Transmission system

A transmission system includes a housing having a sump. A crown wheel and pinion are positioned within the housing. The transmission system further includes a reservoir having an inlet system and an outlet system. Rotation of the crown wheel causes the oil to be transferred from the sump to the reservoir via the inlet system, and the outlet system allows oil to pass from the reservoir to the sump.

RELATED APPLICATION

This is the U.S. national phase of PCT/IB2010/051106 filed 15 Mar. 2010, which claims priority to EP 09155395.8, filed 17 Mar. 2009.

TECHNICAL FIELD

The present invention relates to a transmission system, in particular a transmission system including a crown wheel and pinion, especially a transmission system including a crown wheel and pinion in an axle housing.

BACKGROUND OF THE INVENTION

A driven axle for automotive vehicles is known whereby a drive shaft aligned generally longitudinally relative to the vehicle drives a pinion which is in meshing engagement with a crown wheel in an axle housing. The crown wheel drives a right hand drive shaft connected to a right hand wheel and also drives a left hand drive shaft connected to a left hand wheel, thereby propelling the vehicle. Typically the crown wheel will drive the right and left hand drive shafts via a differential assembly.

In order to ensure longevity of the crown wheel and pinion gears, it is important to ensure that the pinion is positioned in the correct longitudinal position relative to the crown wheel, and it is also important to ensure that the crown wheel is positioned at the correct lateral position relative to the pinion. For these reasons, typically the pinion will be shimmed to ensure it is in its correct longitudinal position. Typically, screw thread adjustments can be made to move the crown wheel laterally to ensure that it is also in its correct lateral position. In view of the necessary accuracy required for positioning of the crown wheel and the pinion, these components are typically mounted on a carrier as a sub-assembly. The correct positioning of the crown wheel and pinion can therefore be achieved on the carrier remotely from the associated vehicle, for example on a workbench. Once the settings have been correctly carried out, the sub-assembly of the carrier, crown wheel and pinion can then be fitted to the vehicle. By providing a carrier sub-assembly including a crown wheel and pinion, the crown wheel and pinion can be correctly positioned relative to each other in a clean environment, and then the carrier can be fitted to the vehicle with the fitting taking place in a traditionally less clean environment, typically beneath the vehicle where road dirt and the like will have accumulated.

In most vehicles the carrier sub-assembly will include a differential assembly, and as such the carrier is known as a “differential carrier”.

Such carriers or differential carriers will include a generally circular flange. The carrier sub-assembly will be assembled into the axle through a generally circular hole in the axle. The crown wheel, pinion and differential (if fitted) will pass through the hole in the axle and the carrier flange will then effectively close off the hole. Typically a series of bolts will fix the carrier flange to the axle.

Oil is provided in the axle housing for lubricating and cooling the crown wheel, pinion, differential gears and associated bearings. However, the rotation of the crown wheel, pinion and differential housing in this oil leads to power losses due to oil churning, thereby increasing the overall fuel consumption of the vehicle.

SUMMARY OF THE INVENTION

A transmission system includes a housing having a sump. A crown wheel and pinion are positioned in the housing. The transmission system further includes a reservoir having an inlet system and an outlet system. Rotation of the crown wheel causes the oil to be transferred from the sump to the reservoir via the inlet system, and the outlet system allows oil to pass from the reservoir to the sump.

Advantageously, storing of oil in the reservoir means that that stored oil can no longer be churned by the crown wheel, pinion, etc., and as such churning losses are reduced.

The housing may contain the reservoir. Advantageously, by positioning the reservoir in the housing, the reservoir is protected from the environment. Furthermore, it is not necessary to provide space outside of the housing for the reservoir.

The reservoir may be C-shaped. Advantageously, the reservoir can be fitted around the differential and/or around a drive shaft. One arm of the C-shaped reservoir may be positioned above the differential and/or drive shaft, while another arm of the C-shaped reservoir may be positioned below the differential and/or drive shaft.

The reservoir may include a wall that faces teeth of the crown wheel.

A lower portion of the reservoir may be positioned in the sump. Thus, by positioning part of the reservoir in the sump, and then partially or fully filling the reservoir results in lubricant being positioned in the reservoir in the sump and therefore the oil cannot be churned. This reduces churning losses as positioning part of the reservoir within the sump reduces the volume of churnable oil in the sump.

The housing may be defined by an axle housing having an opening sized to receive the crown wheel and a carrier upon which the crown wheel and pinion are mounted, the carrier having a flange sized to substantially close the opening.

The reservoir may be mounted on the carrier. When the reservoir is mounted on the carrier, it is possible to perform this mounting operation away from the associated axle, typically in a clean environment such as on a workbench. Thus, the reservoir system and any associated inlets, outlets, adjustable outlets, motors or flexible shafts or the like can be set up and tested away from the axle. Once the reservoir and its associated system is fully functional and tested, the carrier sub-assembly can be mounted onto the axle.

The outlet system may be selectively variable to vary the amount of lubricant flowing from the reservoir to the sump. Advantageously, depending upon the working conditions of the associated vehicle, by reducing the amount of oil flow from the reservoir, the reservoir will progressively fill, thereby reducing churching losses. Alternatively, when conditions require more oil in the sump, the opening in the reservoir can be opened thereby allowing more oil to flow from the reservoir into the sump, thereby better lubricating the crown wheel, pinion, etcetera.

The outlet system may be varied to substantially prevent any lubricant flowing from the reservoir to the sump. Advantageously, by preventing oil flowing from the reservoir to the sump, the reservoir will progressively fill and the sump will progressively empty to a particular level. This reduces churning losses.

The outlet system may comprise an orifice and a closure moveable to vary the amount of lubricant flowing from the reservoir to the sump.

The closure may be linearly slideable.

The closure may be rotatable to close the orifice.

The outlet system may include a permanent metered orifice. Advantageously, by providing a permanent meted orifice in the event of a malfunction of the outlet system of the reservoir, a continuous supply of lubricant can be fed from the reservoir to the sump. Typically, the continuous supply may be relatively small. Such a system will ensure a continuous supply of oil to the sump.

The metered orifice may be at a lower portion of the reservoir.

The metered orifice may be in the closure.

The inlet system may include a scoop.

The scoop may be positioned at the top of the crown wheel.

The opening of the housing may be generally circular and may include an upper notch sized to receive the crown wheel, the scoop being positioned within the upper notch.

Typically the diameter of the crown wheel is larger than the diameter of the opening in the axle housing. It is for this reason that a notch is provided so that when the carrier (or differential carrier) is assembled onto the axle the crown wheel can pass through the opening. By positioning the scoop within the upper notch, the scoop is positioned in an area where it will readily capture oil spun off from the crown wheel. The scoop is further positioned at a pre-existing notch which is necessary in order for the crown wheel to be assembled into the axle.

The crown wheel may include crown wheel teeth defining a crown wheel tooth plane. The reservoir has a generally vertical wall facing the crown wheel teeth, which defines a plane of the reservoir wall. The scoop projects into the space defined between the crown wheel tooth plane and the plane of the reservoir wall.

As such, the scoop is positioned where it will readily receive lubricant thrown off the crown wheel, and hence cause the reservoir to fill relatively quickly.

The transmission system may include lubricant, in particular liquid lubricant such as oil, wherein the amount of lubricant within the housing is greater than the capacity of the reservoir.

Where the amount of oil in the housing is greater than the capacity of the reservoir, even if the reservoir is filled with oil, there will always remain an excess of oil for lubrication of the crown wheel, pinion, etcetera.

Where the transmission system includes a closure which is rotatable to close the orifice, the closure may be rotatable about a first axis by a flexible drive. The flexible drive has an end remote from the closure that is rotatable about a second axis. The first axis is different from the second axis. Said end may be rotatable by an actuator. The actuator may be mounted on a carrier, such as a differential carrier. The carrier may include a recess for receiving at least a part of the actuator.

A method of operating a transmission system is also provided, wherein the housing is defined by an axle housing having axle housing arms and which includes lubricant. The method comprises the steps of allowing the outlet system to equalize the lubricant level in the reservoir and the sump, operating the transmission system so that the lubricant level in the reservoir rises to a level above a lower edge of the axle housing arm, and alternatively operating the transmission system so the lubricant level in the reservoir rises to a level above an upper edge of the axle housing arm.

Providing a portion of the reservoir above the level of the lower edge of the axle housing arm, or providing a portion of the reservoir above the upper edge of the axle housing arm, creates the ability to store oil above these two levels without that oil passing into the axle housing arms and travelling toward the wheels.

A method of operating a transmission system is provided, wherein the transmission system includes lubricant. The method comprises the steps of allowing the outlet system to equalize the lubricant level in the reservoir and the sump, and operating the transmission system to fill the reservoir.

DETAILED DESCRIPTION

With reference toFIGS. 1 to 5there is shown a transmission system10having an axle housing12with a sump14. Rotatable in the axle housing is a crown wheel16which is driven by a pinion28.

The axle housing12has two axle housing arms12A and12B which receive drive shafts (not shown). Pinion28is driven by a central drive shaft (not shown) and has teeth which engage teeth16C on the crown wheel16. The crown wheel is attached to a differential assembly46. The crown wheel is positioned on the left side (when viewingFIG. 4) of the differential assembly46and the teeth16C face towards the pinion28and arm12A and therefore face away from arm12B.

The axle housing12includes a generally circular aperture48defined by a housing flange49on a front face (seeFIG. 5).

A carrier50includes a carrier flange52which, when bolted to the axle housing12against the housing flange49, substantially closes the aperture48. The axle housing and carrier thus define a housing13.

Mounted on the carrier is the pinion28, crown wheel16, differential assembly46, together with associated bearings in a manner known in the art.

A right hand drive shaft (not shown) extends from the differential assembly46through the axle housing arm12A and a left hand drive shaft (not shown) extends from the differential assembly46through the axle housing arm12B.

The housing flange49has an upper notch54and a lower notch55. The carrier flange52has an upper notch56and a lower notch57. The upper and lower notches56and57provide clearance between the crown wheel16and the flange52. When assembled, the upper and lower notches56and57of the carrier flange52are aligned with the upper and lower notches54and55of the housing flange49. The upper and lower notches54and55of the housing flange49provide clearance between the crown wheel16and the housing flange49.

The teeth on the crown wheel16together with the teeth on the pinion28together define a particular gear ratio of the combined crown wheel and pinion. In an alternate embodiment, a crown wheel and pinion may be fitted which have a higher overall ratio. In an alternative embodiment, a crown wheel and pinion may be fitted which have a lower overall gear ratio.

As shown inFIG. 4, the teeth16C define a plane P. A crown wheel and pinion with a higher gear ratio will have a corresponding plane P displaced to the left when viewingFIG. 4. A crown wheel and pinion with a lower gear ratio will have a corresponding plane P displaced to the right when viewingFIG. 4. Accordingly, the upper and lower notches54and55of the housing flange49and upper and lower notches56and57of the carrier flange52must be sized to accommodate all envisioned gear ratios for a particular axle housing12.

The transmission system10also includes a reservoir18.

When viewingFIG. 2, reservoir18is generally C-shaped having a main body portion19, a forwardly projecting upper arm20and a forwardly projecting lower arm21.

For the purposes of explanation, the axle housing12is assumed to be a rear axle housing of a vehicle, and as such the pinion is positioned in front of the differential. Under circumstances where the axle housing is a front axle housing, typically the differential will be positioned in front of the pinion.

The upper arm20includes an inlet system60and the lower arm21includes an outlet system70. The main body portion19has an arcuate surface22(FIG. 4) sized to pass through the generally circular aperture48. The main body portion also includes a generally vertical wall23which faces teeth16C. The wall23defines a plane R which is spaced from plane P. The wall23is positioned such that the teeth of the crown wheel16having the lowest gear ratio (i.e. the teeth of the crown wheel where plane P is closest to plane R) will nevertheless still provide a clearance between the teeth and the wall23. The main body portion19also has a contoured surface24(FIG. 1) shaped similarly to the adjacent internal surface of the rear of the axle housing.

Fixings (such as bolts25) secure the reservoir to a right hand differential bearing housing30(FIG. 2). In this case the differential bearing housing30is formed integrally with the carrier50.

The inlet system60is in the form of a scoop61which lies between the planes P and R. The scoop61is open on a rearwardly facing mouth portion62and also on a side face63which faces the teeth16C. As the crown wheel16rotates in a clockwise direction when the vehicle is moving in a forward direction (when viewingFIG. 2) a particular tooth16C will pass through the sump14thereby dipping into a liquid lubricant, in this case oil38, and this oil will adhere to the tooth and then be spun off due to centrifugal force. Some of the oil will be spun into the rearward facing mouth portion62of the scoop. That oil will then pass into the upper arm20and then into the main body portion19of the reservoir, as will be further described below.

The outlet system70comprises an orifice71in a lower portion of the reservoir. A closure72can be moved to a rearward position as shown inFIG. 2thereby exposing the orifice71and allowing oil to drain from the reservoir. Alternatively, the closure72can be slid to a forwards position, as shown inFIG. 3, thereby closing the orifice71. A rod73moves the closure72and an actuator74(shown schematically) operates to move the rod73.

The reservoir18can be made from various materials including plastic materials.

In one embodiment, the scoop61is sized so that the side face63lies close to the teeth of the crown wheel16having the highest gear ratio (i.e. when the plane P is displaced to the left when viewingFIG. 4). Depending upon the particular gear ratio used, it is then possible to modify the scoop61e.g. by trimming a portion so that the side face63of the trimmed scoop still lies close to the teeth of the crown wheel. Note that only a small trimming operation is required since the wall23is positioned such that there is a clearance between the wall23and the crown wheel16having the lowest gear ratio (i.e. where plane P is closest to plane R).

A controller, such as an ECU75controls the actuator74as will be further described below. The housing holds the oil38.

The components shown inFIGS. 1 and 3define a carrier sub-assembly, in this case a differential carrier sub-assembly40. The primary components of the sub-assembly are the carrier50, the pinion28, the crown wheel16and the reservoir18. In this case the sub-assembly includes the differential assembly46. Such a sub-assembly allows all the components shown inFIGS. 1 and 3to be assembled and tested in a clean environment prior to fitting to the axle.

Operation of a device is as follows.

Starting with the associated vehicle stationary and the orifice71open, as shown inFIG. 2, the oil level in the reservoir OR is the same as the oil level in the sump OS (FIG. 3). When the vehicle drives off, oil is picked up by teeth16C and some of the oil is centrifuged into the scoop61. It then falls, under gravity rearwardly along the upper arm20and into the main body portion19of the reservoir. However, since the orifice71is fully open, then any oil being transferred into the scoop61from the sump is immediately replaced by oil draining out of the reservoir. As such, oil continues to circulate through the reservoir maintaining the oil level in the sump at substantially the position OS shown inFIG. 2, i.e. the position when the vehicle is stationary.

Under these circumstances there is a plentiful supply of oil to the crown wheel, pinion, differential and bearings as is required under arduous driving conditions, e.g. when the crown wheel is transmitting high power and torque such as when the associated vehicle is a lorry which is fully laden and is ascending a hill. Thus, under these conditions churning power losses are relatively high, but nevertheless a plentiful supply of oil to the crown wheel and pinion is provided to ensure no damage occurs.

However, when driving conditions change and the crown wheel16is only required to transmit low power and low torque, then the ECU75will instruct the actuator74to move the closure72so as to close the orifice71. Under these circumstances oil entering the scoop61can no longer drain out of the outlet system70and the reservoir will progressively fill with oil, thereby reducing the level of oil in the sump. Ultimately, the reservoir will fill completely and the oil level in the reservoir will become OR, as shown inFIG. 3and the corresponding oil level in the sump will become OS, as shown inFIG. 3. As will be appreciated fromFIG. 3the oil level OS is still higher than the lowest point through which part of the teeth16C rotate. Under these circumstances the oil churning power losses are reduced. However, since only low power and low torque is being transmitted by the crown wheel, then the lowered oil level OS is still sufficient to properly lubricate components and ensure no damage occurs. An example of when the crown wheel transmits relatively low power and relatively low torque would be when the associated vehicle is a lorry carrying no load and driving along a flat hard road surface.

The ECU75is capable of determining operating conditions which require more oil in the sump and operating conditions which only require a lower level of oil in the sump. Thus, the ECU75could receive a signal from a torque meter. Alternatively, the ECU75could receive a signal from an accelerator pedal position sensor. Alternatively, the running condition of the engine (especially the engine RPM and the fuel flow) can determine the power and torque output from the engine. The ECU75could be connected to a temperature sensor which senses the temperature of oil38. An appropriate algorithm will determine when the orifice71should be open and when it can be closed by the closure72.

In one embodiment, the ECU75could instruct the actuator74to fully close and fully open the closure72as appropriate, i.e. the closure has only two positions. A more sophisticated system would have the ECU position the closure either fully open, or fully closed, or at one of several intermediate positions as appropriate.

Under certain circumstances it is advantageous to have a metered bleed system, which permanently allows a limited oil flow from the reservoir to the sump. In its simplest form, the metered bleed system could be a relatively small hole in the bottom of the reservoir. Under high speed running conditions the crown wheel would transfer more oil from the sump to the scoop than the metered bleed system returned from the reservoir to the sump. Under these circumstances the oil level in the sump would fall. However, under lower running speed conditions, the crown wheel would transfer a correspondingly smaller flow rate of oil to the scoop and hence the oil level in the sump would progressively rise. When the vehicle comes to a rest the metered bleed would ensure the oil level in the sump is balanced with the level in the reservoir.

The metered bleed could be used in conjunction with, i.e. in addition to orifice71and closure72. When the metered bleed is being used in conjunction with orifices71, as mentioned above, the metered bleed system will be a relatively small hole in the bottom of the reservoir, alternatively the metered bleed system could be a relatively small hole in the closure72.

Note that the metered bleed could be used in place of orifice71and closure72.

As shown inFIG. 3, the reservoir is completely full and there is still an amount of oil in the sump. Therefore the total amount of oil in the housing13is greater than the capacity of the reservoir. Ensuring a minimum amount of oil in the housing13where that minimum is greater than the capacity of the reservoir will ensure a minimum oil level (OS ofFIG. 3) in the sump irrespective of the running conditions of the associated vehicle.

As shown inFIG. 2, the oil level OR and oil level OS is below a lower edge of the axle housing arms12A and12B (FIG. 4). This is a typical oil level of known axle assemblies. The oil level is set at this height to ensure the oil does not pass into the axle housing arms themselves.

Providing a reservoir in housing13allows the oil level in that reservoir to be at a level above the axle housing arm without any oil passing into the axle housing arm. Thus, the reservoir18provides a system whereby oil can be held at a level higher than the axle housing arm when not required to lubricate the crown wheel when the crown wheel is transmitting relatively low torque and low power.

With reference toFIGS. 6 to 9there is shown a crown wheel and pinion carrier150with components that fulfill the same function as those of carrier50, and which are correspondingly labeled100greater. In this case, the orifice171is arcuate and is formed in boss180. Boss180is non-rotatably attached to the reservoir118. The closure172(FIG. 9) is in the form of a disc having an arcuate hole181similar in size and shape to the orifice172. The closure171is rotatable from a closed position (as shown inFIG. 6) wherein the arcuate hole181is misaligned with the orifice171, to an open position where the arcuate hole181is aligned with the orifice171. In the open position, oil within the reservoir can flow through the orifice171and in the closed position oil cannot flow through the orifice171.

The carrier subassembly140as shown inFIG. 6can be assembled into the axle housing12.

The closure172is rotatable between the open and closed positions by a flexible drive182as shown inFIG. 9. Flexible drive182is in the form of a cable (in further embodiments any type of flexible drive could be suitable). A first end183of the flexible drive182is attached to the closure172and a second end184includes a driving boss185. Adjacent second end184is a sleeve186having a flange187. The sleeve186is fixed to the reservoir118by positioning the flange187inside of the reservoir, passing a cylindrical portion188of the sleeve186through a hole in the reservoir and securing the sleeve186in place by a circlip mounted on the outside of the reservoir. The flexible drive182is rotatable within the sleeve186. The driving boss185engages with and is driven by actuator174, which in this case is an electric motor. As best seen inFIGS. 6 and 7, the carrier150includes a recess189within which the actuator174sits.

The first end183of the flexible drive182rotates about axis A and the second end184rotates about axis B. The crown wheel rotates about axis C (FIG. 8) and the pinion rotates about axis D (FIG. 6). As will be appreciated, the closure172is positioned below axis C. The second end184is positioned above axis C. Axis B is substantially parallel to axis D. The actuator174is positioned above axis C.

Advantageously, the flexible drive182allows the closure172to be positioned towards the bottom of the reservoir and the actuator174to be positioned towards the top of the reservoir. In particular, the position of the actuator174is relatively high up on the carrier, and therefore less vulnerable to being damaged by rocks and the like thrown up from the road. Furthermore, the likelihood of damage to the actuator is lessened by positioning it within a recess of the carrier. The flexible drive182allows the actuator174to open and close the orifice171while being positioned remotely from the orifice171. In particular, the flexible drive avoids the differential by passing over the top of the differential and then passing down the back of the differential. In this manner, the actuator can be positioned where it is less likely to be damaged, but nevertheless can drive a closure position towards the bottom of the reservoir.

FIG. 10shows an exploded view of the reservoir118. In this case the reservoir is formed in two halves, molding190and molding191. In this case the moldings190and191are made from a plastic material and are welded or otherwise fixed together. Pins192pass through holes in molding190into holes in molding191to locate the two moldings in their correct relative position either prior to welding or during gluing.

With reference toFIG. 11, there is shown an exploded view of an alternative reservoir218. In this case the reservoir comprises four pressings293,294,295and296. These four pressings together with boss297define the reservoir. Bracket298is attached to pressing293and is used to secure the reservoir218in place on the carrier via bolts equivalent to bolt125.

The pressings, boss and bracket are welded together to form the complete reservoir assembly. In this case the pressings are made from steel.

In further embodiments, the reservoir can be made up of any number of components. The components can be pressings or moldings or a combination of pressings and moldings. The material for the pressings or moldings can be any suitable material, for example steel or a plastic material.