Hydraulic system for crawler-type running gear and crawler-type vehicle equipped therewith

Abstract

This invention provides a configuration that enables more optimal circulation of the hydraulic fluid in the hydraulic system of a crawler-type travel device, such as a crawler-type transport vehicle. [Solution] The hydraulic system Sa is provided for each of the pair of crawlers 16R and 16L and includes closed circuits C1 and C2 through which hydraulic fluid circulates between hydraulic pumps 22 and 24 and hydraulic motors 32R and 32L; a supply oil passage 47 that supplies hydraulic fluid from the hydraulic fluid tank 44 to the closed circuits C1 and C2 by the operation of a charge pump 26; a return oil passage 60 provided with a cooler 63 that returns hydraulic fluid from the closed circuits C1 and C2 to the hydraulic fluid tank 44; and adjustment valve mechanisms 70a and 70b as adjustment means for adjusting the flow rate of hydraulic fluid from the closed circuits to the hydraulic fluid tank via the return oil passage.

Description

Technical Field

[0001] The present disclosure relates to a hydraulic system of a crawler-type traveling device in a crawler-type vehicle such as a crawler-type carrier vehicle, and a crawler-type vehicle equipped with the same.

Background Art

[0002] Some crawler-type vehicles have a drive transmission unit that transmits the power of an engine to a crawler-type traveling device and includes an HST (Hydro Static Transmission: hydrostatic continuously variable transmission or hydraulic transmission) (see, for example, Patent Document 1). The HST includes a hydraulic pump and a hydraulic motor and has a closed circuit in which hydraulic oil circulates between the hydraulic pump and the hydraulic motor. In the HST, the hydraulic pump is driven by the power of the engine, and the hydraulic motor is driven by the hydraulic oil discharged from the hydraulic pump. Then, the power of the hydraulic motor of the HST is transmitted to the left and right crawlers via a power transmission mechanism including drive wheels, that is, drive sprockets.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] By the way, crawler-type vehicles are often so-called work vehicles, operate in various environments, and it is necessary for a hydraulic system having an HST to function smoothly in various environments. For example, a suitable circulation of hydraulic oil in the hydraulic system is desired.

[0005] An object of the present disclosure is to provide a configuration that enables more suitable circulation of hydraulic oil in a hydraulic system of a crawler-type traveling device in a crawler-type vehicle such as a crawler-type carrier vehicle. [Means for solving the problem]

[0006] One aspect of this disclosure is, A closed circuit is provided for each of the pair of crawlers, in which hydraulic fluid circulates between a hydraulic pump, which is driven by the power of a power source, and a hydraulic motor, which is driven by the hydraulic fluid discharged by the hydraulic pump and generates power transmitted to the crawler. A supply oil passage that supplies hydraulic fluid from the hydraulic fluid tank to the closed circuit by the operation of a charge pump driven by the power of the aforementioned power source, A cooler is provided, and a return oil passage is provided to return the hydraulic fluid from the closed circuit to the hydraulic fluid tank, An adjustment means for adjusting the flow rate of hydraulic fluid from the closed circuit to the hydraulic fluid tank via the return oil passage. It is equipped with Hydraulic system for crawler-type vehicles To provide.

[0007] According to one aspect of the present disclosure, the hydraulic system includes the aforementioned closed circuit, the aforementioned supply oil passage, the aforementioned return oil passage, and the aforementioned adjustment means, thereby promoting more favorable circulation of the hydraulic fluid in the hydraulic system.

[0008] Preferably, the hydraulic system described above includes an adjustment valve mechanism having a control valve that controls, according to the rotational speed of the output shaft of the power source, to flow the hydraulic fluid from the low-pressure oil passage of the first and second oil passages connecting the hydraulic pump and the hydraulic motor to the return oil passage. With this configuration, the hydraulic fluid from the low-pressure oil passage can be returned to the hydraulic fluid tank according to the rotational speed of the output shaft of the power source, thereby stably maintaining the required pressure of the low-pressure oil passage while improving the cleanliness and cooling performance of the hydraulic fluid.

[0009] Preferably, the hydraulic system includes a low-pressure selector valve that opens the low-pressure oil passage among the first and second oil passages connecting the hydraulic pump and the hydraulic motor, and a control valve that controls the flow rate of the hydraulic fluid from the low-pressure oil passage to the return oil passage according to the rotational speed of the output shaft of the power source. With this configuration, the low-pressure selector valve can selectively open the low-pressure oil passage, and the control valve can further adjust the flow of hydraulic fluid from the low-pressure oil passage to the return oil passage to a more suitable degree. Therefore, the hydraulic fluid from the low-pressure oil passage can be suitably returned to the hydraulic fluid tank according to the rotational speed of the output shaft of the power source, thereby stably maintaining the required pressure of the low-pressure oil passage while improving the cleanliness and cooling performance of the hydraulic fluid.

[0010] Preferably, the oil passage connecting the low-pressure oil passage and the return oil passage extends to allow the hydraulic fluid from the low-pressure oil passage to flow to the hydraulic fluid tank via the hydraulic motor. With this configuration, the hydraulic fluid from the aforementioned low-pressure oil passage can be used to more effectively return the hydraulic fluid in the hydraulic motor to the hydraulic fluid tank, thereby promoting a more favorable circulation of the hydraulic fluid in the hydraulic system.

[0011] Preferably, a control valve that opens at a predetermined pressure or higher is provided in a bypass oil passage that bypasses the cooler in the return oil passage. With this configuration, for example, when the oil temperature is below a predetermined temperature and its viscosity is above a predetermined level, even if the degree of blockage of the hydraulic fluid in the cooler is relatively high, the hydraulic fluid can be more effectively directed to the hydraulic fluid tank, thereby promoting a more favorable circulation of the hydraulic fluid in the hydraulic system.

[0012] Preferably, the return oil passage includes a pump return oil passage extending from the hydraulic pump to the hydraulic oil tank and a motor return oil passage extending from the hydraulic motor to the hydraulic oil tank. The cooler is preferably located downstream of the confluence of the pump return oil passage and the tank return oil passage. In this case, the hydraulic oil flowing from the pump return oil passage and the tank return oil passage to the hydraulic oil tank can be suitably cooled by the cooler.

[0013] The technology of the present disclosure also exists in a crawler vehicle equipped with the hydraulic system of the aforementioned crawler traveling device.

Advantages of the Invention

[0014] According to the above aspect of the present disclosure, since the above configuration is provided, it becomes possible to promote more suitable circulation of the hydraulic oil in the hydraulic system of the crawler traveling device.

Brief Description of the Drawings

[0015] [Figure 1] It is a perspective view of a crawler carrier according to an embodiment. [Figure 2] It is a right side view of the crawler carrier of FIG. 1. [Figure 3] It is a front view of the crawler carrier of FIG. 1. [Figure 4] It is a top view of the crawler carrier of FIG. 1. [Figure 5] It is a block diagram of the hydraulic system in the crawler carrier of FIG. 1. [Figure 6] Among the hydraulic systems in the crawler carrier of FIG. 1, it is a schematic configuration diagram of the hydraulic circuit of the traveling hydraulic system. [Figure 7] Among the hydraulic systems in the crawler carrier of FIG. 1, it is a block diagram of the control configuration of the adjustment valve mechanism. [Figure 8] It is a diagram showing a modification example of the traveling hydraulic system of the crawler carrier of FIG. 1, and it is a schematic configuration diagram of its hydraulic circuit.

Modes for Carrying Out the Invention

[0016] Hereinafter, embodiments according to the present disclosure will be described based on the attached drawings. The same parts (or configurations) are denoted by the same reference numerals, and their names and functions are also the same. Therefore, detailed descriptions thereof will not be repeated.

[0017] First, a crawler carrier 10 equipped with a hydraulic system S according to an embodiment of the present disclosure will be described based on the drawings.

[0018] FIGS. 1 to 4 are a perspective view, a right side view, a front view, and a top view of a crawler carrier (hereinafter, the carrier) 10. The carrier 10 includes a crawler-type traveling device (hereinafter, the traveling device) 14 that uses an engine 12 as a power source. The traveling device 14 includes crawlers 16, that is, a pair of crawlers 16R and 16L. Specifically, the crawler 16 includes a left crawler (left crawler) 16L and a right crawler (right crawler) 16R, and each constitutes an endless track. The traveling device 14 includes a left traveling device (left traveling device) 14L having a left crawler 16L and a right traveling device (right traveling device) 14R having a right crawler 16R. Note that the power source is not limited to the engine 12. Here, the crawler 16 is a rubber crawler belt, that is, a rubber crawler (in other words, for example, a rubber track), but is not limited thereto.

[0019] A loading platform 20 is arranged behind the driver's seat 18 above the traveling device 14. Note that the space behind the driver's seat 18 is not limited to being used as the loading platform 20 and can be used for various other purposes.

[0020] As shown in Figure 5, the transport vehicle 10 is equipped with a hydraulic system S. The hydraulic system S comprises, in order from the engine 12 side, a hydraulic pump 22, a hydraulic pump 24, a charge pump 26, and a work equipment pump 28. The hydraulic pump 22 receives power from the output shaft 12S of the engine 12 and drives a hydraulic motor 32R. The hydraulic motor 32R drives the drive wheel, i.e., the drive sprocket 30R, of the right travel device 14R. The hydraulic pump 24 receives power from the output shaft 12S of the engine 12 and drives a hydraulic motor 32L. The hydraulic motor 32L drives the drive wheel, i.e., the drive sprocket 30L, of the left travel device 14L. The charge pump 26 receives power from the output shaft 12S of the engine 12 and operates to replenish hydraulic fluid to the hydraulic pumps 22 and 24, respectively. The work equipment pump 28 receives power from the output shaft 12S of the engine 12 and functions to supply hydraulic fluid to a hydraulic cylinder (not shown) for operating the loading platform 20.

[0021] Figure 6 shows a schematic configuration of the hydraulic circuit, focusing only on the hydraulic system Sa of the travel device 14 (hereinafter referred to as the travel hydraulic system) within the hydraulic system S. In Figure 6, for example, the transmission mechanism of the hydraulic motors 32R and 32L, filters, etc., are omitted from the illustration.

[0022] For each of the pair of crawlers 16L and 16R, the hydraulic drive system Sa has a closed HST circuit (hereinafter referred to as HST closed circuit) C1, C2 in which hydraulic fluid circulates between hydraulic pumps 22 and 24 driven by the power of the engine 12 and hydraulic motors 32R and 32L that are driven by the hydraulic fluid discharged by the hydraulic pumps 22 and 24 and generate power transmitted to the crawlers 16L and 16R. In other words, hydraulic pump 22 is connected to the aforementioned hydraulic motor 32R via hydraulic piping, i.e., oil passages 40a and 40b, and forms the HST closed circuit C1 with the hydraulic motor 32R. Similarly, hydraulic pump 24 is connected to the aforementioned hydraulic motor 32L via hydraulic piping 50a and 50b, and forms the HST closed circuit C2 with the hydraulic motor 32L. Hydraulic pumps 22 and 24 are variable displacement pumps. Furthermore, the hydraulic motors 32R and 32L are variable displacement motors, and their output shafts drive the corresponding drive wheels 30R and 30L via a transmission (not shown), thereby rotating the crawler tracks 16R and 16L.

[0023] The hydraulic pump 22 and the hydraulic motor 32R are connected by the upper oil passage (corresponding to the first oil passage) 40a and the lower oil passage (corresponding to the second oil passage) 40b in Figure 6. When the hydraulic pump 22 operates in the forward direction, the hydraulic fluid from the hydraulic pump 22 flows to the hydraulic motor 32R via oil passage 40a, and the hydraulic fluid from the hydraulic motor 32R flows to the hydraulic pump 22 via oil passage 40b, thereby circulating the hydraulic fluid through the HST closed circuit C1. On the other hand, when the hydraulic pump 22 operates in the reverse direction, the hydraulic fluid from the hydraulic pump 22 flows to the hydraulic motor 32R via oil passage 40b, and the hydraulic fluid from the hydraulic motor 32R flows to the hydraulic pump 22 via oil passage 40a, thereby circulating the hydraulic fluid through the HST closed circuit C1 in the reverse direction.

[0024] In this HST closed circuit C1, when the hydraulic pump 22 operates in the forward direction, a high-pressure relief valve 42a is connected to oil passage 40a to adjust the pressure of oil passage 40a, which is the relatively higher-pressure oil passage of oil passages 40a and 40b, to a predetermined pressure. Similarly, when the hydraulic pump 22 operates in the reverse direction, a high-pressure relief valve 42b is connected to oil passage 40b to adjust the pressure of oil passage 40b, which is the relatively higher-pressure oil passage of oil passages 40a and 40b, to a predetermined pressure. The downstream sides of the high-pressure relief valves 42a and 42b are connected to the hydraulic fluid tank 44 via a charge relief valve 46.

[0025] The charge pump 26 is located in the supply oil passage 47 that supplies hydraulic fluid from the hydraulic fluid tank 44 to the HST closed circuits C1 and C2, respectively. The charge pump 26 supplies hydraulic fluid from the hydraulic fluid tank 44 to the hydraulic pump 22 of the HST closed circuit C1 in order to supply hydraulic fluid to the HST closed circuit C1. The aforementioned charge relief valve 46 and check valves 48a and 48b are provided in the hydraulic pump 22 of the HST closed circuit C1 to supply hydraulic fluid to the oil passages 40a and 40b and to maintain the pressure within the circuit.

[0026] Similarly, the hydraulic pump 24 and the hydraulic motor 32L are connected by the upper oil passage (corresponding to the first oil passage) 50a in Figure 6 and the lower oil passage (corresponding to the second oil passage) 50b in Figure 6. When the hydraulic pump 24 operates in the forward direction, the hydraulic fluid from the hydraulic pump 24 flows to the hydraulic motor 32L via oil passage 50a, and the hydraulic fluid from the hydraulic motor 32L flows to the hydraulic pump 24 via oil passage 50b, thereby circulating the hydraulic fluid through the HST closed circuit C2. On the other hand, when the hydraulic pump 24 operates in the reverse direction, the hydraulic fluid from the hydraulic pump 24 flows to the hydraulic motor 32L via oil passage 50b, and the hydraulic fluid from the hydraulic motor 32L flows to the hydraulic pump 24 via oil passage 50a, thereby circulating the hydraulic fluid through the HST closed circuit C2 in the reverse direction.

[0027] In this HST closed circuit C2, similar to the HST closed circuit C1 described above, a high-pressure relief valve 52a connected to the oil passage 50a, a high-pressure relief valve 52b connected to the oil passage 50b, a charge relief valve 56, and check valves 58a and 58b are provided. The high-pressure relief valves 52a and 52b, the charge relief valve 56, and the check valves 58a and 58b correspond to the high-pressure relief valves 42a and 42b, the charge relief valve 46, and the check valves 48a and 48b, respectively, and perform the same functions.

[0028] For each of the HST closed circuits C1 and C2, a return oil passage 60 is provided extending from the HST closed circuits C1 and C2 to the hydraulic oil tank 44. The return oil passage 60 includes a pump return oil passage 61 extending from the hydraulic pumps 22 and 24 to the hydraulic oil tank 44, and a motor return oil passage 62 extending from the hydraulic motors 32R and 32L to the hydraulic oil tank 44. A cooler 63 for cooling the hydraulic oil is provided in the return oil passage 60.

[0029] Of the pump return oil passages 61, pump return oil passage 61a extends from the hydraulic pump 22, or its case 22a, toward the hydraulic oil tank 44. Similarly, of the pump return oil passages 61, pump return oil passage 61b extends from the hydraulic pump 24, or its case 24a, toward the hydraulic oil tank 44. Pump return oil passage 61a merges with pump return oil passage 61b to form a single passage, which extends toward the hydraulic oil tank 44 and connects to the downstream return oil passage 60a. The cooler 63 is installed in this downstream return oil passage 60a.

[0030] Furthermore, of the motor return oil passages 62, motor return oil passage 62a extends from the hydraulic motor 32R, that is, its case 32Ra, toward the hydraulic oil tank 44. Similarly, of the motor return oil passages 62, motor return oil passage 62b extends from the hydraulic motor 32L, that is, its case 32La, toward the hydraulic oil tank 44. Motor return oil passage 62a merges with motor return oil passage 62b to form a single unit, which extends toward the hydraulic oil tank 44 and connects to the aforementioned downstream return oil passage 60a.

[0031] A bypass oil passage 64 is provided in the downstream return oil passage 60a, bypassing the cooler 63 in the downstream return oil passage 60a. The downstream side of the bypass oil passage 64 is connected to the hydraulic oil tank 44. A mechanical check valve 66 is provided in the bypass oil passage 64. This check valve 66 is designed to reduce the pressure in the return oil passages 61 and 62 when the hydraulic pressure (oil pressure) in those passages exceeds a predetermined pressure, that is, to release the hydraulic oil there into the hydraulic oil tank 44. The check valve 66 constitutes a control valve that acts as an adjustment means for adjusting the flow rate of hydraulic oil from the closed circuits C1 and C2 to the hydraulic oil tank 44 via the return oil passage 60.

[0032] On the other hand, adjustment valve mechanisms 70a and 70b are provided to more actively extract the hydraulic fluid from the HST closed circuits C1 and C2, and to circulate it back into the closed circuits C1 and C2 via the hydraulic fluid tank 44 using the charge pump 26, thereby reducing the concentration of impurities in the circulating hydraulic fluid, improving its cleanliness, and enhancing the cooling performance of the circulating hydraulic fluid. One adjustment valve mechanism 70a is provided in the HST closed circuit C1 and is configured to direct the hydraulic fluid from the low-pressure oil passage of the oil passages 40a and 40b into the return oil passage 60. Similarly, the other adjustment valve mechanism 70b is provided in the HST closed circuit C2 and is configured to direct the hydraulic fluid from the low-pressure oil passage of the oil passages 50a and 50b into the return oil passage 60. Each of the adjustment valve mechanisms 70a and 70 is configured as an adjustment means to adjust the flow rate of hydraulic fluid from the HST closed circuits C1 and C2 to the hydraulic fluid tank 44 via the return oil passage 60.

[0033] The regulating valve mechanism 70a is provided at a junction 71d where an oil passage 71a extending from oil passage 40a and an oil passage 71b extending from oil passage 40b merge with an oil passage 71c extending to the motor return oil passage 62. The regulating valve mechanism 70a is configured to control the flow of hydraulic fluid from the low-pressure oil passage of oil passages 40a and 40b to the return oil passage 60. Specifically, the regulating valve mechanism 70a includes a relief valve 74, which is a control valve, and more specifically, a low-pressure selector valve 72 and the aforementioned relief valve 74. The low-pressure selector valve 72 is configured as a three-position valve and is configured to operate automatically by the hydraulic pressure of oil passages 40a and 40b, but is not limited to this. For example, the low-pressure selector valve 72 may be a control valve that is electrically or electronically controlled. The relief valve 74 is a control valve, and in this case, it is an electromagnetic proportional valve. The relief valve 74 is configured as a pilot-operated pressure control valve, but is not limited to this configuration.

[0034] The regulating valve mechanism 70b is provided at a junction 75d where an oil passage 75a extending from oil passage 50a and an oil passage 75b extending from oil passage 50b merge with an oil passage 75c extending to the return oil passage 62. The regulating valve mechanism 70b has the same configuration as the regulating valve mechanism 70a and is configured to control the flow of the hydraulic fluid from the low-pressure oil passage of oil passages 50a and 50b to the return oil passage 60. Specifically, it includes a relief valve 78 which is a control valve, and more specifically, a low-pressure selector valve 76 and its relief valve 78. The low-pressure selector valve 76 corresponds to the low-pressure selector valve 72, has the same configuration and function, and can be modified in the same way. The relief valve 78 corresponds to the relief valve 74, has the same configuration, and can be modified in the same way.

[0035] Figure 7 shows a block diagram of the control configuration of the adjustment valve mechanisms 70a and 70b. The control unit, the control device 80, has a computer configuration and includes a processor (e.g., CPU), memory (e.g., ROM, RAM), communication interface, etc. The control device 80 realizes various functions, for example, by executing a program stored in memory using the processor. The control device 80 may be composed of multiple computers.

[0036] The control device 80 receives output signals from an engine speed sensor 82 for detecting the rotational speed of the output shaft 12S of the engine 12, i.e., the engine speed; a pressure sensor 84a for detecting the pressure in the oil passage 40a; a pressure sensor 84b for detecting the pressure in the oil passage 40b; a pressure sensor 86a for detecting the pressure in the oil passage 50a; and a pressure sensor 86b for detecting the pressure in the oil passage 50b. Based on the output from the engine speed sensor 82, the control device 80 controls the operation of the relief valve 74 of the regulating valve mechanism 70a. The control device 80 also controls the operation of the relief valve 78 of the regulating valve mechanism 70b based on the output from the engine speed sensor 82. However, various sensors that detect a value equivalent to the rotational speed of the output shaft 12S of the engine 12 may be used instead of, or in addition to, the engine speed sensor. In this specification, controlling the control valve according to the rotational speed of the output shaft of the power source should be understood to include controlling the control valve based on the rotational speed of the output shaft itself or a value equivalent thereto. Specifically, the pressures in oil passages 40a and 40b, and in oil passages 50a and 50b, can change according to the engine speed, and are therefore correlated with the engine speed. For example, pressure sensors 84a, 84b, 86a, and 86b may be used in place of, or in addition to, the engine speed sensor 82. In other words, the control device 80 may control the operation of the relief valve 74 based on the outputs of pressure sensors 84a and 84b in addition to or in place of the output of the engine speed sensor 82, and may also control the operation of the relief valve 78 based on the outputs of pressure sensors 86a and 86b in addition to or in place of the output of the engine speed sensor 82.

[0037] Here, since the control of the adjustment valve mechanism 70a and the control of the adjustment valve mechanism 70b are substantially the same, only the control of the adjustment valve mechanism 70a will be explained, and the explanation of the control of the adjustment valve mechanism 70b will be omitted.

[0038] As described above, in the HST closed circuit C1, when the hydraulic pump 22 operates in the forward direction, the hydraulic fluid from the hydraulic pump 22 flows to the hydraulic motor 32R via oil passage 40a, and the hydraulic fluid from the hydraulic motor 32R flows to the hydraulic pump 22 via oil passage 40b, thereby circulating the hydraulic fluid in the HST closed circuit C1. At this time, the pressure in oil passage 40a, through which the hydraulic fluid flows from the hydraulic pump 22 to the hydraulic motor 32R, is higher than the pressure in oil passage 40b, through which the hydraulic fluid flows from the hydraulic motor 32R to the hydraulic pump 22. In other words, of oil passages 40a and 40b, oil passage 40b is the lower-pressure oil passage. Therefore, the valve body of the low-pressure selector valve 72 moves to a position that opens oil passage 40b and closes oil passage 40a, thus opening oil passage 40b.

[0039] 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 rotation speed sensor 82, thereby changing the flow rate (through flow rate) of the hydraulic fluid passing through the relief valve 74. When the engine rotation speed is lower than a predetermined rotation speed, that is, at a low rotation speed, the discharge flow rate from the charge pump 26 is small. If the relief valve 74 is a mechanical (fixed) valve instead of a control valve, the amount of hydraulic fluid supplied from the charge pump 26 to the HST closed circuit C1 may not be sufficient to compensate for the flow rate withdrawn from the low-pressure selector valve 72 and its relief valve, which may prevent the required pressure in the low-pressure oil passage 40b from being stably maintained. Therefore, by using the relief valve 74 as a control valve, when the engine rotation speed is below a predetermined rotation speed, hydraulic fluid is not withdrawn from the oil passage 40b, or the amount withdrawn is reduced, thereby enabling the pressure to be stably maintained in the HST closed circuit C1. For example, in this case, the relief valve 74 may be kept closed, or it may be opened to a predetermined small opening degree corresponding to the engine rotation speed.

[0040] On the other hand, when the engine speed is above a predetermined speed, that is, at a high speed, the discharge pressure from the charge pump 26 is high, so the pressure in the oil passages 40a and 40b is above the minimum required 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 so that the opening degree of the relief valve 74 increases as the engine speed increases. This makes it possible to suitably adjust the amount of hydraulic fluid extracted when the engine speed is high and the pressure of the hydraulic fluid in the oil passages 40a and 40b is high.

[0041] This control of the relief valve 74 in accordance with the engine speed is the same when the hydraulic pump 22 operates in the reverse direction in the HST closed circuit C1. A detailed explanation of this is omitted here.

[0042] The following describes some of the characteristic configurations and their effects regarding the hydraulic system S having the above configuration, and in particular, the hydraulic system Sa for driving. While the following mainly describes the configuration of the HST closed circuit C1 and its effects, the same applies to the HST closed circuit C2, and therefore, redundant explanations are largely omitted.

[0043] The hydraulic system S, and in particular the hydraulic system Sa for traction, have HST closed circuits C1 and C2 for each pair of crawlers 16R and 16L, through which hydraulic fluid circulates between hydraulic pumps 22 and 24 driven by the power of the engine 12 and hydraulic motors 32R and 32L that are driven by the hydraulic fluid discharged by the hydraulic pumps 22 and 24 and generate power transmitted to the crawlers 16R and 16L. The hydraulic systems S and Sa also include a supply oil passage 47 that supplies hydraulic fluid from the hydraulic fluid tank 44 to the HST closed circuits C1 and C2 by the operation of a charge pump 26 driven by the power of the engine 12, and a return oil passage 60 equipped with a cooler 63 that returns hydraulic fluid from the HST closed circuits C1 and C2 to the hydraulic fluid tank 44. Furthermore, the hydraulic systems S and Sa are provided with adjustment means 66, 70a and 70b to adjust the flow rate of hydraulic fluid from the HST closed circuits C1 and C2 to the hydraulic fluid tank. This configuration includes HST closed circuits C1 and C2, a supply oil passage 47, a return oil passage 60, and adjustment means 66, 70a, and 70b, thereby promoting more favorable circulation of the hydraulic fluid in the hydraulic systems S and Sa. The adjustment means is configured to include a valve, and may therefore be referred to as an adjustment valve section or adjustment valve unit.

[0044] Specifically, with respect to the HST closed circuit C1, the hydraulic systems S and Sa are equipped with an adjustment valve mechanism 70a, which has a relief valve 74 that controls the flow of the hydraulic fluid from the low-pressure side of the first oil passage 40a and second oil passage 40b connecting the pump 22 and the motor 32R to the return oil passage 60 according to the rotational speed of the output shaft 12S of the engine 12. With this configuration, the hydraulic fluid from the aforementioned low-pressure side oil passage can be returned to the hydraulic fluid tank 44 according to the rotational speed of the output shaft 12a of the engine 12, thereby stably maintaining the required pressure of the low-pressure side oil passage while improving the cleanliness and cooling performance of the hydraulic fluid.

[0045] More specifically, the hydraulic systems S and Sa, with respect to the HST closed circuit C1, include a low-pressure selector valve 72 that opens the low-pressure oil passage of the first oil passage 40a and the second oil passage 40b, and a relief valve 74 which acts as a control valve and controls the flow rate to change according to the rotational speed of the output shaft 12S of the engine 12. With this configuration, the low-pressure selector valve 72 can selectively open the aforementioned low-pressure oil passage, and furthermore, the relief valve 74, which acts as a control valve, can suitably adjust the flow of hydraulic fluid from the low-pressure oil passage according to the engine rotational speed of the engine 12.

[0046] Furthermore, regarding the HST closed circuit C1, in hydraulic systems S and Sa, a regulating valve, in this case a check valve 66, is provided in a bypass oil passage 64 that bypasses the cooler 63 in the downstream return oil passage 60a of the return oil passage 60, and opens when the pressure exceeds a predetermined level. With this configuration, for example, when the oil temperature is below a predetermined temperature and its viscosity is above a predetermined level, even if the degree of blockage of the hydraulic fluid in the cooler 63 is relatively high, the hydraulic fluid can be more favorably supplied to the hydraulic fluid tank 44. Note that the regulating valve is not limited to a check valve 66, which is a so-called non-return valve, but may also be a control valve.

[0047] Furthermore, the return oil passage 60 includes a pump return oil passage 61 extending from the hydraulic pumps 22 and 24 toward the hydraulic oil tank 44, and a motor return oil passage 62 extending from the hydraulic motors 32R and 32L toward the hydraulic oil tank 44. The cooler 63 is located downstream of the confluence 60J of the pump return oil passage 61 and the tank return oil passage 62. Therefore, the hydraulic oil flowing from the pump return oil passage 61 and the tank return oil passage 62 toward the hydraulic oil tank 44 can be effectively cooled by the cooler 63.

[0048] Here, Figure 8 shows a modified example of the travel hydraulic system Sa of the hydraulic system S, namely the travel hydraulic system Sb. In the travel hydraulic system Sb, with respect to the HST closed circuit C1, the aforementioned oil passage 71c, which is a relief oil passage connecting the low-pressure oil passage and the return oil passage 60, extends to allow the hydraulic fluid from the low-pressure oil passages 40a and 40b to flow to the hydraulic fluid tank 44 via the hydraulic motor 32R. Similarly, in the travel hydraulic system Sb, with respect to the HST closed circuit C2, the aforementioned oil passage 75c, which is a relief oil passage connecting the low-pressure oil passage and the return oil passage 62, extends to allow the hydraulic fluid from the low-pressure oil passages 50a and 50b to flow to the hydraulic fluid tank 44 via the hydraulic motor 32L. With this configuration, the hydraulic fluid from the aforementioned low-pressure oil passages can more effectively circulate the hydraulic fluid in the hydraulic motors 32R and 32L, thereby promoting even more favorable circulation of the hydraulic fluid in the hydraulic systems S and Sb.

[0049] While embodiments and modifications relating thereto have been described above, this disclosure is not limited thereto. Various substitutions and modifications are possible, as long as they do not deviate from the spirit and scope of this disclosure as defined by the claims of this application.

[0050] Each of the aforementioned regulating valve mechanisms 70a and 70b is configured to include the aforementioned low-pressure selector valves 72 and 76, which are mechanical valves, and the aforementioned relief valves 74 and 78, which are control valves, but other configurations are also possible. For example, the low-pressure selector valves 72 and 76 may be control valves controlled according to the engine speed. In this case, the control device 80 controls the low-pressure selector valves 72 and 76 to open the low-pressure oil passage when the engine speed is above a certain predetermined speed, and the relief valves 74 and 78 may remain control valves, but may also be mechanical valves. Alternatively, for example, the regulating valve mechanism may have two control valves, specifically solenoid valves, provided for each of the two aforementioned oil passages 40a, 40b, 50a, and 50b in each of the HST closed circuits C1 and C2, and only the solenoid valve for the low-pressure oil passage may be opened according to the engine speed.

[0051] Furthermore, the crawler vehicles to which the technology of this disclosure applies are not limited to crawler transport vehicles, but may include industrial vehicles such as mobile cranes, agricultural vehicles such as combine harvesters, and various work machines and work vehicles equipped with crawler-type running gear. [Explanation of symbols]

[0052] 10 Crawler-type transport vehicles 12 Engines 14. Crawler-type running gear 16 Crawler 22, 24 Hydraulic pumps 26 Charge pump 32R, 32L Hydraulic Motor 60 Return oil channel 61 Pump return oil passage 62 Motor return oil passage 63 Cooler 66. Check valve (regulating valve) 70a, 70b Adjustment valve mechanism 72, 76 Low-pressure selector valve 74, 78 Relief valves (control valves) C1, C2 HST closed circuit S Hydraulic System Sa, Sb Hydraulic system for traction (hydraulic system for crawler-type traction devices)

Claims

1. A closed circuit is provided for each of the pair of crawlers, in which hydraulic fluid circulates between a hydraulic pump, which is driven by the power of a power source, and a hydraulic motor, which is driven by the hydraulic fluid discharged by the hydraulic pump and generates power transmitted to the crawler. A supply oil passage that supplies hydraulic fluid from the hydraulic fluid tank to the closed circuit by the operation of a charge pump driven by the power of the aforementioned power source, A cooler is provided, and a return oil passage is provided to return the hydraulic fluid from the closed circuit to the hydraulic fluid tank, An adjustment means for adjusting the flow rate of hydraulic fluid from the closed circuit to the hydraulic fluid tank via the return oil passage. It is equipped with Hydraulic system for crawler-type tracked vehicles.

2. The system includes an adjustment valve mechanism having a control valve that controls the flow of the hydraulic fluid from the low-pressure oil passage of the first and second oil passages connecting the hydraulic pump and the hydraulic motor to the return oil passage, according to the rotational speed of the output shaft of the power source. A hydraulic system for a crawler-type travel device according to claim 1.

3. A low-pressure selector valve that opens the low-pressure oil passage of the first and second oil passages connecting the hydraulic pump and the hydraulic motor, A control valve is controlled so that the flow rate of the hydraulic fluid from the low-pressure oil passage to the return oil passage changes according to the rotational speed of the output shaft of the power source. It is equipped with A hydraulic system for a crawler-type travel device according to claim 1.

4. The oil passage connecting the low-pressure oil passage and the return oil passage extends to allow the hydraulic fluid from the low-pressure oil passage to flow to the hydraulic fluid tank via the hydraulic motor. A hydraulic system for a crawler-type travel device according to claim 2 or 3.

5. A bypass oil passage, which is provided in the return oil passage to bypass the cooler, is equipped with a control valve that opens when the pressure exceeds a predetermined level. A hydraulic system for a crawler-type travel device according to any one of claims 1 to 3.

6. The aforementioned return oil passage is A pump return oil passage extending from the hydraulic pump toward the hydraulic oil tank, A motor return oil passage extending from the hydraulic motor toward the hydraulic oil tank and It has, The cooler is installed downstream of the confluence of the pump return oil passage and the tank return oil passage. A hydraulic system for a crawler-type travel device according to any one of claims 1 to 3.

7. A crawler vehicle comprising a hydraulic system for a crawler-type running device according to any one of claims 1 to 3.

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