JP2017020439A - Work vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a work vehicle capable of effectively reducing fuel consumption while avoiding output shortage.SOLUTION: The work vehicle includes a work machine 150 to be driven by a plurality of actuators, a work machine lever 222 for controlling the operation of the plurality of actuators, a hydraulic pump 171 and a hydraulic motor 172 for converting power output from an engine 201 into hydraulic pressure to be transmitted to wheels 1, and a control device 240 for controlling the revolving speed of the engine to be within a range of a reference limit value or lower according to an output request command to the engine. When the actual travel speed of a wheel loader exceeds a travel speed threshold value fixed according to a load amount, the control device 240 executes limit processing to limit the revolving speed of the engine to a value lower than the reference limit value.SELECTED DRAWING: Figure 3

Description

The present invention relates to a work vehicle.

  In a work vehicle such as a wheel loader equipped with an automatic transmission using a torque converter, an operator often depresses the accelerator pedal to the maximum amount and adjusts the traveling speed by switching the gear position. This is because it is difficult for the operator to adjust the traveling speed with the accelerator work because there is no suspension in the vehicle body and the shaking is large considering the ease of excavation work. The engine control of the work vehicle is configured as so-called rotational speed control in which the engine rotational speed is approximately proportional to the amount of depression of the accelerator pedal, unlike an automobile. This is for adjusting the discharge flow rate of the hydraulic pump driven by the engine, that is, the speed of the working machine with the accelerator pedal. As a result, in a work vehicle equipped with a torque converter, the engine speed and the traveling speed, that is, the amount of depression of the accelerator pedal and the traveling speed are approximately proportional to each other because of its characteristics.

  On the other hand, the engine output required when continuously operating at a constant speed without operating the work machine in the wheel loader is used when operating the work machine while running during excavation work or the like (hereinafter referred to as “composite operation”). It is smaller than the required engine power. Nevertheless, the operator depresses the accelerator pedal to the maximum amount in order to increase the productivity by traveling at a high speed during continuous travel, so the engine speed becomes a high speed corresponding to the amount of depression of the accelerator pedal. However, in such a situation, the engine is operated at a high speed even though the required engine output is small, so energy loss due to friction is large, and engine control is improved in terms of fuel efficiency. There was room.

  By the way, some work vehicles including a wheel loader, a dump truck, and a forklift include a continuously variable transmission mechanism in a power transmission device that transmits engine power to wheels. For example, a work vehicle having a hydrostatic continuously variable transmission (HST) drives a hydraulic pump by an engine to send pressure oil to a hydraulic motor, and drives wheels by the hydraulic motor. In a work vehicle equipped with a stepped transmission mechanism, the driving force and traveling speed are linked to the engine speed when the gear stage is fixed. However, in a work vehicle equipped with this type of continuously variable transmission mechanism, the driving force and traveling speed ( The rotational speed of the wheel) does not depend on the engine rotational speed, and the driving force, traveling speed, and engine rotational speed can be controlled independently.

  As an invention for reducing the fuel consumption of an HST-type work vehicle, Patent Document 1 discloses that the upper limit of the accelerator opening (engine speed) becomes closer to the maximum traveling speed when traveling near a predetermined maximum traveling speed. A work vehicle for reducing the size of the vehicle is disclosed. Further, in Patent Document 2, when the low load condition indicating that the vehicle is in a low load condition is satisfied, the upper limit value of the engine output torque is reduced more than when the low load condition is not satisfied. A work vehicle having a control unit for controlling the engine is disclosed.

Japanese Patent No. 5059969 Japanese Patent No. 5222895

  The invention described in Patent Document 1 is only intended for high-speed traveling on flat ground, and does not control the upper limit value (engine speed) of the accelerator opening in consideration of the combined operation. For this reason, there is a possibility that the engine speed cannot be increased quickly when the shift from the high speed traveling to the combined operation is performed, resulting in insufficient output. The invention described in Patent Document 2 estimates the vehicle load in the current work phase, and lowers the engine speed when the load satisfies a low load condition. ) The engine speed is not controlled with due consideration of the load. For this reason, if the next work phase is a high load, priority is given to avoiding engine output shortage, so the engine speed cannot be lowered sufficiently, and the effect of reducing fuel consumption may be insufficient.

  The above indications are not limited to HST work vehicles, but apply to any power transmission device that transmits engine power to wheels provided with a continuously variable transmission function. Specifically, a hydraulic mechanical system that drives a hydraulic pump through an axle mechanically connected to the engine while driving a hydraulic pump by driving a hydraulic pump by the engine and driving the wheels by the hydraulic motor. This also applies to work vehicles having a continuously variable transmission (HMT). Furthermore, the above indication is applicable not only to the work vehicle having the above-described mechanical continuously variable transmission including the CVT but also to the work vehicle having the electric continuously variable transmission. As a work vehicle having an electric continuously variable transmission, for example, a plurality of electric motors connected to an axle are driven using electric power generated by a motor / generator using the rotational force of an engine, thereby There are hybrid work vehicles that drive wheels.

  An object of the present invention is to provide a work vehicle that can effectively reduce fuel consumption during high-speed traveling while avoiding engine output shortage in a high load state.

  In order to solve the above problems, a work vehicle according to the present invention includes an engine, wheels, a work device driven by at least one actuator, an operation device for controlling the operation of the at least one actuator, A power transmission device that converts hydraulic power or electric power output from the engine into hydraulic pressure or electricity and transmits it to the wheels, and controls the engine speed within a range below a limit value according to the engine load or accelerator operation amount. In the control device configured as described above, when the actual traveling speed of the work vehicle exceeds a threshold value determined according to the load amount of the work vehicle, the actual traveling speed is less than the threshold value or less. And a control device configured to execute a restriction process for setting the restriction value to a low value.

  According to the present invention, the load state of the work vehicle is predicted based on the load amount and the actual traveling speed, and the engine speed is reduced when the possibility of the high load state is low. Fuel consumption during high-speed traveling can be effectively reduced while avoiding insufficient output.

The side view of the wheel loader concerning an embodiment of the invention. The system block diagram of the wheel loader 100 shown in FIG. The block diagram of the processing function performed with the control apparatus 240. FIG. The flowchart of the control which the high load estimation part 331 performs. The flowchart of the control which the engine speed limitation part 332 performs. The flowchart of the control which the torque reduction flag output part 334 performs. Flowchart of control executed by hydraulic pump upper limit torque setting unit 333 An example of the control output when the load is large. An example of a control output when the amount of cargo is small. The hardware block diagram of the control apparatus 240. FIG. The system block diagram of an HST type wheel loader. The system block diagram of a HMT type wheel loader. The system block diagram of a hybrid type wheel loader.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Configuration of Wheel Loader 100]
FIG. 1 is a side view of a wheel loader according to an embodiment of the present invention. The wheel loader 100 in this figure includes a vehicle body 110 and an articulated work machine 150 attached to the front of the vehicle body 110.

  The working machine 150 is a working device driven by at least one actuator, and the working machine 150 shown in the drawing is driven to extend and contract to drive the lift arm 155 and the bucket 151 and the lift arm 155 and the bucket 151. A lift cylinder 152 and a bucket cylinder 153 are provided as hydraulic actuators (hydraulic cylinders). Although one lift arm 155 and one lift cylinder 152 are provided on the left and right sides of the vehicle body 112, the right lift arm and lift cylinder hidden in FIG.

  The lift arm 155 pivots up and down (up and down) as the lift cylinder 152 extends and contracts. The bucket 151 rotates (dump operation or cloud operation) as the bucket cylinder 153 expands and contracts. The illustrated wheel loader 100 includes a Z link type (bell crank type) link mechanism for operating the bucket 151.

  Wheels 1a, 1b, 1c, and 1d (hereinafter may be simply referred to as “wheel 1”) are driven by a power transmission device 210 (described later) using an engine 201 (described later) as a power source. The driving force is transmitted to the ground via tires disposed on the outer periphery of the vehicle 1 to move the vehicle body 110 forward or backward.

  FIG. 2 is a system configuration diagram of the wheel loader 100 shown in FIG. Note that the same parts as those in the previous figure may be denoted by the same reference numerals and description thereof may be omitted (the same applies to the subsequent figures).

  The engine 201 supplies power to the power transmission device 210 and the hydraulic pump 211 via the output shaft. Control of the engine 201 will be described later.

  The power transmission device (power transmission mechanism) 210 includes a continuously variable transmission mechanism, and converts a part of the power output from the engine 201 to hydraulic pressure or electricity and transmits it to the wheel 1. A specific example of the power transmission device 210 will be described later with reference to FIGS. The power transmission device 210 in FIG. 11 employs an HST system that converts engine power into hydraulic pressure and transmits it to the wheel 1. The power transmission device 210 in FIG. And the engine 201 drives the hydraulic pump 171 via the power transmission mechanical unit 173 to send the hydraulic oil to the hydraulic motor 172, and adopts the HMT type in which the hydraulic motor 172 drives the wheels 1; The thing of FIG. 13 employ | adopts the hybrid type which converts engine motive power into electricity and transmits to the wheel 1. FIG.

  The hydraulic pump 211 is driven by at least one of the power transmission device 210 and the engine 201. The hydraulic pump 211 supplies pressure oil to the plurality of hydraulic actuators (for example, the lift cylinder 152 and the bucket cylinder 153) related to the work machine 150 via the control valve 212, and appropriately drives the plurality of hydraulic actuators. Since the hydraulic pump 211 uses the engine 201 as an indirect power source, the plurality of hydraulic actuators using the hydraulic pump 211 as a drive source also use the engine 201 as an indirect power source.

  The control valve 212 is operated by a pilot pressure or an electric signal output from a work implement lever (operation device) 222 for controlling the operations of a plurality of hydraulic actuators related to the work implement 150. When the control valve 212 operates, the amount and direction of the pressure oil supplied from the hydraulic pump 211 to the hydraulic actuator (lift cylinder 152, bucket cylinder 153) are adjusted.

  The control device 240 is a computer (for example, a microcomputer) for executing various types of information processing related to the vehicle. The control device 240 is configured to control the engine speed within a range equal to or less than the limit value in accordance with an engine output request command such as a load on the engine 201 or an operation amount of the accelerator pedal 224. The “limit value” here is the maximum value on the horizontal axis in the engine performance curve defined on the plane with the engine torque (or engine output) as the vertical axis and the engine speed as the horizontal axis. The “range below” indicates a range below the maximum value. Therefore, the engine speed control here refers to normal control for controlling the engine speed within a normally usable range allowed by the performance of the engine. Hereinafter, this limit value may be referred to as a “reference limit value”.

  In particular, when the actual traveling speed of the wheel loader 100 exceeds a traveling speed threshold value (details will be described later) determined according to the load amount of the wheel loader 100 (the weight of the transported material in the bucket 151). The process of setting the limit value to a value lower than the value (reference limit value) when the actual travel speed is less than or equal to the travel speed threshold (this process is referred to as “engine speed limit process” or “limit process” in this paper) Is configured to run). Details of the control processing performed by the control device 240 will be described later.

  FIG. 10 shows a hardware configuration of the control device 240. The control device 240 includes an input unit 91, a central processing unit (CPU) 92 that is a processor, a read-only memory (ROM) 93 and a random access memory (RAM) 94 that are storage devices, and an output unit 95. ing. The input unit 91 inputs information and signals from an external device, and performs A / D conversion as necessary. The ROM 93 is a recording medium in which a program or the like is stored, and the CPU 92 performs predetermined arithmetic processing on signals taken from the input unit 91 and the memories 93 and 94 in accordance with the program stored in the ROM 93. The output unit 95 creates an output signal according to the calculation result in the CPU 92 and outputs the signal to an external device. 10 includes a semiconductor memory such as a ROM 93 and a RAM 94 as storage devices, but may include a magnetic storage device such as a hard disk drive and store programs therein.

  The work machine lever operation amount detector 225 detects the operation amount of the work machine lever 222 and outputs it to the control device 240. The accelerator operation amount detector 227 detects the operation amount (depression amount) of the accelerator pedal 224 and outputs it to the control device 240. The traveling speed detector 223 detects the traveling speed of the wheel loader 100 where the wheels 1 are driven by the power transmission device 210 and outputs the detected traveling speed to the control device 240. The lift cylinder pressure detector 220 detects the bottom side pressure of the lift cylinder 152 and outputs it to the control device 240. Bucket cylinder pressure detector 221 detects the bottom side pressure of bucket cylinder 153 and outputs it to control device 240. The hydraulic pump pressure detector 235 detects the discharge pressure of the hydraulic pump 211 and outputs it to the control device 240. The hydraulic pump displacement detector 236 detects the displacement (or tilt angle) of the hydraulic pump 211 and outputs it to the control device 240.

  The work implement lever 222 is not limited to one type in which both the lift cylinder 152 and the bucket cylinder 153 can be operated individually or simultaneously with one lever, and the lift cylinder 152 and the bucket cylinder 153 can be operated with separate levers, respectively. Two types may be used. In the latter case, the work machine lever operation amount detector 225 may detect two lever operation amounts.

  Further, the traveling speed detector 223 detects the speed of the wheel 1 (the number of revolutions), the output number of revolutions of the power transmission device 210 (the number of revolutions of the output shaft), the number of revolutions of the propeller shaft 215, and the like. Thus, the traveling speed of the wheel loader 100 can be calculated.

[Basic control of engine 201]
The engine 201 has an electronic control governor 230 that controls the fuel injection amount, and an engine speed detector 226 that detects the speed of the engine 201. The control device 240 compares the engine speed command with the actual engine speed detected by the engine speed detector 226, and increases the fuel injection amount when the actual engine speed is lower than the engine speed command value. Command the electronic governor 230. On the contrary, when the actual engine speed is higher than the engine speed command value, a command is given to reduce the fuel injection amount. The engine load estimation device 231 mounted on the engine 201 estimates the engine load from the fuel injection amount by the electronic governor 230 and the like. The engine load estimation by the engine load estimation device 231 may be executed in place of the control device 240 by inputting necessary information such as the fuel injection amount by the electronic governor 230 to the control device 240.

[Control device 240]
A block diagram of processing functions executed by the control device 240 is shown in FIG. The control device 240 according to the present embodiment controls the engine speed within a range equal to or less than the reference limit value according to the engine load input from the engine load estimation device 231 or the accelerator operation amount input from the accelerator operation amount detection unit 227. May function as an engine control device.

  Further, as shown in FIG. 3, the control device 240 includes a first engine speed command value setting unit 336, a second engine speed command value setting unit 330, an engine speed command value processing unit 335, and a high load prediction. Functions as a unit 331, a work implement load calculation unit 345, an engine speed limit unit 332, a torque reduction flag output unit 334, and a hydraulic pump upper limit torque setting unit 333.

  The first engine speed command value setting unit 336 increases the engine speed command value (first command value) as the engine load 320 estimated by the engine load estimation device 231 increases. The second engine speed command value setting unit 330 increases the engine speed command value (second command value) as the accelerator operation amount 310 detected by the accelerator operation amount detector 227 increases.

  The engine speed command value processing unit 335 includes an engine speed command value (first command value) determined by the first engine speed command value setting unit 336 and an engine determined by the second engine speed command value setting unit 330. Of the rotational speed command values (second command values), the larger one is selected and output to the engine rotational speed limiter 332.

  The high load prediction unit 331 predicts a future high load state of the wheel loader 100 (vehicle), and outputs an engine speed limit command to the engine speed limit unit 332 when a high load is not expected. When the load is expected, the engine speed limit command is not output. As an index for predicting a high load state, there are, for example, the weight of the load in the bucket 151 (load amount), the traveling speed of the vehicle, the engine load, the working machine lever operation amount, and the load of the working machine 150 (working machine load). . In order to obtain an index for predicting a high load state, the high load prediction unit 331 of the present embodiment detects the lift cylinder pressure 315 detected by the lift cylinder pressure detection unit 220 and the bucket cylinder pressure detection unit 221. The bucket cylinder pressure 350, the traveling speed 314 detected by the traveling speed detector 223, and the engine load 320 estimated by the engine load estimating device 231 are input.

  The work machine load calculation unit 345 is detected by the actual engine speed 317 detected by the engine speed detection unit 226, the hydraulic pump pressure 340 detected by the hydraulic pump pressure detection unit 235, and the hydraulic pump capacity detection unit 236. The working machine load is calculated based on the hydraulic pump capacity 341 and output to the engine speed limiter 332.

  The engine speed limit unit 332 is commanded by the work machine load calculated by the work machine load calculation unit 345, the work machine lever operation amount 316 detected by the work machine lever operation amount detector 225, and the high load prediction unit 331. Based on the engine speed limit command and the actual engine speed 317 detected by the engine speed detection unit 226, the engine speed command value output by the engine speed command value processing unit 335 is limited (engine speed). It is determined whether or not to perform processing for reducing the rotational speed specified by the command value. Then, engine speed limiter 332 outputs to engine control governor 230 an engine speed command value that has been subjected to a limit process as appropriate according to the determination.

  The torque reduction flag output unit 334 is commanded by the actual engine speed 317 detected by the engine speed detection unit 226, the engine speed limit command commanded by the high load prediction unit 331, and the engine speed limit unit 332. A torque reduction flag is set based on the engine speed command value 360 and is output to the hydraulic pump upper limit torque output unit 333.

  The hydraulic pump upper limit torque output unit 333 sets the hydraulic pump upper limit torque command value based on the actual engine speed 317 detected by the engine speed detection unit 226 and the torque reduction flag output from the torque reduction flag output unit 334. Set and output to the hydraulic pump 211.

  The first engine speed command value setting unit 336 is not necessarily provided as a part for outputting the engine speed command value to the engine speed command value processing unit 335, and the second engine speed command value setting unit is not necessarily provided. 330 may be comprised only.

  Further, the high load predicting unit 331 may use only the lift cylinder pressure 315 by the lift cylinder pressure detecting unit 220 when calculating the load amount in the bucket 151, but not limited thereto, as shown in FIG. You may input the bucket cylinder pressure by the pressure detection part 221. FIG.

[High load prediction unit 331]
FIG. 4 is a flowchart of the control related to the high load prediction unit 331 in the control shown in FIG. In the engine load determination step 414, the high load prediction unit 331 inputs the engine load 320 estimated by the engine load estimation device 231, and when the engine load 320 is equal to or less than a predetermined engine load threshold, the load amount detection step 410 proceeds. In other cases (when the engine load 320 exceeds the threshold value), the routine proceeds to step 421 and the engine speed command value is not issued.

  In the load amount detection step 410, the high load prediction unit 331 calculates the load amount in the bucket 151 based on the lift cylinder pressure 315. In the next travel speed threshold setting step 411, the high load prediction unit 331 sets a threshold (travel speed threshold) related to the travel speed determined according to the load amount of the wheel loader 100 at that time. Here, the travel speed threshold is set to be smaller as the load amount detected in the load amount detection step 410 is smaller. In the example shown in the graph of FIG. 4, the travel speed threshold is set so as to decrease linearly as the load amount decreases, but the travel speed threshold monotonously decreases as the load amount decreases. (Including a monotonous decrease in a broad sense including a section in which the traveling speed position is kept constant as the load amount decreases).

  In the high load prediction determination step 412, the magnitude relationship between the travel speed threshold calculated in the travel speed threshold setting step 411 and the travel speed (actual travel speed) 314 detected by the travel speed detection unit 223 is compared. When the traveling speed 314 is higher than the traveling speed threshold, the routine proceeds to step 420, where an engine speed limit command is issued, and when the traveling speed 314 is lower than the traveling speed threshold, it is predicted that a high load may occur. Then, the routine proceeds to step 421, where the engine speed limit command is not issued.

  In the present embodiment, as can be seen from the series of processes in steps 410 to 412, it is determined that the larger the load amount and the lower the traveling speed, the higher the possibility that the traveling operation is shifted to a combined operation with a high load. The control device 240 is configured not to issue an engine speed limit command. For example, when there is a load in the bucket 151, it is conceivable that a high-load operation for lifting the load will come next. Further, as the load amount increases, the engine output required for the lift-up increases and the operation load also increases. Further, when moving from traveling to excavation, the traveling speed of the vehicle decreases due to the reaction force from the excavation target generated by the contact between the bucket 151 and the excavation target. Therefore, in consideration of the transient characteristics of the output increase of the engine 201, the travel speed threshold may be set so that the time until the travel speed decreases and the excavation starts is longer than the time required for the engine 201 to increase the output. preferable.

  In the load amount detection step 410, the load amount may be detected not only from the lift cylinder pressure 315 but also from the bucket cylinder pressure 350. Further, instead of the cylinder pressures 315 and 350, the load amount may be detected from information obtained by measuring the amount of soil loaded in the bucket 151 using a camera or a radar.

  In the flowchart of FIG. 4, the engine load determination step 414 can be omitted, and the process may proceed to step 410 immediately after the start of the flow.

[Engine Speed Limiting Unit 332]
FIG. 5 is a flowchart of the control related to the engine speed limiter 332 in the control shown in FIG. In the work implement lever operation determination step 510, the engine speed limiter 332 determines the work implement lever operation amount 316 detected by the work implement lever operation detector 225 and a predetermined work implement lever operation amount threshold (described later in FIGS. 8 and 9). To determine whether or not the work implement lever 222 has been operated. The work implement lever operation amount threshold is a value for detecting whether or not the work implement lever is operated, and for example, a value slightly higher than the pilot pressure value when the work implement lever is in the neutral position may be set. . If the work implement lever operation amount 316 is equal to or less than the work implement lever operation amount threshold, the engine speed limit unit 332 determines that there is no operation of the work implement lever 222, and proceeds to the work implement load determination step 520. When it is determined that the work implement lever operation amount 316 exceeds the work implement lever operation amount threshold and the work implement lever 222 is operated, the process returns to the beginning of the flowchart.

  In work implement load determination step 520, engine speed limiter 332 compares work implement load 350 calculated by work implement load calculator 345 with a predetermined work load threshold. The work load threshold is a value for detecting the presence or absence of a load on the work implement 150, and may be set to a value slightly higher than the value of the work load in the no-load state, for example. If work implement load 350 is equal to or less than the work load threshold value, engine speed control unit 332 determines that there is no work implement load, and proceeds to engine speed limit command determination step 511. Otherwise, returns to the beginning of the flowchart. .

  In the engine speed limit command determination step 511, the engine speed limit unit 332 determines the presence or absence of the engine speed limit command 313 from the high load prediction unit 331. If there is an output of the engine speed limit command 313, the process proceeds to the first engine speed limit value setting step 512; otherwise, the process proceeds to the second engine speed limit value setting step 513.

  In the first engine speed limit value setting step 512, the engine speed limit value is set to a first engine speed limit value lower than the second engine speed limit value. In the second engine speed limit value setting step 513, the engine speed limit value is set to the second engine speed limit value.

  The second engine speed limit value is set to a value lower than the maximum value (reference limit value) of the engine speed in the engine performance curve described above. Preferably, the second engine speed limit value is set to an engine speed at which the engine can output the maximum torque (in other words, the engine speed at which the torque is maximum on the engine performance curve). The second engine speed limit value may be set to an engine speed at which the fuel consumption rate is highest on the engine performance curve.

  In the engine speed limit processing step 514, the engine speed limit unit 332 replaces the engine speed command value output from the engine speed command value processing unit 335 with the first engine set in step 512 or step 513. The engine speed limit value or the engine speed limit value is output as the engine speed command value (the process according to step 514 corresponds to the above “engine speed limit process” or “limit process”).

  The values of the first engine speed limit value and the second engine speed limit value in step 512 and step 513 may be held at preset values, but input devices such as buttons, dials, and monitors are used. Then, the desired value may be changed afterwards.

  In the engine speed limit processing step 514, the actual engine speed is acquired, and when there is a difference between the actual engine speed and the engine speed limit value, the engine speed command value is output at a constant rate of change. Processing may be performed so as to reach the rotation speed limit value.

  In the flowchart of FIG. 5, the work implement lever operation determination step 510 and / or the work implement load determination step 520 can be omitted. If work implement lever operation determination step 510 is omitted, the engine speed limit value is set to the maximum value of the engine speed in the engine performance curve described above in place of the second engine speed limit value in step 513. Also good.

[Torque reduction flag output unit 334]
It is predicted that the engine will not be in a high load state, an engine speed limit command is issued, and the work implement lever is operated in a state where the engine speed is lowered to the first engine speed limit value or the second engine speed limit value. For example, when shifting to a high load state, the engine may run out of output. In order to avoid this, the controller 240 of the present embodiment uses the torque reduction flag output unit 334 to load the hydraulic pump 211 on the engine 201 based on the comparison between the actual engine speed 317 and the engine speed command value 360. It is determined whether or not it is necessary to reduce.

  FIG. 6 is a flowchart of the control related to the torque reduction flag output unit 334 in the control shown in FIG. In engine speed limit command determination step 920, torque reduction flag output unit 334 determines whether or not an engine speed limit command 313 is issued from high load prediction unit 331. If the engine speed limit command 313 has been issued, the process proceeds to a torque reduction flag setting step 910. Otherwise, the process proceeds to a torque reduction flag determination step 921.

  In the torque reduction flag determination step 921, the torque reduction flag output unit 334 determines the presence or absence of the torque reduction flag. The torque reduction flag is used in the processing in the hydraulic pump upper limit torque setting unit 333, which will be described later with reference to FIG. 7, and in this embodiment, the processing content is changed depending on the presence or absence of the torque reduction flag. In addition, “present” indicates that the torque reduction flag is “present” and “torn” indicates that “the flag is not set”. In step 921, if the torque reduction flag is present, the process proceeds to engine speed determination step 922. Otherwise, the process proceeds to torque reduction flag release step 912.

  In the engine speed determination step 922, the torque reduction flag output unit 334 determines whether the actual engine speed 317 and the engine speed command value 360 are large or small. If the actual engine speed 317 is smaller than the engine speed command value 360, the process proceeds to the torque reduction flag setting step 910. Otherwise, the process proceeds to the torque reduction flag release step 912.

  In the torque reduction flag setting step 910, the torque reduction flag output unit 334 sets the torque reduction flag to “present”. On the other hand, in the torque reduction flag release step 912, the torque reduction flag is set to none. Both steps 910 and 912 then proceed to step 913 to perform processing (torque reduction flag output processing) for outputting the presence or absence of a torque reduction flag to the hydraulic pump upper limit torque output unit 333.

  As a result of the above calculation, when there is an engine speed limit command, or when there is no engine speed limit command and the actual engine speed is smaller than the engine speed command value, the torque reduction flag output unit 334 outputs the hydraulic pump It is determined that the load of 211 needs to be reduced, and the torque reduction flag is set to “present”.

[Hydraulic pump upper limit torque setting unit 333]
FIG. 7 is a flowchart of the control related to the hydraulic pump upper limit torque setting unit 333 in the control shown in FIG. In the torque reduction flag determination step 810, the hydraulic pump upper limit torque setting unit 333 determines whether there is a torque reduction flag output from the torque reduction flag output unit 334. If the torque reduction flag output from the torque reduction flag output unit 334 is present, the process proceeds to the second hydraulic pump upper limit torque setting step 812. Otherwise (if the torque reduction flag is not present), the first hydraulic pump upper limit torque setting is performed. Proceed to step 811.

  In the first hydraulic pump upper limit torque setting step 811, the hydraulic pump upper limit torque setting unit 333 sets the hydraulic pump upper limit torque based on the actual engine speed 317 detected by the engine speed detection unit 226 and the graph in FIG. 7. To do. The engine speed indicated by a dotted line (dotted line labeled “second”) in the graph of FIG. 7 indicates a second engine speed limit value (step 513 in FIG. 5). In the graph in FIG. 7, the hydraulic pump upper limit torque is kept constant at an engine speed 317 equal to or higher than the second engine speed limit value, and the engine speed decreases at an engine speed 317 less than the second engine speed limit value. At the same time, the hydraulic pump upper limit torque is set to decrease.

  Similarly, in the second hydraulic pump upper limit torque setting step 812, the hydraulic pump upper limit torque setting unit 333 sets the hydraulic pump upper limit torque based on the actual engine speed 317 and the graph in FIG. The one on the right side of the two dotted lines in the graph of FIG. 7 (dotted line labeled “second”) indicates the second engine speed limit value (step 513 in FIG. 5), and the one on the left side (“first” The dotted line marked with “” indicates the first engine speed limit value (step 512 in FIG. 5). In the graph of FIG. 7, the hydraulic pump upper limit torque is kept constant at an engine speed 317 equal to or higher than the second engine speed limit value. When the engine speed 317 is less than the second engine speed limit value, the hydraulic pump upper limit torque is minimized while reaching a value between the second engine speed limit value and the first engine speed limit value. Is set to decrease rapidly.

  As described above, the upper limit torque setting process executed in the first hydraulic pump upper limit torque setting step 811 and the second hydraulic pump upper limit torque setting step 812 is the same as the graph in FIG. The upper limit torque of the hydraulic pump is increased as the engine speed 317 increases. However, the set value of the second hydraulic pump upper limit torque is set to a value equal to or smaller than the first hydraulic pump upper limit torque set value for the same engine speed. This is to prioritize acceleration of the actual engine speed when there is a torque reduction flag.

  In the hydraulic pump upper limit torque processing step 813, the hydraulic pump upper limit torque setting unit 333 outputs the hydraulic pump upper limit torque value set in step 812 or step 811 to the hydraulic pump 211 as the hydraulic pump upper limit torque command value. As a result, the upper limit torque value of the hydraulic pump 211 is limited to the value set in step 812 or step 811. The upper limit torque value limit control of the hydraulic pump 211 is performed, for example, by setting the displacement (tilt angle) of the hydraulic pump 211 to the discharge pressure so that the product of the discharge pressure and the displacement of the hydraulic pump 211 is kept below a predetermined value. It is possible by appropriately controlling accordingly.

  When the torque reduction flag output unit 334 and the hydraulic pump upper limit torque setting unit 333 limit the upper limit torque value of the hydraulic pump 211 as described above, the engine speed is set to the first engine speed limit value or the second engine speed limit value. When a shift to a high load state in which the hydraulic pump load increases due to operation of the work implement lever 222 in the lowered state is required, the engine output is first used to increase the engine speed. After that, when the engine speed is increased moderately, the amount of engine output allocated to the hydraulic pump is increased, so that a smooth transition to high-load work is possible without causing engine stall.

  The torque reduction flag output unit 334 and the hydraulic pump upper limit torque setting unit 333 can be omitted.

[Actual operation]
8 and 9 show an example of the operation of the wheel loader according to the present embodiment configured as described above. In each figure, a graph 620 represents a load amount transition, a graph 621 represents a travel speed transition (actual travel speed transition), a graph 622 represents an engine speed limit command transition, a graph 623 represents a work implement lever operation amount transition, a graph 624 Indicates the engine speed command value transition. The graph 623 shows a work implement lever operation amount threshold value 630, and the graph 624 shows an engine speed determined by the engine speed command value processing unit 335 (see FIG. 3) based on the engine load or the accelerator operation amount. 604 is shown.

  FIG. 8 shows an example in which the load amount is relatively larger than in the case of FIG. In this case, since the load amount is large, the high load prediction unit 331 sets the travel speed threshold (step 411 in FIG. 4) to be higher. For this reason, even if the accelerator pedal depression amount is increased from time 0 600 and the travel speed is increased, the travel speed is smaller than the travel speed threshold and the time is relatively long. Is not issued. As a result, the engine speed limiter 332 sets the second engine speed limit value (second limit) as the engine speed limit value, and the engine speed command value does not reach the second limit depending on the depression of the accelerator pedal. To rise.

  After the time point 601 when the travel speed exceeds the travel speed threshold, the engine speed limit command 313 is issued to the engine speed limit section 332 because the high load prediction section 331 predicts that no high load will occur. Thus, the engine speed limit unit 332 sets the first engine speed limit value (first limit) as the engine speed limit value, so that the limit value of the engine speed command value is from the second limit to the first limit. descend.

  At a time 602, when the traveling speed decreases and falls below the traveling speed threshold by decreasing the accelerator pedal depression amount, the high load predicting unit 331 predicts that a high load may occur, and limits the engine speed. Release the command 313. Thereby, the limit value of the engine speed command value increases from the first limit to the second limit.

  At a time 603 when the operation amount of the work implement lever 222 exceeds a predetermined work implement lever operation amount threshold value 630, the engine speed limit unit 332 interrupts the execution of the engine speed limit processing, and the accelerator operation amount and load at that time are reduced. The engine speed is increased to a corresponding engine speed 604 (a value determined by the engine speed command value processing unit 335 in FIG. 3).

  FIG. 9 shows an example of the operation of the wheel loader incorporating the present invention, as in FIG. FIG. 8 shows an example when the load amount is large, whereas FIG. 9 shows an example when the load amount is relatively small. Also in this case, even if the amount of depression of the accelerator pedal is increased from time 700, the traveling speed is smaller than the traveling speed threshold, and the high load predicting unit 331 does not issue an engine speed limit command. Therefore, the engine speed limit unit 332 sets the second limit as the engine speed limit value, and the engine speed command value increases until the second limit.

  However, in this case, since the amount of cargo is small and the traveling speed threshold is set to be low, the traveling speed reaches the traveling speed type position at a time point 701 earlier than the case of FIG. 8 (time point 601).

  After the time point 701 when the travel speed exceeds the travel speed threshold value, the limit value of the engine speed command is the first value until the time point 702 when the travel speed decreases and falls below the travel speed threshold value by, for example, decreasing the accelerator pedal depression amount. Keep in limits. As a result, it takes longer to travel at the first engine speed than when the load is large, so that the fuel consumption can be reduced.

  At a time 703 when the work machine lever operation amount exceeds a predetermined work machine lever operation amount threshold value 730, the engine speed limit unit 332 interrupts execution of the engine speed limit process, and according to the accelerator operation amount and load at that time Increases to engine speed.

  In the present embodiment configured as described above, it is determined whether the high load operation is likely to occur based on the load amount and the traveling speed, and when it is determined that the possibility is low, the engine speed is set. It was set as the structure which positively increases the time to reduce. By controlling in this way, the smaller the load amount and the higher the traveling speed, the longer the time during which the engine speed is reduced, and the shortage of the engine output during high load conditions is avoided, while the fuel consumption during high-speed traveling is reduced. It can be effectively reduced.

  Furthermore, in the above embodiment, whether or not the work implement lever 222 is operated is also taken into consideration in step 510 in FIG. Then, when the work implement lever 222 is operated, it is determined that there is a high possibility that a high load operation will occur, and the execution of the engine speed command limiting process in step 514 of FIG. 5 is interrupted. With this configuration, since the increase in engine speed can be started before actual high load operation is performed, it is possible to avoid a shortage of engine output when the high load operation is actually performed.

[Power transmission device 210]
Finally, a specific example of the power transmission device 210 will be described with reference to FIGS. FIG. 11 is a system configuration diagram of an example of a wheel loader that employs an HST system that converts engine power into hydraulic pressure and transmits it to the wheel 1 as the power transmission device 210. The wheel loader shown in this figure includes a hydraulic pump 171 connected to the output shaft of the engine 201 and a hydraulic motor 172 that is rotationally driven by pressure oil discharged from the hydraulic pump 171. The hydraulic motor 172 rotationally drives each wheel 1 via an axle (propeller shaft) 215.

  The power transmission device 210 of FIG. 12 drives the wheel 1 via the power transmission mechanical unit 173 by the engine 201 and also drives the hydraulic pump 171 via the power transmission mechanical unit 173 by the engine 201 to apply pressure oil to the hydraulic motor 172. 1 is a system configuration diagram of an example of a wheel loader adopting an HMT system in which a hydraulic motor 172 drives a wheel 1. In the wheel loader shown in this figure, the power transmission mechanical unit 173 is a mechanical mechanism that mechanically connects the output shaft of the engine 201, the axle 215, and the hydraulic pumps 211 and 171. For example, there is one using a planetary gear. .

  FIG. 13 is a system configuration diagram of an example of a wheel loader that employs a hybrid system that converts engine power into electricity and transmits it to the wheel 1 as the power transmission device 210. The wheel loader shown in this figure includes a motor generator (motor / generator (M / G)) 176 that is mechanically connected to the engine 201 and driven by the engine 1, an inverter device 177 that controls the motor generator 176, and A traveling motor 179 that is attached to the propeller shaft 215 via the differential gear (Dif) and the gear (G) and drives the four wheels 1, an inverter device 180 that controls the traveling motor 179, and an inverter 177 via the DCDC converter 182. , 180 (motor generator 6, travel motor 9) and a power storage device (for example, a secondary battery or a capacitor) 181 that is connected to inverters 177, 180 and is connected to inverter 177, 180. The hybrid system shown in FIG. 13 has a so-called series type (series type) configuration, but a parallel type (parallel type) hybrid system can also be used.

[Additional notes]
In the above description, the engine speed limit value is changed depending on whether the travel speed exceeds the travel speed threshold (whether there is an engine speed limit command). However, after the travel speed exceeds the travel speed threshold, You may perform control which makes an engine speed limit value small, so that the difference of a driving speed threshold value becomes large.

  In the above example, the travel speed threshold value is determined based on the load amount in the bucket 151, but the travel speed threshold value may be determined based on an increased weight from the vehicle weight. The increased weight may or may not include the actual weight (body weight) of the passenger or the like, which is a variable value, or the assumed weight. In this paper, it is a concept including these, and the increased weight from a predetermined vehicle weight value is called “loading amount”.

  The work vehicle to which the present invention is applied includes not only the wheel loader described above but also a forklift and a dump truck. In this case, the work machine includes a hydraulic cylinder and a dump truck bed in a lifting device that lifts and lowers the fork of the forklift. This corresponds to a hydraulic cylinder (hoist cylinder) for raising and lowering (vessel).

  The present invention is not limited to the above-described embodiment, and includes various modifications within the scope not departing from the gist of the present invention. For example, the present invention is not limited to the one having all the configurations described in the above embodiment, and includes a configuration in which a part of the configuration is deleted. In addition, part of the configuration according to one embodiment can be added to or replaced with the configuration according to another embodiment.

  Each configuration related to the above-described control device 240, functions and execution processing of each configuration, etc. are realized by hardware (for example, logic for executing each function is designed by an integrated circuit). Also good. The configuration related to the control device 240 may be a program (software) that realizes each function related to the configuration of the control device 240 by being read and executed by an arithmetic processing device (for example, a CPU). Information related to the program can be stored in, for example, a semiconductor memory (flash memory, SSD, etc.), a magnetic storage device (hard disk drive, etc.), a recording medium (magnetic disk, optical disc, etc.), and the like.

  DESCRIPTION OF SYMBOLS 100 ... Wheel loader, 110 ... Vehicle body, 150 ... Working machine (working apparatus), 151 ... Bucket, 152 ... Lift cylinder, 153 ... Bucket cylinder, 154 ... Z link 155... Lift arm 201 201 engine 210 drive force transmission device 211 hydraulic pump 212 control valve 220 lift cylinder bottom pressure detector 221 .. Bucket cylinder bottom pressure detector, 222... Working machine lever (operating device), 223... Traveling speed detector, 224 ... Accelerator operation amount detector, 225. 230 ... electronic governor 240 ... control device 330 ... second engine speed command value setting unit 331 ... high load prediction unit 332 ... d Jin rotational speed limiting section, 333 ... hydraulic pump upper limit torque setting unit, 334 ... torque decrease flag output unit, 336 ... first engine rotation speed command value setting portion

Claims (3)

Engine,
Wheels,
A working device driven by at least one actuator;
An operating device for controlling the operation of the at least one actuator;
A power transmission device for converting the power output from the engine into hydraulic pressure or electricity and transmitting it to the wheels;
A control device configured to control the rotational speed of the engine within a range equal to or less than a limit value in response to an output request command to the engine, wherein an actual traveling speed of the work vehicle is set to a load amount of the work vehicle. And a control device configured to execute a restriction process for setting the restriction value to a lower value than when the actual traveling speed is equal to or less than the threshold value when a threshold value determined in response thereto is exceeded. Feature work vehicle. The work vehicle according to claim 1,
The at least one actuator uses the engine as an indirect power source;
The control device performs the restriction process while the operation device is being operated even when the actual traveling speed of the work vehicle exceeds a threshold value determined according to a load amount of the work vehicle. A work vehicle characterized by being suspended. The work vehicle according to claim 2,
The work vehicle is characterized in that the threshold value is set to be smaller as a load amount of the work vehicle is smaller.

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