GB2202010A - Lubrication of motor vehicle transmission units - Google Patents

Abstract

A transmission unit, e.g. an axle differential unit, for a motor vehicle comprises a housing containing gearing means (13) including a rotary element (14) supported by taper roller bearings (16, 17) and a chamber (26) arranged to receive lubricant pumped by one (17) of said bearings. From the chamber, lubricant flows to an external cooler, e.g. a simple pipe (28), and thence is returned to the housing. <IMAGE>

Description

LUBRICATION OF MOTOR VEHICLE TRANSMISSION UNITS This invention relates to a transmission unit for a motor vehicle, and more particularly to the lubrication thereof. The invention has been developed in relation to a transmission unit which is an axle differential unit providing for power transmission between an input, which will usually be arranged to be connected to a propeller shaft extending longitudinally of the vehicle, to two laterally extending outputs arranged to be connected to a pair of the vehicle's wheels.

An axle differential unit for a motor vehicle usually comprises a crown wheel and pinion gearing, of which the pinion is on an input shaft and the crown wheel is rotatable about a transversely extending axis. The crown wheel has associated with it a differential gearing to provide for the necessary differential action between the outputs to the wheels of the vehicle. All this gearing is lubricated by a quantity of liquid lubricant contained within a housing of the unit, ana there have been many proposals for arrangements by which the lubricant is circulated in the housing to ensure that all the operative parts are properly lubricated. In use, considerable heat may be generated, particularly under conditions of sustained high speed driving, and accordingly it is desirable to provide the unit with some means by which the lubricant can be cooled.

It is the object of the present invention to provide a simple and effective means for cooling the lubricant in a transmission unit such as an axle differential unit.

According to the present invention, we provide a transmission unit for a motor vehicle, comprising a housing containing gearing means including a rotary element supported by taper roller bearings; and a quantity of liquid lubricant in the housing for lubricating said gearing means and bearings, wherein there is provided a formation arranged to receive lubricant pumped by at least one of said bearings, and a passage for flow of said lubricant from said formation to the exterior of the housing, through a cooling element, and thence back into the lubricant contained in the housing.

The invention makes use of the well known property of a taper rolling bearing that, somewhat in the manner of a centrifugal pump, it will pump oil from the smaller diameter of the rollers to the larger diameter thereof.

If a formation for receiving such lubricant, e.g. an annular space surrounding the rotary element which the bearing supports, is provided at the end of the bearing having the larger diameter of the rollers, a significant flow of lubricant will result through any passage leading from such formation. It is relatively straightforward to arrange for such lubricant to flow through a cooler before returning to the main body of lubricant contained within the housing of the unit.

In an axle differential unit, the pinion shaft is usually supported by taper roller bearings and the unit is usually designed to ensure a good flow of lubricant to such bearings which are heavily loaded in use. It has hitherto been usual to provide for return flow of lubricant from such bearings to the main body of lubricant in the housing of the unit by way of an internal passage or passages incorporated in such housing. In a unit according to the invention, however, such return flow of lubricant may be by way of an external pipe constituting the cooling element. In practice, it is not likely to be necessary to provide a cooler of complex form, since merely a length of external pipe will provide sufficient cooling of the lubricant.

A taper roller bearing does not generate a very large head as a result of its centrifugal pumping action on the lubricant. Accordingly, when the unit is cold and the lubricant relatively viscous, a great flow will not occur through the cooler. However, when the unit is hot and the lubricant less viscous, significant flow through the cooler will occur so that lubricant temperature does not rise excessively.

The invention will now be described by way of example with reference to the accompanying drawings, of which: Figure 1 is a section through part of an axle differential unit according to the invention; Figure 2 is a section on the line A-A of Figure 1.

Referring firstly to Figure 1, there is shown part of an axle differential unit for a motor vehicle, which unit provides, in known manner, for power transmission between an input, which is arranged to be connected to a propeller shaft extending longitudinally of the vehicle, and two laterally extending outputs arranged to be connected to a pair of the vehicle's wheels. For a vehicle with independent suspension for the pair of wheels, the outputs would be arranged to be connected to universally jointed drive shafts through which such wheels are driven, while the axle differential unit is fixed to the vehicle structure. It is to be appreciated, however, that the invention is applicable to other types of axle differential unit, e.g. live axles, and more broadly to transmission units generally wherein the problem overcome by the invention arises.

The illustrated axle differential unit comprises a housing with a forward part 10 and a detachable rear part 11 assembled thereto. The housing contains a crown wheel and pinion gearing of which the crown wheel, not shown, is rotatable about an axis 12 which extends transversely of the vehicle in use, and meshes with a pinion 13 at the end of a pinion shaft 14 rotatable about axis 15. Axis 15 does not intersect axis 12, and the crown wheel and pinion may be of hypoid type. Associated with the crown wheel, and also not shown, there would be provided a differential gearing which permits the necessary differential action between the outputs from the unit, which outputs would also be rotatable about the axis 12.

The pinion shaft 14 is supported for rotation about the axis 15 by two taper roller bearings 16, 17 each of which has an inner race on shaft 14 and an outer race held in the housing part 10. The end of shaft 14 remote from the pinion 13 carries a drive element 18, engaging splines 19 on the shaft and held thereon by a nut 20.

The drive element 18 is arranged for torque transmitting connection to a propeller shaft, e.g. by way of splines 21. An oil seal 22 is held in the housing, and co-operates with the drive element 18 to prevent escape of lubricant where the latter emerges from the housing.

The part 10 of the housing defines, above the part of shaft 14 adjacent the pinion 13, a passage 23 having a mouth 24 facing the periphery of the crown wheel not shown. Passage 23 leads to an annular chamber 25 surrounding shaft 14 between the bearings 16, 17. A further annular chamber 26 is defined by the housing between the bearing 17 and the oil seal 22. A union 27 is fitted to the housing at the lowermost part of chamber 26, and provides a passage leading to an external pipe 28.

Pipe 28 leads to a further union 29 fitted to the side of the rear part 11 of the housing.

A quantity of liquid lubricant is contained within the housing 10, 11 for lubricating the crown wheel and pinion gearing, and the differential gearing, contained therein. Usually the static level of such lubricant will be somewhat below the axis of rotation 15 of the pinion 13, but in use such lubricant will be thrown around inside the housing, particularly by the crown wheel therein. Because the mouth 24 of passage 23 is in alignment with the periphery of the crown wheel, a significant quantity of the lubricant will enter the passage 23 and annular chamber 25, as indicated by the arrows in the drawing.

As is well known, the taper roller bearings 16, 17 act somewhat in the manner of centrifugal pumps to pump lubricant from the smaller diameter ends thereof to the larger diameter ends. Lubricant thus pumped through the bearing 16 is returned immediately to the quantity of lubricant within the housing, whereas lubricant pumped through the bearing 17 enters the annular chamber 26 and thence flows through the union 27 and pipe 28. From pipe 28, such lubricant re-enters the housing by way of union 29 in the rear portion of the housing.

By virtue of passing through the external pipe 28, the lubricant which is pumped by the bearing 17 will lose heat to the external atmosphere. In practice, it is believe sufficient cooling will be provided merely by the length of pipe 28 on the outside of the housing, and it will be unnecessary to provide any additional cooler in the pipe or equip the pipe with fins or gills to assist cooling. It will be appreciated, however, that such expedients could be adopted if exceptionally severe operational conditions are encountered.

Claims (6)

1. A transmission unit for a motor vehicle, comprising a housing containing gearing means including a rotary element supported by taper roller bearings; and a quantity of liquid lubricant in the housing for lubricating said gearing means and bearings, wherein there is provided a formation arranged to receive lubricant pumped by at least one of said bearings, and a passage for flow of said lubricant from said formation to the exterior of the housing, through a cooling element, and thence back into the lubricant contained in the housing.

2. A unit according to Claim 1 which is an axle differential unit containing a crown wheel and pinion gearing and a differential gearing.

3. A unit according to Claim 2 wherein said pinion is on a shaft supported by taper roller bearings, and said formation is arranged to receive lubricant pumped by one of said bearings.

4. A unit according to Claim 3 wherein said formation comprises an annular chamber surrounding said pinion shaft.

5. A unit according to any one of the preceding claims wherein said cooling element comprises an external pipe.

6. An axle differential unit substantially as hereinbefore described with reference to the accompanying drawings.