Hydraulic excavator drive system

Abstract

A hydraulic excavator drive system (1A) of one embodiment includes a first pump (22) connected to a head side chamber (13a) of a boom cylinder (13) and a second pump (32) that supplies working fluid to at least one of a stick cylinder (14) and a bucket cylinder (15). The first pump (22) is driven by an electric motor (61). Further, the drive system (1A) includes a first switching valve (51) provided in a rod side line (24) and a second switching valve (52) provided in a relay line (25). The first switching valve (51) opens the rod side line (24) during boom raising operation and blocks the rod side line (24) other than during boom raising operation. The second switching valve (52) blocks the relay line (25) during boom raising operation and opens the relay line (25) during body raising operation.

Description

TECHNICAL FIELD

[0001] The present application relates to a hydraulic excavator drive system. BACKGROUND

[0002] Generally, in a hydraulic excavator, a boom is swingably connected at a distal end thereof to a stick, and a bucket is swingably connected at a distal end thereof to the stick. A drive system of the hydraulic excavator includes a boom cylinder for elevating the boom, a stick cylinder for swinging the stick, a bucket cylinder for swinging the bucket, and the like, and working fluid is supplied from a pump to these hydraulic actuators.

[0003] For example, Patent Document 1 discloses a boom cylinder drive device for a hydraulic excavator. In this boom cylinder drive device, a head side chamber of the boom cylinder is directly connected to a pump driven by an electric motor. Therefore, at the time of boom lowering operation, the electric motor functions as a generator to regenerate the potential energy of the boom.

[0004] On the other hand, a rod side chamber of the boom cylinder is connected to a tank and a hydraulic source via a switching valve. The switching valve is switched between a normal position in which the rod side chamber of the boom cylinder is communicated to the tank and an offset position in which the rod side chamber is communicated to the hydraulic source. The switching valve is controlled in accordance with the pressure of the head side chamber of the boom cylinder.

[0005] More specifically, when the pressure of the head side chamber is greater than a predetermined value, the switching valve is positioned at the normal position, and working fluid flows from the rod side chamber of the boom cylinder to the tank or reversely thereto. On the contrary, when the pressure of the head side chamber is less than the predetermined value, the switching valve is switched to the offset position, and working fluid is supplied from the hydraulic source to the rod side chamber of the boom cylinder. Thus, the pressure of the rod side chamber of the boom cylinder can be increased.

[0006] Further, a representative example when the pressure of the head side chamber is greater than the predetermined value is at the time of boom raising operation, and a representative example when the pressure of the head side chamber is less than the predetermined value is at the time of body lifting operation in which the boom cylinder is attempted to be shortened even after the bucket touches the ground due to an external force of the boom (expressed as "body raising" in Patent Document 1).

[0007] PRIOR ART DOCUMENTS

[0008] PATENT DOCUMENTS

[0009] Patent Document 1: Japanese Patent Application Publication No. 2005-315312 SUMMARY

[0010] PROBLEMS TO BE SOLVED BY THE INVENTION

[0011] However, in the boom cylinder drive device described in Patent Document 1, a dedicated pressure source is required for an operation in which the pressure of the head side chamber is relatively low, such as body lifting operation.

[0012] Therefore, an object of the present application is to provide a hydraulic excavator drive system capable of increasing the pressure of the rod-side chamber of the boom cylinder during the body-raising operation without using a dedicated pressure source.

[0013] Means for solving the problem:

[0014] To solve the problem, the hydraulic excavator drive system of the present application is characterized by comprising: a boom cylinder; a first pump connected to a head-side chamber of the boom cylinder through a head-side line and driven by an electric motor; a second pump for supplying working fluid to at least one of a stick cylinder and a bucket cylinder; a first switching valve provided on a rod-side line connecting a rod-side chamber of the boom cylinder and a tank, which opens the rod-side line during the boom-raising operation and blocks the rod-side line during the body-raising operation; and a second switching valve provided on a relay line connecting a portion between the rod-side chamber in the rod-side line and the first switching valve and a supply line extending from the second pump, which blocks the relay line during the boom-raising operation and opens the relay line during the body-raising operation.

[0015] According to the above-described structure, during the body-raising operation, the working fluid discharged from the second pump for the stick cylinder and / or the bucket cylinder is supplied to the rod-side chamber of the boom cylinder. Therefore, the body-raising operation can be performed without using a dedicated pressure source, and the pressure of the rod-side chamber of the boom cylinder during the body-raising operation can be increased.

[0016] Effects of the Invention

[0017] According to the present application, the body-raising operation can be performed without using a dedicated pressure source, and the pressure of the rod-side chamber of the boom cylinder during the body-raising operation can be increased. BRIEF DESCRIPTION OF DRAWINGS

[0018] Figure 1 is a schematic configuration view of a hydraulic excavator drive system of a first embodiment of the present application;

[0019] Figure 2 is a side view of a hydraulic excavator;

[0020] Figure 3 is a schematic configuration view of a hydraulic excavator drive system of a second embodiment of the present application;

[0021] Figure 4 is a schematic configuration view of a hydraulic excavator drive system of a modification example. DETAILED DESCRIPTION

[0022] (First Embodiment)

[0023] Figure 1 A hydraulic excavator drive system 1A of a first embodiment of the present application is shown, Figure 2 A hydraulic excavator 10 equipped with the drive system 1A is shown.

[0024] Figure 2 The hydraulic excavator 10 shown is self-propelled and includes a traveling body 11. Also, the hydraulic excavator 10 includes a swing body 12 rotatably supported on the traveling body 11 and a boom that is pitched with respect to the swing body 12. The tip end of the boom is swingably connected to a stick, and the tip end of the stick is swingably connected to a bucket. On the swing body 12, a cabin 16 provided with a driver's seat is provided. Also, the hydraulic excavator 10 can not be self-propelled.

[0025] As shown in FIG. 1, the drive system 1A includes the boom cylinder 13, the stick cylinder 14, and the bucket cylinder 15 as hydraulic actuators. As shown in FIG. 2, the boom cylinder 13 pitches the boom, the stick cylinder 14 swings the stick, and the bucket cylinder 15 swings the bucket. Also, the swing motor and the pair of left and right traveling motors omitted from the illustration can be included in the drive system 1A or in other drive systems. Figure 1 Figure 2 As shown in FIG. 1, the drive system 1A includes the boom cylinder 13, the stick cylinder 14, and the bucket cylinder 15 as hydraulic actuators. As shown in FIG. 2, the boom cylinder 13 pitches the boom, the stick cylinder 14 swings the stick, and the bucket cylinder 15 swings the bucket. Also, the swing motor and the pair of left and right traveling motors omitted from the illustration can be included in the drive system 1A or in other drive systems.

[0026] Also, the drive system 1A includes a first pump 22 for the boom cylinder 13 and a second pump 32 for the stick cylinder 14 and the bucket cylinder 15. The first pump 22 supplies working fluid to the boom cylinder 13 when the boom is raised. The second pump 32 supplies working fluid to the stick cylinder 14 when the stick is operated (when the stick is retracted and when the stick is extended) and supplies working fluid to the bucket cylinder 15 when the bucket is operated (when the bucket is excavated and when the bucket is dumped).

[0027] However, the second pump 32 need not necessarily supply working fluid to both the stick cylinder 14 and the bucket cylinder 15, but can supply working fluid to either one. For example, when the second pump 32 supplies working fluid to only the stick cylinder 14, working fluid can be supplied to the bucket cylinder 15 from a third pump.

[0028] More specifically, the second pump 32 supplies working fluid to the stick cylinder 14 via a stick control valve 41 and supplies working fluid to the bucket cylinder 15 via a bucket control valve 42. The second pump 32 is connected to a tank via a suction line 31 and is connected to the stick control valve 41 and the bucket control valve 42 via a supply line 33. In other words, the supply line 33 extends from the second pump 32, branches off midway, and is connected to the stick control valve 41 and the bucket control valve 42.

[0029] The stick control valve 41 controls the supply and discharge of working fluid with respect to the stick cylinder 14. The stick control valve 41 is connected to the stick cylinder 14 via a pair of supply and discharge lines 34, 35 and is connected to the tank via a tank line 36.

[0030] Similarly, the bucket control valve 42 controls the supply and discharge of working fluid with respect to the bucket cylinder 15. The bucket control valve 42 is connected to the bucket cylinder 15 via a pair of supply and discharge lines 37, 38 and is connected to the tank via a tank line 39.​

[0031] In this embodiment, the stick control valve 41 and the bucket control valve 42 operate via pilot pressure. A pair of pilot ports of the stick control valve 41 are connected to a pair of electromagnetic proportional valves (not shown in the diagram), and a pair of pilot ports of the bucket control valve 42 are also connected to a pair of electromagnetic proportional valves (not shown in the diagram). The stick control valve 41 and the bucket control valve 42 are controlled by the control device 7 (described later) via the aforementioned pair of electromagnetic proportional valves.

[0032] However, the stick control valve 41 and the bucket control valve 42 can also operate via electrical signals. In this case, the stick control valve 41 and the bucket control valve 42 are directly controlled by the control device 7.

[0033] The first pump 22 for boom cylinder 13 is connected to the tank via suction / discharge line 21, and directly connected to the head side chamber 13a of boom cylinder 13 via head side line 23. The rod side chamber 13b of boom cylinder 13 is connected to the tank via rod side line 24. A first switching valve 51 is provided on rod side line 24.

[0034] The first switching valve 51 is in the open position on the open rod side of the line 24. Figure 1 The left side position (neutral position in this embodiment) and the closed position of the blocking rod side line 24 ( Figure 1 The switching valve 51 is located between the right-hand and left-hand positions. In this embodiment, the first switching valve 51 is in the open position during boom raising operation and in the closed position during boom lowering operation and vehicle body lifting operation. Furthermore, boom lowering operation refers to the operation of lowering the boom while the bucket is in the air, and vehicle body lifting operation refers to the operation of lifting the vehicle body (driving body 11 and rotating body 12) by pressing the bucket against the ground, etc.

[0035] The portion of the pole-side chamber 13b in the pole-side line 24 between the pole-side chamber 13b and the first switching valve 51 is connected to the aforementioned supply line 33 via a relay line 25. A second switching valve 52 is provided on the relay line 25.

[0036] The second switching valve 52 is in the closed position when blocking the relay line 25. Figure 1 The lower position (neutral position in this embodiment) and the open position of the open relay line 25 ( Figure 1 The second switching valve 52 is configured such that its opening area is variable in the open position.

[0037] In this embodiment, the second switching valve 52 is in the closed position during boom raising and lowering operations, and in the open position during vehicle lifting operations. Therefore, the working fluid flows only in the relay line 25 during vehicle lifting operations.

[0038] Furthermore, in this embodiment, the second switching valve 52 is provided with (assembled with) a check valve 26 that allows flow from the supply line 33 toward the rod-side line 24 but prohibits reverse flow during the vehicle body lifting operation. However, the check valve 26 may also be provided on the relay line 25 on the upstream or downstream side of the second switching valve 52.

[0039] Furthermore, in this embodiment, the suction / ejection line 21 is connected via the regeneration line 27 to the portion between the rod-side chamber 13b and the first switching valve 51 in the rod-side line 24. The regeneration line 27 is equipped with a third switching valve 53. Additionally, the suction / ejection line 21 is equipped with a fourth switching valve 91 to divide it into a tank-side flow path 21a and a pump-side flow path 21b. That is, the regeneration line 27 connects the pump-side flow path 21b of the suction / ejection line 21 to the portion between the rod-side chamber 13b and the first switching valve 51 in the rod-side line 24.

[0040] The third switching valve 53 is in the closed position, blocking the regeneration line 27. Figure 1 The upper position (neutral position in this embodiment) and the open position of the open regeneration line 27 ( Figure 1 The third switching valve 53 is in the open position during boom lowering operation and in the closed position otherwise.

[0041] The fourth switching valve 91 is connected to the tank via a parallel line 92. A check valve 93 with a specified cracking pressure (e.g., 0.1–3.0 MPa) is provided on the parallel line 92. The fourth switching valve 91 is in its normal position ( Figure 1 The right-hand position (neutral position in this embodiment) and the regeneration position ( Figure 1 The fourth switching valve 91 switches between the left and right positions. In the normal position, it blocks the parallel line 92 and connects the pump-side flow path 21b of the suction and discharge lines 21 with the tank-side flow path 21a. In the regeneration position, it blocks the tank-side flow path 21a and connects the pump-side flow path 21b with the parallel line 92. The fourth switching valve 91 is in the regeneration position during boom lowering operation and in the normal position otherwise.

[0042] In this embodiment, the first switching valve 51, the second switching valve 52, the third switching valve 53, and the fourth switching valve 91 operate via electrical signals. These valves are controlled by the control device 7. However, at least one of the valves can operate via a pilot pressure. For example, when the first switching valve 51 operates via a pilot pressure, it is controlled by the control device 7 via an electromagnetic proportional valve.

[0043] The first pump 22 is driven by the first electric motor 61, and the second pump 32 is driven by the second electric motor 62. The first electric motor 61 and the second electric motor 62 are connected to the battery 65 via converters 63 and 64, respectively. That is, when the first electric motor 61 drives the first pump 22, power is supplied from the battery 65 to the first electric motor 61; when the second electric motor 62 drives the second pump 32, power is supplied from the battery 65 to the second electric motor 62. Alternatively, a capacitor can be used instead of the battery 65. Furthermore, the first electric motor 61 and the second electric motor 62 are controlled by the control device 7 via converters 63 and 64, respectively.

[0044] The cab 16 is equipped with a boom operating device 81, a stick operating device 82, and a bucket operating device 83. The boom operating device 81 includes a lever for operating in the boom raising and lowering directions; the stick operating device 82 includes a lever for operating in the stick retraction and extension directions; and the bucket operating device 83 includes a lever for operating in the bucket digging and dumping directions. Furthermore, the boom operating device 81, stick operating device 82, and bucket operating device 83 each output operating signals corresponding to the operating direction and amount (tilt angle) of the levers.

[0045] Specifically, the boom operating device 81 outputs a boom raising operation signal corresponding to the amount of operation when the operating stick is operated in the boom raising direction, and outputs a boom lowering operation signal corresponding to the amount of operation when the operating stick is operated in the boom lowering direction. Similarly, the stick operating device 82 outputs a stick operation signal (stick retraction operation signal or stick extension operation signal) corresponding to the amount of operation when the operating stick is operated in the stick retraction direction or stick extension direction, and the bucket operating device 83 outputs a bucket operation signal (bucket digging operation signal or bucket dumping operation signal) corresponding to the amount of operation when the operating stick is operated in the bucket digging direction or bucket dumping direction.

[0046] In this embodiment, the boom operating device 81, the stick operating device 82, and the bucket operating device 83 are all electric control levers that output electrical signals as operating signals. However, the stick operating device 82 and the bucket operating device 83 can also be pilot operating valves that output pilot pressure as operating signals. In this case, a pair of pilot ports of the stick control valve 41 can be connected to the stick operating device 82, and a pair of pilot ports of the bucket control valve 42 can be connected to the bucket operating device 83.

[0047] Operating signals (electrical signals) output from the boom operating device 81, stick operating device 82, and bucket operating device 83 are input to the control device 7. For example, the control device 7 is a computer with memory such as ROM or RAM, storage such as HDD or SSD, and a CPU. The program stored in the ROM or storage is executed by the CPU.

[0048] When the control device 7 outputs a stick operation signal from the stick operation device 82 (during stick operation), it controls the stick control valve 41 via a solenoid proportional valve (not shown) in a manner that the larger the operation amount of the stick operation device 82's lever, the larger the opening area of ​​the stick control valve 41. Alternatively, when only the stick operation device 82's lever is operated, the control device 7 can also adjust the speed of the second motor 62 via a converter 64 in a manner that the larger the operation amount, the larger the discharge flow rate of the second pump 32. The speed of the second motor 62 can also be constant.

[0049] Similarly, when the control device 7 outputs a bucket operation signal from the bucket operating device 83 (during bucket operation), it controls the bucket control valve 42 via a solenoid proportional valve (not shown) in a manner that the larger the amount of operation of the operating lever of the bucket operating device 83, the larger the opening area of ​​the bucket control valve 42. Alternatively, when only the operating lever of the bucket operating device 83 is operated, the control device 7 can also adjust the speed of the second motor 62 via a converter 64 in a manner that the larger the amount of operation, the larger the discharge flow rate of the second pump 32. The speed of the second motor 62 can also be constant.

[0050] When the boom lifting operation signal is output from the boom operating device 81 (during boom lifting operation), the control device 7 adjusts the speed of the first motor 61 via the converter 63 in such a way that the greater the operation amount of the operating lever of the boom operating device 81, the greater the discharge flow of the first pump 22.

[0051] Furthermore, during boom lifting operation, control device 7 maintains the first switching valve 51 in the open position, the second switching valve 52 in the closed position, the third switching valve 53 in the closed position, and the fourth switching valve 91 in the normal position. That is, control device 7 does not send command current to any of the first switching valve 51, the second switching valve 52, the third switching valve 53, and the fourth switching valve 91. As a result, working fluid is drawn from the tank into the first pump 22 through the suction and discharge lines 21 (tank-side flow path 21a, fourth switching valve 91, and pump-side flow path 21b), and working fluid discharged from the rod-side chamber 13b of the boom cylinder 13 flows into the tank through the rod-side line 24.

[0052] When the boom lowering operation signal is output from the boom operating device 81, the control device 7 determines whether a boom lowering operation or a vehicle body lifting operation has been performed. In this embodiment, the control device 7 is electrically connected to a pressure sensor 71 that detects the pressure Ph of the head chamber 13a of the boom cylinder 13. In the illustration, the pressure sensor 71 is located in the head side line 23, but the pressure sensor 71 can also be located in the head chamber 13a of the boom cylinder 13.

[0053] When the boom lowering operation signal is output from the boom operating device 81 and the pressure Ph detected by the pressure sensor 71 is greater than a predetermined value (e.g., set within the range of 0.5 to 10 MPa), the control device 7 determines that a boom lowering operation has been performed. Conversely, when the boom lowering operation signal is output from the boom operating device 81 and the pressure Ph detected by the pressure sensor 71 is less than the predetermined value, the control device 7 determines that a vehicle body lifting operation has been performed. That is, during the operation of the operating lever of the boom operating device 81 in the boom lowering direction, if the pressure Ph detected by the pressure sensor 71 is lower than the predetermined value, the control device 7 determines that a vehicle body lifting operation has begun.

[0054] However, the method for determining whether a boom lowering operation or a vehicle body lifting operation has been performed when the boom operating device 81 outputs a boom lowering operation signal is not limited to this. For example, the control device 7 may determine that a boom lowering operation has been performed when the boom operating device 81 outputs a boom lowering operation signal and the regenerative current generated by the first motor 61 is greater than a predetermined value, and determine that a vehicle body lifting operation has been performed when the boom operating device 81 outputs a boom lowering operation signal and the regenerative current generated by the first motor 61 is less than the predetermined value. That is, the control device 7 may also determine that a vehicle body lifting operation has started when the regenerative current generated by the first motor 61 is lower than the predetermined value during the operation of the boom operating device 81's operating lever in the boom lowering direction.

[0055] Alternatively, the control device 7 may determine that a boom lowering operation has been performed when the boom operating device 81 outputs a boom lowering operation signal and the pressure Pr of the rod side chamber 13b of the boom cylinder 13 is less than a specified value; and it may determine that a vehicle body lifting operation has been performed when the boom operating device 81 outputs a boom lowering operation signal and the pressure Pr of the rod side chamber 13b is greater than the specified value.

[0056] During the boom lowering operation, the control device 7 keeps the second switching valve 52 in the closed position, switches the first switching valve 51 to the closed position, and switches the third switching valve 53 to the open position. Then, the control device 7 switches the fourth switching valve 91 to the regeneration position. That is, the control device 7 sends a command current to the first switching valve 51, the third switching valve 53, and the fourth switching valve 91. As a result, a portion of the working fluid discharged from the head chamber 13a of the boom cylinder 13 and passing through the first pump 22 flows into the rod chamber 13b through the regeneration line 27 and the rod side line 24, while the remainder flows into the tank through the fourth switching valve 91 and the parallel line 92.

[0057] During boom lowering operation, the first pump 22 is driven by the working fluid discharged from the head chamber 13a of the boom cylinder 13, acting as a motor. Thus, the first electric motor 61 functions as a generator, regenerating the boom's potential energy. The generated electricity is stored in the battery 65. During boom lowering operation, the control device 7 reduces the regenerative torque (braking force) of the first electric motor 61 as the operating lever of the boom operating device 81 is operated more.

[0058] As described above, when the control device 7 determines that the vehicle body lifting operation has begun, it switches the second switching valve 52 from the closed position to the open position via the electromagnetic proportional valve (not shown in the diagram). More specifically, during the vehicle body lifting operation, the control device 7 maintains the third switching valve 53 in the closed position and the fourth switching valve 91 in the normal position, switches the first switching valve 51 to the closed position, and switches the second switching valve 52 to the open position. That is, the control device 7 sends a command current to the first switching valve 51 and the second switching valve 52. As a result, the working fluid discharged from the second pump 32 is supplied to the boom cylinder 13's boom-side chamber 13b via the supply line 33, the relay line 25 (second switching valve 52), and the boom-side line 24. Furthermore, the working fluid discharged from the boom cylinder 13's head-side chamber 13a and passed through the first pump 22 flows into the tank via the suction-discharge line 21 (pump-side flow path 21b, fourth switching valve 91, and tank-side flow path 21a).

[0059] Furthermore, during the vehicle lifting operation, the control device 7 adjusts the discharge flow rate of the second pump 32 according to the amount of operation of the boom operating device 81's operating lever. For example, if neither the stick operating device 82 nor the bucket operating device 83 is operated, the control device 7 adjusts the speed of the second motor 62 via the converter 64 during the vehicle lifting operation, such that the greater the amount of operation of the boom operating device 81's operating lever, the greater the discharge flow rate of the second pump 32.

[0060] Furthermore, when the vehicle body is lifted, if neither the stick operating device 82 nor the bucket operating device 83 is operated, the control device 7 maximizes the opening area of ​​the second switching valve 52. If either the stick operating device 82 or the bucket operating device 83 is operated, the control device 7 controls the second switching valve 52 to function as a throttling device.

[0061] As explained above, in the hydraulic excavator drive system 1A of this embodiment, during the vehicle lifting operation, working fluid discharged from the second pump 32 for the boom cylinder 14 and bucket cylinder 15 is supplied to the rod side chamber 13b of the boom cylinder 13. Therefore, the pressure in the rod side chamber 13b of the boom cylinder 13 can be increased during the vehicle lifting operation without the need for a dedicated pressure source.

[0062] Furthermore, in this embodiment, the discharge flow rate of the second pump 32 is adjusted during the vehicle body lifting operation, so the second pump 32 can prevent cavitation from occurring in the rod side chamber 13b of the boom cylinder 13.

[0063] Furthermore, in this embodiment, a third switching valve 53 is used, so that during boom lowering operation, the working fluid discharged from the first pump 22 can be regenerated without returning to the tank. Moreover, during boom lowering operation, the fourth switching valve 91 switches to the regeneration position, so the pressure of the regenerated working fluid remains high during boom lowering operation. As a result, cavitation in the rod-side chamber 13b of the boom cylinder 13 can be effectively prevented.

[0064] Furthermore, in this embodiment, a check valve 26 is provided on the second switching valve 52, so that even when the vehicle body lifting operation is performed simultaneously with the stick operation or the bucket operation, the extension of the boom cylinder 13 can be prevented.

[0065] Furthermore, in this embodiment, during vehicle lifting operation, if neither the stick operating device 82 nor the bucket operating device 83 is operated, the opening area of ​​the second switching valve 52 is at its maximum, thereby suppressing pressure loss at the second switching valve 52 relative to the working fluid supplied from the second pump 32 to the stick side chamber 13b. On the other hand, if either the stick operating device 82 or the bucket operating device 83 is operated, the second switching valve 52 functions as a throttling device, thereby ensuring the discharge pressure of the second pump 32.

[0066] <Variation Example>

[0067] In this embodiment, the second switching valve 52 is in the closed position during boom lowering operation, but it can also be in the open position during boom lowering operation. Insufficient intake of working fluid into the rod-side chamber 13b during boom lowering operation can cause cavitation. Therefore, switching the second switching valve 52 to the open position during boom lowering operation to supply working fluid (pressure oil) discharged from the second pump 32 to the rod-side chamber 13b can prevent such cavitation.

[0068] Furthermore, when the second switching valve 52 is in the open position during boom lowering operation, the opening area of ​​the second switching valve 52 is controlled in the same way as during vehicle lifting operation. That is, during boom lowering operation, when neither the stick operating device 82 nor the bucket operating device 83 is operated, the control device 7 maximizes the opening area of ​​the second switching valve 52; when either the stick operating device 82 or the bucket operating device 83 is operated, the control device 7 controls the second switching valve 52 so that it functions as a throttling device.

[0069] Therefore, similarly to the vehicle body lifting operation in the aforementioned embodiment, during the boom lowering operation, if neither the stick operating device 82 nor the bucket operating device 83 is operated, pressure loss at the second switching valve 52 can be suppressed; if either the stick operating device 82 or the bucket operating device 83 is operated, the discharge pressure of the second pump 32 can be ensured. Furthermore, when the second switching valve 52 is in the open position during the boom lowering operation, the check valve 26 also functions during the boom lowering operation.

[0070] Furthermore, all of the above-described modifications can also be used in the second embodiment.

[0071] (Second Implementation)

[0072] Figure 3 The hydraulic excavator drive system 1B according to the second embodiment of the present invention is shown. Furthermore, in this embodiment, the same reference numerals are used for components identical to those in the first embodiment, and repeated descriptions are omitted. Figure 3 The drawings of the first motor 61, the second motor 62, and the control device 7 are omitted.

[0073] In this embodiment, the head-side line 23 is connected to the tank via a bypass line 94. The bypass line 94 is equipped with a vehicle body lifting switching valve 95. The vehicle body lifting switching valve 95 is controlled by a control device 7 (not shown) to be in the closed position, blocking the bypass line 94, except during vehicle body lifting operations. Figure 3 The right-hand position (neutral position in this embodiment) is located in the open position of the open bypass line 94 during the vehicle body lifting operation. Figure 3 (The left side position).

[0074] This embodiment also achieves the same effect as the first embodiment. Furthermore, in this embodiment, the working fluid discharged from the head chamber 13a of the boom cylinder 13 during the vehicle lifting operation does not return to the tank via the first pump 22, thus improving energy efficiency compared to the case in the first embodiment where the working fluid returns to the tank via the first pump 22.

[0075] (Other implementation methods)

[0076] This invention is not limited to the above-described embodiments, and various modifications can be made without departing from the spirit of this invention.

[0077] For example, in the first and second embodiments, the first pump 22 and the second pump 32 do not necessarily have to be fixed-capacity pumps; they can also be variable-capacity pumps. When the second pump 32 is a variable-capacity pump, it can also be driven by an engine (internal combustion engine).

[0078] When the second pump 32 is a variable capacity pump, the control device 7 can also adjust the discharge flow rate of the second pump 32 according to the operation amount of the operating lever of the boom operating device 81 by changing the tilt angle of the second pump 32.

[0079] Furthermore, the regeneration line 27 with the third switching valve 53 and the fourth switching valve 91 can be omitted. In this case, the first switching valve 51 is in the open position during the boom lowering operation.

[0080] Or, such as Figure 4 In the modified hydraulic excavator drive system 1C shown, in the first and second embodiments, instead of the third switching valve 53, a check valve 54 can be provided on the regeneration line 27 to allow flow from the intake / exhaust line 21 toward the rod-side line 24 but prevent its reverse flow. With such a structure, pressure loss tends to increase, but the circuit structure becomes simpler, thus reducing costs.

[0081] (Summarize)

[0082] The hydraulic excavator drive system of the present invention is characterized by comprising: a boom cylinder; a first pump connected to the head side chamber of the boom cylinder via a head side line and driven by an electric motor; a second pump supplying working fluid to at least one of a stick cylinder and a bucket cylinder; a first switching valve disposed on a stick side line connecting the stick side chamber of the boom cylinder to the tank, the stick side line being open during boom lifting operation and closed during vehicle lifting operation; and a second switching valve disposed on a relay line connecting the portion of the stick side line between the stick side chamber and the first switching valve to a supply line extending from the second pump, the relay line being closed during boom lifting operation and open during vehicle lifting operation.

[0083] According to the above structure, during vehicle lifting operations, working fluid discharged from a second pump used for the boom cylinder and / or bucket cylinder is supplied to the rod-side chamber of the boom cylinder. Therefore, vehicle lifting operations do not require a dedicated pressure source, and the pressure in the rod-side chamber of the boom cylinder can be increased during vehicle lifting operations.

[0084] For example, the second switching valve may be in the closed position, blocking the relay line, during boom raising and lowering operations, and in the open position, opening the relay line, during vehicle lifting operations. Alternatively, the aforementioned hydraulic excavator drive system may include: a boom operating device with an operating lever that operates in the boom raising and lowering directions; and a control device that controls the motor and the second switching valve; wherein, during the boom operating device's operation in the boom lowering direction, if the regenerative current generated by the motor is lower than a predetermined value, the control device determines that a vehicle lifting operation has begun and switches the second switching valve from the closed position to the open position.

[0085] Alternatively, when the second switching valve is in the closed position during boom lowering operation, the aforementioned hydraulic excavator drive system includes: a boom operating device with an operating lever that operates in the boom lifting direction and the boom lowering direction; a pressure sensor that detects the pressure in the head chamber of the boom cylinder; and a control device that controls the electric motor and the second switching valve; wherein, during the operation of the operating lever of the boom operating device in the boom lowering direction, when the pressure detected by the pressure sensor is lower than a predetermined value, the control device determines that the vehicle body lifting operation has started and switches the second switching valve from the closed position to the open position.

[0086] Alternatively, the second switching valve may be in the closed position, blocking the relay line, during boom lifting operation, and in the open position, opening the relay line, during boom lowering operation and vehicle body lifting operation, while the first switching valve blocks the rod-side line during boom lowering operation.

[0087] Alternatively, the aforementioned hydraulic excavator drive system may include a boom operating device, a stick operating device, a bucket operating device, and a control device for controlling the motor and the second switching valve. The second switching valve is configured such that its opening area is variable when the relay line is open. When the second switching valve is in the open position, the opening area of ​​the second switching valve is at its maximum if neither the stick operating device nor the bucket operating device is operated. If either the stick operating device or the bucket operating device is operated, the control device controls the second switching valve to function as a throttling mechanism. According to this structure, when the second switching valve is in the open position, if neither the stick operating device nor the bucket operating device is operated, the opening area of ​​the second switching valve is at its maximum, thereby suppressing pressure loss at the second switching valve relative to the working fluid supplied from the second pump to the boom chamber. On the other hand, if either the stick operating device or the bucket operating device is operated, the second switching valve functions as a throttling mechanism, ensuring the discharge pressure of the second pump.

[0088] Alternatively, the aforementioned hydraulic excavator drive system may include: a boom operating device comprising an operating lever for operating in the boom lifting and lowering directions; and a control device for controlling the electric motor and adjusting the discharge flow rate of the second pump; wherein, during boom lifting operation, the control device adjusts the discharge flow rate of the second pump according to the amount of operation of the operating lever of the boom operating device. With this structure, cavitation in the rod-side chamber of the boom cylinder can be prevented by the second pump.

[0089] Alternatively, the second switching valve or the relay line may be equipped with a check valve that allows flow from the supply line toward the boom-side line but prohibits reverse flow during the vehicle lift operation. With this configuration, boom cylinder extension can also be prevented when the vehicle lift operation is performed simultaneously with boom or bucket operation.

[0090] Alternatively, the first pump can be connected to the tank via an intake / exhaust line. The aforementioned hydraulic excavator drive system includes a third switching valve, which is located on the regeneration line connecting the intake / exhaust line to the portion of the boom-side line between the boom-side chamber and the first switching valve. This third switching valve opens the regeneration line during boom lowering operations and closes it during boom lowering operations. The first switching valve closes the boom-side line during boom lowering operations. With this structure, regeneration is achieved by preventing the working fluid discharged from the first pump from returning to the tank during boom lowering operations.

[0091] Alternatively, the intake / output line may be equipped with a fourth switching valve to divide it into a tank-side flow path and a pump-side flow path. The regeneration line connects the pump-side flow path of the intake / output line to the portion between the rod-side chamber and the first switching valve in the rod-side line. The fourth switching valve is connected to the tank via a parallel line, which is equipped with a check valve having a specified cracking pressure. During boom lowering operations, the fourth switching valve connects the pump-side flow path to the parallel line; otherwise, it connects the pump-side flow path to the tank-side flow path. With this structure, the pressure of the regenerated working fluid remains high during boom lowering operations, thus effectively preventing cavitation in the rod-side chamber.

[0092] Alternatively, the aforementioned hydraulic excavator drive system may include a body-lifting switching valve located on a bypass line connecting the boom side line and the tank. This valve opens the bypass line during body-lifting operations and closes it during other operations. With this configuration, during body-lifting operations, the working fluid discharged from the boom cylinder's boom side chamber does not return to the tank via the first pump, thus improving energy efficiency compared to the case where the working fluid returns to the tank via the first pump.

[0093] Symbol explanation:

[0094] 1A and 1B Hydraulic Excavator Drive Systems

[0095] 10 Hydraulic Excavators

[0096] 13 Boom Cylinder

[0097] 13a Cephalic ventricle

[0098] 13b pole side chamber

[0099] 14. Bucket cylinder

[0100] 15 Bucket Cylinder

[0101] 21 Inhalation and Ejaculation Circuit

[0102] 21a Tank-side flow path

[0103] 21b Pump-side flow path

[0104] 22 First Pump

[0105] 23 Head Side Line

[0106] 24 pole side line

[0107] 25 trunk lines

[0108] 26 Check valve

[0109] 27 Recycling Circuit

[0110] 32 Second Pump

[0111] 33 Supply Lines

[0112] 51 First switching valve

[0113] 52 Second switching valve

[0114] 53 Third switching valve

[0115] 61 First Electric Motor

[0116] 62 Second motor

[0117] 7. Control device

[0118] 71 Pressure Sensor

[0119] 81 Boom Operating Device

[0120] 82. Stick Operating Device

[0121] 83 Bucket Operating Device

[0122] 91 Fourth switching valve

[0123] 92 parallel lines

[0124] 93 Check valve

[0125] 94 Bypass Line

[0126] 95. Use the switching valve to lift the vehicle body.

Claims

1. A hydraulic excavator drive system, characterized by, Possessing: a boom cylinder; a first pump connected to a head side chamber of the boom cylinder through a head side line and connected to a tank through a suction / discharge line and driven by an electric motor; a second pump that supplies working fluid to at least one of a stick cylinder and a bucket cylinder; a first switching valve provided on a rod side line connecting a rod side chamber of the boom cylinder to the tank, opened during a boom raising operation, and blocked during a boom lowering operation and a body raising operation; a second switching valve provided on a relay line connecting a portion between the rod side chamber in the rod side line and the first switching valve to a supply line extending from the second pump, blocked during the boom raising operation, and opened during the body raising operation; and a third switching valve provided on a regeneration line connecting the suction / discharge line to a portion between the rod side chamber in the rod side line and the first switching valve, opened during the boom lowering operation, and blocked except during the boom lowering operation.

2. The hydraulic excavator drive system according to claim 1, wherein the second switching valve is in a closed position blocking the relay line during the boom raising operation and the boom lowering operation, and in an open position opening the relay line during the body raising operation.

3. The hydraulic excavator drive system according to claim 2, wherein an arm operation device including an operation lever operated in a boom raising direction and a boom lowering direction is provided; and a control device that controls the electric motor and the second switching valve is provided; the control device determines that the body raising operation has started when a regenerated current generated by the electric motor is lower than a predetermined value during operation of the operation lever of the arm operation device in the boom lowering direction, and switches the second switching valve from the closed position to the open position.

4. The hydraulic excavator drive system according to claim 2, wherein an arm operation device including an operation lever operated in a boom raising direction and a boom lowering direction is provided; a pressure sensor that detects a pressure of a head side chamber of the boom cylinder is provided; and a control device that controls the electric motor and the second switching valve is provided; the control device determines that the body raising operation has started when the pressure detected by the pressure sensor is lower than a predetermined value during operation of the operation lever of the arm operation device in the boom lowering direction, and switches the second switching valve from the closed position to the open position.

5. The hydraulic excavator drive system according to claim 1, wherein the second switching valve is in a closed position blocking the relay line during the boom raising operation, and in an open position opening the relay line during the boom lowering operation and the body raising operation.

6. The hydraulic excavator drive system according to any one of claims 1 to 5, wherein an arm operation device, a stick operation device, and a bucket operation device are provided; and a control device that controls the electric motor and the second switching valve is provided; the second switching valve is configured to have a variable opening area in the open position opening the relay line. ​ ​ ​ The control device controls the second switching valve so that the second switching valve functions as a throttle when either of the boom operating device and the bucket operating device is operated.

7. The hydraulic excavator drive system according to any one of claims 1 to 5, characterized in that a boom operating device that includes an operation lever operated in a boom raising direction and a boom lowering direction is provided; and a control device that controls the electric motor and adjusts the discharge flow rate of the second pump is provided; the control device adjusts the discharge flow rate of the second pump in accordance with an operation amount of the operation lever of the boom operating device when a body raising operation is performed.

8. The hydraulic excavator drive system according to any one of claims 1 to 5, characterized in that a check valve that allows flow from the supply line toward the rod-side line but prohibits reverse flow thereof at least when a body raising operation is performed is provided on the second switching valve or the relay line.

9. The hydraulic excavator drive system according to any one of claims 1 to 5, characterized in that a fourth switching valve is provided on the suction-discharge line to divide the suction-discharge line into a tank-side flow path and a pump-side flow path, and the regeneration line connects the pump-side flow path of the suction-discharge line and a portion between the rod-side chamber and the first switching valve in the rod-side line; the fourth switching valve is connected to the tank through a parallel line on which a check valve having a prescribed cracking pressure is provided; the fourth switching valve communicates the pump-side flow path and the parallel line when a boom lowering operation is performed, and communicates the pump-side flow path and the tank-side flow path other than when a boom lowering operation is performed.

10. The hydraulic excavator drive system according to any one of claims 1 to 5, characterized in that a body raising switching valve is provided on a bypass line that connects the head-side line and the tank, and opens the bypass line when a body raising operation is performed, and blocks the bypass line other than when a body raising operation is performed.

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