192 clutches and power-stop control – Transmission control and clutch control – Common control
Reexamination Certificate
1999-12-09
2001-03-06
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Transmission control and clutch control
Common control
C474S019000
Reexamination Certificate
active
06196367
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a power transmission apparatus of a working machine having a clutch for transmitting engine power to a drive wheel of the working machine, particularly to a power transmission apparatus of a self-propelled working machine such as a lawn mower and a grass mower in which engine power is transmitted to a clutch through a belt and a pulley for disconnecting and connecting the power with a drive wheel.
Japanese Laid-Open Patent Publication No.
61-55412
or U.S. Pat. No. 4,117,652 discloses a power transmission apparatus having a clutch provided at a rear axle to which engine power is transmitted through a belt device for driving a rear wheel of a working machine.
In the prior art, an engine mounted on a body of a self-propelled lawn mower has an output shaft extending vertically downward and a cutter blade and a drive pulley are fitted to the output shaft. On the one hand, a rear axle of the lawn mower is provided with a clutch for disconnecting and connecting engine power with the rear wheel. An input shaft for transmitting engine power to the clutch extends vertically in a transmission case holding the rear axle supported rotatably. A driven pulley is attached to the input shaft. A belt is wound round the drive pulley and the driven pulley. The driven pulley has a fixed sheave and a movable sheave which is movable in an axial direction of the input shaft toward or away from the fixed sheave to change an effective diameter of the pulley for speed change. The engine power is transmitted to the driven pulley from the drive pulley through the belt to rotate the input shaft. When claws of the clutch are engaged so that the clutch connects, rotation of the input shaft is transmitted to the rear axle to rotate the rear wheel and lawn mower can be self-propelled.
In the above-mentioned power transmission apparatus, when the clutch connects, power of the drive pulley acts on the clutch abruptly through the input shaft and also reaction force due to rapid drive of the stopped wheel acts on the clutch so that the clutch is burdened with a large load. Therefore, it is required to raise rigidity of the clutch to cause enlargement and weigh increasing of the apparatus. As a result, working and operation of the lawn mower are deteriorated. Further, the above-mentioned reaction force influences the belt wound round both the pulleys too, so as to give the belt an excessive tension to shorten its life.
In a lawn mower having the power transmission apparatus mounted, because on connection of the clutch, engine power is transmitted to the rear wheel abruptly and the rear wheel having been stopped is driven rapidly at a high rotative speed, grasses are fallen down or torn and sometimes the ground is scraped by the rear wheel, so that finished state of the lawn is not necessarily good.
An object of the present invention is to overcome the above-mentioned difficulties and provide a power transmission apparatus of a working machine in which on connection of the clutch, an abrupt transmission of engine power is avoided and the engine power can be transmitted gradually.
SUMMARY OF THE INVENTION
The present invention provides a power transmission apparatus of a working machine comprising a clutch disconnecting and connecting power of an engine with a drive wheel, an input shaft transmitting the power to the clutch, a pulley having a movable sheave fitted to the input shaft rotatably and movably in an axial direction of the input shaft and a fixed sheave fixed to the input shaft, a belt wound round the pulley transmitting the power to the input shaft through the pulley, and movable sheave position control means for moving the movable sheave away from the fixed sheave when the clutch disconnects and move the movable sheave toward the fixed sheave when the clutch connects.
According to the invention, when the clutch disconnects, the movable sheave is moved away from the fixed sheave so that both the sheaves are most distant from each other. Therefore, the belt wound round the pulley is moved in a radial direction of the pulley to be contacted with the pulley at a position of smallest diameter and runs slipping in a state that the belt tension is smallest, while the pulley driven by the belt rotates on a non-load condition. In this state, abrasion of the belt due to contact with the pulley is little since the belt tension is smallest, and life of the belt can be prolonged since stress caused in the belt is small.
When the clutch connects from the above-mentioned disconnecting state, the movable sheave is moved toward the fixed sheave to gradually reduce the distance between the sheaves, therefore the contact position of the belt with the pulley moves radially outward (that is, the effective diameter of the pulley increases) while the running of the belt with slippage is maintained. Then, the belt tension is gradually increased and the slippage of the belt is gradually decreased. When approach of the movable sheave to the fixed sheave is completed and the effective diameter of the pulley becomes maximum, a predetermined pulley tension is generated to diminish the belt slippage so that engine power is transmitted to the drive wheel efficiently.
Thus, when the clutch begins to connect, the belt is running with slippage, therefore engine power is not transmitted to the drive wheel abruptly but transmitted gradually. Accordingly, a large load does not act on the clutch suddenly so that rigidity of the clutch can be made lower than that of a conventional clutch. Further, miniaturization and lightening of the apparatus are possible. Since no excessive tension is generated in the belt, life of the belt is prolonged.
In the above power transmission apparatus, the movable sheave position control means may comprise a spring having an end fixed to the movable sheave and another end fixed to the fixed sheave or the input shaft for moving the movable sheave away from the fixed sheave when the clutch disconnects, a first engagement section provided on the movable sheave, and a second engagement section provided on the fixed sheave or the input shaft which is engaged with the first engagement section by relative rotation between the movable sheave and the fixed sheave to move the movable sheave toward the fixed sheave against spring force of the spring when the clutch connects.
In this apparatus, when the clutch is in a disconnecting state, the movable sheave rotates together with the fixed sheave which is connected to the movable sheave by spring force of the spring, further the movable sheave has been moved away from the fixed sheave by spring force of the spring and both the sheaves are most distant from each other. When the clutch connects, load of the drive wheel acts on the input shaft through the clutch and the fixed sheave is subjected to a resistant force in a direction opposing rotation of it. On the one hand, to the movable sheave which is rotatively independent of the input shaft is not directly transmitted the load of the drive wheel. As a result, when a force based on a frictional force acting on the movable sheave and the resistant force acting on the fixed sheave becomes larger than the spring force, a relative rotation or a difference of rotational speeds occurs between the movable sheave and the fixed sheave against the spring force. Due to this relative rotation, the first and second engagement sections engage with each other to move the movable sheave toward the fixed sheave so as to decrease the distance between both the sheaves gradually. Thus, movement of the movable sheave toward the fixed sheave on connection of the clutch is performed automatically by engaging of both engagement sections utilizing the relative rotation between both sheaves.
The first engagement section may be a circumferential slant formed on the movable sheave, and the second engagement section may be a pin fixed to the input shaft. These engagement sections formed by the slant and the pin are simple in construction.
The spring may be a torsion coil spring. Torsional for
Hanabusa Jitsumi
Ohta Yoshitaka
Armstrong, Westerman Hattori, McLeland & Naughton
Honda Giken Kogyo Kabushiki Kaisha
Lorence Richard M.
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