Work Machine and Control Method for Work Machine

This application is a U.S. National stage application of International Application No. PCT/JP2023/034515, filed on Sep. 22, 2023. This U.S. National stage application claims priority under 35 U.S.C. § 119(a) to Japanese Patent Application No. 2022-155536, filed in Japan on Sep. 28, 2022, the entire contents of which are hereby incorporated herein by reference.

The present invention relates to a work machine and a control method for a work machine.

When a work machine such as a wheel loader has a fault, it is necessary to take measures to prevent the vehicle from continuing to be operable. A common measure is to stop the vehicle completely.

However, if a self-propelled work machine such as a wheel loader stops in place, issues can arise, such as obstructing traffic or being unable to return to a repair shop for maintenance.

For example, WO2015/111549 discloses a work machine that can still travel to a location that does not obstruct traffic or to a destination such as a repair shop, even in the event of a fault.

However, when the work machine is able to travel to the destination, if the work implement can also operate and travel, the ongoing work can continue despite the fault.

The present disclosure aims to provide a work machine and a control method for a work machine that can prevent the continuation of work when a fault occurs and that can prompt a user to deal with the fault.

A work machine according to a first aspect of the present disclosure includes a traveling unit, a work implement, a parking brake, and a controller. The work implement is mounted to the traveling unit. When the controller detects a fault that allows the work machine to remain operable, in a state where the parking brake is released, the controller is configured to restrict operation of the work implement.

According to the present disclosure, a work machine and a control method for a work machine are provided that can prevent the continuation of the ongoing work when a fault occurs and that can prompt a user to deal with the fault.

A wheel loader as an example of a work machine according to the present disclosure will be described below with reference to the drawings.

is a schematic diagram illustrating the configuration of a wheel loader(an example of a work machine) according to the present embodiment. The wheel loaderaccording to the present embodiment includes a traveling unit, a work implement, and a control system(see). The work implementis mounted to the traveling unit. The traveling unitincludes a vehicular body frame, a pair of front tires, a cab, an engine room, a pair of rear tires, and a steering cylinder.

The wheel loaderperforms work such as loading earth and sand using the work implement.

The vehicular body frameis of a so-called articulated type, and has a front frame, a rear frame, and a connecting shaft portion. The front frameis disposed in front of the rear frame. The connecting shaft portionis centered in the vehicle-width direction to connect the front frameand the rear frameso that both of them are swingable. The pair of front tiresis attached to the left and right of the front frame, respectively. The pair of rear tiresis attached to the left and right of the rear frame, respectively. It should be noted that, in the following description, the “front,” “rear,” “right,” “left,” “up,” and “down” refer to the directions based on the state as seen from the driver's seat. Also, the “vehicle-width direction” and “left-right direction” are synonymous.

The work implementis driven by hydraulic oil from a work implement pump(seewhich will be described below). The work implementincludes a boom, a bucket, a boom cylinder(an example of hydraulic actuator), a bucket cylinder(an example of hydraulic actuator), and a bell crank. The boomis attached to the front frame. The bucketis attached to the tip of the boom.

The boom cylinderand the bucket cylinderare hydraulic cylinders. One end of the boom cylinderis attached to the front frame, and the other end of the boom cylinderis attached to the boom. The boom cylinderextends and contracts, causing the boomto swing up and down. One end of the bucket cylinderis attached to the front frame, and the other end of the bucket cylinderis attached to the bucketvia the bell crank. The bucket cylinderexpands and contracts, causing the bucketto swing up and down.

The cabis mounted on the rear frame. Inside the cab, for example, a steering wheel(seewhich will be described below) for steering operations, a lever for operating the work implement, and various display devices are arranged. The engine roomis mounted on the rear framebehind the caband houses an engine.

is a diagram illustrating the control systemin the wheel loader.

The control systemfurther includes a work implement drive circuit, a work-implement lock switch(an example of a restriction-operating section), a work-implement lock valve(an example of a restricting valve), a parking brake switch, a parking brake, and an HST controller(an example of a controller).

The work implement drive circuitincludes a work implement pump, a boom valve(an example of a work-implement valve), a bucket valve(an example of a work-implement valve), a boom lever, a bucket lever, a self-depressurizing valve, a pair of boom pilot valves(an example of a pilot valve), a pair of bucket pilot valves(an example of a pilot valve), and a first pipeto an eleventh pipe.

The work implement pumpsupplies hydraulic oil to the boom cylindervia the boom valve. The work implement pumpsupplies hydraulic oil to the bucket cylindervia the bucket valve.

The boom cylinderhas a cylinder chamber including an extension chamberand a contraction chamberwhich are separated by a piston. The boom cylinderextends when hydraulic oil is supplied to the extension chamberand the hydraulic oil is discharged from the contraction chamberThe boom cylindercontracts when hydraulic oil is supplied to the contraction chamberand the hydraulic oil is discharged from the extension chamber

The boom valveis a directional control valve. The boom valveand the work implement pumpare connected by the first pipe. The boom valveand the extension chamberare connected by the second pipe. The boom valveand the contraction chamberare connected by the third pipe.

The boom valvehas a sleeve and a spool that is movable relative to the sleeve. The spool is movable to four positions relative to the sleeve. When the spool moves to a first position P, the boom valveconnects the first pipeto the second pipeand connects the third pipeto a drain pipe (not shown). With this configuration, the hydraulic oil supplied from the work implement pumpis supplied to the extension chamberand the hydraulic oil is discharged from the contraction chamberWhen the spool moves to a second position P, the boom valveconnects the first pipeto the third pipeand connects the second pipeto the drain pipe. With this configuration, the hydraulic oil supplied from the work implement pumpis supplied to the contraction chamberand the hydraulic oil is discharged from the extension chamberWhen the spool moves to a third position P, the boom valvedoes not connect the first pipe, the second pipe, the third pipe, and the drain pipe to each other, and the supply and discharge of the hydraulic oil is stopped. When the spool moves to a fourth position P, the boom valveconnects the first pipeand the second pipeto the drain pipe, and the third pipeis not connected to any pipe.

The bucket cylinderhas a cylinder chamber including an extension chamberand a contraction chamberwhich are separated by a piston. When hydraulic oil is supplied to the extension chamberand the hydraulic oil is discharged from the contraction chamberthe bucket cylinderextends, and the bucketperforms a tilt motion. When hydraulic oil is supplied to the contraction chamberand the hydraulic oil is discharged from the extension chamberthe bucket cylindercontracts and the bucketperforms a dump motion.

The bucket valveis a directional control valve. The fourth pipebranched from the first pipeis connected to the bucket valve. The bucket valveand the work implement pumpare connected by the first pipeand the fourth pipe. The bucket valveand the extension chamberare connected by the fifth pipe. The bucket valveand the contraction chamberare connected by the sixth pipe.

The bucket valvehas a sleeve and a spool that is movable relative to the sleeve. The spool is movable to three positions relative to the sleeve. When the spool moves to a first position Q, the bucket valveconnects the fourth pipeto the fifth pipeand connects the sixth pipeto a drain pipe (not shown). With this configuration, the hydraulic oil supplied from the work implement pumpis supplied to the extension chamberand the hydraulic oil is discharged from the contraction chamberWhen the spool moves to a second position Q, the bucket valveconnects the fourth pipeto the sixth pipeand the fifth pipeto the drain pipe. With this configuration, the hydraulic oil supplied from the work implement pumpis supplied to the contraction chamberand the hydraulic oil is discharged from the extension chamberWhen the spool moves to a third position Q, the bucket valvedoes not connect the fourth pipe, the fifth pipe, the sixth pipe, and the drain pipe to each other, and the supply and discharge of the hydraulic oil is stopped.

The boom leveris arranged in the cab. The boom levercontrols the opening of the boom valve. The spool moves relative to the sleeve in response to the operation of the boom lever, so that the hydraulic oil supplied to the boom cylinderis adjusted.

The bucket leveris arranged in the cab. The bucket levercontrols the opening of the bucket valve. The spool moves relative to the sleeve in response to the operation of the bucket lever, so that the hydraulic oil supplied to the bucket cylinderis adjusted.

The self-depressurizing valvereduces the pressure of the hydraulic oil discharged from the work implement pump. The hydraulic oil reduced in pressure is used as pilot hydraulic oil. The self-depressurizing valveis arranged in a seventh pipethat connects the first pipewith the pair of boom pilot valvesand the bucket pilot valves

The pair of boom pilot valvesis connected to the boom lever, and their openings are adjusted by the manipulation of the boom lever. The hydraulic oil reduced in pressure by the self-depressurizing valveis supplied to the pair of boom pilot valves,One of the pair of boom pilot valvesthat is the boom pilot valveis connected to the first pilot chamberof the boom valvevia the eighth pipe. The other boom pilot valveis connected to the second pilot chamberof the boom valvevia the ninth pipe.

The amount of hydraulic oil supplied from the boom pilot valvesis adjusted by manipulation of the boom lever, so that the amount of hydraulic oil supplied to the first pilot chamberand the second pilot chamberis adjusted. Depending on the amount of hydraulic oil supplied to the first pilot chamberand the second pilot chamberthe spool in the boom valvemoves relative to the sleeve, and the amount of hydraulic oil supplied to the boom cylinderis adjusted. For example, when the boom leveris tilted to the left in Figure, the amount of hydraulic oil supplied from the boom pilot valveincreases, and thereby, the spool of the boom valvemoves to the first position P. This movement causes the boom cylinderto extend, which moves the boomupward.

The pair of bucket pilot valvesis connected to the bucket lever, and their opening degrees are adjusted by manipulation the bucket lever. The hydraulic oil decreased in pressure by the self-depressurizing valveis supplied to the pair of bucket pilot valvesOne of the pair of bucket pilot valvesthat is the bucket pilot valveis connected to the first pilot chamberof the bucket valvevia the tenth pipe. The other bucket pilot valveis connected to the second pilot chamberof the bucket valvevia the eleventh pipe.

The amount of hydraulic oil supplied from the bucket pilot valveand the bucket pilot valveis adjusted by manipulation of the bucket lever, and thereby, the amount of hydraulic oil supplied to the first pilot chamberand the second pilot chamberis adjusted. Depending on the amount of hydraulic oil supplied to the first pilot chamberand the second pilot chamberthe spool in the bucket valvemoves relative to the sleeve, and the amount of hydraulic oil supplied to the bucket cylinderis adjusted. For example, when the bucket leveris tilted to the right in Figure, the amount of hydraulic oil supplied from the bucket pilot valveincreases, so that the spool of the bucket valvemoves to the second position Q. This causes the bucket cylinderto contract, and the bucketperforms a dump operation.

The work-implement lock switchis a switch for restricting (hereinafter, also referred to as locking) or releasing the restriction (hereinafter, also referred to as releasing the lock) of the operation of the work implement. The work-implement lock switchis operated by an operator. The work-implement lock switchis located in the cab.is a diagram illustrating the steering wheeland the vicinity of the steering wheelin the cab. As illustrated in, in the present embodiment, the work-implement lock switchis located on the right side of the driver's seat. The work-implement lock switchis operated to an on-state or an off-state by the operator. In response to an operation of the work-implement lock switch, a signal corresponding to the operation is input to the HST controller.

The work-implement lock valveis positioned in the seventh pipe. The work-implement lock valveis arranged downstream of the self-depressurizing valve. The work-implement lock valveis an electromagnetic valve and is driven by a signal from the HST controller. The work-implement lock valveis switchable between a locked state in which the supply of hydraulic oil to the pilot valvesandthrough the seventh pipeis stopped and an unlocked state in which the supply of hydraulic oil is enabled. When the work-implement lock switchis operated to turn on the on-state and a signal indicating the on-state is input to the HST controller, the HST controllerstops outputting a signal to the work-implement lock valve, which switches the work-implement lock valveinto the locked state. In contrast, when the work-implement lock switchis operated to turn on the off-state and a signal indicating the off-state is input to the HST controller, the HST controlleroutputs a signal to the work-implement lock valve, which switches the work-implement lock valveinto the unlocked state.

While the work-implement lock valveis in the locked state, pilot hydraulic oil is not supplied to the pair of boom pilot valvesand the pair of bucket pilot valves,Consequently, the boom valveand the bucket valvebecome inoperable. As a result. the work implementcannot be driven regardless operation of the boom leverand the bucket lever. In this way, while the work-implement lock valveis in the locked state, the work implementis locked. In contrast, when the work-implement lock valveis in the unlocked state, pilot hydraulic oil can be supplied to the pair of boom pilot valvesand the pair of bucket pilot valvesTherefore, the boom valveand the bucket valvebecome operable, and the work implementcan be driven by operation of the boom leverand the bucket lever. In this way, while the work-implement lock valveis in the unlocked state, the limitation (lock) of operation of the work implementis also released.

The parking brake switchis a switch for locking and releasing the lock of the parking brake. The parking brake switchis operated by an operator. As illustrated in, the parking brake switchis positioned to the side of the steering wheelinside the cab. The parking brake switchis operated to an on-state or an off-state by the operator.

The parking brakeis used to stop the traveling unitand brakes the traveling unit. The parking brakeis mounted, for example, to a transfer (not shown). The transfer divides the output from the engine between the front axle to which the front tiresare connected and the rear axle to which the rear tiresare connected. For example, a wet multi-stage brake that is switchable between a braking state and a non-braking state, or a disk brake may be used as the parking brake.

While the parking brake switchis in the on-state, no electricity flows to the parking brake solenoidof the parking brake, and the parking brakeis in an applied state. In contrast, while the parking brake switchis in the off-state, electricity flows to the parking brake solenoidand the parking brakeis in a released state. Additionally, a signal from the parking brakeis also input to the HST controller. The signal causes the HST controllerto determine whether the parking brakeis in the applied state or the released state.

The HST controllerincludes a processor and a storage device. The processor is, for example, a central processing unit (CPU). Alternatively, the processor may be a different processor from the CPU. The processor enforces processing for controlling the wheel loaderaccording to a program. The storage device includes non-volatile memory such as read only memory (ROM) and volatile memory such as random access memory (RAM). The storage device may include an auxiliary storage device such as a hard disk or a solid state drive (SSD). The storage device is an example of a non-transitory processor-readable recording intermediate. The storage device stores programs and data for controlling the wheel loader.

The HST controllerdetects a fault. When the HST controllerdetects that the fault is an intermediate one (which will be described below), it enforces a functional restriction F. The functional restriction F is designed so that the operation of the work implementand the traveling do not occur simultaneously. While the HST controllerdoes not detect an intermediate fault, it operates the work-implement lock valvein response to a signal input from the work-implement lock switchas described above, thereby limiting or releasing the limitation on the operation of the work implement.

First, the types of faults are described.is a table Texplaining classification of the faults. Faults can be divided into minor, intermediate, and major faults. A minor fault is, for example, a seat heater fault, and is a fault in which the safety function has not failed and does not affect the continuation of the ongoing work. In the case of a minor fault, there is no problem in carrying out the ongoing work, requiring no need to enforce the functional restriction F. A major fault is, for example, a fault in the forward/reverse switch (FNR) lever or a fault in the work implement pump, and is a fault in which the safety function has failed and the machine cannot continue to operate. In the event of a major fault, the ongoing work cannot continue, eliminating the need to execute the functional restriction F. An intermediate fault is a state in which the safety function has failed, but the work machine remains operable. An intermediate fault can be described as a state in which the work machine continues to be operable, although there is a risk that safety could be compromised when subsequent fault arises.

In the present embodiment, when an intermediate fault is detected, the HST controllerenforces the functional restriction F. On the other hand, minor and major faults are not subject to the functional restriction F, and no functional restriction F is enforced on them.

An example of an intermediate fault will be described with reference to. A fault occurring in a fault diagnosis signal for an electric lever for attachment operation will be described as an example of an intermediate fault. In the wheel loaderof the present embodiment, an attachment can be mounted via an additional link instead of the bucketas an optional configuration.is a diagram illustrating a control system for operating such an attachment. As illustrated in, an attachment cylinderis additionally mounted to the control systemofin order to drive the attachment. In addition, an attachment valveis provided to adjust the flow rate of hydraulic oil supplied to the attachment cylinder. Two EPC valvesandare provided to supply pilot hydraulic oil to a first pilot chamberand a second pilot chamberof the attachment valve. A signal from an electric leverfor operating the attachment is input to the HST controller, and then the HST controllercontrols the EPC valvesaccording to the degree of manipulation of the lever. As a result, the attachment valveadjusts the flow rate of hydraulic oil supplied from the work implement pumpto the attachment cylinder, causing the attachment cylinderto expand and contract, and the attachment operates accordingly.

In such a system for electrically operating an attachment, the electric leverfor operating the attachment outputs an attachment operation signal (hereinafter, referred to as a signal s) and a fault diagnosis signal (hereinafter, signal s) to the HST controller.illustrates the signals sand sin the normal state. The signals sand seach indicate the value of the output voltage for the degree of manipulation of the electric leverfor operating an attachment. The output voltages of the signals sand sare set to be larger as the degree of manipulation of the lever increases. The signals sand soutput the same value. The HST controllerdetermines the degree of manipulation of the lever from the signal sand outputs an output for operating the attachment to the EPC valvesandThe HST controllercompares the signals sand s, and when the values of the signals sand sare the same, it determines that no fault has occurred.

As illustrated in, on the other hand, if the fault diagnosis signal sis not input to the HST controllerdue to a disconnection in the wire, the lever manipulation degree can be determined from the input signal s. However, no determination on a fault can be made because the signal sis not input.

That is, in the state with no input of the signal sas illustrated in, the attachment remains operable and the operation can continue. However, when the signal shas malfunctioned in this state, the attachment may perform an unexpected operation. In other words, an intermediate fault can be defined as a state in which the safety function has failed, but the work machine is still able to operate. An intermediate fault includes cases where one of the redundant configurations for the safety function fails.

Furthermore, an intermediate fault may include, for example, a power fault on the output side of the HST controller.

Next, the functional restriction F enforced by the HST controller(an example of a controller) upon detection of an intermediate fault will be described. When the functional restriction F is executed, it ensures a setting where the operation of the work implementand the traveling cannot occur simultaneously.

is a diagram illustrating a state transition of the controls in the functional restriction F. As illustrated in, the functional restriction F includes a first functional restriction Fthat allows the traveling while restricting the operation of the work implement, and a second functional restriction Fthat allows the operation of the work implementwhile restricting the traveling.