FIELD OF THE INVENTION

The present invention relates to a differential locking assembly for use on vehicles, particularly vehicles intended for off-road use. Also included is a method of installing a differential locking device onto a range of vehicle axles.

BACKGROUND TO THE INVENTION

The differential locking assembly is an already well known component, particularly in the field of off road and agricultural vehicles. The effect of the engagement of a differential lock system overrides the differential internal sun and planet gears, effectively locking them in position, thus the power is transferred to both opposing drive shafts, giving continuous and uninterrupted drive to the road wheels when activated in locked position. This facility is very useful in situations when a vehicle drive wheel begins to spin, for example in mud, when driving force is quite removed from the other drive wheel.

The retrofit diff locking systems presently available tend to be complicated and/or costly to produce and fit, particularly in the case of pneumatic, vacuum or cable systems, as well as being intrusive to the axle tubing or main differential casing itself, thus interfering perhaps with the structural integrity of the axle assembly.

In one known differential lock system, described in EP Specification EP1725416 (Al), there has to be installed a separate pneumatic or vacuum pump or cable lever in the vehicle cab and, for retrofit action, the axle adapted via welding of the casing thereof to accept external mounting points for the mechanism.

For such a system the installer has to be able to fabricate and weld, as well has having engineering skills. Retrofit fitting time can be at least eight hours with these systems.

Other known differential lock systems, described in US Patent Specifications US2005250613A1 and 2009176613A1 for example, utilize one large solenoid mounted external to the main body of the carrier.

SUMMARY OF THE INVENTION

According to a first aspect of the present invention a transmission differential unit comprising sun and planet gears and a carrier which in use rotates driven by the

transmission input has, located on the carrier, at least one electrically powered actuator, and a component arranged to be movable by the at least one actuator into a locking engagement with a sun gear, thus to lock the sun gear against rotation with respect to a planet gear. It will be appreciated that the planet gears may be bevel or worm gears.

According to a feature of the invention the said component may be a locking member which may be movable between a first location in which it is not engaged, or engaged effectively only with the carrier and a second location in which it is engaged with both the sun gear and effectively with the carrier. Alternatively the said component may be for example a somewhat floating cap to the carrier.

Typically the unit comprises also a crown wheel and pinion and the carrier is attachable, usually by bolts, to the crown wheel.

The at least one actuator may be a solenoid or a stepping motor or both.

Where solenoids are employed it is preferable that there are at least three, and four has been found sufficient. These may be let into recesses formed in the carrier, preferably with such a tight fit as will ensure heat transfer between the carrier and the solenoids but at the same time will permit ready replacement of a faulty solenoid. Where the planet gears are worm gears the solenoids may be inside the worm gears, in which case a sleeve may be incorporated between the solenoid and the worm gear bore (if the solenoid itself does not have a sufficiently wear resistant casing), with ready access by lubricating oil.

Where stepper motors are employed these will advantageously be anchored against rotation with respect to the carrier.

It will be appreciated that an important feature of the invention is that the actuators, operating within a differential surrounded by a casing, will be immersed in the transmission oil. This has the great advantage that the temperature of the solenoids can be ensured not substantially to exceed that of the oil. Solenoids can lose more than 30% efficiency if they are allowed to become too hot. The efficiency of stepper motors can be likewise diminished.

Where the use of solenoids risks the generation of significant magnetic fields such that the casing can itself become magnetized an insulative gasket can be applied between the bottom of the locking ring and the inside of the main differential housing to reduce the likelihood of the components being held together with any residual magnetic force. Impellor means such as slots may be formed in the carrier at such an angle as to pump oil transmission oil into and out of the differential center. These attentions to the modus operandi of using transmission oil as a coolant permit the use of more powerful solenoids within the available size envelope than would have been the case otherwise.

For solenoid plunger rods to move freely within the solenoid body, oil escape means are advisable and a hole in the rear end of the solenoid body may provide for this. Alternatively or additionally oil escape means may be provided in the plunger. Moreover, a gap between the solenoid windings and the solenoid casing may also be accessed by the oil if the casing is perforated in at least two locations one remote from the other. In that instance the solenoid windings may be insulated from the oil by a suitable membrane. Typically the solenoids are at least 5cm long and 2cm diameter. Solenoids for use in a transmission unit according to the invention form a second aspect thereof and comprise a case containing solenoid windings, a space between the windings and the case and perforations through the case ends arranged for the flow of transmission oil therethrough. The solenoids are preferably employed to pull the solenoid plungers and thence a locking ring mounted thereon, from a neutral location in which the locking ring is constrained to rotate only with the carrier into a locking location in which the locking ring is both constrained to rotate with the carrier and constrains a sun gear also to rotate with the carrier. With the power supply off springs can be arranged to drive the locking ring back to the neutral configuration. These springs are preferably located in pockets in the carrier and the locking ring has suitable protruberances. However the springs may surround the solenoid plunger rods,

According to a feature of the invention the relevant external sun gear tooth profile may be formed slightly smaller than the mating external locking ring teeth, thus producing a backlash tooth play. This aids the smooth engagement and disengagement of the mating locking teeth. The play may typically be between 0.5 and 1.5mm, with 1.2mm having been found acceptable. Advantageously the engaging faces of the locking ring and the sun gear are rounded or otherwise faired to ease engagement and reduce the likelihood of chipping.

About 6mm has been found to allow sufficient movement of the locking component between the neutral (disengagement) location and full engagement.

Standard gear hobbing cutting teeth may be then used for locking engagement. This also means that standard proprietary planet gears can be used.

If the at least one actuator comprises a stepper motor in place of the solenoids, then this may be arranged to drive a worm gear, likewise to move the locking ring into and out of engagement with a sun gear.

Where a stepper motor is employed, clutch means may also be incorporated. This can enable the realization of a transmission having a variable limited slip differential facility. Where such a facility is desired it may be advantageous to employ both solenoids and at least one stepper motor, to ensure both complete locking when that is required and, on the other hand, variable slip when that is required.

Alternatively stepping motors may provide both differential locking and limited slip differential facilities.

In order to convey power to the actuator means at least one slip ring may be provided on a mounting integral with the carrier and separated from the mounting by insulators including O-rings and neoprene gaskets. Contact brushes may then be mounted in a bracket which can be secured via transmission unit bearing attachment caps within the casing. The slip rings may be formed of phosphor bronze. However, it having been realized that most vehicle transmission differential units operate within a bath of oil, hardened steel slip rings, which are considerably cheaper, can be employed instead of phosphor bronze.

For simple actuation only one slip ring may be needed, with the transmission housing providing an earth return. However, sensors may be incorporated in the at least one actuator to provide for indication of function, in which case there may be at least two slip rings.

Whilst the engagement of a difflock according to the invention may be controlled by a switch in the driver's cab it may alternatively or additionally be controlled automatically, for example by an electronic control unit (ECU), in which case sensing of the actuator condition may be important.

Ultimately this construction means that transmission casing need only be additionally penetrated by the electrical conduits required to power the actuators together with, if desired as is most likely, a function indicator signal conduit connected to an indicator in the vehicle cab. Another important advantage of the invention is that it enables the use of a plurality of actuators, in balanced and strategic locations, without having a multiplicity transmission casing penetrations.

Of course, it is expected that a transmission differential unit can be installed ab initio upon construction of the unit. However, an important advantage of the invention is that the unit can be constructed to be capable of being installed as a retrofit, replacing an existing unit within the transmission casing and performing a minimum modification to the casing. This casing modification may comprise simply drilling a hole through the casing of a suitable size and location and fitting a power cable (together with an indicator cable where required) gland, therein so that the passage of cable therethrough can be sealed. In other words no welding or other modification to the casing need be required. It is reckoned that such a retrofit operation can be carried out inside four hours. Moreover it can be readily arranged not to foul any exhaust, brake line or suspension components etc. It will be appreciated that an exchange unit incorporating the present invention can be constructed so that the carrier can be substituted for an existing, unmodified carrier bolted to the existing crown wheel.

This retrofit operation provides a third aspect of the present invention.

Preferably the unit employs four planet gears to ensure coping with the increased torque transfer that will occur upon locking the differential. In more lightly loaded and smaller units two or three planet gears alone may suffice. The sun and planet gears do not have to have straight cut profiles; helical worm gear tooth profile can be used. In the case of worm helical gears sun and planet torque biassing applications, the orientation of the Sun gears can differ from horizontal and vertical. Then solenoids or stepper motors can be similarly fitted in the space environment between the worm planet gear and the differential casing. If the space environment does not permit this the operating system can be fitted inside the planet gear center, as these are normally elongated and the actuator array can readily be adapted accordingly.

DRAWINGS

Embodiments of the invention will now be described by way of an example, with reference to the accompanying drawings, of which:

Figures 1 and la are exploded views of a first embodiment of a transmission unit in accordance with the invention;

Figure 2 is an illustrated schedule of the components of the transmission unit;

Figure 3 is a cut away view of an assembled unit;

Figure 4 illustrates oil impellor arrangements on a carrier

Figure 5 is a longitudinal cross section of the unit; Figure 6 is a section of a solenoid;

Figure 6 is an end view of a transmission unit mounted in a casing with a back cover thereof removed;

Figures 7a and 7b illustrate the spatial relationship of the actuators with a locking ring; Figures 8 and 8a are sketches showing the mounting of brushes; Figure 9 is a wiring diagram;

Figures 10a, 10b, 11 and 12 illustrate further embodiments of the invention.

SPECIFIC DESCRIPTION

In the description of various embodiments of the invention set out below, like parts have similar reference numbers

The transmission unit shown in figures 1 to 5 comprises a carrier 2 and an associated top hat member 1 boltable thereto. The carrier 2 has slots 2a in which lie a cross shaft 31 carrying at the extremities thereof planet gears 12. The carrier 2 also has boltable thereto a crown wheel end flange 3 arranged for the bolting thereto of a crown wheel 50. On either side of the cross shaft 31 are sun gears 8 and 13.

Carried in recesses formed in the carrier are four solenoids 4 which are a tight but readily removable fit within the recesses.

A locking ring 9 is received into the crown wheel end flange 3 and has four lugs 9a and four lugs 9b by which the ring 9 is prevented from rotating in the flange 3 by matching recesses in the latter. To the lugs 9a are mounted solenoid plungers 40 for the solenoids 4. The lugs 9b in fact protrude into recesses in the carrier 2, which recesses contain return springs 16. An insulative gasket 3a is inserted between the locking ring 9 and the crown wheel end flange 3.

The locking ring 9 has internal teeth 9c arranged for engagement with peripheral teeth 8a on the sun gear 8. As can be seen particularly in figures 1 and 2 the internal teeth 9c are rebated, as is the rear face of the peripheral teeth 8a on the sun gear 8, to ease

enmeshment and reduce the likelihood of chipping.

Around the top hat member 1 are two slip rings 5 to which the solenoids 40 are connected. The slip rings 5 are insulated one from another and from the top hat member 1 by neoprene insulators 10 and O-ring seals 14, which latter also serve to mount and centralize the slip rings 5. The slip rings 5 are made of hardened steel and are prevented from rotating with respect to the top hat member 1 by a slip ring retainer 6 boltable to the top hat member 1.

Attachment of the top hat member 1 to the carrier 2 serves to retain the solenoids 4 in the recesses 2a. The carrier 2 slots 2c in which lie a cross shaft 31 have rebates 2b which serve to impel transmission fluid into and out from the carrier 2 interior when the carrier is rotating. This is illustrated particularly in figure 4. The solenoids 4 and their plungers 40 are shown in detail in figures 5 and 6. The solenoids 4 comprise a bobbin 4a carrying solenoid windings 4b, an outer casing 4c and end plates 4d and 4e. The end plate 4d is perforated to allow transmission fluid to exit ahead of the plunger 40 and both end plates 4d and 4e are perforated to allow transmission fluid to flow through the interior of the solenoid 4. Two leads 4p are connected appropriately to the slip rings 5. The solenoids 4 also contain sensors with an associated lead 4s arranged to indicate solenoid operation, the lead 4s being also for connection to an appropriate slip ring 5. The plunger 40 is also hollowed, as at 4i, to enable the flow of transmission oil therethrough also.

Figures 8 and 8a show the assembly of the transmission unit of figures 1 to 5 into a transmission casing 70. Brackets 71 attached within the casing 70 mount the unit which is secured in place by bracket caps 72. Upon a convenient cap 72 is mounted a bracket 7 for brushes 19 so that the latter engage with the slip rings 5. A gland 34 is fitted to the casing 70 and serves for the sealed passage of conduits 7 to the brushes 19. The brushes 19 are secured to the bracket 7 using simply star washers 20. The sun gears 8 and 13 are mounted to drive driving wheel shafts 75. The operation of the transmission unit described with reference to figures 1 to 7 is as follows.

In normal operation of the differential transmission unit, the carrier 2 rotating with the crown wheel 50, the solenoids 4 are not energized and the locking ring 9 is not engaged with the sun gear 8 but rests engaged in a recess in the crown wheel end flange 3.

Accordingly the sun gears 8 and 13 are free to rotate with respect to the planet gears 12 and thus permit the nearside and offside vehicle wheels to rotate independently one of the other via the shafts 75.

When electrical power is conveyed to the solenoids 4 via the conduits 74, the brushes 19 and the slip rings 5, the solenoids 4 are energized and pull the locking ring 9 into

engagement with the sun gear 8 whilst remaining in engagement with pockets in the recess in the flange 3. This locks the sun gear 8 against rotation with respect to both the carrier 2 and the planet gears 12 and the sun gear 13 and the nearside and offside vehicle wheels cannot rotate with respect to each other.

When the electrical power is switched off the springs 16 drive the plungers 40 and hence the locking ring 9 out of engagement with the sun gear 8. This permits the sun gears 8 and 13 again to rotate independently one of the other and thus the nearside and offside vehicle wheels also.

During vehicle movement the transmission unit components will be immersed in

transmission oil and rotating according to their role. By virtue of the rebates 2b and 2c in slots 2a of the carrier 2, transmission oil will be caused to flow into and out of the interior of the carrier 2. As well as lubricating the components the oil will moderate the temperature of the components, especially the solenoids 4. In particular the oil will be free to enter and leave the solenoids 4 ahead of the plungers 40 via the central perforation in the solenoid end plate 4d and to enter and flow through the solenoids as such. As mentioned above it is a valuable feature of this invention that an existing transmission unit not incorporating a differential lock can be readily be replaced as a retrofit by a unit incorporating a differential lock facility according to the invention. After draining the oil, the casing rear cap (not shown) can be removed, exposing the whole transmission unit. With the drive shafts 75 withdrawn and the caps 72 removed from the brackets 71 the existing transmission unit can be withdrawn from the casing 70. The crown wheel 50 is then unbolted from the end flange 3 and, after any necessary inspection and approval, attached to that of a unit which accords to the invention.

The casing 70 is drilled at an appropriate location and a gland 34 fitted. After appropriate cleaning the replacement unit is offered to the brackets 71 of the casing 70 and the caps 72 attached, except that the bolt for that of the caps which is closest to the gland 34 is only emplaced when a bracket 7 has been offered thereto. When these bolts have been tightened a conduit 74 fed through the gland 73 is connected as appropriate to the brushes 19. The gland 19 is then tightened to prevent oil loss therethrough.

An electrical circuit for the invention is illustrated in figure 9. Basically the circuit comprises a power supply leading via a fuze/connector/switch box 94, brushes 19 and slip rings 5 to actuators 4. Sensors in the actuators are arranged to send a signal to cab indicators 95, a light showing that the differential lock is engaged, and a gauge 96 indicating, in the case of a stepper motor/limited slip differential combination, the extent of limited slip.

In a second embodiment, illustrated in figure 7a, four stepper motors 80 driving worm gears 81 are mounted in the carrier 2, in a manner similar to the solenoids 4 except that anchor means (not shown) prevent rotation of the stepper motors 80 with respect to the carrier 2. The worm gears have mating threads in the external teeth 9a of the locking ring 9. In this embodiment springs 16 are not necessary and a reversal of stepper motor polarity will return the locking ring 9 to the rest position.

Figures 10a and 10b, 11 and 12 illustrate basically a third and a fourth embodiment of the invention. In particular figure 10a shows a transmission unit embodiment in which the planet gears 12 are helical gears and figure 10b shows a transmission unit embodiment in which helical planet gears are employed in a torque biasing context.

In the third embodiment, illustrated in figure 10a and 12, solenoids 4 are mounted inside helical planet gears 12. A sleeve 90 protects the solenoid 4 and acts as a bearing around which a gear 12 can rotate. The solenoid 4 is a tight fit in the sleeve 90 and is secured to the carrier 2 by a screw thread 91. This is also shown in figure 6.

A variant of this third embodiment is shown in figure 12 where the actuators comprise stepper motors secured within the helical gears 12, secured in a similar manner to that of the solenoids 4.

In the fourth embodiment, shown in figures 10b and 11, planet gears 93 operate in a torque biasing context. The gears 93 have a significantly lower helix angle than the helical planet gears 12. The solenoids 4 (or stepper motors) are not mounted within the planet gears 4 but in separate recesses in the carrier 2.