Wheel loader

Abstract

To provide a wheel loader capable of shortening a cycle time of a loading work and increasing a work amount.SOLUTION: A wheel loader 1 comprises: a work device 2 having a lift arm 21 that can rotate up and down relative to a vehicle body; an engine 3 for driving the vehicle body and operating the work device 2; a brake device 8 for applying brake to the vehicle body; and a controller 5 for controlling the engine 3 and the brake device 8. When a loading operation in which the lift arm 21 moves upward while a vehicle is driving forward is performed, the controller 5 sets a rotational speed of the engine 3 to a value R2 that is smaller than the maximum rotational speed R1 and greater than a target rotational speed R3 at which a vehicle speed becomes a target vehicle speed St when the brake device 8 is not activated, and activates the brake device 8 with a brake set pressure P that is set based on a difference between an actual vehicle speed and the target vehicle speed St, to limit the vehicle speed.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a wheel loader for carrying out cargo handling operations. [Background technology]

[0002] When a wheel loader loads a load onto a dump truck or other such object, it moves its lift arm upward while driving forward toward the destination. During this loading operation, it is important to strike a balance between the time it takes for the lift arm to fully lift and the distance traveled to the destination. If the time it takes for the lift arm to fully lift is long compared to the distance traveled, it becomes necessary to set a correspondingly longer distance to travel to the destination. A longer travel distance results in more fuel consumption by the wheel loader.

[0003] Therefore, for example, in the wheel loader described in Patent Document 1, the maximum engine rotation speed is reduced to limit the vehicle speed during loading operations, thereby shortening the required driving distance to the loading destination and suppressing fuel consumption. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-65574 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the case of the wheel loader described in Patent Document 1, reducing the maximum rotational speed of the engine reduces the flow rate of hydraulic oil discharged from the hydraulic pump, which is the power source for the lift arms, and the operating speed of the lift arms decreases. As a result, the lift arms may not be able to fully rise by the time the wheel loader arrives at the loading destination, which could lengthen the cycle time of the loading work and reduce the amount of work done.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a wheel loader that can shorten the cycle time of loading work and increase the amount of work that can be performed. [Means for solving the problem]

[0007] In order to achieve the above object, the present invention provides a wheel loader comprising a vehicle body, a working device having lift arms that can rotate up and down relative to the vehicle body, a prime mover that serves as a power source for traveling the vehicle body and operating the working device, a brake device that applies brakes to the vehicle body, a traveling condition detection device that detects the traveling condition of the vehicle body, a motion detection device that detects the motion state of the lift arms, and a controller that controls the prime mover and the brake device, respectively; the controller determines whether a loading operation is being performed in which the lift arms are moving upward while the vehicle body is traveling forward, based on the traveling condition of the vehicle body detected by the traveling condition detection device and the motion state of the lift arms detected by the motion detection device, and if it determines that a loading operation is being performed, the controller sets the rotational speed of the prime mover to a value that is smaller than the maximum rotational speed and greater than a target rotational speed at which the vehicle speed would become a predetermined target vehicle speed if the brake device were not activated, and executes a first control process to activate the brake device at a brake set pressure that is set based on the difference between the actual vehicle speed and the target vehicle speed, thereby limiting the vehicle speed. [Effects of the Invention]

[0008] According to the present invention, it is possible to shorten the cycle time of the loading operation and increase the amount of work. Problems, configurations and effects other than those described above will become apparent from the following description of the embodiment. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is an external side view showing an example of the configuration of a wheel loader according to an embodiment of the present invention. [Figure 2] FIG. 1 is an explanatory diagram illustrating V-shape loading by a wheel loader. [Figure 3] FIG. 1 is an explanatory diagram illustrating loading work by a wheel loader. [Figure 4] 1 is a system configuration diagram showing an example of the configuration of a drive system of a wheel loader. [Figure 5] FIG. 2 is a functional block diagram showing functions of a controller. [Figure 6] 10 is a graph showing the relationship between the rise of brake pressure and the change in vehicle speed over time. [Figure 7] FIG. 2 is an explanatory diagram for explaining the control contents of the controller in chronological order. [Figure 8] 10 is a flowchart showing the flow of processing executed by a controller. DETAILED DESCRIPTION OF THE INVENTION

[0010] <Overall configuration of wheel loader 1> First, the overall configuration of a wheel loader 1 according to an embodiment of the present invention will be described with reference to FIG.

[0011] FIG. 1 is an external side view showing an example of the configuration of a wheel loader 1 according to an embodiment of the present invention.

[0012] The wheel loader 1 is an articulated work vehicle that is steered by bending the vehicle body near the center, with a front frame 1A forming the front part of the vehicle body and a rear frame 1B forming the rear part of the vehicle body connected by a center joint 10 so that the front frame 1A can rotate freely in the left-right direction relative to the rear frame 1B. In the following explanation, within the left-right direction of the vehicle body, the direction to the left relative to the forward direction is referred to as the "left direction," and the direction to the right relative to the forward direction is referred to as the "right direction."

[0013] The vehicle body is provided with four wheels 11, two of which are front wheels 11A and are provided on both the left and right sides of the front frame 1A, and the remaining two are rear wheels 11B and are provided on both the left and right sides of the rear frame 1B. Of the four wheels 11, only the front wheel 11A and the rear wheel 11B, which are provided on the left side, are shown in Fig. 1.

[0014] A hydraulically driven working device 2 is attached to the front of the front frame 1A to perform loading and unloading operations, such as digging up work objects such as soil and minerals and loading the excavated work objects into a loading destination such as a dump truck or hopper.

[0015] The working device 2 has a lift arm 21 attached to the front frame 1A so as to be rotatable in the vertical direction, two lift arm cylinders 22L, 22R (see FIG. 4) as hydraulic cylinders that drive the lift arm 21, a bucket 23 attached to the tip of the lift arm 21 so as to be rotatable in the vertical direction, a bucket cylinder 24 that serves as a hydraulic cylinder that drives the bucket 23, and a bell crank 25 rotatably connected to the lift arm 21 and that forms a link mechanism between the bucket 23 and the bucket cylinder 24.

[0016] The two lift arm cylinders 22L, 22R are arranged side by side at a predetermined distance in the left-right direction of the vehicle body, and in FIG. 1, only the lift arm cylinder 22L arranged on the left side is shown by a dashed line.

[0017] The lift arm 21 rotates vertically relative to the front frame 1A as two lift arm cylinders 22L, 22R extend and retract. The lift arm 21 is operated by a lift arm operating lever 210 (see FIG. 4) provided in the operator's cab 12.

[0018] Bucket 23 rotates vertically relative to lift arm 21 as bucket cylinder 24 expands and contracts. This allows bucket 23 to scoop up and discharge (dig and dump) work objects such as earth and sand or minerals. Bucket 23 is operated by bucket operating lever 230 (see FIG. 4) provided in operator's cab 12.

[0019] The bucket 23 can be replaced with various attachments, such as a blade, and the wheel loader 1 can perform various tasks such as snow removal and earth-raising in addition to loading and unloading operations using the bucket 23.

[0020] In this embodiment, the lift arm operation lever 210 and bucket operation lever 230, which serve as operation devices for operating the working implement 2, are each an electric operation lever, and when operated by an operator, an operation signal (operation direction and operation amount) is output to a controller 5, which will be described later. The lift arm operation lever 210 is also one aspect of an operation detection device that detects the operating state of the lift arm 21.

[0021] In addition, in this embodiment, the lift arm operation lever 210 for operating the lift arm 21 and the bucket operation lever 230 for operating the bucket 23 are provided separately, but this is not limited to this, and for example, the lift arm 21 and the bucket 23 may be operated by a single cargo handling operation lever.

[0022] The rear frame 1B is provided with a cab 12 in which the operator sits, a machine room 13 that houses various devices required for driving the wheel loader 1, and a counterweight 14 that maintains balance with the work implement 2 to prevent the vehicle body from tilting. On the rear frame 1B, the cab 12 is located at the front, the counterweight 14 at the rear, and the machine room 13 between the cab 12 and the counterweight 14.

[0023] <About cargo handling operations> Next, the cargo handling operation performed by the wheel loader 1 will be described with reference to FIGS.

[0024] Fig. 2 is an explanatory diagram illustrating V-shape loading by the wheel loader 1. Fig. 3 is an explanatory diagram illustrating loading work by the wheel loader 1.

[0025] The wheel loader 1 performs loading and unloading work by using the work implement 2 to excavate work objects such as earth and sand or minerals and load them into a loading destination such as a dump truck or hopper. In other words, the loading and unloading work is divided into an excavation work to excavate the work object, and a loading work to load the work object (load) into a loading destination.

[0026] 2, first, the wheel loader 1 moves forward toward the mound of natural ground α, which is the work target, as indicated by arrow X1, and performs excavation work by plungeing the bucket 23 into the mound of natural ground α to scoop up earth, sand, minerals, etc. Once the excavation work is completed, the wheel loader 1 moves back to its original location as indicated by arrow X2.

[0027] In the subsequent loading operation, the wheel loader 1 moves forward, as indicated by arrow Y1, towards the dump truck β onto which the load in the bucket 23 is to be loaded, and stops in front of the dump truck β. At this time, the wheel loader 1 operates the working implement 2 in an upward direction while traveling forward. Note that in Figure 2, the wheel loader 1 stopped in front of the dump truck β is shown by a dashed line.

[0028] As shown in Fig. 3, in loading work, first, the operator fully depresses the accelerator pedal (full accelerator) and raises the lift arm 21 (the state shown on the right side in Fig. 3). Next, the operator, while keeping the accelerator pedal in the full accelerator state, further raises the lift arm 21 (the state shown in the center in Fig. 3). Then, the operator activates the brakes to stop the truck in front of the dump truck β, dumps the bucket 23, and loads the load (earth, sand, minerals, etc.) in the bucket 23 into the dump truck β.

[0029] When the loading operation is completed, the wheel loader 1 retreats to its original location, as shown by arrow Y2 in Figure 2. This method of performing excavation and loading operations by the wheel loader 1 traveling back and forth in a V shape between the mound of ground α and the dump truck β is called "V-shape loading."

[0030] In the following description, among the various operations of the wheel loader 1 during loading work, the "loading operation" refers to when the lift arm 21 moves upward while the vehicle body travels forward. Therefore, the "loading operation" below does not include the operation of dumping the bucket 23 and loading the load (earth, sand, minerals, etc.) in the bucket 23 onto the dump truck β.

[0031] <Wheel loader 1 drive system> Next, the drive system of the wheel loader 1 will be described with reference to FIG.

[0032] FIG. 4 is a system configuration diagram showing an example of the configuration of the drive system of the wheel loader 1.

[0033] The wheel loader 1 has its vehicle body travel controlled by a torque converter type travel drive system, and is configured to include an engine 3 as a prime mover that serves as the power source for the wheel loader 1, a torque converter 41 (hereinafter referred to as "torque converter 41") whose input shaft is connected to the output shaft of the engine 3, and a transmission 42 connected to the output shaft of the torque converter 41. Each device, such as the engine 3, torque converter 41, and transmission 42, is controlled by a controller 5.

[0034] In a torque converter type traveling drive system, first, when the operator depresses the accelerator pedal 61 provided in the cab 12, the engine 3 starts to rotate, and the input shaft of the torque converter 41 rotates in conjunction with the rotation of the engine 3. The output shaft of the torque converter 41 rotates according to a set torque converter speed ratio. Then, the output torque from the torque converter 41 is transmitted to the front wheels 11A and rear wheels 11B via the transmission 42, propeller shaft 15, and axle 16, causing the wheel loader 1 to travel.

[0035] The depression amount of accelerator pedal 61 (hereinafter referred to as "accelerator pedal depression amount") is detected by depression amount sensor 610 and input to controller 5. Controller 5 determines a target engine rotation speed based on the acquired accelerator pedal depression amount, and outputs a command signal related to the target engine rotation speed to engine 3. As a result, engine 3 is controlled to a rotation speed in accordance with the target engine rotation speed. The target engine rotation speed increases as the accelerator pedal depression amount increases.

[0036] The torque converter 41 is a fluid clutch made up of an impeller, turbine, and stator, and has the function of increasing the output torque relative to the input torque, i.e., the function of making the torque ratio (= output torque / input torque) equal to or greater than 1. This torque ratio decreases as the torque converter speed ratio (= output shaft rotation speed / input shaft rotation speed), which is the ratio of the rotation speed of the input shaft of the torque converter 41 to the rotation speed of the output shaft, increases. As a result, the torque converter 41 changes the rotation speed of the engine 3 before transmitting it to the transmission 42.

[0037] The transmission 42 is a transmission having multiple solenoid valves that switch to a maximum vehicle speed corresponding to multiple speed stages (for example, 1 to 4 speed stages), and changes the rotation of the output shaft of the torque converter 41. Selection of each speed stage is performed by the operator by operating a speed stage switch 62. This speed stage switch 62 is mainly used for forward travel of the wheel loader 1.

[0038] When the operator selects the desired speed step with the speed step switch 62, a speed step signal related to the selected speed step is output from the speed step switch 62 to the controller 5. The controller 5 then outputs a command signal based on the acquired speed step signal to the transmission 42. The transmission 42 drives a plurality of solenoid valves in accordance with the command signals output from the controller 5, thereby switching the speed step.

[0039] For example, when transmission 42 is switched between speed stages 1 to 4, the maximum vehicle speed increases in the order of speed stage 1, speed stage 2, speed stage 3, and speed stage 4. The operator selects speed stage 1, which provides the lowest maximum vehicle speed, for excavation work, and speed stage 2, which provides a maximum vehicle speed greater than the maximum vehicle speed of speed stage 1 (for example, 9 to 15 km / h), for loading work.

[0040] The direction of travel of the wheel loader 1, that is, forward or reverse, is selected by a forward / reverse selector switch 63 provided in the operator's cab 12.

[0041] When the operator switches the forward / reverse selector switch 63 to the forward position, a switch signal indicating forward travel is output to the controller 5. The controller 5 outputs a command signal to the transmission 42 to engage the forward clutch of the transmission 42. When the transmission 42 receives the command signal relating to forward travel output from the controller 5, the forward clutch is engaged. This switches the traveling direction of the vehicle body to forward travel. Note that the same mechanism is used to switch the vehicle body to reverse travel.

[0042] The depression amount sensor 610, the speed gear switch 62, and the forward / reverse switch 63 are each an aspect of a driving condition detection device that detects the driving condition of the vehicle body. The determination of the driving condition of the vehicle body does not necessarily have to be based on the accelerator pedal depression amount, the forward / reverse switching state, and the selected speed gear, but may be made comprehensively based on, for example, each piece of data detected by a plurality of other driving condition detection devices mounted on the vehicle body.

[0043] The travel drive system of the wheel loader 1 is also equipped with a brake device 8 that can be manually operated by an operator or automatically operated by the controller 5. The brake device 8 is hydraulically driven, and the brakes are applied or released by a brake valve 81 controlling the flow of hydraulic oil discharged from the charge pump 43A. The brake valve 81 corresponds to the braking control section of the brake device 8, and the temperature is detected by a temperature sensor 810.

[0044] When manually applying or releasing the brakes, a pilot pressure is generated according to the amount of operation of the brake pedal 82 provided in the driver's cab 12, and the generated pilot pressure controls the operation of the brake valve 81.

[0045] On the other hand, when the brakes are to be automatically applied or released, the brake pilot pressure reducing valve 83 reduces the pressure of the hydraulic oil guided from the charge pump 43A based on a command signal output from the controller 5 to generate pilot pressure, and the generated pilot pressure controls the operation of the brake valve 81.

[0046] The drive system of the work implement 2 is hydraulically driven and includes two lift arm cylinders 22L, 22R, a bucket cylinder 24, a hydraulic pump 43 that supplies hydraulic oil to each of the two lift arm cylinders 22L, 22R and the bucket cylinder 24, and a loading valve device 44 that controls the flow (direction and flow rate) of hydraulic oil supplied from the hydraulic pump 43 to each of the two lift arm cylinders 22L, 22R and the bucket cylinder 24.

[0047] The hydraulic pump 43 is driven by the engine 3 and pumps up and discharges hydraulic oil stored in the hydraulic oil tank 430. Although the hydraulic pump 43 is shown as a variable displacement hydraulic pump in Fig. 4, it does not necessarily have to be a variable displacement type and may be a fixed displacement type.

[0048] Although not shown, the cargo handling valve device 44 is configured to include a lift arm directional control valve provided between the hydraulic pump 43 and the two lift arm cylinders 22L, 22R, a bucket directional control valve provided between the hydraulic pump 43 and the bucket cylinder 24, a first lift arm electromagnetic control valve and a second lift arm electromagnetic control valve that control the lift arm directional control valve, and a first bucket electromagnetic control valve and a second bucket electromagnetic control valve that control the bucket directional control valve.

[0049] In the cargo handling valve device 44, the lift arm directional control valve controls the flow (direction and flow rate) of hydraulic oil discharged from the hydraulic pump 43 and guided to each of the two lift arm cylinders 22L, 22R. The first lift arm electromagnetic control valve and the second lift arm electromagnetic control valve each control the lift arm directional control valve based on a command signal output from the controller 5.

[0050] For example, when an operator operates the lift arm operation lever 210 to perform a lift arm 21 raising operation, a lift arm operation signal is output from the lift arm operation lever 210 to the controller 5. When the controller 5 acquires the lift operation signal output from the lift arm operation lever 210, it outputs a lift operation command signal to each of the first lift arm electromagnetic control valve and the second lift arm electromagnetic control valve to raise the lift arm 21.

[0051] The first lift arm electromagnetic control valve and the second lift arm electromagnetic control valve each control the operation of the spool of the lift arm directional control valve based on a lifting operation command signal output from the controller 5 so as to connect the hydraulic pump 43 to each bottom chamber of the two lift arm cylinders 22L, 22R.

[0052] As a result, the hydraulic oil discharged from the hydraulic pump 43 flows into the bottom chambers of the two lift arm cylinders 22L, 22R, and each rod 220 extends, causing the lift arm 21 to rotate upward relative to the front frame 1A.

[0053] Furthermore, when the operator operates the lift arm operation lever 210 to lower the lift arm 21, a lowering operation signal is output from the lift arm operation lever 210 to the controller 5. When the controller 5 acquires the lowering operation signal output from the lift arm operation lever 210, it outputs a lowering operation command signal to each of the first lift arm electromagnetic control valve and the second lift arm electromagnetic control valve to lower the lift arm 21.

[0054] Based on a lowering operation command signal output from the controller 5, the first lift arm electromagnetic control valve and the second lift arm electromagnetic control valve each control the operation of the spool of the lift arm directional control valve so as to connect the hydraulic pump 43 to each rod chamber of the two lift arm cylinders 22L, 22R.

[0055] As a result, the hydraulic oil discharged from the hydraulic pump 43 flows into the rod chambers of the two lift arm cylinders 22L, 22R, causing the rods 220 to contract and the lift arms 21 to rotate downward relative to the front frame 1A.

[0056] The lift arm operating lever 210 is one aspect of an operating state detection device that detects the operating state of the lift arm 21. Note that the operating state of the lift arm 21 does not necessarily have to be determined based on the operation signal output from the lift arm operating lever 210, and may be determined based on, for example, the discharge pressure of the hydraulic pump 43 or the position of the lift arm 21 detected by a lift arm position sensor (e.g., an angle sensor).

[0057] In cargo handling valve device 44, the bucket directional control valve controls the flow (direction and flow rate) of hydraulic oil discharged from hydraulic pump 43 and guided to bucket cylinder 24. The first bucket electromagnetic control valve and the second bucket electromagnetic control valve each control the bucket directional control valve based on a command signal output from controller 5.

[0058] For example, when the operator operates bucket operation lever 230 to perform a tilt operation (backward tilt operation) of bucket 23, a tilt operation signal is output from bucket operation lever 230 to controller 5. When controller 5 acquires the tilt operation signal from bucket operation lever 230, it outputs a backward tilt operation command signal to each of the first bucket electromagnetic control valve and the second bucket electromagnetic control valve to tilt bucket 23 backward.

[0059] Then, the first bucket electromagnetic control valve and the second bucket electromagnetic control valve each control the operation of the spool of the bucket directional control valve so as to connect hydraulic pump 43 and the bottom chamber of bucket cylinder 24, based on a rearward tilt operation command signal output from controller 5.

[0060] As a result, hydraulic oil discharged from the hydraulic pump 43 flows into the bottom chamber of the bucket cylinder 24, the rod 240 extends, and the bucket 23 rotates upward relative to the lift arm 21 and tilts backward (towards the vehicle body).

[0061] Furthermore, when the operator operates bucket operation lever 230 to perform a dump operation (forward tilt operation) of bucket 23, a dump operation signal is output from bucket operation lever 230 to controller 5. Upon receiving the dump operation signal output from bucket operation lever 230, controller 5 outputs a forward tilt operation command signal to each of the first bucket electromagnetic control valve and the second bucket electromagnetic control valve to tilt bucket 23 forward.

[0062] Then, the first bucket electromagnetic control valve and the second bucket electromagnetic control valve each control the operation of the spool of the bucket directional control valve so as to connect hydraulic pump 43 and the rod chamber of bucket cylinder 24, based on the forward tilting operation command signal output from controller 5.

[0063] As a result, the hydraulic oil discharged from the hydraulic pump 43 flows into the rod chamber of the bucket cylinder 24, the rod 240 contracts, and the bucket 23 rotates downward relative to the lift arm 21 and tilts forward (towards the front of the vehicle body).

[0064] In this embodiment, the hydraulic oil discharged from the hydraulic pump 43 is supplied to the two lift arm cylinders 22L, 22R and the bucket cylinder 24, as well as to the pair of steering cylinders 71L, 71R.

[0065] The flow (direction and flow rate) of hydraulic oil discharged from hydraulic pump 43 and guided to the pair of steering cylinders 71L, 71R is controlled by a steering valve 72. An internal spool of the steering valve 72 is driven based on the operation of a handle 700 provided in the cab 12. As a result, rods 710 of the pair of steering cylinders 71L, 71R extend and retract in accordance with the operation of the handle 700, thereby turning the steering.

[0066] A priority valve 73 is provided on the discharge side of the hydraulic pump 43, and has a first position in which the hydraulic oil discharged from the hydraulic pump 43 is directed to the loading valve device 44, and a second position in which the hydraulic oil discharged from the hydraulic pump 43 is directed to the steering valve 72.

[0067] <Configuration of Controller 5> Next, the configuration of the controller 5 will be described with reference to FIGS.

[0068] Fig. 5 is a functional block diagram showing the functions of the controller 5. Fig. 6 is a graph showing the relationship between the rise in brake pressure and the change in vehicle speed over time. Fig. 7 is an explanatory diagram explaining the control contents of the controller 5 in chronological order.

[0069] The controller 5 is configured by interconnecting a CPU, RAM, ROM, HDD, input I / F, and output I / F via a bus. Various operating devices such as the speed switch 62, forward / reverse switch 63, and lift arm operating lever 210, as well as various sensors such as the depression amount sensor 610 and temperature sensor 810, are connected to the input I / F, and the engine 3 and brake pilot pressure reducing valve 83 are connected to the output I / F.

[0070] In such a hardware configuration, the CPU reads out a control program (software) stored on a recording medium such as a ROM, HDD, or optical disk, expands it on RAM, and executes the expanded control program, whereby the control program and hardware work together to realize the functions of the controller 5.

[0071] In this embodiment, the configuration of the controller 5 is described as a combination of software and hardware, but this is not limiting and the controller 5 may also be configured using an integrated circuit that realizes the functions of a control program executed on the wheel loader 1 side.

[0072] As shown in FIG. 5, the controller 5 includes a data acquisition unit 51, an operation determination unit 52, a temperature determination unit 53, a storage unit 54, a processing determination unit 55, and a command signal output unit 56.

[0073] The data acquisition unit 51 acquires the speed stage signal output from the speed stage switch 62, the forward / reverse switching signal output from the forward / reverse switching switch 63, the operation signal output from the lift arm operation lever 210, the accelerator pedal depression amount detected by the depression amount sensor 610, and the temperature T of the brake valve 81 detected by the temperature sensor 810.

[0074] The operation determination unit 52 determines whether the vehicle body is moving forward based on the speed stage signal, the forward / backward switching signal, and the accelerator pedal depression amount acquired by the data acquisition unit 51. Specifically, when the forward / backward switching signal indicates forward movement, the speed stage signal indicates the second speed stage, and the accelerator pedal depression amount indicates a value of full throttle, the operation determination unit 52 determines that the wheel loader 1 is in forward movement during the loading operation.

[0075] Further, the operation determination unit 52 determines the operating state of the lift arm 21 based on the operation signal from the lift arm operation lever 210 acquired by the data acquisition unit 51. Specifically, the operation determination unit 52 determines whether the lift arm 21 is moving upward and whether the upward movement of the lift arm 21 has stopped.

[0076] The temperature determination unit 53 determines whether the temperature T of the brake valve 81 acquired by the data acquisition unit 51 is equal to a predetermined temperature threshold value Tth. Here, the "predetermined temperature threshold value Tth" is a value set based on the temperature of the brake valve 81 in the brake device 8 in an overheat state.

[0077] The various condition threshold values used by the operation determination unit 52 and the predetermined temperature threshold value Tth used by the temperature determination unit 53 are stored in the storage unit 54, respectively.

[0078] When the processing determination unit 55 determines that the vehicle body is in the loading operation where the lift arm 21 moves upward while moving forward by the operation determination unit 52 and determines that the temperature T of the brake valve 81 is lower than the temperature threshold value Tth (T < Tth) by the temperature determination unit 53, the content of the control process is determined as the first control process.

[0079] This "first control process" is a process that sets the rotational speed of the engine 3 to a value R2 that is smaller than the maximum rotational speed R1 of the engine 3 and is greater than the target rotational speed R3 at which the vehicle speed becomes the predetermined target vehicle speed St when the braking device 8 is not operating (R3 < R2 < R1), and operates the braking device 8 with a brake set pressure P set based on the difference between the actual vehicle speed and the target vehicle speed St.

[0080] The brake set pressure P is set based on the difference between the actual vehicle speed and the target vehicle speed St so that the vehicle body accelerates smoothly during forward travel, as shown by the solid line in FIG. 6. If the brake set pressure P were set without being based on the difference between the actual vehicle speed and the target vehicle speed St, the rise of the brake pressure would be too fast and the acceleration of the vehicle body would be too slow (in the case of the two-dot chain line shown in FIG. 6), or conversely, the rise of the brake pressure would be too slow and the vehicle speed would suddenly decelerate after exceeding the target vehicle speed St (in the case of the broken line shown in FIG. 6).

[0081] In the present embodiment, as shown in FIG. 7, the controller 5 executes the first control process by adding an additional process to the limiting process, that is, by executing the limiting process and the additional process in parallel (limiting process on · additional process on).

[0082] The "limiting process" is a process that sets the rotational speed of the engine 3 to the target rotational speed R3. The "additional process" is an additional process that adds a predetermined additional rotational speed R4 set based on the target rotational speed R3 to the target rotational speed R3.

[0083] Therefore, the rotational speed R2 of the engine 3 limited by the first control process is a value obtained by adding the additional rotational speed R4 to the target rotational speed R3 (R2 = R3 + R4). In the first control process, it is not necessarily required that the limiting process and the additional process be executed in parallel, and the rotational speed of the engine 3 may be directly controlled to R2 in one process.

[0084] In addition, when the processing determination unit 55 determines that the lift arm 21 has stopped moving upward after the operation determination unit 52 determines that the loading operation is in progress, the content of the control process is determined as the second control process.

[0085] This "second control process" is a process of restricting the rotational speed of the engine 3 to the target rotational speed R3 and stopping the operation of the brake device 8. In the present embodiment, as shown in FIG. 7, the controller 5 executes the restriction process and the additional process in the first control process (restriction process on · additional process on), while in the second control process, the restriction process is continuously executed while the execution of the additional process is stopped (restriction process on · additional process off).

[0086] As shown in FIG. 7, during the loading operation, the wheel loader 1 starts moving forward at the maximum rotational speed R1 of the engine 3 toward the loading destination (dump truck β). After the loading operation starts, the rotational speed of the engine 3 is restricted to R2 (R2 < R1), and the brake device 8 operates to increase the brake pressure to the brake set pressure P (first control process). Then, when the upward movement of the lift arm 21 stops due to the operator's operation or when the vehicle body arrives in front of the loading destination, the rotational speed of the engine 3 is restricted to R3 (R3 < R2), and the operation of the brake device 8 stops and the brake pressure decreases (second control process).

[0087] In this way, while restricting the vehicle speed to the target vehicle speed St and suppressing the fuel consumption, the wheel loader 1 can perform the loading operation without reducing the upward movement speed of the lift arm 21 by restricting the rotational speed of the engine 3 in two stages (R2 → R3). As a result, the wheel loader 1 can shorten the cycle time of the loading operation and increase the work amount.

[0088] Furthermore, in this embodiment, as shown in Fig. 7, in the first control process, the brake device 8 operates to gradually increase the brake pressure toward the brake set pressure P, thereby smoothly decelerating the vehicle speed and suppressing spillage of the load from the bucket 23. When transitioning from the first control process to the second control process, the operation of the brake device 8 is immediately stopped, thereby preventing a sudden deceleration of the vehicle speed.

[0089] In this embodiment, even if the operation determination unit 52 determines that a loading operation is being performed in which the lift arms 21 are moving upward while the vehicle body is traveling forward, the process determination unit 55 determines the content of the control process to be the second restriction process if the temperature determination unit 53 determines that the temperature T of the brake valve 81 is equal to or higher than the temperature threshold value Tth (T≧Tth), that is, the brake device 8 is in an overheated state. In this case, when the operation determination unit 52 determines that the lift arms 21 have stopped moving upward, the controller 5 continues to execute the second control process.

[0090] When the processing content is determined to be the first control processing by the processing determination unit 55, the command signal output unit 56 outputs a command signal to the engine 3 to set the rotation speed to R2 (target rotation speed R3 + additional rotation speed R4), and also outputs a command signal to the pressure reducing valve 83 to operate the brake device 8 at the brake set pressure P.

[0091] Furthermore, when the processing content is determined to be the second control processing by the processing determination unit 55, the command signal output unit 56 outputs a command signal to the engine 3 to set the rotation speed to the target rotation speed R3 (to cancel the addition of the additional rotation speed R4), and also outputs a command signal to the pressure reducing valve 83 to stop the operation of the brake device 8.

[0092] <Processing executed by controller 5> Next, the flow of processing executed within the controller 5 will be described with reference to FIG.

[0093] FIG. 8 is a flowchart showing the flow of processing executed by the controller 5.

[0094] In the controller 5, first, the data acquisition unit 51 acquires the forward / backward switching signal output from the forward / backward switching switch 63, the operation signal output from the lift arm operation lever 210, the speed step signal output from the speed step switch 62, and the accelerator pedal depression amount detected by the depression amount sensor 610 (step S501).

[0095] Next, based on the forward / backward switching signal, operation signal, speed step signal, and accelerator pedal depression amount acquired in step S501, the operation determination unit 52 determines whether the wheel loader 1 is in the loading operation, that is, whether it is performing the raising operation of the lift arm 21 while traveling forward (step S502).

[0096] If it is determined in step S502 that the wheel loader 1 is in the loading operation (step S502 / YES), the data acquisition unit 51 acquires the temperature T of the brake valve 81 detected by the temperature sensor 810 (step S503).

[0097] On the other hand, if it is determined in step S502 that the wheel loader 1 is not in the loading operation (step S502 / NO), the processing in the controller 5 ends.

[0098] Subsequently, the temperature determination unit 53 determines whether the temperature T acquired in step S503 is lower than the temperature threshold Tth, that is, whether the braking device 8 is not in the overheat state (step S504).

[0099] If it is determined in step S504 that the temperature T is lower than the temperature threshold Tth (T < Tth), that is, the braking device 8 is not in the overheat state (step S504 / YES), the processing determination unit 55 determines the processing content as the first control processing (limiting processing + additional processing), and the command signal output unit 56 outputs the command signal related to the first control processing to each of the engine 3 and the pressure reducing valve 83 (step S505).

[0100] On the other hand, if it is determined in step S504 that the temperature T is equal to or greater than the temperature threshold value Tth (T≧Tth), i.e., that the brake device 8 is in an overheated state (step S504 / NO), the processing decision unit 55 decides the processing content to be the second control processing (only restriction processing), and the command signal output unit 56 outputs a command signal related to the second control processing to each of the engine 3 and the pressure reducing valve 83 (step S506).

[0101] After steps S505 and S506, the data acquiring unit 51 again acquires the operation signal output from the lift arm operating lever 210 (step S507).

[0102] Next, the operation determination unit 52 determines whether the raising operation of the lift arm 21 has been stopped based on the operation signal acquired again in step S507 (step S508).

[0103] If it is determined in step S508 that the lifting operation of the lift arm 21 has been stopped (step S508 / YES), the processing decision unit 55 decides the processing content to be the second control processing, the command signal output unit 56 outputs a command signal related to the second control processing to each of the engine 3 and the pressure reducing valve 83 (step S509), and the processing in the controller 5 ends.

[0104] On the other hand, if it is determined in step S508 that the lifting operation of the lift arm 21 has not been stopped, that is, that the lifting operation of the lift arm 21 is continuing (step S508 / NO), the process returns to step S501 and is repeated.

[0105] The above describes an embodiment of the present invention. However, the present invention is not limited to the above embodiment and includes various modifications. For example, the above embodiment has been described in detail to clearly explain the present invention, and is not necessarily limited to an embodiment including all of the described configurations. Furthermore, it is possible to replace part of the configuration of this embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of this embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of this embodiment with other configurations.

[0106] For example, in the above embodiment, the engine 3 is used as an example of the prime mover, but the present invention is not limited to this and may be, for example, an electric motor. In other words, the present invention can be applied not only to torque converter type wheel loaders 1 but also to electrically driven wheel loaders and the like.

[0107] In addition, in the above embodiment, the controller 5 stops the operation of the brake device 8 in the second control process, but this is not limited to this, and it is sufficient if the brake pressure is limited to a pressure value that is at least smaller than the set brake pressure P.

[0108] Furthermore, in the above embodiment, the controller 5 determines whether or not the first control process is to be executed based on whether or not the brake device 8 is in an overheated state, but this is not limited to this, and it is sufficient to determine at least whether or not a loading operation is in progress. [Explanation of symbols]

[0109] 1: Wheel loader 1A: Front frame (body) 1B: Rear frame (body) 2: Work equipment 3: Engine (prime mover) 5: Controller 8: Brake device 21: Lift arm 62: Speed ​​switch (driving condition detection device) 63: Forward / reverse switch (driving condition detection device) 81: Brake valve (braking control unit) 210: Lift arm operation lever (motion detection device) 610: Pedal amount sensor (driving state detection device) 810: Temperature sensor P: Brake pressure setting R1: Maximum rotation speed R3: Target rotation speed St: Target vehicle speed

Claims

1. The car body and a working device having a lift arm that can rotate up and down relative to the vehicle body; a prime mover that serves as a power source for propelling the vehicle body and operating the working device; a braking device that applies braking to the vehicle body; a running state detection device for detecting the running state of the vehicle body; a motion detection device for detecting the motion state of the lift arm; a controller that controls the prime mover and the brake device; In a wheel loader equipped with The controller determining whether or not the vehicle is in a loading operation in which the lift arms are moving upward while the vehicle is traveling forward, based on the traveling state of the vehicle body detected by the traveling state detection device and the operating state of the lift arms detected by the operation detection device; When it is determined that the loading operation is in progress, a first control process is executed to limit the vehicle speed by setting the rotation speed of the prime mover to a value smaller than the maximum rotation speed and larger than a target rotation speed at which the vehicle speed becomes a predetermined target vehicle speed when the brake device is not activated, and activating the brake device with a brake set pressure set based on the difference between the actual vehicle speed and the target vehicle speed. A wheel loader characterized by:

2. The wheel loader according to claim 1, The controller When it is determined that the lift arm has stopped moving upward after determining that the loading operation is in progress, a second control process is executed to limit the rotation speed of the prime mover to the target rotation speed and to limit the brake pressure of the brake device to a pressure value smaller than the set brake pressure. A wheel loader characterized by:

3. The wheel loader according to claim 2, The second control process includes: A process of limiting the rotation speed of the prime mover to the target rotation speed and stopping the operation of the brake device. A wheel loader characterized by:

4. The wheel loader according to claim 2, The controller In the first control process, a limiting process for limiting the rotational speed of the prime mover to the target rotational speed, and an adding process for adding a predetermined additional rotational speed, which is set based on the target rotational speed, to the target rotational speed; In the second control process, The restriction process continues to be executed, while the execution of the additional process is stopped. A wheel loader characterized by:

5. The wheel loader according to claim 1, The controller In the first control process, A limiting process is executed to set the rotation speed of the prime mover to the target rotation speed, and an adding process is executed to add a predetermined additional rotation speed set based on the target rotation speed to the target rotation speed. A wheel loader characterized by:

6. The wheel loader according to claim 5, a temperature sensor for detecting a temperature of a braking control unit of the brake device; The controller When the temperature detected by the temperature sensor reaches a predetermined temperature threshold value set based on the temperature of the braking control unit of the brake device in an overheated state, the first control process does not execute the additional process and does not operate the brake device. A wheel loader characterized by:

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