JP2007192348A - Hydrostatic continuously variable transmission of work vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a hydrostatic continuously variable transmission of a work vehicle for shortening idling, by quickly raising the oil temperature of oil flowing in an HST. <P>SOLUTION: This hydrostatic continuously variable transmission has two sets of a pair of hydraulic pump 8 and hydraulic motor 7 mutually connected by a closed circuit, and continuously variably shifts rotation of the hydraulic motor 7, and is constituted to return drain oil from residual ports T1 and T2 to an oil tank 17 by cooling via an oil cooler 18, by directly returning the drain oil from a partial port T3 to the oil tank 17 in a plurality of drain ports T1, T2 and T3 of the hydraulic pump 8 draining the drain oil including leakage oil of the hydraulic pump 8. For example, the drain oil of directly returning to the oil tank 17 is drained from one drain port T3 of setting a discharge quantity of the drain oil among the plurality of drain ports T1, T2 and T3 more than a discharge quantity of the drain oil from the other drain ports T1 and T2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a hydrostatic continuously variable transmission for a work vehicle such as a tractor.

2. Description of the Related Art Conventionally, a tractor using a hydraulic continuously variable transmission (HST) as a traveling transmission is known (see, for example, Patent Document 1).
JP-A-3-134370 (FIG. 8)

  In the HST, the oil drained from the hydraulic motor side and the oil drained from the hydraulic pump side merge and are returned to the hydraulic oil tank via the oil cooler. For this reason, there has been a problem that cooling of the waste oil from the HST is strongly performed, and it takes time to raise the oil temperature of the oil flowing through the HST to an appropriate temperature.

  In order to solve the above problems, a hydrostatic continuously variable transmission for a work vehicle according to the present invention comprises two pairs of a hydraulic pump 8 and a hydraulic motor 7 connected to each other by a closed circuit, and the rotation of the hydraulic motor 7 is possible. In a hydrostatic continuously variable transmission for a work vehicle provided with a plurality of drain ports T1, T2, and T3 of a hydraulic pump 8 that is continuously stepped and discharges exhaust oil including leakage oil of the hydraulic pump 8. Of the drain ports T1, T2, T3, the oil discharged from some of the ports T3 is directly returned to the oil tank 17, and the oil discharged from the remaining ports T1, T2 is cooled via the oil cooler 18 to be supplied to the oil tank 17. The first feature is that it is configured so as to return to the above.

  Secondly, the amount of discharged oil that is returned directly to the oil tank 17 is larger than the amount of discharged oil from the other drain ports T1, T2 among the plurality of drain ports T1, T2, T3. Oil drained from one drain port T3 and drained from the hydraulic pump 8 side returned to the oil tank 17 via the oil cooler 18 is drained from the other drain ports T1 and T2. .

  Thirdly, the oil discharged from the hydraulic motor 7 is merged with the oil returned to the oil tank 17 via the oil cooler 18, cooled via the oil cooler 18, and returned to the oil tank 17. It is characterized by.

  According to the structure of the present invention configured as described above, even if the oil is cold immediately after the engine is started or the like, the exhausted oil discharged from some of the plurality of drain ports is discharged. Since the oil is directly returned to the oil tank, the temperature of the oil in the oil tank easily rises even when the hydraulic motor is stopped without rotating. As a result, the oil temperature can be raised quickly and smoothly to an appropriate temperature, and the idling time can be shortened.

  In particular, the oil that is returned directly to the oil tank is drained from one drain port, where the amount of discharged oil is greater than the amount of discharged oil from other drain ports. By using the oil drained from the hydraulic pump that returns to the oil tank through the cooler as the oil drained from the other drain port, a relatively large amount of oil can be used from the time when the oil is cold, such as immediately after the start of operation. By returning the waste oil directly to the oil tank, the oil temperature can be raised quickly and smoothly as described above. After the oil temperature rises, the waste oil from the other drain ports passes through the oil cooler. Since it is cooled and returned to the oil tank, it is possible to suppress an excessive temperature rise. When the amount of oil drained from the drain port returned to the oil tank via the oil cooler increases with the temperature rise of the oil, the effect of suppressing the temperature rise more than necessary is particularly high.

  In addition, when the traveling vehicle travels, the oil discharged from the hydraulic motor is combined with the waste oil returned to the oil tank via the oil cooler, cooled via the oil cooler, and returned to the oil tank. As a result, the amount of oil to be cooled increases, and the temperature rise suppression effect that is more than necessary when the traveling vehicle is running can be improved.

  1 and 2 are a side view and a plan view of a crawler tractor which is a work vehicle employing the hydrostatic continuously variable transmission of the present invention. The traveling machine body 1 includes left and right crawler-type traveling devices (crawler traveling devices) 2. The traveling machine body 1 moves straight forward or backward by driving the left and right crawler traveling devices 2 at a constant speed. By providing a difference between the driving speeds of the left and right crawler traveling devices 2, the traveling machine body 1 turns toward the crawler traveling device 2 that is driven at a low speed.

  The crawler traveling device 2 has a structure in which a crawler belt 6 is wound between a drive sprocket 3 that is rotationally driven and an idler wheel 4 that is attached to the frame 5 side. The crawler belt 6 is rotated by driving the drive sprocket 3. Based on the above, the traveling machine body 1 travels by the rotation of the crawler belt 6.

  As shown in FIG. 3, a hydrostatic continuously variable transmission (HST) including two pairs of a hydraulic pump 8 and a hydraulic motor 7 connected to each other by a closed circuit is provided on the traveling machine body 1 side. ing. Both hydraulic pumps 8 are accommodated in the housing 9 of one HST pump unit 11.

  Both hydraulic motors 8 are housed in separate hydraulic motor units 12. The HST pump unit 11 and both hydraulic motor units 12 are connected by hydraulic piping to constitute the HST.

  Both hydraulic motor units 12 are incorporated in each crawler traveling device 2 so that the drive sprocket 3 is driven by the hydraulic motor 8. One crawler travel device 2 (drive sprocket 3) is driven by one hydraulic motor 7, and the other crawler travel device 2 (drive sprocket 3) is driven by the other hydraulic motor 7.

  In this HST, the driving speed of the hydraulic motor 7 is steplessly changed by adjusting the slope angle of the hydraulic pump 8 as in the prior art. Both hydraulic pumps 8 are simultaneously driven to rotate by a drive shaft 13 that is driven to rotate by the engine E. By independently adjusting the slope angle of each hydraulic pump 8, the driving speed of each hydraulic motor 7 is adjusted separately. Thereby, the steering of the traveling machine body 1 can be controlled as described above.

  Although each hydraulic pump 8 and the corresponding hydraulic motor 7 are connected by a closed circuit, oil leakage occurs inside and the oil decreases. Correspondingly, the HST pump unit 11 is provided with a charge pump 14 that is driven simultaneously with the hydraulic pump 8 by the drive shaft 13.

  Oil is supplied from the hydraulic oil tank 17 through the HST oil filter 16 to the hydraulic circuit between the hydraulic pumps 8 and the hydraulic motor 7 by the charge pump 14. Thereby, the reduced amount of oil is supplied.

  As shown in FIG. 4, the housing 9 of the HST pump unit 11 discharges a plurality of (three in the present embodiment) exhaust oil including the leaked oil and excess oil when the charge pump 14 supplies the oil. Drain ports T1, T2 and T3. The drain oil passage through which the waste oil flows is formed in the housing 9 of the HST pump unit 11.

  The oil discharged from both hydraulic pumps 8 joins in the drain oil passage in the housing 9 and is discharged from the drain ports T1, T2, T3. Of the three drain ports, one drain port (main drain port) T3 has a larger amount of discharged oil than the other two drain ports (sub-drain ports) T1 and T2.

  As shown in FIG. 3, the oil discharged from the main drain port T3 is directly returned to the hydraulic oil tank 17 by the hydraulic line L3 without passing through the oil cooler. Oil discharged from both sub-drain ports T1 and T2 is joined by hydraulic lines L1 and L2, and returned to the hydraulic oil tank 17 via the oil cooler 18 by the hydraulic line L4.

  The oil temperature of the oil discharged from the drain ports T1, T2, T3 rises as the hydraulic pump 8 rotates. For this reason, the oil temperature of the hydraulic oil tank 17 to which the oil discharged from the drain ports T1, T2, T3 is returned rises. For this reason, as the hydraulic pump 8 rotates, the oil temperature of the oil flowing through the HST rises recursively.

  On the other hand, the oil discharged from both hydraulic motors 7 is taken out from each hydraulic motor 7 through a hydraulic line L5. The oil discharged from the hydraulic motor 7 through the hydraulic line L5 is merged with the oil discharged from the sub drain ports T1 and T2. As a result, the oil discharged from both hydraulic motors 7 is returned to the hydraulic oil tank 17 via the oil cooler 18.

  The oil cooler 18 is provided with a check valve 21 in parallel. When the oil pressure of the exhaust oil to the hydraulic oil tank 17 increases due to clogging of the oil cooler 18 or the like, the check valve 21 is opened, and the exhaust oil is returned to the hydraulic oil tank 17 via the check valve 21.

  If the temperature of the oil that circulates HST is too low, the viscosity will increase, and problems such as increased friction of the hydraulic motor 7 will occur. If the temperature is too high, the viscosity of the oil will decrease, causing oil leakage and oil leakage. Performance degradation occurs. For this reason, it is desirable to maintain the oil temperature of the oil flowing through the HST (the oil in the hydraulic oil tank 17) at an appropriate temperature that does not cause the above problem.

  In the present embodiment, part of the drained oil from the hydraulic pump 8 is returned directly to the hydraulic oil tank 17. The oil discharged directly to the hydraulic oil tank 17 is oil discharged from the main drain port T3, and the amount of discharged oil is larger than the oil discharged from the other two drain ports T1 and T2. For this reason, the hydraulic oil tank 17 is directly supplied with a relatively large amount of waste oil whose temperature has increased due to the rotation of the hydraulic pump 8.

  Oil drainage from the hydraulic pump 8 occurs without rotating the hydraulic motor 7. Therefore, even when the oil is cold immediately after the engine is started, the temperature of the oil in the hydraulic oil tank 17 is raised to an appropriate temperature in a short time without rotating the hydraulic motor 7, that is, without running the tractor. be able to. For this reason, idling of the tractor can be completed in a short time. In addition, it is possible to prevent damage to the hydraulic equipment due to long-term back pressure rise at low temperatures.

  The oil drained from the sub drain ports T1 and T2 is returned to the hydraulic oil tank 17 via the oil cooler 18. On the other hand, the amount of oil discharged from the two sub-drain ports T1 and T2 increases as the oil temperature rises. Therefore, when the oil is cooled, the amount of oil discharged from the sub-drain ports T1 and T2 is A small amount. For this reason, the cooled drain oil from the two sub drain ports T1 and T2 does not greatly hinder the temperature rise of the oil due to the uncooled drain oil from the main drain port T3.

  When the temperature of the oil in the hydraulic oil tank 17 rises and the temperature of the oil flowing through the HST rises, the amount of oil discharged from the sub drain ports T1 and T2 increases. The discharged oil discharged from the sub drain ports T1 and T2 joins with the discharged oil from the hydraulic motor 7, is cooled by the oil cooler 18, and returns to the hydraulic oil tank 17.

  For this reason, when the temperature of the oil flowing through the HST rises, the amount of the cooled oil returned to the hydraulic oil tank 17 increases, and the oil temperature in the hydraulic oil tank 17 is prevented from rising more than necessary. As a result, the temperature of the oil in the hydraulic oil tank 17 is maintained at an appropriate temperature.

  In particular, since the oil discharged from the hydraulic motor 7 is cooled by the oil cooler 18 and returned to the hydraulic oil tank 17, the amount of oil that is cooled increases when the hydraulic motor 7 rotates, that is, when the tractor travels. Therefore, the temperature rise of the oil in the hydraulic oil tank 17 more than necessary is suppressed during traveling of the tractor.

  As shown in FIG. 5, a throttle valve 22 may be provided in the hydraulic line L <b> 3 from the main drain port T <b> 3 to the hydraulic oil tank 17. The aperture of the throttle valve 22 is controlled by an oil temperature sensor 23 that measures the oil temperature of the oil in the hydraulic oil tank 17. Based on the information from the oil temperature sensor 23, the throttle valve 22 is throttled as the oil temperature rises and is controlled so as to reduce the amount of oil discharged from the main drain port T3 to the hydraulic oil tank 17.

  As a result, as the temperature of the oil in the hydraulic oil tank 17 rises, the amount of oil that is returned directly to the hydraulic oil tank 17 is reduced, and the amount of oil that is cooled by the oil cooler 18 and returned to the hydraulic oil tank 17 is reduced. Can be increased. With this structure, an increase in the oil temperature of the oil in the hydraulic oil tank 17 can be more positively suppressed.

It is a side view of a crawler tractor. It is a top view of a crawler tractor. It is a hydraulic circuit diagram around HST. (A), (b), (c) is a rear view, a top view, and a front view of a single HST pump unit. It is the schematic of the hydraulic circuit figure of other embodiment.

Explanation of symbols

7 Hydraulic motor 8 Hydraulic pump 17 Hydraulic oil tank
18 Oil cooler T1 Sub-drain port (drain port)
T2 Sub-drain port (drain port)
T3 Main drain port (drain port)

Claims (3)

  Two pairs of a hydraulic pump (8) and a hydraulic motor (7) connected to each other by a closed circuit are provided, the rotation of the hydraulic motor (7) is steplessly changed, and oil leaking from the hydraulic pump (8) is included. In a hydrostatic continuously variable transmission for a work vehicle provided with a plurality of drain ports (T1), (T2), (T3) of a hydraulic pump (8) that discharges waste oil, the plurality of drain ports (T1), Of (T2) and (T3), the oil discharged from some ports (T3) is directly returned to the oil tank (17), and the oil discharged from the remaining ports (T1) and (T2) is returned to the oil cooler (18). ) Through a hydrostatic continuously variable transmission for a work vehicle configured to be returned to the oil tank (17).   The drained oil that is returned directly to the oil tank (17) is discharged from the other drain ports (T1), (T2), out of the drain ports (T1), (T2), (T3). Oil discharged from one drain port (T3), which is larger than the amount of oil discharged, is discharged from the hydraulic pump (8) side that is returned to the oil tank (17) via the oil cooler (18). The hydrostatic continuously variable transmission for a work vehicle according to claim 1, wherein oil is discharged from the drain ports (T1) and (T2).   The oil discharged from the hydraulic motor (7) is combined with the oil returned to the oil tank (17) through the oil cooler (18), cooled through the oil cooler (18), and cooled to the oil tank (17). The hydrostatic continuously variable transmission for a work vehicle according to claim 1 or 2, wherein the continuously variable transmission is configured to be returned to the position.

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