A drive axle for vehicles, particularly agricultural tractors

Abstract: An axle is disclosed wherein each wheel hub (4) is pre-arranged for installation of an epicyclic speed reducing mechanism (20-24) and a disc brake (36), and wherein each epicyclic speed reducing mechanism (20-24) includes a gear carrier (24) which is rigid for rotation with a stationary part (8) of the corresponding wheel hub (4) so that the gear carrier structure (24), additionally to providing support for the brake (36), where provided, can be drilled and machined to form channels (34,35) therein as required for the brake to be operated.

Description: This invention relates to a drive axle for vehicles, in particular agricultural tractors, comprising a beam having a corresponding wheel hub mounted on the opposite ends thereof, each wheel hub being associated with a respective stub shaft and including: a stationary part attached to the beam and a part which is rotatable relative to the stationary part and rigid for rotation with the corresponding wheel; and an epicyclic speed reduction mechanism adapted to be fitted between the stub shaft and the turning part of the hub, said speed reduction mechanism comprising a sun gear, ring gear, and planet gear carrier whereby said sun gear is in driving connection with said ring gear, said planet gear carrier being non-rotatably attached to the stationary part of the corresponding wheel hub, in said planet gear carrier being provided at least one conduit of a braking circuit of the vehicle. An axle having the above-outlined features is known from DE-A-3606876. Other axles with a more common structure are known from French patent applications No. 2517003 and No. 2518703. These axles are customarily provided with an epicyclic speed reduction mechanism between the stub shaft and the turning part of the wheel hub. The reduction mechanism is mounted such that the gear carrier, sun gear, and ring gear are respectively rigid for rotation with the turning part of the hub, the corresponding stub shaft, and the stationary part of the hub. Said axles may be optionally provided with brakes, usually of the disc type. Accordingly, it becomes necessary to arrange for manufacture of the axles in two versions, one of which would have the wheel hubs equipped with brakes, as in the instance of the above-mentioned two documents, and the other without a brake system. Lastly, the brake-fitted versions require that the brakes be readily accessed for servicing in view of some parts of the brake, like the brake linings, being subject to wear and periodic replacement. The construction of the axle according to the aforementioned documents has some deficiencies versus the above-noted technical requirements. One of these deficiencies is attributable to that the brake operating mechanisms, including the corresponding actuator and hydraulic supply system therefor, are a comparatively complex design and, therefore, expensive to manufacture and assemble. It follows that such a structure cannot be reasonably adopted for axles without brake systems, which therefore must be designed, produced and stored separately. Another drawback is that, also on account of the above-mentioned structural complexity, the brake cannot be readily accessed far servicing the brake linings, for example. The underlying problem of this invention is to provide an axle structure wherein the wheel hubs can be equipped with brakes, and equally well fabricated in the brake-less version, while overcoming all of the drawbacks with which the cited prior art is beset. This problem is solved according to the invention by an axle having the features mentioned in claim 1. With the axle, and specifically the two wheel hubs, so configured, it becomes possible to utilise the gear carrier structure both for supporting the brake and for providing channels and whatever else is required to operate the same. Thus, the axle can be made with or without a brake system and yet involve no major design alterations or significant differences in manufacturing cost. Further, the axle may be conveniently equipped with brakes any time after its manufacture, thereby allowing of later adaptation once assembled and storage as a single version adapted to be completed with a brake system where desired to fill specific marketing demands. The features and advantages of this invention will be more readily apparent from the following detailed description of two preferred embodiments thereof, given by way of illustration and not of limitation with reference to the accompanying drawings, in which: Figure 1 is a fragmentary longitudinal section view of one of the wheel hubs of an axle embodying this invention; Figure 2 is a sectional view taken along line II-II in Figure 1 showing just the stationary part of the wheel hub of said axle; Figure 3 is a corresponding view of the wheel hub of the axle shown in Figure 1 as incorporating a brake; and Figure 4 is a fragmentary view in longitudinal section, corresponding to Figure 1, of an other embodiment of the invention. In the drawing figures, generally shown at 1 is a drive/steering axle such as the steering front axle of a four-wheel drive agricultural tractor, which embodies this invention. The axle 1 comprises a box-type beam 2 having a wheel hub, generally indicated at 4, pivoted on its axially opposite ends for oscillation about respective pivot pins 3. For each wheel hub 4, there is provided an axle shaft (not shown) supported rotatably on the beam 2 and being associated with the corresponding hub through a coupling 6 and a stub shaft 7. Each wheel hub 4 comprises a stationary part 8, through which the hub 4 is pivoted on the beam 2, and a turning part 9 which is supported on the stationary part 8 exterior through bearings 10. The combination of the stationary 8 and turning 9 parts, together with a cap 11 fitting over the latter in sealed relationship, confine a lubricant-tight chamber 12 within the hub 4. This chamber 12 is sealed against leakage by respective ring seals 13, 14 known per se which fit between the turning part 9 and the stationary part 8, and between the latter and the stub shaft 7. Formed on the turning part 9 is a flange 15 which extends radially outwards and has captive screws 16 for attaching a wheel, not shown. Also fastened to the flange 15 by means of screws 17 is the cap 11. The drive from the stub shaft 7 to the turning part 9 of hub 4 is accomplished through an epicyclic speed reducing mechanism including a sun gear 20, which is made integral with the stub shaft 7 by gear-cutting the same on the remote end from the coupling 6, and a ring gear 21, formed by gear-cutting the inside cylindrical surface of the turning part 9. It is to be noted, therefore, that both the ring gear 21 and the flange 15 for connecting the wheel (or another driven part) are obtained in the unitary structure of the turning part 9. On the same part 9 are also obtained, by appropriate machining, the two tracks 10a,b of the bearings 10. The sun and ring gears enmesh with each other through three planet gears 22, of which only one has been depicted in the drawing. Each planet gear 22 is supported via a pin 23 on a gear carrier 24 which, according to the invention, is made integral with the stationary part 8 of the hub 4 and, therefore, rotatively rigid therewith. In order to have the stationary part 8 configured in the gear carrier form, it is provided with two walls 25, 26 which are set apart and interconnected by three pillar formations 27 lying parallel to the axis of the hub 4 and angularly offset 120°. These pillar formations 27 are brought out in the cross-sectional view of the stationary hub part 8 shown in Figure 2. Wall 25 is provided with a central opening 28 receiving a bearing 29 for the sun gear 20, and three holes 30 in registry with respective holes 31 in wall 26 and adapted to receive spindles 23 for the planet gears 22. These spindles are retained in the holes 30, 31 by an annular flange 32 fastened to wall 25 by means of screws 33. It matters to observe that said flange is also effective to shut off two conduits 34, 35 formed in the stationary part 8 of the hub through one of the pillar formations 27. These conduits, being both open to wall 25, belong to the feed circuit for a brake generally shown at 36 (Figures 3 and 4). The axle of Figure 1 can be conveniently equipped with a brake 36 for each hub. For this purpose, the cap 11 and annular flange 32 only should be removed, and the latter replaced with a pre-assembled brake unit 36, thereafter the cap 11 is replaced with another cap 11a which differ from the former by its dimensions being adapted to accommodate said brake 36 additionally to the turning part of the hub. The brake comprises a bell-shaped piece 37 made rigid with the stationary part 8 of hub 4 by means of screws 38, and a package of discs 39 and counter-discs 40 which are respectively rigid for rotation with the sun gear 20 of the epicyclic speed reducer through a coupling sleeve 41, and with the bell-shaped piece 37, which is purposely provided with a splined skirt 42. Said brake 36 further comprises a hydraulic actuator having an annular piston 43 tightly slidable within an annular seat 44 in the bell-shaped piece, a pair of pressure plates 45, 46 embracing said disc 39 and counter-disc 40 package, an elastic return mechanism 47 including a Belleville washer package 49 active between the bell-shaped piece 37 and the plate 45 via a tubular link 47a, to return the plate to a home position, and a plurality of devices 48 for taking up the backlash between the discs and counter-discs. The latter are of a type disclosed in European Patent Application No. 90122311.5 by this same Applicant. When the brake 36 is mounted against the wall 25 of the gear carrier 24, the annular seat 44 for the piston 43 is put in fluid communication with the conduits 34, 35 to operate the actuator through a suitable medium, such as a pressurised oil, and respectively bleed off any air present in the brake system. By supplying oil under a pressure to the actuator of brake 36, the disc and counter-disc package 39, 40 is compressed between the pressure plates 45, 46 clamped, in turn, between the piston 43 and a stop ring 46a provided on the bell-shaped piece 37. Shown in Figure 4 is a variation, generally denoted by 50, of the axle according to the previously described embodiment which is specially conceived for use on agricultural tractors capable of attaining relatively high top speeds. Similar or equivalent parts of the axle 1 are denoted by the same reference numerals. In the axle 50, located between the sun gear 51 of the epicyclic reducer and the coupling 6 is a face dog clutch including first and second clutch members 52, 53 which are respectively keyed to that portion of the stub shaft 7 which is fast with the coupling 6, and the corresponding end of the sun gear 51. The clutch 52, 53 is selectively actuatable by axially sliding the sun gear 51 to make the sun gear and coupling rotatively rigid with each other whenever the speed of the vehicle equipped with axle 50 is a relatively slow one, and release the sun gear from the coupling on predetermined speed values being exceeded. A piston actuator 54 is provided for the purpose which is fed through a conduit 54a and has a piston rod 55 carrying a flange 56 on an intermediate portion thereof. The actuator has a forked working arm 57 engaging in a groove 58 on the sun gear 51, thereby the latter is allowed to rotate relative to said arm 57, but made rigid for translation therewith. This arm 57 extends square from a sleeve body 58 guided on the stationary part 8 of hub 4 at the location of a drilled bracket 59. The body 58 is, in turn, fitted over the piston rod 55 and abuts against the flange 56. Two bias springs 60, 61 extend respectively between the bell-shaped piece 37 of the brake 36 and the flange 56, and between the piston 54 and the sleeve body 58. The function served by such springs 60, 61 is one of transforming the piston 54 movement, resulting from operation of the same through a suitable medium such as a pressurised oil, into an elastic load tending to urge the sun gear 52 to slide relative to the sleeve 41 and the planet gears 22 and thereby mutually engage, or respectively disengage, the clutch members 52, 53. In this way, operation of the clutch members, especially under load, can be made easier. It should be further noted that, even with the clutch disengaged to uncouple the reducer from the corresponding axle shaft, the operability of the brake 36 would be still retained by the braking action, which applies between the stationary part of hub 4 (with which the brake bell-shaped piece is rigid) and the sun gear (with which the sleeve coupling 41 is rotatively fast), being transferred to the turning part of the hub through the planet gears 22. Among the principal advantages afforded by the invention is that it enables the brake to be located on the hub exterior, where it is easier to reach for inspection and servicing. Also, the axle can be supplied with or without brakes, and in the latter case fitted with brakes at some later time with a greatly simplified operation. In addition, pre-arranging the axle to accommodate a brake system would not affect its production cost significantly. Lastly, an ability to disengage the reducer from its corresponding axle shaft is provided while travelling on the road at high speed, while still ensuring a braking function for the hub, since the turning part of the latter would remain connected drivingly with the sun gear through the planet gears, even with the reducer disengaged.

Claims: A drive axle for vehicles, in particular agricultural tractors, comprising a beam (2) having a corresponding wheel hub (4) mounted on the opposite ends thereof, each wheel hub (4) being associated with a respective stub shaft (7) and including: a stationary part (8) attached to the beam (2), and a part (9) which is rotatable relative to the stationary part (8) and rigid for rotation with the corresponding wheel; and an epicyclic speed reduction mechanism (20-24) adapted to be fitted between the stub shaft (7) and the turning part of the hub (4), said speed reduction mechanism comprising a sun gear (20), ring gear (21), and planet gear carrier (24) whereby said sun gear (20) is in driving connection with said ring gear (21), said planet gear carrier (24) being non-rotatably attached to the stationary part (8) of the corresponding wheel hub (4), in said planet gear carrier (24) being provided at least one conduit (34,35) of a braking circuit of the vehicle, characterized in that said conduit (34,35) is open through a wall (25) of said planet gear carrier (24) axially remote from said beam (2), said wall (25) of the planet gear carrier (24) being provided for removably connecting thereto either a closure (32) for closing said conduit (34,35) or a stationary part (37) of a brake (36), said brake having a brake hydraulic actuator (43,44) which is hydraulically connected to said at least one conduit (34,35) when the brake is mounted to said planet gear carrier wall (25). An axle according to claim 1, wherein the brake (36) comprises a disc (39) and counter-disc package (40), with the ones being rigid for rotation with a bell-shaped piece of the stationary part of the brake (37), and the others rigid for rotation with the sun gear (20) of said speed reducing mechanism, said bell-shaped piece (37) forming in combination with said actuator (43) and said disc (39) and counter-disc package (40) an individually handled unit associated with said gear carrier (24). An axle according to either Claim 1 or 2, wherein the planet gear carrier (24) comprises a plurality of pillar formations (27) extending between respective walls of said stationary part (8) of the hub, with said conduit (34,35) extending through said pillar formations (27). An axle according to Claim 2, wherein those members of said package (39) which are rigid for rotation with said sun gear are made rigid for rotation with a sleeve (41) which is made releasably rigid for rotation with the sun gear (20), at a free end thereof. An axle according to one or more of the preceding claims, wherein there is provided, between said sun gear (20) and the corresponding stub shaft (7), a clutch means (52,53) adapted to be selectively operated to connect, and respectively disconnect, said speed reducing mechanism drivingly to/from said stub shaft (7). An axle according to Claim 5, wherein the clutch means comprises first and second clutch members (54,53) on the facing ends of said stub shaft (7) and said sun gear (51), and an actuator (54) active on said sun gear (51) to shift it axially within said speed reducing mechanism into and out of an engaged condition of said members. An axle according to Claim 6, wherein said actuator (54) is active on said sun gear (51) through at least one elastic element (60,61) for elastically urging said sun gear (51) into and out of said engaged condition. An axle according to one or more of the preceding claims, in which said rotatable part (9) has a unitary structure including means for connection to the corresponding wheel and the ring gear (21) of the epicyclic speed reduction mechanism. An axle according to Claim 8, in which respective tracks (10a,b) for bearings (10) intended for supporting said rotatable part (9) on said stationary part (8) are obtained in the unitary structure of said rotatable part (9).

Inventors: CARRARO TIMANTE, MASSACCESI GIANNI, CARRARO, TIMANTE, MASSACCESI, GIANNI
Applicants: CARRARO SPA, CARRARO S.P.A.
Application year: 1992
Main classification: B60K17
IPC codes: F16D55, B60K17