Power plants – Pressure fluid source and motor – Input pump and rotary output motor system having...
Reexamination Certificate
1999-03-31
2001-12-04
Verdier, Christopher (Department: 3745)
Power plants
Pressure fluid source and motor
Input pump and rotary output motor system having...
C060S490000, C060S438000, C060S441000
Reexamination Certificate
active
06324843
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a hydraulic-mechanical type continuously variable transmission for a vehicle, in which a hydraulic pump having an input rotary member coupled to a vehicle engine and a hydraulic motor having an output rotational axis coupled to a driving wheel are connected via a first oil passageway that has a low oil pressure during a normal load operation of the vehicle engine but has a high oil pressure during a reverse load operation of the vehicle engine and a second oil passageway that has a high oil pressure during the normal load operation but has a low oil pressure during the reverse load operation, thereby forming a closed hydraulic circuit. At least either the hydraulic pump or the hydraulic motor has a variable capacity.
2. Description of Background Art
A continuously variable transmission of the foregoing type is well-known and disclosed in Japanese Patent Publication Hei7-23746, for example.
In the foregoing continuously variable transmission, when engine braking is applied, the hydraulic motor functions as a pump while the hydraulic pump functions as a motor. In such a case, a first oil passageway tends to have an increased oil pressure. Specifically, the first oil passageway connecting an outlet side of the hydraulic pump to an inlet side of the hydraulic motor constitutes a closed hydraulic circuit together with a second oil passageway connecting an outlet side of the hydraulic motor and an inlet side of the hydraulic pump. In order to prevent this problem, throttle valves are provided between the first and second oil passageways in an existing continuously variable transmission, thereby protecting the first oil passageway against a large oil pressure when engine braking is applied.
However, such throttle valves cannot sufficiently reduce the oil pressure in the first oil passageway. Further, if a large transmission ratio (i.e. a low gear side) is produced by the continuously variable transmission immediately before engine braking is applied, the transmission ratio cannot be sufficiently reduced, which means that engine braking is sometimes too effective.
SUMMARY AND OBJECTS OF THE INVENTION
The present invention has been contemplated in order to overcome the foregoing problem of the related art, and is intended to provide a hydraulic-mechanical type continuously variable transmission for a vehicle that can moderate the efficiency of engine braking when the transmission produces a large transmission ratio.
In order to accomplish the foregoing object, the invention provides a hydraulic-mechanical type continuously variable transmission for a vehicle, wherein: a hydraulic pump having an input rotary member connected to a vehicle engine and a hydraulic motor having an output rotational axis coupled to a driving wheel are connected via a first oil passageway that has a low oil pressure during a normal load operation of the vehicle engine but has a high oil pressure during a reverse load operation of the vehicle engine and a second oil passageway that has a high oil pressure during the normal load operation but has a low oil pressure during the reverse load operation; at least either the hydraulic pump or the hydraulic motor has a variable capacity; and a one-way clutch is provided between the input rotary member and the output rotational axis, and couples the input rotary member and the output rotational axis as the number of rotations of the output rotational axis exceeds the number of rotations of the input rotary member during the reverse load operation of the engine.
According to a first feature, the one-way clutch functions to directly couple the input rotary member and the output rotational axis as the input rotary member rotates faster than the output rotational axis during reverse load operations of the engine, i.e. during engine braking. Therefore, even when a large transmission ratio is produced by the continuously variable transmission immediately before engine braking, the output rotational axis and the input rotary member can be coupled without going via the continuously variable transmission, thereby moderating the efficiency of engine braking.
In accordance with a second feature of the present invention, the pressure regulating valves are provided in the first oil passageway in order to prevent the first oil passageway from having an increased oil pressure, in addition to the first feature. In this arrangement, during a reverse load operation, the hydraulic motor functions as a pump while the hydraulic pump functions as a motor. In this state, the hydraulic pump functioning as the motor causes the pressure regulating valves to reduce the oil pressure in the first oil passageway. Therefore, the first oil passageway is prevented from having a very high oil pressure. Further, since the oil pressure is reduced in the first oil passageway before the one-way clutch directly couples the input rotary member and the output rotational axis, it is possible to reduce reverse load applied to the input rotary member via the continuously variable transmission. Therefore, smooth engine braking can be assured by avoiding excessive variations in reverse loads placed on the engine. Still further, the pressure regulating valves are not required to regulate the oil pressure in the first oil passageway until the input rotary member and the output rotational axis are directly coupled via the one-way clutch. This is effective in reducing a load applied to the pressure regulating valves and means that the pressure regulating valves themselves can be made smaller.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description
REFERENCES:
patent: 4916901 (1990-04-01), Hayashi et al.
patent: 723746 (1995-03-01), None
Hayashi Tsutomu
Iizuka Toru
Kikuchi Hiroyuki
Yasuda Kazuhiro
Birch & Stewart Kolasch & Birch, LLP
Honda Giken Kogyo Kabushiki Kaisha
Lazo Thomas E.
Verdier Christopher
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