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Patent Searching and Data


Title:
VEHICLE DIFFERENTIAL CONTROL SYSTEM
Document Type and Number:
WIPO Patent Application WO/1981/002049
Kind Code:
A1
Abstract:
A control system (29) for a lockable drive differential (22) of a vehicle (11) locks up the differential (22) during straight travel within a predetermined lower portion of the total range of vehicle speeds and unlocks the differential (22) during turns other than minor or momentary turning movements, manually initiated lock up being available to the operator during a turn if wheel slippage occurs. The control system (29) also maintains the differential (22) in an unlocked condition when the vehicle transmission (16) is in neutral or is shifted to a high speed range. By controlling the lockable differential (22) in response to changes of the mode of travel of the vehicle (11), rather than in response to speed differences between the differential output members (24, 26), better control of vehicle motion is realized and power dissipation and component wear in the differential is reduced. Although the control system (29) is adaptable to a variety of vehicles it is particularly advantageous in earthmoving vehicles such as loaders, for example, which are often operated on rough terrain providing poor traction.

Inventors:
AVERY B (US)
DENNING R (US)
URBANC D (US)
Application Number:
PCT/US1980/000028
Publication Date:
July 23, 1981
Filing Date:
January 14, 1980
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
AVERY B
DENNING R
URBANC D
International Classes:
F16D48/12; F16H48/30; (IPC1-7): F16H1/44
Foreign References:
US3732752A1973-05-15
US3400610A1968-09-10
US2803150A1957-08-20
GB1534227A1978-11-29
CA974794A1975-09-23
US3871249A1975-03-18
US3845671A1974-11-05
US3138970A1964-06-30
US3133454A1964-05-19
US2874790A1959-02-24
US2830670A1958-04-15
GB790541A1958-02-12
Download PDF:
Claims:
Clai s
1. In a differential control system (29) for a steerable vehicle (11) having a differential (22) which may be locked to cause plural drive out put elements (24, 26) to turn at the same speed and " which may be unlocked to enable turning of said out¬ put elements (24, 26) at different relative speeds, the improvement comprising: means (47) for establishing a locked condition in said differential (22) during travel of said vehicle (11) along a substantially straight path at least at predetermined speeds, and turn sensing means (49) for establishing an unlocked condition in said differential (22) during turning of the travel direction of said vehicle (11) .
2. A differential control system (29) as defined in claim 1 wherein said turn sensing means (49) includes means (49*) for preventing unlocking of said differential (22) in response to steering of said vehicle (11) into a turn of travel direction until the travel path of said vehicle (11) has at least a predetermined degree of curvature.
3. A differential control system (29) as defined in claim 1 further including time delay means (66) for delaying unlocking of said differential (22) in response to steering of said vehicle (11) into a turn of travel direction until the turning of travel direction has persisted for a predetermined period of time.
4. A differential control system (29) as defined in claim 1 further including means (52) for limiting said predetermined speeds at which said, differential (22) is locked in response to steering of said vehicle (11) along a substantially straight travel path to less than the total range of speeds of which said vehicle (11) is capable.
5. A differential control system (29) as defined in claim 1 wherein said vehicle (11) has a transmission (16) providing any of a plurality of speed ranges, further including speed range sensing means (52) for preventing locking of said diffeiεntial (22) in response to travel of said vehicle (11) along a. straight path when said transmission (16) is conditioned to establish the highest speed range thereof.
6. A differential control system (29) as defined In claim 1 wherein said vehicle (11) has a transmission (16) shiftable from a neutral condition to at least one drive transmitting condition, further including neutral sensing means (51) for maintaining said differential (22) in said unlocked condition while said transmission (16) is in said neutral condition.
7. A differential control system (29) as defined in claim 1 further including manual override means (61) for selectively locking said differential (22) during said turning of the travel direction of said vehicle (11) .
8. Control means (29) for a vehicle differential (22) which has an unlocked mode of _O«PI operation enabling drive output elements (24, 26) to turn at different relative speeds and which has lock up means (27) for constraining said output elements (24, 26) to turn at the same speed in response to a lock up signal, the vehicle (11) having a steering system element (57) which is in a first position when said vehicle (11) is traveling along a substantially straight path and which moves away from said first position during turning of the travel of said vehicle (11) comprising in combination: means (36) for transmitting said lock up signal to said lock up means (27) of said differential (22) during predetermined operating conditions of said vehicle, and turn sensing means (49) for suppressing said lock up signal in response to movement of said steering system element (57) away from said first position thereof.
9. Control means (29) for a vehicle differential (22) as defined in claim 8, the vehicle (11) having a transmission (16) shiftable to establish any of a plurality of speed ranges, further including speed range sensing means (52) for suppressing said lock up signal while said transmission (16) is establishing at least one predetermined speed range of said' plurality of speed ranges thereof, 1Q. Control means (29) for a vehicle differential (22) as defined in claim 8, the vehicle (11) having a transmission (16) shiftable between a neutral condition and a drive transmitting condition, further Including neutral sensing means (51) for suppressing said lock up signal while said trans¬ mission (16) is in said neutral condition thereof.
Description:
Description

Vehicle Differential Control System

Technical Field

This invention relates to vehicle drive differential ' s and more particularly to the control of differentials which have lock up means for temporarily suppressing the differential action under predetermined conditions.

Background Art Differentials which enable one drive wheel or the like of a vehicle to rotate at a different rate than the.other during a turn are a practical necessity in most powered vehicles but are also a source of problems under certain conditions . Most notably, if one drive wheel loses traction because of a slick road surface, loose gravel, excess drive torque or some other cause, a free differential reacts by reducing the torque available to the other, nonslipping wheel. The torque which can then be supplied to the nonslipping wheel is limited to the relatively low torque needed to overcome such resistance to rotation of the slipping wheel as might be present. Under this condition loss of control and stalling of the vehicle may occur. The wheel slippage can also cause very rapid tire wear.

In some vehicles, the operator is provided with manually controlled means for braking a slipping drive wheel. Such systems complicate the operator's task and are highly dependent on operator skill. A variety of self controlled slip limiting or locking differentials have heretofore been developed to minimize the adverse consequences of a

loss of traction at one drive wheel or the like without requiring operator intervention. Such - differentials typically include ' means for resisting turning of one output element of the differential at a different rate than the other or which respond to a predetermined excessive degree of speed difference by locking the two elements together to temporarily constrain them to turn at the same speed.

Prior slip limiting differentials typically introduce some degree of frictional resistance to free differential action. The resistance is present at all times during motion of the vehicle including during turns as well as during straight travel. When this resistance is overcome by external forces which cause the drive wheels to turn at different speeds, such as during a turn of the vehicle, the torque delivered to the faster wheel is reduced by an amount proportional to the resistance while the torque applied to the slower inner wheel is increased by the same amount. This produces several undesirable effects during a turn of vehicle travel. One such effect is that the vehicle resists the turn and tends to follow a larger than desired turn radius. Any tendency of the slower inner wheel to lose traction and to spin is aggravated by the increased torque which is being applied to that wheel during the turn. If spin of the inner wheel is avoided, the total wheel pull exerted by the drive wheels is still reduced during the turn. As the resistance elements within the differential undergo relative motion, power is dissipated and rapid wearing tends to occur during straight travel as well as during turns . To avoid these problems, some locking differentials do not rely on resistance elements to

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sense wheel slippage but instead employ a control circuit having electrical means for sensing the speeds of the two differential output elements. The control circuit holds the lock up means disengaged until the speed ratio exceeds a predetermined limit indicative of wheel slippage, the φeed ratio at which lock up is initiated being greater than that normally encountered in a minimum radius turn of the vehicle. While this avoids certain problems discussed above such as continual power dissipation by resistance elements, it is subject to further problems. As the control must allow for a normal radius turn of the vehicle without locking the differential, the predetermined drive wheel speed ratio which triggers the lock up under wheel slippage conditions must be undesirably large. Further, such a system exhibits cyclic operation when prolonged slippage of the drive wheel occurs. After the system initially locks the differential in response to wheel slippage, the speed difference between the two drive wheels is momentarily elimina¬ ted. The control then reacts by disengaging the lock up mechanism and this cycle occurs repetitively as long as the wheel slippage condition exists. This repeated engagement and disengagement of the lock up is not conducive to optimum control of the vehicle nor to component durability.

In any of the prior locking differentials of the kind discussed ' above the control means is essentially responsive to sensing of a speed difference between the output elements of the differential. It has not heretofore been recognized that control of a locking differential might be made responsive to other factors and that

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the problems discussed above might be avoided by such means.

The present invention is directed to overcoming one or more of the problems set forth abov .

Disclosure of the Invention

In one aspect of this invention a differen¬ tial control system is provided for a steerable vehicle having a differential which may be locked to cause plural drive output elements to turn at the same speed and which may be unlocked to enable turning of the output elements at different relative speeds. The differential control system includes means for establishing a locked condition in the differential during travel of the vehicle along a straight path at least at predetermined speeds and further includes turn sensing means for establishing an unlocked condition in the differential during turning of the travel direction of the vehicle. In another aspect of the invention, the differential control system includes means for preventing unlocking of the differential in response to steering of the vehicle into a turn until the travel path has at least a predetermined degree of curvature. In still another aspect, the invention provides time delay means for delaying unlocking of the differential in response to steering of the vehicle into a turn of travel direction until the turning has persisted for a predetermined period of time. In another aspect of the invention, the predetermined speeds at which the differential con¬ trol system locks the differential in response to steering of the vehicle along a straight travel path are limited to less than the total range of speeds of

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which the vehicle is capable.

In still another aspect of the invention wherein the vehicle has a transmission shif able from a neutral condition to at least one drive transmit- ting condition, the differential control system includes means for maintaining the differential in the unlocked condition while the transmission is -in_ the neutral condition.

The invention differs from prior locking differential controls by locking and unlocking a differential in response to vehicle travel direction changes and, in some cases, to other changes of the mode of operation of the vehicle rather than In response to a predetermined difference in the -relative speeds of the differential output elements. The adverse effects of prior slip resisting differential controls, such as continual power dissipation and rapid component wear and an undesir¬ able torque distribution during turns, are avoided as resistance producing control elements need not be present in the diff rential.

Brief Description of the ' Drawing

The accompanying drawing is a diagrammatic view of a vehicle having a lockable drive differential and depicts a differential control system including an embodiment of the present invention.

Best Mode of Carrying Out the ' Invention

Referring to the drawing, drive system components of a vehicle 11 typically include right' and left drive wheels 12 and 13 respectively, which are driven by an engine 14 through a transmission 16. The transmission 16 in this particular example

is of the known form which is selectively shiftable between forward, neutral and reverse drive modes by positioning of a directional shift lever 19 and which provides for a plurality of speed ranges or drive ratios in either of the forward or reverse modes by operator positioning of a speed range selector lever 21. In this particular example of the invention in which the vehicle 11 is an articulated loader of the kind used in earthmoving operations, the transmission 16 provides for four speed ranges in both the forward and reverse modes of operation.

To transmit rotational drive from transmission 16 to both drive wheels 12 and 13 while enabling one drive wheel to turn at a different rate than the other during a turn of travel direction, a differential system 10 is provided. Transmission 16 is coupled to the drive wheels 12 and 13 through a differential 22 having an input element 23 coupled to the transmission and which has plural output elements 24 and 26 which in this example are right and left drive axles coupled to right and left drive wheels 12 and 13 respectively. Differential 22 is of the locking type which includes lock up means 27 which may be actuated by a fluid pressure lock up signal received at a lock up signal port 28 to eliminate the free differential action by constrain¬ ing the two output elements 24 and 26 to turn at the same speed. Suitable detailed constructions for a locking differential 22 of this kind are known to the art, one example being disclosed in prior United States patent 3,138,970, issued June 30, 1964 to P.J. Costa et al.

The differential system 10 includes a

differential control system or control means 29 for establishing a locked condition in the differential 22 in response to travel of the vehicle 11 along a straight path at predetermined speeds and for establishing an unlocked condition in the differen¬ tial during turning of the travel direction of the vehicle.

Thus locking and unlocking of differential 22 occurs in response to changes in the mode of travel of the vehicle 11 rather than in reaction to changes of the relative speeds of the differential output elements 24 and 26 as in prior differential controls .

Aside from locking the differential 22 during straight travel of the. vehicle 11 at least at certain predetermined travel speeds and aside from unlocking the differential during turns, the further conditions under which the differential is locked and unlocked may vary in different specific types of vehicle. In this particular example, the differential 22 is locked during straight or substantially straight travel when transmission 16 is in any of the lower three of the four available speed ranges. Free differential action is not needed during this mode of vehicle travel and may frequently be disadvantageous. Loader vehicles 11 are often operated on rough terrain offering poor traction and free differential action may.cause frequent wheel slippage. The. differential is not automatically locked during straight travel, in this particular example, when transmission 16 is in the fourth or highest speed range since in a loader that particular speed range is normally employed when the unloaded vehicle is traveling at relatively high speeds on a road or other good terrain. An empty

loader traveling at high speed often undergoes bouncing and a free differential facilitates control under these conditions .

Differential control means 29 also unlocks differential 22 while the transmission 16 is in neutral. This is desirable in connection with repair ' procedures which require that one drive wheel 12 or 13 be elevated on a wheel jack. If the. differential 22 should be locked at that time then an inadvertent turning of the other wheel 12 or 13 could cause the- vehicle 11 to be driven off the jack.

To lock and unlock differential 22 for the above described purposes, differential control means 29 includes, a pressurized fluid source 31 having a pump 32 which may be driven directly by engine 14 or from the output of transmission 16 or other suitable means. Pump 32 draws fluid from a reservoir 33 and discharges the fluid under pressure into a fluid supply line 34 which connects with a solenoid operated control valve 36. A relief valve 37 connected between supply line 34 and reservoir 33 limits pressure and discharges excess fluid.

Control valve 36 is a two position valve and is spring biased to an unactuated position at which fluid supply line 34 is blocked at the valve while the lock up signal line 38 to signal port 28 of the differential 22 is vented to reservoir 33 through, a drain line 39. Upon being electrically actuated, control valve 36 shifts to an alternate position at which supply line 34 is communicated with line 38 to actuate the lock up means 27 of the differential 22.

Electrical current for actuating control valve 36 is obtained from the vehicle battery 39

which has one terminal grounded to the vehicle chassis and the other terminal connected to a B+ conductor 41 through engine start switch 42 when the switch is in the run position. Solenoid 43 of control valve 36 is connected between B+ conductor 41 and chassis ground through a set of normally open relay contacts 44 which close in response to energization of a relay driver coil 46.

Accordingly, lock up means 27 of differen- tial 22 is locked when relay driver coil 46 is energized and is unlocked to allow free differential action when the relay driver coil is unenergized. Energization of driver coil 46 for this purpose is controlled by signal processing means 47 in response tq_ signals generated by sensing means 48 for detect¬ ing changes in the directional- and drive controls of the vehicle 11.

Sensing means 48 includes turn sensing means 49 having a turn sensing switch 49', neutral sensing means 51 having a transmission neutralization sensing switch 51', and speed range sensing means 52 having a speed range sensing switch 52' each of switches 49', 51' and 52' being connected between B+ conductor 41 and separate signal input terminals 53, 54 and 56 respectively, of the signal processing means 47.

Turn sensing switch 49' closes to electrically energize terminal 53 when the vehicle 11 is conditioned for straight travel or substantially straight travel, substantially straight travel in this particular embodiment, for example, being defin¬ ed as travel which does not deviate from a straight path by more than 10°. Other tolerances of variation from straight travel may be appropriate for other

vehicles or for certain vehicle applications. Switch 49' is mechanically coupled to elements 57 and 58 of the vehicle which move relative to each other in conjunction with steering of the vehicle into a turn and is opened by such movement. In this particular case in which the vehicle 11 is of the articulated . type, elements 57 and 58 are the front and rear body members which pivot about a vertical pivot hitch 59 when a turn of the vehicle is initiated. The turn sensing switch 49' may also be operated by other elements of the vehicle 11 steering system which undergo relative movement as a turn is Initiated such as a steering wheel, elements of the steering linkage or the like. In vehicles having fluid pressure operated steering systems, switch 49' may be fluid operated in response to the pressures which actuate the system to turn the vehicle.

Neutral sensing switch 51' is arranged to be open when directional shift lever 19 is in the neutral setting and to be closed when the shift lever 19 is moved to either the forward or reverse drive positions. In this example switch 51' is depicted as being operated by lands and grooves on a spool 19' which is shifted by lever 19 but as will be apparent the switch can also be operated by other elements of the transmission system which undergo movement or fluid pressure changes in response to shifting of the transmission control.

Speed range sensing switch 52 * is position- ed to be held in an open condition when speed range selector lever 21 is in the highest or fourth speed range position and to be closed when the speed range selector lever is in any of the lower speed range settings. Again, in this particular example, the

switch 52' is depicted as being controlled by lands and grooves on a spool 21' which moves with selector lever 21, but the switch can equally well be operated by other elements of the drive system which undergo movement or change pressure when the transmission is shifted between speed ranges.

It is preferable that the operator be able to override the automatic actions of the differential control means 29 under certain conditions to lock the differential 22 at times when it would otherwiseallow free differential action. This is desirable, for example, if wheel spinning should occur during a turn.

Manual override means 61 for this purpose includes a normally open switch 61' connected between B-f conductor 41 and a fourth signal input terminal 62 of signal processing means 47.

Signal processing means 47 locks and unlocks differential 22, by energizing and de-energizing relay driver coil 46, In response to changes in the electrical signals at input terminals 53, 54, ' 56 and 62. In particular, coil 46 is energized to lock differential 22 if each of terminals 54 and 56 are energized at a time when either or both of terminals 53 and 62 are energized although, in this preferred embodiment, energization of terminal 53 in particular must occur for a predetermined period of time before it is effective as will hereinafter be described in more detail. The above described functions of the signal processing means 47 can be realized by simply connecting switches 49* , 51' and 52' in series relationship between B+ conductor 41 and solenoid 43 of the control valve 36, switch 61' being connected in parallel with switch 49' . Such an arrangement

requires that the sizable current needed for operation of control valve 36 be transmitted through the " switches 49', 51', 52' and 61' and the sometimes lengthy electrical leads or wires which interconnect such components and the valve. Smaller and more- economical components can be used and other advantages, such as reduced power dissipation, may be realized if the arrangement depicted in the drawing is employed in which the signal processing means 47 is a miniature special purpose computer of the known microprocessor form connected between terminals 53, 54, 56, 62 and relay driver coil 46. The microprocessor 47' may also serve to perform other control functions for vehicle 11 additional to the lock up signal analyzing operations described herein.

One-suitable Internal programming circuit for causing microprocessor 47' to perform the above described signal analyzing functions is depicted in the drawing by means of standard logic circuit symbols. tn particular, terminal 62 is connected- to one input of a two input, nonexclusive OR gate 64. Terminal 53 is connected to the other input of OR gate 64 through time delay means 66 such as a clock pulse counter 66' . A. three input AND gate 63 has one input, connected to OR gate 64 with the other two inputs being separately connected to terminals 54 and 56. A current amplifier 67 transmits output signals from AND gate 63 to relay driver coil 46 to lock differential 22 when the AND gate is enabled. Thus if both of switches 51' and 52' and at least one of switches 49' and 61' are closed, all three inputs of AND gate 63 are receiving enabling signals and the gate transmits a lock up signal to driver coil 46 through amplifier 67, although the

enabling of g ' ate 63 is delayed for a predetermined period following closure of turn sensing switch 49', if manual override switch 61' is open at that time, owing to the time delay means 66. Conversely, AND gate 63 is disabled, unlocking differential 22, if either or both of switches 51' and 52' are open or if both of switches 49' and 61' are open although unlocking of the differential 22 in response to opening of turn sensing switch 49' is delayed for a predetermined period.

Time delay means 66 prevents lockup of the differential 22 in response to momentary closures of turn sensing switch 49' which may occur during essentially nonlinear travel of the ' vehicle 11 and similarly prevents unlocking of the differential in response to brief openings of the turn sensing switch that do not persist long enough to ' be indicative of a significant turn of travel direction. In a loader vehicle 11, the time delay period may typically be 0.5 seconds although other periods may be appropriate in other vehicles or under specialized operating conditions.

While the described embodiment is in part an electrical ' system, control valve 36 may be fluid pressure operated and the electrical switches 49', 51', 52' and 61' and logic circuit elements 63, 64, 66 and 67 may be replaced with the known equivalent fluidic circuit elements .

Industrial Applicability The differential control system 29 was designed for usage in an articulated loader of the kind used in earthmoving operations. The invention is equally adaptable to diverse other power driven

vehicles which have lockable diff rentials.

In operation, the operator's closure of engine start switch 42 electrically energizes B+ conductor 41 and, after starting of the engine 14, causes pump 32 to pressurize fluid_ supply line 34. Differential 22 remains unlocked during start μp as directional shift lever 19 is at the neutral position setting at that time and therefore at least switch 51', of switches 49', 51' and 61', is open. Consequently, at least terminal 54 of microprocessor 47' Is unenergized and AND gate 63 is thus disabled. As relay driver coil 46 is unenergized, control valve 36 remains in the unactuated position at which lock up means 27 is vented to reservoir 33. - Subsequent shifting of directional shift lever 19 to either the forward or reverse drive positions, in order to initiate travel of vehicle 11, closes switch 51' and energizes terminal 54. The effect, if any, of this energization of terminal 54 then depends on the condition of turn sensing switch 49' and speed range sensing switch 52'. If switch 49' is closed due to steering system elements 57 and 58 being positioned for straight or substantially straight travel and if switch 51' is also closed due to positioning of speed range selector lever 21 at any of the lower three speed range settings, then terminals 53, 54 and 56 are all energized. As this enables AND gate 63, microprocessor 47' energizes relay driver coil 46 causing relay contacts 44 to close and actuate control valve 36. Valve 36 then shifts to pressurize lock up means 27 thereby locking the differential 22.

The differential 22 is not locked in the above described manner upon closure of neutral sensing

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switch 51' following start up if either or both of turn sensing switch 49' and speed range sensing switch 52' are open at the time. AND gate 63 remains disabled due to the absence of an enabling signal on at least one input and the microprocessor 47' does not energize relay driver coil 46. Locking of the differential 22 in the above described manner does occur subsequently in the further travel of the vehicle 11 at such time as speed range selector lever 21 has been placed in one of the. lower three speed range settings and steering system elements 57 and 58 are positioned for straight or substantially straight trave1.

With the differential 22 locked as a result of the vehicle 11 being traveled along a straight or substantially-straight path with transmission 16 at one of the lower three speed ranges, unlocking occurs automatically in response to either or both of two changes in the controls of the vehicle. If steering system elements 57 and 58 are repositioned to turn the vehicle, switch 49' opens and after a brief interval determined by time delay means 66', this disables AND gate 63. Relay driver coil 46 is de-energized and valve 36 shifts to unlock the differential 22 during the turn. At the conclusion of the turn, switch 49' recloses and again energizes terminal 53. After the brief time delay, micro¬ processor 47' responds by relocking of the differen¬ tial 22. . If wheel slippage occurs during a turn the operator may override the above described automatic actions of the differential control means 29 and lock the differential 22 by closing manual override, switch 61' . Through OR gate 64 this supplies the

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enabling signal to AND gate 63 that was interrupted by the opening of the turn sensing switch 49' at the " start of the turn.

The other condition under which differential control means 29 unlocks differential 22 during . travel of vehicle 11 is movement of speed range selector lever 21 to the highest or fourth speed range setting. This opens switch 52' and de- energizes ' terminal 56 which in turn disables AND gate 63. Thus microprocessor 47' de-energizes relay driver coil 46 and differential 22 is unlocked until such time as transmission 16 is downshifted into one of the lower speed ranges.

The differential control means 29 also assures the differential 22 is unlocked at all times when transmission 16 is in neutral. Directional shift lever 19 opens switch 51' under this condition thereby de-energizing terminal 54 and disabling AND gate 63. Relay driver coil 46 is de-energized caus- ing valve 36 to vent the lock up means 27 to reservoir33. Thus the differential control means 29 holds the differential 22 In a locked condition during straight or substantially straight travel at pre¬ determined lower travel speeds and automatically unlocks the differential, to provide free differential action, while turns of a significant degree and duration are underway and when the vehicle is travel¬ ing at relatively high speeds, The control means 29 also assures unlocking of the. differential 22 when the vehicle 11 is not being traveled and also enables an optional manually controlled lock up of the differen¬ tial during turns at the operator's discretion. These particular modes of vehicle operation which cause locking and unlocking of the differential 22 nay

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readily be modified as necessary to accommodate to differing operating conditions or different kinds of vehicles.

Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.