Patent Description:
In a work vehicle known from <CIT>, a controller is configured to determine a work phase of the work vehicle based on an operating state of a travel device and a work implement, and determine whether low-load conditions are satisfied based on the work phase. The low-load conditions include that the work phase is a no-cargo state in which cargo is not loaded into the work implement.

<CIT> shows a wheel loader, which includes an excavation determination unit. Said excavation determination unit determines whether or not excavation is being performed. When it is determined that excavation is being performed, a control unit starts to raise a boom while a tire compressed in a vertical direction rebounds and stretches in the vertical direction.

An amount of production is important in managing productivity and fuel efficiency of a wheel loader. A load weight is also important in obtaining the information about the amount of production. The technique of measuring the load weight in the wheel loader is disclosed in <CIT>, for example.

In the above-mentioned literature, the load weight in a bucket is measured by the operation of raising a boom after excavation. Also, the load weight is measured a prescribed number of times from the time when the boom starts to rise to the time when the boom stops.

When excavation and loading onto a dump truck is performed in a plurality of separate steps, an excess of the weight loaded onto the dump truck needs to be avoided. Thus, for last loading onto a dump truck, after excavation, the load weight in a bucket needs to be adjusted to be smaller than the difference between the loading capacity of the dump truck and the current loaded weight in the dump truck.

In the method of measuring a load weight disclosed in the above-mentioned literature, at the time point when it is sensed that the load in the bucket exceeds the loading capacity of the dump truck, the wheel loader has already traveled to the position away from the excavation site. Thus, if the wheel loader goes back to the excavation site and unloads a part of the load in the bucket and again measures the load weight for loading onto the dump truck, the work time is increased.

Furthermore, when it is sensed that the load in the bucket exceeds the loading capacity of the dump truck, the load needs to be loaded onto the dump truck while leaving a part of the load in the bucket in accordance with the above-mentioned difference so as not to exceed the loading capacity of the dump truck, which is difficult even for a skillful operator.

In the case where the load weight is measured by the operation of raising a boom after excavation as disclosed in the above-mentioned literature, when the traveling distance is relatively long, the attitude becomes unstable in the state where the boom is kept raised. Thus, the boom needs to be lowered once, with the result that the operator's operation becomes complicated.

An object of the present invention is to provide a work machine and a system including a work machine, by which a load weight can be measured in a short work time period by a simple operation.

This object is achieved by a work machine according to independent claim <NUM>, and a system including a work machine according to independent claim <NUM>. Advantageous further developments of the work machine are disclosed in dependent claims <NUM> to <NUM>.

The present invention can implement a work machine and a system including a work machine, by which a load weight can be measured in a short work time period by a simple operation.

The embodiments will be hereinafter described with reference to the accompanying drawings. In the following description, the same components will be designated by the same reference characters. Names and functions thereof are also the same. Accordingly, the detailed description thereof will not be repeated.

In the embodiment, a wheel loader <NUM> will be described as an example of a work machine. <FIG> is a side view of wheel loader <NUM> as an example of the work machine according to the embodiment.

As shown in <FIG>, wheel loader <NUM> includes a vehicular body frame <NUM>, a work implement <NUM>, a traveling unit <NUM>, and a cab <NUM>. Vehicular body frame <NUM>, cab <NUM> and the like constitute a vehicular body of wheel loader <NUM>. Work implement <NUM> and traveling unit <NUM> are attached to the vehicular body of wheel loader <NUM>.

Traveling unit <NUM> cause the vehicular body of wheel loader <NUM> to travel and includes running wheels 4a and 4b. Wheel loader <NUM> is movable as running wheels 4a and 4b are rotationally driven and can perform a desired work using work implement <NUM>.

Vehicular body frame <NUM> includes a front frame <NUM> and a rear frame <NUM>. Front frame <NUM> and rear frame <NUM> are attached to each other so as to be swingable in a left-right direction. A steering cylinder <NUM> is attached to front frame <NUM> and rear frame <NUM>. Steering cylinder <NUM> is a hydraulic cylinder. As steering cylinder <NUM> extends and contracts by hydraulic oil from a steering pump (not shown), the traveling direction of wheel loader <NUM> is laterally changed.

In the present specification, the direction in which wheel loader <NUM> travels straightforward is referred to as a front-rear direction of wheel loader <NUM>. In the front-rear direction of wheel loader <NUM>, the side where work implement <NUM> is located with respect to vehicular body frame <NUM> is referred to as a frontward direction, and the side opposite to the frontward direction is referred to as a rearward direction. The left-right direction of wheel loader <NUM> is orthogonal to the front-rear direction as seen in a plan view. The right side and the left side in the left-right direction in facing forward are defined as a right direction and a left direction, respectively. A top-bottom direction of wheel loader <NUM> is orthogonal to a plane defined by the front-rear direction and the left-right direction. In the top-bottom direction, the ground side is defined as a lower side and the sky side is defined as an upper side.

Work implement <NUM> and running wheel (front wheel) 4a are attached to front frame <NUM>. Work implement <NUM> includes a boom <NUM> as a work tool and a bucket <NUM>. A base end of boom <NUM> is rotatably attached to front frame <NUM> by a boom pin <NUM>. Bucket <NUM> is rotatably attached to boom <NUM> by a bucket pin <NUM> located at a tip end of boom <NUM>. Front frame <NUM> and boom <NUM> are coupled to each other by a boom cylinder <NUM>. Boom cylinder <NUM> is a hydraulic cylinder and also is a work tool cylinder. As boom cylinder <NUM> extends and contracts by hydraulic oil from a work implement pump <NUM> (see <FIG>), boom <NUM> is raised and lowered. Boom cylinder <NUM> drives boom <NUM>.

Work implement <NUM> further includes a bell crank <NUM>, a tilt cylinder <NUM> and a tilt rod <NUM>. Bell crank <NUM> is rotatably supported on boom <NUM> by a support pin 18a located substantially in the center of boom <NUM>. Tilt cylinder <NUM> couples a base end of bell crank <NUM> to front frame <NUM>. Tilt rod <NUM> couples a tip end of bell crank <NUM> to bucket <NUM>. Tilt cylinder <NUM> is a hydraulic cylinder and also is a work tool cylinder. As tilt cylinder <NUM> extends and contracts by hydraulic oil from work implement pump <NUM> (see <FIG>), bucket <NUM> pivots upward and downward. Tilt cylinder <NUM> drives bucket <NUM>.

Cab <NUM> and running wheel (rear wheel) 4b are attached to rear frame <NUM>. Cab <NUM> is disposed behind boom <NUM>. Cab <NUM> is placed on vehicular body frame <NUM>. A seat on which the operator sits, an operation apparatus and the like are arranged in cab <NUM>.

<FIG> is a schematic block diagram showing the configuration of wheel loader <NUM>. Wheel loader <NUM> includes an engine <NUM>, a motive power extraction unit <NUM>, a motive power transmission mechanism <NUM>, a cylinder driving unit <NUM>, a first angle detector <NUM>, a second angle detector <NUM>, and a first processor <NUM> (controller).

Engine <NUM> is, for example, a diesel engine. In place of engine <NUM>, a motor driven by a power storage unit may be used, or both an engine and a motor may be used. An output from engine <NUM> is controlled by adjusting the amount of fuel to be injected into a cylinder of engine <NUM>. Rotation sensor <NUM> detects the rotation speed of the rotation shaft inside engine <NUM> and outputs a signal of the detected rotation speed to first processor <NUM>.

Motive power extraction unit <NUM> is an apparatus that distributes the output from engine <NUM> to motive power transmission mechanism <NUM> and cylinder driving unit <NUM>.

Motive power transmission mechanism <NUM> is a mechanism that transmits the driving force from engine <NUM> to front wheel 4a and rear wheel 4b, and serves as a transmission, for example. Motive power transmission mechanism <NUM> changes the speed of rotation of an input shaft <NUM> and outputs the resultant rotation to an output shaft 23a.

A vehicle speed detection unit <NUM> for detecting a vehicle speed of wheel loader <NUM> is attached to output shaft 23a of motive power transmission mechanism <NUM>. Wheel loader <NUM> includes vehicle speed detection unit <NUM>. Vehicle speed detection unit <NUM> is a vehicle speed sensor, for example. Vehicle speed detection unit <NUM> detects the rotation speed of output shaft 23a, thereby detecting a movement speed of wheel loader <NUM> by traveling unit <NUM>. Vehicle speed detection unit <NUM> functions as a rotation sensor that detects the rotation speed of output shaft 23a. Vehicle speed detection unit <NUM> functions as a movement detector that detects the movement by traveling unit <NUM>. Vehicle speed detection unit <NUM> outputs a detection signal showing the vehicle speed of wheel loader <NUM> to first processor <NUM>.

Cylinder driving unit <NUM> includes work implement pump <NUM> and a control valve <NUM>. The output from engine <NUM> is transmitted to work implement pump <NUM> through motive power extraction unit <NUM>. The hydraulic oil discharged from work implement pump <NUM> is supplied to boom cylinder <NUM> and tilt cylinder <NUM> through control valve <NUM>.

A sensor <NUM> detects the angle of a swash plate of work implement pump <NUM>, and outputs a signal of the detected swash plate angle to first processor <NUM>. A pressure sensor <NUM> detects the pressure discharged from work implement pump <NUM>, and outputs a signal of the detected discharged pressure to first processor <NUM>.

First hydraulic pressure detectors 28a and 28b that detect hydraulic pressure in an oil chamber of boom cylinder <NUM> are attached to boom cylinder <NUM>. Wheel loader <NUM> includes first hydraulic pressure detectors 28a and 28b. First hydraulic pressure detectors 28a and 28b include a pressure sensor 28a for detecting head pressure, and a pressure sensor 28b for detecting bottom pressure, for example.

Pressure sensor 28a is attached to the head side of boom cylinder <NUM>. Pressure sensor 28a can detect the pressure (head pressure) of the hydraulic oil in the cylinder-head-side oil chamber of boom cylinder <NUM>. Pressure sensor 28a outputs a detection signal showing the head pressure of boom cylinder <NUM> to first processor <NUM>.

Pressure sensor 28b is attached to the bottom side of boom cylinder <NUM>. Pressure sensor 28b can detect the pressure (bottom pressure) of the hydraulic oil in the cylinder-bottom-side oil chamber of boom cylinder <NUM>. Pressure sensor 28b outputs a detection signal showing the bottom pressure of boom cylinder <NUM> to first processor <NUM>.

First angle detector <NUM> is, for example, a potentiometer attached to boom pin <NUM>. First angle detector <NUM> detects a boom angle showing a lift angle (tilt angle) of boom <NUM>. First angle detector <NUM> outputs a detection signal showing the boom angle to first processor <NUM>.

Specifically, as shown in <FIG>, a boom angle θ refers to an angle of a straight line LB extending in the direction from the center of boom pin <NUM> toward the center of bucket pin <NUM>, with respect to a horizontal line LH extending forward from the center of boom pin <NUM>. In the case where straight line LB is horizontal, boom angle θ = <NUM>°. In the case where straight line LB is located above horizontal line LH, boom angle θ is positive. In the case where straight line LB is located below horizontal line LH, boom angle θ is negative.

First angle detector <NUM> may be a stroke sensor disposed in boom cylinder <NUM>.

Second angle detector <NUM> is, for example, a potentiometer attached to support pin 18a. Second angle detector <NUM> detects an angle of bell crank <NUM> (bell crank angle) with respect to boom <NUM>, thereby detecting a bucket angle showing a tilt angle of bucket <NUM> with respect to boom <NUM>. Second angle detector <NUM> outputs a detection signal showing the bucket angle to first processor <NUM>. The bucket angle is, for example, an angle formed between straight line LB and a straight line that connects the center of bucket pin <NUM> and a cutting edge 6a of bucket <NUM>.

Second angle detector <NUM> may be a stroke sensor disposed in tilt cylinder <NUM>.

As shown in <FIG>, wheel loader <NUM> includes, in cab <NUM>, an operation apparatus operated by the operator. The operation apparatus includes a forward and rearward movement switching apparatus <NUM>, an accelerator operation apparatus <NUM>, a boom operation apparatus <NUM>, a speed change operation apparatus <NUM>, a bucket operation apparatus <NUM>, and a brake operation apparatus <NUM>.

Forward and rearward movement switching apparatus <NUM> includes a forward and rearward movement switching operation member 49a and a forward and rearward movement switching detection sensor 49b. Forward and rearward movement switching operation member 49a is operated by the operator to give an instruction to switch the movement of the vehicle between forward movement and rearward movement. Forward and rearward movement switching operation member 49a can be switched to each of a forward movement (F) position, a neutral (N) position and a rearward movement (R) position. Forward and rearward movement switching detection sensor 49b detects the position of forward and rearward movement switching operation member 49a. Forward and rearward movement switching detection sensor 49b outputs, to first processor <NUM>, a detection signal (forward movement, neutral, rearward movement) of the forward and rearward movement command indicated by the position of forward and rearward movement switching operation member 49a. Forward and rearward movement switching apparatus <NUM> includes a forward and rearward movement switching lever that can perform switching among forward movement (F), neutral (N) and rearward movement (R).

Accelerator operation apparatus <NUM> includes an accelerator operation member 51a and an accelerator operation detection unit 51b. Accelerator operation member 51a is operated by the operator to set any one of rotation of engine <NUM>, outputs such as torque. Accelerator operation detection unit 51b detects an amount of operation (amount of accelerator operation) of accelerator operation member 51a. Accelerator operation detection unit 51b outputs a detection signal showing the amount of accelerator operation to first processor <NUM>.

Brake operation apparatus <NUM> includes a brake operation member 58a and a brake operation detection unit 58b. Brake operation member 58a is operated by the operator to control the deceleration force of wheel loader <NUM>. Brake operation detection unit 58b detects an amount of operation (amount of brake operation) of brake operation member 58a. Brake operation detection unit 58b outputs a detection signal showing the amount of brake operation to first processor <NUM>. The pressure of brake oil may be used as the amount of brake operation.

Boom operation apparatus <NUM> includes a boom operation member 52a and a boom operation detection unit 52b. Boom operation member 52a is operated by the operator to raise or lower boom <NUM>. Boom operation detection unit 52b detects the position of boom operation member 52a. Boom operation detection unit 52b outputs, to first processor <NUM>, a detection signal of the command to raise or lower boom <NUM>, which is indicated by the position of boom operation member 52a.

Speed change operation apparatus <NUM> includes a speed change operation member 53a and a speed change operation detection unit 53b. Speed change operation member 53a is operated by the operator to control a speed change from input shaft <NUM> to output shaft 23a in motive power transmission mechanism <NUM>. Speed change operation detection unit 53b detects the position of speed change operation member 53a. Speed change operation detection unit 53b outputs, to first processor <NUM>, the detection command for a speed change indicated by the position of speed change operation member 53a.

Bucket operation apparatus <NUM> includes a bucket operation member 54a and a bucket operation detection unit 54b. Bucket operation member 54a is operated by the operator to cause bucket <NUM> to perform an excavation operation or a dumping operation. Bucket operation detection unit 54b detects the position of bucket operation member 54a. Bucket operation detection unit 54b outputs, to first processor <NUM>, a detection signal of the command to operate bucket <NUM> in a tilting back direction or a dumping direction, which is indicated by the position of bucket operation member 54a.

First processor <NUM> is implemented by a microcomputer including a storage device such as a random access memory (RAM) and a read only memory (ROM), and a computing device such as a central processing unit (CPU). First processor <NUM> may be implemented as a part of the function of the controller of wheel loader <NUM> that controls the operations of engine <NUM>, work implement <NUM> (boom cylinder <NUM>, tilt cylinder <NUM> and the like), motive power transmission mechanism <NUM>, display unit <NUM>, and the like.

Wheel loader <NUM> further includes a display unit <NUM> and an output unit <NUM>. Display unit <NUM> is implemented by a monitor disposed in cab <NUM> and viewed by the operator. Display unit <NUM> shows the transportation work information measured by first processor <NUM>.

Output unit <NUM> outputs the transportation work information to a server (second processor <NUM> (a controller)) placed outside wheel loader <NUM>. Output unit <NUM> may, for example, have a communication function such as wireless communication to communicate with an input unit <NUM> of second processor <NUM>. Alternatively, output unit <NUM> may, for example, be an interface of a portable storage device (such as a memory card) that can be accessed by input unit <NUM> of second processor <NUM>. Second processor <NUM> includes a display unit <NUM> corresponding to a monitor function, and can cause display unit <NUM> to show the transportation work information output from output unit <NUM>. Second processor <NUM> is implemented by a microcomputer including a storage device such as an RAM and an ROM, and a computing device such as a CPU, like first processor <NUM>.

First angle detector <NUM>, second angle detector <NUM>, first hydraulic pressure detectors 28a, 28b, forward and rearward movement switching detection sensor 49b, boom operation detection unit 52b, and bucket operation detection unit 54b are included in the work phase sensing unit. The work phase sensing unit senses the information about the work phase of work implement <NUM>.

The work phase includes unloaded forward movement, excavation, loaded rearward movement, loaded forward movement, soil ejection, rearward movement and boom lowering, and simple traveling, for example.

Also, the information about the work phase of work implement <NUM> includes information about a detection signal of a forward and rearward movement command indicated by the position of forward and rearward movement switching operation member 49a (forward movement, neutral, rearward movement), a detection signal of an operation command for boom <NUM> (raising, neutral, lowering), a detection signal of an operation command for bucket <NUM> (dumping, neutral, tilt back), and a pressure detection signal for boom cylinder <NUM> (the differential pressure between the head pressure and the bottom pressure).

The work phase and the information about the work phase of work implement <NUM> will be described later in detail with reference to <FIG>.

Rotation sensor <NUM>, sensor <NUM>, pressure sensor <NUM>, accelerator operation detection unit 51b, and the like are included in a traction sensing unit. The traction sensing unit senses the information about the traction of traveling unit <NUM>.

First processor <NUM> shown in <FIG> has a function of distinguishing the work phase by work implement <NUM> based on the information sensed by the above-mentioned work phase sensing unit. First processor <NUM> has a function of switching correction of the boom pressure (that is, the differential pressure between the head pressure detected by pressure sensor 28a and the bottom pressure detected by pressure sensor 28b, more specifically, an output value obtained after a smoothing process) when distinction of excavation in the work phase is switched.

Furthermore, first processor <NUM> has a function of correcting the boom pressure to calculate the corrected pressure of the boom cylinder when it distinguishes the work phase as excavation. First processor <NUM> has a function of calculating the load weight in bucket <NUM> based on the above-mentioned corrected pressure.

Furthermore, first processor <NUM> has a function of calculating traction pressure included in the boom pressure based on the information about the traction sensed by traction sensing units <NUM> to <NUM> and 51b. First processor <NUM> has a function of subtracting the above-mentioned traction pressure from the boom pressure to correct the boom pressure to calculate the corrected pressure of the boom cylinder. First processor <NUM> has a function of calculating the instantaneous load in bucket <NUM> based on the above-mentioned corrected pressure.

In the following, the functional blocks in first processor <NUM> having the above-described functions will be described.

<FIG> is a diagram showing functional blocks in the first processor. As shown in <FIG>, first processor <NUM> mainly includes a work phase distinction unit 30a, a boom pressure correction unit 30b, a load weight calculation unit 30c, a traction pressure calculation unit 30d, a load weight output unit 30e, a load weight summation unit 30f, a summation value output unit <NUM>, a boom angle sensing unit <NUM>, a differential pressure sensing unit 30i, and a storage unit 30j, for example.

Work phase distinction unit 30a distinguishes the work phase of work implement <NUM>. Work phase distinction unit 30a obtains the information about the work phase of work implement <NUM> that is sensed by the work phase sensing unit. By way of example, work phase distinction unit 30a obtains a detection signal of the forward and rearward movement command output from forward and rearward movement switching apparatus <NUM>, a detection signal of the operation command for boom <NUM> output from boom operation apparatus <NUM>, a detection signal of the operation command for bucket <NUM> output from bucket operation apparatus <NUM>, and a pressure detection signal for boom cylinder <NUM> output from pressure sensor 28b.

Based on the obtained information about the work phase, work phase distinction unit 30a distinguishes the work phase while referring to a table shown in <FIG>. This distinction of the work phase will be described later in detail with reference to <FIG>.

Work phase distinction unit 30a outputs a signal showing the distinguished work phase to boom pressure correction unit 30b.

Differential pressure sensing unit 30i calculates a differential pressure between the head pressure and the bottom pressure of boom cylinder <NUM>, based on the detection signal showing the head pressure of boom cylinder <NUM> that is output from pressure sensor 28a and the detection signal showing the bottom pressure of boom cylinder <NUM> that is output from pressure sensor 28b. Furthermore, differential pressure sensing unit 30i performs a process of smoothing the calculated differential pressure. The smoothing process is a method of summing and averaging values including values detected in the past and can be performed also by a low pass filter and the like. Differential pressure sensing unit 30i outputs the signal of the differential pressure (the signal of the boom pressure) that has been smoothed to boom pressure correction unit 30b.

Traction pressure calculation unit 30d calculates traction pressure based on: the rotation speed of the rotation shaft inside engine <NUM> detected by rotation sensor <NUM>; the angle of the swash plate of work implement pump <NUM> detected by sensor <NUM>; the discharge pressure from work implement pump <NUM> detected by pressure sensor <NUM>; the amount of operation in accelerator operation member 51a detected by accelerator operation detection unit 51b; and the like. Traction pressure calculation unit 30d outputs the signal of the calculated traction pressure to boom pressure correction unit 30b.

Boom pressure correction unit 30b obtains a signal showing the work phase output from work phase distinction unit 30a, a signal of the boom pressure output from differential pressure sensing unit 30i, and a signal of the traction pressure output from traction pressure calculation unit 30d. When the work phase distinguished by work phase distinction unit 30a is excavation, boom pressure correction unit 30b corrects the boom pressure to calculate the corrected pressure of boom cylinder <NUM>.

Correction of the boom pressure will be described later in detail with reference to <FIG> and <FIG>.

The signal of the above-mentioned corrected pressure calculated by boom pressure correction unit 30b is output to load weight calculation unit 30c.

Load weight calculation unit 30c calculates the load weight (or the instantaneous load) in bucket <NUM> based on the boom angle signal output from boom angle sensing unit <NUM> and the signal of the above-mentioned corrected pressure calculated by boom pressure correction unit 30b.

Boom angle sensing unit <NUM> receives the detection signal showing the boom angle that is output from first angle detector <NUM>, calculates a boom angle, and outputs a signal of the calculated boom angle to load weight calculation unit 30c.

The method of calculating the load weight (or the instantaneous load) by load weight calculation unit 30c will be described later in detail with reference to <FIG> and <FIG>. The signal of the load weight (or the instantaneous load) in bucket <NUM> calculated by load weight calculation unit 30c is output to load weight output unit 30e.

Load weight output unit 30e outputs the signal of the load weight (or the instantaneous load) calculated by load weight calculation unit 30c to load weight summation unit 30f, storage unit 30j and display unit <NUM>. Storage unit 30j stores the load weight output from load weight output unit 30e. Display unit <NUM> shows the load weight or the instantaneous load on a screen and the like. Load weight output unit 30e may also output the signal of the load weight (or the instantaneous load) to output unit <NUM> (<FIG>). The signal of the load weight (or the instantaneous load) output to output unit <NUM> may be output to second processor <NUM> and displayed on display unit <NUM> of second processor <NUM>. As described above, each of display units <NUM> and <NUM> shows the load in the bucket.

Load weight summation unit 30f receives the signal of the load weight from load weight output unit 30e, and adds the current load weight to the previous load weights stored in storage unit 30j. Load weight summation unit 30f outputs a signal of a summation value of the summed load weights to summation value output unit <NUM>.

Summation value output unit <NUM> receives the summation value signal from load weight summation unit 30f, and outputs the summation value signal obtained by summation in load weight summation unit 30f to storage unit 30j and display unit <NUM>. Storage unit 30j stores the summation value of the load weights output from summation value output unit <NUM>. Display unit <NUM> shows the summation value of the load weights on the screen and the like. Summation value output unit <NUM> may also output the summation value signal to output unit <NUM> (<FIG>). The summation value signal output to output unit <NUM> may be output to second processor <NUM> and shown on display unit <NUM> of second processor <NUM>.

Then, an outline of a method of calculating an instantaneous load will be first described.

<FIG> shows one example of the relation between a boom angle θ and a differential pressure Pτ for each instantaneous load. In <FIG>, curves A, B and C represent a case in which bucket <NUM> is empty, a case in which bucket <NUM> is loaded half, and a case in which bucket <NUM> is fully loaded, respectively. Based on a graph of the relation between boom angle θ and differential pressure Pτ at two or more instantaneous loads measured in advance, a graph of the relation between the instantaneous load and differential pressure Pτ for each boom angle θ can be obtained as shown in <FIG>. Therefore, when boom angle θ and differential pressure Pτ are obtained, an instantaneous load in each differential pressure sampling can be obtained.

For example, assuming that boom angle θ = θk and differential pressure Pτ = Pτk at certain time mk as shown in <FIG>, an instantaneous load WN can be obtained from <FIG>. In other words, <FIG> is a graph showing the relation between the differential pressure and instantaneous load W at boom angle θ = θk. In this case, PτA refers to a differential pressure when bucket <NUM> is empty at boom angle θ = θk; WA refers to an instantaneous load in the unloaded state at boom angle θ = θk; PτC refers to a differential pressure when bucket <NUM> is fully loaded at boom angle θ = θk; WC refers to an instantaneous load in the fully-loaded state at boom angle θ = θk. When Pτk is located between PτA and PτC, instantaneous load WN is determined by linear interpolation. Alternatively, instantaneous load WN can also be obtained based on a numerical table that stores the above-described relation in advance.

Wheel loader <NUM> according to the present embodiment performs the excavation operation for scooping an excavated object such as soil onto bucket <NUM>, and the loading operation for loading the load (an excavated object <NUM>) in bucket <NUM> onto a transportation machine such as a truck bed (an object to be loaded with a load) of a dump truck <NUM>. <FIG> is a schematic diagram showing an example of a series of steps that constitute the excavation operation and the loading operation of wheel loader <NUM> according to the embodiment. By repeating the sequential execution of a plurality of steps described below, wheel loader <NUM> excavates excavated object <NUM> and loads excavated object <NUM> onto the transportation machine such as dump truck <NUM>.

As shown in <FIG>, wheel loader <NUM> moves forward toward excavated object <NUM>. In this unloaded forward movement step, the operator operates boom cylinder <NUM> and tilt cylinder <NUM> to cause work implement <NUM> to take an excavation attitude in which the tip of boom <NUM> is located at a low position and bucket <NUM> faces horizontally. In this state, the operator causes wheel loader <NUM> to move forward toward excavated object <NUM>.

As shown in <FIG>, the operator causes wheel loader <NUM> to move forward until cutting edge 6a of bucket <NUM> bites into excavated object <NUM>. In this excavation (pushing) step, cutting edge 6a of bucket <NUM> bites into excavated object <NUM>.

As shown in <FIG>, the operator then operates boom cylinder <NUM> to raise bucket <NUM>, and operates tilt cylinder <NUM> to tilt back bucket <NUM>. As a result of this excavation (scooping) step, bucket <NUM> is raised along a bucket trace L as shown by a curved arrow in the figure, and excavated object <NUM> is scooped into bucket <NUM>. Thus, the excavation work for scooping excavated object <NUM> is performed.

Depending on the type of excavated object <NUM>, the scooping step may be completed simply by tilting back bucket <NUM> once. Alternatively, an operation for tilting back bucket <NUM> to bring bucket <NUM> into neutral, and then, tilting back bucket <NUM> again may be repeated in the scooping step.

As shown in <FIG>, after excavated object <NUM> is scooped into bucket <NUM>, the operator causes wheel loader <NUM> to move rearward in a loaded rearward movement step. The operator may perform boom-raising during rearward movement, or may perform boom-raising during forward movement in <FIG>.

As shown in <FIG>, the operator causes wheel loader <NUM> to move forward and come closer to dump truck <NUM> while maintaining bucket <NUM> in the raised state or while raising bucket <NUM>. As a result of this loaded forward movement step, bucket <NUM> is located substantially directly above a truck bed of dump truck <NUM>.

As shown in <FIG>, the operator dumps bucket <NUM> at a prescribed position, and loads the load (excavated object) in bucket <NUM> onto the truck bed of dump truck <NUM>. This step is a so-called soil ejection step. Thereafter, the operator lowers boom <NUM> while causing wheel loader <NUM> to move rearward, and returns bucket <NUM> to the excavation attitude.

The above are typical steps that constitute one cycle of the excavation and loading work.

<FIG> is a table showing a determination method in the series of steps that constitute the excavation work and the loading work of wheel loader <NUM>.

In the table shown in <FIG>, the uppermost line of "work step" shows the designation of the work step shown in each of <FIG>. The lines of "forward and rearward movement switching lever", "work implement operation" and "work implement cylinder pressure" below the uppermost line show various determination criteria used by first processor <NUM> (<FIG> and <FIG>) to determine which step among the work steps is currently performed.

More specifically, the line of "forward and rearward movement switching lever" shows a determination criterion about the forward and rearward movement switching lever, which is indicated by a circle mark.

The line of "work implement operation" shows a determination criterion about an operation performed on work implement <NUM> by the operator, which is indicated by a circle mark. More specifically, the line of "boom" shows a determination criterion about an operation performed on boom <NUM>. Also, the line of "bucket" shows a determination criterion about an operation performed on bucket <NUM>.

The line of "work implement cylinder pressure" shows a determination criterion about a current hydraulic pressure of a cylinder of work implement <NUM>, e.g., hydraulic pressure of the cylinder bottom chamber of boom cylinder <NUM>. Four reference values A, B, C, and P are set in advance for the hydraulic pressure. A plurality of pressure ranges (a range lower than a reference value P, a range of reference values A to C, a range of reference values B to P, and a range lower than reference value C) are defined based on these reference values A, B, C, and P. Also, these pressure ranges are set as the above-described determination criterion. The relation of magnitudes of four reference values A, B, C, and P is defined as A > B > C > P.

By using a combination of determination criteria for "forward and rearward movement switching lever", "boom", "bucket", and "work implement cylinder pressure" for each work step as described above, first processor <NUM> can determine which step among the work steps is currently performed.

A specific operation of first processor <NUM> when performing the control shown in <FIG> will be described below.

A combination of determination criteria for "forward and rearward movement switching lever", "boom", "bucket", and "work implement cylinder pressure" corresponding to the respective work steps shown in <FIG> is stored in advance in storage unit 30j (<FIG>). First processor <NUM> recognizes the currently selected forward and rearward movement switching lever (F, N or R) based on a signal from forward and rearward movement switching apparatus <NUM>. First processor <NUM> recognizes a type (lowering, neutral or raising) of a current operation performed on boom <NUM> based on a signal from boom operation detection unit 52b. First processor <NUM> recognizes a type (dumping, neutral or tilting back) of a current operation performed on bucket <NUM> based on a signal from bucket operation detection unit 54b. Furthermore, first processor <NUM> recognizes a current hydraulic pressure in the cylinder bottom chamber of boom cylinder <NUM> based on a signal from pressure sensor 28b shown in <FIG>.

First processor <NUM> compares a combination of the current forward and rearward movement switching lever, the current boom operation type, the current bucket operation type, and the current lift cylinder hydraulic pressure that have been recognized (i.e., a current work state) with the pre-stored combination of determination criteria for "forward and rearward movement switching lever", "boom", "bucket", and "work implement cylinder pressure" corresponding to the respective work steps. As a result of this comparison process, first processor <NUM> determines a work step that corresponds to the combination of determination criteria best matching with the current work state.

Specifically, the combination of determination criteria corresponding to the excavation and loading operation shown in <FIG> is as follows.

In the unloaded forward movement step, the forward and rearward movement switching lever is F, the boom operation and the bucket operation are both neutral, and the work implement cylinder pressure is lower than reference value P.

In the excavation (pushing) step, the forward and rearward movement switching lever is F, the boom operation and the bucket operation are both neutral, and the work implement cylinder pressure is in the range of reference values A to C. In place of the forward and rearward movement switching lever, the operation of a work tool (a bucket, a boom) may be used as a parameter.

In the excavation (scooping) step, the forward and rearward movement switching lever is F or R, the boom operation is raising or neutral, the bucket operation is tilting back, and the work implement cylinder pressure is in the range of reference values A to C. As to the bucket operation, a determination criterion that tilting back and neutral are alternately repeated may be further added. This is because, depending on the state of the excavated object, the operation of tilting back bucket <NUM> to bring bucket <NUM> into neutral, and then, tilting back bucket <NUM> again may be repeated.

In the loaded rearward movement step, the forward and rearward movement switching lever is R, the boom operation is neutral or raising, the bucket operation is neutral, and the work implement cylinder pressure is in the range of reference values B to P. Determination may be made not only based on the forward and rearward movement switching lever but also based on the actual vehicle speed.

In the loaded forward movement step, the forward and rearward movement switching lever is F, the boom operation is raising or neutral, the bucket operation is neutral, and the work implement cylinder pressure is in the range of reference values B to P.

In the soil ejection step, the forward and rearward movement switching lever is F, the boom operation is raising or neutral, the bucket operation is dumping, and the work implement cylinder pressure is in the range of reference values B to P.

In the rearward movement and boom lowering step, the forward and rearward movement switching lever is R, the boom operation is lowering, the bucket operation is tilting back, and the work implement cylinder pressure is lower than reference value P.

In the above-described excavation and loading operation, wheel loader <NUM> in the present embodiment measures the load weight in bucket <NUM> and calculates the summation value of the load weights.

<FIG> is the first flowchart illustrating a method of controlling the work machine, which includes a method of measuring the load weight in the above-mentioned excavation and loading operation.

As shown in <FIG> and <FIG>, wheel loader <NUM> performs a series of operations in the excavation and loading operation. In order to recognize the current work phase in the series of excavation and loading operations, the information about the work phase is obtained (step S1: <FIG>).

For example, as shown in <FIG>, the information about this work phase is a detection signal of the forward and rearward movement command output from forward and rearward movement switching apparatus <NUM>, a detection signal of the operation command for boom <NUM> output from boom operation apparatus <NUM>, a detection signal of the operation command for bucket <NUM> output from bucket operation apparatus <NUM>, a pressure detection signal for boom cylinder <NUM>, and the like. The information about the work phases as described above is input into work phase distinction unit 30a.

Based on the obtained information about the work phase, work phase distinction unit 30a distinguishes the work phase while referring to the table shown in <FIG> (step S2: <FIG>). As a result of this distinction of the work phase, when the work phase is determined as excavation, the boom pressure (that is, the differential pressure between the head pressure detected by pressure sensor 28a and the bottom pressure detected by pressure sensor 28b, more specifically, the output value obtained after the smoothing process) is corrected (step S3: <FIG>).

As correction of the boom pressure, one of the first correction and the second correction as described below is performed, for example.

In the first correction, as shown in <FIG>, when the work phase is distinguished as excavation, the boom pressure is corrected so as to be set at a reference value. In this case, the reference value includes an invalid value and a prescribed value. The reference value is an invalid value of "<NUM>", for example. It should be noted that the reference values may be a prescribed value other than "<NUM>". The reference value may be reflected in the displayed value. Specifically, the controller (first processor <NUM>, second processor <NUM>) may control display units <NUM> and <NUM> such that the above-mentioned reference value is shown on display units <NUM> and <NUM> before distinction of excavation in the work phase switches.

In the first correction, in a time period from the time when the work phase switches from excavation to loaded rearward movement to a prescribed timing in the middle of the loaded rearward movement, the boom pressure is subjected to the above-mentioned smoothing process to thereby correct the boom pressure so as to gradually rise from the above-mentioned reference value and reach the measurement value.

Also in the first correction, after the boom pressure becomes equal to the measurement value, the boom pressure is kept at the measurement value that is not corrected until loading ends. The measurement value may be reflected in the displayed value. Specifically, the controller (first processor <NUM>, second processor <NUM>) may control display units <NUM> and <NUM> to show the above-mentioned measurement value (the load calculated based on the cylinder pressure) after distinction of excavation in the work phase switches.

Then, in the second correction, as shown in <FIG>, the boom pressure is corrected such that the traction pressure calculated based on traction is subtracted from the boom pressure.

Also in the second correction, the traction pressure is subtracted from the boom pressure while the traction is detected. Thus, when traction is detected even after the work phase switches from excavation to loaded rearward movement, the traction pressure may be subtracted from the boom pressure.

Also in the second correction, from the time point when the traction is no longer sensed to the time point when loading ends, the boom pressure is kept at the measurement value that is not corrected.

The traction mentioned above is calculated as follows.

For a direct transmission vehicle in which a torque converter is not provided between an engine and a transmission, traction is calculated by the following equation (<NUM>).

Furthermore, for a vehicle including a torque converter provided between an engine and a transmission, traction is calculated by the following equation (<NUM>).

Also, for a hydro-static transmission (HST) vehicle including a plurality of travel motors, traction is calculated by the following equation (<NUM>).

In this case, β in the above-mentioned equation (<NUM>) is represented by the following equation (<NUM>).

Units are shown in parentheses [] in the equations (<NUM>) to (<NUM>). In this case, tp in the equation (<NUM>) shows a primal torque coefficient, and t shows a torque ratio. Primal torque coefficient tp and torque ratio t each are a characteristic value of the transmission.

In the equation (<NUM>), F_max shows a maximum traction (unit: kN), R0 shows a default load radius (unit: m), and R shows a tire load radius (unit: m).

Also in the equation (<NUM>), P is HST drive differential pressure (unit: MPa), Rm1 is a reduction ratio of the first motor, q1 is a volume of the first motor (unit: cc/rev), Rm2 is a reduction ratio of the second motor, and q2 is a volume of the second motor (unit: cc/rev).

Also in the equation (<NUM>), Pco is HST cutoff differential pressure (unit: MPa), q1_max is a maximum volume of the first motor (unit: cc/rev), and q2_max is a maximum volume of the second motor (unit: cc/rev).

The engine output shaft torque in the equation (<NUM>) is obtained by the combination of the quantity of injection from engine <NUM> shown in <FIG> and the engine rotation speed. The quantity of injection from engine <NUM> is calculated based on the amount of operation in accelerator operation member 51a that is detected by accelerator operation detection unit 51b. The engine rotation speed is obtained by rotation sensor <NUM> sensing the rotation speed of the rotation shaft inside engine <NUM> shown in <FIG>. Based on the engine rotation speed and the quantity of injection as obtained in this way, the engine output shaft torque is obtained by referring to the table about the combination of the engine rotation speed in engine <NUM> and the quantity of injection from engine <NUM>.

The pump load torque in the equation (<NUM>) is calculated from the pump volume and the discharge pressure of work implement pump <NUM> shown in <FIG>. The pump volume of work implement pump <NUM> is calculated by detecting the angle of the swash plate of work implement pump <NUM> by sensor <NUM> shown in <FIG>. The discharge pressure of work implement pump <NUM> is detected by pressure sensor <NUM> shown in <FIG>.

The engine rotation speed in the equation (<NUM>) is obtained by rotation sensor <NUM> sensing the rotation speed of the rotation shaft inside engine <NUM> shown in <FIG>.

Each of the transmission reduction ratio, the differential reduction ratio, the final reduction ratio, the torque efficiency, tp, and t in the equations (<NUM>) and (<NUM>) is a constant.

The signal of the corrected pressure calculated by the above-mentioned first correction or second correction is output from boom pressure correction unit 30b to load weight calculation unit 30c as shown in <FIG>. Load weight calculation unit 30c calculates the instantaneous load as a load weight in bucket <NUM> based on the boom angle signal output from boom angle sensing unit <NUM> and the signal of the above-mentioned corrected pressure calculated by boom pressure correction unit 30b (step S4: <FIG>). The instantaneous load is calculated as described above with reference to <FIG> and <FIG>.

When work phase distinction unit 30a distinguishes the work phase as a work phase other than excavation (step S2: <FIG>), boom pressure correction unit 30b outputs, to load weight calculation unit 30c, the signal of the differential pressure (the signal of the boom pressure) between the head pressure and the bottom pressure of boom cylinder <NUM> that is output from differential pressure sensing unit 30i without correcting this signal, as shown in <FIG>. Load weight calculation unit 30c calculates the instantaneous load in bucket <NUM> based on the signal of the boom pressure and the boom angle signal output from boom angle sensing unit <NUM> (step S4: <FIG>).

As described above, in both of the first correction and the second correction, correction of the boom pressure is switched when it is distinguished that the work phase is switched from excavation to another phase (for example, loaded rearward movement). In both of the first correction and the second correction, when it is distinguished that the work phase is switched from excavation, for example, to the loaded rearward movement, boom pressure correction unit 30b outputs the signal of the boom pressure to load weight calculation unit 30c without correcting this signal.

In the case of the second correction, while traction is sensed by traction sensing units <NUM> to <NUM> and 51b, and the traction pressure calculated based on this traction is output to boom pressure correction unit 30b, even in the case of loaded rearward movement, boom pressure correction unit 30b may correct the boom pressure and output the corrected pressure to load weight calculation unit 30c.

As shown in <FIG>, the instantaneous load calculated by load weight calculation unit 30c is output from load weight calculation unit 30c to load weight output unit 30e. Load weight output unit 30e outputs the instantaneous load to display unit <NUM>. Thereby, the instantaneous load is shown on display unit <NUM> in real time (step S5: <FIG>).

After wheel loader <NUM> travels rearward by a prescribed distance in the loaded rearward movement, an operator performs the operation of switching from loaded rearward movement to loaded forward movement. Work phase distinction unit 30a shown in <FIG> distinguishes whether or not the work phase is switched from loaded rearward movement to loaded forward movement (step S6: <FIG>).

Switching from loaded rearward movement to loaded forward movement is sensed, for example, based on whether or not the operator has moved forward and rearward movement switching operation member 49a of forward and rearward movement switching apparatus <NUM> shown in <FIG> from the rearward movement (R) position to the forward movement (F) position. When the loaded rearward movement is switched to the loaded forward movement, forward and rearward movement switching apparatus <NUM> (forward and rearward movement switching detection sensor 49b) shown in <FIG> outputs a signal showing forward movement (forward and rearward movement switching signal) to work phase distinction unit 30a. Thus, based on this forward movement signal, work phase distinction unit 30a can sense that the traveling state has been switched from the loaded rearward movement to the loaded forward movement.

Also, switching from loaded rearward movement to loaded forward movement may be sensed, for example, by sensing the movement speed of wheel loader <NUM> that is sensed by vehicle speed detection unit <NUM> shown in <FIG>. When the loaded rearward movement is switched to the loaded forward movement, the movement speed of wheel loader <NUM> sensed by vehicle speed detection unit <NUM> changes from the speed of movement in the rearward direction to the speed of movement in the forward direction. Thus, based on the signal of the movement speed of wheel loader <NUM> indicating forward movement (forward and rearward movement switching signal) that is output from vehicle speed detection unit <NUM>, work phase distinction unit 30a shown in <FIG> can sense that the loaded rearward movement has been switched to the loaded forward movement.

Furthermore, the traveling state of wheel loader <NUM> may be captured by an image pick-up apparatus. Then, based on the captured image, switching from the loaded rearward movement to the loaded forward movement may be sensed.

When work phase distinction unit 30a distinguishes that the work phase has been switched from loaded rearward movement to loaded forward movement, the instantaneous load at the time point of switching from loaded rearward movement to loaded forward movement is calculated as a load weight (step S7: <FIG>).

In this case, in the same manner as described above, boom pressure correction unit 30b outputs, to load weight calculation unit 30c, the signal of the differential pressure (the signal of the boom pressure) between the head pressure and the bottom pressure of boom cylinder <NUM> that is output from differential pressure sensing unit 30i without correcting this signal, as shown in <FIG>. Load weight calculation unit 30c calculates the instantaneous load in bucket <NUM> as a load weight based on the above-mentioned signal of the boom pressure and the boom angle signal output from boom angle sensing unit <NUM>.

The load weight calculated by load weight calculation unit 30c is output from load weight calculation unit 30c to load weight output unit 30e. Load weight output unit 30e outputs the load weight to display unit <NUM>. Thereby, display unit <NUM> shows the load weight as a fixed value (step S8: <FIG>). This load weight is kept shown on display unit <NUM> as a fixed value from the time point when switching from loaded rearward movement to loaded forward movement is sensed to the time point when the work phase is distinguished as loading.

Furthermore, load weight output unit 30e outputs the load weight to storage unit 30j. Storage unit 30j stores the load weight output from load weight output unit 30e.

The above-described excavation and loading operation is repeatedly performed. The load weights are summed based on the load weight that is output for each excavation and loading operation.

As shown in <FIG>, the load weights are summed by load weight summation unit 30f. Load weight summation unit 30f automatically adds the current load weight to the summation value of previous load weights stored in storage unit 30j (i.e., automatically sums a plurality of load weights). The summation value obtained by summation is output from load weight summation unit 30f and input into summation value output unit <NUM>. The summation value obtained by summation is stored in storage unit 30j by summation value output unit <NUM> and shown on display unit <NUM> and shown on display unit <NUM> of second processor <NUM>.

During the above-mentioned excavation and loading operation that is repeatedly performed, the operator can check the instantaneous load shown on display unit <NUM> in real time in step S5 in <FIG>. Specifically, the operator can check the instantaneous load on display unit <NUM> immediately after the end of excavation in the above-mentioned excavation and loading operation (immediately after the loaded rearward movement is started). When the instantaneous load is loaded onto an object to be loaded with a load (this object is, for example, a truck bed of a dump truck), the operator determines whether or not the summation value of the load weights exceeds the loadable capacity in the object to be loaded with a load. When the operator determines that the summation value of the load weights exceeds the loadable capacity in the object to be loaded with a load, the operator unloads a part of the load contained in bucket <NUM> at or near the excavation site. Thereby, the instantaneous load is adjusted such that the summation value of the load weights does not exceed the loadable capacity in the object to be loaded with a load.

After adjusting the instantaneous load as described above, the operator operates wheel loader <NUM> so as to travel rearward from the excavation site (loaded rearward movement). Then, after wheel loader <NUM> travels rearward by a predetermined distance, the movement of wheel loader <NUM> is switched to loaded forward movement. Then, at the position where wheel loader <NUM> approaches the object to be loaded with a load, the operator operates bucket <NUM> to perform a dumping operation so as to load the load (excavated object) in bucket <NUM> onto the truck bed of dump truck <NUM>. Thereby, the above-mentioned excavation and loading operation can be completed without exceeding the loading capacity of the dump truck.

As described above, the control of the work machine including measurement and summation of the load weights in the excavation and loading operation in the present embodiment is performed.

<FIG> is the second flowchart illustrating the method of controlling the work machine, which includes a method of measuring the load weight in the excavation and loading operation as described above. The second flow shown in <FIG> relates to the correction of subtracting the above-mentioned traction pressure from the boom pressure.

As shown in <FIG>, in the second flow, wheel loader <NUM> performs a series of operations in the excavation and loading operation as in the first flow shown in <FIG>. In order to recognize the current work phase in the series of excavation and loading operations, the information about the work phase is obtained (step S1).

Based on the obtained information about the work phase, work phase distinction unit 30a distinguishes the work phase while referring to the table shown in <FIG> (step S2). When the work phase is determined as excavation as a result of this distinction of the work phase, the information about the traction is sensed (step S11). For example, as shown in <FIG>, the information about traction includes a rotation speed of the rotation shaft inside engine <NUM> detected by rotation sensor <NUM>, an angle of the swash plate of work implement pump <NUM> detected by sensor <NUM>, discharge pressure of work implement pump <NUM> detected by pressure sensor <NUM>, an amount of operation in accelerator operation member 51a detected by accelerator operation detection unit 51b, and the like.

Based on this information about the traction, traction is calculated using the above-mentioned equation (<NUM>), (<NUM>), or (<NUM>). Then, based on this traction, traction pressure is calculated (step S12). Then, based on the calculated traction pressure, the boom pressure is corrected (step S3).

Since the subsequent steps are the same as those in the above-described first flow, the description thereof will not be repeated.

In this second flow, the boom pressure is corrected during the time period in which traction is sensed, thereby eliminating the need to perform the step of distinguishing the work phase.

<FIG> each show a change in a display content on display unit <NUM>. As shown in <FIG>, when the work phase is distinguished as unloaded forward movement and excavation, display unit <NUM> shows a target load weight in bucket <NUM>. For example, on a display meter portion having an arc shape labelled as "current" on display unit <NUM>, a target load weight % represented as a bar extending to the "<NUM>%" position along the arc shape is supplementarily shown.

As shown in <FIG>, when the work phase is distinguished as loaded rearward movement, display unit <NUM> shows the current instantaneous load in bucket <NUM>. For example, on the display meter portion having an arc shape labelled as "current" on display unit <NUM>, the current instantaneous load % represented as a bar extending along the arc shape is shown in real time.

The operator checks display unit <NUM>. Then, when the current instantaneous load during loaded rearward movement exceeds the target load weight % (for example, <NUM>%), the operator performs the operation of unloading a part of the load from bucket <NUM>. Thereby, the load in bucket <NUM> can be adjusted. The instantaneous load at this time is represented by the first color, for example.

As shown in <FIG>, display unit <NUM> shows, as a load weight of a fixed value, the instantaneous load calculated when it is sensed that the work phase is switched from loaded rearward movement to loaded forward movement. This load weight as a fixed value is continuously shown on display unit <NUM> from the time point when switching from loaded rearward movement to loaded forward movement is sensed to the time point when loading is sensed.

For example, on the display meter portion having an arc shape labelled as "current" on display unit <NUM>, the load weight % represented as a bar extending along this arc shape is shown as a fixed value. At the time point when loaded rearward movement is switched to loaded forward movement, the measurement value of the load in bucket <NUM> is stable. Thus, less erroneous measurement values can be displayed.

This load weight as a fixed value is shown by the second color different from the first color that shows the instantaneous load. Thereby, the operator can readily visually recognize that the load weight as a fixed value is displayed.

As shown in <FIG>, display unit <NUM> shows: a summation value of the load weights loaded onto the object to be loaded with a load; and a difference obtained by subtracting the summation value of the load weights from the loadable capacity in the object to be loaded with a load. For example, on the display meter portion having an arc shape labelled as "remainder" on display unit <NUM>, the summation value of the load weights loaded onto the object to be loaded with a load is shown as a bar extending along the arc shape. Also, below the indication of "remainder", the difference obtained by subtracting the summation value of the load weights from the loadable capacity in the object to be loaded with a load is shown as a numerical value.

The present inventor checked changes in boom angle, boom cylinder differential pressure, instantaneous load, and load weight in the series of steps of the excavation and loading operation of wheel loader <NUM> according to the present embodiment. The result is shown in <FIG>.

The result in <FIG> shows that each of the boom angle, the boom cylinder differential pressure and the instantaneous load changes significantly during excavation and during soil ejection. It also shows that each of the boom angle, the boom cylinder differential pressure and the instantaneous load changes significantly also in the first half of loaded rearward movement. In contrast, in the latter half of loaded rearward movement and during loaded forward movement, changes over time in boom angle, boom cylinder differential pressure and instantaneous load are small. In particular, immediately before switching from loaded rearward movement to loaded forward movement, changes over time in boom cylinder differential pressure and instantaneous load are very small, which shows that each of the boom cylinder differential pressure and the instantaneous load is stable.

In the present embodiment, the boom cylinder differential pressure (boom pressure) significantly changes over time during excavation, as shown in <FIG>. Thus, in the present embodiment, when the work phase is distinguished as excavation, the boom pressure is corrected. Then, based on this corrected pressure, the instantaneous load in bucket <NUM> is calculated. Thereby, it can be recognized whether or not the instantaneous load in bucket <NUM> exceeds the loading capacity of the object to be loaded with a load (for example, a truck bed of a dump truck) during excavation or immediately after the end of excavation. This can consequently shorten the time period required for going back to the excavation site in order to unload a part of the load in bucket <NUM>, so that an increase in work time can be suppressed.

Furthermore, since the time period required for going back to the excavation site can be shortened as described above, a load does not have to be loaded onto the object to be loaded with a load, while leaving a part of the load in bucket <NUM>. Therefore, the loading operation is facilitated.

Furthermore, the boom raising operation does not have to be performed for measuring the load weight as in the above-mentioned patent literature. This eliminates the need to lower the boom, so that the operator's operation becomes simplified.

As described above, the present embodiment can implement a work machine and a system including the work machine, by which the load weight can be measured in a short work time period by a simple operation.

Also in the present embodiment, wheel loader <NUM> includes traveling unit <NUM> as shown in <FIG>. Thus, based on switching between rearward movement and forward movement of traveling unit <NUM>, it can be distinguished whether the work phase is excavation or not.

Also in the present embodiment, as shown in <FIG>, when the work phase is excavation, the boom pressure is corrected so as to be set at a reference value (for example, "<NUM>"). Then, the instantaneous load is calculated based on this corrected pressure. When the work phase is loaded rearward movement, the instantaneous load is calculated based on the measurement value of the boom pressure. This prevents the operator from determining whether to dump the load in bucket <NUM> or not based on the load measured during excavation with unstable boom pressure.

Also in the present embodiment, as shown in <FIG>, the boom pressure is corrected to be set at a reference value for the entire time period during which the work phase is distinguished as excavation. This prevents the operator from determining whether to dump the load in bucket <NUM> or not for the entire time period of excavation with unstable boom pressure.

Also in the present embodiment, the boom pressure is corrected by subtracting the traction pressure from the boom pressure as shown in <FIG>. The traction resulting from traveling of traveling unit <NUM> acts on the pressure of boom cylinder <NUM> during excavation. This traction is a cause of unstabilized boom pressure during excavation. Thus, by correcting the boom pressure so as to subtract the traction, the instantaneous load can be more accurately calculated.

Also in the present embodiment, as shown in <FIG>, a notification unit (display units <NUM> and <NUM>) is provided for giving a notification of the instantaneous load calculated by the controller (first processor <NUM>, second processor <NUM>). Thereby, the operator and the like can check the instantaneous load given from the notification unit for performing, for example, the operation of unloading the load in bucket <NUM>.

It should be noted that the notification unit is not limited to display units <NUM> and <NUM>, but may be a speaker that gives a notification with a sound.

Also in the present embodiment, as shown in <FIG> and <FIG>, when it is distinguished that loaded rearward movement has been started as a work phase, the controller (first processor <NUM>, second processor <NUM>) causes display units <NUM> and <NUM> to show the calculated instantaneous load as a current load value in real time. Thereby, when the load in bucket <NUM> is unloaded, the operator and the like can immediately check the instantaneous load in bucket <NUM> from which the load has been unloaded. Thus, the load value in bucket <NUM> is readily adjusted.

Also in the present embodiment, as shown in <FIG> and <FIG>, the controller (first processor <NUM>, second processor <NUM>) causes display units <NUM> and <NUM> to show the instantaneous load, which is calculated at a time point of switching from loaded rearward movement to loaded forward movement, as a load weight continuously from the time point when this switching is sensed to the time point when loading is distinguished. Thereby, the operator and the like can readily check the load weight.

Also in the present embodiment, as shown in <FIG>, display units <NUM> and <NUM> show the target load weight (<FIG>), the instantaneous load (<FIG>), the load weight (<FIG>), and the summation value of the load weights, and the difference obtained by subtracting the summation value of the load weights from the loadable capacity (<FIG>). Thereby, the operator can unload the load in bucket <NUM> immediately after excavation based on the information on display unit <NUM> and the like, and also, can readily visually check the above-mentioned load weight, the above-mentioned summation value, and the above-mentioned difference.

A sensor used as the forward and rearward movement switching sensor may be those for vehicle speed detection by a GPS (Global Positioning System), vehicle speed detection using a stereo camera, vehicle speed detection using a rotation sensor of a transmission output shaft, vehicle speed detection using a rotation sensor of a transmission input shaft and a transmission gear ratio, and the like. The forward and rearward movement switching sensor is not limited to the above, but may be any sensor that can detect the traveling direction of the vehicular body.

Also, the above embodiment has been described with regard to the case where the load weight is calculated based on the boom angle and the differential pressure between the head pressure and the bottom pressure of boom cylinder <NUM>, but the load weight may be calculated based on the bottom pressure and the boom angle of boom cylinder <NUM>. In this case, pressure sensor 28a in <FIG> is not required.

Also, the above embodiment has been described with regard to the case where controllers <NUM> and <NUM> switch correction of the boom pressure when distinction of excavation in the work phase switches, as shown in <FIG> and <FIG>. However, controllers <NUM> and <NUM> may switch correction of the cylinder pressure of the work tool cylinder (boom cylinder <NUM> and tilt cylinder <NUM>) that drives at least one of bucket <NUM> and boom <NUM> when distinction of the excavation in the work phase is switched.

Also, the above embodiment has been described with regard to the case where controllers <NUM> and <NUM> correct the boom pressure to calculate the corrected pressure of boom cylinder <NUM> and calculate the instantaneous load in bucket <NUM> based on the corrected pressure, as shown in <FIG> and <FIG>. The present invention is not limited to the above, but controllers <NUM> and <NUM> may correct the cylinder pressure of the work tool cylinder (boom cylinder <NUM> and tilt cylinder <NUM>) that drives at least one work tool of bucket <NUM> and boom <NUM> to calculate the corrected pressure, and then, calculate the instantaneous load in bucket <NUM> based on the corrected pressure.

Also the above embodiment has been described with regard to the case where controllers <NUM> and <NUM> correct the boom pressure so as to be set at a reference value when controllers <NUM> and <NUM> distinguish the work phase as excavation, as shown in <FIG> and <FIG>. The present invention is not limited to the above, but controllers <NUM> and <NUM> may correct the cylinder pressure of the work tool cylinder (boom cylinder <NUM> and tilt cylinder <NUM>) that drives at least work tool of bucket <NUM> and boom <NUM> to be set at a reference value when controllers <NUM> and <NUM> distinguish the work phase as excavation.

Also the above embodiment has been described with regard to the case where, when controllers <NUM> and <NUM> distinguish the work phase as excavation, controllers <NUM> and <NUM> subtract the traction pressure from the boom pressure to correct the boom pressure so as to calculate the corrected pressure, as shown in <FIG>. The present invention is not limited to the above, but, when controllers <NUM> and <NUM> distinguish the work phase as excavation, controllers <NUM> and <NUM> may subtract the traction pressure from the cylinder pressure of the work tool cylinder (boom cylinder <NUM> and tilt cylinder <NUM>) that drives at least one of bucket <NUM> and boom <NUM> to thereby correct the cylinder pressure so as to calculate the corrected pressure.

Although the above embodiment has been described with regard to the case where functional blocks 30a to 30j shown in <FIG> are included in first processor <NUM>, these functional blocks 30a to 30j may be included in second processor <NUM> shown in <FIG>. In this case, the sensing signal from each of forward and rearward movement switching apparatus <NUM>, vehicle speed detection unit <NUM>, first hydraulic pressure detectors 28a and 28b, first angle detector <NUM>, and second angle detector <NUM> may be output to second processor <NUM> through output unit <NUM> shown in <FIG>.

In addition, boom operation apparatus <NUM> and bucket operation apparatus <NUM> may be an integrated steering lever (single lever). In this case, one steering lever serves as both boom operation apparatus <NUM> and bucket operation apparatus <NUM>.

Second processor <NUM> shown in <FIG> may receive and transmit an electric/radio signal to and from output unit <NUM> over a controller area network (CAN), a local area network (LAN), a wireless LAN and the like.

Second processor <NUM> may receive the input information of first processor <NUM> and perform computation.

In the embodiment above, wheel loader <NUM> shown in <FIG> has been described as a work machine to which the configuration of the above-described embodiment is applied. However, in addition to wheel loader <NUM>, the work machine to which the configuration of the above-described embodiment is applied may be a work machine including bucket <NUM> or may be a backhoe loader, for example.

Claim 1:
A work machine (<NUM>), comprising:
a work implement (<NUM>) including a bucket (<NUM>), a boom (<NUM>) that raises and lowers the bucket (<NUM>), and a work tool cylinder (<NUM>, <NUM>) that drives at least one of the bucket (<NUM>) and the boom (<NUM>);
a work phase sensing unit (28a, 28b, <NUM>, <NUM>, 49b, 52b, 54b) that senses information about a work phase of the work implement (<NUM>); and
a cylinder pressure sensing unit (28a, 28b) that senses cylinder pressure of the work tool cylinder (<NUM>, <NUM>),
characterized by further comprising:
a controller (<NUM>) that distinguishes the work phase by the work implement (<NUM>) based on the information sensed by the work phase sensing unit (28a, 28b, <NUM>, <NUM>, 49b, 52b, 54b), and switches correction of the cylinder pressure sensed by the cylinder pressure sensing unit (28a, 28b) when it is distinguished that the work phase is switched from excavation to a work phase other than excavation, wherein
when the controller (<NUM>) distinguishes the work phase as excavation, the controller (<NUM>) corrects the cylinder pressure to calculate corrected pressure of the work tool cylinder (<NUM>, <NUM>), and calculates an instantaneous load in the bucket (<NUM>) based on the corrected pressure.