Dynamically adjustable inch/brake overlap for vehicle transmission control

A motorized vehicle includes a transmission system and an inch/brake device providing at least two ranges of motion. An engagement force of the transmission system is provided in a first range of motion of the inch/brake device, and a braking force of the motorized vehicle is provided in a second range of motion of the inch/brake device. An accelerator device moves between two or more positions, wherein moving the accelerator device from one position to another position causes an amount of overlap between the first and second ranges of motion of the inch/brake device to vary.

BACKGROUND

Inching is the process by which an operator controls the slow forward or reverse travel movement of a motorized vehicle by the light application of clutch torque through the transmission. Certain industrial vehicles including materials handling vehicles or fork lift trucks, include a dual-purpose inch/brake pedal. The inch/brake pedal operates to engage a vehicle braking system, and also to engage a vehicle transmission. Typically the braking system is fully engaged when the inch/brake pedal is fully depressed, whereas the vehicle transmission is fully engaged when the inch/brake pedal is fully released. Inching occurs in an intermediate range of motion of the inch/brake pedal when the vehicle transmission is only partially engaged. Many industrial vehicles further include an accelerator pedal which is used to control the engine speed. The accelerator pedal has no effect on the clutch torque until the vehicle transmission is engaged.

The present state-of-the-art is to provide a fixed or manually adjustable amount of overlap of transmission drive torque to service brake torque according to the position of the inching/brake pedal alone or in combination with the service brake torque or brake pressure. This is known as inch/brake overlap. For vehicles that provide for adjustable overlap, a service technician manually adjusts the amount of overlap while the vehicle is being serviced. The amount of overlap is accordingly fixed at the adjusted amount during subsequent operation of the vehicle, until the overlap is once again manually adjusted by a service technician.

As operating conditions of the vehicle change from one operating shift to the next, or indeed during the same operating shift, the fixed amount of inch/brake overlap is well suited for some operations and not for others. For example, if the inch/brake overlap is manually set at a low value, this works well when the vehicle is operating on level surfaces. The operator is able to control vehicle inching satisfactorily under normal conditions. However this same low value does not work well when the vehicle is operating on an inclined surface, in which case the vehicle will roll down the hill when the brake pressure decreases too low without sufficient transmission force to maintain a position of the vehicle on, or to move the vehicle up, the grade. During loading or unloading operations on an incline, unintended vehicle movement down the grade may cause damage to the load being moved, or to other equipment or vehicles located adjacent the load.

If the inch/brake overlap is manually set at a high level for vehicle operations on an inclined surface, this will improve the hill holding operation of the vehicle. However, the high level of inch/brake overlap will result in an unnecessary buildup of heat in the transmission and braking systems as they work against each other. This results in more frequent and expensive vehicle maintenance requirements, and is undesirable when the primary application of the vehicle is on a level operating surface. Inching operation of the vehicle when the inch/brake overlap is high also affects the degree of fine controllability of the vehicle, tending to cause the vehicle to lurch or operate unevenly.

The present invention addresses these and other problems.

SUMMARY OF THE INVENTION

A motorized vehicle is disclosed herein, as comprising a transmission system and an inch/brake device configured to provide at least two ranges of motion. An engagement force of the transmission system is provided in a first range of motion of the inch/brake device, and a braking force of the motorized vehicle is provided in a second range of motion of the inch/brake device. An accelerator device is configured to move between two or more positions, wherein moving the accelerator device from one position to another position causes an amount of overlap between the first and second ranges of motion of the inch/brake device to vary.

An inching control system is disclosed herein, as comprising an accelerator pedal position (APP) sensor and an inch/brake pedal position (IBPP) sensor. A vehicle processor is configured to selectively engage a transmission system or a vehicle braking system according to input received from the IBPP sensor. The vehicle processor is further configured to vary an amount of transmission engagement force associated with a single vehicle braking force value in an inch/brake overlap region of the inching control system according to input received from the APP sensor.

A method is disclosed herein, comprising monitoring an inch/brake device input and reducing a vehicle braking torque according to the inch/brake device input. The method further comprises monitoring an accelerator input and modifying an inch/brake overlap region according to the accelerator position input. The inch/brake overlap region is associated with simultaneous engagement of both a vehicle transmission system and a vehicle braking system

DETAILED DESCRIPTION

FIG. 1illustrates a simplified block diagram of an inching control system10comprising a controller40configured to provide a dynamically adjustable inch/brake overlap. The inching control system enhances inching control functionality by using acceleration pedal position (APP) to dynamically adjust or automatically vary the overlap of transmission driving torque with the service brake torque. Dynamically adjusting the relationship between transmission torque and brake torque provides the operator maximum controllability of vehicle positioning and inching operations in a variety of applications.

The inching control system10includes an APP sensor212, and an inch/brake pedal position (IBPP) sensor210. The controller40may comprise a vehicle processor, wherein the controller40is configured to selectively engage a transmission control system14or a vehicle braking system4according to input received from the IBPP sensor210. The controller40is further configured to vary an amount of transmission engagement force or transmission torque TT associated with a single vehicle braking force value in an inch/brake overlap region of the inching control system10according to input received from the APP sensor212.

In one embodiment, the transmission control system14and the vehicle braking system4are simultaneously engaged within the inch/brake overlap region. This results in simultaneous application of the transmission torque TT and a braking torque BT to a vehicle drive axle34. The drive axle34may comprise two or more drive wheels39. The braking torque BT may be understood as operating in an opposite direction as the transmission torque TT, as the braking torque BT resists a rotation of the drive axle34due to the rotational force of the transmission torque TT.

FIG. 2Aillustrates a simplified example inch/brake pedal43, shown in multiple operating positions. The inch/brake pedal43is shown mounted to, or otherwise located on, a cowl or operating platform25of a vehicle, however inch/brake pedal43may be located in any position or location within an operator compartment. In one embodiment, inch/brake pedal43pivots about an approximately horizontal axis to form varying angles or ranges of motion with respect to the operating platform25.

The inch/brake pedal43illustrated inFIG. 2Ais shown in solid lines at a fully released position IBP1. The inch/brake pedal43may include a return spring or other device that causes the inch/brake pedal43to remain or return to the released position IBP1anytime that an operator removes their foot from, or ceases to apply a minimum amount of force against, the inch/brake pedal43. At the fully released position IBP1, the inch/brake pedal43is associated with an input from the IBPP sensor210(FIG. 1) that corresponds to a full engagement of the transmission control system14. Various partially and fully depressed positions POP1, POP2, IBP2of the inch/brake pedal43are shown as dashed lines. One skilled in the art will appreciate that partially depressed positions POP1, POP2represent only two of the many possible positions that the inch/brake pedal43may be located at, intermediate the fully released position IBP1and the fully depressed position IBP2.

The fully depressed position IBP2of the inch/brake pedal43is associated with an input from the IBPP sensor210that corresponds to a full engagement of the braking system4(FIG. 1), wherein the transmission control system14(FIG. 1) is fully disengaged. One or more of the partially depressed positions POP1, POP2correspond to a range of motion of the inch/brake pedal43that provides inch/brake overlap.

FIG. 2Billustrates a simplified example accelerator pedal50, shown in multiple operating positions. The accelerator pedal50is shown mounted to, or otherwise located on, a cowl or operating platform25of a vehicle, however accelerator pedal50may be located in any position or location within an operator compartment. In one embodiment, accelerator pedal50pivots about an approximately horizontal axis to form varying angles or ranges of motion with respect to the operating platform25.

The accelerator pedal50illustrated inFIG. 2Bis shown in solid lines at a released position APP1. The accelerator pedal50may include a return spring or other device that causes the accelerator pedal50to remain or return to the fully released position APP1anytime that an operator removes their foot from, or ceases to apply a minimum amount of force against, the accelerator pedal50. At the fully released position APP1, the accelerator pedal50is associated with an input from the APP sensor212(FIG. 1) that corresponds to a zero or minimum request for vehicle speed, or a minimum engine speed, depending on the type of vehicle transmission.

Various partially and fully depressed positions APP0, APP2of the accelerator pedal50are shown as dashed lines. One skilled in the art will appreciate that partially depressed position APP0represents only one of the many possible positions that the accelerator pedal50may be located at, intermediate the fully released position APP1and the fully depressed position APP2. The partially depressed positions APP0of the accelerator pedal50is associated with an input from the APP sensor212that corresponds to an intermediate request for vehicle speed, or an intermediate engine speed, depending on the type of vehicle transmission.

The fully depressed position APP2of the accelerator pedal50is associated with an input from the APP sensor212that corresponds to a maximum request for vehicle speed, or a maximum engine speed, depending on the type of vehicle transmission. In one embodiment, the accelerator pedal50provides speed-based accelerator pedal position functionality, wherein a different vehicle speed is associated with each position or angle of the accelerator pedal50, independent of the engine speed.

In some transmission control systems, the position of the accelerator pedal sets a target travel speed. Transmission torque is controlled in combination with engine rpm to deliver the target travel speed regardless of load or grade. The Transmission Control System illustrated inFIGS. 1 and 3operates similarly as described in U.S. Pat. No. 6,950,737 to Robert Lee Chess, filed Oct. 20, 2003 and entitled “Transmission Control System”, the specification of which is incorporated by reference in its entirety.

Inch/brake pedal43and accelerator pedal50may be understood to comprise one or more pedals, buttons, joysticks, toggles, switches, or any other operating control known in the art. Any reference to pressing, depressing or otherwise changing a location or position of the pedals43,50may be understood to be provided by operations of twisting, rotating, flipping, selecting, toggling, switching, or otherwise actuating the inching, braking, or acceleration devices providing the same or similar functionality as pedals43,50.

FIG. 3illustrates an example block diagram of a transmission control system14. Transmission control system14is connected to an engine12by a hydraulic torque converter15. An output shaft38of the transmission control system14is connected to a drive axle34that drives wheels39. In one example, the transmission control system14is used in a fork lift truck. However, the transmission control system14can also be used in other types of vehicles.

A Central Processing Unit (CPU) or controller40controls the activation of a forward clutch pack (FWD)54and a reverse clutch pack (REV)56in the transmission control system14according to different vehicle parameters. A control valve16in the transmission control system14controls fluid pressure that activates the two clutch packs54and56.

The controller40receives a vehicle speed and direction signal18from a vehicle speed sensor200indicating the rotational speed and direction of the drive axle34. A converter speed signal20is generated from a torque converter speed sensor202and indicates the rotational speed for a shaft17(FIG. 4) of the torque converter15. An engine speed signal30is generated from an engine speed sensor204and indicates how fast an output shaft13(FIG. 4) of the engine12is rotating. An engine governor control signal32controls the speed of engine12. A transmission temperature signal28is generated from a temperature sensor208and indicates the temperature of the transmission fluid in the torque converter15or transmission control system14.

FIG. 4illustrates a further block diagram of the transmission control system14ofFIG. 3. In one embodiment, the transmission control system14comprises a powershift transmission. The inching control system ofFIG. 1may operate with a single speed powershift transmission, a multi-speed powershift transmission, or any other combination of gears, for performing the braking and inching operations described herein.

The torque converter15includes an impeller pump214and a turbine216. A shaft13extends from the impeller pump214and is coupled to the crankshaft of engine12. Shaft17extends from the turbine216and is coupled to the input of transmission control system14. The torque converter15continuously varies the ratio of the speed of the shaft17to the speed of the shaft13in accordance with the load on the shaft17.

The forward clutch54and the reverse clutch56each selectively engages and disengages the shaft17with shaft38through the forward gears21and reverse gears23. The engaging force of the clutches54and56is controlled by changing the oil pressure in oil chambers54C and56C, respectively. The oil pressures are controlled by the control valve16which is controlled by the controller40(FIG. 3). The clutches54and56in one embodiment are multiple disk hydraulic wet clutches.

When the clutch pressures are both zero, the clutches54and56disconnect the shaft38from the shaft17. When the clutch pressure for either of the clutch packs is at a maximum pressure, the corresponding clutch pack maximizes the engaging force (locking). When the clutch pack pressure is between zero and the maximum value, the corresponding clutch pack is partially engaged. The partially engaged condition is referred to as clutch pack slipping. A FWD-1signal24inFIG. 3controls the oil pressure in the forward clutch54. A REV-1signal22inFIG. 3controls the oil pressure in the reverse clutch56. A FWD-2signal26controls the oil pressure in the forward high clutch (not shown).

The controller40receives a brake pedal position signal42from the IBPP sensor210on inch/brake pedal43. An accelerator pedal position signal44is received from the APP sensor212on accelerator pedal50. The accelerator pedal position can alternatively refer to a throttle value, acceleration value, deceleration value, engine speed value, engine torque value, or a target vehicle travel speed value. A forward-reverse direction signal46is generated by a direction sensor52and indicates a forward or backward direction the vehicle operator selects for the vehicle. An internal or external memory48contains mapped parameters identifying clutch pack pressure values and other control parameters used for performing different braking operations.

FIG. 5is a diagram illustrating inching control with manually adjusted, fixed inch/brake overlap. The vertical axis of the diagram represents an amount of torque provided by a transmission system and a braking system, respectively. The horizontal axis of the diagram represents a position or angle of an inch/brake pedal.

A low transmission torque curve58A illustrates an amount of clutch torque actuated according to the inch/brake pedal position. At a zero degrees inch/brake pedal position at the left-hand side of the diagram, the low transmission torque curve58A is at a maximum value (e.g. the transmission is fully engaged). As the inch/brake pedal position moves from zero degrees through a first range of motion (illustrated as being from zero to approximately twelve degrees), the transmission torque value decreases from the maximum value to zero torque. At zero torque, the transmission control system becomes disengaged, such that the vehicle engine is unable to provide any acceleration to the vehicle.

Brake torque curve55illustrates an amount of brake torque applied according to the inch/brake pedal position. At a first braking position55A, the brake torque curve55A is at a minimum value (e.g. the brakes are beginning to engage). The first braking position55A is shown as occurring at approximately fourteen degrees, for illustrative purposes only. As the inch/brake pedal position moves from the first braking position55A through a second range of motion including a second braking position55B, the brake torque value increases from the minimum brake torque value to a maximum brake torque value. The second braking position55B is shown as occurring at approximately twenty two degrees, for illustrative purposes only.

As the inch/brake pedal is moved from the first range of motion associated with the low transmission torque curve58A to the second range of motion associated with the brake torque curve55, the transmission system becomes disengaged and the braking system becomes engaged. There is no inch/brake overlap between the low transmission torque curve58A and the brake torque curve55, rather this region is referred to as underlap. In the underlap region, the vehicle may coast according to any inertia or gravitational forces acting on it, there being no transmission or brake torque being applied to the vehicle drive axle. For certain applications involving operating the vehicle on relatively flat surfaces, this may be acceptable or desirable performance. However, where the vehicle is being operated on an incline, this may result in inadvertent movement of the vehicle prior to or during inching operations.

The torque curve may be manually shifted by a service technician, for example, to be fixed at a high transmission torque curve58B. The high transmission torque curve58B also illustrates an amount of clutch torque actuated according to the inch/brake pedal position. At a zero degrees inch/brake pedal position at the left-hand side of the diagram, the high transmission torque curve58B is at a maximum value (e.g. the transmission is fully engaged). As the inch/brake pedal position moves from zero degrees through a first range of motion (illustrated as being from zero to approximately eighteen degrees), the transmission torque value decreases from the maximum value to zero torque.

As discussed with respect to the low transmission torque curve58A, when the high transmission torque curve58B reaches zero torque the transmission control system also becomes disengaged, such that the engine is unable to provide any acceleration to the vehicle. After the manual adjustment of the transmission torque curve, however, an inch/brake overlap provides an operating condition where the transmission system and the braking system both provide torque to the drive axle. As a result, by the time the high transmission torque curve58B reaches zero, the braking torque curve55has increased to a non-trivial amount that may be sufficient to provide a certain degree of hill holding capability for the vehicle.

If the vehicle is then once again operated on a flat surface, the fixed high transmission torque curve58B will continue to apply the same inch/brake overlap region which results in excessive heating of the transmission and braking system, and may also affect inching control of the vehicle. However, in order to revise the inching control system back to the low transmission torque curve58A, the service technician once must again work on the vehicle to manually adjust the inch/brake overlap.

FIG. 6is an example diagram illustrating inching control with dynamically adjustable inch/brake overlap. The vertical axis of the diagram represents an amount of torque provided by the transmission system14and the braking system4ofFIG. 1, respectively. The horizontal axis of the diagram represents a position or angle of an inch/brake pedal, such as inch/brake pedal43ofFIG. 2A.

A first transmission torque curve60A illustrates an amount of clutch torque actuated associated with the fully released accelerator pedal position APP1ofFIG. 2B. The first transmission torque curve60A may be understood as being operable provided the accelerator pedal50(FIG. 2B) is held or maintained at the fully released pedal position APP1. At the fully released inch/brake pedal position IBP1(FIG. 2A) at the left-hand side of the diagram, the first transmission torque curve60A is at a maximum value. As the inch/brake pedal position moves from the fully released pedal position IBP1through a first range of motion including partially pressed pedal position POP1(FIG. 2A), the transmission torque value decreases from the maximum value to zero torque.

Brake torque curve65illustrates an amount of brake torque actuated according to the inch/brake pedal position. At a first braking position65A, the brake torque curve65is at a minimum value. As the inch/brake pedal position moves from the first braking position65A through a second range of motion including a second braking position65B, the brake torque value increases from the minimum brake torque value to a maximum brake torque value.

As the inch/brake pedal43(FIG. 2A) is moved from the first range of motion associated with the first transmission torque curve60A to the second range of motion associated with the brake torque curve65, the transmission system14(FIG. 1) becomes disengaged and the braking system4(FIG. 1) becomes engaged. The region between the first transmission torque curve60A and the brake torque curve65as illustrated inFIG. 6identifies inch/brake underlap. Inch/brake underlap is indicated when the input received from the accelerator pedal position sensor212(FIG. 1) indicates zero vehicle acceleration, and wherein neither the transmission system14nor the braking system4are engaged.

In one embodiment, only one of the transmission system14or the braking system4is engaged when the inching control system10is outside of the inch/brake overlap region. For example, when the position of the inch/brake pedal43is between pedal position IBP1and POP1, only the transmission system14is engaged. When the position of the inch/brake pedal43is between pedal positions65A and IBP2, and an inch/brake underlap condition exists, only the brake system4is engaged.

The torque curve may be dynamically adjusted or shifted between the first transmission torque curve60A and a second transmission torque curve60B, according to a position of the accelerator pedal50(FIG. 2B). The second transmission torque curve60B is associated with the fully pressed accelerator pedal position APP2(FIG. 2B). The second transmission torque curve60B may be understood as being operable provided the accelerator pedal50(FIG. 2B) is held or maintained at the fully pressed accelerator pedal position APP2.

The second transmission torque curve60B also illustrates an amount of clutch torque actuated according to the inch/brake pedal position. At the released inch/brake pedal position IBP1at the left-hand side of the diagram, the second transmission torque curve60B is at a maximum value. As the inch/brake pedal43moves from the released pedal position IBP1through a first range of motion including partially pressed pedal position POP2(FIG. 2A), the transmission torque value decreases from the maximum value to zero torque. In the embodiment illustrated byFIG. 6, the inch/brake overlap region exists as a function of actuating both the brake pedal43and the accelerator pedal50at the same time. Simultaneously pressing the inch/brake pedal43and the accelerator pedal50causes the transmission driving torque to be available before the brake torque is released.

An inch/brake overlap is illustrated as occurring between the brake torque curve65and the second transmission torque curve60B. The inch/brake overlap may be understood to exist between the inch/brake pedal position65A and the inch/brake pedal position POP2, wherein pedal position POP2indicates that the inch/brake pedal43has been pressed further than indicated by pedal position65A. The inch/brake overlap region provides an operating condition where the transmission system14and the braking system4both simultaneously provide torque to the drive axle34for the same position, or range of positions, of the inch/brake pedal43.

The inch/brake overlap region varies according to input received from the accelerator pedal position sensor212(FIG. 1). In one embodiment, the inch/brake overlap region is largest when the input received from the accelerator pedal position sensor212indicates a request for maximum vehicle travel speed. On the other hand, the inch/brake overlap region may be smallest when the input received from the accelerator pedal position sensor212indicates a request for zero vehicle travel speed.

FIG. 7is a further example diagram illustrating inching control with dynamically adjustable inch/brake overlap. A motorized vehicle may comprise a transmission system, such as transmission system14(FIG. 1), and an inch/brake device, such as inch/brake pedal43(FIG. 2A) configured to provide at least two ranges of motion. The first range of motion may include a position of the inch/brake pedal43between pedal positions65A and65B. A braking force of the motorized vehicle is provided in the first range of motion of the inch/brake pedal43. The second range of motion may include a position of the inch/brake pedal43between pedal positions IBP1and POP1or POP2. An engagement force of the transmission system14is provided in the second range of motion of the inch/brake pedal43.

The motorized vehicle may further comprise an accelerator device, such as accelerator pedal50(FIG. 2B) configured to be moved between two or more positions. In one embodiment, moving the accelerator pedal50from one position to another position causes an amount of overlap between the first and second ranges of motion of the inch/brake pedal43to vary.

The inch/brake pedal43may be configured to simultaneously provide both the braking force of the motorized vehicle and the engagement force of the transmission system14when the first and second ranges of motion of the inch/brake pedal43overlap. The overlap between the first and second ranges of motion of the inch/brake device exists when the position of the accelerator pedal50indicates a request for non-zero acceleration.

FIG. 7further illustrates an intermediate transmission torque curve70A associated with an intermediate, or partially pressed position APP0of the accelerator pedal50. The intermediate transmission torque curve70A overlaps with the brake torque curve65, as identified by a first overlap region OV1. First overlap region OV1provides for a reduced amount of transmission torque for a fixed or selected position of the inch/brake pedal43, for example inch/brake pedal position POP1.

Second transmission torque curve70B is associated with the fully pressed position APP2of the accelerator pedal50. The second transmission torque curve70B overlaps with the brake torque curve65, as identified by a second overlap region OV2. The region identified by the second overlap region OV2is larger than, and includes the region identified by, the first overlap region OV1. The engagement torque of the transmission system14varies as the amount of overlap varies, wherein the braking force of the motorized vehicle remains constant, for a single or select position of the inch/brake pedal43. For example, the transmission torque associated with the second transmission curve70B is greater than the transmission torque associated with the intermediate torque curve70A, for the same position POP1of the inch/brake pedal43.

In one embodiment, the accelerator pedal position may be made to vary, for example between accelerator pedal position APP0and APP2, in order to vary an amount of transmission torque for the selected position of the inch/brake pedal. By way of example, when the vehicle is being operated on an incline, the operator may initially press the accelerator pedal50to position APP0while simultaneously pressing the inch/brake pedal43to position POP1. Depending on the angle of slope or grade that the vehicle is operating on, the amount of braking force or braking torque associated with inch/brake pedal position POP1may be sufficient to keep the vehicle from rolling down the hill. For steeper grades, the braking torque may not be sufficient to hold the vehicle. Similarly, the transmission torque associated with transmission torque curve70A may not be sufficient to propel or accelerate the vehicle up the grade.

By pressing the accelerator pedal50to accelerator pedal position APP2, inch/brake overlap region dynamically increases and results in an increase in transmission torque associated with the transmission torque curve70B without increasing the engine speed. This is shown inFIG. 7by the upward trending transmission torque change75. The increase of transmission torque may therefore cause the vehicle to accelerate up the steep incline without first rolling in the opposite direction. The position of the accelerator pedal50may be varied to any position intermediate pedal positions APP0and APP2, and for that matter between APP1and APP2to incrementally vary the amount of inch/brake overlap and corresponding change in transmission torque.

FIG. 8is an example diagram illustrating inching control with dynamically adjustable inch/brake overlap, and the interaction of the accelerator pedal50(FIG. 2B) and the inch/brake pedal43(FIG. 2A). Inch/brake pedal position42(FIG. 3) corresponds to brake torque curve65. The brake torque curve65may correspond with the braking torque provided by a service brake. The relationship between a inch/brake pedal position42and the brake torque is plotted on the brake torque curve65. As the inch/brake pedal43is pressed, a point is reached where brake torque begins304.

Transmission driving torque is used to move the vehicle. If the inch/brake pedal43is released at inch/brake position IBP1, it corresponds to a maximum transmission driving torque at point350. As the inch/brake pedal43is pressed, the transmission driving torque begins to be reduced during speed control100. The first inching transmission torque curve80A associated with the released accelerator pedal position APP1(FIG. 2B) is plotted against the inch/brake pedal position.

Speed control100remains in effect until point352. Point352may correspond to a partially pressed inch/brake pedal position which is less than inch/brake pedal position POP1. In one embodiment, point352is associated with an inch/brake position of approximately ten degrees, whereas inch/brake position POP1is approximately twelve degrees. The transmission driving torque of speed control100is a function of accelerator pedal position44(FIG. 3), inch/brake pedal position42, engine speed30(FIG. 3), speed of the shaft17(FIG. 4), the target vehicle travel speed, and the actual vehicle travel speed and direction18(FIG. 3).

Inching Control with No Accelerator Pedal Pressed

At point352, if the accelerator pedal50is at APP1(FIG. 2B), then the transmission driving torque drops to a lower level indicated by point354. Then as the inch/brake pedal position42increases further to partially pressed inch/brake pedal position POP1, the transmission driving torque continues to drop to zero at point355. At point355, inch/brake underlap exists. When the inch/brake pedal position42reaches point304, the brake torque begins to increase according to brake torque curve65.

If the inch/brake pedal position42is then steadily decreased from a point on the brake torque curve65towards the partially pressed inch/brake pedal position POP1, the transmission driving torque will begin to increase at point355and follow the first inching transmission torque curve80A upward and to the left to point351. At point351, the inching control transitions back to speed control100.

Inching Control with Accelerator Pedal Pressed

At point352, if the accelerator pedal50is pressed, then the transmission driving torque drops to a lower level indicated by point353on the second inching torque curve80B associated with accelerator pedal position APP2(FIG. 2B). Then as the inch/brake pedal position42increases further towards partially pressed inch/brake pedal position POP2, the transmission driving torque continues to drop along the second inching torque curve80B to zero at point356. At point356, inch/brake overlap exists. At this point, a vehicle will feel like it is driving against the service brakes during inch/brake overlap.

As the inch/brake pedal position42continues to increase towards the fully pressed inch/brake pedal position IBP2, brake torque begins to increase according to the brake torque curve65. If the inch/brake pedal position42is then steadily decreased from a point on the brake torque curve65towards the partially pressed inch/brake pedal position POP2, the transmission driving torque will increase from point356to point357and follow the second inching torque curve80B that was shifted by pressing the accelerator pedal50. In one embodiment, the amount of shift of the inching torque curve is proportional to an amount that the accelerator pedal50is pressed. At point351, the inching control transitions back to speed control100.

If the transmission driving torque is equal to zero before the brake torque begins to rise, then inch/brake underlap exists. If the transmission driving torque is greater than zero after the brake torque begins to rise, then inch/brake overlap exists. If the accelerator pedal50is pressed while inching control is in effect, then the first inching transmission torque curve80A undergoes a dynamic shift to the right to the second inching transmission torque curve80B. This has the affect of dynamically increasing the inch/brake overlap region. This is useful for starting on a grade, and helps prevent the vehicle rolling back down the hill during starting or inching.

FIG. 9is an example block diagram illustrating a system or process90of determining transmission torque for an accelerator pedal based speed control system. Process90comprises several applications, including a speed control based torque application100and an inching control based torque application101. Applications100and101may be implemented in software or hardware, and in one embodiment, operations performed by one or more of the applications100and101are performed by controller40ofFIG. 1.

Speed control based torque application100determines transmission torque target100A. Speed control based torque application100receives input from a number of different components or sensors to determine the transmission torque target100A. Input may be received from one or more of the vehicle speed sensor200, the engine speed sensor204, the torque converter shaft speed sensor202, the APP sensor212, and the IBPP sensor210(seeFIGS. 1 and 3). The transmission torque target100A may be determined as a function of the input from one or more of the sensors200,202,204,210,212.

In one embodiment, a target travel speed is first determined as a function of input from APP sensor212and IBPP sensor210. Next, the transmission torque target100A is determined as a function of the target travel speed, and input from the vehicle speed sensor200, engine speed sensor204, and torque converter output shaft speed sensor202.

The inching control based torque application101(see alsoFIG. 8) determines final transmission torque target101B. During an inching operation, final transmission torque target101B is determined as a function of the transmission torque target100A, and input from the APP sensor212and the IBPP sensor210. A look up table (LUT), such as LUT48ofFIG. 1, or a modified algorithm may be used in addition to, or in place of, the computations or functions described herein.

The process90of determining transmission torque may be configured to dynamically increase transmission torque with braking torque, also known as inch/brake overlap, according to input received from the accelerator pedal50(FIG. 2B) and the inch/brake pedal43(FIG. 2A). Additional features of the one or more embodiments described herein are as follows:Brake pedal position schedules the transmission driving torque.Acceleration pedal position increases inching overlap function by shifting the inch/brake schedule of transmission driving torque to the right.Opposite clutches of the transmission system are slipped at low desired drive torque to provide smooth engagement of torque.The starting inch/brake overlap relationship may be adjusted manually or electrically, so that more or less transmission torque corresponds to a fixed level of braking torque.

FIG. 10illustrates an example method of operation200for providing inching control including a dynamically adjustable inch/brake overlap. At operation205, an inch/brake device input (e.g. inch/brake pedal position) is monitored. The inch/brake device input may indicate a braking position. At operation210, a vehicle braking torque is reduced according to the inch/brake device input.

At operation215, an accelerator input (e.g. accelerator pedal position) is monitored. The accelerator input may indicate a first accelerator position and a second accelerator position. The level of transmission torque associated with the braking position may be zero when the accelerator input indicates the second accelerator position.

At operation220, an inch/brake overlap region is modified according to the accelerator position input, wherein the inch/brake overlap region is associated with simultaneous engagement of both a transmission system and a vehicle braking system. The transmission system may be initially engaged for different inch/brake device input values according to the accelerator input.

In one embodiment a level of transmission torque associated with the braking position is increased when the accelerator input indicates the first accelerator position. A level of transmission torque associated with the braking position may be decreased when the accelerator input indicates the second accelerator position. A transmission torque curve associated with the transmission system may vary depending if the inch/brake device input is increasing or decreasing in value.

When the transmission torque associated with the engagement of the transmission system is greater than the vehicle braking torque, the vehicle begins to move (operation230). In one embodiment, the transmission torque provided during the inching operation varies as a function of both the inch/brake device input and the accelerator input.

FIG. 11illustrates an example method of an inching control system300with dynamic inch/brake overlap. At operation305, an inch/brake pedal position that exceeds an entry criteria (e.g. minimum threshold value) initiates an inching control operation or functionality.

At operation310, a speed input (e.g. accelerator pedal position) is monitored. The speed input may indicate a range from a first accelerator pedal position to a second accelerator pedal position.

At operation320, the speed input is multiplied by a gain factor K. This gain factor enables tuning of the inching control system300to accommodate combinations of different brakes and power trains providing the desired dynamic inch/brake overlap response.

At operation330, a clutch input (e.g. inch/brake pedal position) is monitored. The clutch input may indicate a transmission torque value or range of values. A change in clutch input value may indicate an increase or decrease in transmission torque. The change in clutch input value may further indicate an increase or decrease in braking torque. Clutch input is associated with a torque curve.

At operation340, the effective position of the inch/brake pedal is shifted according to the speed input and gain factor. This may result in a dynamic shift or modification of the torque curve. The dynamic shift may operate to increase the inch/brake overlap associated with simultaneous engagement of both a transmission system and a vehicle braking system as the speed input is increased (e.g. the accelerator pedal is pressed). The transmission system may be initially engaged for different inch/brake device input values according to the speed input.

At operation350, the transmission torque corresponding to the modified torque curve for the shifted inch/brake pedal position is looked up or otherwise determined. The corresponding transmission torque may then be commanded.

At operation360, the clutch input is monitored to determine if the system300should exit from inching control and return to speed control. In one embodiment, the system300exits from inching control when the inch/brake pedal has been released to a predetermined position or angle. If the clutch input remains greater than the predetermined value, then the system300returns to operation320.

By providing a vehicle with dynamic control of how much inch/brake overlap is available for any operation or job function requiring fine position control (e.g. inching) of a vehicle, vehicle operation is improved. For example, one or more of the embodiments described herein may be configured to:Enable a vehicle to start moving up hill from a stop on a grade without rolling downhill.Reduce excessive overlap between transmission torque and braking torque, thereby reducing system heat, increasing fuel economy, and increasing service life of truck components.Provide for fine traction control of the truck for very small movements.Provide an intuitive method to dynamically change the amount of inch/brake overlap, thus reducing operator training and increasing productivity.

The system and apparatus described above can use dedicated processor systems, micro-controllers, programmable logic devices, or microprocessors that perform some or all of the operations. Some of the operations described above may be implemented in software and other operations may be implemented in hardware. It is further understood that computer-readable medium having instructions stored thereon may be provided, wherein when the instructions are executed by at least one device, they are operable to perform some or all of the operations.

Where specific numbers are provided, they are given as examples only and are not intended to limit the scope of the claims. The relationship between inputs and outputs of the various operations, computation, and methods described herein may be established by algorithms or by look up tables contained in processor memory.

For the sake of convenience, the operations are described as various interconnected functional blocks or diagrams. This is not necessary, however, and there may be cases where these functional blocks or diagrams are equivalently aggregated into a single logic device, program or operation with unclear boundaries.

Having described and illustrated the principles of the invention in a preferred embodiment thereof, it should be apparent that the invention may be modified in arrangement and detail without departing from such principles. We claim all modifications and variation coming within the spirit and scope of the following claims.