Work machine

Abstract

In a wheel loader 1, a hydraulic circuit 60 has a fifth oil passage (bypass oil passage) L5 that branches from a branch point 65 provided between a proportional solenoid valve (control valve) 62 and a switching solenoid valve (switching valve) 64 and that connects to a hydraulic oil tank 32, and a throttle (bypass regulation part) 66. When an obstruction is detected by an obstruction detection sensor (obstruction detection device) 54, a brake ECU (control device) 70 places the switching solenoid valve 64 in an open state and outputs controlling hydraulic pressure from the proportional solenoid valve 62. When no obstruction is detected by the obstruction detection sensor 54, the brake ECU places the switching solenoid valve 64 in a closed state and interrupts the output of the controlling hydraulic pressure from the proportional solenoid valve 62.

Description

Working machine

[0001] The present invention relates to a working machine such as a wheel loader provided with a working device such as a bucket.

[0002] Conventionally, as a driving support technology for ensuring safety around a working machine, a technology related to a working machine that activates an automatic brake when an obstacle is detected around the vehicle body is known. For example, Patent Document 1 discloses a wheel loader that supplies hydraulic pressure to a hydraulic brake device to activate an automatic brake when an obstacle is detected around the vehicle body.

[0003] Japanese Patent No. 7002634

[0004] However, in a working machine provided with a hydraulic automatic brake system as described in Patent Document 1, when the automatic brake is not activated, the hydraulic oil remains in the hydraulic circuit for a long time, which lowers the oil temperature of the hydraulic oil and increases the viscosity of the hydraulic oil, which may affect the responsiveness of the automatic brake. On the other hand, activating the automatic brake to suppress the hydraulic oil from remaining in the hydraulic circuit will interfere with the operation of the driver of the working machine.

[0005] The present invention has been made in view of such problems, and an object of the present invention is to provide a working machine that can ensure the responsiveness of an automatic brake even when the hydraulic oil is at a low temperature without interfering with the driver's operation.

[0006] To achieve the above objective, the work machine of the present invention includes a drivable vehicle body, a work device attached to the front of the vehicle body, a hydraulic brake device for applying braking force to the vehicle body, an obstacle detection device for detecting obstacles present around the vehicle body, a control valve that adjusts and outputs the hydraulic pressure of hydraulic fluid supplied from a hydraulic fluid supply source to a predetermined control hydraulic pressure, a hydraulic circuit including a switching valve that switches between an open state in which hydraulic pressure based on the control hydraulic pressure output from the control valve is supplied to the brake device and a closed state in which hydraulic pressure based on the control hydraulic pressure is not supplied to the brake device, and the control valve and the switching valve A work machine comprising a control device for controlling a hydraulic circuit, wherein the hydraulic circuit has a bypass oil passage that branches off from a branching point provided between the control valve and the switching valve and is connected to a tank, and a bypass restricting section that restricts the flow of the hydraulic fluid in the bypass oil passage to the tank, and the control device opens the switching valve and outputs control hydraulic pressure from the control valve when an obstacle is detected by the obstacle detection device, and closes the switching valve and shuts off the output of control hydraulic pressure from the control valve when no obstacle is detected by the obstacle detection device.

[0007] According to the present invention, the responsiveness of the automatic brake can be ensured even when the hydraulic fluid is at a low temperature, without interfering with the operator's operation.

[0008] This is a schematic diagram showing a wheel loader. This is a schematic diagram showing a portion of the hydraulic equipment and hydraulic circuit, including the automatic braking system of the first embodiment. This is a schematic diagram showing the automatic braking system of the first embodiment. This is a flowchart showing an example of automatic brake control. This is an explanatory diagram showing an example of a map defining the relationship between standby pressure and oil temperature. This is a schematic diagram showing a portion of the hydraulic equipment and hydraulic circuit, including the automatic braking system of the second embodiment. This is a schematic diagram showing a portion of the hydraulic equipment and hydraulic circuit, including the automatic braking system of the third embodiment.

[0009] An embodiment of the present invention will be described below with reference to the drawings. In the following description, the vehicle's longitudinal direction, lateral direction (vehicle width direction), and vertical direction will be described primarily from the perspective of the driver riding in the work machine.

[0010] [First Embodiment] Figure 1 is a schematic diagram showing a wheel loader 1. Figure 2 is a schematic diagram showing a part of the hydraulic equipment and hydraulic circuit including the automatic brake system 50A of the first embodiment. The wheel loader 1 as a work machine according to the embodiment is a work machine that performs cargo handling operations, for example, at a work site, excavating work objects such as soil and minerals, and transporting the excavated work objects to other loading destinations such as dump trucks and hoppers.

[0011] As shown in Figure 1, the wheel loader 1 has a front body (body) 1a equipped with a pair of left and right front wheels 2a, and a rear body (body) 1b equipped with a pair of left and right rear wheels 2b. In the following description, each front wheel 2a and each rear wheel 2b will be referred to as wheel 2 as appropriate. The front body 1a and the rear body 1b are rotatably connected to each other by a center pin, and the front body 1a is configured to bend left and right toward the rear body 1b by the driver operating a steering wheel (not shown).

[0012] A working device 10 is provided at the front of the front body 1a. The working device 10 includes an arm 11 and a bucket 13. The arm 11 is mounted to the front body 1a so as to be able to swing up and down. The arm 11 is rotationally driven by the extension and retraction of a hydraulic arm cylinder 11a. The bucket 13 is a working tool mounted to the tip of the arm 11 so as to be able to swing up and down. The bucket 13 is rotationally driven via a bell crank 15 by the extension and retraction of a hydraulic bucket cylinder 13a.

[0013] Meanwhile, the rear body 1b is equipped with a driver's cab 5 where the driver sits, an engine room 6, and a counterweight 7 for maintaining the balance of the vehicle. The driver's cab 5 is equipped with various operating devices for the driver to operate the wheel loader 1. Specifically, the driver's cab 5 is equipped with an arm operating lever 16 for operating the arm 11 shown in Figure 2, a bucket operating lever 17 for operating the bucket 13, an accelerator pedal (not shown) for driving the wheel loader 1, a steering wheel (not shown), and a brake pedal 19 for operating the brake device 40.

[0014] The engine compartment 6 houses the engine 20 shown in Figure 2. The engine 20 is an internal combustion engine, such as a diesel engine. The engine 20 outputs driving force to each wheel 2. The driving force from the engine 20 is appropriately shifted (reduced) by the transmission 22 and transmitted to the front and rear axles 24 via the propeller shaft 23. Furthermore, the driving force transmitted to each axle 24 is transmitted to the left and right wheels 2 via differential gears and final reduction gears (not shown) within each axle 24.

[0015] Furthermore, the rear body 1b is equipped with a main pump 30 that supplies hydraulic fluid to various hydraulic devices such as the bucket cylinder 13a and the arm cylinder 11a. The main pump 30 is driven by the engine 20 and draws hydraulic fluid from a hydraulic fluid tank (tank) 32 mounted on the rear body 1b and discharges it. The hydraulic fluid discharged from the main pump 30 is supplied to the various hydraulic devices such as the bucket cylinder 13a and the arm cylinder 11a from a control valve 34 mounted on the front body 1a, for example. The control valve 34 is configured to switch the hydraulic fluid supply passages to the bucket cylinder 13a and the arm cylinder 11a in response to the driver's operation of the arm operation lever 16 and the bucket operation lever 17.

[0016] (Braking System) The wheel loader 1 is equipped with a braking system 40 that applies braking force to each wheel 2. The braking system 40 includes a plurality of disc brakes 42 and a brake valve 44 that adjusts the pressure of the hydraulic fluid supplied to each disc brake 42. The disc brakes 42 are wet friction brakes provided for each wheel 2. Each disc brake 42 applies friction braking force to the corresponding wheel 2 in accordance with the hydraulic pressure supplied from the brake valve 44. Each disc brake 42 is housed in the cases of the front and rear axles 24.

[0017] The brake valve 44 is connected to an accumulator 46 that temporarily stores the hydraulic pressure of the hydraulic fluid discharged from the main pump 30. When the brake pedal 19 is not pressed by the driver, the brake valve 44 shuts off the supply of hydraulic pressure from the accumulator 46 to each disc brake 42. On the other hand, when the brake pedal 19 is pressed by the driver, the brake valve 44 opens up to reduce the hydraulic pressure supplied from the accumulator 46 according to the amount the brake pedal 19 is pressed and supplies it to each disc brake 42. The brake valve 44 operates so that the greater the amount the brake pedal 19 is pressed, the higher the pressure supplied to each disc brake 42. The brake valve 44 is also configured to operate when a control hydraulic pressure Pc, described later, is supplied to the pilot signal pressure input port 441. The brake valve 44 operates so that the greater the supplied control hydraulic pressure Pc, the greater the hydraulic pressure supplied to each disc brake 42.

[0018] (Automatic Brake System) Furthermore, the wheel loader 1 is equipped with an automatic brake system that automatically applies braking force from the brake device 40 to each wheel 2 when an obstacle is detected around the vehicle body (hereinafter referred to as "automatic brake"). Figure 3 is a schematic configuration diagram showing the automatic brake system 50A. As shown in Figures 2 and 3, the automatic brake system 50A includes the brake device 40, an automatic brake changeover switch 52, an obstacle detection sensor (obstacle detection device) 54, an oil temperature detection sensor 56, a hydraulic circuit 60, and a brake control unit (control device) 70 (hereinafter referred to as "brake ECU 70").

[0019] The automatic brake selector switch 52 is an input switch that allows the driver to instruct whether or not to activate the automatic brake when an obstacle is detected by the automatic brake system 50A. The automatic brake selector switch 52 is located in the driver's cab 5. The automatic brake selector switch 52 outputs the driver's instruction result to the brake ECU 70.

[0020] The obstacle detection sensor 54 is installed at a predetermined position on the rear vehicle body 1b, for example near the counterweight 7, and detects the presence or absence of obstacles behind the rear vehicle body 1b, outputting the detection result to the brake ECU 70. Obstacles include other work machines, workers and various related parties, and structures at the work site. The obstacle detection sensor 54 is, for example, a laser rangefinder or a millimeter-wave radar. Note that the obstacle detection sensor 54 only needs to be capable of detecting obstacles around the vehicle body, and may be attached to the front vehicle body 1a, for example. The wheel loader 1 may also be equipped with an obstacle detection device that detects obstacles by applying known image processing to images captured by an imaging device such as a stereo camera or a monocular camera.

[0021] The oil temperature detection sensor 56 is a sensor that detects the oil temperature T (Figure 5), which is the temperature of the hydraulic fluid used in the wheel loader 1. The oil temperature detection sensor 56 is installed, for example, near the hydraulic fluid tank 32. The oil temperature detection sensor 56 may also detect the oil temperature T of the hydraulic fluid flowing through the hydraulic circuit 60. The oil temperature detection sensor 56 outputs the detected oil temperature T to the brake control unit 70.

[0022] (Hydraulic Circuit) The hydraulic circuit 60 will be described with reference to Figure 2. The hydraulic circuit 60 includes an electromagnetic proportional valve (control valve) 62 and an electromagnetic switching valve (switching valve) 64.

[0023] The electromagnetic proportional valve 62 is a control valve that adjusts the hydraulic pressure of the hydraulic fluid supplied from the main pump 30 to a control hydraulic pressure Pc based on a command signal from the brake ECU 70 and outputs it to the electromagnetic switching valve 64. The electromagnetic proportional valve 62 is connected to the main pump 30 via a pressure reducing valve (not shown).

[0024] The electromagnetic switching valve 64 is connected to the input port 441 of the pilot signal pressure of the electromagnetic proportional valve 62 and the brake valve 44. The electromagnetic switching valve 64 is configured to form an open state in which it outputs the control hydraulic pressure Pc input from the electromagnetic proportional valve 62 as a pilot signal pressure to the brake valve 44, and a closed state in which it does not output the control hydraulic pressure Pc to the brake valve 44, according to the command signal from the brake ECU 70.

[0025] The above-mentioned solenoid proportional valve 62 and solenoid switching valve 64 are connected to the main pump 30, the hydraulic oil tank 32, and the brake valve 44 by multiple oil passages. Specifically, the hydraulic circuit 60 has a first oil passage L1, a second oil passage (first oil passage) L2, a third oil passage (second oil passage) L3, a fourth oil passage (third oil passage) L4, and a fifth oil passage (bypass oil passage) L5.

[0026] The first oil passage L1 is an oil passage connecting the hydraulic fluid discharge port of the main pump 30 and the hydraulic fluid input port of the solenoid proportional valve 62. A pressure reducing valve (not shown) is provided in the middle of the first oil passage L1. The second oil passage L2 is an oil passage extending from the hydraulic fluid output port of the solenoid proportional valve 62. The third oil passage L3 is an oil passage extending from the second oil passage L2 to the hydraulic fluid input port of the solenoid switching valve 64. The fourth oil passage L4 is an oil passage connecting the hydraulic fluid output port of the solenoid switching valve 64 to the pilot signal pressure input port 441 of the brake valve 44. The fifth oil passage L5 is an oil passage extending from the branching point 65, which is the connection point between the second oil passage L2 and the third oil passage L3, toward the hydraulic fluid tank 32. A throttling (bypass restricting section) 66 such as an orifice is provided in the fifth oil passage L5.

[0027] In this configuration, when the electromagnetic switching valve 64 is open, the hydraulic fluid discharged from the main pump 30 is supplied to the electromagnetic proportional valve 62 through the first oil passage L1, adjusted to the control hydraulic pressure Pc by the electromagnetic proportional valve 62, and then supplied to the brake valve 44 through the second oil passage L2 to the fourth oil passage L4. Here, a throttle 66 provided in the fifth oil passage L5 creates a pressure difference between the second oil passage L2 and the fifth oil passage L5, thereby regulating (limiting) the flow rate through the fifth oil passage L5 so as not to exceed what is necessary.

[0028] In contrast, when the electromagnetic switching valve 64 is closed, the hydraulic fluid discharged from the main pump 30 is adjusted to the control hydraulic pressure Pc by the electromagnetic proportional valve 62, as described above, and then flows from the second oil passage L2 through the branching point 65 to the fifth oil passage L5, and is returned to the hydraulic fluid tank 32 and the main pump 30, which serve as the hydraulic fluid supply source. In this case, the pressure upstream of the throttle 66 (on the branching point 65 side) becomes higher than the pressure downstream (on the hydraulic fluid tank 32 side). Thus, the fifth oil passage L5 releases the hydraulic fluid in the hydraulic circuit 60 to the main pump 30 side before the electromagnetic switching valve 64 (bleed-off), and functions as a bypass oil passage for circulating the hydraulic fluid between the hydraulic circuit 60 and the hydraulic fluid tank 32 and the main pump 30. In the following description, the first oil passage L1, the second oil passage L2, and the fifth oil passage L5 will be referred to as the "circulating oil passage Lc" as appropriate.

[0029] Furthermore, in the hydraulic circuit 60, the electromagnetic switching valve 64 is provided within the housing 44h (dotted line in Figure 2) that constitutes the brake valve 44. Also, the branching point 65 is provided within the housing 44h. That is, the branching point 65 is provided within the housing that constitutes the electromagnetic switching valve 64. With this configuration, the hydraulic circuit 60 aims to shorten the third oil passage L3 and the fourth oil passage L4. In the first embodiment, both the third oil passage L3 and the fourth oil passage L4 are formed to be shorter than the second oil passage L2, thereby reducing the pressure loss in the third oil passage L3 and the fourth oil passage L4. However, if the pressure loss in the third oil passage L3 and the fourth oil passage L4 is sufficiently small, the relationship between the lengths of the third oil passage L3 and the fourth oil passage L4 and the second oil passage L2 is not limited to this. Furthermore, the electromagnetic switching valve 64 may be provided at a location other than the housing 44h, and the branching point 65 may be provided at a location other than the housing of the electromagnetic switching valve 64.

[0030] Furthermore, in the hydraulic circuit 60, the branching point 65 is located at a position higher vertically than the brake valve 44. More specifically, the branching point 65 is located at a position higher than the input port 441 for the pilot signal pressure of the brake valve 44. This makes it easier to discharge air accumulated in the fourth oil passage L4 from the branching point 65 to the hydraulic fluid tank 32, for example, immediately after product assembly or after maintenance such as parts replacement. Note that the position of the branching point 65 is not limited to a position higher than the brake valve 44.

[0031] (Brake ECU) Returning to the explanation of Figure 3, the brake ECU 70 is composed of, for example, input / output devices, storage devices, memory (ROM, RAM, non-volatile RAM, etc.), and a central processing unit (CPU). More specifically, the brake ECU 70 includes a storage unit 72, a determination unit 74, and a command signal output unit 76.

[0032] The memory unit 72 stores various data, such as various programs executed by the determination unit 74 and the command signal output unit 76, and data for the hydraulic pressure Pc of the electromagnetic proportional valve 62, which is set according to the control mode of the automatic brake system 50A. The determination unit 74 determines whether the control mode of the automatic brake system 50A should be set to the automatic brake mode or the standby mode, as described later, based on the instruction result from the automatic brake changeover switch 52 and the detection result from the obstacle detection sensor 54, and outputs the determination result to the command signal output unit 76. The command signal output unit 76 receives the determination result from the determination unit 74. The command signal output unit 76 also receives the hydraulic fluid temperature T from the oil temperature detection sensor 56. Based on the received determination result and the oil temperature T, the command signal output unit 76 generates and outputs control signals to the electromagnetic proportional valve 62 and the electromagnetic changeover valve 64.

[0033] (Automatic Brake Control) Next, the details of the automatic brake control performed by the brake ECU 70 will be explained in detail with reference to Figure 4. Figure 4 is a flowchart of an example of automatic brake control. The process shown in Figure 4 is repeatedly performed by the brake ECU 70 at predetermined intervals (for example, a few milliseconds) while the key switch (not shown) of the wheel loader 1 is turned on and the engine 20 is running.

[0034] First, the brake ECU 70, in its determination unit 74, obtains the instruction result from the automatic brake changeover switch 52 regarding whether or not to activate the automatic brake when an obstacle is detected, the detection result of an obstacle around the vehicle body from the obstacle detection sensor 54, and the oil temperature T of the hydraulic fluid detected by the oil temperature detection sensor 56 (step ST1).

[0035] Next, the determination unit 74 determines, based on the information acquired in step ST1, whether or not the automatic brake operation when an obstacle is detected is instructed by the automatic brake changeover switch 52 (step ST2). If the determination unit 74 determines in step ST2 that the automatic brake operation when an obstacle is detected is instructed, it determines whether or not an obstacle has been detected around the vehicle body by the obstacle detection sensor 54 (step ST3). Furthermore, if the determination unit 74 determines in step ST3 that an obstacle has been detected around the vehicle body by the obstacle detection sensor 54, it determines that the control mode of the automatic brake system 50A should be set to automatic brake mode, and outputs the determination result to the command signal output unit 76 (step ST4).

[0036] Upon receiving a determination result from the determination unit 74 indicating that the control mode should be set to automatic brake mode, the command signal output unit 76 opens the electromagnetic switching valve 64 (step ST5). The command signal output unit 76 also sets the hydraulic pressure Pc for controlling the hydraulic fluid discharged from the electromagnetic proportional valve 62 to a predetermined automatic brake pressure P1 stored in the storage unit 72, and controls the electromagnetic proportional valve 62 so that the automatic brake pressure P1 is output (step ST6), and then executes the routine again from the beginning.

[0037] As a result, the hydraulic fluid discharged from the main pump 30 is regulated to an automatic brake pressure P1 by the electromagnetic proportional valve 62 and supplied as a pilot signal pressure to the brake valve 44 from the electromagnetic switching valve 64. Consequently, hydraulic pressure corresponding to the automatic brake pressure P1 is supplied from the brake valve 44 to each disc brake 42, and braking force is applied to each wheel 2. This automatic brake pressure P1 is preset based on experiments and analyses, etc., as the pilot signal pressure that ensures sufficient braking force is applied to each wheel 2 from each disc brake 42, with the aim of avoiding contact between the wheel loader 1 and obstacles.

[0038] In response to this, if the determination unit 74 determines in step ST2 that the automatic brake operation when an obstacle is detected has not been instructed by the automatic brake changeover switch 52, it determines that the control mode should be set to standby mode and outputs the determination result to the command signal output unit 76 (step ST7). Also, if the determination unit 74 determines in step ST3 that no obstacles have been detected around the vehicle body by the obstacle detection sensor 54, it determines that the control mode should be set to standby mode and outputs the determination result to the command signal output unit 76 (step ST7).

[0039] Then, the command signal output unit 76, having obtained a determination result from the determination unit 74 indicating that the control mode should be set to standby mode, closes the electromagnetic switching valve 64 (step ST8). The command signal output unit 76 also sets the control hydraulic pressure Pc of the hydraulic fluid discharged from the electromagnetic proportional valve 62 to a predetermined standby pressure P2 based on the map stored in the storage unit 72 (Figure 5), and controls the electromagnetic proportional valve 62 so that the standby pressure P2 is output (step ST9), and then executes this routine again from the beginning.

[0040] As a result, the hydraulic fluid discharged from the main pump 30 is regulated to a standby pressure P2 by the electromagnetic proportional valve 62 and circulates through the circulating oil passage Lc. Consequently, the hydraulic fluid returned to the hydraulic fluid tank 32 through circulation mixes with the relatively high-temperature hydraulic fluid used in other hydraulic equipment of the wheel loader 1, suppressing the decrease in the oil temperature T of the circulating hydraulic fluid. In addition, the throttle 66 provided in the fifth oil passage L5 and the energy lost in the main pump 30 are converted into thermal energy, causing the oil temperature T to rise. As a result, the decrease in the oil temperature T of the hydraulic fluid, i.e., the increase in viscosity caused by the hydraulic fluid remaining in the hydraulic circuit 60, is suppressed. Therefore, even when operating the wheel loader 1 in a low-temperature environment such as a cold region, it is possible to ensure hydraulic responsiveness in the automatic braking system 50A and activate the automatic brake more quickly when an obstacle is detected.

[0041] Here, the standby pressure P2 is set in advance based on experiments and analyses, as the hydraulic pressure that allows the hydraulic fluid to circulate in the circulating oil passage Lc described above. Figure 5 is an explanatory diagram showing an example of a map that defines the relationship between the standby pressure P2 and the oil temperature T. The command signal output unit 76 obtains the standby pressure P2 corresponding to the oil temperature T obtained in step ST1 from the map shown in Figure 5. As shown in the figure, the standby pressure P2 tends to increase as the oil temperature T decreases.

[0042] More specifically, the standby pressure P2 is set to the maximum value P2max when the oil temperature T is less than the first predetermined value T1. The maximum value P2max is set to a value lower than the automatic brake pressure P1. Furthermore, the standby pressure P2 decreases as the oil temperature T increases within the range of the first predetermined value T1 or higher, and is set to 0 when the oil temperature T is higher than the first predetermined value T1 and equal to or greater than the second predetermined value T2. In other words, when the oil temperature T is equal to or greater than the second predetermined value T2 and the viscosity of the hydraulic fluid is sufficiently low, the circulation of the hydraulic fluid in standby mode is substantially stopped. This stops the circulation of unnecessary hydraulic fluid and improves the fuel efficiency of the wheel loader 1. Note that the standby pressure P2 may also be set to the same value as the automatic brake pressure P1.

[0043] (Effect of the First Embodiment) As described above, in the wheel loader (working machine) 1 of the first embodiment, the hydraulic circuit 60 includes a fifth oil passage (bypass oil passage) L5 branched from a branch point 65 provided between an electromagnetic proportional valve (control valve) 62 and an electromagnetic switching valve (switching valve) 64 and connected to a hydraulic oil tank (tank) 32, and a throttle (bypass restricting portion) 66 that restricts the flow of hydraulic oil in the fifth oil passage L5 to the hydraulic oil tank 32. Further, a brake ECU (control device) 70 opens the electromagnetic switching valve 64 to output a control hydraulic pressure Pc from the electromagnetic proportional valve 62 when an obstacle is detected by an obstacle detection sensor (obstacle detection device) 54, and closes the electromagnetic switching valve 64 to cut off the output of the control hydraulic pressure Pc from the electromagnetic proportional valve 62 when no obstacle is detected by the obstacle detection sensor 54.

[0044] With this configuration, when no obstacle is detected around the vehicle body, the hydraulic oil is returned to the hydraulic oil tank 32 via the fifth oil passage L5, thereby suppressing a decrease in the oil temperature T of the hydraulic oil in the hydraulic circuit 60. As a result, when an obstacle is detected around the vehicle body, the hydraulic oil can be input to the brake valve 44 more quickly, and the automatic brake can be activated more quickly. Therefore, according to the wheel loader 1 of the first embodiment, the responsiveness of the automatic brake can be ensured even when the temperature of the hydraulic oil is low without interfering with the driver's operation.

[0045] Further, the hydraulic circuit 60 includes a brake valve 44 that adjusts the hydraulic pressure supplied from a main pump (hydraulic oil supply source) 30 to the brake device 40 in accordance with the depression amount of the brake pedal 19 (brake operation amount) by the driver or a pilot signal pressure, and the electromagnetic switching valve 64 is configured to supply the control hydraulic pressure Pc to an input port 441 for the pilot signal pressure of the brake valve 44. This configuration makes it possible to reduce the number of parts and downsize the hydraulic circuit 60 compared to a case where the control hydraulic pressure Pc is supplied directly to the brake device 40.

[0046] Furthermore, when an obstacle is detected by the obstacle detection sensor 54, the brake ECU 70 sets the control hydraulic pressure Pc to a predetermined automatic brake pressure P1, and when no obstacle is detected by the obstacle detection sensor 54, the brake ECU 70 sets the control hydraulic pressure Pc to a predetermined standby pressure P2 which is lower than the predetermined automatic brake pressure. With this configuration, the control hydraulic pressure Pc (standby pressure P2) when circulating hydraulic oil in the circulation oil passage Lc is prevented from being unnecessarily increased, thereby reducing the load on the main pump 30 and making it possible to improve the fuel efficiency of the wheel loader 1. Additionally, the pressure loss generated at the throttle 66 can be reduced.

[0047] Furthermore, the electromagnetic proportional valve 62 and the branch point 65 are connected by a second oil passage (first oil passage) L2, the branch point 65 and the electromagnetic switching valve 64 are connected by a third oil passage (second oil passage) L3, and the electromagnetic switching valve 64 and the brake valve 44 are connected by a fourth oil passage (third oil passage) L4. Both the third oil passage L3 and the fourth oil passage L4 are shorter than the second oil passage L2. With this configuration, pressure loss in the third oil passage L3 and the fourth oil passage L4 can be reduced, making it possible to ensure better responsiveness of the automatic brake.

[0048] Furthermore, the branch point 65 is provided in a housing that constitutes the electromagnetic switching valve 64 (in a housing 44h that constitutes the brake valve 44). With this configuration, the length of the third oil passage L3 can be easily shortened. Furthermore, the electromagnetic switching valve 64 is provided in the housing 44h that constitutes the brake valve 44. With this configuration, the length of the fourth oil passage L4 can be easily shortened.

[0049] Furthermore, the branch point 65 is provided at a position higher than the brake valve 44. As described above, this configuration facilitates discharge of air retained in the fourth oil passage L4 to the hydraulic oil tank 32 side from the branch point 65 immediately after product assembly, after maintenance, or in other similar cases.

[0050] Furthermore, the wheel loader 1 is further equipped with an oil temperature detection sensor 56 that detects the oil temperature T of the hydraulic fluid, and the brake ECU 70 sets the standby pressure P2 to tend to increase as the oil temperature T detected by the oil temperature detection sensor 56 decreases. With this configuration, the lower the oil temperature T of the hydraulic fluid, the greater the amount of hydraulic fluid circulating in the circulation oil passage Lc, and the better the decrease in the temperature of the hydraulic fluid can be suppressed. On the other hand, the higher the oil temperature T of the hydraulic fluid, the less hydraulic fluid circulating in the circulation oil passage Lc can be reduced, reducing the load on the main pump 30 and improving the fuel efficiency of the wheel loader 1. In addition, the pressure loss caused by the throttle 66 can be reduced.

[0051] Note that the standby pressure P2 may be set not only based on the oil temperature T, but also on the ambient temperature. That is, the wheel loader 1 is equipped with an ambient temperature detection sensor (not shown) that detects the ambient temperature and is installed near the driver's cab 5 so as to be exposed to the outside air, and the brake ECU 70 may set the standby pressure P2 to tend to increase as the ambient temperature detected by the ambient temperature detection sensor decreases. The brake ECU 70 stores in the storage unit 72 a map that defines the relationship between the standby pressure P2 and the ambient temperature, separate from the map of standby pressure P2 and oil temperature T illustrated in Figure 5, and the command signal output unit 76 can obtain the standby pressure P2 according to the ambient temperature from this map. As a result, in environments where the oil temperature T of the hydraulic fluid tends to be low, the amount of hydraulic fluid circulation is increased to suppress the drop in oil temperature, and in environments where the oil temperature T of the hydraulic fluid tends to be high, the amount of hydraulic fluid circulation is decreased to improve the fuel efficiency of the wheel loader 1.

[0052] [Second Embodiment] Figure 6 is a schematic diagram showing a portion of the hydraulic equipment and hydraulic circuit including the automatic braking system 50B of the second embodiment. The automatic braking system 50B includes a shuttle valve 67 in addition to the configuration of the automatic braking system 50A of the first embodiment. Furthermore, in the automatic braking system 50B, the fourth oil passage L4 is connected to the shuttle valve 67 instead of the brake valve 44. Therefore, in the automatic braking system 50B, the brake valve 44 can be one that does not have the input port 441 for the pilot signal pressure.

[0053] The shuttle valve 67 has a first input port connected to the hydraulic fluid output port of the brake valve 44, and a second input port connected to the fourth oil passage L4. The shuttle valve 67 also has an output port connected to each disc brake 42 of the brake device 40. The shuttle valve 67 outputs the higher of the hydraulic pressure of the hydraulic fluid input to the first input port and the second input port from its output port.

[0054] In this case, it is determined that the control mode should be set to automatic braking mode (step ST4 in Figure 4), and when the electromagnetic proportional valve 62 outputs automatic braking pressure P1 (step ST6), the automatic braking pressure P1 is input to the second input port of the shuttle valve 67 via the electromagnetic switching valve 64. At this time, if hydraulic pressure is not supplied from the brake valve 44 to the shuttle valve 67, the automatic braking pressure P1 is supplied from the output port of the shuttle valve 67 to each disc brake 42, and the automatic brake is activated. Thus, the electromagnetic switching valve 64 may be configured to supply automatic braking pressure P1 (control hydraulic pressure Pc) to the brake device 40. This allows the hydraulic pressure supplied to each disc brake 42 in automatic braking control to be directly controlled by the electromagnetic proportional valve 62, improving controllability. Similar to the first embodiment, if no obstacles are detected around the vehicle body, the hydraulic fluid is returned to the hydraulic fluid tank 32 via the fifth oil passage L5, thereby suppressing a decrease in the oil temperature T of the hydraulic fluid in the hydraulic circuit 60. As a result, if an obstacle is detected around the vehicle, the hydraulic fluid can be supplied to the brake valve 44 more quickly, allowing the automatic brake to be activated more rapidly.

[0055] [Third Embodiment] Figure 7 is a schematic diagram showing a part of the hydraulic equipment and hydraulic circuit including the automatic brake system 50C of the third embodiment. The automatic brake system 50C has an electromagnetic switching valve (bypass restrictor) 69 instead of the throttle 66 of the automatic brake system 50A of the first embodiment. The electromagnetic switching valve 69 is located in the middle of the fifth oil passage L5 and is a switching valve that can form a closed state that restricts the flow of hydraulic fluid in the fifth oil passage L5 to the hydraulic fluid tank 32 and an open state that releases the restriction on the flow of hydraulic fluid in the fifth oil passage L5 to the hydraulic fluid tank 32. The electromagnetic switching valve 69 is controlled by the brake ECU 70.

[0056] Specifically, when the brake ECU 70 determines that the control mode should be set to automatic brake mode (step ST4 in Figure 4) and opens the electromagnetic switching valve 64 (step ST5), it closes the electromagnetic switching valve 69 to restrict the flow of hydraulic fluid in the fifth oil passage L5 to the hydraulic fluid tank 32. On the other hand, when the brake ECU 70 determines that the control mode should be set to standby mode (step ST7) and closes the electromagnetic switching valve 64 (step ST8), it opens the electromagnetic switching valve 69 to release the restriction on the flow of hydraulic fluid in the fifth oil passage L5. In this way, by using the electromagnetic switching valve 69 instead of the throttle 66, the restriction on the flow of hydraulic fluid in the fifth oil passage L5 to the hydraulic fluid tank 32 can be made the same as in the first and second embodiments. As in the first and second embodiments, when no obstacles are detected around the vehicle body, the hydraulic fluid is returned to the hydraulic fluid tank 32 via the fifth oil passage L5, thereby suppressing the decrease in the oil temperature T of the hydraulic fluid in the hydraulic circuit 60. As a result, if an obstacle is detected around the vehicle, the hydraulic fluid can be supplied to the brake valve 44 more quickly, allowing the automatic brake to be activated more rapidly.

[0057] This concludes the description of the embodiments, but the aspects of the present invention are not limited to these embodiments. For example, in the first to third embodiments, the automatic braking systems 50A to 50C were applied to the wheel loader 1, but the automatic braking systems 50A to 50C may also be applied to other work machines, such as a hydraulic excavator, which have a drivable vehicle body, a work device attached to the front of the front vehicle body, and a hydraulic brake device that applies braking force to the vehicle body.

[0058] 1 Wheel loader (working machine) 1a Front body (body) 1b Rear body (body) 10 Working equipment 30 Main pump (hydraulic oil supply source) 32 Hydraulic oil tank (tank) 40 Brake system 42 Disc brake 44 Brake valve 44h Housing 50A-50C Automatic braking system 52 Automatic brake changeover switch 54 Obstacle detection sensor (obstacle detection device) 56 Oil temperature detection sensor 60 Hydraulic circuit 62 Solenoid proportional valve (control valve) 64 Solenoid changeover valve (changeover valve) 65 Branch point 66 Throttle (bypass restriction section) 67 Shuttle valve 69 Solenoid changeover valve (bypass restriction section) 70 Brake control unit (control device, brake ECU) L1 First oil passage L2 Second oil passage (first oil passage) L3 Third oil passage (second oil passage) L4 Fourth oil passage (third oil passage) L5 ​​Fifth oil passage (bypass oil passage) Lc Circulating oil passage P1 Automatic brake pressure P2 Standby pressure Pc Control hydraulic pressure T Oil temperature

Claims

1. A work machine comprising: a drivable vehicle body; a work device attached to the front of the vehicle body; a hydraulic brake system for applying braking force to the vehicle body; an obstacle detection device for detecting obstacles present around the vehicle body; a control valve that adjusts and outputs the hydraulic pressure of hydraulic fluid supplied from a hydraulic fluid supply source to a predetermined control hydraulic pressure; a hydraulic circuit including a switching valve that switches between an open state in which hydraulic pressure based on the control hydraulic pressure output from the control valve is supplied to the brake system and a closed state in which hydraulic pressure based on the control hydraulic pressure is not supplied to the brake system; and a control device for controlling the control valve and the switching valve, wherein the hydraulic circuit has a bypass oil passage that branches off from a branching point provided between the control valve and the switching valve and connects to a tank, and a bypass restricting section that restricts the flow of the hydraulic fluid in the bypass oil passage to the tank. The control device is characterized in that, when an obstacle is detected by the obstacle detection device, it opens the switching valve and outputs control hydraulic pressure from the control valve, and when no obstacle is detected by the obstacle detection device, it closes the switching valve and shuts off the output of control hydraulic pressure from the control valve.

2. The work machine according to claim 1, wherein the hydraulic circuit has a brake valve that adjusts the hydraulic pressure supplied from the hydraulic fluid supply source to the brake device in accordance with the amount of brake operation by the driver or the pilot signal pressure, and the switching valve is configured to supply control hydraulic pressure to the input port of the pilot signal pressure of the brake valve.

3. The work machine according to claim 1, characterized in that the switching valve is configured to supply control hydraulic pressure to the brake device.

4. The work machine according to claim 1, characterized in that the control device sets the control hydraulic pressure to a predetermined automatic brake pressure when an obstacle is detected by the obstacle detection device, and sets the control hydraulic pressure to a predetermined standby pressure lower than the predetermined automatic brake pressure when no obstacle is detected by the obstacle detection device.

5. The work machine according to claim 2, characterized in that the control valve and the branching point are connected by a first oil passage, the branching point and the switching valve are connected by a second oil passage, the switching valve and the brake valve are connected by a third oil passage, and both the second oil passage and the third oil passage are shorter than the first oil passage.

6. The work machine according to claim 5, characterized in that the branching point is provided within the housing constituting the switching valve.

7. The work machine according to claim 5 or 6, characterized in that the switching valve is provided within the housing that constitutes the brake valve.

8. The work machine according to claim 2, wherein the branching point is located at a higher position than the brake valve.

9. The work machine according to claim 4, further comprising an oil temperature detection sensor for detecting the oil temperature, which is the temperature of the hydraulic fluid, wherein the control device sets the predetermined standby pressure to tend to increase as the oil temperature detected by the oil temperature detection sensor decreases.

10. The work machine according to claim 4, comprising an ambient temperature detection sensor for detecting ambient temperature, wherein the control device sets the predetermined standby pressure to tend to increase as the ambient temperature detected by the ambient temperature detection sensor decreases.

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