System for allocating transmission clutch wear

A control system for a transmission engages three clutches to create braking within the transmission to slow a machine during a shuttle shifting operation. The control system may apply the clutches so as to allocate wear between the clutches equally or unequally, as desired.

TECHNICAL FIELD

This disclosure relates generally to a system for controlling a transmission of a machine and, more particularly, to a system for controlling the transmission during shuttle shifting to allocate clutch wear within the transmission.

BACKGROUND

Transmission systems use a number of different transmission configurations and control schemes. Such transmissions typically include a plurality of intermeshing gears that are either fixed to transmission shafts or that rotate freely on the shafts. Clutches associated with the freely rotating gears may be selectively engaged to establish a series of speed ratios between a prime mover output shaft and transmission output shaft to transmit torque at a desired speed to drive a machine. Control systems for controlling the clutches typically include electronic circuitry that responds to operator controls such as those directing speed and/or shuttle shifts. The control system may send electrical signals to hydraulic valves that control the clutches. The control system thus causes the clutches to engage and disengage in predetermined combinations to accelerate, decelerate, and drive a machine as desired by the operator.

Some of the control systems provide a directional or shuttle shifting capability that permits an operator to command direct shifting between a forward gear and a reverse gear by movement of a gear shift lever or similar command device directly to the target gear. Various systems have been used in connection with directional or shuttle shifting operations to slow the velocity of the machine during the operation. In general, such systems disengage the clutches corresponding to the then current gear ratio and eventually engage clutches corresponding to the target gear ratio.

U.S. Pat. No. 4,989,470 discloses a system that permits controlled deceleration of a vehicle during shuttle shifts by disengaging the transmission from the engine by disengaging one of the clutches within the transmission. A different clutch is then engaged to create braking or tie-up within the transmission to create a load on the vehicle and slow the rotation of the transmission and the velocity of the vehicle. Once the vehicle has reached a desired velocity, typically close to zero, the clutch used for braking is disengaged and another clutch engaged for accelerating the vehicle in the desired direction.

The foregoing background discussion is intended solely to aid the reader. It is not intended to limit the innovations described herein nor to limit or expand the prior art discussed. Thus the foregoing discussion should not be taken to indicate that any particular element of a prior system is unsuitable for use with the innovations described herein, nor is it intended to indicate any element, including solving the motivating problem, to be essential in implementing the innovations described herein. The implementations and application of the innovations described herein are defined by the appended claims.

SUMMARY

A clutch control system for a transmission of a machine is provided. In one aspect, the clutch control system allocates clutch wear during shuttle shifting of the transmission. The transmission is operatively connected to a prime mover to propel the machine and has a first directional clutch and a second directional clutch. The first directional clutch and the second directional clutch are operatively connected to an input shaft of the transmission. A plurality of additional clutches are operatively connected to an output shaft of the transmission. A first of the additional clutches operates as an engagement clutch. A second of the additional clutches operates as a first braking clutch. A third of the additional clutches operates as a second braking clutch. A controller is configured to transmit a first engagement signal to engage the engagement clutch and transmit an isolation signal to disengage the first directional clutch and isolate the prime mover from the additional clutches. The controller may also transmit a first braking signal to the first braking clutch to apply a first braking force and transmit a second braking signal to the second braking clutch to apply a second braking force before reducing the first braking force. The engagement clutch, the first braking clutch and the second braking clutch cooperate to apply a combined force to slow rotation of the output shaft. The controller may also transmit a first reduction signal to one of the engagement clutch, the first braking clutch, and the second braking clutch to reduce the combined force and transmit a second reduction signal to another of the engagement clutch, the first braking clutch, and the second braking clutch to reduce the combined force. The controller may also transmit a second engagement signal to engage the second directional clutch upon the occurrence of a designated trigger event.

In another aspect, a clutch control system allocates clutch wear during shuttle shifting of a transmission. The transmission is operatively connected to a prime mover to propel the machine. The transmission has a plurality of clutches in a first set operatively connected to a rotatable input shaft of the transmission, and a plurality of clutches in a second set operatively connected to a rotatable output shaft of the transmission. The first set of clutches may operate to isolate the prime mover from the second set of clutches. The second set of clutches include an engagement clutch, a first braking clutch, and a second braking clutch. A controller is configured to transmit a first engagement signal to engage the engagement clutch and transmit an isolation signal to disengage one of the clutches of the first set to isolate the second set of clutches from the prime mover. The controller may also transmit a first braking signal to the first braking clutch to apply a first braking force and transmit a second braking signal to the second braking clutch to apply a second braking force before reducing the first braking force. The engagement clutch, the first braking clutch and the second braking clutch cooperate to apply a combined force to slow rotation of the output shaft. The controller may also transmit a first reduction signal to one of the engagement clutch, the first braking clutch, and the second braking clutch to reduce the combined force and transmit a second reduction signal to another of the engagement clutch, the first braking clutch, and the second braking clutch to reduce the combined force. The controller may also transmit a second engagement signal to engage another of the clutches of the first set upon the occurrence of a designated trigger event.

In a further aspect, a method of allocating clutch wear during shuttle shifting of a transmission is provided. The method may include engaging an engagement clutch and disengaging a first directional clutch to isolate additional clutches from a prime mover. A first braking clutch may be applied to apply a first braking force and a second braking clutch applied to apply a second braking force before reducing the first braking force. The engagement clutch, the first braking clutch and the second braking clutch may cooperate to apply a combined force to slow rotation of an output shaft. One of the engagement clutch, the first braking clutch, and the second braking clutch may be disengaged to reduce the combined force and another of the engagement clutch, the first braking clutch, and the second braking clutch may be disengaged to reduce the combined force. The second directional clutch may be engaged upon the occurrence of a designated trigger event.

DETAILED DESCRIPTION

FIG. 1depicts a power train20of a machine (not shown) that includes a prime mover such as an internal combustion engine21, a torque converter22, a multi-speed transmission30, and a drive train23. The internal combustion engine21is connected to the torque converter22via shaft24, the torque converter22is connected to the transmission30via rotatable input shaft25, and the transmission30is connected to the drive train23via rotatable output shaft26.

Transmission30includes a plurality of gears (not shown) that may be engaged in various combinations to achieve desired gear ratios between input shaft25and output shaft26. In addition, the gears control the direction of rotation of output shaft26to establish forward and reverse movement of the machine. A plurality of clutches are located within the transmission. Although six clutches51-56are depicted, transmission30may include other numbers of clutches as desired. Gear shifts are accomplished by selectively engaging and disengaging combinations of the clutches. The clutches may be actuated by hydraulic pressure and controlled by an electronic control module or controller41.

The control system40of the power train20may include one or more input devices42to select a desired gear ratio and direction. The controller41receives the gear selection signal and controls the operation of the hydraulic system that engages and disengages the clutches. The controller41may also receive various other input signals representative of various operating parameters. Such other inputs signals may include an engine speed signal from an engine speed sensor43, an transmission input speed signal from a transmission input speed sensor44, one or more internal transmission speed signal from one or more internal transmission speed sensors45, and a transmission output speed signal from a transmission output speed sensor46.

Controller41may be an electronic controller that operates in a logical fashion to perform operations, execute control algorithms, store and retrieve data and other desired operations. The controller41may include or access memory, secondary storage devices, processors, and any other components for running an application. The memory and secondary storage devices may be in the form of read-only memory (ROM) or random access memory (RAM) or integrated circuitry that is accessible by the controller41. Various other circuits may be associated with the controller41such as power supply circuitry, signal conditioning circuitry, driver circuitry, and other types of circuitry. The controller41may be a single controller or may include more than one controller disposed to control various functions and/or features of the machine as well as the transmission30. As used herein, the term “controller” is meant to include one or more controllers that may be associated with the transmission30and that may cooperate in controlling various functions and operations of the transmission. The functionality of the controller41may be implemented in hardware and/or software without regard to the functionality. One or more data maps relating to the operating conditions of the transmission30may be stored in the memory of controller41. Each of these maps may include a collection of data in the form of tables, graphs, and/or equations.

The transmission30may be configured in a number of different manners. In one configuration depicted inFIG. 1, transmission30includes a front section31operatively connected to input shaft25and a rear section32operatively connected to output shaft26. In such configuration, a first set of clutches, such as clutches51-52, is located in the front section31and may operate as a first directional clutch and a second directional clutch for shifting between a first direction (e.g., forward) and a second opposite direction (e.g., reverse). A second set of clutches, such as clutches53-56, is located in rear section32and may operate as speed clutches for shifting between different gear ratios. If desired, an intermediate section33(FIG. 2) may be provided between front section31and rear section32. Intermediate section33may include an additional set of clutches57-58that operates to provide additional functionality within transmission30. The additional clutches may form an additional set of clutches or may be a portion of the first set or a portion of the second set of clutches. In another alternate configuration depicted inFIG. 3, front section131of transmission130includes a first set of clutches, such as speed clutches151-154, that is used for shifting between different gear ratios and rear section132includes a second set of clutches, such as directional clutches155-156, that is used for shifting between forward and reverse. An intermediate section133may be positioned between front section131and rear section132, if desired. The intermediate section133may include an additional set of clutches157-158that operates to provide additional functionality within transmission130. Each of the sections of the transmissions may include other numbers of clutches as necessary for carrying out desired shifting operations.

When engaging or applying clutches to shift gears, it is generally desirable to engage an on-coming clutch and an off-going clutch in a predetermined sequence to avoid undesirable braking or tie-up within the transmission30. Such braking may result in undesirable energy losses during a shifting operation. In some instances, however, such as during directional or shuttle shifting, it may be desirable to utilize such braking to decelerate the machine as described above with respect to U.S. Pat. No. 4,989,470.

Referring toFIG. 4, a directional or shuttle shifting operation is depicted. The off-going directional clutch (such as clutch51inFIG. 1) is released at a first designated trigger event t1which isolates the remaining portion of transmission30from the internal combustion engine21. More specifically, releasing the off-going directional clutch isolates the rear section32of the transmission30from the front section31. By isolating the internal combustion engine21from the load of the transmission30, fuel may be saved during the shuttle shifting operation as the internal combustion engine is not used to slow the machine.

During the shuttle shifting operation or process, a first speed clutch (such as clutch53inFIG. 1) of the rear section32of the transmission30remains engaged with a constant clutch pressure and thus is designated inFIG. 4as the non-changing speed clutch. Maintaining the engagement of the non-changing speed clutch or engagement clutch results in the rear section32of the transmission30remaining operatively connected to output shaft26. Since output shaft26is connected to drive train23, continued movement of the machine due to its momentum will cause the continued rotation of the rear section32of the transmission30.

In order to increase the deceleration of the machine, a second speed clutch (such as clutch54inFIG. 1) may be engaged at a second designated trigger event t2and is designated as a first braking clutch inFIG. 4. The interaction of the non-changing speed clutch and the first braking clutch creates a desired level of braking or tie-up within the transmission30to increase the rate at which the machine is decelerated. However, utilizing the second speed clutch as a braking clutch creates additional wear on that clutch. To reduce the wear on the second speed clutch, a third speed clutch (such as clutch55inFIG. 1) may also be engaged at a second designated trigger event t2that, in conjunction with the first speed clutch and the second speed clutch, provides further braking or tie-up within the transmission. InFIG. 4, the third speed clutch is designated as a second braking clutch and functions to further slow the rotation of the rear section32of transmission30and thus output shaft26. In other words, the non-changing speed clutch, the first braking clutch and the second braking clutch cooperate to apply a combined force that slows the rotation of the output shaft26of transmission30.

As the first braking clutch and the second braking clutch slip, they distribute or allocate the braking function between the two clutches and convert energy in the form of momentum of the machine into energy that is dissipated by the clutches. The first braking clutch and second braking clutch may be engaged generally simultaneously at a designated trigger event or point as depicted at second designated trigger event t2. In the alternative, one may be applied at a second designated trigger event t2and then the other at a subsequent second designated trigger event t2. In other words, each of the first braking clutch and the second braking clutch would have its own second designated trigger event such as t2aand t2b(not shown) inFIG. 4but would be spaced apart along the “Time” axis. As depicted inFIG. 4, greater pressure is applied by the first braking clutch as compared to the second braking clutch. This may be due to one or more factors. For example, as discussed below, the first braking clutch may have a larger surface area than the second braking clutch or may be formed of a different material and thus may be better able to efficiently absorb the energy of the braking operation.

Once the shuttle shifting operation has reached a third designated trigger event t3, the controller41directs a reduction in pressure to the first braking clutch and the second braking clutch so that the tie-up or braking within the transmission30is reduced. As the pressures of the first braking clutch and the second braking clutch are reduced, the second directional clutch (designated as the on-coming directional clutch inFIG. 4) may be engaged at a fourth designated trigger event t4which causes the re-engagement of input shaft25with transmission30and thus causes the machine to accelerate in the desired, opposite direction.

Many alternatives to the timing of the steps of the process depicted inFIG. 4are contemplated. For example, although the first braking clutch and the second braking clutch are depicted as engaging at approximately the same time, the timing of their engagement (at second designated trigger events t2) may be varied based upon many different factors. In some applications, it may be desirable for the first braking clutch and the second braking clutch to be engaged sequentially. However, to reduce the wear on the clutches, it may be desirable for the second braking clutch to begin to be engaged before the first braking clutch begins to disengage. In other words, it may be desirable for the engagement (at second designated trigger event t2) of each braking clutch to occur before the disengagement of the other braking clutch begins at third designated trigger event t3.

Although the disengagement of the first braking clutch and the second braking clutch may begin generally simultaneously at third designated trigger event t3, the disengagement operation could occur sequentially with the disengagement of either braking clutch beginning before the other. Still further, although the second braking clutch is depicted as being completely disengaged (at fifth designated trigger event t5) before the first braking clutch is completely disengaged (at sixth designated trigger event t6), the order of complete disengagement could be reversed or could be simultaneous.

The pressure of the on-coming directional clutch may begin to rise (at fourth designated trigger event t4) before either of the first braking clutch or the second braking clutch is completely disengaged or released (at sixth designated trigger event t6and fifth designated trigger event t5, respectively). In an alternate configuration, the on-coming directional clutch could begin to be engaged (at fourth designated trigger event t4) after either of the first braking clutch or the second braking clutch is completely disengaged. In some applications, it may be desirable for the on-coming directional clutch to begin to be engaged (at fourth designated trigger event t4) after both the first braking clutch and the second braking clutch are completely disengaged.

The timing of the second through fourth designated trigger events t2-t4as well as the rates of change (slopes) of the pressures of the various clutches may be set or determined in a number of different ways. In one example, some aspects of the operation may be based upon real-time monitoring of the operation of the machine. For example, the first braking clutch and the second braking clutch could begin to be engaged at second designated trigger event t2after a designated amount of time or time period has elapsed or passed following the disengagement of the off-going directional clutch at first designated trigger event t1. The velocity of the machine may be monitored such as by transmission output speed sensor46. The timing of the designated trigger event at which the pressure of the first braking clutch and the second braking clutch are reduced (at third designated trigger event t3) may be based upon monitoring of the velocity of the machine as determined by a signal from the transmission output speed sensor46. In some cases, it may be desirable for the third designated trigger event t3to occur when the velocity of the machine, and thus the speed of rotation of output shaft26, reaches a predetermine velocity. In some cases, such velocity may be approximately zero. Similarly, the engagement of the on-coming directional clutch (at fourth designated trigger event t4) may also be based upon monitoring of the velocity of the machine.

In another example, the second through fourth designated trigger events t2-t4may be determined from a data map contained within or accessible by the controller based upon the velocity of the machine and other operating conditions including the current and target gear ratios at the time of the command for shuttle shifting or the inception of the shuttle shifting operation. In still another example, each of the second through fourth designated trigger events t2-t4may be fixed so as not to vary with the velocity and other operating conditions of the machine.

If desired, the data map might also designate the rate of change or slope of the pressure of each of the clutches. For example, the rate of increase in pressure of the first braking clutch, second braking clutch, and the on-coming directional clutch may be based upon the velocity and operating conditions of the machine as well as the current and target gear ratios. In another example, the rate of change or slope of the pressures may be set so as to be constant regardless of the velocity and operating conditions.

It should be noted that the rear section32of transmission30has a plurality of speed clutches that may be used for shifting between different gear ratios, and any of the speed clutches may be used as the non-changing speed clutch or engagement clutch and any of the other speed clutches may be used as the first braking clutch and the second braking clutch. In addition, if desired, additional speed clutches may be used to provide a third or more additional braking clutches. In such case, additional steps may be added to the process ofFIG. 5between stage66and stage67so that the additional braking clutches are engaged and between stage69and stage70so that all but one of the engaged clutches of the rear section32of transmission30are disengaged. If the front section31of transmission30includes more than two directional clutches, any of the directional clutches may be used as the off-going directional clutch and the on-coming directional clutch so long as the off-going directional clutch isolates the transmission30from the internal combustion engine21and the on-coming directional clutch re-engages the connection between the internal combustion engine21and the transmission30.

Referring toFIG. 5, a flowchart showing the process corresponding to the shuttle shifting operation ofFIG. 4is depicted. Controller41initially transmits an engagement signal at stage61to engage a directional clutch. Controller41transmits a first engagement signal at stage62to engage a first speed clutch. The first speed clutch is designated the non-changing speed clutch inFIG. 4and functions as an engagement clutch. Once a command is issued for shuttle shifting at stage63, the controller41transmits an isolation signal at stage64to disengage the directional clutch and isolate the prime mover from the clutches of the rear section32of transmission30. Controller41transmits a first braking signal at stage65to engage a second speed clutch which is designated the first braking clutch inFIG. 4. Controller41transmits a second braking signal at stage66to engage a third speed clutch which is designated the second braking clutch inFIG. 4.

At stage67, the controller41determines whether the third designated trigger event t3has occurred. Once the third designated trigger event t3has occurred, the controller41transmits a first reduction signal at stage68to disengage one of the engagement clutch, the first braking clutch, and the second braking clutch. The controller41then transmits a second reduction signal at stage69to disengage another of the engagement clutch, the first braking clutch, and the second braking clutch. Upon the occurrence of the fourth designated trigger event t4at stage70, controller41transmits a second engagement signal at stage71to engage a second directional clutch which causes the re-engagement of input shaft25with transmission30and thus causes the machine to accelerate in the desired direction.

Referring toFIGS. 6A and 6B, a flowchart and a table show a possible sequence of engagement and disengagement and the overlapping engagement of the clutches but does not reflect the amount of pressure or degree of engagement. The forward clutch (F) and a first speed clutch (S1) are initially engaged at stage81. The forward clutch (F) is designated as the off-going directional clutch at stage82and the first speed clutch (S1) is designated as the engagement clutch (E). A second speed clutch (S2) is engaged at stage83and is designated as the first braking clutch (B1). A third speed clutch (S3) is engaged at stage84and is designated as the second braking clutch (B2). At the third designated trigger event t3, the first braking clutch (B1) (stage85) and the second braking clutch (B2) (stage86) are disengaged. While the engagement clutch (E) remains engaged, the reverse clutch (R) is engaged at stage87and becomes the on-coming directional clutch.

FIGS. 7A-9Aare flowcharts similar toFIG. 6AandFIGS. 7B-9Bare tables similar toFIG. 6Bbut depict some of the many alternate manners in which the engagement clutch (E), the first braking clutch (B1), and the second braking clutch (B2) may be disengaged. InFIGS. 7A and 7B, the first braking clutch (B1) may be disengaged first at stage85but then the engagement clutch (E) is disengaged at stage96leaving the second braking clutch (B2) to take the place of the engagement clutch at stage97. Such configuration not only changes the direction of travel of the machine but also changes the gear ratio. InFIGS. 8A and 8B, the third speed clutch (S3) is engaged at stage103as the first braking clutch (B1) and the second speed clutch (S2) is engaged at stage104as the second braking clutch (B2). During shuttle shifting, the engagement clutch (E) is disengaged at stage105first and then the second braking clutch (B2) is disengaged at stage106leaving the first braking clutch (B1) to take the place of the engagement clutch at stage97. As withFIGS. 7A and 7B, the configuration ofFIGS. 8A and 8Bnot only changes the direction of travel of the machine but also changes the gear ratio.FIGS. 9A and 9Bare is-similar toFIGS. 8A and 8Bbut the first braking clutch (B1) is depicted as being disengaged at stage116after disengagement of the engagement clutch (E) at stage105so that the second braking clutch becomes the engagement clutch at stage117. FromFIGS. 6A-9Aand6B-9B, it can be seen that any two of the engagement clutch (E), the first braking clutch (B1), and the second braking clutch (B2) may be disengaged during shuttle shifting with the remaining clutch functioning as the new engagement clutch and operating to define the on-going gear ratio.

Referring toFIGS. 10A and 10B, another alternate embodiment is depicted.FIGS. 10A and 10Bare similar toFIGS. 6A and 6Bbut includes a second speed clutch (S2) that is engaged and functions as a second engagement clutch (E2) at stage121. A third speed clutch (S3) is engaged at stage123and is designated as the first braking clutch (B1). A fourth speed clutch (4) is engaged at stage124and is designated as the second braking clutch (B2). At the third designated trigger event t3, the first braking clutch (B1) (stage125) and the second braking clutch (B2) (stage126) are disengaged. Both the engagement clutch (E) and the second engagement clutch (E2) remain engaged, and the reverse clutch (R) is engaged at stage127and becomes the on-coming clutch.

Referring toFIGS. 11A and 11B, still another alternate embodiment is depicted.FIGS. 11A and 11Bare similar toFIGS. 6A and 6Bbut the reverse clutch (R) is engaged while the forward clutch (F) remains engaged and before the first braking clutch (B1) at stage132and the second braking clutch (B2) are disengaged. Once a sufficient amount of braking has occurred, the forward clutch (F) (stage137) and two of the first braking clutch (B1) (stage135), the second braking clutch (B2) (stage136), and the engagement clutch (E) may be disengaged to complete the shuttle shift.

An advantage of using two or more braking clutches is that the wear caused in executing a shuttle shifting operation can be allocated or apportioned between the braking clutches in any manner desired. As a result, the wear on any one clutch may be reduced. In some systems, it may be desirable for each clutch to undergo approximately equal amounts of wear and thus allocate wear approximately evenly between the first braking clutch and the second braking clutch. For clutches having equal diameters and equal numbers of wear elements made of the same material, the wear may be evenly allocated or shared by applying equal forces through each clutch. However, the clutches within the transmission30often have different diameters and different numbers of wear elements and thus different amounts of surface area. For clutches made of the same material and having different surface areas, different forces must be applied through each of the first braking clutch and the second braking clutch to evenly allocate wear. Accordingly, the pressure directed to the first braking clutch and the second braking clutch will often be different, as may be seen inFIG. 4.

Temperature rise of the friction material within a clutch may be used to measure wear allocation. Temperature rise is often proportional to the wear of a clutch. As a result, during a particular braking operation, the wear of a braking clutch may be monitored by monitoring the rise in temperature of the clutch. Many of the friction materials typically used with clutches tend to wear at substantially greater rates above a predetermined temperature for each material. Accordingly, in some configurations, it may be desirable to not only monitor the temperature rise within each clutch but to also avoid allowing the temperature of each braking clutch to rise above the predetermined value. Thus, the controller41may be set so that the pressure associated with each of the first braking clutch and the second braking clutch results in the first braking clutch and the second braking clutch each undergoing approximately equal rises in temperature.

The energy absorbed per unit area of a clutch also provides a convenient means of approximating the temperature rise in a clutch. Consequently, another manner of allocating wear between the first braking clutch and the second braking clutch is to set the energy absorbed per unit area of each clutch as approximately equal. This may be accomplished by calculating the areas of each of the first braking clutch and the second braking clutch and applying a different force through each of the clutches. If desired, the amount of energy to be absorbed may be set so as to be maintained below a predetermined threshold. This threshold may be based upon the material from which the wear elements of the clutches is formed.

In some situations, it may be desirable to allocate wear between braking clutches in an unequal manner. As an example, if one clutch is anticipated to be used less than others for shifting gears during the life of the transmission, it may be desirable for that clutch to undergo more wear than others during the various braking processes. In one example, the energy could be shared equally between clutches but with the “lesser used” clutch used more frequently during the braking process (as compared to other clutches). In another example, a greater force could be applied through the “lesser used” clutch which would result in it experiencing greater wear during the braking process as compared to other clutches. In both cases, the overall wear on the “lesser used” clutch due to the braking process would be greater as compared to other clutches. As a result, wear on the other clutches due to the braking process may be reduced and the balancing of wear between the clutches could be used to extend the overall life of the transmission30. In one example, the first braking clutch and the second braking clutch may undergo approximately unequal amounts of wear. In another example, the first braking clutch and the second braking clutch may undergo approximately unequal rises in temperature. In such case, it may be desirable for the temperature of each clutch to be maintained below a predetermined temperature.

INDUSTRIAL APPLICABILITY

The industrial applicability of the system described herein will be readily appreciated from the foregoing discussion. The present disclosure is applicable to transmissions30that may be used for directional or shuttle shifting operations. Shuttle shifting operations require the dissipation of energy in the form of momentum prior to re-engagement of the transmission30. The energy may be dissipated through the use of braking or tie-up within the transmission30. Such braking may cause significant or premature wear on some of the clutches within the transmission. In one aspect, controller41may be configured to allocate the braking forces between more than one clutch of the transmission. Allocating the energy absorption reduces the wear on any one clutch and thus may extend the life of the transmission.

The allocation of energy may be set so as to generally equally share wear between the clutches. In one aspect, the energy may be allocated so that the wear is evenly shared between clutches. In another aspect, the allocation may be made so as to share the wear of a particular shuttle shifting operation in an unequal manner and thus allocate clutch wear over the life of the transmission in a desired manner. In another aspect, the wear may be shared so that the energy dissipated per unit area is generally equal. In another aspect, the wear per unit area may be maintained below a predetermined threshold. In still another aspect, the clutches may under go approximately equal rises in temperature. If desired, the allocation of energy between clutches may be set so that wear is shared unequally between clutches.