Boosting parking brake drive-through torque

A system and method for enabling a machine to drive through its parking brake when in first gear include detecting that the machine transmission is in its lowest gear in a selected direction, that the machine parking brake is activated, such that the machine is stationary, and that the throttle setting of the machine exceeds a predetermined throttle threshold value. In this state, one or more auxiliary loads of the machine are dropped to provide additional torque to the ground engaging elements of the machine, such that there is sufficient torque to drive the machine through the parking brake.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to earthmoving, industrial and agricultural machines (herein, “industrial machines” collectively) and, more particularly, to systems and methods for providing a parking brake system that is overridable in first gear while providing required holding power on a slope.

BACKGROUND OF THE DISCLOSURE

Industrial machines such as those used in construction and mining must often operate on uneven terrain. Not only must such machines be able to traverse, climb and descend steep slopes, but they must also be able to remain stationary on such terrain when appropriate. For example, according to one standard, the machine must be able to remain stationary on a predetermined grade while in second gear. For this reason, such machines are generally equipped with a parking brake that essentially locks the machine's wheels or other ground-engaging elements.

At the same time, for safety reasons, it is sometimes necessary for industrial machines to “drive through” the parking brake in first gear. In other words, when the parking brake is set and the machine is stationary, the operator should be able to force some movement of the machine in first gear, overriding the parking brake.

Thus, parking brakes for industrial machines need to be of sufficient holding power to serve their primary goal, i.e., that of holding the machine stationary, while not being so strong as to prevent the operator from moving the machine in first gear. As such, the maximum holding power of the parking brake is limited by the amount of propulsive torque available to drive through the parking brake in first gear.

An approach to this problem may be to weaken the parking brake until it has insufficient holding power to stop movement of the machine when in first gear under normal operation. However, in some circumstances, this will also yield a parking brake that is too weak to meet other holding power requirements. Similarly, providing a parking brake that is strong enough to meet other holding requirements, e.g., holding the machine stationary in second gear while on a predetermined grade, may yield a brake that cannot be overridden in first gear.

The present disclosure is directed to a system and method that mitigate certain of the noted deficiencies. However, it should be appreciated that the solution of any existing problem is not a limitation on the scope of this disclosure or of the attached claims except to the extent expressly claimed. Additionally, this background section discusses observations made by the inventors; the inclusion of any observation in this section is not an indication that the observation represents known prior art.

SUMMARY OF THE DISCLOSURE

In accordance with one aspect of the present disclosure, a method is provided for enabling a machine to drive through a parking brake of the machine. The method entails detecting that a transmission of the machine is in a first gear, detecting that a parking brake of the machine is activated, such that the machine is stationary, and detecting that a throttle setting of the machine exceeds a predetermined throttle threshold value. In response to the detected gear, parking brake activation and throttle setting, power is withheld from one or more auxiliary loads of the machine to provide additional torque to ground engaging elements of the machine to allow the machine to drive through the parking brake.

In another embodiment, a parking brake system is provided for enabling a machine to drive through a parking brake of the machine. The parking brake system includes a parking brake sensor configured to detect activation of the parking brake, a throttle sensor configured to detect a position of a throttle input, a transmission sensor to detect a transmission gear, and a controller configured to selectively drop auxiliary loads of the machine based on the throttle position, transmission position, and parking brake actuation to provide additional torque to ground engaging elements of the machine to allow the machine to drive through the parking brake.

In yet another embodiment, a machine is provided having a parking brake, a throttle, a transmission having a lowest forward gear and a lowest reverse gear, and a controller configured to detect a transmission gear, a throttle position, and a parking brake state, and to withhold power from one or more auxiliary loads of the machine upon detecting that the transmission is in one of the lowest forward gear and the lowest reverse gear, that the throttle position exceeds a predetermined threshold throttle position and that the parking brake is in an applied state.

DETAILED DESCRIPTION

In an embodiment shown inFIG. 1, a wheel loader10within which the disclosed principles may be implemented includes a body portion12and a non-engine end frame14connected by an articulating joint16. The body portion12houses an engine that drives rear wheels18, and includes an elevated cab20for the operator. The end frame14has front wheels22that are turned by the steering mechanism, with the articulating joint16allowing the end frame14to move from side-to-side to turn the wheel loader machine10. In the illustrated embodiment, an implement in the form of a bucket24is mounted at the front of the end frame14on a coupler26. The bucket24and coupler26may be configured for secure attachment of the bucket24during use of the wheel loader machine10, and for release of the bucket24and substitution of another implement.

The coupler26is connected to the end frame14by a pair of lift arms28. One end of each lift arm28is pivotally connected to the end frame14and the other end is pivotally connected to the coupler26proximate the bottom. The lift arms28rotate about the point of connection to the end frame14, with the rotation of the lift arms28being controlled by corresponding lift cylinders30pivotally coupled to the end frame14and the lift arms28. The lift cylinders30may be extended to raise the lift arms28and retracted to lower the lift arms28. In typical implementations, two lift arms28are provided, with each having a corresponding lift cylinder30. However, a single lift arm28and lift cylinder30, two lift arms28driven by a single lift cylinder30, or other arrangements of lift arms28and lift cylinders30providing similar functionality as kinematic elements may be used.

A parking brake system40of the wheel loader10will be discussed below in conjunction withFIG. 2, and is linked to one or more of the wheel loader engine, transmission (shown inFIG. 2), drive train and wheels18,22, and may brake both the front wheels22and the rear wheels18, or may brake only one of the front wheels22and the rear wheels18.

The schematic diagram ofFIG. 2shows an example parking brake system40in greater detail. In the illustrated embodiment, the parking brake system40includes a parking brake56having a braking element41, which may be a single or multi-disc brake disc brake assembly, a drum brake assembly or other suitable brake assembly. The parking brake56may be mechanically, electrically, hydraulically or pneumatically actuated. The parking brake56of the parking brake system40further includes an actuator42for actuating the braking element41, e.g., an electrically actuated hydraulic or air solenoid valve, a mechanical actuator, or other suitable actuator.

A parking brake sensor43provides a signal indicative of the parking brake56being applied. The parking brake sensor43may be configured to detect an actuation signal or to detect movement at one or both of the braking element41and the actuator42. Similarly, a transmission sensor52is configured to produce a signal indicative of a gear of the machine transmission57(referenced above in the discussion ofFIG. 1but not visible in the external view shown in that figure), e.g., to indicate each gear or to at least indicate when the transmission57is in first gear (the lowest available gear), whether in forward or reverse.

The transmission57may be of any suitable multi-gear configuration including, among others, purely mechanical configurations, electro-hydraulically actuated configurations, and electrically actuated configurations. The transmission57may provide multiple gears in both forward and reverse or may provide multiple forward gears but only a single reverse gear. For transmissions having only a single reverse gear, this single reverse gear is considered to be a first reverse gear for purposes of this disclosure.

The parking brake system40also includes a throttle sensor44configured to produce an indication of a position of a throttle (e.g., by measuring position of a throttle input54, discussed in greater detail further below). For example, the throttle sensor44may detect the extent of throttle requested or applied, or may simply detect whether the commanded or actuated throttle position is beyond a predetermined threshold.

With respect to embodiments wherein machine pitch is taken into account in establishing dropped loads, the parking brake system40also includes a pitch sensor58, sometimes referred to as a main fall sensor, which indicates a direction of steepest slope. The pitch sensor58may be a sensor used by the machine10generally or may be a dedicated sensor.

A transmission gear selector59, e.g., positioned in the cab20of the machine10, may be used by an operator of the machine to set a gear of the machine, e.g., between reverse, neutral, and one or more forward speeds. The position of the transmission gear selector59, and thus the gear of the transmission57, is monitored by the parking brake system40in an embodiment.

The machine10includes a number of auxiliary loads45which may also be referred to as parasitic loads. Such loads represent machine features and functions that require power when active (not dropped) but that may be deactivated or dropped at least momentarily without substantially impacting machine performance or condition negatively. Although these auxiliary loads45are not part of the parking brake system40, the parking brake system40interfaces with these loads in a manner to be described herein with respect to machine behavior while the parking brake56is actuated. The illustrated loads include, for the sake of example, a cooling fan46, an alternator47for charging the machine battery or directly providing electrical power, an air conditioner compressor48, a hydraulic or pneumatic brake charging pump49and a machine water pump50.

The illustrated embodiment of the parking brake system40further includes a controller51, which may be a stand-alone controller or may be implemented within a multi-purpose controller, e.g., a machine controller, engine controller, or transmission controller. The controller51is electrically interfaced to one or more of the parking brake sensor43, the transmission sensor52and the throttle sensor44. In addition, the controller51is electrically interfaced to one or more of the cooling fan46, the alternator47, the air conditioner compressor48, the hydraulic or pneumatic brake charging pump49and the machine water pump50.

In an embodiment, the machine10also includes a user input device or operator interface53. The operator interface53includes the throttle input54indicated above as well as a steering input55and the transmission selector59in the illustrated embodiment. Additional elements of the machine10that are not salient to the disclosed principles are omitted from the illustration for clarity. However, those of skill in the art will be familiar with the elements of various machines.

During operation of the machine10, the controller51monitors certain aspects of the machine10that relate to parking brake56actuation and parking brake drive-through via the available sensors including for example the parking brake sensor43, the transmission sensor52and the throttle sensor44.

When the signals generated by the sensors indicate that the user is attempting to drive through the parking brake56in first gear, the controller51deactivates some or all of the auxiliary loads45, increasing the available torque to the ground engaging elements of the machine10, e.g., the front wheels22and rear wheels18in the illustrated example.

INDUSTRIAL APPLICABILITY

In general, the principles of the present disclosure find utility in various industrial applications, such as in earthmoving, industrial, construction and agricultural machines. In particular, the disclosed torque increasing system and method may be applied to excavators, wheel loaders, track-type tractors, motor graders, articulated trucks, pipe layers, backhoes, and the like. By applying the disclosed system and method to a machine, an operator is able to drive through the machine parking brake56in first gear, while still having sufficient slope-holding power in other gears.

According to one aspect, the controller51drops a fixed set of auxiliary loads when a user is attempting to drive through the parking brake56in first gear. In an alternative embodiment, the controller51determines a variance on the flat level machine operating condition and the torque increase required based on a current machine pitch and direction of travel, and derives a total torque increase required to drive through the first gear as the sum of the flat level torque increase and the pitch/direction-based variance.

In another embodiment, the controller51progressively drops loads. As an alternative to dropping a fixed set of loads at once, this embodiment allows for finer tuning of the additional torque provided. Likewise, as an alternative to dropping an entire predetermined set of loads, this embodiment eliminates the need to perform torque calculations and thus allows for a more rapid start to the torque adjustment.

With the foregoing summary as guidance, a detailed process70of machine operation with respect to parking brake56actuation and drive through is illustrated in the flow chart ofFIG. 3. At stage71of the process70, the controller51detects, e.g., via a sensor such as the parking brake sensor43, whether the machine parking brake56has been applied (activated). If it is detected at stage71that the parking brake56has not been activated, then the process70loops at stage71.

Otherwise, the process70flows to stage72, wherein the processor51detects, e.g., via the transmission sensor52, whether the transmission57is in first gear, whether in forward or reverse. If it is detected at stage72that the transmission57is not in first gear, then the process70loops back to stage71.

Conversely, if it is detected at stage72that the transmission57has been placed in first gear, then the process70flows to stage73, wherein the processor51samples the throttle sensor44to determine the current throttle setting, e.g., at the throttle element itself (e.g., throttle control valve) or at the user interface (e.g., throttle input54).

The processor51compares the detected throttle setting to a predetermined threshold throttle setting at stage74. If it is determined at stage74that the detected throttle setting does not meet or exceed the predetermined threshold throttle setting, then the process70returns to stage71. Otherwise, if it is determined at stage74that the detected throttle setting does meet or exceed the predetermined threshold throttle setting, then the process70proceeds to stage75.

At stage75of the process70, the controller51increases the torque available to the machine ground engaging elements by dropping or deactivating one or more auxiliary loads, e.g., auxiliary loads45(cooling fan46, alternator47, air conditioner compressor48, brake charging pump49and machine water pump50). In an embodiment, an entire predetermined set of auxiliary loads are dropped at stage75. In an alternative embodiment, only as many loads are dropped as are need to provide sufficient torque for the ground engaging elements to overcome the parking brake56as discussed in conjunction withFIG. 5below.

In an embodiment, the controller51awaits expiration of a hysteresis period, e.g., 2 seconds, after dropping the auxiliary loads at stage75before proceeding back to stage71to confirm through stage71and the following stages that the additional torque is or is not still needed. In this way, an oscillation of the throttle input as it crosses the predetermined throttle threshold will not result in rapid oscillating deactivation and reactivation of the dropped loads.

As noted above, in an embodiment, the controller51may selectively drop one or more loads based on the extent to which the available torque to the ground engaging elements is less than is required for driving through the parking brake56. For example, a wheel loader parked along the fall line of a slope, as opposed to across the fall line, will require less torque to drive through the parking brake56in the downhill direction, and will require more torque to drive through the parking brake56in the uphill direction. As the axis of the machine on the incline is changed away from the fall line and toward a cross-slope orientation, there will be a decreasing amount of direction-dependence in the torque required to drive through the parking brake56in first gear until the machine axis is perpendicular to the fall line.

To accommodate the direction-dependence of the torque requirement when on a slope, the controller51modifies the dropping of loads based on the pitch of the machine as detected by the pitch sensor58in an embodiment of the disclosed principles. The flow chart ofFIG. 4illustrates such a process90.

At the outset of the process90, the controller51determines that a torque increase to the ground engaging elements is needed in order for the machine to be able to drive through the parking brake56(stage91). This stage may entail the controller51executing a process such as the previously discussed process70that entails analyzing the machine throttle position, transmission selection and parking brake state to determine that the operator is attempting to drive through the parking brake56in first gear.

At stage92of the process90, the controller51detects the current machine pitch as detected by the pitch sensor58and intended travel direction (based on gear direction). The controller51then determines, e.g., via calculation, or resolves, e.g., via a look up, a variance of the level terrain drive-through torque requirement based on the detected machine pitch and travel direction at stage93. In particular, driving through the parking brake56in an uphill direction would require a greater amount of torque than driving through on level ground, whereas driving through the parking brake56in a downhill direction would require a lower amount of torque than driving through on level ground. Similarly, if the machine has a pitch of zero, then the torque increase will be the same regardless of intended travel direction (that is, there will be no variance).

Having determined the variance in torque needed to allow the operator to drive through the parking brake56in first gear, the controller calculates a total torque increase need at stage94and at stage95drops one or more auxiliary loads in order to make the total torque increase available to the ground-engaging elements

As noted at the outset of this section, the controller may progressively drop loads in an alternative embodiment. This may largely eliminate the need to perform torque calculations, allowing for a more rapid start to the torque adjustment, and may allow for finer control of loads dropped since in most cases it will not be necessary to drop all auxiliary or parasitic loads.

The process100shown in the flowchart ofFIG. 5allows the controller to rapidly begin increasing the torque to the ground engaging elements of a machine while not dropping any more loads than necessary to provide the needed drive through torque. At stage101of the process100, the controller51determines whether a torque increase to the ground engaging elements is needed, that is, whether the operator is attempting to drive the machine through the parking brake56in first gear, and whether additional torque is needed. The extent to which a torque increase is needed may be based on the current incline underlying the machine10, the extent to which the machine is aligned with that incline, and the direction of intended travel (i.e., is whether the transmission57is in the first forward gear or instead in the first reverse gear).

If it is determined at stage101that the operator is not attempting to drive the machine through the parking brake56in first gear such that no torque increase to the ground engaging elements is needed, then the process flows to stage102, wherein the controller51brings any dropped loads back online, and then loops to stage101. If it is determined that the operator is attempting to drive the machine through the parking brake56in first gear but that no torque increase to the ground engaging elements is needed, then the process loops to stage101.

Otherwise, if it is determined at stage101that the operator is attempting to drive the machine through the parking brake56in first gear and that a torque increase to the ground engaging elements is needed, the process100flows to stage103. At stage103, the controller51selects a load (Loadn) from a load list and drops the selected Loadn. In an embodiment, the load list is an ordered list of auxiliary loads to be dropped in order. For example, less important loads may be placed ahead of more important loads. Thus, an air conditioner compressor load may have a lower n in the list than a more important load such as an engine cooling fan load.

The controller51then determines at stage104whether the ground engaging elements now have sufficient torque to drive through the parking brake56. If it is determined that the ground engaging elements now have sufficient torque to drive through the parking brake56, then the process100loops back to stage101. Otherwise, the process100flows from stage104to stage105, wherein the controller increments n. The process100then returns to stage103to identify and drop the next load (Loadn+1). As with the process70, the process100may include a waiting period or hysteresis period to avoid rapid fluctuations in a loads online status.