192 clutches and power-stop control – Transmission control and clutch control – Interrelated
Reexamination Certificate
2001-01-29
2002-09-17
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Transmission control and clutch control
Interrelated
C192S048300, C192S083000
Reexamination Certificate
active
06450309
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a transmission system using a wet type multi-plate clutch for shifting or as a main clutch, wherein the power train is adopted in working vehicles particularly such as tractors and the like.
RELATED ART
In working vehicles such as tractors and the like or ordinary vehicles, a dry type clutch to be pressed against a flywheel of an engine is generally used as a main clutch, which is engaged/disengaged between an engine and a shift mechanism and is half-clutched for generating inching during a transition period between states of engaging and disengaging. In many cases, a dry type multi-plate clutch is used so as to secure transmission torque while being engaged and frictional resistance while being half-clutched. However, since the multi-plate clutch is complex and axially elongated, if possible, a single-plate clutch being simple and compact is desired.
In some cases, a wet type (hydraulic type) multi-plate clutch may be used as the above-mentioned main clutch. However, it has the problem that, while the clutch being disengaged, power is transmitted slightly due to the viscosity of lubricant oil therein so as to generate a creep phenomenon. To protect this problem, it has been considered that a brake is provided in a power train located on the downstream of the wet type multi-plate clutch to brake the downstream power train, and actually this idea becomes known. When such a brake is operated, the downstream side of the clutch is isolated with power transmission, however, the power train on the upstream side of the clutch is still rotated following the engine power. Therefore, the load resulting from the viscosity of lubricant oil in the wet type multi-plate clutch is exerted on the power train on the upstream side of the clutch. The load is further put on the engine at idle, thereby causing incomplete combustion at worst so as to generate the problem that a carbon deposit is accumulated in an engine cylinder.
Then, it is considerable that the creep phenomenon, i.e., a drag of shift mechanism and the like on the downstream side of the disengaged wet type multi-plate clutch resulting from the viscosity of lubricant oil of the wet type multi-plate clutch is prevented by using a conventional dry type clutch whose clutch disc is pressed against the flywheel on the upstream side of the wet type multi-plate clutch. In this case, the dry type clutch is disengaged to isolate only the dragging driving power train with transmission of engine power. Therefore, the dry type clutch can be constituted by a single-plate type clutch, which is simple and compact. This clutch is detached from the flywheel to be disengaged, thereby greatly reducing load on the engine at idle so as to effect an engine protection.
Further, conventionally, there is a well-known working vehicle particularly such as a tractor or the like, which is provided with a shift mechanism including a plurality of parallel power trains with different reduction ratios, wherein the power trains are provided with respective wet type multi-plate clutches. In these shift mechanisms, there is a well-known shift mechanism in which one of the plurality of wet type clutches is selectively engaged and one corresponding speed stage is formed through the power train having the engaged clutch. These wet type multi-plate clutches for shifting are, as they are, used also as a main clutch when all the wet type multi-type clutches are disengaged so as to isolate the transmission system with transmission of engine power. In this case, it is not unnecessary to provide the foregoing wet type multi-plate clutch as a main clutch separately. In this case, the foregoing detriment of the drag inherent to a wet type multi-plate clutch can be dissolved by providing a drag-preventing clutch such as a dry type single-plate clutch which is arranged on the upstream side of the shift mechanism as described above and pressed against the flywheel. Also, therefore, a simple and compact transmission system can be configured.
However, when the wet type multi-plate clutches used for shifting is diverted to a main clutch as they are, each wet type multi-plate clutch possibly come to be half-clutched because a shift operation (operation selecting speed stages) and a main clutch operation are performed separately from each other. To generate a state of half-clutch, each clutch is required to have the larger volume to secure the durability against a load. However, the whole size of shift mechanism becomes significantly large if all the wet type multi-plate clutches used in the shift mechanism have so large volume. Then, it is thought of that only one wet type multi-plate clutch in the shift mechanism has a sufficiently larger volume and a speed stage corresponding to this clutch is selected for the main clutch operation. However, it is too burdensome to be required for such a shift operation in every main clutch operation.
Furthermore, there is the problem associated with the shift operation in such a shift mechanism comprising a plurality of wet type multi-plate clutches that, during the shifting, the fluctuation of hydraulic pressure arises necessarily because the shifting is attended with such a control that hydraulic oil is drained from the clutch previously supplied with the hydraulic oil and the hydraulic oil is supplied to another clutch. When the drainage of hydraulic oil from the clutch and the supply to the other clutch is performed rapidly or the timings of the drainage and the supply are apart, the fluctuation becomes rapid and impact is developed.
DISCLOSURE OF THE INVENTION
A first object of the present invention is to provide a transmission system for a vehicle, wherein, while a wet type multi-plate clutch having high transmission torque and high frictional resistance during its half-clutching is used as a main clutch, a creep phenomenon does not occur when the transmission system is isolated with transmission of engine power and the power trains thereof may be secured to be compact.
According to a vehicle transmission system of the present invention, a plurality of wet type multi-plate clutches for shifting, among which one clutch is selectively engaged to form one speed stage, is utilized as a main clutch. All the wet type multi-plate clutches for shifting are disengaged when the transmission system is isolated with transmission of engine power. Furthermore, a dry type single-plate clutch is provided as a drag-preventing mechanism on the upstream side of the shift mechanism in the transmission system. The dry type single-plate clutch is disengaged when all the wet type multi-plate clutches for shifting are disengaged.
One wet type multi-plate clutch to be half-clutched for generating inching during a transition period of a main clutch between its disengaging and engaging is specified among the plurality of wet type multi-plate clutches for shifting. Only the specified clutch has the largest volume so as to resist against frequent use, thereby securing the whole shift mechanism to be compact. A clutch corresponding to the lowest speed stage in the shift mechanism is used as the clutch for inching.
In this structure, the vehicle transmission system is hydraulically controlled so that, when the main clutch operation is performed while one speed stage corresponding to one wet type multi-plate clutch other than the clutch for inching is determined, only the clutch for inching is half-clutched in the shift mechanism in a transition period between clutching-on and clutching-off during the main clutch operation regardless of the determined speed stage. Therefore, the selected clutch for shifting other than the clutch for inching is prevented from being half-clutched.
The plurality of wet type clutches for shifting in the shift mechanism are engaged with the supply of hydraulic oil and disengaged with the drainage of hydraulic oil.
The drag-preventing clutch apparatus is disengaged and completes engaging while the plurality of wet type clutches play up to a rise of minimum hydraulic fluid pressure therein. I
Hasebe Takeshi
Hirai Tadao
Hirano Takashi
Kawamura Masahisa
Bonck Rodney H.
Kanzaki Kokyukoki Mfg. Co. Ltd.
Sterne Kessler Goldstein & Fox P.L.L.C.
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