Work vehicle and work vehicle control method

Abstract

To provide a work vehicle capable of improving operability when repeating traveling and work, and a control method for the work vehicle.SOLUTION: A work vehicle 1 comprises a travel device 10 that is operated by travel operation means 42 and brake operation means 44, and work devices 12 and 14 that are hydraulically operated. The work vehicle also comprises a main brake circuit 60 for generating a brake force according to control input when the brake operation means 44 is put into an operational state, and an auxiliary brake circuit 70 for generating a predetermined brake force when the travel operation means 42 is put into a nonoperational state.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a work vehicle and a method for controlling a work vehicle. [Background technology]

[0002] As an example of a working vehicle, a wheeled hydraulic excavator has been known which has a lower body to which tires are attached, an upper body disposed on the lower body, and a working device attached to the lower body or the upper body and operated by hydraulic pressure (i.e., hydraulic oil at a predetermined pressure).

[0003] Wheeled hydraulic excavators are equipped with hydraulically operated brake devices. The brake devices are usually used as service brakes to slow down or stop the vehicle while it is moving, but they can also be used as work brakes to firmly hold the vehicle stationary during excavation work and other operations (this is sometimes referred to as "applying the work brakes").

[0004] In the latter case, it is common to operate the brake device continuously by operating a switch installed in the driver's cab to hydraulically lock the brake device (see Patent Document 1: JP 2013-147148 A), or by engaging a locking mechanism when the brake pedal is fully depressed. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2013-147148 Summary of the Invention [Problem to be solved by the invention]

[0006] However, in the above configuration, applying the work brake requires pressing a switch or locking the brake pedal with a locking mechanism, which can be cumbersome when frequently switching between traveling and working. [Means for solving the problem]

[0007] The present invention has been made in view of the above circumstances, and has as its object to provide a work vehicle and a control method for a work vehicle that can improve operability when repeatedly traveling and working.

[0008] The present invention solves the above problems by the solution means described below as one embodiment.

[0009] A work vehicle according to one embodiment is a work vehicle equipped with a travel device operated by a travel operation means and a brake operation means, and a hydraulically operated working device, and the work vehicle is equipped with a main brake circuit that generates a braking force according to the amount of operation of the brake operation means when the brake operation means is in an operated state, and an auxiliary brake circuit that generates a predetermined braking force when the travel operation means is in a non-operated state. an HST that drives the traveling device; and a control device that controls the operation of at least the traveling device and the HST; Equipped with When the travel operating means is in a non-operated state, the control device reduces an output current value that controls the operation of the HST, and when the output current value becomes zero, outputs a first signal to the auxiliary brake circuit to generate an intermediate brake force that is set between zero brake force and a set maximum brake force as the predetermined brake force. The following are requirements.

[0010] According to the above configuration, the work brake can be applied by setting the travel operating means to a non-operated state. Therefore, there is no need to press a switch or lock the brake pedal with a locking mechanism to apply the work brake, improving operability when frequently alternating between travel and work.

[0012] Preferably, the auxiliary brake circuit has a solenoid valve that controls the predetermined braking force based on a control signal output from the control device.

[0013] Furthermore, it is preferable that, after outputting the first signal for a predetermined time, the control device outputs a second signal to the auxiliary brake circuit to generate the set maximum brake force as the predetermined brake force when the vehicle speed is zero, and continues to output the first signal to the auxiliary brake circuit to generate the intermediate brake force as the predetermined brake force when the vehicle speed is not zero.

[0014] It is also preferable that the control device performs control such that the predetermined time is set relatively short in the low-speed traveling mode and set relatively long in the high-speed traveling mode.

[0015] A control method for a work vehicle according to one embodiment is a control method for a work vehicle equipped with a travel device operated by a travel operation means and a brake operation means, and a hydraulically operated work device, wherein when the brake operation means is in an operated state, a braking force corresponding to the amount of operation is generated, and when the travel operation means is in a non-operated state, When the travel operating means is in a non-operated state, an output current value that controls the operation of the HST that drives the travel device is reduced, and when the output current value becomes zero, an intermediate brake force that is set between zero brake force and a set maximum brake force is generated as a predetermined brake force. The following are requirements. [Effects of the Invention]

[0016] According to a work vehicle and a method for controlling a work vehicle according to one embodiment, operability can be improved when traveling and working are repeated. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a perspective view showing an example of a work vehicle according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic diagram for explaining the brake system in the work vehicle shown in FIG. [Figure 3] FIG. 3 is a flowchart showing an example of the processing contents of the control device relating to the automatic work brake function. [Figure 4] FIG. 4 is a schematic diagram showing an example of a timing chart corresponding to the flowchart of FIG. [Figure 5]FIG. 5 is a schematic diagram showing another example of a timing chart corresponding to the flowchart of FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. Fig. 1 is a schematic diagram (perspective view from above the left front) showing an example of a work vehicle 1 according to this embodiment. For ease of explanation, arrows may be used in the drawings to indicate up / down, left / right, and front / rear directions. In addition, in all drawings used to explain the embodiment, members having the same function are given the same reference numerals, and repeated explanations may be omitted.

[0019] As shown in FIG. 1, the work vehicle 1 comprises a drivable lower body 2, a rotatable upper body 3 disposed on the lower body 2, hydraulically operated working devices 12 and 14 attached to the lower body 2 and the upper body 3, and a driver's cab 16 disposed on the upper body 3.

[0020] The lower body 2 is equipped with a traveling device 10 for traveling. The traveling device 10 has a four-wheel drive configuration in which two traveling wheels 18, each with a tire fitted on the outer periphery of the wheel, are arranged on the front and rear sides.

[0021] The work vehicle 1 is equipped with a blade 20 driven by a hydraulic cylinder 30 as an example of a working implement 12. The work vehicle 1 is equipped with a boom 22, an arm 24, and a detachable attachment 26, each driven by hydraulic cylinders 32, 34, and 36, as an example of a working implement 14. Note that, although a bucket is shown as an example of the attachment 26, this is not limiting. The drive mechanism for driving each hydraulic cylinder is made up of, for example, a hydraulic pump (not shown) driven by a drive source, a control valve (not shown), and the like.

[0022] The work vehicle 1 is also equipped with an engine (e.g., a diesel engine, a gasoline engine, etc.) 38 that burns fuel (e.g., diesel oil, gasoline, etc.) as the drive source. The drive source may be configured to use an electric motor, or may be configured to use both an engine and an electric motor (a so-called hybrid system) (neither of which is shown).

[0023] The driver's cab 16 is equipped with a travel pedal 42 as a travel operation means for starting and accelerating the work vehicle 1. The driver's cab 16 is also equipped with a brake pedal 44 as a brake operation means for decelerating and stopping the work vehicle 1. Hereinafter, a state in which the operation amount of the pedals 42, 44 is zero may be referred to as "off" (non-operated state), and a state in which the operation amount of the pedals 42, 44 is other than zero (i.e., a state in which the pedals 42, 44 are depressed) may be referred to as "on" (operated state). Note that the travel operation means and the brake operation means are not limited to pedals.

[0024] The work vehicle 1 is equipped with a control device 50 that performs overall control of the work vehicle 1. The control device 50 is signal-connected to the traveling pedal 42. The control device 50 is also signal-connected to various sensors (one example being a vehicle speed sensor, described below) that detect vehicle information for controlling the work vehicle 1. The control device 50 performs calculations based on vehicle information detected by the traveling pedal 42 and various sensors, and outputs the calculation results to each part of the work vehicle 1 as control signals.

[0025] Next, the travel system of the work vehicle 1 will be described.

[0026] The work vehicle 1 is configured to travel using a hydrostatic continuously variable transmission (HST; Hydraulic Static (Hydro-Static) Transmission). Examples of components that drive the traveling device 10 include a traveling hydraulic pump and a traveling hydraulic motor (neither of which are shown). The traveling hydraulic pump is a variable displacement hydraulic pump driven by the engine 38, and is configured to be able to adjust the amount of pressurized oil discharged by changing the tilt angle of a swash plate (not shown). The tilt angle of the swash plate is set based on the output current (control signal) value output from the control device 50 in response to the amount of operation of the traveling pedal 42. The traveling hydraulic motor is a hydraulic motor driven by pressurized oil delivered from the traveling hydraulic pump. The traveling hydraulic motor is connected to a gear case, and power is transmitted from the gear case to the rear axle, and from the gear case to the front axle via a propeller shaft (neither of which are shown).

[0027] The front axle is provided with a vehicle speed sensor (not shown) that detects vehicle speed information (for example, the rotation speed of a gear (not shown)). The control device 50 calculates the vehicle speed based on the vehicle speed information output from the vehicle speed sensor.

[0028] The work vehicle 1 is also equipped with a speed change mechanism (not shown) that switches between at least a "low-speed traveling mode" and a "high-speed traveling mode." The speed change mechanism is configured to include a speed change control valve (not shown), and switches the traveling mode based on a control signal output from the control device 50. For example, the low-speed traveling mode is a traveling mode in which the rotation speed of the traveling hydraulic motor is low and the driving force is large. On the other hand, the high-speed traveling mode is a traveling mode in which the rotation speed of the traveling hydraulic motor is high and the driving force is small. Note that the work vehicle 1 may be configured to have other traveling modes as well.

[0029] Next, the brake system of the work vehicle 1 will be described with reference to the schematic diagram shown in Fig. 2. In Fig. 2, solid lines simply indicate connections in the hydraulic system, and dashed lines simply indicate connections in the electrical signal system. However, Fig. 2 only shows the main parts related to this embodiment.

[0030] The work vehicle 1 is equipped with a hydraulic pump 46 driven by the engine 38, and a brake device 52 that operates using pressurized oil supplied from the hydraulic pump 46. As an example, the brake device 52 is a typical hydraulic disc brake that includes a disc rotor (not shown) that rotates together with each running wheel 18, a brake pad (not shown) that serves as a friction material, and a hydraulic brake cylinder 54 that presses the brake pad against the disc rotor, and is configured to generate a braking force (friction force) that corresponds to the pressing force of the brake pad.

[0031] Here, the work vehicle 1 is equipped with a main brake circuit 60 and an auxiliary brake circuit 70 connected in parallel to the main brake circuit 60 as hydraulic circuits that supply pressure oil from the hydraulic pump 46 to the brake device 52. The main brake circuit 60 and the auxiliary brake circuit 70 are connected to the brake device 52 via a shuttle valve 80.

[0032] The main brake circuit 60 is equipped with a brake valve 62 whose opening is set in accordance with the amount of operation of the brake pedal 44. As a result, the pressure oil that flows into the main brake circuit 60 is adjusted to a flow rate that corresponds to the opening of the brake valve 62 and is then sent to the shuttle valve 80.

[0033] The main brake circuit 60 also includes a relief valve 64 located upstream of the brake valve 62, and an accumulator 66 connected between the brake valve 62 and the relief valve 64. The relief valve 64 is a pressure control valve that maintains the downstream pressure at a set value. The accumulator 66 is a supply source of pressurized oil when the engine 38 is stopped, for example.

[0034] The auxiliary brake circuit 70 is equipped with a brake valve 72 whose opening is set based on a control signal output from the control device 50. As a result, the pressure oil that flows into the auxiliary brake circuit 70 is adjusted to a flow rate corresponding to the opening of the brake valve 72 and sent to the shuttle valve 80. As an example, the brake valve 72 is a proportional solenoid valve. This enables high-speed and accurate flow rate control.

[0035] The auxiliary brake circuit 70 also includes a switching valve 74 disposed upstream of the brake valve 72. The switching valve 74 is a normally closed solenoid valve that operates in conjunction with the brake valve 72 based on a control signal output from the control device 50. The switching valve 74 suppresses leakage of pressure oil at the brake valve 72 (outflow of pressure oil to the hydraulic oil tank 48) and reduces the operating load of each hydraulic device, including the hydraulic pump 46.

[0036] The shuttle valve 80 is a high-pressure selection valve that selects the higher-pressure oil between the pressurized oil (main brake circuit pressure) delivered from the main brake circuit 60 and the pressurized oil (auxiliary brake circuit pressure) delivered from the auxiliary brake circuit 70 and supplies it to the brake device 52.

[0037] Therefore, when the brake pedal 44 is depressed to operate the brake valve 62 and the main brake circuit pressure becomes greater than the auxiliary brake circuit pressure, pressure oil that has passed through the main brake circuit 60 is supplied to the brake device 52 via the shuttle valve 80. As a result, the brake device 52 operates in response to depression of the brake pedal 44, and can be used as a service brake while the vehicle is traveling.

[0038] On the other hand, when the brake valve 72 is actuated by a control signal output from the control device 50 and the auxiliary brake circuit pressure becomes greater than the main brake circuit pressure, the pressure oil that has passed through the auxiliary brake circuit 70 is supplied to the brake device 52 via the shuttle valve 80. This causes the brake device 52 to actuate regardless of whether the brake pedal 44 is depressed, and the brake device 52 can be used as a work brake during work.

[0039] In this embodiment, the control device 50 outputs a control signal to open the brake valve 72 to a predetermined opening when the traveling pedal 42 is released. Therefore, when the traveling pedal 42 is released, the pressure oil that has flowed into the auxiliary brake circuit 70 is adjusted to a predetermined flow rate and sent to the shuttle valve 80 (supplied to the brake device 52). In other words, the auxiliary brake circuit 70 is a hydraulic circuit that generates a predetermined braking force when the traveling pedal 42 is released.

[0040] In this way, the work vehicle 1 is equipped with a function (hereinafter sometimes referred to as the "automatic work brake function") that automatically applies the work brakes when the travel pedal 42 is turned off as a trigger. This eliminates the need to press a switch to apply the work brakes or to engage the brake pedal with a locking mechanism (travel and work braking can be controlled simply by operating (on / off) the travel pedal 42). This improves operability when traveling and working are frequently repeated.

[0041] Furthermore, the work vehicle 1 in this embodiment has excellent assembly properties because it achieves the automatic work braking function with a simple mechanism and hydraulic circuit. As an application example of this embodiment, it is also possible to retrofit an automatic work braking function to an existing work vehicle equipped with only the main brake circuit 60 by attaching the auxiliary brake circuit 70 and shuttle valve 80.

[0042] The automatic work brake function is turned on and off by an automatic work brake switch 82 provided in the cab 16. The automatic work brake switch 82 is signal-connected to the control device 50. When the automatic work brake function is turned on, the control device 50 is able to output control signals that drive the brake valve 72 and the switching valve 74. At this time, an icon indicating that the automatic work brake function is on is displayed on the cluster provided in the cab 16 (neither is shown).

[0043] Next, the processing contents of the control device 50 related to the automatic work brake function will be described. Fig. 3 is a flowchart showing the processing contents of the control device 50. Fig. 4 is a schematic diagram showing an example of a timing chart corresponding to the flowchart of Fig. 3, and shows the operation state of the travel pedal 42, the output signal value that controls the operation of the HST (that drives the swash plate of the travel hydraulic pump), the control signal value that drives the brake valve 72, the control signal value that drives the switching valve 74, and changes over time in the vehicle speed of the work vehicle 1. Fig. 5 is a schematic diagram showing another example of a timing chart corresponding to the flowchart of Fig. 3.

[0044] In step S1, the control device 50 determines whether the automatic work brake function is on or off. When the control device 50 determines that the automatic work brake function is on, the process proceeds to step S2. On the other hand, when the control device 50 determines that the automatic work brake function is off, there is no need to control the automatic work brake, and the process flow reaches END.

[0045] In step S2, the control device 50 determines whether the traveling pedal 42 is on or off. If the control device 50 determines that the traveling pedal 42 is off, the process proceeds to step S3. On the other hand, if the control device 50 determines that the traveling pedal 42 is on, the process flow reaches END.

[0046] In step S3, the control device 50 reduces the output current value that drives the swash plate of the traveling hydraulic pump to 0. After step S3, the process proceeds to step S4.

[0047] In step S4, control device 50 performs control to generate an intermediate braking force over a predetermined time Ta (between time t2 and time t4). The intermediate braking force is a braking force that is set between zero braking force and a set maximum braking force, which will be described later, and its purpose is to reduce the vehicle speed of work vehicle 1 to zero. Specifically, control device 50 outputs a first signal to auxiliary brake circuit 70 to switch (turn on) selector valve 74 from position A to position B, and set brake valve 72 to a predetermined opening (opening that allows pressure oil to flow at a flow rate that generates the intermediate braking force). After step S4, the process proceeds to step S5.

[0048] In step S5, the control device 50 determines whether the vehicle speed of the work vehicle 1 is zero. In this embodiment, the control device 50 is able to make this determination based on vehicle speed information detected by the vehicle speed sensor described above. If the control device 50 determines that the vehicle speed is zero, the process proceeds to step S8. On the other hand, if the control device 50 determines that the vehicle speed is not zero, the process proceeds to step S6.

[0049] In step S6, the control device 50 performs control to continuously maintain the intermediate braking force. After step S6, the process proceeds to step S7.

[0050] In step S7, the control device 50 determines whether the vehicle speed of the work vehicle 1 is zero. If the control device 50 determines that the vehicle speed is zero, the process proceeds to step S8. On the other hand, if the control device 50 determines that the vehicle speed is not zero, the process returns to the position before step S6 (i.e., the control device 50 performs control to continue to maintain the intermediate braking force).

[0051] In step S8, the control device 50 performs control to generate a set maximum braking force. The set maximum braking force is a braking force that firmly holds the work vehicle 1 stopped during work. Specifically, the control device 50 outputs a second signal to the auxiliary brake circuit 70 to set the brake valve 72 to a predetermined opening (an opening that allows pressure oil to flow at a flow rate that generates the set maximum braking force).

[0052] According to this embodiment, the control device 50 performs stepwise brake control, generating an intermediate braking force for at least the predetermined time Ta and then generating a set maximum braking force, thereby preventing sudden braking when the work brakes are applied. Also, even if a malfunction occurs in the vehicle speed sensor, causing the vehicle speed to be determined to be zero even when the work vehicle 1 is traveling, for example, it is possible to prevent the set maximum braking force from being suddenly generated and causing sudden braking.

[0053] Furthermore, the control device 50 determines the vehicle speed after generating the intermediate braking force (at time t4), and if the vehicle speed is not zero, performs control to continue maintaining the intermediate braking force, so that the set maximum braking force can be generated when the work vehicle 1 has reliably stopped (at time t4').This makes it possible to achieve good braking that does not cause discomfort to the worker.

[0054] Furthermore, it is preferable that the control device 50 determines whether the vehicle is in low-speed traveling mode or high-speed traveling mode, and when it determines that the vehicle is in low-speed traveling mode, sets the predetermined time Ta relatively short, and when it determines that the vehicle is in high-speed traveling mode, sets the predetermined time Ta relatively long. In this way, by configuring the vehicle 1 so that the application time (predetermined time) Ta of the intermediate braking force can be set according to the traveling state of the work vehicle 1, the work brakes can be applied efficiently.

[0055] As one example, a delay time T1 (between time t1 and time t2) is set between when the travel pedal 42 is turned off and when the intermediate braking force is generated, thereby preventing abrupt changes in the behavior of the work vehicle 1.

[0056] Furthermore, it is preferable that the intermediate braking force and the set maximum braking force are gradually increased. In this embodiment, a signal filter 84 is provided between the control device 50 and the brake valve 72. By providing the signal filter 84, the control device 50 can output control signals (first signal and second signal) to the brake valve 72 with delay times T2 (between time t2 and time t3) and T3 (between time t4 (t4') and time t5), thereby enabling the intermediate braking force and the set maximum braking force to be gradually increased. This allows for better braking. Here, it is preferable that the delay time T2 is set relatively short in the low-speed traveling mode and relatively long in the high-speed traveling mode.

[0057] As described above, the above-described work vehicle and work vehicle control method can improve operability when repeatedly traveling and working.

[0058] The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the scope of the present invention. In particular, the description has been given using an example of an automatic work brake function that generates an intermediate brake force and a set maximum brake force in stages, but the control may be such that only the set maximum brake force is generated, or the control may be such that another brake force is additionally generated. [Explanation of symbols]

[0059] 1. Work vehicles 10 Running gear 12, 14 Work equipment 42 Travel pedal 44 Brake pedal 50 Control device 52 Brake device 60 Main brake circuit 62 Brake valve 70 Auxiliary brake circuit 72 Brake valve 80 Shuttle valve

Claims

1. A work vehicle equipped with a travel device operated by a travel operation means and a brake operation means, and a hydraulically operated work device, a main brake circuit that generates a brake force corresponding to an amount of operation of the brake operating means when the brake operating means is in an operated state; an auxiliary brake circuit that generates a predetermined braking force when the travel operating means is in a non-operated state; an HST that drives the traveling device; a control device that controls the operation of at least the traveling device and the HST, When the travel operating means is in a non-operated state, the control device reduces an output current value that controls the operation of the HST, and when the output current value becomes zero, outputs a first signal to the auxiliary brake circuit to generate an intermediate brake force that is set as the predetermined brake force between zero brake force and a set maximum brake force. A work vehicle characterized by:

2. The auxiliary brake circuit has a solenoid valve that controls the predetermined braking force based on a control signal output from the control device.

2. The work vehicle according to claim 1, wherein:

3. After outputting the first signal for a predetermined time, the control device When the vehicle speed is zero, a second signal is output to the auxiliary brake circuit to generate the set maximum brake force as the predetermined brake force; When the vehicle speed is not zero, the first signal for generating the intermediate braking force as the predetermined braking force is continuously output to the auxiliary brake circuit.

3. The work vehicle according to claim 1 or 2, wherein:

4. The control device performs control to set the predetermined time relatively short in a low-speed running mode and to set the predetermined time relatively long in a high-speed running mode.

4. The work vehicle according to claim 3, wherein:

5. A control method for a work vehicle equipped with a travel device operated by a travel operation means and a brake operation means, and a hydraulically operated work device, comprising: When the brake operating means is in an operated state, a braking force is generated in accordance with the amount of operation, When the travel operating means is in a non-operated state, an output current value for controlling the operation of the HST that drives the travel device is reduced, and when the output current value becomes zero, an intermediate brake force set between zero brake force and a set maximum brake force is generated as a predetermined brake force. A method for controlling a work vehicle, comprising:

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