Patent ID: 12241221

DESCRIPTION OF EMBODIMENTS

Embodiments will be described below with reference to the drawings. It is originally planned to utilize configurations of the embodiments in appropriate combination. In addition, some of constituent elements are not employed occasionally.

A description will be given of a wheel loader with reference to the drawings. In the following description, the terms “upper”, “lower”, “front”, “rear”, “left”, and “right” are defined with respect to an operator who sits in an operator's seat.

A dump truck will be described as an example of a loading target onto which an excavated object is loaded; however, the loading target is not limited thereto, but may be a non-self-propelled loading target such as a soil container.

First Embodiment

<Overall Configuration>

FIG.1is a side view of a wheel loader1according to a first embodiment. FIG. is a top view of wheel loader1.

As illustrated inFIGS.1and2, wheel loader1includes a main body5, a work implement30, wheels3aand3b, and an operator's cab6. Wheel loader1is self-propelled in such a manner that wheels3aand3bare rotated. In addition, wheel loader1performs desired operations/services using work implement30.

Main body5includes a front frame5aand a rear frame5b. Front frame5aand rear frame5bare connected to each other by a center pin81so as to be swingable laterally.

Steering cylinders82are provided in a pair so as to extend from front frame5ato rear frame5b. Each steering cylinder82is a hydraulic cylinder to be driven by hydraulic oil from a steering pump (not illustrated). Front frame5aswings relative to rear frame5bby expansion and contraction of steering cylinders82. This action changes a traveling direction of wheel loader1.

Work implement30and a pair of front wheels3aare mounted to front frame5a. Work implement30is disposed forward of main body5. Work implement30is driven by hydraulic oil from a hydraulic pump119(seeFIG.3). Work implement30includes a boom31, a pair of lift cylinders33, a bucket32, a bell crank34, a tilt cylinder35, and a tilt rod36connecting a distal end of bell crank34to bucket32.

Boom31is rotatably supported by front frame5a. Boom31has a proximal end (proximal end) mounted to front frame5aby a boom pin7such that boom31is swingable. Each lift cylinder33has a first end mounted to front frame5a. Each lift cylinder33has a second end mounted to boom31. Preferably, the second end of each lift cylinder33is mounted to a lower end of boom31. Front frame5aand boom31are connected to each other by lift cylinders33. Boom31swings upward and downward about boom pin7by expansion and contraction of lift cylinders33using the hydraulic oil from hydraulic pump119.

FIG.1illustrates only one of lift cylinders33.

Bucket32is rotatably supported by a leading end of boom31. Bucket32is swingably directed to a distal end of boom31by a bucket pin39. Tilt cylinder35has a first end mounted to front frame5a. Tilt cylinder35has a second end mounted to bell crank34. Bell crank34and bucket32are connected to each other by a link apparatus (not illustrated). Front frame5aand bucket32are connected to each other by tilt cylinder35, bell crank34, and the link apparatus. Bucket32swings upward and downward about bucket pin39by expansion and contraction of tilt cylinder35using the hydraulic oil from hydraulic pump119.

Operator's cab6and a pair of rear wheels3bare mounted to rear frame5b. Operator's cab6is mounted on main body5. Operator's cab6includes, for example, a seat in which an operator sits, and devices for operations (to be described later).

Wheel loader1further includes a sensor40configured to measure a distance between boom31and a dump truck as a loading target. Sensor40is disposed on boom31. Sensor40therefore moves together with boom31.

Specifically, sensor40is disposed at a predetermined position in boom31. The predetermined position is closer to the proximal end of boom31than to the distal end of boom31. Sensor40is disposed on the lower end of boom31. Sensor40is disposed near boom pin7. As used herein, the phrase “lower end of boom31” refers to the lower (ground side) half of boom31, including a lower face of boom31.

As will be described later, sensor40measures a distance (hereinafter, also referred to as “distance D”) between boom31and a vessel of the dump truck. Sensor senses the lower end of boom31. Sensor40may be any device for measuring a distance. Examples of sensor40may include various devices such as an ultrasonic sensor, a laser sensor, an infrared sensor, and a camera.

FIG.3is a perspective view of wheel loader1. As illustrated inFIG.3, boom is raised based on an operation by the operator, so that bucket32is also raised. The operator decreases a tilt angle (angle θ inFIG.14) of bucket32with an excavated object such as excavated soil loaded on the bucket. The excavated object is thus loaded onto the loading target such as the dump truck.

FIGS.4A and4Beach illustrate a positional relationship between left boom31and sensor40. As illustrated inFIGS.4A and4B, sensor40is disposed on lower end31aof boom31. Sensor40includes a housing, and a lens41disposed in the housing at a position near the distal end of boom31.

In wheel loader1, lens41is disposed on the right side of left boom31(i.e., is disposed on left boom31at a position near right boom31); however, the present disclosure is not limited to this configuration. For example, lens41may be disposed on the left side of left boom31. Alternatively, the sensor may be disposed on right boom31.

FIG.5schematically illustrates a sensing area of sensor40. As illustrated inFIG.5, sensor40is disposed such that an optical axis48of sensor40extends along boom31.

Sensor40senses an area covering lower end31aof boom31. Sensor40may sense an area closer to the distal end of boom31than to the proximal end of boom31, in lower end31aof boom31. Preferably, sensor40senses an area ranging from the position of the second end of each lift cylinder33mounted to boom31to the distal end of boom31, in lower end31aof boom31. Alternatively, sensor40may sense a part of each area described above.

Sensor40disposed as described above measures a distance between boom31and the dump truck as the loading target. Information acquired by sensor40is sent to a controller110(FIG.8) of wheel loader1and then is subjected to data processing in controller110as will be described later.

<Dump Approach>

FIG.6illustrates a typical operation by the operator in dump approach. As illustrated inFIG.6, the operator initiates acceleration in a section Q11. Specifically, the operator presses an accelerator pedal (not illustrated). Also in section Q11, the operator actuates a boom control lever122(FIG.8) to raise boom31as will be described later. In section Q11, wheel loader1thus travels toward dump truck900while performing boom-raising.

The operator initiates acceleration in section Q11for the purpose of supplying a satisfactory amount of oil to lift cylinders33, rather than for the purpose of causing wheel loader1to travel. Increasing an engine speed ensures an output of hydraulic oil from the hydraulic pump. Accordingly, the operator still presses the accelerator pedal even when he or she presses a brake pedal to decrease a vehicle speed in section Q11.

In a section Q12subsequent to section Q11, the operator ceases the acceleration and then initiates braking. Specifically, the operator presses the brake pedal (not illustrated) instead of the accelerator pedal. The operator thus brings wheel loader1to a stop in front of dump truck900. Thereafter, the operator actuates a bucket control lever123(FIG.8) to load soil scooped by bucket32onto a bed of dump truck900as will be described later.

A broken line La represents a path along which bucket32typically moves in the series of operations.

FIGS.7A and7Beach illustrate a situation in which the operator does not raise boom31to a position where an excavated object is loadable onto vessel901of dump truck900, in the dump approach.FIG.7Aillustrates the dump approach on the assumption that an output from sensor40is not utilized.FIG.7Billustrates the dump approach on the assumption that an output from sensor40is utilized.FIG.7Aillustrates a comparative example for clarifying a feature of the damp approach inFIG.7B.

As illustrated inFIG.7A, if the operator does not raise boom31to a height illustrated inFIG.6in section Q11, the following event can occur in section Q12. In order to avoid a leading end of each front wheel3ain wheel loader1from colliding with a lateral side of dump truck900, the operator causes wheel loader1to travel forward while seeing front wheels3a. As a result, the lower end of boom31collides with an upper portion of vessel901of dump truck900before each front wheel3aarrives at a position where the operator intends to stop wheel loader1. According to this embodiment, the use of sensor40enables avoidance of this event. With reference toFIG.7B, a description will be given of how to avoid this event. InFIG.7A, a broken line Lb represents a path of bucket32.

If the operator does not raise boom31to the height illustrated inFIG.6in section Q11, wheel loader1(specifically, controller110) controls boom-raising as illustrated inFIG.7B.

Wheel loader1determines whether distance D to be measured by sensor40(i.e., the distance between boom31and dump truck900) takes a value less than or equal to a threshold value. When wheel loader1determines that the value of distance D measured is less than or equal to the threshold value, then wheel loader1starts to raise boom31. For example, wheel loader1does not raise boom31in a section Q21during which the value of distance D measured is larger than the threshold value. When wheel loader1arrives at a section Q22during which the value of distance D measured is less than or equal to the threshold value, then wheel loader1starts to raise boom31.

As described above, wheel loader1includes sensor40configured to measure distance D between boom31and dump truck900. Controller110of wheel loader1causes wheel loader1to perform boom-raising on condition that distance D to be measured by sensor40when wheel loader1travels takes a value less than or equal to the threshold value.

As described above, wheel loader1moves boom31away from vessel901before collision of boom31with vessel901in the dump approach. Wheel loader1accordingly avoids the collision of boom31with dump truck900even when the operator neglects to confirm the position of boom31because he or she pays excessive attention to the position of each front wheel3a. Wheel loader1therefore assists the operation by the operator in the dump approach.

<Functional Configuration>

FIG.8is a block diagram of a system configuration of wheel loader1. As illustrated inFIG.8, wheel loader1includes boom31, bucket32, lift cylinders33, tilt cylinder35, sensor40, controller110, a boom angle sensor112, a bucket angle sensor113, an engine118, hydraulic pump119, a control lever120, control valves131and141, a monitor151, and a speaker152.

Control lever120includes a fore/aft traveling switch control lever121, boom control lever122, bucket control lever123, and vibrators124,125, and126. Controller110includes a determination unit1101.

Controller110controls the overall actions of wheel loader1. Controller110controls, for example, a rotation speed of engine118, based on the actuation of the accelerator pedal. In addition, the controller receives a signal based on the actuation of control lever120by the operator, and then causes wheel loader1to perform an action in accordance with the actuation.

Hydraulic pump119is driven by an output from engine118. Hydraulic pump supplies the hydraulic oil to lift cylinders33via control valve131such that boom is driven. Boom31is raised or lowered by actuation of boom control lever122in operator's cab6. Hydraulic pump119also supplies the hydraulic oil to tilt cylinder via control valve141such that bucket32is driven. Bucket32is acted by actuation of bucket control lever123in operator's cab6.

Controller110successively receives results of sensing from sensor40. In the dump approach, determination unit1101of controller110determines whether distance D to be measured by sensor40takes a value less than or equal to threshold value Th. When determination unit1101determines that the value of distance D is less than or equal to threshold value Th, controller110starts to raise boom31.

Controller110receives a signal according to a boom angle from boom angle sensor112. Controller110also receives a signal according to a tilt angle from bucket angle sensor113. A description will be given of how to utilize signals (results of sensing) output from boom angle sensor112and bucket angle sensor113, later.

Controller110causes monitor151to display various images. Controller110causes speaker152to output a predetermined sound. A description will be given of how to utilize monitor151and speaker152, later.

Vibrator124is configured to vibrate fore/aft traveling switch control lever121. Vibrator125is configured to vibrate boom control lever122. Vibrator126is configured to vibrate bucket control lever123. A description will be given of how to utilize vibrators124to126, later.

<Control Structure>

FIG.9is a flowchart of a processing flow in wheel loader1. As illustrated inFIG.9, in step S2, controller110determines whether wheel loader1is traveling forward. When controller110determines that wheel loader1is traveling forward (YES in step S2), then, in step S4, controller110determines whether distance D measured by sensor40takes a value less than or equal to threshold value Th. When controller110determines that wheel loader1is not traveling forward (NO in step S2), the processing goes back to step S2.

When controller110determines that the value of distance D is less than or equal to threshold value Th (YES in step S4), then, in step S6, controller110starts to raise boom31. When controller110determines that the value of distance D is larger than threshold value Th (NO in step S4), the processing goes back to step S2. In step S8, controller110determines whether distance D measured by sensor40takes a value less than or equal to threshold value Th.

When controller110determines that the value of distance D is larger than threshold value Th (YES in step S8), then, in step S14, controller110stops boom31being raised. In step S16subsequent to step S14, controller110determines whether wheel loader1is traveling forward. When controller110determines that wheel loader1is traveling forward (YES in step S16), the processing goes back to step S4. When controller110determines that wheel loader1is not traveling forward (NO in step S16), the processing ends.

When controller110determines that the value of distance D is less than or equal to threshold value Th (NO in step S8), then, in step S10, controller110determines whether an angle (a boom angle) of boom31is maximum. Specifically, controller110determines whether each of lift cylinders33has extended to its stroke end.

When controller110determines that the boom angle is maximum (YES in step S10), then, in step S12, controller110brings wheel loader1to a stop. Typically, controller110initiates braking even when the operator does not press the braking pedal. When controller110determines that the boom angle is not maximum (NO in step S10), the processing goes to step S8.

As described above, controller110causes wheel loader1to raise boom31on condition that distance D takes a value less than or equal to threshold value Th. Wheel loader1may be configured to allow the operator to forcibly cease the control by controller110. Examples of such an operation by the operator may include an operation to press down a predetermined button (not illustrated), an operation to actuate boom control lever122to lower boom31, and an operation to shift fore/aft traveling switch control lever121from a fore traveling position to an aft traveling position. In wheel loader1, the operator performs the operation to shift fore/aft traveling switch control lever121from the fore traveling position to the aft traveling position even when wheel loader1is traveling forward (i.e., is not stopping).

<Advantages>

(1) As described above, sensor40is disposed at the predetermined position in boom31. The predetermined position is closer to the proximal end of boom31than to the distal end of boom31. Controller110causes wheel loader1to perform the predetermined action for collision avoidance, that is, the action to raise boom31on condition that distance D to be measured by sensor40when wheel loader1travels takes a value less than or equal to threshold value Th.

With this configuration, wheel loader1moves boom31away from vessel901as shown with section Q22inFIG.7Bbefore collision of boom31with vessel901in the dump approach. Wheel loader1therefore avoids the collision of boom31with dump truck900even when the operator neglects to confirm the position of boom31. Wheel loader1thus assists the operation by the operator in the dump approach.

(2) Specifically, the predetermined position corresponds to lower end31aof boom31. This configuration enables sensing on lower end31aof boom31.

(3) Sensor40senses lower end31aof boom31. This configuration enables measurement of distance D between boom31and vessel901of dump truck900.

(4) Controller110brings wheel loader1to a stop on condition that the angle of boom31is maximum. This configuration prevents collision of boom31with vessel in a situation in which boom31collides with vessel901even when boom31is retreated as much as possible.

Second Embodiment

A description will be given of a wheel loader according to a second embodiment with reference to the drawings. It should be noted that a description will be given of different configurations of the wheel loader according to the second embodiment from those of wheel loader1according to the first embodiment; therefore, no description will be given of similar configurations of the wheel loader according to the second embodiment to those of wheel loader1according to the first embodiment.

FIG.10is a side view of wheel loader1A according to the second embodiment.FIG.11is a top view of wheel loader1A.FIG.12is a perspective view of wheel loader1A.

As illustrated inFIGS.10,11, and12, wheel loader1A has a hardware configuration similar to the hardware configuration of wheel loader1A, except for a sensor40A provided instead of sensor40.

Sensor40A is disposed on an upper face of a front frame5a. Sensor40A is disposed at a predetermined position that is closer to a position where a boom31is supported than to a front end51(seeFIG.13) of front frame5a. Specifically, sensor40A is disposed closer to a boom pin7than to the front end of front frame5a.

Sensor40A is disposed between a position where left boom31is supported and a position where a tilt cylinder35is supported, as seen in top view in a Y direction illustrated inFIG.11. Sensor40A may be disposed between a position where right boom31is supported and the position where tilt cylinder35is supported, as seen in top view.

Sensor40A measures a distance D between boom31and dump truck900in dump approach, as in a manner similar to that of sensor40. Specifically, sensor40A measures distance D between boom31and vessel901of dump truck900, as in a manner similar to that of sensor40. Sensor40A senses a lower end of boom31with boom31raised, as in a manner similar to that of sensor40. Sensor40A may be any device for measuring distance D. Examples of sensor40A may include various devices such as an ultrasonic sensor, a laser sensor, an infrared sensor, and a camera.

FIG.13schematically illustrates a sensing area of sensor40A. As illustrated inFIG.13, sensor40A is disposed such that an optical axis49of sensor40A approximately extends along boom31with boom31raised at an angle greater than or equal to a predetermined angle. The sensing area of sensor40A is set in advance with a boom angle in the dump approach taken into consideration.

Sensor40A senses an area covering a lower end31aof boom31. Sensor40A may sense an area closer to a distal end of boom31than to a proximal end of boom31, in lower end31aof boom31. Preferably, sensor40A senses an area ranging from a position of a second end of each lift cylinder33mounted to boom31to the distal end of boom31, in lower end31aof boom31. Alternatively, sensor40A may sense a part of each area described above.

Sensor40A disposed as described above measures distance D between boom31and the dump truck as the loading target. Information acquired by sensor40A is sent to a controller110of wheel loader1A and then is subjected to data processing in controller110.

Controller110of wheel loader1A operates like controller110of wheel loader1. Specifically, controller110causes wheel loader1to perform a predetermined action for collision avoidance, that is, an action to raise boom31on condition that distance D to be measured by sensor40A when wheel loader1A travels takes a value less than or equal to a threshold value Th.

With this configuration, wheel loader1A moves boom31away from vessel901before collision of boom31with vessel901in the dump approach. Wheel loader1A therefore avoids the collision of boom31with dump truck900even when the operator neglects to confirm the position of boom31because he or she operates wheel loader1A while directing his or her line of sight to front wheels3a.

<<Modifications>>

A description will be given of a modification of wheel loader1according to the first embodiment and a modification of wheel loader1A according to the second embodiment with reference to the drawings.

(1) Predetermined Action for Collision Avoidance

In the first and second embodiments, controller110causes wheel loader1to perform the predetermined action, that is, the action to raise boom31on condition that distance D to be measured by sensor40A when wheel loader1A travels takes a value less than or equal to threshold value Th. However, the predetermined action is not limited to the action to raise boom31.

Controller110may cause speaker152to output a predetermined audible notification (audible alarm), in place of the control for raising boom31. Alternatively, controller110may cause monitor151to display a predetermined warning. These configurations each make the operator aware of an abnormal state. Specifically, the operator is able to recognize that wheel loader1,1A almost collides with the dump truck.

Controller110may send a command to each of vibrators124to126such that vibrators124to126start to vibrate. The vibrations of vibrators124,125, and126vibrate corresponding control levers121,122, and123. This configuration also makes the operator aware of an abnormal state.

Wheel loader1,1A may be configured to perform the action to raise boom31, the output of the predetermined audible alarm from speaker152, the display of the predetermined warning on monitor151, and the vibrations of vibrators124to126in appropriate combination.

(2) Control with Tilt Angle Taken into Consideration

FIG.14illustrates a tilt angle θ of bucket32. It should be noted thatFIG.14illustrates wheel loader1. As illustrated inFIG.14, since an excavated object such as soil is loaded on bucket32in the dump approach, the operator needs to set tilt angle θ to be larger than a predetermined angle (hereinafter, also referred to as “angle θ1”).

Therefore, wheel loader1,1A is not configured to always perform the predetermined action on condition that distance D takes a value less than or equal to threshold value Th, but may be configured to perform the predetermined action on condition that the tilt angle of bucket32is greater than or equal to predetermined angle θ1.

With this configuration, in a situation in which wheel loader1,1A approaches dump truck900with an excavated object loaded on bucket32, wheel loader1,1A performs the predetermined action on condition that distance D takes a value less than or equal to threshold value Th. On the other hand, in a situation in which wheel loader1,1A approaches dump truck900with no excavated object loaded on bucket32, wheel loader1,1A does not perform the predetermined action on condition that the value of distance D is less than or equal to threshold value Th.

As described above, wheel loader1,1A approaching dump truck900does not perform the predetermined action on condition that no excavated object is loaded on bucket32.

FIG.15illustrates how to level off an excavated object. It should be noted thatFIG.15illustrates wheel loader1. As illustrated inFIG.15, when the operator operates wheel loader1to load an excavated object onto vessel901of dump truck900, the excavated object can be heaped on vessel901beyond the height of vessel901. In such a case, the operator sets the tilt angle of bucket32to be less than or equal to a predetermined angle (hereinafter, referred to as “angle θ2”) that is smaller than angle θ1. The operator then operates bucket32to drop the excavated object heaped beyond the upper side of vessel901. Typically, tilt angle θ of bucket32is set at zero (i.e., a state in which a cutting edge32ais horizontal to main body5), and then the soil heaped beyond the upper side of vessel901is dropped onto the ground opposite from wheel loader1,1A across dump truck900.

The operator fails to level off the excavated object if boom31is automatically raised since the value of distance D is less than or equal to threshold value Th. Hence, controller110causes wheel loader1to stop the predetermined action, that is, boom-raising on condition that tilt angle θ is less than or equal to angle θ2that is smaller than angle θ1. This configuration allows the operator to level off the excavated object.

(3) Stop of Control in Aft Traveling

In aft traveling of wheel loader1,1A, boom31never collides with vessel901even when the value of distance D is less than or equal to threshold value Th. Wheel loader1,1A therefore has no necessity to perform the predetermined action such as the action to raise boom31. Hence, controller110may be configured to cause wheel loader1,1A to stop the predetermined action after a transition of wheel loader1,1A from a fore traveling state to an aft traveling state. This configuration avoids execution of unnecessary control.

<<Additional Remarks>>

A wheel loader for loading an excavated object onto a loading target includes: a front frame; a bucket; a boom having a distal end connected to the bucket, and a proximal end rotatably supported by the front frame; a sensor configured to measure a distance between the boom and the loading target; and a controller configured to control an action of the wheel loader. The controller causes the wheel loader to perform a predetermined action for collision avoidance on condition that a distance to be measured by the sensor when the wheel loader travels takes a value less than or equal to a threshold value.

With this configuration, the wheel loader traveling forward performs the predetermined action for collision avoidance before collision of the boom with the loading target. The wheel loader therefore avoids the collision of the boom with the loading target even when an operator neglects to confirm a position of the boom. The wheel loader thus assists an operation by the operator in loading the excavated object onto the loading target.

Preferably, the sensor is disposed at one of a first position in the boom, the first position being closer to the proximal end of the boom than to the distal end of the boom, and a second position in the front frame, the second position being closer to a position where the boom is supported than to a front end of the front frame. Also preferably, the first position corresponds to a lower end of the boom.

This configuration allows the sensor of the wheel loader to sense the lower end of the boom.

Preferably, the sensor is disposed at the first position and is configured to sense an area covering a lower end of the boom, the area being closer to the distal end of the boom than to the proximal end of the boom.

This configuration allows the wheel loader to measure the distance between the boom and the loading target.

Preferably, the wheel loader further includes a lift cylinder having one end mounted to a lower end of the boom, the lift cylinder being configured to drive the boom. The sensor is disposed at the first position and is configured to sense an area ranging from a position of the lift cylinder mounted to the boom to the distal end of the boom, in the lower end of the boom.

This configuration allows the wheel loader to measure the distance between the boom and the loading target.

Preferably, the predetermined action corresponds to an action to raise the boom.

This configuration allows the wheel loader traveling forward to move the boom away from the loading target before collision of the boom with the loading target. This configuration therefore allows the wheel loader to avoid the collision of the boom with the loading target even when the operator neglects to confirm the position of the boom.

Preferably, the predetermined action corresponds to an action to output a predetermined audible notification.

This configuration allows the operator to perform an operation to avoid collision of the boom with the loading target in such a manner that the operator listens to the audible notification before the collision of the boom with the loading target.

Preferably, the wheel loader further includes a control lever configured to operate the wheel loader. The predetermined action corresponds to an action to vibrate the control lever.

This configuration allows the operator to perform the operation to avoid collision of the boom with the loading target in such a manner that the operator feels the vibration of the control lever before the collision of the boom with the loading target.

Preferably, the controller brings the wheel loader to a stop on condition that the boom is raised at a maximum angle by the predetermined action.

This configuration prevents collision of the boom with the loading target in a situation in which the boom collides with the loading target even when the boom is retreated as much as possible.

Preferably, the controller causes the wheel loader to perform the predetermined action on condition that a tilt angle of the bucket takes a value greater than or equal to a first value.

This configuration prevents the wheel loader approaching the loading target from performing the predetermined action for collision avoidance on condition that no excavated object is loaded on the bucket.

Preferably, the predetermined action corresponds to an action to raise the boom. The controller causes the wheel loader to stop the action to raise the boom on condition that the tilt angle takes a value less than or equal to a second value that is smaller than the first value.

With this configuration, the operator levels off the excavated object since the wheel loader stops automatic control for boom-raising.

Preferably, the controller causes the wheel loader to stop the predetermined action on condition that the controller receives a predetermined input based on an operation by the operator.

With this configuration, the operator forcibly stops the control for raising the boom on condition that the distance between the boom and the loading target takes a value less than or equal to the threshold value.

Preferably, the predetermined action corresponds to an action to raise the boom. The operation by the operator corresponds to an operation to lower the boom.

With this configuration, the operator performs the operation to lower the boom when the boom is automatically raised. This operation enables a forcible stop of the control for automatically raising the boom.

Preferably, the wheel loader further includes a fore/aft traveling switch lever configured to switch between fore traveling of the wheel loader and aft traveling of the wheel loader. The operation by the operator corresponds to an operation to shift the fore/aft traveling switch lever from a fore traveling position to an aft traveling position.

With this configuration, the fore/aft traveling switch lever switching operation allows a forcible stop of the control for raising the boom on condition that the distance between the boom and the loading target takes a value less than or equal to the threshold value.

Preferably, the controller causes the wheel loader to stop the predetermined action after a transition of the wheel loader from a fore traveling state to an aft traveling state.

With this configuration, the controller causes the wheel loader in the aft traveling state to stop the action to raise the boom on condition that the distance between the boom and the loading target takes a value less than or equal to the threshold value.

A method for controlling a wheel loader configured to load an excavated object onto a loading target includes the steps of: measuring a distance between a boom of the wheel loader and the loading target; determining that the distance measured takes a value less than or equal to a threshold value when the wheel loader travels; and causing the wheel loader to perform a predetermined action for collision avoidance on condition that the value of the distance measured is less than or equal to the threshold value.

By this method, the wheel loader traveling forward performs the predetermined action for collision avoidance before collision of the boom with the loading target. The wheel loader therefore avoids the collision of the boom with the loading target even when the operator neglects to confirm the position of the boom. The wheel loader thus assists an operation by the operator in loading the excavated object onto the loading target.

It should be understood that the embodiments disclosed herein are in all aspects illustrative and not restrictive. The scope of the present invention is defined by the appended claims rather than the foregoing description, and all changes that fall within metes and bounds of the claims, or equivalence such metes and bounds thereof are therefore intended to be embraced by the claims.

REFERENCE SIGNS LIST

1,1A: wheel loader,3a: front wheel,3b: rear wheel,5: main body,5a: front frame,5b: rear frame,6: operator's cab,7: boom pin,30: work implement,31: boom,31a: lower end,32: bucket,32a: cutting edge,33: lift cylinder,34: bell crank,35: tilt cylinder,36: tilt rod,39: bucket pin,40,40A: sensor,41: lens,48,49: optical axis,900: dump truck,901: vessel