WO2009018836A1

WO2009018836A1 - Differential gear unit

Info

Publication number: WO2009018836A1
Application number: PCT/EP2007/006938
Authority: WO
Inventors: Hendrikus Jan Kapaan; Jacobus Zwarts; Cornelius Petrus Antonius Visser
Original assignee: Ab Skf
Priority date: 2007-08-06
Filing date: 2007-08-06
Publication date: 2009-02-12

Abstract

The invention relates to a differential gear unit (1), especially for a vehicle, having a pinion (2) with a pinion gear (3) and a pinion shaft (4), wherein the pinion shaft (4) is supported in a housing (5) by means of a bearing arrangement (6', 6') and wherein the pinion gear (3) meshes with a gear element (7) which drives a housing of a bevel gear arrangement. To allow a downsizing of the differential gear unit, the invention is characterized in that the pinion gear (3) is surrounded at least partially by a gear pump housing (8), wherein the gear pump housing (8) has at least one opening (9) for allowing the meshing contact between the pinion gear (3) and the gear element (7).

Description

Differential Gear Unit

Technical Field

The invention relates to a differential gear unit, especially for a vehicle, having a pinion with a pinion gear and a pinion shaft, wherein the pinion shaft is supported in a housing by means of a bearing arrangement and wherein the pinion gear meshes with a gear element which drives a housing of a bevel gear arrangement.

Background

A differential gear is well known in the field of vehicle drives. The differential has a housing element in which a bevel gear arrangement (consisting of satellite gears and side gears) is mounted. The housing is driven by the gear element (crown gear). The bevel gear arrangement inside the housing element allows a speed compensation movement between inner and outer driven wheels when e.g. driving a curve with the vehicle.

Examples of such a differential gear are shown in US 6,325,737 Bl, in US 7,160,219 B2, in EP 0 167 388 Bl, in EP 1 666 771 Al and in US 3,618,712. Thus, the differential in a driveline is a device that splits the engine torque two ways, allowing each output to spin at a different speed and is found on all modern cars and trucks, and also in many all-wheel-drives.

The basic differential design e.g. for a driven rear axle of a truck, consists of the pinion gear arrangement with pre-loaded bearing supports which are fixed in the outer differential housing. The pinion gear drives the gear element (crown gear) at a defined reduction ratio. Ideally the pinion gear arrangement is located in the middle of the rear or front axle to provide where possible uniformity of components, e.g. same drive shaft length to the wheel ends.

The crown gear is fixed on the differential gear/housing which housing is supported mostly with two separate single taper roller bearings in a housing and arranged in an "X" configuration.

The differential housing is often split and supports the bearing radially by means of bolts fixed in the outer differential housing. Alternatively the differential crown gear can be supported at one side with a unitized bearing arrangement.

The differential housing is normally filled with a synthetic oil or an organic based fluid to lubricate the support bearings for the crown gear, the pinion gear and the gear contacts, in order to keep the system running at minimal friction and at an acceptable running temperature.

The lubrication liquid at the lowest point in the differential housing is splash- transported during rotation by the crown gear teeth to the crown gear support bearings, to the pinion gear teeth and support bearings. For an adequate lubrication and cooling of the differential system, a substantial quantity of lubricating fluid is needed.

Improved fuel efficiency is a constant goal of vehicle designers, and one way of achieving this is by means of an overall weight reduction.

To reduce the weight of a driven axle / differential, the differential components may be downsized. As a result, the quantity of lubricating fluid present in the housing will be reduced. Given that the downsized differential should produce the same torque output, the reduction of the lubricating fluid quantity will have a negative influence on the running temperature, the service life of the support bearings and the overall differential system efficiency, as the cooling power / heat transfer will also be reduced.

To provide an optimal downsized differential system with an adequate lubrication for the support bearings and gear contacts with an acceptable running temperature / heat transfer, a pressurized lubrication system by means of a pump is then required, sometimes in combination with a heat exchanger.

However, the pump and associated controls make such a pressurized lubrication system expensive, as well as adding to the overall weight of the vehicle.

Summary of the invention

According to the invention, a design for a differential gear unit is suggested by which the supply of lubricant is improved and downsizing is allowed in an easy manner. Furthermore, a compact design of such a unit is obtained which takes up relatively little space and eliminates the need for an additional lubrication pump.

Therefore, it is an o bj e c t of the invention to supply a design for a differential gear unit, which allows an efficient lubrication of the bearings used in the unit and the meshing gears, without the provision of separate lubrication pumps.

These and other advantages are obtained according to the invention by a differential gear unit, especially for a vehicle, having a pinion with a pinion gear and a pinion shaft, wherein the pinion shaft is supported by means of a bearing arrangement in a pinion bearing housing and wherein the pinion gear meshes with a gear element which drives a housing of a bevel gear arrangement.

A s o l u t i o n according to the invention is characterized in that the pinion gear is surrounded at least partially by a gear pump housing, wherein the gear pump housing has at least one opening for allowing the meshing contact between the pinion gear and the gear element.

Preferably the gear pump housing is formed to leave a radial gap between the pinion gear and the gear pump housing. The pinion gear has a small diameter end and a large diameter end. Rotation of the gear generates a pumping action that pumps the lubricating fluid from the small diameter end to the large diameter end of the pinion gear. A pump inlet is located at the contacts between the pinion gear and the gear element (crown gear). A pump outlet can be provided in the gear pump housing at the large-diameter end of the pinion gear, as this is where the maximum fluid pressure will be developed. By providing the pump outlet with suitable connections, e.g. tubes, pressurized lubricating fluid can be pumped to the bearing supports for the pinion gear and crown gear and to the gear contacts.

To enhance the pumping action, the radial gap between the circumference of the pinion gear and the opposing surface of the gear pump housing preferably varies in a radial plane. This can be achieved by means of a gear pump housing that has a substantially circular cross-section and is arranged eccentrically to the axis of the pinion gear. The same result can be achieved with a gear pump housing section that has a non-circular cross section and is arranged concentrically with the axis of the pinion gear.

To further enhance the pumping action, it is also advantageous if the radial gap varies in a longitudinal direction, and tapers towards the large diameter end of the pinion gear. A preferred embodiment of the differential gear suggests that the size of the radial gap is between 0.5 % and 10 % of the medium diameter of the pinion gear. The medium diameter of the pinion is the diameter measured in the axial middle of the geared section of the pinion gear.

The gear pump housing preferably covers the pinion gear along at least 240° of the circumference of the pinion gear, such that lubricating fluid is present at all times in the bottom of the housing.

The bearing arrangement can consist of two bearings. In a first embodiment of the invention, the two bearings are arranged coaxially at one side of the pinion gear. In a second embodiment, the bearings are arranged one at either side of the pinion gear. To maintain a proper gear mesh between the pinion gear and the crown gear, the bearing arrangement can suitably be preloaded. The bearing arrangement can be a roller or ball bearing arrangement, or a combination thereof. When a roller bearing arrangement is employed, the arrangement may comprise two taper roller bearings in an "X" or "O" configuration.

The bearing arrangement can be greased or oil lubricated and sealed. The bearing arrangement can comprise one or more add-on or integrated sensors for monitoring the moment load, torque, speed and/or temperature in a coupled transmission.

In the first embodiment of the invention, with one-sided bearing support, the gear pump housing is preferably an add-on piece which is fitted over the pinion gear and connected to the pinion bearing housing by e.g. mechanical means, such as bolts. A snap-on connection is also possible, in which case the pinion bearing housing can have a ring-shaped groove in which a projecting portion of the gear pump housing is inserted. The connection may also be achieved by means of cold forming. Energy welding is a further alternative.

The add-on gear pump housing may be made from a sheet material, which is advantageous in terms of reducing the overall weight of the unit.

In the second embodiment of the invention, with bearing support at either side of the pinion gear, the gear pump housing may form an integral part of the pinion bearing housing. The resulting single piece housing may be made from ferrous or non-ferrous cast metal. An add-on gear pump housing element made of sheet material is also possible in this embodiment.

The pinion gear may be a separate part that is fitted on the pinion shaft. The drive flange for the pinion can also be a separate part fitted on the pinion shaft. The drive torque connection between the pinion shaft and the separate parts may be achieved by means of mating splines or mating non-circular cross-sections, e.g. a polygon configuration. Bearing raceways could also be machined directly onto the pinion shaft, thereby eliminating the need for separate bearing inner rings. This would increase the compactness of the unit and further reduce its weight.

The design of the unit demands less space compared with previously known solutions. Thus, the overall design is compact. The differential gear unit according to the invention enables downsizing, and therefore weighs less than a conventional unit. Material costs are also reduced and there is no need for an expensive additional lubrication pump.

Any of the above mentioned features of the invention and its parts can be combined in any desired manner, as long as the features of the combination do not conflict. Further preferred embodiments of the invention are defined below and in the claims.

Brief description of the drawings

The drawings show embodiments of the differential gear unit according to the invention.

Fig. 1 shows a cross sectional view through a differential gear unit according to the invention, wherein a pinion is supported by a preloaded bearing arrangement and wherein a pinion gear meshes with a gear element, Fig. 2 shows the cross sectional view according the section A-B of fig. 1 ,

Fig. 3 shows view C according fig. 2,

Fig. 4 shows a perspective view of the arrangement according fig. 2,

Fig. 5 shows view D according fig. 4.

Fig. 6 shows the cross sectional view according the section A-B of fig. 1 of an alternative embodiment of the invention,

Fig. 7 shows view E according fig. 6 and

Fig. 8 shows a perspective view of the arrangement according fig. 6, partially sectioned.

Detailed description of the invention

Fig. 1 shows a differential gear unit 1 (at least the most essential parts of it which are necessary for the understanding of the present invention) having a pinion 2 which drives a gear element 7 (crown gear). A differential housing (not depicted) is driven by the gear element 7, in which a bevel gear arrangement (not depicted) is arranged. This design as such is well known in the art.

The pinion 2 has a pinion shaft 4; at one end of the pinion shaft 4 a pinion gear 3 is arranged (bevel gear) which can mesh with the respective gear element 7 (crown gear). The pinion shaft 4 is supported in a pinion bearing housing 5 by means of a bearing arrangement 6', 6". In the present case the bearing arrangement 6', 6" consists of two taper roller bearings 6' and 6" which are arranged in an "O" configuration and which are pre-loaded. The pinion 2 can thus rotate around the axis 11.

To obtain a lubricating pumping effect without employing a special lubrication pump, the pinion gear 3 is surrounded partially by a gear pump housing 8. The gear pump housing 8 has an opening 9 for allowing the meshing contact between the pinion gear 3 and the gear element 7.

As can be seen better in fig. 2, where the section A-B according to fig. 1 is shown, the gear pump housing 8 is designed in such a way that a radial gap 10 is left between the circumference of the pinion gear 3 and the inner surface of the gear pump housing 8.

As can be further seen in fig. 2 a pump outlet 17 is arranged in the gear pump housing 8. In the depicted embodiment the pump outlet 17 is located in a bottom region (at the deepest point) of the gear pump housing 8. Thus, the opening 9 functions as a pump inlet and the lubricant is then pumped to the pump outlet 17 by the rotational movement of the pinion gear 3.

Furthermore, as can be seen from fig. 3 the size of the radial gap 10 changes in a circumferential direction of the pinion gear 3. More specifically, the gear pump housing 8 has a substantially circular cross section and is arranged eccentrically to the axis 11 of the pinion gear 3; the eccentricity is denoted with e in fig. 3. In an alternative embodiment, the gear pump housing 8 can have a non-circular cross-section and be arranged concentrically with the axis 1 1. With regard to the size of the radial gap 10 it can be said that a preferred embodiment suggests that the radial gap lies between 0.5 % and 10 % of the medium diameter D of the pinion gear 3; the medium diameter D is denoted in fig. 2 and is basically the diameter of the pinion gear in the axial midpoint of the toothed section of the gear 3. The size of the radial gap 10 can also vary in a longitudinal direction, tapering towards a large-diameter end of the pinion gear 3.

In fig. 3 it can also be seen how the opening 9 is formed to allow the pinion gear 3 to mesh with the gear element 7 (crown gear). The gear pump housing 8 in the embodiment of fig. 3 envelops the pinion gear 3 along at least 240° of the circumference of the pinion gear 3.

In fig. 4 and fig. 5 the form of the opening 9 can be seen. Fig. 4 shows a perspective view, while fig. 5 shows the view D according fig. 4.

Fig. 2 discloses another preferred embodiment of the invention: The gear pump housing 8 is attached to the pinion bearing housing 5 by means of a cold-forming or snap-on connection 14. The gear pump housing 8 is made from a sheet metal part by deep-drawing. At an axial end region (the large- diameter end), the gear pump housing 8 has a projecting portion extending radially inwardly. The pinion bearing housing 5 has a congruent ring-shaped groove in a cylindrical section. Thus, the gear pump housing 8 can be pushed axially onto the pinion bearing housing 5 until the projecting portion 16 snaps into the ring-shaped groove 15 in the housing 5.

In figures 6 till 8 another embodiment of the invention is shown. Here, the pinion 2 is supported again by two taper roller bearings 6' and 6'". In this case the two bearings 6', 6'" are arranged in an "X" configuration. Furthermore, one of the bearings - the left bearing 6'" - is designed as a nose bearing supporting the corresponding axial end of the pinion 2.

Another feature of this solution is that the pinion bearing housing 5 has an elongated housing structure 13 for supporting the outer ring of the bearing 6'". For this, a circular opening 12 is formed in the housing structure 13.

Thus, to exclude an additional pump for the lubrication of the pinion gear 3 / crown gear 7 support bearings and heat transfer of the gear contacts as a result of downsizing a differential with the same output torque with optimized efficiency, the pinion gear 3 can also directly function as a (low) pressure pump by applying the dedicated housing 8 around the pinion gear 3.

The housing has the opening 9 to drive the crown gear 7, which opening serves as a pump inlet, and at the remaining covered part of the pinion gear 3 the enveloping circumference is designed such that a gradual pressure buildup takes place. Suitably, the pump outlet 17 is provided in a region of the housing 8 where maximum lubricant pressure is generated. The pump outlet 17 has one or more lubrication connections, such as tubes, which are arranged such that pressurized lubricant can be supplied to the support bearings of the crown and pinion gear and the gear contacts.

Reference Numerals:

1 Differential gear unit

2 Pinion

3 Pinion gear

4 Pinion shaft

5 Pinion bearing housing

6' Bearing arrangement

6" Bearing arrangement

6'" Bearing arrangement

7 Gear element (crown gear)

8 Gear pump housing

9 Opening (Pump inlet)

10 Radial gap

1 1 Axis

12 Circular opening

13 Housing structure

14 Snap-on connection

15 Ring-shaped groove

16 Projecting portion

17 Pump outlet

e Eccentricity D Medium diameter of the pinion gear

Claims

Claims:

1. Differential gear unit (1), especially for a vehicle, having a pinion (2) with a pinion gear (3) and a pinion shaft (4), wherein the pinion shaft (4) is supported in a pinion bearing housing (5) by means of a bearing arrangement (6', 6") and wherein the pinion gear (3) meshes with a gear element (7) which drives a housing of a bevel gear arrangement,

characterized in that

the pinion gear (3) is surrounded at least partially by a gear pump housing (8), wherein the gear pump housing (8) has at least one opening (9) for allowing the meshing contact between the pinion gear (3) and the gear element (7).

2. Differential gear unit according to claim 1, characterized in that the gear pump housing (8) is formed to leave a varying radial gap (10) between the pinion gear (3) and the gear pump housing (8).

3. Differential gear unit according to claim 2, characterized in that the size of the radial gap (10) changes in a circumferential direction of the pinion gear (3).

4. Differential gear unit according to claim 2 or 3, characterized in that the size of the radial gap (10) changes in a longitudinal direction of the pinion gear (3).

5. Differential gear unit according to at least one of claims 2 till 4, characterized in that the gear pump housing (8) has a substantially circular cross-section and is arranged eccentrically (e) to the axis (1 1) of the pinion gear (3).

6. Differential gear unit according to at least one of claims 2 till 4, characterized in that the gear pump housing (8) has a non-circular cross- section and is arranged concentrically with the axis (1 1) of the pinion gear (3).

7. Differential gear unit according to at least one of claims 2 till 6, characterized in that the size of the radial gap (10) varies between 0.5 % and 10 % of the medium diameter (D) of the pinion gear (3).

8. Differential gear unit according to at least one of claims 1 till 7, characterized in that the gear pump housing (8) is provided with a pump outlet (17).

9. Differential gear unit according to claim 8, characterized in that the pump outlet (17) is arranged in the bottom region of the gear pump housing (8).

10. Differential gear unit according to at least one of claims 1 till 9, characterized in that the gear pump housing (8) covers the pinion gear (3) along at least 240° of the circumference of the pinion gear (3).

11. Differential gear unit according to at least one of claims 1 till 10, characterized in that the bearing arrangement (6', 6") comprises two bearings arranged coaxially.

12. Differential gear unit according to at least one of claims 1 till 11, characterized in that the bearing arrangement (6', 6") is a roller bearing arrangement.

13. Differential gear unit according to claim 12, characterized in that the roller bearing arrangement (6', 6") consists of taper roller bearings.

14. Differential gear unit according to at least one of claims 10 till 13, characterized in that one bearing (6'") supports the pinion (2) at an axial end of the pinion (2) where the pinion gear (3) is arranged, wherein the gear pump housing (8) has a circular opening (12) at the location of this bearing (6'").

15. Differential gear unit according to claim 14, characterized in that the gear pump housing (8) is formed by a housing structure (13) for supporting the bearing (6'").

16. Differential gear unit according to claim 15, characterized in that the gear pump housing (8) forms one piece with the housing structure (13) and the pinion bearing housing (5).

17. Differential gear unit according to claim 16, characterized in that the one- piece housing is made from a ferrous or non-ferrous casting.

18. Differential gear unit according to at least one of claims 1 till 13, characterized in that the gear pump housing (8) is connected to the pinion bearing housing (5) by means of a snap-on connection (14).

19. Differential gear unit according to claim 18, characterized in that the pinion bearing housing (5) has a ring-shaped groove (15) in which a projecting portion (16) of the gear pump housing (8) is inserted.

20. Differential gear unit according to at least one of claims 1 till 14, claim 18 or claim 19, characterized in that the gear pump housing (8) is made from sheet metal.