JP2014145447A - Clutch control device of work vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To smoothly stop a work vehicle by disengaging a clutch at a timing corresponding to a state of the work vehicle.SOLUTION: A clutch control device loaded on a wheel loader 1 comprises: a pressure sensor 37 detecting a brake pressure Pb; and a temperature detector 38 detecting a temperature T of a brake portion 19A. A controller 27 determines whether a clutch cutoff condition is satisfied or not on the basis of the brake pressure Pb detected by the pressure sensor 37 and the temperature T of the brake portion 19A detected by the temperature detector 38. The controller 27 controls engagement/disengagement of a forward clutch 24 and a reverse clutch 25 so that the forward clutch 24 and the reverse clutch 25 are disengaged when it is determined that the clutch cutoff condition is satisfied.

Description

  The present invention relates to a clutch control device for a work vehicle mounted on a work vehicle such as a wheel loader or a forklift.

  In general, for example, a wheel loader is known as a wheel-type work vehicle. In this wheel loader, a front vehicle body is connected to the front side of a rear vehicle body so as to be able to swing leftward and rightward, and a cargo handling device (working device) including an arm, a bucket, and the like is attached to the front vehicle body. In addition, an engine, a torque converter, a transmission, a hydraulic pump, and the like are mounted on the rear vehicle body, and the power of the engine is transmitted to the transmission via the torque converter.

  The wheel loader repeats the work of moving forward and thrusting the bucket into a pile of earth and sand, lifting the bucket together with a large amount of earth and sand, and loading the earth and sand on a truck or the like. In this series of operations, the operator sometimes depresses the brake pedal and decelerates the wheel loader while stepping on the accelerator pedal to raise the bucket when loading earth and sand on the truck.

  On the other hand, a clutch control device is known in which the clutch is disengaged and transmission of the driving force to the wheels is cut off according to the vehicle speed and the magnitude of the braking force generated by the operation of the brake pedal (for example, Patent Documents). 1).

  In this clutch control device, the braking force at which the clutch is released at high speed is set larger than the braking force at which the clutch is released at low speed. Therefore, during high speed traveling, even if the brake pedal operation amount is such that the clutch is released during low speed traveling, the clutch is not released, and the vehicle can be decelerated while effectively exerting the engine brake and suppressing the service brake load. It has a configuration.

JP 2005-299732 A

  By the way, the clutch control device described in Patent Document 1 described above determines the traveling state of the work vehicle based on whether the vehicle speed is low or high, and the brake pressure at which the clutch is released at low speed and high speed. A brake pressure cut-off threshold value that is the determination value is set. In this case, it cannot be said that the state of the work vehicle is sufficiently considered, and depending on the state of the work vehicle, the release timing of the clutch may not be appropriate.

  The present invention has been made in view of the above-described problems of the prior art, and releases the clutch at an appropriate timing corresponding to the state of the work vehicle so that the work vehicle can be smoothly decelerated and stopped. The object is to provide a device.

  In order to solve the above-described problems, a clutch control device for a work vehicle according to the present invention includes a braking force detection unit that detects a braking force of the work vehicle, a temperature detection unit that detects a temperature of the brake device of the work vehicle, Determination means for determining whether or not a clutch cutoff condition is satisfied based on the braking force of the work vehicle detected by the braking force detection means and the temperature of the braking device detected by the temperature detection means; And a clutch control means for controlling engagement and release of the clutch so as to release the clutch when the determination means determines that the clutch cutoff condition is satisfied.

  According to a second aspect of the present invention, there is provided a work vehicle clutch control device comprising: a braking force detection unit that detects a braking force of the work vehicle; a cargo handling device position detection unit that detects a position of the cargo handling device of the work vehicle; and the braking force detection unit. A determination unit that determines whether a clutch cutoff condition is satisfied based on the detected braking force of the work vehicle and the position of the cargo handling device detected by the cargo handling device position detection unit; And clutch control means for controlling engagement and release of the clutch so as to release the clutch when it is determined by the means that the clutch cutoff condition is satisfied.

  According to a third aspect of the present invention, there is provided a work vehicle clutch control device comprising: a braking force detection means for detecting a braking force of the work vehicle; a temperature detection means for detecting a temperature of the brake device of the work vehicle; and a position of the cargo handling device of the work vehicle. The load handling device position detection means for detecting the braking force of the work vehicle detected by the braking force detection means, the temperature of the braking device detected by the temperature detection means, and the load handling device position detection means Determining means for determining whether or not a clutch cutoff condition is satisfied based on the position of the cargo handling device, and when the determination means determines that the clutch cutoff condition is satisfied, the clutch And clutch control means for controlling engagement and release of the clutch so as to release the clutch.

  The invention according to claim 4 is that the clutch cutoff condition is set so that the clutch is released with a higher braking force as the temperature of the braking device is higher.

  The invention of claim 5 is that the clutch cutoff condition is set so that the higher the position of the cargo handling device is, the lower the clutch is released with a lower braking force.

  According to the first aspect of the present invention, the braking force of the work vehicle and the temperature of the braking device are configured as the clutch cutoff operation determination condition. Since the braking force of the braking device is changed by changing the friction coefficient depending on the temperature of the braking device, the temperature of the braking device is configured as a clutch cutoff operation determination condition, so that the braking device corresponds to the temperature of the braking device. The clutch can be released at an appropriate timing. Thereby, irrespective of the temperature of the braking device (high or low), the timing at which the clutch cutoff is actuated can be made equal, and the work vehicle can be smoothly decelerated and stopped. As a result, the stability and reliability of the work vehicle can be improved.

  According to the second aspect of the present invention, the braking force of the work vehicle and the position (operating position, operating position, operating position) of the cargo handling device are configured as the clutch cutoff operation determining condition. Since the position of the center of gravity of the work vehicle changes in accordance with the position of the loading / unloading device, an appropriate timing according to the position of the loading / unloading device is configured by configuring the position of the loading / unloading device as a clutch cutoff operation determination condition. Can release the clutch. Thereby, regardless of the position of the cargo handling device (whether it is high or low), it is possible to suppress the pitching when the clutch cutoff is activated, and to smoothly decelerate and stop the work vehicle. As a result, the stability and reliability of the work vehicle can be improved.

  According to the third aspect of the present invention, the braking force of the work vehicle, the temperature of the braking device, and the position of the cargo handling device (operating position, operating position, operating position) are configured as the clutch cut-off operation determination conditions. In the braking device, the braking force is changed by changing the friction coefficient depending on the temperature of the braking device, and the position of the center of gravity of the work vehicle is changed in accordance with the position of the cargo handling device. For this reason, the clutch can be released at an appropriate timing by configuring the temperature of the braking device and the position of the cargo handling device as the clutch cutoff operation determination condition. Accordingly, the timing at which the clutch cutoff is activated can be made equal regardless of the temperature of the braking device and the position of the cargo handling device, and pitching when the clutch cutoff is activated can be suppressed. Therefore, the work vehicle can be smoothly decelerated and stopped.

  According to the invention of claim 4, the clutch cutoff condition is configured such that the clutch is released with a higher braking force as the temperature of the braking device is higher. The braking device has a lower friction coefficient and a lower braking force as the temperature of the braking device increases. Therefore, the clutch cutoff condition is such that the higher the braking device temperature is, the higher the braking force is released, so that the same braking force is applied regardless of the braking device temperature level. In addition, the clutch can be released. Thereby, the work vehicle can be smoothly decelerated and stopped.

  According to the invention of claim 5, the clutch cutoff condition is configured such that the higher the position of the cargo handling device is, the lower the clutch is released with a lower braking force. The higher the position of the cargo handling device, the higher the position of the center of gravity of the work vehicle, and it becomes easier to induce pitching during braking / stopping. Accordingly, the higher the position of the cargo handling device in the clutch cutoff condition, the more the clutch is released with a lower braking force, so that the pitching associated with the sudden deceleration due to the delayed clutch cutoff timing is achieved. Can be suppressed. Thereby, the work vehicle can be smoothly decelerated and stopped.

It is a side view of the wheel loader which is an example of a work vehicle. It is a figure which shows schematic structure of the control system of a wheel loader. It is a characteristic diagram which shows the relationship between the vehicle speed for every speed stage, and driving force. It is a figure which shows schematic structure of a transmission. It is a characteristic diagram which shows the relationship between a torque converter speed ratio and a speed stage. It is a characteristic diagram which shows the relationship between the operation amount of a brake pedal, and a brake pressure. It is a characteristic diagram which shows the relationship between the operation amount (depression amount) of an accelerator pedal, and a target engine rotational speed. It is a figure shown about V shape loading. It is a figure explaining the state of the wheel loader at the time of loading earth and sand etc. on a dump truck. It is a figure explaining the state of the wheel loader at the time of working on an inclined road. It is a characteristic diagram which shows the clutch cutoff condition at the time of 1st speed. It is a characteristic diagram which shows the clutch cutoff condition at the time of 2nd speed. It is a characteristic diagram which shows the relationship between an axle oil temperature and the friction coefficient of a brake disc. It is a flowchart which shows the operation | movement of the clutch control process in the wheel loader by the 1st Embodiment of this invention. It is a flowchart which shows the operation | movement following A in FIG. It is a flowchart which shows the operation | movement following B in FIG. 16 is a flowchart showing an operation following C in FIG. 15. It is a characteristic diagram which shows the relationship between a cargo handling apparatus position and vehicle body pitching. It is the flowchart which showed the operation | movement of the clutch control process in the wheel loader by the 2nd Embodiment of this invention. It is the flowchart which showed the operation | movement of the clutch control process in the wheel loader by the 3rd Embodiment of this invention.

  Hereinafter, an embodiment of a clutch control device for a work vehicle according to the present invention will be described in detail with reference to the accompanying drawings, taking as an example a case where the embodiment is applied to a clutch control device mounted on a wheel loader.

  1 to 17 show a first embodiment of a clutch control device for a work vehicle according to the present invention. In FIG. 1, reference numeral 1 denotes a wheel loader as an example of a work vehicle to which the clutch control device according to the first embodiment is applied. In this wheel loader 1, a front vehicle body 3 provided with left and right front wheels 2 and a rear vehicle body 5 provided with left and right rear wheels 4 are bent left and right via a center pin 6. Connected as possible. The wheel loader 1 is configured as an articulated work vehicle that performs steering by bending the front vehicle body 3 and the rear vehicle body 5 leftward and rightward by a steering cylinder (not shown).

  Here, the front vehicle body 3 of the wheel loader 1 is provided with a cargo handling device (working device) 9 including an arm 7 and a bucket 8 so as to be able to move up and down. On the other hand, the rear vehicle body 5 of the wheel loader 1 is provided with a cab 10 that defines a cab, an engine 13, a transmission 17, and the like, which will be described later.

  The arm 7 of the cargo handling device 9 is rotated upward (downwardly and vertically) by driving the arm cylinder 11 with the base end side as a rotation fulcrum. Further, a bucket 8 as a working tool is provided at the tip of the arm 7, and the bucket 8 is rotated (cloud or dumped) upward and downward by driving a bucket cylinder 12.

  Reference numeral 13 denotes an engine mounted on the rear vehicle body 5, and an output shaft of the engine 13 is connected to an input shaft 15 (see FIG. 4) of a torque converter 14 (hereinafter referred to as torque converter 14). An output shaft 16 (see FIG. 4) of the torque converter 14 is connected to the transmission 17. The torque converter 14 is a fluid clutch including a known impeller, turbine, and stator, and the rotation of the engine 13 is transmitted to the transmission 17 via the torque converter 14.

  As will be described later, the transmission 17 has a hydraulic clutch that switches the speed stage from the first speed to the fourth speed, and the rotation of the output shaft 16 of the torque converter 14 is changed by the transmission 17. Then, the rotation after the shift is transmitted to the left and right front wheels 2 and the left and right rear wheels 4 via the propeller shaft 18 and the axle device 19 so that the wheel loader 1 travels.

  The axle device 19 is provided with a brake portion 19A as a braking device for decelerating and stopping the wheel loader 1. When the brake oil is supplied from the hydraulic oil tank 20 via the brake valve 21, the brake unit 19A generates a braking force according to the pressure of the hydraulic oil.

  The brake valve 21 is a pressure reducing valve that reduces the pressure oil supplied from the hydraulic pump 22 to a pressure corresponding to the compression force of the spring 21A. When a brake pedal 23 provided in the cab 10 is depressed by an operator and the spring 21A is compressed according to the depression force of the brake pedal 23, the brake valve 21 is supplied from a hydraulic pump 22 serving as a hydraulic source. The pressure oil is reduced to a pressure corresponding to the depression force of the brake pedal 23. The brake valve 21 reduces the pressure of the hydraulic oil so that the higher the compression force of the spring 21A (that is, the depression force of the brake pedal 23) is, the higher the hydraulic oil is supplied to the brake portion 19A.

  A hydraulic pump (not shown) driven by the engine 13 discharges hydraulic oil toward a working actuator (for example, the arm cylinder 11) via a direction control valve (not shown). This directional control valve is driven by operation of an operation lever (not shown) in the cab 10, and the working actuator is driven in accordance with the operation amount of the operation lever.

  The torque converter 14 has a function of increasing the output torque with respect to the input torque, that is, a function of setting the torque ratio to 1 or more. The torque ratio decreases as the torque converter speed ratio e (= Nt / Ni), which is the ratio of the rotational speed Ni of the input shaft 15 of the torque converter 14 to the rotational speed Nt of the output shaft 16, increases. For example, when the traveling load increases during traveling with the engine speed kept constant, the rotational speed Nt of the output shaft 16 of the torque converter 14 decreases, that is, the vehicle speed decreases, and the torque converter speed ratio e decreases. At this time, since the torque ratio increases, the vehicle can travel with a larger travel driving force (traction force).

  Next, the transmission 17 will be described.

  Reference numeral 17 denotes a transmission that changes the torque converter output to any one of the first to fourth speeds. As shown in FIG. 3, the relationship between the vehicle speed and the travel driving force at each speed stage is that when the vehicle speed is slow, the travel drive force is large (low speed high torque), and when the vehicle speed is fast, the travel drive force is small. (High speed, low torque) Also, the smaller the speed stage, the greater the driving force that can be obtained at the same vehicle speed.

  FIG. 4 is a diagram illustrating a schematic configuration of the transmission 17. The transmission 17 includes a plurality of clutch shafts SH1 to SH3, an output shaft SH4, a transmission shaft SH5, a plurality of gears G1 to G13, a forward hydraulic clutch (forward clutch) 24, and a reverse hydraulic clutch (reverse). Clutch) 25 and hydraulic clutches (transmission clutches) C1 to C4 for the first to fourth speeds. The forward clutch 24, the reverse clutch 25, and the transmission clutches C1 to C4 are engaged or disengaged by pressure oil (clutch pressure) supplied via the transmission control device 26. That is, when the clutch pressure supplied to the forward clutch 24, the reverse clutch 25, and the transmission clutches C1 to C4 increases, the forward clutch 24, the reverse clutch 25, and the transmission clutches C1 to C4 are engaged and released when the clutch pressure decreases. The operation is performed.

  The output shaft 16 of the torque converter 14 is connected to the clutch shaft SH1, and both end portions of the output shaft SH4 are connected to the axle device 19 disposed at the front and rear of the vehicle via the propeller shaft 18 (FIG. 2). FIG. 4).

  In FIG. 4, the forward clutch 24 and the first speed clutch C1 are engaged, and the reverse clutch 25 and the second to fourth speed clutches C2 to C4 are in a released state. In this case, the gear G1 and the clutch shaft SH1 rotate together, and the gear G6 and the clutch shaft SH2 rotate together.

  At this time, the output torque of the engine 13 is such that the input shaft 15 and output shaft 16 of the torque converter 14, the clutch shaft SH1, the forward clutch 24, the gear G1, the gear G3, the transmission shaft SH5, the gear G5, as indicated by the thick line in FIG. It is transmitted to the output shaft SH4 through the gear G6, the first speed clutch C1, the clutch shaft SH2, the gear G8, and the gear G12. As a result, the first speed traveling is possible.

  When shifting from the first speed to the second speed, the first speed clutch C1 is released and the second speed clutch C2 is engaged by the clutch pressure supplied via the transmission control device 26. Thereby, the output torque of the engine 13 is the input shaft 15 of the torque converter 14, the output shaft 16, the clutch shaft SH1, the forward clutch 24, the gear G1, the gear G3, the gear G7, the second speed clutch C2, the clutch shaft SH2, the gear G8, It is transmitted to the output shaft SH4 via the gear G12, and second speed traveling is possible. Similarly, shifting from the 1st speed to the 2nd speed, that is, shifting from the 2nd speed to the 3rd speed, the 3rd speed to the 4th speed, the 4th speed to the 3rd speed, the 3rd speed to the 2nd speed, and the 2nd speed to the 1st speed is performed similarly. This is done by controlling C4 to the engaged state and the released state.

  Here, there are two types of automatic shift control: torque converter speed ratio reference control that shifts when the torque converter speed ratio e reaches a predetermined value, and vehicle speed reference control that shifts when the vehicle speed reaches a predetermined value. In the present embodiment, the speed stage of the transmission 17 is controlled by torque converter speed ratio reference control.

  FIG. 5 is a diagram showing the relationship between the torque converter speed ratio e and the speed stage. When the travel load decreases, the torque converter speed ratio e increases, and the torque converter speed ratio e becomes equal to or greater than the predetermined value eu, the speed stage is shifted up by one stage. As a result, the torque converter speed ratio e becomes e1 (ed <e1 <eu). On the contrary, when the traveling load increases, the torque converter speed ratio e decreases and the torque converter speed ratio e becomes equal to or less than the predetermined value ed, the speed stage is shifted down by one stage. Thereby, the torque converter speed ratio e becomes e2 (ed <e2 <eu). The predetermined values eu and ed are set in advance in the controller 27 described later. Further, the controller 27 detects the currently set speed stage of the transmission 17 (hereinafter referred to as a set speed stage).

  Reference numeral 27 denotes a controller including an arithmetic processing unit having a CPU, ROM, RAM, and other peripheral circuits. The controller 27 includes determination means for determining whether or not a clutch cutoff condition described later is satisfied. The controller 27 includes a pedal operation amount detector 28A that detects the pedal operation amount (depression amount) s (pedal stroke or pedal angle) of the accelerator pedal 28, and a rotation number that detects the rotation number Ni of the input shaft 15 of the torque converter 14. A detector 29 and a rotational speed detector 30 for detecting the rotational speed Nt of the output shaft 16 of the torque converter 14 are connected. The controller 27 is connected to a vehicle speed detector 31 that detects the rotational speed of the propeller shaft 18, and calculates the vehicle speed v of the wheel loader 1 based on the output value from the vehicle speed detector 31.

  When the pedal operation amount s from the pedal operation amount detector 28A is equal to or greater than a predetermined value s1 (see FIG. 7), the controller 27 determines that the accelerator pedal 28 is depressed, and the pedal operation amount detector 28A When the pedal operation amount s is less than the predetermined value s1, it is determined that the accelerator pedal 28 is not depressed. The predetermined value s1 is also set as a threshold value for increasing the target engine speed Ns from a low idle speed (for example, 1200 rpm) (see FIG. 7), and is stored in advance in the ROM or RAM of the controller 27.

  As shown in FIG. 2, the controller 27 includes a forward / reverse selector switch 32 that commands forward / backward movement of the vehicle, a clutch cutoff selection switch 33 that selects whether or not to perform clutch cutoff described later, and a transmission 17. A shift means switching device 34 for switching whether the shift is performed automatically or manually is connected. Further, the controller 27 includes a shift switch 35 for instructing a maximum speed step between the first gear to the fourth gear at the time of manual shift or automatic shift, and clutches 24 and 25 for forward / reverse movement as will be described later. A clutch cut-off operation mode changeover switch 36 (first mode / second mode) for changing the conditions for cut-off is connected. The controller 27 detects the current operation mode (first mode / second mode) by the clutch cut-off operation mode changeover switch 36.

  The controller 27 includes a pedal operation amount detector 23A that detects an operation amount (pedal stroke or pedal angle) of the brake pedal 23, and a pressure as a braking force detection unit that detects the pressure of hydraulic oil supplied to the brake unit 19A. A sensor 37 is connected. As shown in FIG. 6, when the operation amount of the brake pedal 23 increases, the brake pressure Pb increases, and a braking force acts on the wheel loader 1 according to the pedal operation amount. Therefore, in the present embodiment, the brake pressure Pb is detected as the braking force.

  The controller 27 controls the rotational speed (the number of revolutions) of the engine 13 according to the operation amount of the accelerator pedal 28 detected by the pedal operation amount detector 28A. As shown in FIG. 7, when the operation amount s of the accelerator pedal 28 increases, the target engine rotation speed Ns increases, and the target engine rotation speed Ns when the pedal is fully depressed becomes the rated rotation speed. The controller 27 outputs a control signal corresponding to the target engine rotation speed Ns to an engine control unit (not shown), and controls the actual rotation speed of the engine 13 to be the target engine rotation speed Ns. When the operator wants to increase the vehicle speed or increase the driving force, the operator increases the operation amount s of the accelerator pedal 28 and increases the engine rotation speed.

  The controller 27 is connected to a temperature detector 38 as temperature detecting means for detecting the temperature of the lubricating oil stored in the axle device 19 that rotationally drives the left and right wheels (rear wheel 4). The temperature detector 38 can notify the operator of an axle oil temperature overheat warning when the lubricating oil (axle oil temperature) in the axle device 19 becomes high. Further, the axle oil temperature detected by the temperature detector 38 is also used for clutch cutoff operation determination described later.

  An arm angle detector 39 that detects the position of the arm 7 is connected to the controller 27. As a result, the position of the arm 7 can be detected, and an automatic bucket height adjustment mechanism can be provided, thereby improving the operator's work efficiency. In the second and third embodiments to be described later, the position of the cargo handling device 9 detected by the arm angle detector 39 is also used for the clutch cutoff operation determination.

  When carrying out the work of loading earth and sand on the dump truck with the wheel loader 1, the operator depresses the brake pedal 23 and decelerates the wheel loader 1 while approaching the dump truck, and the accelerator pedal is used to raise the bucket 8. 28 is stepped on so that the rotational speed of the engine 13 is maintained at a high speed. When the clutch cut-off selection switch 33 is selected so as to operate the clutch cut-off, the controller 27 determines that a later-described clutch cut-off condition is satisfied, and the forward clutch 24 and the reverse clutch A control signal (cut-off signal) for setting 25 to a released state (cut-off) is output to the transmission control device 26.

  In the transmission control device 26, when the cut-off signal is received, the clutch cut-off valve 40 (see FIG. 2) provided in the transmission control device 26 decreases the clutch pressure for operating the forward clutch 24 and the reverse clutch 25. . As a result, the forward clutch 24 and the reverse clutch 25 are released, and transmission of traveling driving force (hereinafter simply referred to as driving force) is interrupted. Release of the forward clutch 24 and the reverse clutch 25 is referred to as clutch cutoff.

  When the clutch cutoff selection switch 33 is selected so as not to perform clutch cutoff, the controller 27 does not output a cutoff signal even if the clutch cutoff condition is satisfied. Therefore, when the clutch cutoff selection switch 33 is selected so as not to perform the clutch cutoff, the above-described clutch cutoff is not performed.

  Next, V-shape loading, which is one of the methods by which the wheel loader 1 loads earth and sand on a dump truck, will be described.

  As shown in FIG. 8, in the V shape loading, first, as shown by an arrow A, the wheel loader 1 is moved forward to scoop up soil and the like, and then, as shown by an arrow B, the wheel loader 1 is temporarily retracted. . Then, the wheel loader 1 is moved forward toward the dump truck as indicated by the arrow C, and the scooped earth and sand is loaded on the dump truck, and the wheel loader 1 is moved back to the original position as indicated by the arrow D. .

  Here, when the earth and sand are loaded onto the dump truck (in the state of arrow C in FIG. 8), since a large driving force is not required as in excavation, the operator usually sets the maximum speed stage by the shift switch 35. The speed stage is set to be fixed to the second speed after the speed is changed to manual transmission by the transmission means switching device 34 by the transmission means switching device 34.

  The wheel loader 1 will be described with reference to FIG. 9 when the earth and sand are loaded on the dump truck (in the state of arrow C in FIG. 8). For convenience of explanation, an initial period when the wheel loader 1 approaches the dump truck after accelerating the wheel loader 1 when carrying out the work of loading earth and sand or the like is an initial approach. Further, the middle period from when the wheel loader 1 is decelerated to when it stops is referred to as a mid-approach period. Then, the period from when the wheel loader 1 is stopped until the earth and sand in the bucket 8 is completely discharged to the dump truck is defined as the latter half of the approach.

  As shown in FIG. 9, at the initial stage of the approach, the operator depresses the accelerator pedal 28 to the maximum to accelerate the wheel loader 1 and raise the bucket 8.

  Next, in the middle of the approach, the operator depresses the accelerator pedal 28 as much as possible to raise the bucket 8 and gradually depresses the brake pedal 23 to decelerate the wheel loader 1. In the middle of the approach, the brake pedal 23 may be gradually depressed to decelerate the wheel loader 1 in a state where the lifting of the bucket 8 is completed during traveling and the accelerator pedal 28 is returned. In the late approach, the operator depresses the brake pedal 23 to the maximum in order to stop the wheel loader 1.

  Here, when the clutch cutoff selection switch 33 is selected so as to perform the clutch cutoff, the clutch cutoff condition described later is satisfied when the brake pedal 23 is depressed by an operator in the middle of the approach, etc. Cut-off is performed.

  Next, the clutch cutoff in the middle of the approach will be described.

  When the clutch cut-off condition is satisfied when the operator gradually depresses the brake pedal 23 and decelerates the wheel loader 1 while depressing the accelerator pedal 28 and raising the bucket 8 in the middle of the approach, When the forward clutch 24 and the reverse clutch 25 are released (cut off) when approaching, the transmission of the driving force is cut off, so there is no need to decelerate and stop the wheel loader 1 against the driving force.

  Thereby, compared with the case where the wheel loader 1 is decelerated and stopped against the driving force without clutch cut-off, the load on the brake portion 19A can be reduced, and the temperature rise of the brake portion 19A is suppressed. The consumption of each part of the brake part 19A can be suppressed. Even if the wheel loader 1 is decelerated and stopped while operating the clutch cutoff to maintain the engine 13 at a high speed, the torque converter speed ratio e, which is the speed ratio between the input shaft 15 and the output shaft 16. Is almost 1, and the input torque from the engine 13 to the torque converter 14 is very small. Therefore, the power loss in the torque converter 14 can be reduced, and the fuel consumption can be reduced.

  However, if the clutch cutoff timing is too early, transmission of the driving force is suddenly interrupted by the clutch cutoff before the driving force is sufficiently suppressed by the braking force. May suddenly decrease, and the entire vehicle body of the wheel loader 1 may be pitched. Moreover, when performing the operation | work which loads earth and sand etc., since the position of the bucket 8 is high, it exists in the tendency for pitching to become larger. When pitching occurs, not only the ride comfort is deteriorated, but also earth and sand accumulated in the bucket 8 may be spilled off. Therefore, the operator is driving while paying attention to the operation of the brake portion 19A in order to smoothly decelerate and stop the vehicle.

  Therefore, when an operator who dislikes pitching loads a dump truck with a wheel loader, he selects the clutch cutoff selection switch 33 so as not to perform the clutch cutoff, and the clutch cutoff described above is performed. There are things that are not to be broken. In this case, although there is no possibility of inducing pitching, the wear of each part of the brake part 19A and an increase in power loss in the torque converter 14 are caused.

  In order to prevent pitching that occurs when the timing of the clutch cutoff is too early and to smoothly decelerate and stop the work vehicle, the wheel (by the braking force of the brake portion 19A before the clutch cutoff is activated) It is necessary to sufficiently suppress the driving force transmitted to the front wheels 2 and the rear wheels 4). Here, since the driving force increases as the vehicle speed decreases at the same speed stage, the forward clutch 24 and the reverse clutch 25 are released with a high braking force as the vehicle speed decreases, and the forward clutch 24 and the reverse drive with a low braking force as the vehicle speed increases. It is desirable to release the clutch 25.

  As described above, even when the vehicle speed is low, that is, when the driving force is large, the clutch cut-off can be operated while sufficiently suppressing the driving force with a high braking force, so that the wheel loader 1 is smoothly decelerated. Can be made. If the clutch cut-off timing is too late, the transmission of the driving force is interrupted by the clutch cut-off and a high braking force is applied, so that the wheel loader 1 stops suddenly and pitching as described above. It is necessary to consider the points that may induce

  As described above, in the middle phase of the approach, the operator gradually raises the brake pedal 23 in order to decelerate the wheel loader 1 while the lifting of the bucket 8 is completed while the wheel loader 1 is traveling and the accelerator pedal 28 is returned. You may step in. In a traveling state in which the accelerator pedal 28 is not depressed, the driving force is small, and the vehicle is decelerated by the engine brake.

  Therefore, even if the clutch cutoff is actuated at an early timing, the vehicle can be smoothly stopped without inducing pitching. However, if the braking force after the clutch cut-off is too small, the braking distance becomes unnecessarily long. Therefore, it is desirable to perform the clutch cutoff with a certain braking force. Accordingly, the clutch is cut off after the vehicle is sufficiently decelerated by the braking force of the engine brake and the brake portion 19A, so that the braking distance can be shortened.

  Further, as shown in FIG. 10, when working while climbing a steep slope (for example, an inclination angle of about 25 degrees), a large driving force is generally required. The stage is set to a slow first speed. On such a steep slope, the weight of the wheel loader 1 acts as a traveling load in the direction in which the wheel loader 1 descends (reverse direction). Therefore, if the clutch is cut off under the same conditions as the flat ground, the braking force is sufficient. In such a state, the driving force is cut off by the clutch cutoff, so that the wheel loader 1 starts to descend on the ramp contrary to the previous state. In this case, since the operator further depresses the brake pedal 23 to stop the wheel loader 1, the wheel loader 1 may stop suddenly and induce pitching as described above.

  Therefore, it is desirable to operate the clutch cutoff early in loading work such as earth and sand accompanied by the rise of the bucket 8 on a flat ground, and to operate clutch clutch off late in the work on a steep slope. .

  The above-described clutch cut-off operation mode changeover switch 36 is configured so that the clutch cut-off timing can be manually changed between the first mode and the late second mode by an operator's operation. In other words, the clutch cutoff operation mode changeover switch 36 is a first mode in which the forward clutch 24 and the reverse clutch 25 are released with a low braking force, and a second mode in which the forward clutch 24 and the reverse clutch 25 are released with a high braking force. The clutch cutoff condition can be selected between the two. The first mode in which the clutch cut-off operates early is suitable for loading work such as earth and sand on flat ground. On the other hand, the second mode in which the clutch cut-off operates later is suitable for work on a steep slope (for example, an inclination angle of 25 degrees or more).

  In the wheel loader 1 of the present embodiment, the operation timing of the clutch cutoff is automatically set as described below. Thereby, in this Embodiment, the timing of a clutch cut-off becomes suitable according to various driving | running | working / work situations.

  (1) In a traveling state in which the accelerator pedal 28 is fully depressed to raise the bucket 8 and the brake pedal 23 is gradually depressed to decelerate the wheel loader 1 and approach the dump truck, the higher the vehicle speed, the faster Activate the clutch cutoff.

  (2) In a traveling state where the accelerator pedal 28 is returned and the brake pedal 23 is gradually depressed to decelerate the wheel loader 1 and approach the dump truck, the clutch cutoff is performed at a predetermined timing regardless of the vehicle speed. Operate.

  (3) Compared to the operation timing of clutch cut-off such as work on a flat ground performed with the speed stage of the transmission 17 set to the second speed, the transmission 17 is performed with the speed stage of the transmission 17 set to the first speed. The operation timing of the clutch cut-off for working on a steep ramp is delayed.

  (4) The clutch cut-off operation timings (1) to (3) are early in the state set in the first mode and late in the state set in the second mode.

  (5) The clutch cut-off operation timings (1) to (4) are corrected so as to be delayed when the temperature of the brake portion 19A is high.

  Specifically, the controller 27 determines whether or not the accelerator pedal 28 is depressed, the vehicle speed v, the set speed stage of the transmission 17, the clutch cutoff operation mode (first / second mode), the brake pressure Pb, and the brake portion 19A. Based on the information of the axle oil temperature T as temperature, it is determined whether or not the clutch cutoff condition is satisfied, and when it is determined that the clutch cutoff condition is satisfied, the forward clutch 24 and the reverse clutch 25 are released. Thus, the engagement / release of the forward clutch 24 and the reverse clutch 25 is controlled.

  FIG. 11 and FIG. 12 are diagrams showing clutch cutoff conditions, in which the horizontal axis represents the vehicle speed v and the vertical axis represents the brake pressure Pb. FIG. 11 shows the relationship between the vehicle speed v that activates the clutch cutoff when the speed stage is set to the first speed and the brake pressure Pb. In FIG. 12, when the speed stage is set to the second speed. The relationship between the vehicle speed v for operating the clutch cutoff and the brake pressure Pb is shown.

  FIG. 11 shows characteristics N1 and D1 of a brake pressure cutoff threshold Pt, which is a brake pressure for operating the clutch cutoff when the accelerator pedal 28 is depressed.

  On the other hand, FIG. 12 shows characteristics N2 and D2 of a brake pressure cutoff threshold value Pt that is a brake pressure for operating the clutch cutoff when the accelerator pedal 28 is depressed.

  These characteristics N1, D1, N2, and D2 are stored in the ROM or RAM of the controller 27 in a look-up table format. Further, in FIGS. 11 and 12, a brake pressure cutoff threshold Pt (PbN21, PbD21, PbN22, PbD22), which is a brake pressure for operating the clutch cutoff when the accelerator pedal 28 is not depressed, is indicated by a broken line. ing. These predetermined values PbN21, PbN22, PbD21, PbD22 are stored in the ROM or RAM of the controller 27.

  The characteristics N1 and D1, N2, and D2 of the brake pressure cutoff threshold Pt are such that at least the vehicle speed v can be reduced against the driving force even when the accelerator pedal 28 is fully depressed. The value corresponds to the brake pressure Pb that generates the braking force.

  Here, the characteristic N1 is used when the speed stage is set to the first speed, the operation mode of the clutch cutoff is set to the first mode, and the accelerator pedal 28 is depressed. The characteristic D1 is used when the speed stage is set to the first speed, the clutch cutoff operation mode is set to the second mode, and the accelerator pedal 28 is depressed.

  On the other hand, the characteristic N2 is used when the speed stage is set to the second speed, the operation mode of the clutch cutoff is set to the first mode, and the accelerator pedal 28 is depressed. The characteristic D2 is used when the speed stage is set to the second speed, the operation mode of the clutch cutoff is set to the second mode, and the accelerator pedal 28 is depressed. The vehicle speed corresponding to the intersection of each of the characteristics N1 and D1 and N2 and D2 and the brake pressure cutoff threshold Pt (PbN21, PbD21, PbN22, PbD22) without depression of the accelerator pedal 28 is set as the reference vehicle speed. The vehicle speed that is lower than the reference vehicle speed is the vehicle speed on the low speed side and the vehicle speed that is higher than the reference vehicle speed is the vehicle speed on the high speed side.

  When the brake pressure cut-off threshold value Pt is set based on the characteristic N1, the range (va) where the vehicle speed v is not less than the low speed side vehicle speed threshold value va (for example, 2 km / h) and not more than the high speed side vehicle speed threshold value vb (for example, 5 km / h). ≤ v ≤ vb), the brake pressure cutoff threshold Pt decreases linearly as the vehicle speed v increases. When the vehicle speed v is smaller than the low speed side vehicle speed threshold va, the brake pressure cutoff threshold Pt is Pn1H, and when the vehicle speed v is greater than the high speed side vehicle speed threshold vb, the brake pressure cutoff threshold Pt is Pn1L (see FIG. 11).

  Similarly, when the brake pressure cut-off threshold value Pt is set based on the characteristic D1, the vehicle speed v increases in a range (va ≦ v ≦ vb) where the vehicle speed v is not less than the low speed side vehicle speed threshold value va and not more than the high speed side vehicle speed threshold value vb. Accordingly, the brake pressure cutoff threshold Pt decreases linearly. When the vehicle speed v is smaller than the low speed side vehicle speed threshold va, the brake pressure cutoff threshold Pt is Pd1H, and when the vehicle speed v is greater than the high speed side vehicle speed threshold vb, the brake pressure cutoff threshold Pt is Pd1L (see FIG. 11).

  When the brake pressure cut-off threshold value Pt is set based on the characteristic N2, when the vehicle speed v is in the range (va ≦ v ≦ vb) between the low speed side vehicle speed threshold value va and the high speed side vehicle speed threshold value vb, braking is performed as the vehicle speed v increases. The pressure cutoff threshold Pt decreases linearly. When the vehicle speed v is smaller than the low speed side vehicle speed threshold va, the brake pressure cutoff threshold Pt is Pn2H, and when the vehicle speed v is greater than the high speed side vehicle speed threshold vb, the brake pressure cutoff threshold Pt is Pn2L (see FIG. 12).

  Similarly, when the brake pressure cut-off threshold value Pt is set based on the characteristic D2, the vehicle speed v increases in a range (va ≦ v ≦ vb) where the vehicle speed v is not less than the low speed side vehicle speed threshold value va and not more than the high speed side vehicle speed threshold value vb. Accordingly, the brake pressure cutoff threshold Pt decreases linearly. When the vehicle speed v is smaller than the low speed side vehicle speed threshold va, the brake pressure cutoff threshold Pt is Pd2H, and when the vehicle speed v is higher than the high speed side vehicle speed threshold vb, the brake pressure cutoff threshold Pt is Pd2L (see FIG. 12).

  That is, when the accelerator pedal 28 is depressed, the forward clutch 24 and the reverse clutch 25 are released with a higher braking force as the vehicle speed v is lower, and the forward clutch 24 and the reverse clutch 25 are released with a lower braking force as the vehicle speed v is higher. The clutch cut-off conditions are determined so that

  With such control, for example, when the accelerator pedal 28 is fully depressed to raise the bucket 8 in the middle of the approach and the brake pedal 23 is gradually depressed to decelerate the wheel loader 1, the vehicle speed v As the vehicle speed v is higher, the clutch cutoff can be operated at an earlier timing as the vehicle speed v is higher.

  When the speed stage is set to the second speed, the driving force is smaller than when the speed stage is set to the first speed, so that the wheel loader 1 can be decelerated or completely stopped. The required braking force may be small. Therefore, in the present embodiment, in the state where the speed stage is set to the first speed, the brake pressure cut-off threshold value Pt is set larger than the state where the speed stage is set to the second speed (Pn1H> Pn2H, Pn1L> Pn2L, Pd1H> Pd2H, Pd1L> Pd2L). That is, the clutch cutoff condition is set so that the forward clutch 24 and the reverse clutch 25 are released with a lower braking force when the speed stage is the second speed than when the speed stage is the first speed.

  The brake pressure Pn1L is smaller than Pd1L (Pn1L <Pd1L), and the brake pressure Pn1H is smaller than Pd1H (Pn1H <Pd1H). The brake pressure Pn2L is smaller than Pd2L (Pn2L <Pd2L), and the brake pressure Pn2H is smaller than Pd2H (Pn2H <Pd2H). In other words, the clutch cutoff condition is set so that the forward clutch 24 and the reverse clutch 25 are released with a low braking force in the first mode, and the forward clutch 24 and the reverse clutch 25 are released with a high braking force in the second mode. Has been.

  FIG. 11 shows a brake pressure that activates the clutch cutoff when the speed stage is set to the first speed, the operation mode of the clutch cutoff is set to the first mode, and the accelerator pedal 28 is not depressed. The brake pressure cut-off threshold value Pt = PbN21 is shown by a broken line. Similarly, this is a brake pressure that activates the clutch cutoff when the speed stage is set to the first speed, the operation mode of the clutch cutoff is set to the second mode, and the accelerator pedal 28 is not depressed. The brake pressure cutoff threshold Pt = PbD21 is indicated by a broken line.

  FIG. 12 shows a brake pressure that activates the clutch cutoff when the speed stage is set to the second speed, the clutch cutoff operation mode is set to the first mode, and the accelerator pedal 28 is not depressed. The brake pressure cut-off threshold value Pt = PbN22 is shown by a broken line. Similarly, it is a brake pressure that activates the clutch cutoff when the speed stage is set to the second speed, the operation mode of the clutch cutoff is set to the second mode, and the accelerator pedal 28 is not depressed. The brake pressure cutoff threshold Pt = PbD22 is indicated by a broken line. That is, when the accelerator pedal 28 is not depressed, the clutch cutoff condition is set so that the forward clutch 24 and the reverse clutch 25 are released with a predetermined braking force regardless of the vehicle speed v.

  In the state where the speed stage is set to the first speed, the brake pressure cutoff threshold Pt is larger than the state where the speed stage is set to the second speed (PbN21> PbN22, PbD21> PbD22). That is, the clutch cutoff condition is set so that the forward clutch 24 and the reverse clutch 25 are released with a lower braking force in the case of the second speed than in the case of the first speed.

  The brake pressure PbN21 is smaller than PbD21 (PbN21 <PbD21), and the brake pressure PbN22 is smaller than PbD22 (PbN22 <PbD22). In other words, the clutch cutoff condition is such that the forward clutch 24 and the reverse clutch 25 are released with a low braking force in the first mode, and the forward clutch 24 and the reverse clutch 25 are released with a high braking force in the second mode. Is set.

  The brake pressure PbN21 is smaller than Pn1H and larger than Pn1L (Pn1L <PbN21 <Pn1H). The brake pressure PbD21 is smaller than Pd1H and larger than Pd1L (Pd1L <PbD21 <Pd1H). The brake pressure PbN22 is smaller than Pn2H and larger than Pn2L (Pn2L <PbN22 <Pn2H). The brake pressure PbD22 is smaller than Pd2H and larger than Pd2L (Pd2L <PbD22 <Pd2H).

  In other words, on the low speed side, the clutch cut is performed so that the forward clutch 24 and the reverse clutch 25 are released with a lower braking force when the accelerator pedal 28 is not depressed than when the accelerator pedal 28 is depressed. An off condition is set. On the other hand, on the high speed side, the clutch cutoff condition is such that the forward clutch 24 and the reverse clutch 25 are released with a higher braking force when the accelerator pedal 28 is not depressed than when the accelerator pedal 28 is depressed. Is set.

  With such a condition setting, for example, when the accelerator pedal 28 is returned in a state where the wheel loader 1 is traveling at a low speed in the middle of the approach, and the brake pedal 23 is gradually depressed to decelerate the wheel loader 1, The clutch cutoff can be actuated at an earlier timing than when the accelerator pedal 28 is depressed. On the other hand, in a state where the wheel loader 1 is traveling at a high speed, the clutch cutoff can be operated at a later timing than when the accelerator pedal 28 is depressed.

  When the controller 27 determines that the clutch cutoff condition is satisfied based on the various information input and the characteristics N1 and D1 and N2 and D2 or the predetermined values PbN21, PbN22, PbD21, and PbD22, the cutoff is performed. The signal is output to the transmission control device 26.

  Next, the relationship between the axle oil temperature and the brake disc will be described.

  FIG. 13 is a diagram showing the axle oil temperature and the friction coefficient of the brake disc (friction material). Since the brake part 19A is immersed in the lubricating oil (axle oil) stored in the axle device 19, the temperature of the brake part 19A and the axle oil temperature are substantially equivalent (those having a correlation). It becomes. Therefore, in the present embodiment, the axle oil temperature is approximately used as the temperature of the brake disk of the brake portion 19A. Here, since the friction coefficient of the brake disk decreases as the temperature increases, correction is performed to increase the brake pressure cutoff threshold value Pt in FIGS. 11 and 12 as the axle oil temperature increases. Specifically, when the axle oil temperature becomes equal to or higher than a predetermined value (Ts ° C.), the brake pressure cutoff threshold Pt is corrected to Pt1, and the clutch cutoff condition is satisfied based on the corrected brake pressure cutoff threshold Pt1. It is determined whether or not. The correction value Pt1 is larger than Pt (Pt1> Pt).

  Hereinafter, the clutch cutoff control will be described with reference to the flowcharts of FIGS.

  14 to 17 are flowcharts showing the operation of the clutch control process in the wheel loader 1 of the present embodiment. When an ignition switch (not shown) of the wheel loader 1 is turned on, a program for performing the processing shown in FIGS. 14 to 17 is started and repeatedly executed by the controller 27.

  In step 1, information on the brake pressure Pb detected by the pressure sensor 37, information on the pedal operation amount s detected by the pedal operation amount detector 28A, information on the vehicle speed v detected by the vehicle speed detector 31, and information on the controller 27 Information on the detected speed stage of the transmission 17 detected, information on the current clutch cutoff operation mode (first / second mode), information on the axle oil temperature T detected by the temperature detector 38, Go to step 2.

  In step 2, it is determined whether or not the vehicle speed detector 31 is normal. For example, the controller 27 determines that there is an abnormality when the output value from the vehicle speed detector 31 hardly changes even if the set speed stage or the engine speed changes. If an affirmative determination is made in step 2, that is, if the vehicle speed detector 31 is determined to be normal, the process proceeds to step 3. If a negative determination is made in step 2, the process proceeds to step 9, the brake pressure cutoff threshold Pt is set to a predetermined value Pa previously stored in the ROM or RAM of the controller 27, and the process proceeds to step 13.

  In step 13, it is determined whether or not the brake pressure Pb acquired in step 1 is equal to or greater than a set brake pressure cutoff threshold Pt. If an affirmative determination is made in step 13, the routine proceeds to step 14, where a clutch cut-off signal is output to the transmission control device 26 and the routine returns. If a negative determination is made in step 13, the process returns without outputting a clutch cut-off signal to the transmission control device 26.

  The brake pressure cutoff threshold Pt = Pa set when the vehicle speed detector 31 is determined to be abnormal is, for example, the brake pressure PbN21 when the speed stage is set to the first speed and the operation mode is set to the first mode, When the speed stage is 2nd and the operation mode is set to the first mode, the brake pressure is set to PbN22. When the speed stage is 1st and the operation mode is set to the second mode, the brake pressure PbD21 is set. When the speed stage is 2nd and the operation mode is set to the second mode, the brake pressure PbD22 is set. To do.

  That is, if it is determined in step 2 that the vehicle speed detector 31 is abnormal, the clutch cutoff is operated with a predetermined braking force regardless of whether or not the accelerator pedal 28 is depressed and the vehicle speed v. Thereby, it is possible to prevent the clutch cutoff timing from being set based on an abnormal output value from the vehicle speed detector 31.

  In step 3, it is determined whether or not the clutch cut-off selection switch 33 is selected so that the clutch is cut off. If an affirmative determination is made in step 3, that is, if it is determined that the clutch cutoff selection switch 33 is selected so as to perform clutch cutoff, the routine proceeds to step 4 where the clutch cutoff operation mode changeover switch 36 is set to the first. It is determined whether or not the mode is set. If an affirmative determination is made in step 4, that is, if it is determined that the clutch cut-off operation mode changeover switch 36 is set to the first mode, the process proceeds to step 5 to check whether the set speed stage of the transmission 17 is the first speed. Determine whether or not.

  If an affirmative determination is made in step 5, that is, if it is determined that the set speed stage of the transmission 17 is the first speed, the process proceeds to step 6 to determine whether or not the accelerator pedal 28 is depressed. If an affirmative determination is made in step 6, that is, if it is determined that the accelerator pedal 28 is depressed, the process proceeds to step 8, and the vehicle speed v acquired in step 1 is referred to with reference to the table (FIG. 11) storing the characteristic N1. Is set based on the brake pressure cutoff threshold Pt (Pn1L ≦ Pt ≦ Pn1H). If a negative determination is made in step 6, that is, if it is determined that the accelerator pedal 28 is not depressed, the process proceeds to step 7 where the brake pressure cutoff threshold Pt is set to PbN21 (Pt = PbN21). When the brake pressure cut-off threshold value Pt is set in step 7 or step 8, the process proceeds to step 10.

  If a negative determination is made in step 4, the process proceeds to step 15 shown in FIG. 15 to determine whether or not the set speed stage of the transmission 17 is the first speed. If an affirmative determination is made in step 15, that is, if it is determined that the set speed stage of the transmission 17 is the first speed, the process proceeds to step 16 to determine whether or not the accelerator pedal 28 is depressed.

  If the determination in step 16 is affirmative, that is, if it is determined that the accelerator pedal 28 is depressed, the process proceeds to step 18 where the vehicle speed v acquired in step 1 is referred to with reference to the table storing the characteristic D1 (FIG. 11). Is set to the brake pressure cutoff threshold Pt (Pd1L ≦ Pt ≦ Pd1H). If a negative determination is made in step 16, that is, if it is determined that the accelerator pedal 28 is not depressed, the process proceeds to step 17, and the brake pressure cutoff threshold Pt is set to PbD21 (Pt = PbD21). When the brake pressure cut-off threshold value Pt is set in step 17 or step 18, the process proceeds to step 10 shown in FIG.

  If a negative determination is made in step 5, the process proceeds to step 19 shown in FIG. 16 to determine whether or not the set speed stage of the transmission 17 is the second speed. If an affirmative determination is made in step 19, that is, if it is determined that the set speed stage of the transmission 17 is the second speed, the process proceeds to step 20 to determine whether or not the accelerator pedal 28 is depressed.

  If the determination in step 20 is affirmative, that is, if it is determined that the accelerator pedal 28 is depressed, the process proceeds to step 22 where the vehicle speed v acquired in step 1 is referred to with reference to the table storing the characteristic N2 (FIG. 12). Is set to a brake pressure cutoff threshold Pt (Pn2L ≦ Pt ≦ Pn2H). If a negative determination is made in step 20, that is, if it is determined that the accelerator pedal 28 is not depressed, the process proceeds to step 21, and the brake pressure cutoff threshold Pt is set to PbN22 (Pt = PbN22). When the brake pressure cut-off threshold value Pt is set in step 21 or step 22, the process proceeds to step 10 shown in FIG.

  If a negative determination is made in step 15 shown in FIG. 15, the process proceeds to step 23 shown in FIG. 17, and it is determined whether or not the set speed stage of the transmission 17 is the second speed. If an affirmative determination is made in step 23, that is, if it is determined that the set speed stage of the transmission 17 is the second speed, the routine proceeds to step 24, where it is determined whether or not the accelerator pedal 28 is depressed.

  If an affirmative determination is made in step 24, that is, if it is determined that the accelerator pedal 28 is depressed, the process proceeds to step 26, and the vehicle speed v acquired in step 1 is referenced with reference to the table (FIG. 12) storing the characteristic D 2. Is set to the brake pressure cutoff threshold Pt (Pd2L ≦ Pt ≦ Pd2H). If a negative determination is made in step 24, that is, if it is determined that the accelerator pedal 28 is not depressed, the process proceeds to step 25, where the brake pressure cutoff threshold Pt is set to PbD22 (Pt = PbD22). When the brake pressure cut-off threshold value Pt is set in step 25 or step 26, the process proceeds to step 10 shown in FIG.

  In step 10, it is determined whether the axle oil temperature T acquired in step 1 is less than Ts ° C. Here, Ts ° C., which is the threshold value for the axle oil temperature, can be set to a temperature at which the friction coefficient fluctuation (braking force fluctuation) becomes significant, for example, 60 to 80 ° C. (preferably 70 ° C.). If an affirmative determination is made in step 10, that is, if the axle oil temperature T is determined to be less than Ts ° C., the brake pressure cutoff threshold Pt is not corrected, and the brake pressure cutoff threshold Pt when proceeding to step 10 is corrected. Is set as the brake pressure cutoff threshold value Pt as it is, and the routine proceeds to step 13.

  In step 13, it is determined whether or not the brake pressure Pb acquired in step 1 is equal to or greater than a set brake pressure cutoff threshold Pt. If an affirmative determination is made in step 13, the routine proceeds to step 14, where a clutch cut-off signal is output to the transmission control device 26 and the routine returns.

  If a negative determination is made in step 10, that is, if the axle oil temperature T is determined to be equal to or higher than Ts ° C., the process proceeds to step 11 and the brake pressure cutoff threshold Pt when the process proceeds to step 10 is corrected to Pt1. In this case, the brake pressure cut-off threshold value Pt is set so that the forward clutch 24 and the reverse clutch 25 are released at a higher brake pressure Pb as the axle oil temperature T is higher. That is, the correction value Pt1 is larger than Pt (Pt1> Pt). Specifically, Pt1 is set to a value of, for example, 1.03 to 1.1 times Pt (Pt1 = 1.03Pt to 1.1Pt). Preferably, it can be set to 1.05 times Pt (Pt1 = 1.05Pt), more preferably 1.04 times (Pt1 = 1.04Pt).

  When the brake pressure cut-off threshold is set (corrected) to Pt1 in this way, the process proceeds to step 12 to determine whether or not the brake pressure Pb acquired in step 1 is equal to or greater than the brake pressure cut-off threshold Pt1. If an affirmative determination is made in step 12, the routine proceeds to step 14, where a clutch cut-off signal is output to the transmission control device 26, and the routine returns.

  Note that the flowchart of FIG. 14 illustrates a case where the threshold value Ts ° C. of the axle oil temperature for determining whether or not to correct the brake pressure cutoff threshold value Pt is one. However, the present invention is not limited to this, and a configuration may be adopted in which a plurality of threshold values for the axle oil temperature are set and correction is performed so that the brake pressure cutoff threshold increases as the axle oil temperature increases for each threshold value.

  If a negative determination is made in step 3, step 12, step 13, step 19, or step 23, the routine returns without outputting a clutch cutoff signal to the transmission control device 26.

According to this Embodiment described above, there can exist the following effects.
(1) The controller 27 sets the brake pressure cut-off threshold value Pt for operating the clutch cut-off based on whether or not the accelerator pedal 28 is depressed. Therefore, the forward clutch 24 and the reverse clutch 25 can be released at appropriate timings in a state where the accelerator pedal 28 is depressed and a state where the accelerator pedal 28 is returned.

  (2) When the accelerator pedal 28 is depressed, the controller 27 sets the brake pressure cut-off threshold value Pt to be lower as the vehicle speed v is higher, and the brake pressure cut-off threshold value Pt is set to be higher as the vehicle speed v is lower (FIG. 11). Characteristics N1, D1 and characteristics N2, D2 in FIG. 12). As a result, in the working state such as approaching the dump truck while gradually depressing the brake pedal 23 while depressing the brake pedal 23 while depressing the accelerator pedal 28 to raise the bucket 8 to the maximum, it corresponds to the magnitude of the driving force. The driving force transmitted to the wheels (front wheel 2, rear wheel 4) immediately before the operation of the clutch cutoff can be sufficiently suppressed by the braking force. As a result, the wheel loader 1 can be smoothly decelerated and stopped without inducing pitching resulting from the clutch cutoff operating with a large driving force remaining.

  (3) On the low speed side, the controller 27 sets the brake pressure cutoff threshold value Pt for operating the clutch cutoff lower when the accelerator pedal 28 is not depressed than when the accelerator pedal 28 is depressed. I made it. When the accelerator pedal 28 is not depressed, that is, when the driving force is small and the vehicle is decelerated by the engine brake, the vehicle is smoothed without inducing pitching even if the clutch cutoff is operated with a low braking force. Can be stopped.

  On the other hand, as described in the above (2), in the low-speed traveling state where the accelerator pedal 28 is depressed, that is, the traveling state where the driving force is large, the wheels (front wheels 2, 2) before the clutch is cut off with a high braking force. The wheel loader 1 can be decelerated so as to sufficiently suppress the driving force transmitted to the rear wheels 4). As a result, the wheel loader 1 can be smoothly decelerated and stopped without inducing pitching resulting from the clutch cutoff operating with a large driving force remaining.

  (4) The controller 27 sets the brake pressure cutoff threshold Pt lower in the case of the second speed than in the case of the first speed (see FIGS. 11 and 12). As a result, for example, when the wheel loader 1 is performing work on a steep slope requiring a large driving force at the first speed, and loading work such as earth and sand accompanied by the rising of the bucket 8 on a flat ground is performed at the second speed. The forward clutch 24 and the reverse clutch 25 can be released at a timing appropriate for each of the cases.

  (5) When the first mode is selected by the clutch cut-off operation mode changeover switch 36, the controller 27 releases the forward clutch 24 and the reverse clutch 25 with a low braking force, and the clutch cut-off operation mode changeover switch 36 sets the first mode. When the two mode is selected, the brake pressure cutoff threshold Pt is set so that the forward clutch 24 and the reverse clutch 25 are released with a high braking force. Thereby, the timing at which the operator releases the forward clutch 24 and the reverse clutch 25 can be changed according to various traveling / working conditions such as a difference in the inclination angle of the traveling path, a load amount of the bucket 8 and a difference in work contents. Therefore, the work efficiency can be improved.

  (6) The controller 27 can release the forward clutch 24 and the reverse clutch 25 at a higher brake pressure cutoff threshold Pt1 as the axle oil temperature T as the temperature of the brake portion 19A is higher. Accordingly, the forward clutch 24 and the reverse clutch 25 can be released at an appropriate timing according to the temperature of the axle oil temperature T.

  (7) As described in (1) to (6) above, the controller 27 determines whether or not the accelerator pedal 28 is depressed, the vehicle speed v, the braking force (brake pressure Pb), the set speed stage of the transmission 17, and the clutch cutoff operation mode. Based on the information of (the first mode or the second mode), the brake pressure cutoff threshold Pt is set. Then, based on the axle oil temperature T as the temperature of the brake portion 19A, the brake pressure cutoff threshold Pt for operating the clutch cutoff is corrected. Therefore, the forward clutch 24 and the reverse clutch are operated at appropriate timings according to the axle oil temperature T together with various traveling / working conditions such as earth and sand loading work on the flat ground of the wheel loader 1 and work on the ramp. 25 can be released. Thereby, the pitching resulting from the operation of the clutch cutoff can be suppressed, and the wheel loader 1 can be smoothly decelerated and stopped.

  On the other hand, in a wheel loader equipped with a clutch control device that allows the operator to arbitrarily adjust the brake pressure cutoff threshold Pt in a stepless manner or in multiple steps, the operator needs to adjust frequently according to the traveling / working situation. This makes the operator feel bothersome. Furthermore, it is difficult to determine which one is optimal in accordance with the situation, and it is necessary to have a skilled skill to manually set the optimum brake pressure cutoff threshold Pt while driving.

  (8) When the controller 27 determines that the vehicle speed detector 31 is abnormal, the brake pressure cut-off threshold value Pt is set to a predetermined value regardless of whether the accelerator pedal 28 is depressed and the vehicle speed v of the wheel loader 1. Set to Pa. Thereby, it is possible to prevent the brake pressure cutoff threshold Pt from being set based on an abnormal output value from the vehicle speed detector 31.

  Thus, according to this embodiment, the braking force (brake pressure Pb) of the wheel loader 1, the pedal operation amount s, the vehicle speed v, the speed stage (1st to 4th speed), and the operation mode (first / first). In addition to (2 mode), the temperature (≈ axle oil temperature T) of the braking device (brake portion 19A) is configured as the clutch cutoff operation determination condition. In the brake unit 19 </ b> A, the braking force that is actually applied to the wheel loader 1 changes as the friction coefficient changes depending on the temperature of the brake disk. Therefore, the forward clutch 24 and the reverse clutch 25 are released at an appropriate timing according to the temperature of the brake portion 19A by configuring the temperature of the brake portion 19A (axle oil temperature T) as a clutch cut-off operation determination condition. be able to. Thereby, irrespective of the temperature of the brake part 19A (high or low), the timing at which the clutch cutoff is activated can be made equal, and the wheel loader 1 can be smoothly decelerated and stopped.

  Further, as temperature detection means of the brake portion 19A, the temperature (axle oil temperature) T of the lubricating oil stored in the axle device 19 that rotationally drives the left and right wheels (rear wheels 4) of the wheel loader 1 is detected. It was configured as follows. The axle oil temperature changes according to a change in the temperature of the brake part 19A in the axle device 19. Also, a sensor that detects the temperature of the lubricating oil is often originally attached to determine overheating of the axle oil temperature. Therefore, it is not necessary to newly install a dedicated temperature detector as the temperature detecting means of the brake part 19A, and it is possible to suppress an increase in failure risk accompanying an increase in the number of parts, and to suppress an increase in cost.

  In the present embodiment, the processing of Step 10, Step 11, Step 12, and Step 13 shown in FIG. 14 shows a specific example of determination means that is a constituent element of Claim 1 of the present invention.

  In the present embodiment, the process of step 14 shown in FIG. 14 shows a specific example of the clutch control means that is a constituent of the present invention.

  Next, FIG. 18 and FIG. 19 show a second embodiment of the present invention. The features of the present embodiment are the presence / absence of depression of the accelerator pedal 28, the vehicle speed v, the set speed stage of the transmission 17, the clutch cutoff operation mode (first / second mode), the brake pressure Pb, the arm angle detector 39. It is determined whether or not the clutch cutoff condition is satisfied based on information on the position (arm angle H) of the cargo handling device 9 by the forward clutch 24 and the clutch when the clutch cutoff condition is determined to be satisfied. The purpose is to control the engagement / release of the forward clutch 24 and the reverse clutch 25 so as to release the reverse clutch 25. In the present embodiment, the same reference numerals as those in the first embodiment described above are attached, and the description thereof will be focused on portions that are different from the first embodiment.

  FIG. 18 is a diagram showing the relationship between the position of the cargo handling device 9 (height position of the bucket 8) and the pitching of the vehicle body (wheel loader 1). Since the position of the center of gravity of the wheel loader 1 increases as the position of the cargo handling device 9 increases, that is, as the height of the bucket 8 increases, it becomes easier to induce pitching during braking / stopping. From this, the higher the position of the cargo handling device 9, more specifically, the larger the arm angle H (see FIG. 1) corresponding to the location of the cargo handling device 9, the greater the position based on the characteristic lines of FIGS. 11 and 12. The set brake pressure cutoff threshold Pt is corrected to Pt2 that is a low value. That is, the higher the position of the cargo handling device 9 (the larger the arm angle H), the earlier the clutch cut-off timing, so that the pitching due to the late clutch cut-off timing can be suppressed.

  The controller 51 (see FIG. 2) is connected to an arm angle detector 39 as a cargo handling device position detecting means for detecting the angle H of the arm 7. The controller 51 includes an automatic height adjustment mechanism that automatically adjusts the height of the bucket 8 based on the angle H of the arm 7 detected by the arm angle detector 39 (the height position of the bucket 8 having a correlation with the arm 7). I have. As a result, the operator's work efficiency is improved. Further, the controller 51 corrects the brake pressure cutoff threshold Pt to Pt2 based on the angle H of the arm 7 detected by the arm angle detector 39, and the clutch cutoff based on the corrected brake pressure cutoff threshold Pt2. It is configured to determine whether or not the condition is satisfied. In this case, the correction value Pt2 is a value smaller than Pt (Pt2 <Pt).

  FIGS. 19 and 15 to 17 are flowcharts illustrating the operation of the clutch control process according to the second embodiment. In step 31, information on the brake pressure Pb detected by the pressure sensor 37, information on the pedal operation amount s detected by the pedal operation amount detector 28A, information on the vehicle speed v detected by the vehicle speed detector 31, and by the controller 51 Information on the detected speed setting of the transmission 17, information on the current clutch cutoff operation mode (first / second mode), and information on the angle H of the arm 7 detected by the arm angle detector 39 are acquired. Then, the process proceeds to step 32.

  Steps 32 to 39 are the same as steps 2 to 9 in FIG. 14 of the first embodiment. Steps after a negative determination in step 34 are the same as steps 15 to 18 in FIG. 15 and steps 23 to 26 in FIG. 17 of the first embodiment. The steps after the negative determination in step 35 is the same as steps 19 to 22 in FIG. 16 of the first embodiment. Therefore, description of these steps is omitted, and processing after step 40 after the brake pressure cutoff threshold Pt is (temporarily) set will be described.

  In step 40, it is determined whether or not the arm angle H acquired in step 31 is less than Ht degrees. Here, the Ht degree serving as the arm angle threshold can be set to an angle at which pitching becomes remarkable, for example, 20 to 30 degrees (preferably 30 degrees). If an affirmative determination is made in step 40, that is, if the arm angle H is determined to be less than Ht degrees, the brake pressure cutoff threshold Pt is not corrected, and the brake pressure cutoff threshold Pt when proceeding to step 40 is set. The brake pressure cutoff threshold value Pt is set as it is, and the routine proceeds to step 43.

  In step 43, it is determined whether or not the brake pressure Pb acquired in step 31 is greater than or equal to the set brake pressure cutoff threshold Pt. When an affirmative determination is made at step 43, the routine proceeds to step 44, where a clutch cut-off signal is output to the transmission control device 26 and the routine returns.

  If a negative determination is made in step 40, that is, if the arm angle H is determined to be equal to or greater than Ht degrees, the process proceeds to step 41, and the brake pressure cutoff threshold Pt when the process proceeds to step 40 is corrected to Pt2. In this case, Pt is set so that the forward clutch 24 and the reverse clutch 25 are released at a lower brake pressure Pb as the arm angle H is larger. That is, the correction value Pt2 is smaller than Pt (Pt2 <Pt). Specifically, Pt2 is set to a value of, for example, 0.90 times to 0.97 times Pt (Pt2 = 0.90 Pt to 0.97 Pt). Preferably, it can be set to 0.95 times Pt (Pt2 = 0.95Pt), more preferably 0.96 times (Pt2 = 0.96Pt).

  When the brake pressure cutoff threshold is set (corrected) to Pt2 in this way, the process proceeds to step 42, and it is determined whether or not the brake pressure Pb acquired in step 31 is equal to or higher than the brake pressure cutoff threshold Pt2. When an affirmative determination is made at step 42, the routine proceeds to step 44, where a clutch cut-off signal is output to the transmission control device 26 and the routine returns. On the other hand, if a negative determination is made in step 42, the clutch cut-off signal is not output to the transmission control device 26, and the process returns.

  Note that the flowchart in FIG. 19 illustrates a case where the arm angle threshold value Ht for determining whether or not to correct the brake pressure cutoff threshold value Pt is one. However, the present invention is not limited to this, and a configuration may be adopted in which a plurality of arm angle threshold values are set and correction is performed so that the brake pressure cutoff threshold value Pt decreases as the arm angle increases for each threshold value.

  According to the second embodiment described above, in addition to the operational effects (1) to (5) and (8) of the first embodiment described above, the following operational effects can be achieved. .

  (9) The controller 51 releases the forward clutch 24 and the reverse clutch 25 at a lower brake pressure cutoff threshold Pt2 as the position of the cargo handling device 9 is higher (the arm angle H is larger), that is, as the position of the bucket 8 is higher. be able to. Therefore, the forward clutch 24 and the reverse clutch 25 can be released at an appropriate timing according to the position (arm angle H) of the cargo handling device 9.

  (10) The controller 51 determines whether or not the accelerator pedal 28 is depressed, the vehicle speed v, the braking force (brake pressure Pb), the set speed stage of the transmission 17, and the clutch cut-off operation mode (first mode or second mode). Based on the above, the brake pressure cutoff threshold Pt is set. And based on the position (arm angle H) of the cargo handling apparatus 9, the brake pressure cutoff threshold Pt which operates a clutch cutoff is correct | amended. Therefore, the wheel loader 1 is loaded with earth and sand on the flat ground and various traveling / working situations such as work on the ramp, and at an appropriate timing according to the position of the cargo handling device 9 (arm angle H) at that time. The forward clutch 24 and the reverse clutch 25 can be released. Thereby, the pitching resulting from the operation of the clutch cutoff can be suppressed, and the wheel loader 1 can be smoothly decelerated and stopped.

  The clutch control device according to the second embodiment performs the clutch cutoff as described above, and there is no particular difference in basic operation from that according to the first embodiment.

  In particular, according to the present embodiment, the brake pressure Pb of the wheel loader 1 and the arm angle H corresponding to the position (operating position, operating position, operating position) of the cargo handling device 9 are configured as the clutch cutoff operation determination condition. doing. The arm angle H corresponding to the position of the cargo handling device 9 changes the position of the center of gravity of the wheel loader 1 according to the angle H. Therefore, by configuring this arm angle H as a clutch cut-off operation determination condition, the arm angle H The clutch can be released at an appropriate timing according to H. Accordingly, regardless of the arm angle H (high or low), it is possible to suppress the pitching when the clutch cut-off is activated, and to smoothly decelerate and stop the wheel loader 1.

  Moreover, according to this Embodiment, it comprised so that the angle H of the arm 7 might be detected as a cargo handling apparatus position detection means. The arm angle detector 39 that detects the angle H of the arm is often attached in order to automatically adjust the height of the bucket 8. Therefore, it is not necessary to newly install a dedicated angle detector as the cargo handling device position detection means, an increase in failure risk accompanying an increase in the number of parts can be suppressed, and an increase in cost can be suppressed.

  In the present embodiment, the processing of step 40, step 41, step 42, and step 43 shown in FIG. 19 is a specific example of the determining means that is a constituent feature of claim 2 of the present invention.

  Further, in the present embodiment, the process of step 44 shown in FIG. 19 shows a specific example of the clutch control means that is a constituent element of the present invention.

  Next, FIG. 20 shows a third embodiment of the present invention. The feature of this embodiment is that the brake pressure cutoff threshold Pt is corrected based on both the axle oil temperature T and the arm angle H. In the present embodiment, the same reference numerals as those in the first embodiment described above are attached, and the description thereof will be focused on portions that are different from the first embodiment.

  The controller 61 (see FIG. 2) includes a temperature detector 38 as temperature detecting means for detecting the temperature of the lubricating oil stored in the axle device 19 that rotationally drives the left and right wheels (rear wheels 4); An arm angle detector 39 as a cargo handling device position detecting means for detecting the position of the arm 7 is connected.

  20 and FIGS. 15 to 17 are flowcharts showing the operation of the clutch control process of the third embodiment. In step 51, information on the brake pressure Pb detected by the pressure sensor 37, information on the pedal operation amount s detected by the pedal operation amount detector 28A, information on the vehicle speed v detected by the vehicle speed detector 31, and by the controller 61 Information on the detected speed stage of the transmission 17, information on the current clutch cutoff operation mode (first / second mode), information on the axle oil temperature T detected by the temperature detector 38, arm angle detector Information on the angle H of the arm 7 detected at 39 is acquired, and the process proceeds to step 52.

  Steps 52 to 59 are the same as steps 2 to 9 in FIG. 14 of the first embodiment. Steps after a negative determination in step 54 are the same as steps 15 to 18 in FIG. 15 and steps 23 to 26 in FIG. 17 of the first embodiment. The steps after the negative determination in step 55 is the same as steps 19 to 22 in FIG. 16 of the first embodiment. Therefore, description of these steps is omitted, and processing after step 60 after the brake pressure cutoff threshold Pt is (temporarily) set will be described.

  In step 60, it is determined whether the axle oil temperature T acquired in step 51 is less than Ts ° C. Here, Ts ° C., which is the threshold value of the axle oil temperature, is the same as the threshold value Ts ° C. of the axle oil temperature according to the first embodiment. If an affirmative determination is made in step 60, that is, if the axle oil temperature T is determined to be lower than T ° C., the process proceeds to step 61.

  In step 61, it is determined whether or not the arm angle H detected by the arm angle detector 39 is less than Ht degrees. Here, the Ht degree serving as the arm angle threshold is the same as the arm angle threshold Ht of the second embodiment. If an affirmative determination is made in step 61, that is, if the arm angle H is determined to be less than Ht degrees, the brake pressure cutoff threshold Pt when proceeding to step 60 is set as the brake pressure cutoff threshold Pt as it is, Proceed to step 66.

  In step 66, it is determined whether or not the brake pressure Pb acquired in step 51 is greater than or equal to the set brake pressure cutoff threshold Pt. If an affirmative determination is made in step 66, the routine proceeds to step 67, where a clutch cut-off signal is output to the transmission control device 26 and the routine returns.

  On the other hand, if a negative determination is made in step 60, that is, if the axle oil temperature T is determined to be equal to or higher than Ts ° C., the process proceeds to step 62, and the brake pressure cutoff threshold Pt when the process proceeds to step 60 is corrected to Pt1. To do. In this case, similarly to the first embodiment, Pt is set so that the forward clutch 24 and the reverse clutch 25 are released at a higher brake pressure Pb as the axle oil temperature T is higher.

  When the brake pressure cutoff threshold is set (corrected) to Pt1 in step 62, the process proceeds to step 64, and it is determined whether or not the brake pressure Pb acquired in step 51 is equal to or higher than the brake pressure cutoff threshold Pt1. When an affirmative determination is made at step 64, the routine proceeds to step 67, where a clutch cut-off signal is output to the transmission control device 26 and the routine returns.

  If a negative determination is made in step 64, that is, if it is determined that the brake pressure Pb acquired in step 51 is less than the brake pressure cut-off threshold value Pt1, the process proceeds to step 68, and Pt1 corrected in step 62 is set as a step. The process returns to the brake pressure cutoff threshold value Pt when proceeding to 60 and proceeds to step 69.

  In step 69, it is determined whether or not the arm angle H acquired in step 51 is less than Ht degrees. If an affirmative determination is made in step 69, that is, if the arm angle H is determined to be less than Ht degrees, the routine returns without outputting a clutch cutoff signal to the transmission control device 26.

  On the other hand, if a negative determination is made in step 69, that is, if the arm angle H is determined to be equal to or greater than Ht degrees, the process proceeds to step 63.

  If a negative determination is made in step 61, that is, if the arm angle H is determined to be equal to or greater than Ht degrees, the process proceeds to step 63.

  In step 63, the brake pressure cutoff threshold Pt when the routine proceeds to step 60 is corrected to Pt2. In this case, as in the second embodiment, Pt is set so that the forward clutch 24 and the reverse clutch 25 are released with a smaller brake pressure Pb as the arm angle H increases.

  If the brake pressure cutoff threshold value is set (corrected) to Pt2 in step 63, the process proceeds to step 65, and it is determined whether or not the brake pressure Pb acquired in step 51 is equal to or higher than the brake pressure cutoff threshold value Pt2. If an affirmative determination is made in step 65, the routine proceeds to step 67, where a clutch cut-off signal is output to the transmission control device 26 and the routine returns. On the other hand, if a negative determination is made in step 65, the clutch cut-off signal is not output to the transmission control device 26, and the process returns.

  The clutch control device according to the third embodiment performs the clutch cutoff as described above, and there is no particular difference between the basic operation and that according to the first embodiment and the second embodiment. .

  In particular, according to the present embodiment, in addition to the operational effects (1) to (10) of the first embodiment and the second embodiment described above, the following operational effects can be achieved. .

  (11) By configuring the temperature T of the braking device (brake portion 19A) and the position of the cargo handling device 9 (arm angle H) as the clutch cutoff operation determination condition, the traveling state and work status of the wheel loader 1 can be determined. The clutches 24 and 25 can be released at a more appropriate timing with detailed judgment. Thereby, the pitching resulting from the operation of the clutch cutoff can be suppressed, and the wheel loader 1 can be smoothly decelerated and stopped.

  In the present embodiment, the processing of step 64, step 65, and step 66 shown in FIG. 20 shows a specific example of determination means that is a constituent feature of claim 3 of the present invention.

  In the present embodiment, the process of step 67 shown in FIG. 20 shows a specific example of the clutch control means that is a constituent of the present invention.

  The following modifications are also within the scope of the present invention, and one or a plurality of modifications can be combined with the above-described embodiment.

  In the above description, the braking force detection means for detecting the braking force of the wheel loader 1 is the pressure sensor 37 for detecting the brake pressure Pb, but the present invention is not limited to this. For example, instead of the pressure sensor 37, a pedal operation amount detector 23A for detecting the operation amount (pedal stroke or pedal angle) of the brake pedal 23, or a detector (not shown) for detecting the depression force of the brake pedal 23 is used. It can be set as a braking force detection means. That is, the parameter considered as the clutch cutoff condition is not limited to the brake pressure Pb, and any detection means that can directly or indirectly detect the operating state of the brake (the magnitude of the braking force) may be used.

  In the above description, the temperature detector 38 for detecting the temperature of the axle oil in the axle device 19 is used as the detecting means for detecting the temperature of the brake portion 19A (braking device), but the present invention is not limited to this. For example, instead of the temperature detector 38 that detects the temperature of the axle oil, a temperature detector that detects the temperature of the casing of the axle device 19 may be used. Further, the constituent members of the brake part 19A may be directly detected by a contact type temperature detector, or the temperature of the brake disk of the brake part 19A may be detected by a non-contact type temperature detector.

  In the above description, the temperature detector 38 is provided in the axle device 19 on the rear wheel 4 side, but the present invention is not limited to this. For example, a temperature detector may be provided in the axle device 19 on the front wheel 2 side. Moreover, you may provide a temperature detector in the axle apparatus 19 of both the front-wheel 2 side and the rear-wheel 4 side, and can set the average value of both as an axle oil temperature in this case, for example.

  In the above description, the arm angle detector 39 for detecting the angle of the arm 7 is used as the cargo handling device position detecting means for detecting the position of the cargo handling device 9, but the present invention is not limited to this. For example, the position of the loading / unloading device 9 is detected by an expansion / contraction length detector (stroke sensor) that detects the expansion / contraction length of the arm cylinder 11 or a height detector (position sensor) that directly detects the height of the bucket 8 from the ground. May be detected.

  In the above description, the controller 27, 51, 61 determines whether or not the accelerator pedal 28 is depressed based on the pedal operation amount s of the accelerator pedal 28 input to the controllers 27, 51, 61 from the pedal operation amount detector 28A. However, the present invention is not limited to this. Instead of the pedal operation amount s, for example, the actual rotational speed of the engine 13 may be detected, and the controller 27, 51, 61 may determine whether or not the accelerator pedal 28 is depressed based on the actual engine rotational speed. Whether or not the accelerator pedal 28 is depressed may be determined based on the accelerator opening or the target engine speed.

  In the above description, the clutch cutoff condition can be set to the first mode or the second mode by operating the clutch cutoff operation mode changeover switch 36, but the present invention is not limited to this. For example, the clutch cut-off operation mode can be set to three modes, and the clutch cut-off timing can be selected from one of the “early” first mode, the “late” second mode, and the third mode at an intermediate timing. It may be. That is, the clutch cut-off operation mode is at least two modes or more, and the clutch cut-off timing may be set to at least one of “early” and “late”.

  In the above description, when the clutch is cut off, the controller 27, 51, 61 outputs a cut-off signal for cutting off the forward clutch 24 and the reverse clutch 25 to the transmission control device 26. However, the present invention is not limited to this. For example, the controller 27, 51, 61 may be configured to output a cut-off signal to the transmission control device 26 so that only the clutch that is engaged at the time of clutch cut-off is cut off. That is, when the clutch cut-off is performed while the wheel loader 1 is moving forward, the controllers 27, 51, 61 output a cut-off signal to the transmission control device 26 so that only the forward clutch 24 is cut off. You may comprise.

  In the above description, the number of selectable speed stages in the transmission 17 is four. However, the present invention is not limited to this, and may be, for example, three stages or five stages or more.

  In the above description, it is determined whether or not the clutch cutoff condition is satisfied only when the transmission 17 is set to the first speed or the second speed which is the low speed stage, but the present invention is not limited to this. . For example, when there are five speed stages, it may be determined whether or not the clutch cutoff condition is satisfied only when the first to third speeds are set as the low speed stages. In this case, the clutch cut-off condition is that the forward clutch 24 and the reverse clutch 25 are released with a lower braking force in the case of the second speed than in the case of the first speed, and the third speed than in the case of the second speed. However, the forward clutch 24 and the reverse clutch 25 are set to be released with a low braking force.

  In the above description, the presence / absence of depression of the accelerator pedal 28, vehicle speed v, brake pressure Pb, set speed stage of the transmission 17, information on the clutch cutoff operation mode (first mode or second mode), and axle oil temperature T Whether or not the clutch cutoff condition is satisfied is determined based on the position information (arm angle H) of the cargo handling device 9, but the present invention is not limited to this. For example, it may be determined whether or not the clutch cutoff condition is satisfied without taking into account any one of the information on the set speed stage of the transmission 17 and the operation mode of the clutch cutoff. Further, without considering both the information on the set speed stage of the transmission 17 and the operation mode of the clutch cutoff, information on whether or not the accelerator pedal 28 is depressed, vehicle speed v, brake pressure Pb, axle oil temperature T and / or Based on the information on the position (arm angle H) of the cargo handling device 9, it may be determined whether or not the clutch cutoff condition is satisfied.

  Further, without considering any information on the vehicle speed v, the set speed stage of the transmission 17 and the operation mode of the clutch cut-off, information on whether or not the accelerator pedal 28 is depressed and the brake pressure Pb, the axle oil temperature T and / or Based on the information on the position (arm angle H) of the cargo handling device 9, it may be determined whether or not the clutch cutoff condition is satisfied. In this case, the clutch cutoff condition is determined so that the forward clutch 24 and the reverse clutch 25 are released with a lower braking force when the accelerator pedal 28 is not depressed than when the accelerator pedal 28 is depressed. Can do. Further, as in the above embodiment, the transmission 17 is set in the information on the presence or absence of the accelerator pedal 28 and the brake pressure Pb and the information on the axle oil temperature T and / or the position (arm angle H) of the cargo handling device 9. It may be determined whether or not the clutch cutoff condition is satisfied in consideration of the speed stage.

  Information on vehicle speed v and brake pressure Pb, axle oil temperature T, and / or cargo handling device without taking into account information on whether the accelerator pedal 28 is depressed, information on the set speed stage of the transmission 17 and the operation mode of the clutch cutoff. Whether or not the clutch cut-off condition is satisfied may be determined based on the position 9 (arm angle H) information. In this case, as in the above embodiment, the clutch cutoff condition can be set so that the forward clutch 24 and the reverse clutch 25 are released with a lower braking force as the vehicle speed v is higher. Further, similarly to the above embodiment, the set speed stage of the transmission 17 is also added to the information on the vehicle speed v and the brake pressure Pb and the information on the axle oil temperature T and / or the position (arm angle H) of the cargo handling device 9. Then, it may be determined whether or not the clutch cutoff condition is satisfied.

  Information on brake pressure Pb, axle oil temperature T, and / or cargo handling device without taking into account any information on whether or not the accelerator pedal 28 is depressed, the set speed stage of the transmission 17, the operation mode of the clutch cutoff, and the vehicle speed v Whether or not the clutch cut-off condition is satisfied may be determined based on the position 9 (arm angle H) information.

  In the above description, when the vehicle speed detector 31 is abnormal, the brake pressure cut-off threshold Pt is set to PbN21, PbD21, PbN22 according to the set operation mode and the set speed stage, as in the case where the accelerator pedal 28 is not depressed. , PbD22, but the present invention is not limited to this. For example, when the vehicle speed detector 31 is abnormal, the brake pressure cut-off threshold value Pt can be set within a condition range where the accelerator pedal 28 is depressed according to the set operation mode and the set speed stage.

  In the above description, when the accelerator pedal 28 is not depressed, a constant value is set for each set operation mode and set speed stage. However, the present invention is not limited to this. For example, the brake pressure cutoff threshold Pt may be set higher on the high speed side than on the low speed side. In this case, in the high-speed running state, by delaying the timing of performing the clutch cutoff, the engine brake can be effectively exhibited, and the vehicle can be decelerated without imposing a large burden on the brake portion 19A.

  In the above description, the characteristics N1, N2, D1, and D2 set the brake pressure cutoff threshold Pt so as to decrease linearly as the vehicle speed v increases in the range of the vehicle speeds va to vb. The present invention is not limited to this. For example, the brake pressure cutoff threshold value Pt may decrease in a quadratic curve as the vehicle speed v increases, or the brake pressure cutoff threshold value Pt decreases stepwise as the vehicle speed v increases. There may be.

  In the first embodiment described above, the case where the brake pressure cutoff threshold Pt is corrected to 1.03 Pt to 1.1 Pt when the axle oil temperature T is equal to or higher than the predetermined value Ts ° C. has been described as an example. The present invention is not limited to this. For example, the threshold value Ts of the axle oil temperature may be set to a plurality of Ts1 and Ts2 (Ts1 <Ts2). When the axle oil temperature T exceeds Ts1, Pt1 is set to 1.03 Pt and further exceeds Ts2. In some cases, the brake pressure cutoff threshold Pt may be corrected to be larger as the axle oil temperature T increases, such as by correcting Pt1 to 1.05 Pt.

  In the second embodiment described above, a case where the brake pressure cutoff threshold Pt is corrected to 0.90 Pt to 0.97 Pt when the cargo handling device position (arm angle) H is equal to or greater than the predetermined value Ht degrees is taken as an example. However, the present invention is not limited to this. For example, the handling device position threshold Ht may be set to a plurality of Ht1, Ht2 (Ht1 <Ht2), and when the handling device position H exceeds Ht1, Pt2 is set to 0.95 Pt and further exceeds Ht2. In some cases, the brake pressure cutoff threshold Pt may be corrected to be smaller as the angle of the cargo handling device position H increases, such as correcting Pt2 to 0.97 Pt.

  In the third embodiment described above, of the determination of the axle oil temperature T and the determination of the position (arm angle H) of the cargo handling device 9, the determination of the axle oil temperature T is performed first, and the axle oil temperature T is the threshold value Ts. Although not described above or when the position (arm angle H) of the cargo handling device 9 is determined as an example when Pb is not equal to or greater than Pt1, the present invention is not limited to this. For example, among the determination of the axle oil temperature T and the determination of the position of the cargo handling device 9 (arm angle H), the determination of the position of the cargo handling device 9 (arm angle H) may be performed first. Also, the axle oil temperature T is determined first, and when Pb is equal to or greater than Pt1, the position of the cargo handling device 9 (arm angle H) is determined without outputting the clutch cutoff signal to the transmission control device 26. The brake pressure cutoff threshold Pt may be corrected based on the determination of the axle oil temperature T and the determination of the position (arm angle H) of the cargo handling device 9.

  In the above description, the wheel loader 1 has been described as an example of the work vehicle. However, the present invention is not limited to this, and for example, other work vehicles such as a forklift, a telescopic handler, and a lift truck may be used. Good.

  The present invention is not limited to the above-described embodiment, and can be freely changed and improved without departing from the gist of the invention.

1 Wheel loader (work vehicle)
2 Front wheels
4 Rear wheels
7 Arm 8 Bucket 9 Cargo Handling Device 19 Axle Device 19A Brake Unit 26 Transmission Control Device 27, 51, 61 Controller 37 Pressure Sensor (Braking Force Detection Means)
38 Temperature detector (temperature detection means)
39 Arm angle detector (loading device position detection means)
40 Clutch cutoff valve

Claims (5)

Braking force detection means for detecting the braking force of the work vehicle;
Temperature detecting means for detecting the temperature of the braking device of the work vehicle;
Determination means for determining whether or not a clutch cutoff condition is satisfied based on the braking force of the work vehicle detected by the braking force detection means and the temperature of the braking device detected by the temperature detection means. When,
A work vehicle comprising: clutch control means for controlling engagement and release of the clutch so as to release the clutch when the determination means determines that the clutch cutoff condition is satisfied. Clutch control device. Braking force detection means for detecting the braking force of the work vehicle;
A loading device position detection means for detecting a position of the loading device of the work vehicle;
Based on the braking force of the work vehicle detected by the braking force detector and the position of the cargo handling device detected by the cargo handling device position detector, it is determined whether or not a clutch cutoff condition is satisfied. A determination means;
A work vehicle comprising: clutch control means for controlling engagement and release of the clutch so as to release the clutch when the determination means determines that the clutch cutoff condition is satisfied. Clutch control device. Braking force detection means for detecting the braking force of the work vehicle;
Temperature detecting means for detecting the temperature of the braking device of the work vehicle;
A loading device position detection means for detecting a position of the loading device of the work vehicle;
Based on the braking force of the work vehicle detected by the braking force detection means, the temperature of the braking device detected by the temperature detection means, and the position of the cargo handling apparatus detected by the cargo handling apparatus position detection means. Determining means for determining whether or not a clutch cutoff condition is satisfied;
A work vehicle comprising: clutch control means for controlling engagement and release of the clutch so as to release the clutch when the determination means determines that the clutch cutoff condition is satisfied. Clutch control device.   The clutch control device for a work vehicle according to claim 1 or 3, wherein the clutch cutoff condition is set so that the clutch is released with a higher braking force as the temperature of the braking device is higher.   The clutch control device for a work vehicle according to claim 2 or 3, wherein the clutch cutoff condition is set such that the higher the position of the material handling device is, the more the clutch is released with a lower braking force.

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