WO2009012792A1

WO2009012792A1 - A differential housing and a crown for a differential gearbox in a vehicle

Info

Publication number: WO2009012792A1
Application number: PCT/EP2007/006542
Authority: WO
Inventors: Hendrikus Jan Kapaan; Jacobus Zwarts; Carl Petrus Antonius Visser
Original assignee: Ab Skf
Priority date: 2007-07-23
Filing date: 2007-07-23
Publication date: 2009-01-29

Abstract

The present invention concerns a differential gearbox for a vehicle, comprising a housing (1) accommodating two opposite side gears (16) on a common shaft axis for driving two axle shafts (14) and at least one planet gear (15) between the side gears and a crown gear (2) mounted on the housing for receiving torque from the vehicle engine via a pinion gear or intermediate gear for driving the axle shafts, wherein the housing is provided with a polygon- shaped crown gear receiving surface (4) concentric with the shaft axis, where said polygon receiving surface is tapered relative to said shaft axis, and wherein the crown gear is provided with a corresponding tapered polygon- shaped bore (5).

Description

A DIFFERENTIAL HOUSING AND A CROWN FOR A DIFFERENTIAL GEARBOX IN A VEHICLE

TECHNICAL FIELD

The present invention relates to a differential gearbox for a vehicle, the differential gearbox comprising a differential housing and a crown gear, and is more particularly directed to the means by which the crown gear is mounted to the housing. 0

BACKGROUND

In a vehicle, the differential allows each of the driving wheels to rotate at different speeds, while supplying equal torque to each of them. A pair of wheels on axle of a vehicle may rotate at different speeds, especially when turning corners. The 5 differential is designed to drive a pair of wheels with equal force, while allowing them to rotate at different speeds. Power is supplied from the engine, via the gearbox directly to the differential housing for front wheel driven axle, or to a propeller shaft, which drives the differential of a rear axle. A pinion gear at the end of the propeller shaft engages with the large crown gear on the differential housing. The crown gear0 is attached to the housing, which holds a set of small planet gears. Typically two or more planet gears are set up in such a way that the two side gears can rotate in opposite directions relative to each other. The two side gears drive the axle shafts to each of the wheels. The entire differential housing rotates in the same direction as the crown gear, but within that motion, the side gears can counter-rotate relative to5 each other.

DISCLOSURE OF THE INVENTION

According to the invention, there is provided a differential gearbox for a vehicle, the differential comprising a housing accommodating two opposite side gears on a0 common shaft axis for driving two axle shafts and at least one planet gear between the side gears and further comprising a crown gear, with bevel, helical, spur or any other gear teeth configuration, mounted on the housing for receiving torque from the vehicle engine via a pinion gear or intermediate gear with mating gear teeth, wherein the housing is provided with a polygon-shaped crown gear receiving surface concentric with the shaft axis, where said polygon receiving surface is tapered relative to said shaft axis, and wherein the crown gear is provided with a corresponding tapered polygon-shaped bore.

Hereby, a polygon mounting connection is provided having a high torque transmission capacity. The cross-sections of the polygon torque connection are executed using smooth polygon profiles, i.e. the receiving surface has convex surfaces and the grown gear bore has congruent concave surfaces. Consequently, there are no sharp corners whereby stress concentration points in the crown gear are significantly reduced. The polygon profile can have two or more lobes evenly spaced around the circumference.

Moreover, the polygon mounting connection is self-centering. This self-centering characteristic offers a good balance in the power transmission to the crown gear and thereby to the differential gearbox at high speeds. The close fits of polygon profiles and in particular the tapering of the polygon-shaped mounting surface on the differential housing and the corresponding bore of the crown gear provide optimal stiffness resulting in minimal gear backlash. This minimal gear backlash and high strength of the polygon crown gear mounting results in a crown gear fixation capable of withstanding great shock loads under extreme torque conditions, e.g. during braking and acceleration of the vehicle.

By a differential gearbox according to the invention, a rigid mounting of the crown gear is realized. Moreover, the need for fixation by e.g. a series of bolts may be eliminated by the tapered mounting surfaces, as the pinion exercises a force on the crown gear which retains the crown gear in its predetermined position, since the tapered polygon bore is tapered towards the side of the crown gear which is provided with teeth.

To achieve a self-locking connection, the tapered polygon crown gear mounting may be executed with a tapering angle of less than 6 degrees. In a preferred embodiment, the tapering angle is between 2.5 and 3 degrees, as this eliminates the need for additional axial fixation of the crown gear on the housing by means of e.g. bolts or welding. If a detachable connection is desired, the polygon mounting connection may be provided with a tapering angle of at least 6 degrees, in which case the mounting connection may be secured by mechanical locking means, e.g. bolts, or by means of energy welding, e.g. laser spot welding.

In an embodiment of the invention, the receiving surface is provided on a radial flange portion on the housing. Preferably, this radial flange portion has the largest radial dimension on the housing. Hereby, the crown gear can easily be mounted over the housing for the fixation of the crown gear on the receiving surface.

The differential housing may be provided with bearing support at one side of the crown gear or at both sides of the gear. In one embodiment, a one-sided bearing support may comprise a unitized pre-loaded bearing with a flanged inner ring for the fixation onto the differential housing. In a further embodiment, the flange portion of the inner ring may be provided with a tapered polygon surface to receive the crown gear. In a still further embodiment, the housing may serve as the bearing inner ring, by providing at least one bearing raceway on a carrier portion of the housing. In the aforementioned embodiments, the inner ring is rotatable and the outer ring is mounted to a non-rotating component. Alternatively, the one-sided and/or two-sided bearing support may be provided by means of one and/or two bearings with outer ring rotation.

According to the invention, the differential housing can be made of a cast ferrous or non-ferrous metal, ferrous or non-ferrous sheet metal, carbon fibre or a combination of these.

In a further embodiment of the invention, the differential housing can be equipped with sensors, e.g. speed sensors or load sensors with wired or wireless data transmission for monitoring the speed or torque data.

BRIEF EXPLANATION OF THE DRAWINGS

In the following, the invention is described with reference to the accompanying drawings, in which: Fig. 1 is a cross-section of a differential gearbox housing according to an embodiment of the invention with the crown gear mounted thereon; fig. 2 is a perspective view of a differential gearbox housing according to a preferred embodiment of the invention; fig. 3 is a cross-section side view of the housing in fig. 2; fig. 4 is an end view of the housing in fig. 2; fig. 5 is a perspective view of a crown gear according to a preferred embodiment of the invention; fig. 6 is a cross-section side view of the crown gear in fig. 5; fig. 7 is an end view of the crown gear in fig. 5; fig. 8 is a cross-section of a differential gearbox according to an embodiment of the invention with a side-mounted crown gear on the differential housing, fig. 9 is a cross-section of a differential gearbox according to another embodiment of the invention with a centrally mounted crown gear on the differential housing; fig. 10 is an end view of the housing in fig. 9; fig. 11 is an end view of the differential gearbox in fig. 9; figures 12 to 15 show an embodiment of the invention involving a crown gear and differential housing having two lobes.

MODES FOR CARRYING OUT THE INVENTION

In figures 1 or 8, a differential gearbox housing 1 for a rear wheel driven axle is shown where a crown gear 2 is mounted on the outside of the housing concentric with axle shafts 14 accommodated in housing portions 13. A differential gearbox allows each of the driving wheels to rotate at different speeds, while supplying equal torque to each of them. A pair of wheels on the axle of a vehicle may rotate at different speeds, especially when turning corners. Power is supplied from the engine, via the gearbox to a propeller shaft 21 , which runs to the axle. A pinion gear 20 at the end of the propeller shaft 21 engages with the large crown gear 2 on the differential housing 1. The crown gear 2 is attached to the housing 1 , which holds a set of small planet gears 15 rotatably mounted on a shaft 12' (see fig. 12 or 13) in support openings 12 in the housing 1. Typically, two or three planet gears 15 are set up in such a way that the two side gears 16 can rotate in opposite directions relative to each other. The two side gears 16 drive the axle shafts 14 to each of the wheels. The entire differential housing 1 rotates in the same direction as the crown gear 2 about the same axis, but within that motion, the side gears 16 can counter-rotate relative to each other.

With reference to figures 2 to 4, the housing 1 is provided with a mounting flange 3 having an exterior receiving surface 4 which is tapered at an angle v. Thus, the receiving surface 4 has a large diameter end which tapers towards a small diameter end. As shown in figures 5 to 7, the crown gear 2 is provided with a corresponding bore 7 which has a tapered mounting surface 5. The crown gear bore 7 also has a large diameter end which tapers towards a small diameter end, with a tapering angle v. The large and small diameter ends of the receiving surface 4 and the crown gear bore 7 are arranged such the small diameter end is located at a toothed side 6 of the crown gear 2.

To facilitate the transmission of torque, the tapered receiving surface 4 on the housing 1 and the tapered mounting surface 5 on the crown gear 2 have corresponding polygonal cross-sections. According to one embodiment as shown in fig. 4, the polygon shape of the receiving surface 4 of the flange 3 on the housing 1 is generally triangular with smooth rounded surfaces. The polygon has three lobes 8 evenly spaced apart. Between the lobes 8, convex surfaces 9 are formed. Referring to fig. 7, the bore 7 in the crown gear 2 is provided with a congruent polygon shape with three lobes 10 with concave surfaces 11 therebetween. A polygon with three lobes is particularly advantageous when the differential housing 1 accommodates three planet gears 15. Some heavy-duty vehicles have a differential gearbox with four planet gears, in which case a polygon with four lobes is advantageous. Thus, the number of lobes 8 on the mounting flange 3 and the number of lobes 10 in the crown gear bore 7 may correspond to the number of planet gears 15.

With reference to figures 12 to 15, the differential housing 1 may be provided with two lobes 8, as an alternative to the embodiment shown in figures 4 and 7. Accordingly, the crown gear 2 is provided with a polygon bore of a corresponding shape. As it may be appreciated by these two embodiments, the term "polygon" is to be understood in a broad sense, as any non-circular shape. The term "lobe" used in this patent specification is to be understood as a projection on a rotating element or a recess in the bore of a rotating element, where the projection or recess extends in a radial direction, thereby at least contributing to providing the element or the bore with a non-circular cross-section.

The mounting flange 3 extends radially so that the receiving surface 4 on the flange defines the outermost contour of the housing 1 when viewed from an axial side (see fig. 4). This ensures an easy mounting of the crown gear 2 onto the housing 1. The mating tapered surfaces 4 and 5 are inclined at an angle of approximately 2-3 degrees, enabling straightforward mounting and locking of the crown gear 2 on the mounting flange 3 of the housing 1.

Since the inclination of the tapered mating surfaces 4, 5 is such that the distance to an axial centreline decreases in the direction of the crown gear teeth 6, the pinion 20 in propelling the crown gear 2 with power from the engine of the vehicle (via the gearbox) exercises a lateral force on the crown gear 2 maintaining the crown gear 2 in position on the tapered receiving surface 4 on the housing flange 3, as this force "pushes" the crown gear towards the large diameter end of the mating tapered surfaces 4, 5. This simplifies the assembly process as the tapered mating surfaces 4, 5 in principle eliminate the need for fasteners such as bolts for fixing the crown gear 2 to the housing 1 and also ensure a self-centering of the crown gear 2 on the receiving surface 4 due to the polygon cross-sectional shape. The pinion 20 and the crown gear 2 may be provided with bevel, spiral bevel, spur or helical teeth configuration.

The crown gear 2 may be directly mounted on a tapered polygon surface 4 on the housing 1 or a flange 3 thereon, or could be mounted with an intermediate part there between. Accordingly, the tapered polygon receiving surface 4 in this embodiment should be provided on said intermediate part.

Figure 8 illustrates an embodiment of a differential gearbox according to the invention for a driven rear axle, where the gearbox comprises a cast iron differential housing 1 and where the housing 1 is provided with bearing support 17 at both sides of the crown gear 2. The bearings 17 in this embodiment are configured for inner ring rotation. The crown gear 2 may be side-mounted on the housing 1 as shown in figure 8 or centrally mounted as shown in figure 9. Figures 9 to 11 illustrate an example of a differential gearbox that is suitable for a driven front axle. In this example, the differential housing 1 is made of sheet metal and has bearing support 17 at both sides of the crown gear 2, where the bearings 17 are configured for outer ring rotation.

Above, some preferred embodiments of the invention are described, but it is to be understood that other embodiments may be provided without departing from the scope of the invention as defined in the accompanying claims.

Claims

Patent Claims:

1. A differential gearbox for a vehicle, comprising a differential housing (1) accommodating two opposite side gears (16) on a common shaft axis for driving two axle shafts (14) and accommodating at least one planet gear (15) between the side gears (16) and further comprising a crown gear (2) mounted on the differential housing for receiving torque from the vehicle engine for driving the axle shafts, characterized in that the differential housing (1) is provided with a polygon-shaped crown gear receiving surface (4) concentric with the shaft axis, where said polygon receiving surface is tapered relative to said shaft axis, and that the crown gear (2) is provided with a correspondingly tapered polygon-shaped bore

(5).

2. A differential gearbox according to claim 1 , wherein the tapering angle is less than approximately 6 degrees, preferably between 2.5 and 3.0 degrees.

3. A differential gearbox according to claim 1 , wherein the tapering angle is larger than approximately 6 degrees.

4. A differential gearbox according to any of the preceding claims, wherein the tapered polygon bore (5) is tapered towards a toothed side (6) of the crown gear (2).

5. A differential gearbox according to any of the preceding claims, wherein the receiving surface (4) is provided on a radial flange portion (3) of the housing (1 ).

6. A differential gearbox according to claim 5, wherein said radial flange portion (3) has the largest radial dimension on the housing (1).

7. A differential gearbox according to any of the preceding claims, wherein the polygon receiving surface (4) is provided with two or more lobes (8) for the transmission of torque.

8. A differential gearbox according to claim 7, wherein the polygon shape comprises three evenly radially spaced lobes (8), preferably with exclusively convex surfaces (9) therebetween.

9. A differential gearbox according to claim 7 or 8, wherein the number of lobes (8) corresponds to the number of planet gears (15) of the differential gearbox

10. A differential gearbox according to any of the preceding claims, wherein the differential housing (1) is made of a cast ferrous metal, such as cast iron.

11. A differential gearbox according to any of claims 1 to 10, wherein the differential housing (1) is made of a cast non-ferrous metal.

12. A differential gearbox according to any of claims 1 to 10, wherein the differential housing (1) is made of a ferrous or non-ferrous sheet metal, or carbon fibre or a combination thereof.

13. A differential gearbox according to any of the preceding claims, wherein the differential housing (1) is equipped with sensors, such as speed sensors or load sensors with wired or wireless data transmission for monitoring the speed or torque characteristics in the differential gearbox.

14. A differential gearbox according to any of the preceding claims, wherein the differential housing (1) is mounted on at least one differential bearing support (17).

15. A differential gearbox according to claim 14, wherein a carrier portion of the differential housing (1 ) is provided with at least one bearing raceway.

16. A differential gearbox according to claim 14, wherein a differential bearing support (17) is provided on the differential housing (1) at both sides of the crown gear (2).

17. A differential gearbox according to claim 14, wherein the crown gear (2) is fitted directly on the differential housing (1 ) or on a flanged inner ring of a bearing (17), where the housing is adapted for a one-sided differential bearing support.

18. A differential housing, wherein the differential housing (1) comprises a tapered receiving surface (4) for the fixation of a crown gear (2), said receiving surface (4) having a polygon-shaped cross-section.

19. A differential housing according to claim 18, wherein the differential housing (1 ) forms part of a differential gearbox according to any of claims 1 to 17.

20. A crown gear, wherein the crown gear (2) has a tapered bore (7) with a polygon- shaped cross-section.

21. A crown gear according to claim 20, wherein the crown gear (2) forms part of a differential gearbox according to any of claims 1 to 17.