Hydraulic system of crawler-type walking device and crawler-type vehicle with hydraulic system

Abstract

The utility model provides a hydraulic system of a crawler-type walking device and a crawler-type vehicle with the hydraulic system, and provides a structure capable of promoting better circulation of working oil in the hydraulic system of the crawler-type walking device such as a crawler-type carrying vehicle. A hydraulic system (Sa) is provided with: closed circuits (C1, C2) that are respectively provided with respect to a pair of crawler belts (16R, 16L) and that circulate hydraulic oil between hydraulic pumps (22, 24) and hydraulic motors (32R, 32L); an oil supply passage (47) that supplies hydraulic oil from the hydraulic oil tank (44) to the closed circuit by the operation of the oil supply pump (26); a return oil passage (60) in which the cooler (63) is provided, the return oil passage returning the hydraulic oil from the closed circuit to the hydraulic oil tank (44); and adjustment valve mechanisms (70a, 70b) as adjustment means for adjusting the flow rate of the hydraulic oil from the closed circuit to the hydraulic oil tank via the return oil passage.

Description

Technical Field

[0001] This disclosure relates to a hydraulic system for the tracked walking device of tracked vehicles such as tracked transport vehicles, and to a tracked vehicle having the system. Background Technology

[0002] Among tracked vehicles, there are vehicles that incorporate an HST (Hydro Static Transmission) in the drive transmission unit that transmits engine power to the tracked walking device (see, for example, Patent Document 1). The HST includes a hydraulic pump and a hydraulic motor, forming a closed loop that circulates working oil between the pump and the motor. In the HST, the engine power drives the hydraulic pump, and the working oil discharged from the pump drives the hydraulic motor. Furthermore, the power from the HST's hydraulic motor is transmitted to the left and right tracks via a power transmission mechanism that includes a drive sprocket.

[0003] Patent Document 1: Japanese Patent Application Publication No. 2022-12004

[0004] Furthermore, tracked vehicles are mostly so-called work vehicles, operating in a wide variety of environments, and the hydraulic system with HST needs to operate smoothly in these environments. For example, good circulation of the working oil in the hydraulic system is expected. Utility Model Content

[0005] The purpose of this disclosure is to provide a structure that promotes better circulation of the working oil in the hydraulic system of the tracked walking device of a tracked vehicle such as a tracked transporter.

[0006] One aspect of this disclosure is a hydraulic system for a tracked walking device, characterized in that the hydraulic system comprises: a closed-loop circuit disposed about a pair of tracks, wherein working oil circulates between a hydraulic pump and a hydraulic motor, the hydraulic pump being driven by a power source, and the hydraulic motor being driven by the working oil discharged from the hydraulic pump and generating power to be transmitted to the tracks; a supply oil circuit that supplies working oil from a working oil tank to the closed-loop circuit by the action of a supply oil pump driven by the power source; a return oil circuit, in which a cooler is disposed, the return oil circuit returning the working oil from the closed-loop circuit to the working oil tank; and an adjustment unit that adjusts the flow rate of the working oil from the closed-loop circuit to the working oil tank via the return oil circuit.

[0007] The hydraulic system described above according to one aspect of this disclosure has the aforementioned closed circuit, the aforementioned supply oil circuit, the aforementioned return oil circuit, and the aforementioned adjustment unit, thereby promoting better circulation of the working oil in the hydraulic system.

[0008] Preferably, the aforementioned hydraulic system includes an adjusting valve mechanism with a control valve that is controlled according to the rotational speed of the output shaft of the power source, so that the working oil in the low-pressure side of the first and second oil circuits connecting the hydraulic pump and the hydraulic motor flows to the return oil circuit. According to this structure, the working oil in the low-pressure side of the aforementioned oil circuit can be returned to the working oil tank according to the rotational speed of the output shaft of the power source, thereby stably maintaining the necessary pressure in the low-pressure side oil circuit and improving the cleanliness and cooling properties of the working oil.

[0009] Preferably, the aforementioned hydraulic system includes: a low-pressure selector valve that opens the low-pressure side of the first and second oil circuits connecting the hydraulic pump and the hydraulic motor; and a control valve that is controlled according to the rotational speed of the output shaft of the power source to vary the flow rate of the working oil in the low-pressure side oil circuit to the return oil circuit. According to this structure, the low-pressure side oil circuit can be selectively opened using the low-pressure selector valve, and the flow of working oil from the low-pressure side oil circuit to the return oil circuit can be more effectively adjusted using the control valve. Therefore, the working oil in the low-pressure side oil circuit can be returned to the working oil tank more effectively according to the rotational speed of the output shaft of the power source, thereby stably maintaining the necessary pressure in the low-pressure side oil circuit and improving the cleanliness and cooling properties of the working oil.

[0010] Preferably, the oil passage connecting the low-pressure side and the return oil passage extends in a manner that allows the working oil from the low-pressure side oil passage to flow to the working oil tank via the hydraulic motor. According to this structure, the working oil from the aforementioned oil passage on the low-pressure side can be used to more effectively return the working oil in the hydraulic motor to the working oil tank, thereby promoting better circulation of the working oil in the hydraulic system.

[0011] Preferably, a regulating valve that opens when a predetermined pressure is applied is provided in the bypass oil passage of the return oil passage, which is arranged to bypass the cooler. According to this structure, for example, when the oil temperature is below a predetermined temperature and the oil viscosity is above a predetermined level, even if the working oil in the cooler is relatively clogged, the working oil can flow more effectively to the working oil tank, thereby promoting better circulation of the working oil in the hydraulic system.

[0012] Preferably, the return oil circuit includes: a pump return oil circuit extending from the hydraulic pump toward the working oil tank; and a motor return oil circuit extending from the hydraulic motor toward the working oil tank. Furthermore, the cooler is located downstream of the confluence of the pump return oil circuit and the motor return oil circuit. In this case, the cooler can effectively cool the working oil flowing from the pump return oil circuit and the motor return oil circuit to the working oil tank.

[0013] The technology disclosed herein also exists in tracked vehicles with hydraulic systems having the aforementioned tracked walking devices.

[0014] According to one of the embodiments of this disclosure, having the above-described structure, it is possible to promote better circulation of the working oil in the hydraulic system of the tracked walking device. Attached Figure Description

[0015] Figure 1 This is a perspective view of one implementation of a tracked transport vehicle.

[0016] Figure 2 yes Figure 1 Right view of a tracked transport vehicle.

[0017] Figure 3 yes Figure 1 Front view of the tracked transport vehicle.

[0018] Figure 4 yes Figure 1 A top view of a tracked transport vehicle.

[0019] Figure 5 yes Figure 1 A block diagram of the hydraulic system of a tracked transporter.

[0020] Figure 6 yes Figure 1 A schematic diagram of the hydraulic circuit of the hydraulic system for travel in the hydraulic system of a tracked transport vehicle.

[0021] Figure 7 yes Figure 1 A block diagram of the control structure of the adjusting valve mechanism in the hydraulic system of a tracked transport vehicle.

[0022] Figure 8 It is shown Figure 1 The figure shows a modified example of the hydraulic system for traveling of a tracked transport vehicle, which is a schematic structural diagram of the hydraulic circuit of the hydraulic system for traveling.

[0023] Label Explanation

[0024] 10: Tracked transport vehicle; 12: Engine; 14: Tracked travel unit; 16: Track; 22, 24: Hydraulic pump; 26: Oil supply pump; 32R, 32L: Hydraulic motor; 60: Return oil circuit; 61: Pump return oil circuit; 62: Motor return oil circuit; 63: Cooler; 66: Inspection valve (adjusting valve); 70a, 70b: Adjusting valve mechanism; 72, 76: Low-pressure selector valve; 74, 78: Relief valve (control valve); C1, C2: HST closed circuit; S: Hydraulic system; Sa, Sb: Hydraulic system for travel (hydraulic system of tracked travel unit). Detailed Implementation

[0025] Hereinafter, embodiments of the present disclosure will be described with reference to the accompanying drawings. Identical components (or structures) are labeled with the same reference numerals, and their names and functions are also the same. Therefore, detailed descriptions of them will not be repeated.

[0026] First, a tracked transport vehicle 10 having a hydraulic system S according to one embodiment of the present disclosure will be described with reference to the accompanying drawings.

[0027] Figures 1 to 4 These are perspective views, right views, front views, and top views of a tracked transport vehicle (hereinafter referred to as the transport vehicle) 10. The transport vehicle 10 has a tracked traveling device (hereinafter referred to as the traveling device) 14 powered by an engine 12. The traveling device 14 has tracks 16, namely a pair of tracks 16R and 16L. Specifically, the tracks 16 have a left track (left track) 16L and a right track (right track) 16R, which respectively form a circular track. The traveling device 14 has: a left-side traveling device (left traveling device) 14L with the left track 16L; and a right-side traveling device (right traveling device) 14R with the right track 16R. In addition, the power source is not limited to the engine 12. In addition, the tracks 16 here are rubber track belts, i.e., rubber tracks (in other words, for example, rubber tracks), but are not limited to this.

[0028] A cargo platform 20 is arranged on the upper part of the traveling device 14, behind the driver's seat 18. In addition, the space behind the driver's seat 18 is not limited to being used as a cargo platform 20, but can also be used for various other purposes.

[0029] like Figure 5 As shown, the transport vehicle 10 has a hydraulic system S. This hydraulic system S, starting from the engine 12 side, includes a hydraulic pump 22, a hydraulic pump 24, an oil supply pump 26, and a working machine pump 28. The output shaft 12S of the engine 12 transmits driving force to the hydraulic pump 22, which drives the hydraulic motor 32R. The hydraulic motor 32R drives the drive wheel of the right travel device 14R, i.e., the drive sprocket 30R. The output shaft 12S of the engine 12 transmits driving force to the hydraulic pump 24, which drives the hydraulic motor 32L. The hydraulic motor 32L drives the drive wheel of the left travel device 14L, i.e., the drive sprocket 30L. The output shaft 12S of the engine 12 transmits driving force to the oil supply pump 26, which operates by replenishing working oil to the hydraulic pumps 22 and 24 respectively. The output shaft 12S of the engine 12 transmits driving force to the working machine pump 28, which functions to supply working oil to the hydraulic cylinders (not shown) of the loading platform 20.

[0030] Figure 6This diagram shows a schematic structure of the hydraulic circuit of the hydraulic system Sa, which focuses solely on the traveling device 14 (hereinafter referred to as the traveling hydraulic system). Figure 6 For example, the diagrams of the speed change mechanism of the hydraulic motors 32R and 32L, the filter, etc. are omitted.

[0031] Regarding the pair of tracks 16L and 16R, the hydraulic system Sa for travel has closed-loop HST circuits (hereinafter referred to as HST closed-loop circuits) C1 and C2 that circulate working oil between hydraulic pumps 22 and 24 and hydraulic motors 32R and 32L, respectively. The hydraulic pumps 22 and 24 are driven by the power of the engine 12, and the hydraulic motors 32R and 32L are driven by the working oil discharged from the hydraulic pumps 22 and 24, generating power transmitted to the tracks 16L and 16R. That is, hydraulic pump 22 is connected to the aforementioned hydraulic motor 32R via hydraulic piping, i.e., oil lines 40a and 40b, forming HST closed-loop circuit C1 with hydraulic motor 32R. Similarly, hydraulic pump 24 is connected to the aforementioned hydraulic motor 32L via hydraulic piping, i.e., oil lines 50a and 50b, forming HST closed-loop circuit C2 with hydraulic motor 32L. Hydraulic pumps 22 and 24 are variable-capacity pumps. In addition, hydraulic motors 32R and 32L are variable capacity motors. The output shafts of hydraulic motors 32R and 32L drive the corresponding drive wheels 30R and 30L via a transmission (not shown), thereby causing the tracks 16R and 16L to rotate.

[0032] Hydraulic pump 22 and hydraulic motor 32R are connected by means of Figure 6 The upper and middle oil passages (equivalent to the first oil passage) 40a and Figure 6 The hydraulic pump 22 is connected to the lower oil passage (equivalent to the second oil passage) 40b. When the hydraulic pump 22 operates in the forward direction, the working oil from the hydraulic pump 22 flows to the hydraulic motor 32R via oil passage 40a, and the working oil from the hydraulic motor 32R flows to the hydraulic pump 22 via oil passage 40b, thereby circulating the working oil in the HST closed circuit C1. On the other hand, when the hydraulic pump 22 operates in the reverse direction, the working oil from the hydraulic pump 22 flows to the hydraulic motor 32R via oil passage 40b, and the working oil from the hydraulic motor 32R flows to the hydraulic pump 22 via oil passage 40a, thereby circulating the working oil in the reverse direction in the HST closed circuit C1.

[0033] In this HST closed circuit C1, a high-pressure relief valve 42a is connected to oil circuit 40a to adjust the pressure of the relatively high-pressure side of oil circuit 40a to a specified pressure when the hydraulic pump 22 operates in the forward direction. Similarly, a high-pressure relief valve 42b is connected to oil circuit 40b to adjust the pressure of the relatively high-pressure side of oil circuit 40b to a specified pressure when the hydraulic pump 22 operates in the reverse direction. The downstream sides of each of the high-pressure relief valves 42a and 42b are connected to the working oil tank 44 via a supply relief valve 46.

[0034] Furthermore, the oil supply pump 26 is installed on the oil supply line 47 that supplies working oil from the working oil tank 44 to the HST closed circuits C1 and C2 respectively. The oil supply pump 26 supplies working oil from the working oil tank 44 to the hydraulic pump 22 of the HST closed circuit C1 in order to supply working oil to the hydraulic lines 40a and 40b in the HST closed circuit C1. To supply working oil to the oil lines 40a and 40b in the hydraulic pump 22 of the HST closed circuit C1 and to maintain the pressure within the circuit, the aforementioned oil supply relief valve 46 and check valves 48a and 48b are provided.

[0035] Similarly, the hydraulic pump 24 and the hydraulic motor 32L are connected by means of... Figure 6 The upper and middle oil passages (equivalent to the first oil passage) 50a and Figure 6 The hydraulic pump 24 is connected to the lower oil passage (equivalent to the second oil passage) 50b. When the hydraulic pump 24 operates in the forward direction, the working oil from the hydraulic pump 24 flows to the hydraulic motor 32L via oil passage 50a, and the working oil from the hydraulic motor 32L flows to the hydraulic pump 24 via oil passage 50b, thereby circulating the working oil in the HST closed circuit C2. On the other hand, when the hydraulic pump 24 operates in the reverse direction, the working oil from the hydraulic pump 24 flows to the hydraulic motor 32L via oil passage 50b, and the working oil from the hydraulic motor 32L flows to the hydraulic pump 24 via oil passage 50a, thereby circulating the working oil in the reverse direction in the HST closed circuit C2.

[0036] In this HST closed circuit C2, similar to the aforementioned HST closed circuit C1, a high-pressure relief valve 52a connected to oil circuit 50a, a high-pressure relief valve 52b connected to oil circuit 50b, an oil supply relief valve 56, and check valves 58a and 58b are provided. The high-pressure relief valves 52a and 52b, the oil supply relief valve 56, and the check valves 58a and 58b correspond to the high-pressure relief valves 42a and 42b, the oil supply relief valve 46, and the check valves 48a and 48b, respectively, and perform the same functions.

[0037] Regarding the HST closed circuits C1 and C2, return oil passages 60 are respectively provided extending from the HST closed circuits C1 and C2 to the working oil tank 44. The return oil passages 60 include a pump return oil passage 61 extending from the hydraulic pumps 22 and 24 to the working oil tank 44, and a motor return oil passage 62 extending from the hydraulic motors 32R and 32L to the working oil tank 44. A cooler 63 for cooling the working oil is provided in the return oil passages 60.

[0038] Pump return oil passage 61a in pump return oil passage 61 extends from the housing 22a of hydraulic pump 22 toward the working oil tank 44. Similarly, pump return oil passage 61b in pump return oil passage 61 extends from the housing 24a of hydraulic pump 24 toward the working oil tank 44. Pump return oil passages 61a and 61b merge to form a single unit, extending toward the working oil tank 44 and connecting to the downstream return oil passage 60a. Cooler 63 is disposed in the downstream return oil passage 60a.

[0039] Furthermore, motor return oil passage 62a in motor return oil passage 62 extends from the housing 32Ra of hydraulic motor 32R towards the working oil tank 44. Similarly, motor return oil passage 62b in motor return oil passage 62 extends from the housing 32La of hydraulic motor 32L towards the working oil tank 44. Motor return oil passages 62a and 62b merge into one, extending towards the working oil tank 44 and connecting to the aforementioned downstream return oil passage 60a.

[0040] A bypass oil passage 64 is provided in the downstream return oil passage 60a, which bypasses the cooler 63 of the downstream return oil passage 60a. The downstream side of the bypass oil passage 64 is connected to the working oil tank 44. A test valve 66, which is a mechanical check valve, is provided in the bypass oil passage 64. The test valve 66 is configured to reduce the pressure of the working oil (hydraulic pressure) in the pump return oil passage 61 and motor return oil passage 62 upstream of the cooler 63 when the pressure is above a specified pressure, that is, to release the working oil in the pump return oil passage 61 and motor return oil passage 62 to the working oil tank 44. The test valve 66 constitutes an adjustment valve as an adjustment unit, which adjusts the flow rate of the working oil from the HST closed circuit C1 and C2 to the working oil tank 44 via the return oil passage 60.

[0041] On the other hand, in order to more actively extract the working oil from the HST closed loops C1 and C2 and supply it to the HST closed loops C1 and C2 via the working oil tank 44 to circulate the working oil, thereby reducing the concentration of impurities in the circulating working oil and improving its cleanliness, and also to improve the cooling performance of the circulating working oil, regulating valve mechanisms 70a and 70b are provided. One regulating valve mechanism 70a is provided in the HST closed loop C1 and is configured to allow the working oil in the low-pressure side of the oil passages 40a and 40b to flow to the return oil passage 60. Similarly, the other regulating valve mechanism 70b is provided in the HST closed loop C2 and is configured to allow the working oil in the low-pressure side of the oil passages 50a and 50b to flow to the return oil passage 60. The regulating valve mechanisms 70a and 70b are each configured as regulating units that adjust the flow rate of the working oil from the HST closed loops C1 and C2 to the working oil tank 44 via the return oil passage 60.

[0042] A regulating valve mechanism 70a is provided at the confluence 71d where oil passages 71a (extending from oil passage 40a) and 71b (extending from oil passage 40b) merge with oil passage 71c (extending to the motor return oil passage 62). The regulating valve mechanism 70a is structured to control the flow of working oil from the low-pressure side of oil passages 40a and 40b to the return oil passage 60. Specifically, the regulating valve mechanism 70a has a relief valve 74 as a control valve; more specifically, it has a low-pressure selection valve 72 and the aforementioned relief valve 74. The low-pressure selection valve 72 is configured as a three-position valve, having a structure that automatically operates under the hydraulic pressure of oil passages 40a and 40b, but is not limited thereto. For example, the low-pressure selection valve 72 can be a control valve controlled electrically or electronically. Additionally, the relief valve 74 is a control valve, in this case, an electromagnetic proportional valve. The relief valve 74 is configured as a pilot-operated pressure control valve, but is not limited thereto.

[0043] A regulating valve mechanism 70b is provided at the confluence section 75d where oil passages 75a (extending from oil passage 50a) and 75b (extending from oil passage 50b) merge with oil passage 75c (extending to the motor return oil passage 62). The regulating valve mechanism 70b has the same structure as the regulating valve mechanism 70a, and is controlled to allow the working oil from the low-pressure side of oil passages 50a and 50b to flow to the return oil passage 60. Specifically, it has a relief valve 78 as a control valve, and more specifically, it has a low-pressure selection valve 76 and a relief valve 78. The low-pressure selection valve 76 corresponds to the low-pressure selection valve 72, has the same structure and function, and can be modified in the same way. Similarly, the relief valve 78 corresponds to the relief valve 74, has the same structure, and can be modified in the same way.

[0044] Figure 7A block diagram showing the control structure of the regulating valve mechanisms 70a and 70b is provided. The control device 80, serving as the control unit, has a computer-like structure, including a processor (e.g., CPU), memory (e.g., ROM, RAM), and a communication interface. The control device 80, for example, uses the processor to execute programs stored in the memory to perform various functions. The control device 80 may also be composed of multiple computers.

[0045] Output signals from an engine speed sensor 82 (for detecting the rotational speed of the output shaft 12S of engine 12, i.e., engine speed), a pressure sensor 84a (for detecting the pressure of oil line 40a), a pressure sensor 84b (for detecting the pressure of oil line 40b), a pressure sensor 86a (for detecting the pressure of oil line 50a), and a pressure sensor 86b (for detecting the pressure of oil line 50b) are respectively input to the control device 80. The control device 80 controls the operation of the relief valve 74 of the adjusting valve mechanism 70a based on the output from the engine speed sensor 82. Additionally, the control device 80 controls the operation of the relief valve 78 of the adjusting valve mechanism 70b based on the output from the engine speed sensor 82. However, various sensors that detect values ​​equivalent to the rotational speed of the output shaft 12S of engine 12 can be used instead of the engine speed sensor or based on it. In this specification, the phrase "the control valve is controlled according to the rotational speed of the output shaft of the power source" should be understood to include cases where the control valve is controlled according to the rotational speed of the output shaft itself or a value equivalent to it. Specifically, the pressures in oil lines 40a and 40b, as well as the pressures in oil lines 50a and 50b, can vary according to the engine speed, and are therefore related to the engine speed. Therefore, for example, pressure sensors 84a, 84b, 86a, and 86b can be used instead of the engine speed sensor 82, or based on it. That is, the control device 80 can control the operation of the relief valve 74 based on the output of the engine speed sensor 82, or instead based on the output of the pressure sensors 84a and 84b. Additionally, the control device 80 can control the operation of the relief valve 78 based on the output of the engine speed sensor 82, or instead based on the output of the pressure sensors 86a and 86b.

[0046] Here, the control of the regulating valve mechanism 70a is essentially the same as the control of the regulating valve mechanism 70b. Therefore, only the control of the regulating valve mechanism 70a will be described, and the description of the control of the regulating valve mechanism 70b will be omitted.

[0047] As described above, in the HST closed circuit C1, when the hydraulic pump 22 operates in the forward direction, the working oil from the hydraulic pump 22 flows to the hydraulic motor 32R via oil passage 40a, and the working oil from the hydraulic motor 32R flows to the hydraulic pump 22 via oil passage 40b, thus circulating the working oil in the HST closed circuit C1. At this time, the pressure of the working oil flowing from the hydraulic pump 22 to the hydraulic motor 32R via oil passage 40a is higher than the pressure of the working oil flowing from the hydraulic motor 32R to the hydraulic pump 22 via oil passage 40b. That is, the low-pressure side of oil passages 40a and 40b is oil passage 40b. Therefore, the valve core of the low-pressure selector valve 72 moves to the position of opening oil passage 40b and closing oil passage 40a, thus opening oil passage 40b.

[0048] At this time, the control device 80 controls the set pressure or opening degree of the relief valve 74 based on the output of the engine speed sensor 82, thereby changing the flow rate (through flow) of the working oil passing through the relief valve 74. When the engine speed is lower than the specified speed, that is, at low speed, the discharge flow from the oil supply pump 26 is small. Therefore, if the relief valve 74 is configured as a mechanical (fixed) valve instead of a control valve, the replenishment flow of working oil from the oil supply pump 26 to the HST closed circuit C1 is insufficient compared to the flow rate drawn from the low-pressure selector valve 72 and the relief valve. Therefore, it may be impossible to stably maintain the necessary pressure in the low-pressure side oil passage 40b. Therefore, by using the relief valve 74 as a control valve, when the engine speed is lower than the specified speed, working oil is not drawn from the oil passage 40b, or its drawing amount is suppressed, thereby stably maintaining the pressure in the HST closed circuit C1. For example, at this time, the relief valve 74 can either be kept closed or opened at a specified small opening degree corresponding to the engine speed.

[0049] On the other hand, when the engine speed is above the specified speed, that is, at high speed, the discharge pressure from the oil supply pump 26 is high, and therefore the pressure in oil lines 40a and 40b is above the minimum necessary pressure. Therefore, the set pressure or opening degree of the relief valve 74 is variably controlled according to the engine speed. For example, the control device 80 can control the relief valve 74 in such a way that the opening degree of the relief valve 74 is larger as the engine speed increases. Thus, when the engine speed is high and the pressure of the working oil in oil lines 40a and 40b is high, the amount of working oil extracted can be appropriately adjusted.

[0050] The control of the relief valve 74, which corresponds to the engine speed, is also the same when the hydraulic pump 22 operates in the reverse direction in the HST closed circuit C1. Its explanation is omitted here.

[0051] The following describes a portion of the characteristic structure and its effects on the hydraulic system S having the above-described structure, particularly the hydraulic system Sa for travel. Furthermore, the following primarily describes the structure and its effects related to the HST closed-loop circuit C1; the same applies to the HST closed-loop circuit C2, and its repetitive description is essentially omitted.

[0052] The hydraulic system S, particularly the traveling hydraulic system Sa, has HST closed circuits C1 and C2 for each pair of tracks 16R and 16L. These HST closed circuits C1 and C2 circulate working oil between hydraulic pumps 22 and 24 and hydraulic motors 32R and 32L. The hydraulic pumps 22 and 24 are driven by the power of the engine 12, and the hydraulic motors 32R and 32L are driven by the working oil discharged from the hydraulic pumps 22 and 24, generating power to be transmitted to the tracks 16R and 16L. Furthermore, the hydraulic systems S and Sa include: a supply oil passage 47 that supplies working oil from the working oil tank 44 to the HST closed circuits C1 and C2 via the operation of an oil supply pump 26 driven by the power of the engine 12; and a return oil passage 60, in which a cooler 63 is provided, which returns the working oil from the HST closed circuits C1 and C2 back to the working oil tank 44. Furthermore, in the hydraulic systems S and Sa, adjustment units 66, 70a, and 70b are provided to adjust the flow rate of working oil from the HST closed circuits C1 and C2 to the working oil tank. With this structure, including the HST closed circuits C1 and C2, the supply oil passage 47, the return oil passage 60, and the adjustment units 66, 70a, and 70b, better circulation of the working oil in the hydraulic systems S and Sa can be promoted. Moreover, since the adjustment unit is configured with a valve, it can also be called an adjustment valve section or adjustment valve unit, etc.

[0053] Specifically, regarding the HST closed circuit C1, the hydraulic systems S and Sa have an adjusting valve mechanism 70a as an adjusting unit. This adjusting valve mechanism 70a has a relief valve 74 as a control valve. The relief valve 74 is controlled according to the rotational speed of the output shaft 12S of the engine 12, so that the working oil in the low-pressure side of the oil passage connecting the pump 22 and the motor 32R in the first oil passage 40a and the second oil passage 40b flows to the return oil passage 60. According to this structure, the working oil in the aforementioned low-pressure side oil passage can be returned to the working oil tank 44 according to the rotational speed of the output shaft 12a of the engine 12, thereby stably maintaining the necessary pressure of the low-pressure side oil passage and improving the cleanliness and cooling properties of the working oil.

[0054] More specifically, regarding the HST closed circuit C1, the hydraulic systems S and Sa include: a low-pressure selector valve 72 that opens the low-pressure side of the oil passages in the first oil passage 40a and the second oil passage 40b; and a relief valve 74 as a control valve, which is controlled according to the rotational speed of the output shaft 12S of the engine 12 to vary the flow rate. According to this structure, the low-pressure side oil passages can be selectively opened using the low-pressure selector valve 72, and the flow of working oil from the low-pressure side oil passages can be effectively adjusted according to the engine speed of the engine 12 using the relief valve 74 as a control valve.

[0055] Furthermore, regarding the HST closed circuit C1, in the hydraulic systems S and Sa, in the bypass oil passage 64 located downstream of the return oil passage 60a, bypassing the cooler 63, a regulating valve (here, a test valve 66) is provided that opens upon reaching a specified pressure. According to this structure, for example, when the oil temperature is below a specified temperature and the oil viscosity is above a specified level, even if the working oil in the cooler 63 is relatively clogged, the working oil can flow more effectively to the working oil tank 44. Moreover, the regulating valve is not limited to the so-called check valve, i.e., the test valve 66, but can also be a control valve.

[0056] Furthermore, the return oil passage 60 includes a pump return oil passage 61 extending from the hydraulic pumps 22 and 24 toward the working oil tank 44, and a motor return oil passage 62 extending from the hydraulic motors 32R and 32L toward the working oil tank 44. The cooler 63 is located downstream of the confluence section 60J of the pump return oil passage 61 and the motor return oil passage 62. Therefore, the cooler 63 can effectively cool the working oil flowing from the pump return oil passage 61 and the motor return oil passage 62 to the working oil tank 44.

[0057] Here, Figure 8 The diagram shows a modified example of the travel hydraulic system Sa, which is the travel hydraulic system S. In the travel hydraulic system Sb, regarding the HST closed loop C1, the overflow oil passage 71c, which connects the low-pressure side oil passage and the return oil passage 60, extends in such a way that the working oil from the low-pressure side oil passages 40a and 40b flows to the working oil tank 44 via the hydraulic motor 32R. Similarly, in the travel hydraulic system Sb, regarding the HST closed loop C2, the overflow oil passage 75c, which connects the low-pressure side oil passage and the motor return oil passage 62, extends in such a way that the working oil from the low-pressure side oil passages 50a and 50b flows to the working oil tank 44 via the hydraulic motor 32L. According to this structure, the working oil in the hydraulic motors 32R and 32L can be circulated better using the working oil from the aforementioned oil passages on the low-pressure side, thereby promoting better circulation of the working oil in the hydraulic systems S and Sb.

[0058] The embodiments and variations thereof involved in this disclosure have been described above, but this disclosure is not limited thereto. Various substitutions and modifications can be made as long as they do not depart from the spirit and scope of this disclosure as defined in the claims of this application.

[0059] The aforementioned regulating valve mechanisms 70a and 70b are respectively configured with the aforementioned low-pressure selector valves 72 and 76 as mechanical valves and the aforementioned relief valves 74 and 78 as control valves, but they may also have other structures. For example, the low-pressure selector valves 72 and 76 may also be control valves controlled according to the engine speed. In this case, the low-pressure selector valves 72 and 76 are controlled by the control device 80 so that the low-pressure side oil passage is opened when the engine speed is above a certain specified speed, and the relief valves 74 and 78 may remain as control valves or be mechanical valves. In addition, for example, regarding the regulating valve mechanism, the HST closed circuits C1 and C2 may each have two control valves (specifically solenoid valves) respectively provided for the two aforementioned oil passages 40a, 40b, 50a, and 50b, and only the solenoid valve of the low-pressure side oil passage is opened according to the engine speed.

[0060] Furthermore, the tracked vehicles using the technology disclosed herein are not limited to tracked transport vehicles, but may include industrial vehicles such as mobile cranes, agricultural vehicles such as combine harvesters, and various operating machinery and vehicles with tracked walking devices.

Claims

1. A hydraulic system for a tracked walking device, characterized in that, The hydraulic system of this tracked walking device has the following features: A closed-loop circuit is provided for each pair of tracks, allowing working oil to circulate between a hydraulic pump and a hydraulic motor. The hydraulic pump is driven by a power source, and the hydraulic motor is driven by the working oil discharged from the hydraulic pump and generates power to be transmitted to the tracks. The oil supply circuit supplies working oil from the working oil tank to the closed circuit through the action of an oil supply pump driven by the power source. A return oil circuit is provided, in which a cooler is installed, which allows the working oil to return from the closed circuit to the working oil tank; as well as The adjustment unit adjusts the flow rate of working oil from the closed loop to the working oil tank via the return oil path.

2. The hydraulic system of the tracked walking device according to claim 1, characterized in that, The hydraulic system of the tracked walking device has an adjusting valve mechanism with a control valve that is controlled according to the rotational speed of the output shaft of the power source so that the working oil in the low-pressure side of the first and second oil circuits connecting the hydraulic pump and the hydraulic motor flows to the return oil circuit.

3. The hydraulic system of the tracked walking device according to claim 1, characterized in that, The hydraulic system of this tracked walking device has the following features: A low-pressure selector valve that opens the low-pressure side of the first and second oil circuits connecting the hydraulic pump and the hydraulic motor; and A control valve is controlled according to the rotational speed of the output shaft of the power source to change the flow rate of the working oil in the low-pressure side of the oil circuit to the return oil circuit.

4. The hydraulic system of the tracked walking device according to claim 2 or 3, characterized in that, The oil circuit connecting the low-pressure side and the return oil circuit extends in such a way that the working oil of the low-pressure side oil circuit flows to the working oil tank via the hydraulic motor.

5. The hydraulic system of the tracked walking device according to any one of claims 1 to 3, characterized in that, In the bypass oil circuit that is arranged to bypass the cooler in the return oil circuit, an adjustment valve is provided that opens when the pressure exceeds a specified level.

6. The hydraulic system of the tracked walking device according to any one of claims 1 to 3, characterized in that, The return oil path has: The pump return line extends from the hydraulic pump toward the working oil tank; and The motor return oil circuit extends from the hydraulic motor toward the working oil tank. The cooler is located downstream of the confluence of the pump return oil circuit and the motor return oil circuit.

7. A tracked vehicle, characterized in that, The tracked vehicle has a hydraulic system for the tracked walking device as described in any one of claims 1 to 3.

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