introduction of force from the vehicle weight via the layshaft casing adjacent the wheel also results in a reduction in the bending stresses in the axle casing itself, so that the latter must act essentially merely as a spacing and anti-dirt element.

The construction according to claim 2 is an arrangement in which the intermediate gears are so disposed that the tooth-meshing forces neutralise one another to the greatest extent. In such construction the lowest possible radial forces occur in the bearings. As a result the casing can be of small dimensions. There is also a further reduction in sensitivity to impacts during gear-change operation and alternating output forces.

According to claim 3, the input pinion can be adjusted between the intermediate gears; this enables any wear which may have occurred or errors in manufacturing tolerances to be compensated for.

In the construction of claim 4, the input pinion is disposed overhung at the free end of the particular layshaft part opposite the output gear, so that there is no need to dispose a bearing rigidly connected to the casing on both sides of the pinion. The particular layshaft part can share in the relatively small vertical adjusting movements of the pinion, since the shaft part has enough clearance for movement in the differential bearing casing. Overall length is reduced by the elimination of fixed bearings.

The construction of claim 5 ensures that the input pinion can operate self-adjustably due to a narrow bearing bridge, disposed radially adjustably in the casing, by means of a springing and an adjusting means (for example, a bolt and nut).

The construction of claim 6 ensures that the advantage derived from the reduction of the stressings of the axle casing are further enhanced by the casing being of a light-weight construction, for example made of light metal alloy. In combination with efforts to save energy, the resulting redusbons in the overall weight of the vehicle are of consider-; able importance.

In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example embodiments thereof, and in which Figure 7 illustrates the general outlay of the driving axle construction, Figure 2 is a side elevation of the double reduction gearing, Figure 3 shows a construction ofe cornpletewheffli set with attached double reduction gearing and the introduction of the universal-joint shaft into the differential, Figure 4 is a side elevation, corresponding to Figure 3, showing the arrangement of the intermediate gears in the double reduction gearing, and Figure 5 is a partial section, corresponding to Figure 3, showing a possible alternative device for resiliently supporting the input pinion.

Figure 1 shows that the initiation of driving force starts from an engine 1 and a change-speed gear 2 which are secured to the loading surface of a motor vehicle 3. From a universal-joint shaft 4, connected to the change-speed gear 2, the driving force is distributed to the two vehicle wheel sets via a bevel gearing with differential 5 which is disposed on a divided layshaft 6. A bevel pinion 7 of the bevel gearing 5 is driven by the universal-joint shaft 4. A crown wheel 8 is connected rotationally fast to both parts of the layshaft 6, i.e. a shorter stub shaft 9 and a longer stub shaft 10. The stub shaft 10 passes through an axle casing 11 and connects the bevel gearing 5 drivably to that spur wheel reduction gearing 12 which is not combined in one casing part with the gearing 5. This reduction gearing is thus disposed at the opposite end of the driving axle.An input pinion 13 and a pinion bearing 14 are so attached to the respective stub shafts 9 and 10, respectively driven by the crown wheel 8, that an adjusting device 16, which may include a spring 17, can be operated via a bearing bridge 15 to control the branching of power and the tooth-meshing forces on both sides.

The reduction gear casing part 18 contains jointly the pinion 13, and intermediate gears 19 with their shafts 20 and bearings 21, preferably so incorporated that the latter have a common axial central plane 22 at a distance P from the vehicle wheel axis.

The casing 18 also contains an output gear 23 and an output gear bearing 24. The output gear 23 is fast with the wheel driving shaft 25 extending through a rotationally fast hub carrier 26 which is rigidly connected to the casing 18 and has a rigid connection to the axle casing 11 a hub carrier flange 27. A wheel bearing 28 is arranged on the hub carrier 26.

The hub carrier 26 acts at the same time as a carrier 29 for brake cylinder 36 and constitutes, together with wheel hub 31, a brake casing 20 which is sealed in the direction of the wheel bearing 28 and is vented only in the direction of the hub flange 32. The hub flange 32 and the adjoining flange 33 of casing 30 and wheel rims 34 connectible therewith are entrainable by the screws of hub cover 35 in the direction of rotation.

Referring to Figure 2, the arrangement of intermediate gears 19 in relation to the pinion 13 is such that the pinion does not mesh with the output gear 23, but always meshes with the intermediate gears 19.

The latter always mesh at the same time with the output gear 23. The preferred arrangement of the pinion 13 in relation to the intermediate gears 19 is such that the axes of these gears always lie in a common axial central plane 22, while the axis of the output gear 23 is at the portal distance P from the axial central plane 22.

Figure 2 also shows clearly how it is exclusively due to the principle of operation of the double reduction gearing used that in spite of a considerable transmission stage between the differential and the wheel driving shaft, the portal distance does not have to be substantially much greater than would be the case with standard, single spur wheel reduction gearing.

Figure 3 shows the construction of the essential elements contained in the arrangement illustrated in Figure 1 in a similarly appropriate manner, but for only one wheel set. Features clearly seen are the advantageous arrangements of the differential and bevel gearing in a common casing with the double reduction gearing and the advantageous construction of the cross-section transitions between the axle casing and the hub carrier. (To simplify the drawing, the position of connection between the universaljoint shaft 4 and the brake cylinder 36 is shown offset by about 90 ).

Figure 4 is a side elevation of the double reduction gearing casing and the layshaft extending therethrough. The possibility of constructing this transmission casing rigidly and its positioning very near the wheel enables the casing to be used for the attachment of the axle-tree bed bolster to the lateral attaching points for the chassis support 37. Since height is also available alongside the gearing casing for very large brake cylinders 36 the latter can also be disposed conveniently for maintenance at this place, without any adverse effect on the ground clearance B. The lateral arrangement of the differen tial and the introduction of the universal-joint shaft 4 thereinto produces a very small angle of bending W even in the case of the transversely mounted drive unit preferred for short-distance buses.

Figure 5 shows how the pinion 13 can be automatically adjusted, in dependence on the distribution of driving force, in the reduction gearing 12, radially in relation to the stub shaft 9,10 and against the force of spring 17 in a bearing bridge 15.

Figures 1 and 2 show clearly the function of the driving axle of the invention and the influences which it exerts on the favourable geometrical conditions. Although a further reduction gearing is dispensed with, the portal distance P can be so adapted to the usual minimum boarding height E that a full gangway width Lover a hardly reducing ground clearance B can be achieved with even a narrow wheelbase R.

The advantages of the invention can also be obtained if an individual wheel drive is preferred to a differential.

Claims (7)

1. A driving axle for a motor vehicle, comprising an axle casing having at each end a casing part which accommodates a spur wheel reduction gearing and an intermediate part which accommodates a layshaft interconnecting the two reduction gearings, a differential gear with a crown wheel and a meshing bevel pinion combined with the reduction gearing within one of the end parts of the casing, said crown wheel being connected rotationally fast to said layshaft and said bevel pinion being connectible via a cardan shaft to a change-speed gear and the engine of the vehicle, each said reduction gearing being constructed as a double reduction gearing having an input pinion carried by said layshaft and an output gear which is drivingly connected to said input pinion via two intermediate gears each meshing with the output gear and said input pinion to provide a power branching, each said output gear being mounted rotationallyfaston a respective vehicle wheel driving shaft which is arranged in relation to the layshaft at a portal distance (P) which is determined by the transmission ratio of the reduction gearing, each wheel driving shaft having an input end carrying said output gear and an output end having a wheel hub cover which is connected rotationally fast to a wheel hub which is rotatably mounted by means of bearings on a wheel hub carrier which receives the wheel driving shaft and which is connected rotationally fast to the adjacent end part of the axle casing, further bearings being providedforthespurwheel reduction gearings,the differential gear and the layshaft, both end casing parts having mounting means for supporting a vehicle chassis, the layshaft being constructed in two parts of unequal length of which the longer part is mounted as a continuous shaft within the intermediate part of the axle casing which interconnects the two end parts of the casing.

2. A driving axle as claimed in claim 1, wherein the input pinion and the intermediate gears of each reduction gearing are arranged with their axes parallel to one another and with the centres of their axes in a common plane, said plane being located remote from the axis of the respective wheel driving shaft by substantially the portal distance (P), whereby the teeth of ail the gear elements of the reduction gearing mesh uniformly with minimum radial loading of the input pinion.

3. A driving axle as claimed in claim 1 or 2, wherein each input pinion is arranged adjustably between the intermediate gears so as to obtain optimum tooth clearance.

4. A driving axle as claimed in any of claims 1 to 3, wherein each input pinion or that end of the layshaft part which carries the input pinion is disposed in relation to the associated output gear overhung or with only one fixed bearing at the other end of the respective layshaft part.

5. A driving axle as claimed in any of claims 1 to 4, wherein each input pinion is seif-adjusting in the direction of producing optimum tooth clearance in the gear elements of the reduction gearing by means of a bearing bridge and a springing which supports the bearing bridge on the adjacent end part of the axle casing.

6. A driving axle as claimed in any of claims 1 to 5, wherein the intermediate part of the axle casing is of light-weight construction, for example made of light metal alloy.

7. A driving axle for a motor vehicle, substantially as herein described with reference to and as shown in the accompanying drawings.