Transmitting system for small-sized vehicle

In a small-sized vehicle comprising an engine having a crankshaft and a multi-stage transmission having an input shaft, a transmitting system is interposed between the crankshaft and the input shaft and comprises a fluid transmitting means, said crankshaft and said input shaft being connected to each other through said fluid transmitting means including a pump impeller leading to the engine, and a turbine impeller leading to said multi-stage transmission,

• wherein said transmitting system includes a shifting clutch which is interposed between said crankshaft of the engine and said input shaft of said multi-stage transmission, said shifting clutch being in a series relation to said fluid transmitting means, and a lock-up clutch, which is interposed between said pump impeller and said turbine impeller of said fluid transmitting means, said lock-up clutch being capable of connecting both said impellers directly to each other;
• wherein said lock-up clutch is constructed such that it depends on the rotational speed of the pump impeller and it automatically operates, when the rotational speed of the pump impeller becomes equal to or higher than a predetermined value;
• and
• wherein said lock-up clutch comprises a pump extension connected to said pump impeller and surrounding said turbine impeller, a pressure receiving plate coupled to a tip end of said pump extension to define, within said pump extension, a hydraulic pressure chamber communicating with an oil chamber defined between said pump impeller and said turbine impeller, a pressing plate opposed to said pressure receiving plate for advancing and retracting movements, an annular friction clutch plate interposed between said pressure receiving plate and said pressing plate and connected to said turbine impeller, a return spring for biasing said pressing plate in a direction to be retracted relative to said pressure receiving plate, and an escape bore which permits communication between the inside and outside of said pressure receiving plate on an inner peripheral side of said friction clutch plate, wherein when the rotational speed of said pump impeller becomes equal to or higher than the predetermined value, said pressing plate clamps said friction clutch plate in cooperation with said pressure receiving plate under the action of a centrifugal hydraulic pressure which is raised in said hydraulic pressure chamber in accordance with the rotational speed of said pump impeller.

In a small-sized vehicle comprising an engine having a crankshaft and a multi-stage transmission having an input shaft, a transmitting system is interposed between the crankshaft and the input shaft and comprises a fluid transmitting means, said crankshaft and said input shaft being connected to each other through said fluid transmitting means including a pump impeller leading to the engine, and a turbine impeller leading to said multi-stage transmission,

• wherein said transmitting system includes a shifting clutch which is interposed between said crankshaft of the engine and said input shaft of said multi-stage transmission, said shifting clutch being in a series relation to said fluid transmitting means, and a lock-up clutch, which is interposed between said pump impeller and said turbine impeller of said fluid transmitting means, said lock-up clutch being capable of connecting both said impellers directly to each other;
• wherein said lock-up clutch is constructed such that it depends on the rotational speed of the turbine impeller and it operates automatically when the rotational speed of the turbine impeller becomes equal to or higher than a predetermined value;
• wherein said lock-up clutch comprises a clutch cylinder connected to said turbine impeller, a pressing piston slidably received in a cylinder bore in said clutch cylinder to define a hydraulic pressure chamber, a piston return spring for biasing said pressing piston toward said hydraulic pressure chamber, a means for introducing oil into said hydraulic pressure chamber, and a friction engagement means provided between said clutch cylinder and said pump impeller, wherein when the rotational speed of the turbine impeller becomes equal to or higher than the predetermined value, said pressing piston operates said friction engagement means under the action of a centrifugal hydraulic pressure risen within said hydraulic pressure chamber which is raised in accordance with the rotational speed of the turbine impeller to connect said clutch cylinder and said pump impeller directly to each other;
• and
• wherein said clutch cylinder is provided with an escape bore which opens an outer periphery of said hydraulic pressure chamber to the outside, and a centrifugal valve which is adapted to open said escape bore, when the rotational speed of said clutch cylinder is lower than a predetermined value, and to close said escape bore, when the rotational speed of said clutch cylinder is equal to or higher than the predetermined value.