Retarding system implementing torque converter lockup

A retarding system for a work machine is disclosed. The retarding system has a power source, a transmission, and a torque converter operatively coupling the power source and the transmission. The torque converter has a lockup clutch. The retarding system also has a controller in communication with the lockup clutch. The torque converter is configured to receive an input indicative of a desired work machine acceleration, to determine a status of the lockup clutch, and to determine if engaging the lockup clutch will cause a speed of the power source to drop below a low idle speed. The controller is also configured to engage the lockup clutch if the input indicates that the desired work machine acceleration is below a predetermined amount, the lockup clutch is disengaged, and the speed of the power source will remain above the low idle speed after engagement of the lockup clutch.

TECHNICAL FIELD

The present disclosure relates generally to a retarding system and, more particularly, to a retarding system that implements torque converter lockup.

BACKGROUND

Work machines, including on and off-highway haul and vocational trucks, wheel loaders, motor graders, and other types of heavy machinery generally include a multi-speed, bidirectional, automatic transmission drivingly coupled to an engine by way of a hydraulic torque converter. The hydraulic torque converter multiplies and/or absorbs torque fluctuations transmitted from the engine to the transmission by allowing slippage between an output shaft of the engine and an input shaft of the engine. To improve fuel consumption and reduce power loss due to the slippage, the torque converter typically includes a lockup clutch for mechanically coupling the engine output and transmission input shafts.

When the engine output and transmission input shafts are mechanically coupled, the engine can be used to slow the work machine's travel. For example, power can be transferred from the wheels of the work machine in reverse direction through the transmission to drive the mechanically coupled engine. The natural resistance of the engine then dissipates some of the transferred power, thereby slowing the work machine. Additional power may be dissipated by the use of engine or exhaust braking that increases the resistance of the engine. However, because typical torque converters disengage the lockup clutch at low vehicle speeds to minimize the likelihood of stalling the engine, the retarding capacity of the work machine may be greatly reduced at these low vehicle speeds. That is, little or no power may be transferred from the wheels to the engine when the lockup clutch is disengaged and slippage is allowed to occur.

One method of improving the retarding capacity of a work machine at low travel speeds is described in U.S. Pat. No. 6,152,853 (the '853 patent) issued to Banks, III Nov. 28, 2000. The '853 patent describes an exhaust braking system that includes a vehicle speed sensor, an exhaust brake valve, and a controller in communication with a lockup clutch and a transmission. If a sensed vehicle speed is greater than a speed value preset by an operator via a user interface, the controller engages the lockup clutch and closes the exhaust brake valve to bring the vehicle speed back down to the preset speed value. If it is determined that the vehicle speed is greater than the preset speed value and increasing, additional retarding may be implemented by downshifting the transmission.

Although the exhaust braking system of the '853 patent may sufficiently control the travel speed of a vehicle, it may be inadequate for some situations and excessive for others. In particular, because the exhaust braking system of the '853 patent only engages when the vehicle speed exceeds the operator preset speed value, it may do nothing to retard the vehicle when the vehicle operates at speeds lower than the preset speed value, even if engine retarding is desired. In addition, because the lockup clutch only engages when the exhaust brake valve is activated, lower levels of retarding that require only the natural resistance of the engine may not be possible.

The disclosed retarding system is directed to overcoming one or more of the problems set forth above.

SUMMARY OF THE INVENTION

In one aspect, the present disclosure is directed to a retarding system for a work machine. The retarding system includes a power source, a transmission, and a torque converter operatively coupling the power source and the transmission. The torque converter has a lockup clutch. The retarding system also includes a controller in communication with the lockup clutch. The controller is configured to receive an input indicative of a desired work machine acceleration, determine a status of the lockup clutch, and determine if engaging the lockup clutch will cause a speed of the power source to drop below a low idle speed. The retarding system is further configured to engage the lockup clutch if the input indicates that the desired work machine acceleration is below a predetermined amount, the lockup clutch is disengaged, and the speed of the power source will remain above the low idle speed after engagement of the lockup clutch.

In yet another aspect, the present disclosure is directed to a method of decelerating a work machine. The method includes receiving an input indicative of a desired work machine acceleration, determining a status of a torque converter lockup clutch, and determining if engaging the torque converter lockup clutch will cause a speed of a work machine power source to drop below a low idle speed. The method also includes engaging the torque converter lockup clutch if the input indicates that a desired work machine acceleration is below a predetermined amount, the torque converter lockup clutch is currently disengaged, and the speed of the work machine power source will remain above the low idle speed after engagement of the torque converter lockup clutch.

DETAILED DESCRIPTION

FIG. 1illustrates an exemplary work machine10. Work machine10may embody a mobile machine that performs some type of operation associated with an industry such as mining, construction, farming, transportation, or any other industry known in the art. For example, work machine10may be an earth moving machine such as an off-highway haul truck, a wheel loader, a motor grader, or any other suitable earth moving machine. Work machine10may alternatively embody an on-highway vocational truck, a passenger vehicle, or any other operation-performing work machine. Work machine10may include, among other things, a power source12, a torque converter14, a transmission16operably connected to a traction device18, a brake mechanism20, and an operator station21.

Power source12may be configured to produce a power output and may include an internal combustion engine. For example, power source12may include a diesel engine, a gasoline engine, a gaseous fuel-powered engine, or any other engine apparent to one skilled in the art. It is contemplated that power source12may alternatively include a non-combustion source such as, for example, a battery, a fuel cell, a motor, or any other known non-combustion source of power.

Torque converter14may be a hydro-mechanical device configured to couple power source12to transmission16. In particular, torque converter14may conduct pressurized fluid between the output of power source12and the input of transmission16to thereby drive transmission16, while still allowing power source12to rotate somewhat independently of transmission16. In addition, torque converter14may include a lockup clutch22for directly mechanically coupling the output of power source12to the input of transmission16. Lockup clutch22may engage and disengage in response to one or more inputs, as will be described in more detail below. In this arrangement, torque converter14may selectively absorb and multiply the torque transferred between power source12and transmission16by either allowing or preventing slippage between the output rotation of power source12and input rotation of transmission16. It is contemplated that lockup clutch22may generate a signal indicative of the status of lockup clutch22(i.e., engaged or disengaged) during operation f torque converter14. It is also contemplated that the status of lockup clutch22may alternatively be determined by comparing an output rotational speed of power source12to an input rotational speed of transmission16. It is further contemplated that torque converter14may alternatively embody a non-hydraulic device such as, for example, a mechanical diaphragm clutch.

Transmission16may include numerous components that interact to transmit power from power source12to traction device18. In particular, transmission16may embody a multi-speed, bidirectional, mechanical transmission having a neutral gear ratio, a plurality of forward gear ratios, a reverse gear ratio, and one or more clutches (not shown). The clutches may be selectively actuated to engage predetermined combinations of gears (not shown) that produce a desired output gear ratio. Transmission16may be an automatic-type transmission, wherein shifting is based on a power source speed, a maximum selected gear ratio, and a shift map stored within a transmission controller. The output of transmission16may be connected to rotatably drive traction device18via a shaft23, thereby propelling work machine10.

Traction device18may include wheels24located on each side of work machine10(only one side shown). Alternately, traction device18may include tracks, belts, or other driven traction devices. Traction device18may be driven by transmission16to rotate in accordance with an output rotation of transmission16.

Brake mechanism20may be configured to retard the motion of work machine10and may be operably associated with each wheel24of work machine10. In one embodiment, brake mechanism20is a hydraulic pressure-actuated wheel brake such as, for example a disk brake or a drum brake disposed intermediate wheel24and a drive assembly26. It is contemplated that brake mechanism20may alternatively embody another non-hydraulic type of wheel brake such as an electric motor or any other similar mechanism known in the art.

Operator station21may be configured to receive input from a work machine operator indicative of a desired acceleration of work machine10. Specifically, as illustrated inFIG. 2, operator station21may include one or more operator interface devices46such as a throttle pedal46aand a brake pedal46blocated forward of an operator seat. Operator interface devices46may embody proportional-type controllers configured to increase or decrease the acceleration of work machine10by producing an acceleration signal that is indicative of a desired work machine acceleration. It is contemplated that different operator interface devices may alternatively or additionally be included within operator station21such as, for example, single or multi-axis joysticks, wheels, knobs, push-pull devices, switches, and other operator interface devices known in the art.

Throttle pedal46amay be manually actuated to increase the rotational speed of power source12and the resulting travel speed work machine10. In particular, a degree of throttle pedal actuation may represent a desired acceleration and proportionally control an amount of fuel supplied to power source12. It is contemplated that throttle pedal46amay embody a mechanical device, an electrical device, a hydraulic device, or any other type of device known in the art.

A throttle sensor (not shown) may be provided for indicating whenever throttle pedal46ais actively indicating a desired acceleration of work machine10, and the magnitude of the desired acceleration. The throttle sensor may embody, for example, a switch or a pressure sensor capable of producing an electric signal indicating that positive acceleration is being requested. A switch may indicate a position or angle of throttle pedal46a, while a pressure sensor may indicate a pressure of a pilot fluid pressurized by the motion of throttle pedal46a.

Brake pedal46bmay be manually operated to direct pressurized fluid to brake mechanism20. A degree of brake pedal actuation may proportionally control a pressure and/or a flow rate of the fluid supplied to brake mechanism20. It is contemplated that brake mechanism20may alternatively be pneumatically actuated, mechanically actuated, electrically actuated, or actuated in any other manner known in the art.

A brake sensor (not shown) may be provided for indicating whenever active retarding (e.g. negative acceleration) of work machine travel is desired and what magnitude of retarding is desired. The brake sensor may embody, for example, a switch or a pressure sensor capable of producing an electric signal indicating that negative acceleration is requested. A switch may indicate a position or angle of brake pedal46b, while a pressure sensor may indicate a pressure of a pilot fluid pressurized by brake pedal46b.

As also illustrated inFIG. 2, work machine10may further include a retarding system28having components that cooperate with brake mechanism20and transmission16to decelerate work machine10. In particular, retarding system28may include an engine-retarder30and a controller32.

Engine retarder30may embody any device that selectively increases the natural resistance of power source12to motion. For example, engine retarder30may embody an engine brake or an exhaust brake. An engine brake may function to open the exhaust valves (not shown) of power source12near the top dead center (TDC) position of a piston's compression stroke. By opening the exhaust valves near top dead center of the compression stroke, highly-compressed air may be vented to the atmosphere, thereby removing stored energy from the associated pistons of power source12. On the ensuing downward power stroke, essentially no energy is returned to the piston (and to traction device18), resulting in a deceleration of work machine10. In contrast, an exhaust brake may include a butterfly-type valve disposed within an exhaust manifold of power source12to restrict the exiting flow of exhaust gases. The restricted flow of exhaust gases may cause a backup of pressure within power source12that increases the work that the pistons of power source12must perform during the compression and exhaust strokes of power source12, resulting in a deceleration of work machine10. It is contemplated that engine retarder30may alternatively be located immediately upstream of torque converter14(referring to the flow of power during normal operation of work machine10) to directly remove power from the input of transmission16(e.g., transmission braking). It is further contemplated that engine retarder30may be hydraulically operated, mechanically operated, electrically operated, pneumatically operated, or operated in any other suitable manner.

Controller32may embody a single microprocessor or multiple microprocessors that include a means for controlling an operation of retarding system28. Numerous commercially available microprocessors can be configured to perform the functions of controller32. It should be appreciated that controller32could readily embody a general work machine microprocessor capable of controlling numerous work machine functions. Various other known circuits may be associated with controller32, including power supply circuitry, signal-conditioning circuitry, solenoid driver circuitry, communication circuitry and other appropriate circuitry.

Controller32may be in communication with various components of work machine10. In particular, controller32may be in communication with a power source speed sensor34via a communication line36to receive an indication of a rotational speed of power source12, with transmission16via a communication line38to affect downshifting of transmission16, with a work machine travel speed sensor40via a communication line42to receive an indication of a travel speed of work machine10, with brake mechanism20via a communication line44to determine whether brake mechanism20is active or inactive, and with engine retarder30via a communication line45. Controller32may also be in communication with throttle pedal46a, brake pedal46b, a lockup clutch switch48, and an inclinometer49via communication lines50,52,54, and56, respectively.

Power source and work machine travel speed sensors34and40may both embody magnetic pickup-type sensors. In particular, power source speed sensor34may be associated with a flywheel58of power source12and configured to sense a rotational speed and produce a corresponding speed signal. Similarly, work machine travel speed sensor40may be associated with shaft23and configured to sense a travel speed and produce a corresponding speed signal.

Lockup clutch switch48and inclinometer49may embody commonly known devices. For example, lockup clutch switch48may embody a wheel actuator, a knob actuator, a push-pull device, a switch, or any other operator interface device manually selectable to indicate that engagement of lockup clutch22is desired. Inclinometer49may be configured to monitor the grade on which work machine10is operating and to generate a signal indicative of the grade. It is contemplated that one or both of lockup clutch switch48and inclinometer49may be omitted, if desired.

As described above, lockup clutch22may be engaged to retard the motion of work machine10in response to one or more inputs. Specifically, controller32may receive input associated with throttle pedal46a, brake pedal46b, power source speed sensor34, work machine travel speed sensor40, and inclinometer49, and engage lockup clutch22in response to the input. Controller32may automatically engage lockup clutch22in response to the input or only after receiving, via lockup clutch switch48, a manual indication that lockup is desired. When lockup clutch22is engaged, wheels24may transmit power in a reverse direction through transmission16and lockup clutch22to power source12, where the natural resistance of power source12may act to dissipate the power.

Controller32may include one or more maps stored within an internal memory of controller32and reference these maps to determine the affect of lockup clutch engagement on the speed of power source12before lockup clutch22is engaged. Each of these maps may include a collection of data in the form of tables, graphs, and/or equations. In one example, work machine travel speed and the current gear ratio of transmission16may form the coordinate axis of a 2-D table for determining the resulting speed of power source12after engagement of lockup clutch22. In another example, work machine travel speed, the current gear ratio of transmission16, and the current rotational speed of power source12may form the coordinate axis of a 3-D table. Controller32may compare the resulting speed of power source12to a predetermined low idle speed threshold (e.g., the speed at or about the stall speed of power source12) and engage or prevent engagement of lockup clutch22in response to the comparison. It is contemplated that an operator of work machine10may be allowed to directly modify these maps and/or to select specific maps from available relationship maps stored in the memory of controller32to affect engagement of lockup clutch22. It is further contemplated that the maps may alternatively be manually or automatically selectable based on modes of work machine operation.

Controller32may increase the natural resistance of power source12, if it is determined that the current amount of retarding (e.g., the current rate of deceleration) after engagement of lockup clutch22is insufficient. Specifically, controller32may receive input associated with throttle pedal46aand brake pedal46band determine whether or not additional deceleration is desired. Additional desired deceleration may be indicated by reducing an actuation position of throttle pedal46a, increasing the actuation position of brake pedal46b, and/or continued actuation of brake pedal46bfor an extended predetermined period of time. Alternatively, the current deceleration rate of work machine10may be directly monitored via power source speed sensor34or work machine travel speed sensor40and compared to a deceleration rate threshold value stored within the memory of controller32. Controller32may then activate engine retarder30to increase the natural resistance of power source12, thereby increasing the retarding affect.

In addition, controller32may initiate or increase accessory loading of power source12and/or work machine10if the current level of retarding is insufficient. Accessory loading of power source12and/or work machine10may include, among other things, the activation of a cooling fan, an air conditioning pump, a hydraulic implement pump, an electric generator, and other such devices that draw power from power source12and/or work machine10.

Controller32may also be configured to initiate a downshift of transmission16to thereby increase the retarding effect of engine retarder30. In particular, controller32may determine that engine retarder30is active and may determine a current deceleration rate of work machine10resulting from the operation of engine retarder30. If the current deceleration rate of work machine10is less than desired or less than the predetermined deceleration threshold value, controller32may actuate the clutches of transmission16to selectively engage a predetermined combination of gears, thereby effecting the desired downshift.

FIG. 3illustrates an exemplary operation of retarding system28.FIG. 3will be described in detail below.

INDUSTRIAL APPLICABILITY

The disclosed retarding system may be applicable to any work machine where retarding at low travel speeds is desired. The disclosed retarding system may selectively engage a lockup clutch of a hydro-mechanical torque converter to allow power transfer to and dissipation from a power source of the work machine. Operation of retarding system28will now be explained.

Referring toFIG. 3, the operation of retarding system28may initiate in one of two ways. In particular, an operator may manually initiate the operation of retarding system28via lockup clutch switch48or, alternatively, the operation of retarding system28may automatically be initiated in response to one or more input (Step100). Retarding system28may be configured for automatic operation during a manufacturing process or, alternatively, may be configured by a service technician according to customer preference upon purchase or leasing of work machine10.

Following activation of retarding system28, controller32may determine whether or not acceleration of work machine10is desired (Step110). As described above, signals generated by throttle pedal46aand brake pedal46bmay provide the indication of operator-desired acceleration. For example, if throttle pedal46ais situated in a depressed position and then released, it can be assumed that a negative acceleration (e.g., deceleration) of work machine10is desired. The rate of releasing may provide an indication of the magnitude of the desired deceleration. In contrast, if throttle pedal46ais depressed to a greater extent, it can be assumed that a positive acceleration of work machine10is desired. Similarly, if brake pedal46bis depressed, it can be assumed that a negative acceleration of work machine10is desired. The rate of depressing may provide an indication of the magnitude of the desired deceleration. In contrast, if brake pedal46bis released from a depressed position, it can be assumed that the amount of deceleration is sufficient or that deceleration is no longer desired.

If positive acceleration is undesired (e.g., deceleration is desired), controller32may then determine the status of lockup clutch22(i.e., engaged or disengaged) (Step120). Lockup clutch22may provide this status information automatically or only when prompted by controller32. Alternatively, controller32may determine the status of lockup clutch22by comparing the rotational speed of power source12to the travel speed of work machine10and the current gear ratio of transmission16. If positive acceleration is desired, control may return to step110.

If lockup clutch22is disengaged, controller32may monitor both engine rotational and work machine travel speeds (Step130). It is contemplated that step130may be performed continuously, before steps100-120, or after steps110-120. If lockup clutch22is already engaged, control may return to step110.

Once controller32has determined that lockup clutch22is disengaged and has monitored the engine rotational and work machine travel speeds, controller32may then determine if the engagement of lockup clutch22will reduce the rotational speed of power source12below a predetermined low idle speed (Step140). Controller32may determine the affect of lockup clutch engagement on power source12speed by comparing the input signals received via power source and travel speed sensors34and40, and the gear ratio of transmission16with the maps stored in the memory of controller32. If the speed of power source12drops below low idle speed, it may be possible for power source12to stall. Therefore, if the engagement of lockup clutch22will cause the rotational speed of power source12to drop below the low idle speed, control may return to step110without engagement of lockup clutch22. Otherwise, if the speed of power source12will remain above the low idle speed after engagement of lockup clutch22, controller32may synchronize the output speed of power source12to the input speed of transmission16and cause engagement of lockup clutch22(Step150). The speeds of power source12and transmission16may be synchronized by increasing or decreasing the amount of fuel supplied to power source12to thereby raise or lower the speed of power source12, by operating a motor (not shown) associated with power source12to drive power source12to a higher speed, by operating engine retarder30to reduce the speed of power source12, by operating a transmission brake (not shown) to reduce a speed of transmission16, or in any other suitable manner. By synchronizing the output speed of power source12and the input speed of transmission16prior to the engagement of lockup clutch22, smooth engagement of lockup clutch22may be facilitated without complex and expensive pressure modulation systems or algorithms.

After engagement of lockup clutch22, deceleration of work machine10should begin. Controller32may then determine if the current rate of retarding is sufficient (Step160) and affect the rate of retarding in response to the determination. In particular, if controller32determines that the rate of retarding after engagement of lockup clutch22is insufficient (e.g., additional deceleration is desired), controller32may then activate engine retarder30to increase the resistance of power source12(Step170). As described above, controller32may determine if the current rate of retarding is sufficient by monitoring the actuation of throttle and brake pedals46aand46bor, alternatively, by comparing the rate of deceleration to a predetermined deceleration threshold value. If the rate of retarding is sufficient, control may return to step110without activation of engine retarder30.

After activation of engine retarder30, deceleration of work machine10should increase. Controller32may then again determine if the current rate of retarding is sufficient (Step180). If controller32determines that the rate of retarding after activation of engine retarder30is insufficient, controller32may then activate accessory loading to increase the resistance of power source12. Activation of accessory loading may include, among other things, operating a cooling fan, operating an air conditioning system, operating an electric generator, operating a hydraulic implement pump, or operating any other component of work machine10that draws power from power source12. It is contemplated that if the rate of deceleration is still insufficient after the activation of accessory loading transmission16, controller32may automatically trigger transmission16to initiate a downshift, thereby transferring a greater amount of power to power source12for dissipation. If the rate of retarding is sufficient, control may return to step110without activating accessory loading.

An alternative condition may be required of retarding system28prior to the initial engagement of torque converter lockup clutch22. Specifically, between steps110and120, controller may communicate with inclinometer49, if desired, to determine if work machine10is operating on an incline (Step200). Controller32may then continue on to step120if work machine is operating on an incline greater than a predetermined amount, or return control to step110if working on a substantially level surface. In this manner, lockup clutch22may only engage if the likelihood exists of work machine10involuntarily accelerating down an incline.

Several advantages of retarding system28may be realized over the prior art. In particular, because controller32can engage lockup clutch22at nearly any travel speed of work machine10, retarding system28may provide a broader speed range of retarding. In addition, because retarding system28can engage lockup clutch22without having to activate engine retarder30, retarding system28may provide a more efficient retarding system, with the levels of retarding tailored to meet the needs of work machine10and its operator.

It will be apparent to those skilled in the art that various modifications and variations can be made to the retarding system of the present disclosure. Other embodiments of the retarding system will be apparent to those skilled in the art from consideration of the specification and practice of the retarding system disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the disclosure being indicated by the following claims and their equivalents.