BACKGROUND OF THE INVENTION

( 1 ) Field of the Invention

This invention relates to transmission systemsfor vehicles.

(2) Prior Art

In my International Application Nos. PCT/AU83/00170 and PCT/AU85/00048, there are described a number of transmission systems for vehicles which employ a sliding gear movably mounted on a drive shaft with teeth on the sliding gear engageable with teeth on the body to releasably connect the drive shaft to the normally faster rotating body when the two are rotating at the same speed. Application for the transmission systems include controlling unnecessary wheel spin between a pair of wheels on an axle and connecting the front and rear differentials of a four wheel drive vehicle to allow the front differential to rotate faster during a turn. The transmission systems described in the above applications have generally proved to be successful. However, in certain applications, e.g. heavy earth moving equipment, problems may arise as the teeth on the sliding gear and the body must apply the full driving force as they begin to mesh. This places a great strain on the teeth and also retards their meshing.

SUMMARY OF THE PRESENT INVENTION It is an object of the present invention to provide a transmission system of the types hereinbefore described where the sliding gear and the body are at least partially meshed before drive is applied between the gear and the body.

It is a preferred object to provide such a system where the meshing of the teeth can be adjusted for maximum efficiency.

It is a further preferred object to-provide a system where the movement of the sliding gear . along the drive shaft can be blocked against inadvert¬ ent meshing with the teeth on the body. Other preferred objects of the present invention will become apparent from the following description.

In a broad aspect the present invention resides in a transmission system for vehicles including: a substantially tubular body; a respective set of teeth provided circum- ferentially around the interior of the body at each end of the body; a shaft rotatably mounted in the body coaxially therewith; a sliding gear mounted on the shaft having a set of external gear teeth at each end of the sliding gear engageable with a respective set of teeth on the body; means to translationally move the sliding gear along the shaft; and means to operably drivingly connect the sliding gear to the shaft; so arranged that, on translational movement of the sliding gear along the shaft from a first position intermediate the length of the shaft where both sets of the external gear teeth on the driving gear are dis-engaged from both sets of teeth in the body to a second or third position where one set of external gear teeth is engaged with a respective set of teeth in the body, the external gear teeth and teeth in the body are at least partially meshed before the driving means conn¬ ects the sliding gear to the shaft.

In a second aspect, the present invention resides in a transmission system for vehicles including:

a shaf ; a sliding gear mounted on the shaft having a set of external .gear teeth at each end of the sliding gear; means to translationally move the sliding gear along the shaft; means to operably drivingly connect the sliding gear to the shaft; a body comprising a pair of body members rotatably mounted on the shaft coaxially therewith, each body member having a respective set of teeth provided around the inner faces of the body members engageable with a respective set of teeth on the sliding gear; and means to operably drivingly connect the pair of body members to rotate the body members in unison, so arranged that, on translational movement of the sliding gear along the shaft from a first position intermediate the length of the shaft where both sets of external gear teeth on the driving gear are dis-engaged from both sets of teeth in the body to a second or third position where one set of external gear teeth is engaged with a respective set of teeth in the body, the external gear teeth and teeth in the body are at least partially meshed before the driving means connects the sliding gear to the shaft.

Preferably the driving means connecting the sliding gear to the shaft is fully engaged before the teeth on the sliding gear and the body (or body members) are fully meshed. Preferably the teeth in the body (or body members)are provided around the ends of the body (or body members) or on end plates fitted into the body, the shaft preferably being journalled in bearings or bushes in the end plates. Preferably the means to translationally move

.li¬ the sliding gear along the shaft includes a plurality of grooves or splines on the shaft, and balls, p ^' egs or teeth on the sliding gear engaged with the grooves or splines. Preferably the driving means include a pair of gears on the shaft, one at each end of the sliding gear and each having a set of teeth operably to engage a second set of external gear teeth on the sliding gear when the sliding gear moves to its second or third positions. The gear may be fixed to the shaft by splines with a fewer number of splines than teeth on the gears to enable the relationship of the gear to the shaft to be changed.

To prevent the sliding gear inadvertently engaging the body when the rotation of the shaft is stopped suddenly, an overrun sleeve may be provided on the sliding gear and arranged to lag relative to the sliding gear, the sleeve engaging the body (or body members). Alternatively, a pair of fingers may be prov- ided to limit the movement along the shaft, a magnetic coupling operating a rocker arm to selectively move the fingers into, or out of, engagement with the sliding gear. A further alternative is a solenoid operated finger to selectively engage the sliding gear. BRIEF DESCRIPTION OF THE DRAWINGS

To enable the invention to be fully understood, a number of preferred embodiments will now be described with reference to the accompanying drawings, in which: FIG. 1 is a schematic view of a coupling between a transfer case and propellor shaft of a four wheel drive vehicle of the type shown in FIG. 1 of International Patent Application No. PCT/AU82/00170 incorporating one embodiment of the present invention;

FIG. 2 is a sectional side view of the teeth on the sliding gear and the body;

FIG. 3 is a sectional end view of one of the balls in the sliding gear in its groove on the shaft;

FIG. 4 is a similar view as FIG. 1 of a second embodiment provided with the overrun sleeve on the sliding gear;

FIG. 5 is a front view of the overrun sleeve of FIG. 4;

FIG. 6 is a schematic sectional view of one half of a differential of the type disclosed in my

International Application No. PCT/AU85/00048 incorpor¬ ating a third embodiment and mechanically operated finger to limit overrun of the sliding gear;

FIG. 7 is a sectional end view taken on line 7-7 on FIG. 6; and

FIG. 8 is a schematic part sectional view of a coupling incorporating a solenoid-operated finger to limit overrun of the sliding gear.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, the transmission system, in the form of a coupling 10, has a drive shaft 11 jour¬ nalled in bushes 12 in the end plates 13 of a tubular body 14 connected to a propellor shaft of a four wheel drive vehicle (not shown). A sliding gear 15 is provided on the shaft

11 to operatively engage or disengage the body 14 from the drive shaft 11.

Referring to FIG. 2, a set of teeth 16 are provided circumferentially around the inner face of each end plate 13 to mesh with a corresponding set of external teeth 17 on the adjacent side face of the sliding gear 15. To assist in the meshing of the teeth 16, 17, the teeth 17 are formed with the angles 90°< <-* -^ 120° and 90° - /3 .93° and with the nose of the teeth 16 relieved by the angle 0°^. & ^ ²⁰ °• ^{Wnen tne} teeth 16, 17 are

meshed, the sliding gear 15 operatively drives the body 14. However, should the body 14 rotate faster than the sliding gear 15, the teeth 16, 17 will freely become disengaged to break the driving engagement. To move the sliding gear 15 along the shaft, a plurality of grooves 18 are provided around the shaft 11 at an angle Δ. to the axis of the shaft, with the angle being preferably FIG. 3, the grooves 18 have inclined sides. At each end the grooves 18 have end portion 19 at an angle -Δ. = 90°. A ball 20 rolls in each groove and is received at the inner end of a respective radial bore 21 in the sliding gear. Each ball 20 is pressed into the groove 18 by a spring-loaded plunger 22 where the spring 23 is supported by a removable plug 24. When the sliding gear rotates relative to the shaft, the balls 20 move along the grooves 18 causing the sliding gear to be moved along the shaft. When the teeth 16, 17 are meshed, the balls 20 are received in the end portions 19 so that no side forces are applied to the balls.

To provide the driving engagement between the sliding gear 15 and the shaft 11, a set of sawteeth 26 are provided at each end of the sliding gear 15 coaxial with the teeth 17. Each tooth has a front face parallel with the axis of the shaft and a rear face at the angle thereto.

Corresponding teeth 25 are provided on an adjacent gear 25a which has its hub 27 fitted with splines which mesh with splines 28 on the drive shaft. Preferably the number of splines 28 is less than the number of teeth 25 to enable the gears 25a to be rotated relative to the shaft to ensure optimum meshing of the teeth 16, 17. A thrust plate 29 is provided between each gear 25a and the adjacent end plate 13 of the body. Spring loaded plungers 30 are received in longitudinal bores 31 in the sliding

gear 15 urging the sliding gear to a position inter¬ mediate the gears 25a.

The operation of the coupling will now be described. Assume that the sliding gear 15 is in the first, central position as shown in FIG. 1 at rest. As the drive shaft 11 begins to turn, the rotation causes the balls 20 to roll along the grooves 18 to move the sliding gear 15 to the right. As the teeth 25 on the gear 25a and the teeth

24 on the sliding gear 15 are relieved e.g. by 1mm relative to the teeth 16 on the end plate 13 and teeth 17 on the sliding gear teeth 16, 17 will initially mesh before any driving connection occurs between the drive shaft 11 and the sliding gear 15 via the gear 25a.

As the sliding gear 15 continues to move to the right, both teeth 16,17 and teeth 24, 25 will become fully engaged or meshed to provide an operative driving connection between the drive shaft 11 and the body 14. However, as the teeth become fully meshed, the balls 20 enter, the end portion 19 at the grooves 18 and so no side forces are applied to them. During the meshing step, the balls 20 can ride up the side faces of the grooves 18, against the plunger 22, to relieve any large side forces on them.

The teeth 25, 26 are so designed to mesh after teeth 16, 17 as hereinbefore described. However, they are fully meshed at or before the teeth 16, 17 become fully meshed so that the sliding gear is fully connected to the shaft before it is fully connected to the body. When the drive shaft 11 rotates slower than the body 14 e.g. when the front propellor shaft rotates faster than the transfer case during a turn, the balls 20 roll back along the grooves to disengage the sliding gear from the body and so break the driving connection between the drive shaft and the body.

In alternative embodiments, not shown the balls 20 may be replaced by legs (which may be spring loaded) in the sliding gear or short teeth in the sliding gear may engage helical splines on the drive shaft. The coupling 10 may be used in all applications illustrated in my International applications where a coupling or control unit employs a sliding gear to provide a disengageable drive between a drive shaft and a body. Referring now to FIGS. 4 and 5, the coupling

40 is generally similar to coupling 10 with the sliding gear 41 movable along the shaft 11 to provide a releas- able driving connector between gear 42 and the body 43. As will be readily apparent, the teeth 44, 45 on the body 43 and sliding gear 41 are brought into mesh before the teeth 46, 47 on the gear 42 and sliding gear 41.

The movement of the sliding gear 41 along the shaft 11 is controlled by the balls 20 but the grooves

48 do not have end portions corresponding to the end portion 19 in FIG. 1.

When the coupling is stopped suddenly e.g. when travelling in a forward direction, the sliding gear is moved out of engagement with the body 43. However, it is liable to overshoot its central neutral position and engage the teeth at the other end of the body (i.e. be in the position for travelling in a reverse direction) .

To prevent this occurring, an overrun sleeve

49 is provided around the sliding gear and is supported on balls 50.

Three pegs 51 in the sliding gear are received in respective slots 52 in the overrun sleeve 49. The overrun sleeve 49 lags behind the sliding gear with the pins 51 in the F or R position respectively as the coupling is being driven forwards or backwards. The

sleeve is dimensioned so that it will engage the. body 43 before the sliding gear 41 and will only allow the sliding gear to move to its neutral position with the pins 51 in either of the N positions. FIG. 6 shows one half of a differential based on the differentials in my International Application No. PCT/AU85/00048.

In each coupling 60, the tubular body (i.e. corresponding to tubular bodies 13 and 43 in FIGS. 1 and 4) is replaced by a pair of body members 61 each rotatably mounted on the shaft 62 and having teeth 63 which engage complimentary teeth 64 on the sliding gear 65. The sliding gear 65 has internal splines 66 which engage complimentary splines 67 on the shaft 62, the splines 66, 67 being of opposite hand to the teeth 63, 64 to provide a releasable driving connection between the shaft 62 and body members 61 via the slid¬ ing gear 65 in the manner described in my International Application No. PCT/AU82/00170. To enable the body members 61 to be driven in unison, they are provided with external teeth 68 which mesh with complimentary teeth 69 on respective pinion gear 70 fixed on a shaft 71. The shaft 71 is journalled in bearings 72 in the differential housing (not shown) and is driven via a pinion 73 which meshes with a gear 74 driven by the crown wheel 75.

As the differential housing contains suitable lubricant e.g. S.A.E. 90 hypoid oil or automatic trans¬ mission fluid (ATF), this will lubricate the couplings 60 and so an enclosed tubular body to contain the lubricant is not required.

To prevent overrun of the sliding gear 65, a block 76 is rotatably mounted on the shaft 71 but is prevented from rotation therewith. A brass collar 77 has a pair of rings 78 connected by a bridge 79.

Each ring 78 has a permanent horseshoe magnet 80 - which rubs against the adjacent pinion gear 70 to provide a lagging connection between the collar 77, which has limited rotational movement e.g. ^" t - 3 about a neutral position, and the pinion gear.

A rocker arm 81 is pivotally mounted on a pin 82 on the block 76 and is movable by a pin 83 on the bridge 79. The pin 83 on the bridge 79 and a pin 84 on the rocker arm 81 alternately extend and retract a pair of fingers 85 slidably mounted on the block 76. The fingers can selectively engage a peripheral flange 86 on the sliding gear 65.

When the drive to the coupling 60 is stopped, the sliding gear 65 moves out of engagement with one of the body members 61. However, the lagging connection between the collar 77 and the pinion gears has caused the collar to move to one of its limit positions and so one of the fingers 85 is extended to engage the flange 86 to prevent the sliding gear 65 moving past its neutral position and becoming engaged with the other body member 61.

In the embodiment of FIG. 8, the coupling 90 has a sliding gear 91 which is prevented from overrunning to the reverse position by a finger 92 which can releas- ably engage the peripheral flange 93 on the sliding gear. The finger 92 is connected to the plunger 94 of a solenoid 95 mounted on the housing 96 of the coup¬ ling on the differential in which it is fitted. The solenoid 95 is- connected to earth and to the reversing light switch (not shown) so that the finger 92 is only retracted, to allow the sliding gear to engage the body member 97 in the reverse position, when the vehicle transmission is in reverse.

It will be readily apparent to the skilled addressee that the selection of tubular body or body

- 1.1 -

members ; driving engagement and translational movement between the sliding gear and the shaft; driving engagement between the sliding gears and the body or body members; and the selection of overrun limiting mechanism, will be determined by the intended applic¬ ation.

Various changes and modifications may be made to the embodiments described without departing from the scope of the present invention defined in the appended claims.