A WHEEL-END ASSEMBLY

Abstract: A wheel-end assembly is described which includes a hub (100) and a planetary gear system (110). The planetary gear system (110) includes a sun gear (120), planetary gears (130), and an outer gear (140). The planetary gear system (110) is arranged so that drive provided by a shaft (160) is transmitted by the outer gear (140) to a wheel on the hub (100). A planetary gear carrier (150) attached to a shaft casing (170) remains stationary. The arrangement of the gears allows a breaking mechanism (195, 200) to be positioned out-board of the planetary gear system.

Description: A WHEEL-END ASSEMBLY This invention relates to a wheel -end assembly for a vehicle and in particular to a wheel -end assembly including an improved gear and/or braking mechanism for use, for example, with tractors, heavy goods vehicles, mining cars or construction vehicles. The invention is particularly applicable when an oil immersed wet brake system is used. Conventional axles include wheel -end assemblies with planetary gear systems which consist of an inner sun gear, which typically rotates with the transverse drive shaft from the differential, a planetary gear carrier, planetary gears and a stationary outer gear. The hub is connected to the planetary gear carrier so that both the hub and the gear carrier precess about the sun gear. When the sun gear rotates it is desirable that the hub precesses with the gear carrier so that appropriate gear reduction is developed in the wheel-end assembly. This arrangement requires not only the manufacture of a sun gear, planetary gears, a stationary outer gear, a rotatable hub and a planetary gear carrier but also a rotating driving connection which extends radially between the hub and the planetary gear carrier and causes the hub to precess with the gear carrier. Conventionally, the driving connection between the gear carrier and the hub is provided in the form of the rotating end cap at the outermost end of the wheel -end assembly. If it were located inwardly of this point it would extend across the wheel -end assembly in the central cavity, preventing the location of other components . Conventionally, a braking mechanism for braking the wheels is positioned in-board of the planetary gear system adjacent the differential gear system which connects the transverse shafts to the transmission shaft. When the braking system needs to be repaired, replaced or serviced, the position of the braking system gives rise to considerable difficulties. To gain access to the braking system the wheel, hub, planetary gear system, transverse shaft and its associated casing must all be removed. Accordingly, accessing the brake system is both time consuming and awkward even before any work is carried out on the brake system itself. The inconvenience of this arrangement is particularly troublesome should brake failure occur in a remote or difficult to reach location where the necessary tools and vehicle jacks may not be available. Indeed, in heavy duty vehicles which venture into remote locations, the likelihood of failure occurring in such a location is high. In addition, it can also be troublesome to access the gear system itself in such arrangements. It is, therefore, an object of the present invention to alleviate the problems described above. According to a first aspect of the present invention there is provided a wheel -end assembly for a vehicle comprising: a housing; a hub for carrying a wheel ; a planetary gear system for driving the hub including an outer gear which rotates with the hub, a sun gear and at least one planetary gear which rotates about an axis fixed with respect to the housing whereby rotation of the sun gear causes the hub to rotate with respect to the housing; and a brake system positioned out-board of the gear system within the hub. The structural simplicity of this arrangement improves design flexibility. For example, by providing an outer gear which rotates with the hub any means for connecting the outer gear and the hub, so that the hub rotates with the outer gear, is positioned radially outward of the outer gear. Thus, there is no need to provide a driving connection between the planetary gear carrier and the hub in the form of an end cap. This enables other parts to be positioned out-board of or extend through the gear system. For example, an actuation piston for the out-board braking system or a hydraulic feed, can be positioned radially inward of the outer gear; it may extend from say the inboard side of the gear system to the out -board side of the gear system without being impeded by or impeding a rotating driving connection between the carrier and the hub. Preferably, the hub has an inner diameter out-board of the planetary gears which is substantially the same or larger than that opposite the planetary gears so that the planetary gears can be slid into and out of a working position. Preferably, out-board of the planetary gears, the hub, or the outer gear, provide splines on which the planetary gears can be slid into and out of a working position. The teeth of the outer gear may extend out-board of the planetary gears to form the splines. The sun gear, or a member rotating with the sun gear has an outer diameter, out-board of the planetary gears, which is substantially the same or smaller than that of the sun gear opposite the planetary gears so that the planetary gears can be slid into and out of a working position. Preferably, out-board-of the gear system, the sun gear, or the member rotating with it, provides splines on which the planetary gear can be slid into and out of a working position. The teeth of the sun gear may extend out -board of the planetary gears to form the splines. Preferably, the braking system is arranged to act between the hub and the sun gear or a shaft driving the sun gear. Preferably, the braking system extends from a position adjacent an inner surface of the hub to a position adjacent an outer surface of the sun gear, or an extension of the sun gear, out-board of the planetary gears. Preferably, one or more first friction discs extend radially inwards from the inner surface of the outer gear, or the hub, and have splines which key in to splines on the inner surface of the gear or the hub to fix the discs rotationally with respect to the outer gear and the hub. The discs may be annular. Preferably, the splines on the outer gear or hub are the teeth of the outer gear. Preferably, one or more second friction discs have splines which key into splines on the outer surface of the sun gear, or a member which rotates with the sun gear, to rotationally fix the discs with respect to the sun gear, or the member. Preferably, the one or more second friction discs overlap with the first friction discs. Preferably, the splines on the sun gear or member are the teeth of the sun gear. In a preferred embodiment the wheel-end assembly includes a stationary planetary gear carrier about which the hub and outer gear rotate . In a preferred embodiment, the wheel -end assembly further includes a brake system positioned out-board of the gear system. This provides easy access to the brakes in case of brake failure or repair. Preferably, the brake system acts between the hub and the shaft. The braking system could be a compression braking system for example it may comprise friction discs. One or more friction discs may extend radially inwards from the inner surface of the outer gear or the hub to overlap with one or more friction discs extending radially outwards from the outer surface of the sun gear or the shaft . It is also preferred that the wheel-end assembly includes one or more pistons arranged to act on the friction discs. The outer gear and hub rotate in the opposite direction to that of the shaft and the sun gear driven by the shaft . This provides efficient differential braking between the hub and shaf . Preferably, the hub is integral with the outer gear. Alternatively, it may be connected to the outer gear with bolts or the like. Preferably, the sun gear is integral with the shaft, though it may be separate from and adapted to be connected to the shaft . In a preferred embodiment, the hub rotates on bearings about the housing and means are provided to hold the hub in position on the bearings so that the planetary gear system can be removed without disturbing the bearings. The means may be one or more bolts or lock nut assembly. Preferably, the wheel -end assembly includes two or more planetary gears. Preferably, there are three planetary gears equi-spaced around the sun gear. The present invention also extends to a vehicle comprising a wheel -end assembly as described in the preceding paragraphs and a wheel-end assembly and axle substantially as described herein with reference to the accompanying drawings . The invention will now be described, by way of example, with reference to the accompanying drawings. Figure 1 is a schematic diagram of a conventional transaxle system. Figure 2A is a cross-sectional end-view through a planetary gear system and a wheel -end assembly of one embodiment of the present invention. Figure 2B is a cross-sectional side view of the wheel-end assembly of Figure 2A. Figure 3A is a cross-sectional end-view through a planetary gear system and wheel-end assembly of another embodiment of the invention. Figure 3B is a cross-sectional side view of the wheel-end assembly of Figure 3A. An axle including wheel -end assemblies positioned in relation to a main drive shaft is shown in figure 1. Figure 1 is a cross-section schematic representation of the wheel -end assemblies within a vehicle. A main shaft 10, for transmitting drive from a gear box, is connected to first and second shafts 20. A differential gear system 30 is positioned between the shafts 20 and transmits drive from the shaft 10 to the shafts 20. Shafts 20 in turn, transmit drive from the motor to a planetary gear system 50. The planetary gear system 50 drives wheels 60, mounted on hubs 65, and causes them to rotate. As shown in figures 2A and 2B, the wheel-end assembly of the present invention includes an annular hub 100 and a planetary gear system 110. The planetary gear system 110 includes a sun gear 120, planetary gears 130, and an outer annular or ring gear 140. The planetary gear system generally indicated at 110 is arranged so that drive provided by a shaft 160 is transmitted by the outer annular gear 140 to a wheel (not shown) on the hub 100. A planetary gear carrier 150 is attached to shaft casing 170 and remains stationary. The arrangement of the gears allows a braking mechanism to be positioned out-board of the planetary gear system. The gear arrangement of the invention will now be described in more detail . Studs 105 fix the wheel (not shown) to hub 100 so that when it rotates the wheel also rotates. The outer gear 140 of the planetary gear system 110 is located on the inner surface of the hub . As shown in figure 2A, the three planetary gears 130 engage with sun gear 120, and outer gear 140 engages with planetary gears 130. The stationary planetary gear carrier 150 supports planetary gears 130. As shown in figure 2B, shaft 160 is housed in shaft casing or housing 170. The planetary gear carrier 150 is connected to the axle housing 170 by means of inter- engaging splines 255. The housing 170 is suspended on the vehicle chassis by means of a conventional suspension (not shown) , whereas gear carrier 150 is simply slid into position along splines 255 and held in position by spring clips 265 locating behind the lock-nut assembly 260. In-board of the gear system 110, roller bearings 180 support hub 100 on axle casing 170. Lock nut assembly 260 clamps the roller bearings into a pre-loaded position between the shaft casing 170 and the hub 100. Therefore, the gear carrier and planetary gear system can be removed without disturbing the pre-loaded bearings. Thus, the wheel does not need to be removed and the vehicle need not be jacked up. Out-board of the gear system, the braking system is provided. The braking system is an oil immersed wet brake system and comprises several compression or friction discs positioned between an actuating piston 210 and a back stop 212 located on the inside surface of an end cap 214. The active area of overlap between the discs is situated between the piston and the back stop. Typically the discs are bathed in cooling fluid such as oil. An annular braking plate 190 is provided adjacent piston 120 to act on the compression discs. There are six overlapping compression or friction discs 195, 200 arranged in two alternating sets of three. One set 195 rotates with the sun gear in a first direction. The other set 200 rotates with the outer gear in the opposite direction. Braking plate 190 is arranged to act on a friction plate 195 attached to sun gear 120 when piston 210 is actuated. Three pistons 210 are provided in the stationary gear- carrier in between the planetary gears . A brake fluid distributor 250 is clamped to the gear carrier by bolts 222 to feed fluid from spiral fluid line 220 to piston 210. Thus, in the brake fluid feed system there are no rotating parts. This reduces the risk of leakage, wear and breakages as well as providing simplicity of design and manufacture . In the preferred embodiments shown, the annular gear 140 is integral with the hub and extends out-board of the planetary gears so that the teeth of the gear can be used as splines for locating the friction discs of the brake system and for sliding the planetary gears in and out of a working position. It may be however that splines distinct from the gear teeth are used, though preferably these are contiguous with some of the gear teeth of the outer gear so that the planetary gears are held in position rotationally whilst being slid in and out. This also aids location in the working position on reassembly. Similarly, sun gear 120 extends out-board of the planetary gears 110. The teeth of the sun gear also extend beyond the planetary gears to form splines on which the planetary gears can be slid into and out of a working position. The splines are also used to key brake discs 200 rotationally in position with the sun gear. The number of splines can be less than the number of gear teeth in both the outer gear 140 and sun gear 120, nevertheless it is preferably that at least some if not all of the gear teeth extend outboard beyond a position opposite the planetary gears to form splines, so that sliding extraction of the planetary gears can take place in one continuous motion. The ease of extraction of both the braking system and the planetary gear system and gear carrier is facilitated by the guide means or splines along which each of these items may be slid into and out of position. The design is particularly advantageous in this respect because the brakes have the same lateral extent as the planetary gears and so the same splines can be used. A tube 220 connects piston 210 to a braking fluid inlet 225. The tube 220 spirals around shaft 160 to accommodate the fully floating planetary gear carrier 150. The splines 255 holding the gear carrier in position are a loose fit, so there is some play in the movement of the gear carrier both axially and radially. The gear carrier finds its own, substantially, stationary, position between the outer annular gear and the sun gear. Spiral tube 220 provides some flexibility to accommodate this movement of the floating gear carrier. Release of gear carrier is achieved by unscrewing bolts 115 and 222 at which point, the gear carrier can be slid out of position leaving behind brake fluid distributor 250 and fluid inlet 220. The operation of the wheel -end assembly of the present invention will now be described. Shaft 160 is rotated through a differential gear system by a drive-shaft connected to the vehicle engine (not shown) . As shaft 160 rotates, sun gear 120 rotates. Rotation of sun gear 120 causes planetary gears 130 to rotate. The planetary gear carrier 150 does not precess, however, because it is anchored to shaft casing 170 by splines 255. Thus, the outer gear 140, hub 100 and wheel (not shown) are driven by rotation of the planetary gears within the stationary gear carrier. Because the gear carrier is held stationary, the planetary gears serve as idler gears and simply rotate about axes which are fixed in position with respect to the main shaft. The sun gear rotates in the opposite direction to the outer gear and hub. The hub rotates on the bearings 180 about the shaft 160. When the operator of a vehicle applies the brakes, pressure is applied to the braking fluid through the braking fluid inlet 225. The piston head 215 is driven towards the braking plate 190. When the piston head 215 contacts the braking plate 190, plates 195 and 200 are compressed together between the piston and backstop 212, braking the hub and shaft against one another. Because the plates 195 and 200 rotate in opposite directions, this arrangement of differential braking is particularly efficient. As shown in figure 2b, the braking system is located outboard of the planetary gear system 110. Out-board positioning is possible because of the gear arrangement of the present invention which eliminates the need for a connection between the inwardly mounted planetary gear carrier 150 and the outer hub. Specifically, outer gear 140 is adjacent to and, in this particular embodiment, integral with, hub 100. The planetary gear carrier 150 is connected to the axle housing 170 by means of splines 255 and is stationary relative to the housing 170. Figures 3A and 3B show a very similar arrangement to Figures 2A and 2B. Like reference numerals refer to like features unless otherwise stated. The main points of difference are that an annular ring 265 is used to fix the planetary gear carrier in position with bolts 115. Also a double row of angular contact bearings 180, 181 are used in place of the more expensive taper roller bearings 180 shown in Figure 2B. Also, the hub 100 is split into a front section 275 and a rear section 270 to provide for clamping the bearings and, in this particular embodiment, an oil reservoir 300. The annular ring 265 is formed from a steel pressing with tapped holes to receive bolts 115. In the present invention, to access the brake system and in particular the brake discs, e.g. for replacement, only end cap 214 need be removed. Release of bolts 240 allows removal of end cap 214. Thus, the wheel, hub 100 and preloaded mounting bearings 180 need not be disturbed. This contrasts with conventional wheel -end assemblies in which the planetary gear system, wheel, and hub must all be removed to access the brakes . Removable end cap or flange 214 is provided with a seal about its periphery (not shown) for sealing oil within the wheel assembly. Because the planetary gear system is in-board of the brake system the pumping action of the gears is somewhat remote from the seal and is less likely to affect it and cause it to leak. The brakes are cooled by oil and tend to cause the oil to be squeezed out from the friction plates at the outer periphery. Oil is circulated around the brakes by providing channels at the inner surface of the hub to direct this oil back to the main portion of the hub circulating around the planetary gears and the bearings before being drawn back into the brake system. By elimination of a driving connection between the hub and gear carrier, the wheel assembly of the present invention has fewer elements than that of the known assemblies. It is thus simpler to manufacture and easier to align in manufacture or repair. The present invention also provides easy access to the planetary gear system 100. The gear system is accessed by simply removing the end cap 214 and brake discs 195, 200. The planetary gear carrier and planetary gears, after releasing spring clips 265, may then simply be slid out of the hub along splines 255 and outer gear 140, whereas the hub is retained on the housing 170 by lock nut assembly 260. Thus, the brake discs 195, 200 can be slid out of position along splines on sun gear 120 and outer gear 140 respectively. To remove the stationary gear carrier 150, bolts 115 must be undone, releasing the carrier from spring clips 265 (Figure 2B) or annular ring 265 (Figure 3B) . The feed to the brake system is undone by releasing bolts 222. The gear carrier is then free to slide out along splines 255 providing access to the pistons 210 within it. The planetary gears can be slid along splines provided on the outer gear and sun gear towards the entrance to the hub (left in Figures 2B and 3B) . Thus, by providing a wheel -end assembly with the gear system of the invention an easily accessible braking mechanism can be positioned out-board of the planetary gear system.

Claims: CLAIMS 1. A wheel -end assembly for a vehicle comprising: a housing; a hub for carrying a wheel ; a planetary gear system for driving the hub including an outer gear which rotates with the hub, a sun gear and at least one planetary gear which rotates about an axis fixed with respect to the housing whereby rotation of the sun gear causes the hub to rotate with respect to the housing; and a brake system positioned out-board of the gear system within the hub. 2. A wheel-end assembly according to claim 1, in which the hub has an inner diameter out-board of the planetary gears which is substantially the same or larger than that opposite the planetary gears so that the planetary gears can be slid into and out of a working position. 3. A wheel -end assembly according to claim 2, in which, out-board of the planetary gears, the hub, or the outer gear, provide one or more splines on which the planetary gears can be slid into and out of a working position. 4. A wheel-end assembly according to claim 3, in which one or more teeth of the outer gear extend out-board of the planetary gears to form the splines. 5. A wheel -end assembly according to claim 1, 2, 3 or 4 , in which the sun gear, or a member rotating with the sun gear, out-board of the planetary gears system, has an outer diameter which is substantially the same or smaller than that of the sun gear opposite the planetary gears so that the planetary gears can be slid into and out of a working position. 6. A wheel -end assembly according to claim 5, in which, out-board-of the gear system, the sun gear, or the member rotating with it, provides one or more splines on which the planetary gear can be slid into and out of a working position. 7. A wheel-end assembly according to claim 6, in which one or more teeth of the sun gear extend out-board of the planetary gears to form the splines. A wheel -end assembly according to any preceding claim, in which the braking system is arranged to act between the hub and the sun gear or a shaft driving the sun gear. 9. A wheel-end assembly according to claim 8, in which the braking system extends from a position adjacent an inner surface of the hub to a position adjacent an outer surface of the sun gear or an extension of the sun gear out-board of the planetary gears. 10. A wheel -end assembly according to claim 9, in which one or more first friction discs extend radially inwards from the inner surface of the outer gear or the hub and have one or more splines which key into one or more splines on the inner surface of the gear or the hub to fix the discs rotationally with respect to the outer gear and the hub. 11. A wheel-end assembly according to claim 10, in which the one or more splines on the outer gear or hub are teeth of the outer gear. 12. A wheel-end assembly according to claim 10 or 11, in which one or more second friction discs have splines which key into splines on the outer surface of the sun gear or a member which rotates with the sun gear to rotationally fix the discs with respect to the sun gear or the member . 13. A wheel -end assembly according to claim 12 in which the one or more splines on the sun gear or member are teeth of the sun gear. 14. A wheel -end assembly according to any preceding claim in which the hub is integral with the outer gear. 15. A wheel -end assembly according to any preceding claim, in which a stationary planetary gear carrier is provided about which the hub rotates. 16. A wheel-end assembly according to claim 15, in which the planetary gear carrier is connected to the housing. 17. A wheel-end assembly according to claim 15 or 16 further including interengaging splines on the planetary gear carrier and housing to hold the planetary gear carrier rotationally fixed with respect to the housing. 18. A wheel-end assembly according to claim 17, in which the splines on the housing and the planetary gear carrier are arranged so that the gear carrier can be slid out of position along the splines. 19. A wheel-end assembly according to any of claims 15 to 18 including one or more brake actuating means located in the stationary gear carrier. 20. A wheel-end assembly according to claim 19, in which the brake activating means comprise one or more pistons . 21. A wheel-end assembly according to any preceding claim in which the hub rotates on bearings about the housing and means are provided to hold the hub in position on the bearings so that the planetary gear system can be removed without disturbing the bearings . 22. A wheel-end assembly according to claim 21, in which the means comprises one or more bolts or lock nut assembly. 23. A wheel-end assembly according to any preceding claim, in which there are two or more planetary gears . 24. A wheel -end assembly according to claim 23, in which there are three planetary gears equi-spaced around the sun gear. 25. A wheel-end assembly according to any preceding claim, including an end cap which rotates with the hub. 26. A axle or vehicle comprising a wheel-end assembly according to any preceding claim. 27. A wheel-end assembly or axle substantially as described herein with reference to the accompanying drawings.

Inventors: DOWNTON PETER GEORGE, DOWNTON, PETER, GEORGE
Applicants: DAVID BROWN TRANSAXLES LIMITED, DOWNTON PETER GEORGE, DOWNTON, PETER, GEORGE
Application year: 1998
Main classification: B60K17
IPC codes: B60K17, B60T1