CLUTCH SWITCHING CIRCUIT OF NONSTAGE TRANSMISSION

Abstract: The invention relates to a clutch switching circuit which can be utilised suitably for a multi-stage static hydraulic mechanical nonstage transmission. If pressure regulating valves having good override characteristics are used, slip or breakage of a clutch will occur. Therefore, this invention provides a clutch switching circuit which provides communicating throttle passages (311) in the valve body of the pressure regulating valves (211) so that a working fluid flows towards the clutch when the valves are closed. When the clutch is switched, the working fluid flows in a quantity equivalent at least to the oil leakage flow quantity so that the slip or breakage of the clutch can be prevented while pressure regulating valves having good override characteristics are used. The invention provides also a clutch switching circuit wherein common oil passages leading to a plurality of clutches corresponding to the gears which are not adjacent to one another are provided, and the pressure regulating valves and pressure reducing valves used commonly for a plurality of gears are installed in the common oil passages.

Description: BACKGROUND OF THE INVENTION: The present invention relates to a clutch changeover circuit for a non-stage transmission, and more particularly to a clutch changeover circuit suitable for use in a hydro-mechanical transmission with a non-stage hydrostatic and a multi-stage mechanical path. As a multi-stage type stationary hydraulic mechanical non-stage transmission, the one having the arrangement shown in Fig. 1 is generally known. In this transmission, an input shaft 1 and an output shaft 2 are connected to each other via the following: a planetary gear P1 for accelerating the mechanical input of the second speed, a synthetic planetary gear P2 for a mechanical drive system and a hydraulic drive system for the second and fourth speeds, and a synthetic planetary gear P3 for a mechanical drive system and a hydraulic drive system for the first, second, third, and fourth speeds. A variable-discharge-capacity pump 3 driven via gears 5, 6, 7 as well as a volume-fixing motor 4 driven by this pump 3 are connected to the input shaft 1. The output of the pump 3 is transmitted to a sun gear of the synthetic planetary gear P2 via gears 8, 9, 10 and to a sun gear of the synthetic planetary gear P3 via gears 8, 9, 11, 12. These gears are provided with clutches for changing over the speed stage. Specifically, a clutch C1 for the first speed is provided for connecting or disconnecting the rotation of a ring gear of the synthetic planetary gear P3 on the output shaft 2 side, and a clutch C2 for the second speed is provided for connecting or disconnecting the rotation of a ring gear of the planetary gear P1 on the input shaft 1 side. Furthermore, a clutch C3 for the third speed for connecting or disconnecting the transmitted rotation from the input shaft 1 is provided on a shaft member which connects together the ring gears of the synthetic planetary gear P2 and the synthetic planetary gear P3, while a clutch C4 for the fourth speed for connecting or disconnecting the transmitted rotation from the input shaft 1 is provided on an arm wihch connects together the planetary gears of the planetary gear P1 and the synthetic planetary gear P2. In such a transmission, since a speed change is effected at a point where there is no difference in the relative speed with respect to the following-stage clutch, it is possible to change the speed-change stage in which there is no shock which is caused by the changeover of the clutch. In addition, the speed change is always effected in the order of the respective adjacent speed stages and is not effected by jumping a midway speed stage. A hydraulic circuit such as the one shown in Fig. 2 (Japanese Utility Model Application No. 151193/1984) is used to effect a changeover among the clutches C1, C2, C3, and C4 with respect to the above-described transmission. This circuit is so arranged that oil circuits for the respective clutches C1, C2, C3, and C4 are provided to a hydraulic pump 101 in parallel, and pressure regulating valves 111, 121, 131, 141, reducing valves 112, 122, 131, 142, and clutch changeover valves 113, 123, 133, 143 are disposed in these oil passages in the order mentioned from the upstream side, the clutch changeover valves being respectvely opened and closed by solenoid valves 114, 124, 134, 144. Hydraulic pressure from the hydraulic pump 101 acts on each of the solenoid valves via a reducing valve 102 serving as a pilot valve, the clutch changeover valve is actuated upon activation of the solenoid valve, and a corresponding clutch is adapted to operate. Hydraulic oil from the hydraulic pump 101 is returned to the tank via a pressure regulating valve 103. In accordance with such a hydraulic circuit, since the pressure regulating valves 111, 121, 131, 141 are provided in the oil circuits leading to the respective clutches C1, C2, C3, C4, it is possible to prevent the pressure of the presently engaged clutch from falling, until a following-stage clutch is engaged during a speed change. Hence, it is possible to obtain an advantage in that the clutch engaging period can be minimized with respect to the flow rate of the hydraulic pump. Accordingly, when an attempt is made to engage the clutch C2 from the state in which the clutch C1 is engaged, if the oil passage to the clutch C2 is opened, the pressure regulating valve 103 placed in a supply oil passage 200 from the hydraulic pump 101 is closed due to a drop in the circuit pressure. However, since the pressure regulating valve 121 is actuated, the pressure within the supply oil passage 200 is maintained above a set pressure of the regulating valve 121, so that the pressure of the clutch C1 is maintained at a set pressure of the regulating valve 121. However, with the conventional clutch changeover circuit, although the pressure within the supply oil passage 200 is maintained above a set pressure of the regulating valve concerned, there has been a drawback which stems from the fact that the override characteristics of the regulating valves are good. For instance, when an attempt is made to effect a changeover operation between, for instance, the clutches C1 and C2, it is assumed that, as shown in Fig. 3, the pressure gradients of the regulating valves 111, 121, and the regulating valve 103 disposed in the supply oil passage 200 are small with respect to a flow rate Q of the pump, and that the set pressures P111, P121 of the clutch-side regulating valves 11, 121 fluctuate vertically, as illustrated in the drawing, due to production errors or the like (P111 > P121). If the clutch C2 is operated in such a state, even if oil flows from the hydraulic pump 101 at a full flow rate QA, the supply pressure rises only up to the full bore hydraulic pressure PB of the regulating valve 121, so that the pressure does not reach the set pressure of the C1 clutch-side regulating valve 111. In such a case, the hydraulic oil does not flow to the clutch C1, and since leakage usually occurs downstream of the regulating valve, the pressure fails to rise, and the pressure of this clutch hence declines. Consequently, there has been a problem in that this can result in the sliding of the clutch, ultimately resulting in the possible damage to the clutch. For this reason, it has conventionally been necessary to positively use regulating valves having poor override characteristics, as shown in Fig. 4. In this case, since the pressure gradients with respect to the flow-rate Q of the pump are large, the characteristic line of the full bore hydraulic pressure PB on the side of the clutch to which a changeover is to be effected intersects the characteristic line of the set pressure P111 of the regulating valve on the side of the already operating clutch (PB >P111). As a result, the line pressure acts on the already operating clutch, so that no damage to the clutch results even if the oil may leak. Thus, it has hitherto been impossible to use regulating valves having good override characteristics, and there has been the drawback that regulating valves having poor override characteristics have to be used positively, which has been a large disadvantage. In addition, in correspondence with the poor override characteristics, it has been necessary to set the pressure of the regulating valve 103 provided in the supply oil passage 200 at a high level, which disadvantageously necessitates the capacity of the hydraulic pump 101 to be increased. Furthermore, with the conventional clutch changeover circuit, it has been necessary to provide pressure regulating valves separately in oil passages leading to the clutches. This has brought about the problem of the circuit configuration becoming complicated and the valve mechanisms incorporated in this circuit becoming large in size. A first step to overcome these disadvantages has been disclosed in the DE-A-29 34 269, in which oil pressure regulating valves are provided between a pump and several clutches by using only one oil passage downstream of the regulating valve for all clutches. SUMMARY OF THE INVENTION: Accordingly, an object of the present invention is to provide a clutch changeover circuit for a non-stage transmission having a structure that allows valve mechanisms to be simplified, thereby overcoming the above-described drawbacks. To this end, in accordance with the present invention, there is provided a clutch changeover circuit for a non-stage transmission, specifically, a hydro-mechanical transmission with non-stage hydrostatic and a multi-stage mechanical path, in which at least pressure regulating valves are provided in a common oil passages leading from a pump to respective clutches, the clutch changeover circuit comprising: throttle passages each provided at the valve-closing position of each of the pressure regulating valves in such a manner as to communicate with each of the pressure regulating valves. By virtue of the above-described arrangement, at the time of changing over the clutch, even if the full bore hydraulic pressure of the regulating valve after a changeover is smaller than the set pressure of the regulating valve before the changeover, and this regulating valve is closed, this regulating valve is provided with a flow passage. The arrangement is such that hydraulic oil flows to the clutch side at least by the rate of flow of leaking oil, with the result that the line pressure acts on the clutch, thereby preventing the clutch from sliding or becoming damaged. Accordingly, it is possible to use regulating valves having excellent override characteristics. BRIEF DESCRIPTION OF THE DRAWINGS: Fig. 1 is a diagram schematically illustrating the configuration of a multi-stage type stationary hydraulic mechanical non-stage transmission; Fig. 2 is a diagram schematically illustrating the configuration of a conventional clutch changeover circuit for a non-stage transmission; Figs. 3 and 4 are diagrams respectively illustrating a case in which the override characteristics of regulating valves are good and a case in which they are poor; Fig. 5 is a diagram schematically illustrating the configuration of a clutch changeover circuit for a non-stage transmission in accordance with a first embodiment of the present invention; DESCRIPTION OF THE PREFERRED EMBODIMENTS: Fig. 5 is a schematic diagram of a clutch changeover circuit for a non-stage transmission in accordance with a first embodiment of the present invention. This hydraulic circuit is used for the non-stage transmission shown in Fig. 1. This circuit is arranged such that, as shown in Fig. 5, oil passages 201, 202, 203, 204 leading from a hydraulic pump 101 to respective clutches C1, C2, C3, C4 are connected to a supply oil passage 200 in such a manner as to be parallel with each other so as to cause hydraulic pressure to act on the respective clutches C1, C2, C3, C4. Pressure regulating valves 211, 221, 231, 241 are provided in the oil passages 201, 202, 203, 204 leading to the clutches C1, C2, C3, C4 on the uppermost-stream sides thereof. Throttle passages 311, 321, 331, 341, communicating in such a manner that hydraulic oil flows to the clutches particularly when the valves are closed, are respectively formed in these regulating valves. These throttle passages 311, 321, 331, 341 suffice if they are capable of allowing the oil to flow by a portion compensating for the amount of leakage from component members on the downstream sides of the regulating valves 211, 221, 231, 241, and these throttle passages can be provided simply by being formed on the valve bodies of the respective regulating valves. It should be noted that, in the same way as the conventional arrangement, the clutches C1, C2, C3, C4 are connected to the downstream sides of the regulating valves 211, 221, 231, 241 via the clutch changeover valves 113, 123, 133, 143, and the clutch changeover operations are conducted by means of solenoid valves 114, 124, 134, 144. In accordance with this first embodiment, at the time of changing over the clutch, the hydraulic pressure of the supply oil passage 200 is transmitted to the clutches C1, C2, C3, C4 already in operation via the throttle passages 311, 321, 331, 341 of the corresponding regulating valves 211, 221, 231, 241. When the following-stage clutch is operated at the time of a speed change, even if the full bore hydraulic pressure of the corresponding regulating valve 211, 221, 231, or 241 is lower than the set pressure of the preceding-stage clutch, it is possible to prevent the sliding of the clutch. Accordingly, the drawback caused by the good characteristics of the regulating valves 211, 221, 231, 241 can be overcome substantially. In addition, the set pressure of the regulating valve provided in the supply oil passage 200 can be set to a low level, and the horsepower consumption by the hydraulic pump 101 can be reduced. As a result, it is possible to obtain a clutch changeover circuit for a non-stage transmission having small power losses. As described above, the clutch changeover circuit for a non-stage transmission in accordance with the present invention is useful as a circuit having small power losses since it is capable of preventing the clutch from sliding or becoming damaged while using regulating valves having good override characteristics. In addition, since the number of regulating valves can be reduced while preventing a decline in the preceding-stage clutch at the time of a clutch changeover, and since the number of the reducing valves can also be decreased, this clutch changeover circuit is suitable for a circuit in which the adoption of simplified valve mechanisms is preferable.

Claims: A clutch changeover circuit for a non-stage transmission, specifically, a hydro-mechanical transmission with a non-stage hydrostatic and a multi-stage mechanical path, in which at least pressure regulating valves are provided in a common oil passages leading from a pump to respective clutches, said clutch changeover circuit characterised in that it comprises throttle passages (311, 321, 331, 341) each provided at the valve-closing position of each of said pressure regulating valves (211, 221, 231, 241) in such a manner as to communicate with each of said pressure regulating valves.

Inventors: ISHINO TSUTOMU, MARUYAMA RYOICHI, ISHINO, TSUTOMU, MARUYAMA, RYOICHI
Applicants: KOMATSU MFG CO LTD, KABUSHIKI KAISHA KOMATSU SEISAKUSHO
Application year: 1989
Main classification: F16H61
IPC codes: F16D48, F16H61