A central gear unit and a work machine comprising the central gear unit

FIELD OF THE INVENTION AND PRIOR ART

The present invention relates to a central gear unit for a wheel axle, wherein the central gear unit comprises a differential and a differential locking mechanism, which comprises a clutch pack and a piston for actuating the clutch pack. The central gear unit is especially adapted for a work machine.

The term ^λλ work machine" comprises different types of material handling vehicles like construction machines, such as a wheel loader and a dump truck (such as an articulated hauler) . A work machine is provided with a bucket, container or other type of work implement for carrying/ transporting a load. Further terms frequently used for work machines are "earth-moving machinery", "off-road work machines" and "construction equipment".

In connection with transportation of heavy loads, e.g. in contracting work, work machines are frequently used. A work machine may be operated with large and heavy loads in areas where there are no roads, for example for transports in connection with road or tunnel building, sand pits, mines and similar environments.

The differential has the job of adapting the speed of the driving wheels at the same time as retaining the total driving power. This is necessary, as when cornering the outside wheel has a longer stretch to

roll than the inside wheel, which means that- it has to rotate more quickly.

The differential locking mechanism has the job of locking the drive shafts to the left and right wheel together so that the differential can be put out of action in case of wheel slip. Activation and deactivation of the differential locking mechanism is improved due to the clutch pack (in comparison with a conventional fork locking mechanism) .

SUMMARY OF THE INVENTION

The purpose of the invention is to achieve a central gear unit, which is more cost-efficient in production while maintaining a long life.

This purpose is achieved by the central gear unit according to claim 1. Thus, it is achieved by a central gear unit for a wheel axle, wherein the central gear unit comprises a differential and a differential locking mechanism, which comprises a clutch pack and a piston for actuating the clutch pack, characterized in that the central gear unit comprises a first bearing arranged between a housing for the piston and a differential housing part adapted for rotation.

By this arrangement of the first bearing, some previously required production steps, such as machining of a bearing cap in the differential housing, may be eliminated. Preferably, an outer surface of the first bearing is arranged in contact with the differential housing part.

According to a preferred embodiment, an inner surface of the first bearing is arranged in contact with the piston housing. Thus, no seat for the bearing is required on the piston housing. Instead, only a flat outer surface of the piston housing requires machining.

According to a further preferred embodiment, the central gear unit comprises a second tapered bearing arranged on an opposite side of the clutch pack relative to the first tapered bearing, and that the first and second bearings are arranged with an inclination in the same direction with regard to an axial direction. This design creates conditions for a facilitated assembly of the central gear unit, especially when an outer ring of the first bearing is arranged in contact with the differential housing.

Other advantageous features and functions of various embodiments of the invention are set forth in the following description and in the dependent claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be explained below, with reference to the embodiments shown on the appended drawings , wherein FIG 1 schematically shows a wheel loader in a side view, and FIG 2 schematically shows a disk differential of the wheel loader in fig. 1 in a cross section.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

Figure 1 shows a frame-steered work machine constituting a wheel loader 101. The body of the wheel loader 101 comprises a front body section 102 and a

rear body section 103 , which sections each has an axle

112,113 for driving a pair of wheels. The rear body section 103 comprises a cab 114. The body sections 102,103 are connected to each other in such a way that they can pivot in relation to each other around a vertical axis by means of two first actuators in the form of hydraulic cylinders 104,105 arranged between the two sections. The hydraulic cylinders 104,105 are thus arranged one on each side of a horizontal centerline of the vehicle in a vehicle traveling direction in order to turn the wheel loader 101.

The wheel loader 101 comprises an equipment 111 for handling objects or material. The equipment 111 comprises a load-arm unit 106 and an implement 107 in the form of a bucket fitted on the load-arm unit. A first end of the load-arm unit 106 is pivotally connected to the front vehicle section 102. The implement 107 is pivotally connected to a second end of the load-arm unit 106.

The load-arm unit 106 can be raised and lowered relative to the front section 102 of the vehicle by means of two second actuators in the form of two hydraulic cylinders 108,109, each of which is connected at one end to the front vehicle section 102 and at the other end to the load-arm unit 106. The bucket 107 can be tilted relative to the load-arm unit 106 by means of a third actuator in the form of a hydraulic cylinder 110, which is connected at one end to the front vehicle section 102 and at the other end to the bucket 107 via a link-arm system 115.

Figure 2 shows a central gear unit 201 in a rear axle housing 203. The rear axle is adapted to transmit power from the engine to the wheels 117. The central gear unit 201 comprises a pinion gear 205 forming an input to the rear axle. The pinion gear 205 introduces the driving rotational movement into a differential 207. A crown wheel 209 engages the pinion gear 205 and is fitted to a rotating differential housing 211.

The differential 207 has the job of adapting the speed of the driving wheels at the same time as retaining the total driving power. The differential 207 is fitted in the differential housing 211 and comprises four gear wheels, the differential side pinions, which are fitted on a joint cross. These pinions mesh with two differential side gears 215,217, which run on two independent drive shafts 219,221.

A differential locking mechanism 223 is adapted to brake the differential gear. The differential locking mechanism 223 comprises a clutch pack 225 of interleaved discs alternately connected to one of the drive shafts 221 and to a differential housing part

227. More specifically, the discs are connected via splines to an external surface of the drive shaft 221 and via splines to an internal surface of the differential housing part 227. The clutch pack 225 forms a wet brake. The differential housing part 227 is in turn rotationally rigidly connected to the differential housing 211 via a screw joint.

A fluid-actuated annular piston 229 is provided for actuating the clutch pack 225. A piston housing 231 forms a separate part rigidly connected to a stationary

housing 232 via a screw connection. The central gear unit 201 comprises a pair of differential bearings 233,235. A first bearing 233, in the form of a conical roller bearing, is provided between the piston housing 231 and the differential housing part 227. More specifically, the bearing 233 is positioned in contact with an outer surface of the piston housing 231. Thus, the bore of the bearing 233 is now incorporated into the piston housing. The bearing 233 is positioned in contact with an inner surface of the differential housing part 227. The bearing 233 is a single row bearing.

Further, the bearing 233 is tapered, see the line 239, indicating the bearing direction. Thus, a roller element 234 in the bearing 233 is arranged between conical surfaces. The roller elements 234 are angled or tapered to a common point known as the apex 241.

A second tapered bearing 235, also in the form of a conical roller bearing, is positioned on an opposite side of the differential 207 with regard to the first bearing 233. The two bearings 233,235 are arranged with an inclination in the same direction with regard to an axial direction 237 of the rear axle, see lines 239,245.

The invention is not in any way limited to the above described embodiments, instead a number of alternatives and modifications are possible without departing from the scope of the following claims .

The differential locking mechanism has above been described only with regard to locking the differential.

The term "differential locking mechanism" should. however be interpreted as a mechanism which is suitable for locking the differential. Since the mechanism comprises a clutch pack, it may be used for decreasing a differential rotation without actually locking the shafts together. For example, the clutch pack is configured for a variable (stepless) actuation. Thus, the mechanism creates conditions for allowing a limited slip. Thus, flexibility is substantially increased in comparison with a conventional fork locking mechanism.