Machine control system and method

A control system for a machine may include a processor configured to communicate with a power source. The processor may also be configured to communicate with a transmission assembly. The processor may be configured to determine whether the power source is in a potential stall condition based at least in part on an actual speed of the power source and a requested speed of the power source. If the power source is in the potential stall condition, the processor may be configured to request that fuel be supplied to the power source although the fuel is not currently required by the power source, in anticipation of an increase in load on the machine.

TECHNICAL FIELD

This disclosure relates generally to a control system for a machine, and more particularly, to a feed-forward control system and method.

BACKGROUND

A machine including, for example, a loader, a tractor, or other type of heavy machinery, may be used for performing a variety of tasks. An operator may use an operator interface to control components of the machine. The machine may also include a control system to assist with controlling machine components. Machine components may include, for example, an engine for generating power, a traction assembly configured to propel the machine using power from the engine, a transmission assembly configured to transfer power from the engine to the traction assembly, and an implement assembly for engaging materials.

In some machines, during deceleration, the power source may be driven by the traction assembly through the transmission assembly. When this happens, the power source may be driven above a desired speed by the traction assembly, through the transmission assembly. Because the power source speed is above the desired speed, a governor associated with the power source may attempt to drive the power source speed to the desired speed by cutting fuel supply to the power source. With no fuel, the power source will not produce output. If the machine encounters a load, such as a grade, pile, and/or an obstacle, during such a zero fuel condition, the power source may stall.

The disclosed machine control system and method is directed at overcoming one or more of the problems set forth above, as well as other problems known in the art.

SUMMARY

According to one aspect of the present disclosure, a control system for a machine may include a processor configured to communicate with a power source. The processor may also be configured to communicate with a transmission assembly. The processor may be configured to determine whether the power source is in a potential stall condition based at least in part on an actual speed of the power source and a requested speed of the power source. If the power source is in the potential stall condition, the processor may be configured to request that fuel be supplied to the power source although the fuel is not currently required by the power source, in anticipation of an increase in load on the machine

According to another aspect of the present disclosure, a method for controlling a machine including a power source and a transmission assembly may include determining whether the power source is in a potential stall condition based on an actual speed of the power source and a requested speed of the power source. The method may also include, if the power source is in the potential stall condition, determining whether a requested transmission assembly torque is increasing. The method may further include informing the power source that a load is coming based at least in part on the requested transmission assembly torque to prepare the power source for the oncoming load, in anticipation of the oncoming load.

According to yet another aspect of the present disclosure, a machine may include a power source. The machine may also include a governor configured to control power source fueling based on an actual speed of the power source and a requested speed of the power source. The machine may further include a transmission assembly operatively coupled to the power source. The machine may also include a control system operatively coupled to the power source and the transmission assembly. The control system may be configured to determine whether the power source is in a potential stall condition due to a response of the governor to a difference between the actual power source speed and the requested power source speed. The control system may also be configured to request that fuel be supplied to the power source to remedy the potential condition in anticipation of an increase in load on the machine.

DETAILED DESCRIPTION

The present disclosure is used in a machine. In the embodiment described below, a wheel loader machine10is disclosed. However, it can be appreciated that other types of machines can benefit from the embodiments disclosed herein, including, for example, any type of ground-borne vehicle, such as an automobile, a truck, an agricultural vehicle, and/or a construction vehicle, such as, a track loader, a dozer, a tractor, an excavator, a grader, an on-highway truck, an off-highway truck, and/or any type of machine known to persons skilled in the art.

As shown inFIG. 1, machine10includes an operator station12, a power source14, a transmission assembly16, a traction assembly18, an implement assembly20, as well as other machine components known to persons skilled in the art. Each of these machine components will now be described.

As illustrated inFIG. 2, operator station12includes an operator interface22. Operator interface22includes devices capable of being manipulated by a machine operator to produce signals, requests, and/or commands that are indicative of desired machine travel, maneuvers, and/or control. In one embodiment, operator interface22includes a joystick control26, an acceleration or throttle pedal28. It should be understood that any other control devices known to persons skilled in the art may be included in operator interface22. The position of acceleration pedal28provides an indication of a power source speed that is desired or requested by the operator. As the operator manipulates acceleration pedal28by, for example, applying pressure, the operator may expect and effect a corresponding increase in the power source speed, and thus, an increase in the propulsion or travel of machine10. As the operator releases the acceleration pedal28, a decrease in the power source speed may be expected and effected, and thus, a corresponding decrease in the propulsion or travel of machine10may be expected and effected.

Referring toFIG. 3, during “normal” operation, fuel supply to power source14may be controlled by a governor24operatively coupled to power source14. Governor24may increase fuel supply to power source14to bring the actual power source speed up to the requested power source speed if the actual power source speed is lower than the requested power source speed, and may decrease fuel supply to power source14to bring the actual power source speed down to the requested power source speed if the actual power source speed is higher than the requested power source speed. Basically, governor24attempts to keep the actual power source speed at or within a predetermined range of the requested power source speed, under “normal” operation.

Power source14may include, for example, an internal combustion engine, including but not limited to a spark-ignition engine, a compression ignition engine, a rotary engine, a gas turbine engine, and/or an engine powered by gasoline, diesel fuel, bio-diesel, ethanol, methanol, and combinations thereof. Power source14may also include a hydrogen-powered engine, a fuel cell, a solar cell, and/or any other power source known to persons skilled in the art.

Power source14and transmission assembly16are operatively coupled, and together form a power train. Transmission assembly16may include any transmission assembly that can back drive power source14. Back driving may occur when machine10is decelerating and traction assembly18provides power to power source14via transmission assembly16. For example, transmission assembly16may be a single or multipath hydrostatic transmission including at least one pump and at least one fluid motor that are fluidly coupled, with the pump being configured to convert rotational motion of power source14into fluid flow, and the fluid motor converting the fluid flow back into rotational motion that is used to drive traction assembly18. During back driving, motion of traction assembly18may be converted by the fluid motor into fluid flow, the fluid flow may be used to drive the pump, and the pump may convert the fluid flow into rotational motion of power source14. Traction assembly18includes at least one traction device, such as a wheel, track, or any other suitable traction device known in the art.

Machine10also includes one or more sensors34. Sensors34may be located throughout machine10, and may provide information related to machine10. In one embodiment, sensors34are operable to monitor operator interface22, power source14, transmission assembly16, traction assembly18, implement assembly20, as well as other machine components known to persons skilled in the art, and provide signals. Sensors34may provide signals indicative of and/or used to calculate operating parameters related to transmission assembly16, including transmission assembly torque (i.e., actual torque being used by transmission assembly16). Sensors34may also be operable to provide signals indicative of operating parameters related to power source14, including, for example, power source speed. It is also contemplated that sensors34may provide signals indicative of the position of acceleration pedal28to provide data for determining a requested transmission assembly torque and a requested power source speed. The signals may be in the form of digital, analog, mechanical, and/or hydraulic signals.

Machine10also includes a control system36operatively coupled to operator station12, power source14, transmission assembly16, traction assembly18, implement assembly20, and/or sensors34. Control system36may include one or more processors, microprocessors, central processing units, on-board computers, electronic control modules, and/or any other computing and control devices known to those skilled in the art. Control system36may run one or more software programs or applications stored in a memory location, read from a computer readable medium, and/or accessed from an external device operatively coupled to the control system36by any suitable communications network.

Control system36is configured to help the operator control operation of machine components. Control system36is operable to control power source14by supplying control signals to power source14that may inform power source14of an oncoming load, and instruct power source14to prepare for the oncoming load. For example, control system36may supply control signals to power source14that may affect the timing and/or quantity of fuel in or received by power source14, and/or consumed by power source14. The control signals may be in the form of digital, analog, mechanical, and/or hydraulic signals. Control system36may, for example, initiate a supply of fuel to power source14in conditions where governor24may not initiate supplying of fuel.

By controlling fueling of power source14, control system36may help to ensure that power source14does not stall when traction assembly18, implement assembly20, and/or any other part of machine10, encounters a grade, obstacle, pile, and/or any other load. For example, during operation of machine10, the operator may want to increase a speed of machine10. The operator may manipulate acceleration pedal28by, for example, exerting pressure, which may increase a speed of power source14. Where acceleration pedal28is positioned indicates the power source speed requested by the operator. As the power source speed increases, power source14may generate additional power that can be transferred to traction assembly18through transmission assembly16, to speed up traction assembly18.

In order to decrease the machine speed, the operator may release pressure from acceleration pedal28, allowing acceleration pedal28to return toward a more neutral position. Power source14may decelerate, and thus, machine10may decelerate. The actual power source speed, however, may not decrease as quickly as the requested power source speed. For example, while the requested power source speed falls almost instantaneously from 1800 rpm to 800 rpm when the operator releases acceleration pedal28, the power source speed may hold at around 1400 rpm for a period of time, and then afterwards, decrease at a relatively slow rate. This is because during deceleration, traction assembly18and/or implement assembly20, through transmission assembly16, may back drive power source14, thus hindering the decrease in the actual power source speed toward the requested power source speed. That is, traction assembly18and/or implement assembly20may provide power to power source14through transmission assembly16, thus increasing the actual power source speed or preventing the actual power source speed from falling as quickly as the requested power source speed, where the requested power source speed may be determined based on a position of acceleration pedal28.

If governor24determines that the actual power source speed minus the requested power source speed is greater than a predetermined value, governor24may put power source14in the zero fuel condition. This may occur because governor24may try to reduce the difference between the actual and requested power source speeds by cutting the fuel supply to power source14, in an attempt to drive down the actual power source speed. The zero fuel condition is a potential stall condition for power source14. That is, if machine10encounters a load in the zero fuel condition, power source14could stall. As explained below, control system36takes action to help ensure that power source14does not stall under such conditions.

Referring toFIGS. 4 and 5, the action that control system36takes may have three stages: a monitoring stage, a command stage, and an exit stage. During the monitoring stage, control system36may monitor power source14(step62). Control system36may determine if watch conditions are met. One of the watch conditions is whether a difference between the actual power source speed and the desired or requested power source speed is greater than a predetermined value. If the actual power source speed minus the requested power source speed is greater than the predetermined value (step64), this indicates that traction assembly18and/or implement assembly20, through transmission assembly16, may be back driving power source14. Control system36may recognize that a risk exists that power source14will stall when encountering a load because power source14is likely in a zero fuel condition.

Another watch condition is whether the actual power source speed has reached a predetermined value (step66), such as a minimum speed of 1200 rpm, at any time during a period of time. This watch condition is set so that entry into the command stage does not occur at undesirable times, such as during machine starting conditions and power source throttling. Yet another watch condition control system36may be looking for is whether the actual power source speed is currently greater than a predetermined value (step68), such as 1350 rpm. This watch condition is set so that entry into the command stage doesn't occur if the power source speed is above a speed corresponding to peak torque. Peak torque is a maximum torque or torque limit that power source14can produce, and is achieved at a corresponding power source speed. After the torque peaks, it will decrease with increasing power source speed. If the power source speed exceeds the speed corresponding to peak torque, and a load is applied to power source14, the speed of power source14may decrease. The decrease in the power source speed brings the power source speed to a speed that is closer to or at the speed value corresponding to peak torque. As such, power source14may produce more torque as the power source speed decreases, and that torque can be used to deal with the oncoming load without resorting to command stage operations. The watch conditions act as a safeguard to prevent control system36from entering the command stage at inappropriate or undesirable times. The exact values provided here are exemplary only and may change depending on the characteristics of the machine, type of fuel being used, the work environment, and/or due to other characteristics.

If all three watch conditions are met, control system36may enter the command stage (step70). Until the watch conditions are met, control system36may be in a “normal” or governor-controlled state of operation. However, once all three watch conditions are met, control system36may enter the command stage where fuel supply to power source14may be affected by more than just governor24.

During the command stage, control system36may determine requested transmission assembly torque values. The requested transmission assembly torque is indicative of an amount of torque the operator wants delivered to transmission assembly16, and may be determined by control system36based on the position of acceleration pedal28. For example, the position of acceleration pedal28may correspond to a requested power source speed. Power source speeds may have corresponding power source torque values (i.e., torque values that power source14can produce at various power source speeds). Together, the power source speed values and power source torque values may form a speed-torque curve, as would be apparent to one skilled in the art. The requested transmission assembly torque may be the power source torque value corresponding to the requested power source speed on the speed-torque curve.

Control system36will determine that a first command stage condition is met if the current requested transmission assembly torque is greater than the sum of a minimum negative requested transmission assembly torque and a predetermined value (step72). The requested transmission assembly torque is negative when the operator decelerates machine10, allowing power source14to be back driven by traction assembly18. If the first condition is met, the current requested transmission assembly torque has increased sufficiently from a minimum value during a current session or period of time to indicate that a load is coming on.

Control system36will determine that a second command stage condition is met if the current requested transmission assembly torque is greater than zero and the minimum requested transmission assembly torque (for the current session or period of time or operation) is less than zero (step74). This indicates that transmission assembly16was previously decelerating (indicative of a negative requested torque or back driving of power source14) and now wants to consume torque from power source14.

The first and second conditions are early indicators that a load is coming on. Thus, if either of the first and second conditions of the command stage are met, control system36will issue a fire command (step76). The fire command may be a command for an amount of fuel to be supplied to power source14and/or consumed by power source14. The fuel is supplied regardless of whether machine10has actually encountered a load that is significant enough to cause power source14to stall. By supplying the fuel upon meeting either of the two conditions, control system36may ensure that if the conditions experienced by machine10are actually being caused due to machine10encountering a significant load, fuel will have been supplied to and/or injected in power source14in time such that power source14does not remain in a zero fuel state until the load causes power source14to stall.

The first and second command conditions are shown in graph38ofFIG. 6, where curve40corresponds to the first command condition, and curve42corresponds to the second command condition. It should be understood that only one curve would actually exist for a given operation, and that the two curves40and42are shown together on one graph for ease of comparison. Points44and46correspond to minimum requested torques, and lines48,50,52, and54correspond to the predetermined value added to the minimum requested transmission assembly torque for the first command condition.

The curves40and42show similarities in the requirements of the first and second command conditions that trigger the fire command. For example, in both of curves40and42, the requested transmission assembly torque is increasing, indicating that a load is coming on, thus resulting in a fire command.

The curves40and42also show differences in the requirements of the first and second command conditions. With respect to curve40, a decreasing positive portion of the curve is indicative of the operator releasing pressure from acceleration pedal28. Where curve40crosses the x-axis and becomes negative is indicative of back driving of power source14by transmission assembly16. Curve40hits a low point at minimum negative requested transmission assembly torque44. Line50runs through minimum negative requested assembly torque44. Line48is offset from line50by a predetermined value. The rising portion of curve40toward the right of minimum negative requested assembly torque44is indicative of a decrease in the back driving of power source40. As shown, if the requested transmission assembly torque is greater than the sum of minimum negative requested transmission assembly torque44and the predetermined value (the sum value represented by line48), control system36will determine that the first command stage condition is met, and will issue a fire command. This is because if the requested transmission assembly torque has increased sufficiently from a minimum value during a current session or period of time to indicate that a load may be coming on, fuel should be supplied to power source14to prevent power source14from stalling when the load actually comes on to machine10, since back driving of power source14may not be able to supply enough power to prevent a stall.

With respect to curve42, a decreasing positive portion of the curve is indicative of the operator releasing pressure from acceleration pedal28. Where curve42crosses the x-axis and becomes negative is indicative of back driving of power source14by transmission assembly16. Curve42hits a low point at minimum negative requested transmission assembly torque46. Line54runs through minimum negative requested transmission assembly torque46. Where curve42crosses the x-axis and becomes positive again is indicative of power source14driving transmission assembly16. Line52is offset from line54by a predetermined value. As shown, if the requested transmission assembly torque is greater than zero and the minimum requested transmission assembly torque46is less than zero, it indicates that transmission assembly16was previously decelerating quickly (indicative of a negative requested torque or back driving of power source14) and now wants to consume torque from power source14. As such, control system36will determine that the second command stage condition is met, and will issue a fire command although the requested transmission assembly torque is not greater than the sum of the minimum negative requested transmission assembly torque46and the predetermined value (the sum value represented by line52).

The amount of fuel supplied with the fire command, and/or the rate of fuel supply due to the fire command, may be selected by control system36based on which of the two command conditions are met, the magnitudes of the above-described transmission assembly torque values, the rate of change of the above-described transmission assembly torque values over a period of time, and/or any other suitable factors. It is also contemplated that the amount of fuel supplied and/or the rate of fuel supply due to the fire command may be selected based on a look-up table or map listing amounts and/or rates for a variety of conditions. It is further contemplated that the amount and/or rate may be set by a manufacturer or machine operator, and may remain substantially constant.

Control system36may remain in the command stage until exiting back to the monitoring stage via the exit stage. During any of the steps outlined above, control system36may check for exit or abort conditions (step78). Control system36enters the exit stage from the command stage when any of three conditions are met. One condition is met if the actual power source speed is greater than a minimum actual power source speed plus a predetermined value or tolerance, for the current session or a predetermined period of time (step80). This condition indicates that a fire command occurred when it should not have occurred (which caused the actual power source speed to increase), that power source14is being back driven by another machine component, and/or that back driving of power source14has increased in magnitude. In order to prevent further power source speed overshoot, control system36immediately stops firing and exits from the command stage.

Another exit condition is met if the current requested power source speed is greater than a minimum requested power source speed plus a predetermined value or tolerance, for a predetermined period of time (step82). This condition indicates that the operator has depressed accelerator pedal28, and power source14should begin supplying fuel to power source14by normal governor control. As such, control system36should not add to the increase in power source speed, so control system36stops firing and exits from the command stage.

Yet another exit condition is if the actual power source speed is greater than the requested power source speed for a period of time, then the actual power source speed is less than the requested power source speed for a period of time, and then the actual power source speed increases to approach the requested power source speed (step84). If this occurs, control system36will exit the command stage before the actual power source speed reaches the requested power source speed (i.e., when the requested power source speed minus the actual power source speed reaches a predetermined value). This condition indicates that a fire command was successfully executed during the command stage. A curve58of the actual power source speed relative to the requested power source speed60, when the fire command has been successfully executed, is shown inFIG. 7.

When any of the three exit/abort conditions are met, the exit stage is completed and control system36will exit from the command stage (step86), and may return to the monitoring stage. The above-outlined steps may be repeatedly carried out during machine operation.

INDUSTRIAL APPLICABILITY

The disclosed control system36may have applicability in machines, such as machine10, and may have may have particular applicability in machines including a power source14and a transmission assembly16. During operation of a machine10, in order to decrease the speed of machine10, the operator may release pressure from an acceleration pedal28. Power source14may decelerate, and thus, machine10may decelerate. A traction assembly18of machine10, through transmission assembly16, may back drive power source14, thus hindering the decrease in the actual power source speed toward the requested power source speed. Under such conditions, a governor24may put power source14in a zero fuel state, increasing the risk of power source14stalling upon encountering a load.

Control system36may take action to help ensure that power source14does not stall under such conditions. Control system36may monitor for the existence of conditions that are early indicators that a load is coming on. When conditions indicate that a load is coming on, control system36will issue a command for an increase in fuel supply to power source14. Thus, control system36may ensure that if the conditions experienced by machine10are actually being caused due to machine10encountering a significant load, fuel will have been supplied to and/or injected in power source14in time such that power source14does not remain in a zero fuel state until the load causes power source14to stall. Reducing the likelihood of stalling may enhance machine performance and reliability.