Fluid pressure circuit of working machine

Abstract

[Problem] To provide a hydraulic circuit for a working machine, which can reliably and smoothly increase the running speed of an accessory when the accessory is individually operated. Solution: A controller (27) feeds back the pressure of another pump (25) to control the opening amount of a bypass control valve (37) of one pump (25) so that the pressure of the one pump (25) is closer to the pressure of the other pump (25), and then merges hydraulic oil from the other pump (25) with hydraulic oil from the one pump (25) via a linear travel valve (28).

Description

Technical Field

[0001] The present invention relates to a fluid pressure circuit for a working machine, which supplies working fluid from a pump to a plurality of fluid pressure actuators. Background Technology

[0002] Traditionally, in machine tools that employ a dual-pump system (such as hydraulic excavators), hydraulic oil from only one pump is typically used to control the opening and closing of the bucket.

[0003] On the other hand, in working machinery, it is necessary to increase the opening and closing speed, especially when operating the bucket alone.

[0004] In this regard, while it is conceivable to provide two hydraulic pumps to the bucket cylinder, equipping the bucket with two control valves or using a flow control valve would increase space requirements and costs.

[0005] Therefore, it is known that two hydraulic pumps can be combined and the operating speed of a hydraulic actuator (such as a bucket cylinder) can be increased by using a merging switching valve (such as a forward travel valve for a straight travel function) provided in the hydraulic circuit. This straight travel function integrates left and right travel into one pump for operation, thereby preventing travel bends during simultaneous operation with other hydraulic actuators (see, for example, Patent Documents 1 to 4).

[0006] Existing technical documents

[0007] Patent documents

[0008] Patent Document 1: JP 1999-6174 A

[0009] Patent Document 2: JP 2000-45340 A

[0010] Patent Document 3: JP 2004-100847 A

[0011] Patent Document 4: JP 2011-247365 A Summary of the Invention

[0012] The problem to be solved by the present invention

[0013] Specifically, within the bucket cylinder, the pressure of the pump supplying hydraulic oil to the bucket cylinder varies significantly depending on the presence or absence of soil. For example, if hydraulic oil from another pump with relatively low pressure is combined with this higher pressure, the pump pressure may be reduced, and proper acceleration may not be achieved.

[0014] Therefore, the object of the present invention is to provide a fluid pressure circuit for a working machine that can reliably and smoothly increase the operating speed of the attachment when the attachment is operated alone.

[0015] Problem Solving

[0016] The invention according to claim 1 is a fluid pressure circuit for a machine tool, the fluid pressure circuit comprising: multiple pumps; multiple control valves controlling the supply of working fluid from the pumps to multiple fluid pressure actuators; a linear travel valve; a bypass control valve bypassing the working fluid discharged from the pumps into a tank; and a controller that, when an attachment is operated individually, operates the linear travel valve and the bypass control valve to combine the working fluid from one pump with the working fluid from another pump, and introduces the working fluid into an attachment control valve according to the flow rate of the working fluid required by the fluid pressure actuator of the attachment, wherein the controller feeds back the pressure of one pump to control the opening amount of the bypass control valve of the other pump to bring the pressure of the other pump closer to the pressure of the first pump, and then combines the working fluid from the first pump with the working fluid from the other pump via the linear travel valve. A fluid pressure circuit for a machine tool that combines working fluid from other pumps.

[0017] The invention according to claim 2 is a fluid pressure circuit for a working machine, the fluid pressure circuit being configured with a groove region that suppresses the change in opening area relative to stroke in the opening characteristics.

[0018] The invention according to claim 3 is a fluid pressure circuit for a working machine, wherein the fluid pressure actuator of the attachment in the fluid pressure circuit of the working machine according to claim 1 or 2 is a bucket cylinder.

[0019] Effects of the present invention

[0020] According to the invention of claim 1, when the fluid pressure actuator of the attachment is operated alone, the working fluid from the multiple pumps can be supplied with less impact by using the linear travel valve for linear travel, and the operating speed of the attachment can be reliably and smoothly increased.

[0021] According to claim 2, the flow rate of the confluenced working fluid can be smoothly changed in the groove region, and the impact when the confluenced working fluid is inserted through the linear travel valve can be suppressed more reliably.

[0022] According to the invention of claim 3, the speed can be appropriately increased based on the load pressure of a pump, which fluctuates according to the load of the bucket. Attached Figure Description

[0023] Figure 1This is a circuit diagram illustrating a first embodiment of the fluid pressure circuit of the machine tool according to the present invention, wherein (a) shows the state in which the simultaneous operation and linear travel functions are turned off, (b) shows the state in which the simultaneous operation and linear travel functions are turned on, and (c) shows the state in which the attachment operates alone.

[0024] Figure 2 This is a flowchart illustrating the control of the use decision of the linear travel valve when the device is operated alone by the controller in the above-mentioned fluid pressure circuit.

[0025] Figure 3 The diagram illustrates an example of the relationship between the following: the operating amount of the operating device of the above fluid pressure circuit; the pump's requested flow rate; and the stroke between the device control valve and the linear travel valve.

[0026] Figure 4 This is a diagram illustrating an example of the groove-controlled opening characteristics of a linear travel valve in the aforementioned fluid pressure circuit.

[0027] Figure 5 This is a side view illustrating an example of a working machine that includes the fluid pressure circuit described above.

[0028] Figure 6 This is a circuit diagram illustrating a second embodiment of the fluid pressure circuit of the working machine according to the present invention, wherein (a) shows the state in which the simultaneous operation and linear travel functions are turned off, (b) shows the state in which the simultaneous operation and linear travel functions are turned on, and (c) shows the state in which the attachment operates alone.

[0029] Embodiments for implementing the present invention

[0030] In the following text, based on Figures 1 to 5 The first embodiment shown and Figure 6 The second embodiment shown describes the present invention in detail.

[0031] First, the description Figures 1 to 5 The first embodiment shown.

[0032] exist Figure 5 In the example, 1 represents a working machine. In the illustrated example, the working machine 1 is a hydraulic excavator, taking a rotary working machine as an example. The working machine 1 is provided with a lower traveling body 2 and an upper rotating body 3, the upper rotating body being a rotating body rotatably disposed in the lower traveling body 2.

[0033] The lower traveling body 2 includes a pair of left and right tracked traveling devices 5. Each tracked traveling device 5 is provided with a sprocket 7, a driven wheel (idler wheel) 8, and multiple track rollers 9. Each track roller is rotatably located at the front and rear of the long frame 6, and an annular track 10 surrounds the aforementioned sprocket, driven wheel (idler wheel), and multiple track rollers. The sprocket 7 is rotatably driven by a traveling motor 11 (which is a fluid pressure motor acting as a fluid pressure actuator), thereby rotatably driving the track 10.

[0034] The upper rotating body 3 is rotatably supported by a slewing support 13 relative to the frame 6 of the lower traveling body 2. The upper rotating body is rotated about the slewing support 13 relative to the lower traveling body 2 by a slewing motor 14, which is a fluid pressure motor that acts as a fluid pressure actuator.

[0035] The working device 17 is axially connected to the upper slewing body 3 on one side of the cab 16, which is the operator's cab where the operator sits. Additionally, the upper slewing body 3 is provided with a machine room 18, which houses the engine, pump, control valves, etc.; across the working device 17, various tanks (such as hydraulic oil tanks and fuel tanks) are provided on the side opposite to the cab 16; and counterweights 19 are installed at the end portion opposite to the working device 17 for the machine room 18 and the various tanks.

[0036] The working device 17 includes multiple linkage members 28, which are operated by the extension and retraction of hydraulic cylinders 22, which are fluid pressure cylinders acting as fluid pressure actuators. In this embodiment, the working device 17 includes a boom 21a in the form of linkage members, a stick (arm) 21b in the form of linkage members, and a bucket 21c in the form of linkage members serving as attachments. The base end of the boom 21a is axially connected to the upper rotating body 3, the base end of the stick 21b is axially connected to the distal end of the boom 21a, and the bucket 21c is axially connected to the distal end of the stick 21b. The boom 21a, stick 21b, and bucket 21c are rotated by boom cylinder 22a (which is a hydraulic cylinder), stick cylinder (arm cylinder) 22b (which is a hydraulic cylinder), and bucket cylinder 22c (which is a hydraulic cylinder), respectively. The boom 21a can rotate vertically about the engine body (i.e., the upper slewing body 3) by extending and retracting the boom cylinder 22a; the boom 21b can rotate back and forth about the boom 21a by extending and retracting the stick cylinder 22b; and the bucket 21c can rotate back and forth about the bucket 21c by extending and retracting the bucket cylinder 22c. Note that the configuration of the working device 17 is not limited to this configuration and can be constructed to include four or more linkage members 21, or can be equipped with suitable attachments instead of the bucket 21c.

[0037] Machine tool 1 is equipped with a hydraulic circuit, which is Figure 1(a) to Figure 1 (c) shows the fluid pressure circuit. The hydraulic circuit includes: multiple pumps (main pumps) 25; multiple control valves 26 for controlling hydraulic fluid, which is the working fluid supplied from the pumps 25 to the multiple fluid pressure actuators; and a controller 27 for controlling the operation of the control valves 26.

[0038] The number of pumps 25 can be three or more, but in this embodiment, for example, a pair of first pumps 25a and second pumps 25b are provided. The pumps 25 are connected to the output shaft of the engine and are driven by the engine. For example, a variable displacement pump is used as one of the pumps 25.

[0039] Control valve 26 is a spool valve, arranged in such a way that it is included within a valve block as a control valve. Hydraulic oil discharged from pump 25 is supplied to control valve 26, and the direction and flow of the hydraulic oil are controlled according to the displacement direction and amount of these control valves 26, respectively, to supply the fluid pressure actuator. Each control valve 26 is controlled according to the operation amount of an operating device (such as a control lever or pedal). A signal corresponding to the operation amount of the operating device is input to the input side of controller 27, and the discharge amount of hydraulic oil from pump 25 is controlled according to the current value of a command signal for flow command output from controller 10 based on the input signal. In other words, pump 25 is of the current-controlled type and can be adjusted by a regulator based on the load from the lowest flow rate under no-load conditions by means of control of a displacement regulating component (such as a swashplate), which is operated by a solenoid valve (solenoid proportional valve) that receives the command signal output from controller 10.

[0040] In this embodiment, the control valve 26 is provided with a control valve group corresponding to each pump in the pump 25. That is, one control valve group is provided for each pump 25. In the illustrated example, a first control valve group BGa is provided, which mainly supplies hydraulic oil discharged from the first pump 25a to the fluid pressure actuator; and a second control valve group BGb is provided, which mainly supplies hydraulic oil discharged from the second pump 25b to the fluid pressure actuator.

[0041] One of the first control valve group BGa and the second control valve group BGb includes at least a travel control valve 26, which is used to control the flow of power to a travel motor 11. Figure 5 The flow and direction of the hydraulic oil supplied, and the other includes at least a travel control valve 26 for controlling the flow of hydraulic oil to another travel motor 11. Figure 5 The flow rate and direction of the supplied hydraulic oil.

[0042] As an example, the first control valve group BGa in this embodiment includes at least, for example, a travel control valve 26trR, which is used to control the right travel motor 11 ( Figure 5 The flow and direction of the hydraulic oil supplied; boom control valve 26bm, which is used to control the flow of hydraulic oil to boom cylinder 22a ( Figure 5 The flow and direction of the hydraulic oil supplied; and the attachment (bucket) control valve 26at, which controls the flow of hydraulic oil to the bucket cylinder 22c. Figure 5 The flow rate and direction of the supplied hydraulic oil, the bucket cylinder being the fluid pressure actuator of the attachment.

[0043] The second control valve assembly BGb also includes, for example, a travel control valve 26trL, which is used to control the left travel motor 11 ( Figure 5 The flow and direction of the hydraulic oil supplied; the stick control valve 26st, which controls the flow of hydraulic oil to the stick cylinder 22b ( Figure 5 The flow and direction of the hydraulic oil supplied; and the rotary control valve 26sw, which is used to control the flow of hydraulic oil to the rotary motor 14 ( Figure 5 The flow rate and direction of the supplied hydraulic oil.

[0044] The diagram omits the hydraulic oil supply passage from each control valve 26 to each fluid pressure actuator, as well as the return passage that returns the supplied hydraulic oil to the tank.

[0045] In addition, for each control valve group BGa and BGb, control valve 26 is shown in common except for travel control valves 26trL ​​and 26trR.

[0046] Furthermore, for control valve 26 (which may include components for controlling the flow and direction of hydraulic oil supplied to any other operating component), it is optional whether control valve 26 is included in the first control valve group BGa or the second control valve group BGb, and for clarity, an example of this control valve is omitted in this embodiment.

[0047] Then, a linear travel valve 28 for linear travel is provided between these two control valve groups BGa and BGb. The linear travel valve 28 ensures the left and right travel motors 11 ( Figure 5 The control valve 26 of the machine tool 1 supplies hydraulic oil equally to the machine tool 1. Figure 5It is capable of linear travel. The linear travel valve 28 is located at a first position X (i.e., the linear travel function is off) and a second position Y (i.e., the linear travel function is on). The on / off state of the linear travel function is set by an operator using, for example, a setting component (such as a switch). In this embodiment, a proportional control valve is used in the linear travel valve 28. That is, the linear travel valve 28 is configured to continuously change the opening amount (stroke amount) between the first position X and the second position Y.

[0048] In this embodiment, a groove portion is formed in each of the outflow and inflow sides of the valve core of the linear travel valve 28. This groove portion provides a groove region that suppresses changes in the opening area relative to the stroke amount (valve core movement) in the opening characteristics of the linear travel valve 28, and mitigates the impact of sudden operation of the linear travel valve 28 during opening and closing by rectifying the hydraulic oil. For example, the groove portion consists of multiple grooves formed along the valve core movement direction at the outer periphery of the valve core platform portion. Figure 4 An example of the opening characteristics of the linear travel valve 28 of this embodiment is shown. Conventional linear travel valves have only a minimal recessed area compatible with simplified manufacturing and reduced shock during switching; in contrast to conventional linear travel valves, in the illustrated example, the recessed area AN is expanded to its opening amount with a controlled opening amount (an opening amount that continuously varies and adapts to pressure losses acceptable to the hydraulic system), which allows control of the flow rate of the pump into the fluid pressure actuator of the attachment compared to the conventional example shown by the double dashed lines. The recessed area AN includes at least the central portion of the total stroke and is positioned within a range where the opening area is 0. Furthermore, within the recessed area AN, the opening characteristics of the linear travel valve 28 tend towards an opening area of ​​0, and changes in the opening area relative to the stroke amount are suppressed. Therefore, the opening characteristics of the linear travel valve 28 of this embodiment are configured such that the rate of change of the opening area relative to the stroke amount changes at two points: the location where the general region and the recessed area AN meet; and a location near the location where the opening area in the recessed area AN is 0.

[0049] Then, as Figure 1 (a) to Figure 1As shown in (c), one of the pump passages 30a and 31a of the first pump 25a (e.g., pump passage 30a) is connected to the travel control valve 26trR, and the other (e.g., pump passage 31a) is connected to the linear travel valve 28. Similarly, one of the pump passages 30b and 31b of the second pump 25b (e.g., pump passage 30b) is connected to the boom control valve 26st and the swing control valve 26sw, respectively, while the other (e.g., pump passage 31b) is connected to the linear travel valve 28. Furthermore, pump 25 is also provided with a bypass control valve 37. The bypass control valve 37 allows hydraulic oil discharged from pump 25 to bypass to tank 38. The system pressure of pump 25 is controlled by the pump discharge rate and the opening amount of the bypass control valve 37. In this embodiment, a first bypass control valve 37a and a second bypass control valve 37b are provided corresponding to the first pump 25a and the second pump 25b. Bypass control valves 37a and 37b are connected to pump passages 30a and 30b via bypass channels 36a and 36b. Boom control valve 26bm, attachment control valve 26at, and travel control valve 26trL ​​are connected to parallel supply channels 32 and 33 for supplying hydraulic oil to the linear travel valve 28, respectively. Parallel supply channel 32 and travel control valve 26trR are connected via channel 35 for supplying hydraulic oil and including a check valve 34.

[0050] The operation of the linear travel valve 28, along with the operation of the control valve 26 and the bypass control valve 37, is controlled by the controller 27. The controller 27 is, for example, installed in the driver's cab 16 (…). Figure 5 The vehicle-mounted controller on the vehicle.

[0051] When the operator operates multiple fluid pressure actuators, the controller 27 generates and outputs a command signal that controls the linear travel valve 28 to be set to the first position X when the linear travel function is off, and to the second position Y when the linear travel function is on.

[0052] When the linear travel function is off, the linear travel valve 28, which is in the first position X due to the command signal from the controller 27, connects the pump channel 31a to the parallel supply channel 32 and the pump channel 31b to the parallel supply channel 33, as shown. Figure 1As shown in (a). In this state, hydraulic oil discharged from the first pump 25a is introduced into the travel control valve 26trR, boom control valve 26bm, attachment control valve 26at, etc., and hydraulic oil discharged from the second pump 25b is introduced into the travel control valve 26trL, stick control valve 26st, slewing control valve 26sw, etc. Signals generated based on the operator's input to the control device and the direction of operation are input to the controller 27, and the controller 27 generates and outputs command signals based on these signals, causing each control valve 26 to operate independently and hydraulic oil to be supplied to each fluid pressure actuator. Therefore, Figure 5 The direction and speed of rotation of each travel motor 11, the direction and speed of rotation of the slewing motor 14, the extension and speed of the boom cylinder 22a, the extension and speed of the stick cylinder 22b, the extension and speed of the bucket cylinder 22c, and the extension and speed of the bucket cylinder 22c are each controlled independently, and the travel of the lower travel body 2, the rotation of the upper slewing body 3, and the operation of the working device 17 are performed according to the operator's operation of the operating device.

[0053] In addition, such as Figure 1 As shown in (b), when the straight travel function is activated, the controller 27 generates and outputs a command signal to control the straight travel valve 28 to switch to the second position Y. In the second position Y, the straight travel valve 28 connects pump passage 31a to parallel supply passage 33 and pump passage 31b to parallel supply passage 32. In this state, hydraulic oil discharged from the first pump 25a is introduced into the travel control valves 26trR and 26trL, and hydraulic oil discharged from the second pump 25b is introduced into the boom control valve 26bm, attachment control valve 26at, stick control valve 26st, slewing control valve 26sw, etc. Signals generated based on the operator's operation amount and direction are input to the controller 27, and the controller 27 generates and outputs a command signal based on this signal, causing each control valve 26 to operate independently and supply hydraulic oil to each fluid pressure actuator. Therefore, by making... Figure 5 Each travel motor 11 shown rotates at the same speed in the same direction (the same amount of hydraulic oil is supplied from the common first pump 25a in these travel motors), the working machine 1 travels in a straight line, and at the same time, the rotation direction and speed of the slewing motor 14, the extension and speed of the boom cylinder 22a, the extension and speed of the stick cylinder 22b, and the extension and speed of the bucket cylinder 22c are controlled independently, and the rotation of the upper slewing body 3 and the operation of the working device 17 are performed according to the operator's operation of the operating device.

[0054] In addition, such as Figure 1 As shown in (c), when the operator operates the attachment (bucket 21c in this embodiment) alone... Figure 5When the hydraulic oil flow rate is required (i.e., the amount of operation of the operating device (such as a lever or pedal for operating the attachment) is reached), the controller 27 generates and outputs a command signal for operating the linear travel valve 28.

[0055] That is, such as Figure 2 As shown, controller 27 determines whether an operating device operation for the attachment has been input (step S1), and if the controller determines that an operating device operation for the attachment has been input (if "yes" in step S1), it determines whether an operating device operation for an operation other than the attachment has been input (step S2); and if the controller determines that no operating device operation for an operation other than the attachment has been input (if "no" in step S2), it determines whether the requested flow rate is greater than or equal to a predetermined flow rate, which is less than the maximum discharge capacity of one pump 25 (in this embodiment, the first pump 25a) (step S3); and if the controller determines that the requested flow rate is greater than the predetermined flow rate, it operates the linear travel valve 28 to compensate for the difference between the requested flow rate and the discharge capacity of one pump 25 from another pump 25 (in this embodiment, the second pump 25b). In other determination results, the process returns to step S1.

[0056] Figure 3 The operating parameters of the attachment's operating device and pumps 25a and 25b are shown. Figure 1 (c) The pump requests flow rates Qa, Qb, and the accessory control valve 26at ( Figure 5 Example of the relationship between the strokes St1 and St2 of the travel control valve 28 and the linear travel valve 28. In the illustrated example, for a flow rate exceeding a predetermined flow rate Q based on the operating amount of the operating device, the travel control valve 28 ( Figure 1 (c) The opening amount is controlled to gradually increase to the maximum stroke St according to the operation amount.

[0057] In this embodiment, as Figure 1 As shown in (c), via the attachment (bucket cylinder 22c) Figure 5 In a single operation of the fluid pressure actuator, the travel control valve 26trR is in the neutral position, such that hydraulic oil from the first pump 25a is introduced from the control valve 26trR via passage 35 and from the parallel supply passage 32 into the attachment control valve 26at, according to the operating amount of the operating device for attachment operation. When the operating amount of the operating device for attachment operation is greater than a predetermined operating amount, the linear travel valve 28 is actuated, and hydraulic oil from the second pump 25b is combined according to the opening amount and introduced into the attachment control valve 26at. Therefore, in this embodiment, the operation of the attachment, i.e., the bucket 21c ( Figure 5 The opening and closing operations of () can be accelerated.

[0058] At this point, the controller 27 transitions from controlling the simultaneous operation of multiple fluid pressure actuators to controlling the attachment (bucket cylinder 22c). Figure 5 During a single operation of the fluid pressure actuator, it is preferable to control the rate limiter (i.e., the switching speed of the linear travel valve 28) to ensure a gradual and smooth transition. Similarly, when transitioning from a single operation of the fluid pressure actuator of the control attachment to the simultaneous operation of multiple fluid pressure actuators, it is preferable to implement rate limiter control so that the transition is gradual and smooth.

[0059] Specifically, the attachment is bucket 21c ( Figure 5 When the load pressure fluctuates significantly depending on the presence or absence of soil to be excavated, the ground surface, etc., the pressure of the first pump 25a supplying hydraulic oil to the actuator of the attachment also fluctuates significantly. When the pump pressure of the first pump 25a is high, and this pressure is transmitted to the second pump 25b with a relatively low pressure, the pressurized oil of the first pump 25a is diverted via the second bypass control valve 37b on the side of the second pump 25b, otherwise a shock would occur during the merging.

[0060] To avoid this situation, when the hydraulic oil of the second pump 25b is combined via the linear travel valve 28, the controller 27 generates a command signal that feeds back the pressure of the first pump 25a and controls the opening amount of the second bypass control valve 37b so that the pressure of the second pump 25b is closer to the pressure of the first pump 25a, and then the pressure of the second pump 25b is combined to be closer to the pressure of the first pump 25a.

[0061] Therefore, when the fluid pressure actuator of the attachment is operated individually in a space-saving and low-cost manner, the linear travel valve 28 for linear forward movement can be used to supply hydraulic oil from multiple pumps 25 with less impact, and the operating speed of the attachment can be reliably and smoothly increased.

[0062] Specifically, when the fluid pressure actuator of the attachment is the bucket cylinder 22c of the bucket 21c, it can be appropriately accelerated according to the load pressure of the first pump 25a (which fluctuates according to the load of the bucket 21c).

[0063] By making the linear travel valve 28 a proportional control valve, the impact generated in the operating device (such as the control lever) when the hydraulic oil flows together can be reduced, and smooth operation can be achieved.

[0064] Furthermore, since the opening characteristics of the linear travel valve 28 are provided with a large groove area AN, which suppresses the change in opening area relative to the stroke, the flow rate of the hydraulic oil to be merged can be changed smoothly, and the impact of the hydraulic oil when merging through the linear travel valve 28 can be suppressed more reliably.

[0065] Next, we will describe Figure 6 The second embodiment is shown.

[0066] In this embodiment, one of the pump passages 30a and 31a of the first pump 25a (e.g., pump passage 30a) is connected to the boom control valve 26bm and the attachment control valve 26at, respectively, while the other (e.g., pump passage 31a) is connected to the linear travel valve 28. Similarly, one of the pump passages 30b and 31b of the second pump 25b (e.g., pump passage 30b) is connected to the travel control valve 26trL, while the other (e.g., pump passage 31b) is connected to the linear travel valve 28. The travel control valve 26trL, the boom control valve 26st, and the swing control valve 26sw are connected to the linear travel valve 28 via parallel supply passages 40 and 41 to supply hydraulic oil. Additionally, the parallel supply passage 41 and the travel control valve 26trL ​​are connected to a passage 44 including a check valve 43 to supply hydraulic oil.

[0067] Then, as in the first embodiment, when as Figure 6 As shown in (a), when the straight travel function is off, the straight travel valve 28, which is in the first position X due to the command signal from the controller 27, connects the pump passage 31a to the parallel supply passage 40 and the pump passage 31b to the parallel supply passage 41. In this state, hydraulic oil discharged from the first pump 25a is introduced into the travel control valve 26trR, the boom control valve 26bm, the attachment control valve 26at, etc., and hydraulic oil discharged from the second pump 25b is introduced into the travel control valve 26trL, the boom control valve 26st, the slewing control valve 26sw, etc., and a signal generated based on the operator's operation amount and direction of the operating device is input to the controller 27, and the controller 27 generates and outputs a command signal based on the signal, so that each control valve 26 operates independently and hydraulic oil is supplied to each fluid pressure actuator. Therefore, the direction and speed of rotation of each travel motor 11, the direction and speed of rotation of the slewing motor 14, the extension and speed of the boom cylinder 22a, the extension and speed of the stick cylinder 22b, and the extension and speed of the bucket cylinder 22c are each controlled independently, and the travel of the lower travel body 2, the slewing of the upper slewing body 3, and the operation of the working device 17 are performed according to the operator's operation of the operating device.

[0068] Additionally, when the linear travel function is activated, a command signal is generated and output to control the linear travel valve 28, thereby switching the linear travel valve 28 to the second position Y. For example... Figure 6As shown in (b), the linear travel valve 28 in the second position Y connects pump passage 31a to parallel supply passage 41 and pump passage 31b to parallel supply passage 40. In this state, hydraulic oil discharged from the first pump 25a is introduced into boom control valve 26bm, attachment control valve 26at, stick control valve 26st, slewing control valve 26sw, etc., and hydraulic oil discharged from the second pump 25b is introduced into travel control valves 26trR and 26trL. Signals generated based on the operator's input amount and direction of operation are input to controller 27, and controller 27 generates and outputs command signals based on these signals, causing each control valve 26 to operate independently and hydraulic oil to be supplied to each fluid pressure actuator. Therefore, by making... Figure 5 Each travel motor 11 shown rotates at the same speed in the same direction (the same amount of hydraulic oil is supplied from the common first pump 25a in these travel motors), the working machine 1 travels in a straight line, the rotation direction and speed of the slewing motor 14, the extension and speed of the boom cylinder 22a, the extension and speed of the stick cylinder 22b, and the extension and speed of the bucket cylinder 22c are controlled independently, and the rotation of the upper slewing body 3 and the operation of the working device 17 are performed according to the operator's operation of the operating device.

[0069] In addition, such as Figure 6 As shown in (c), when the operator operates the attachment (bucket 21c in this embodiment) alone... Figure 5 When the hydraulic oil flow rate is required (i.e., the amount of operation of the operating device (such as a lever or pedal) used to operate the attachment), the controller 27 generates and outputs a command signal for operating the linear travel valve 28.

[0070] In this embodiment, hydraulic oil from the first pump 25a is introduced into the attachment control valve 26at according to the operating amount of the operating device used to operate the attachment. If the operating amount of the operating device used to operate the attachment is greater than a predetermined operating amount, the linear travel valve 28 is operated, and according to its opening amount, hydraulic oil introduced from the second pump 25b into the travel control valve 26trL ​​flows from the neutral position of the travel control valve 26trL, through channel 44, parallel supply channel 41, linear travel valve 28 and pump channel 31a, into pump channel 30a, and merges into the attachment control valve 26at. Therefore, in this embodiment, the operation of the attachment, bucket 21c ( Figure 5 The opening and closing operations of () can be accelerated.

[0071] At this time, when the hydraulic oil from the second pump 25b is combined via the linear travel valve 28, the controller 27 generates a command signal that feeds back the pressure of the first pump 25a and controls the opening amount of the second bypass control valve 37b, so that the pressure of the second pump 25b is closer to the pressure of the first pump 25a, and then the pressure of the second pump 25b is combined to be closer to the pressure of the first pump 25a. Therefore, effects similar to those of the first embodiment can be achieved: for example, by using the linear travel valve 28 for straight-line travel, hydraulic oil from multiple pumps 25 can be combined with less impact when operating the fluid pressure actuator of the attachment individually in a space-saving and low-cost manner, and the operating speed of the attachment can be reliably and smoothly increased.

[0072] Industry Applicability

[0073] This invention is applicable to industries such as manufacturing and selling machine tools that include hydraulic circuits.

Claims

1. A fluid pressure circuit for a machine tool, the fluid pressure circuit comprising: Multiple pumps; Multiple control valves control the working fluid supplied from the pump to multiple fluid pressure actuators; Linear travel valve; A bypass control valve that bypasses the working fluid discharged from the pump into the tank; The controller, when operating the attachment alone, operates the linear travel valve and the bypass control valve to combine the working fluid from one pump with the working fluid from another pump, and introduces the working fluid into the attachment control valve according to the flow rate of the working fluid required by the fluid pressure actuator of the attachment. The controller provides feedback on the pressure of one pump to control the opening amount of the bypass control valve of the other pump, so that the pressure of the other pump is closer to the pressure of the first pump, and then the working fluid from the first pump is combined with the working fluid from the other pump via the linear travel valve.

2. The fluid pressure circuit of the machine tool according to claim 1, wherein the linear travel valve is configured with a groove region, the groove region suppressing the change in opening area relative to the stroke in the opening characteristic.

3. The fluid pressure circuit of the working machine according to claim 1 or 2, wherein the fluid pressure actuator of the attachment is a bucket cylinder.

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