192 clutches and power-stop control – Clutches – Operators
Reexamination Certificate
1999-10-08
2001-06-26
Bonck, Rodney H. (Department: 3681)
192 clutches and power-stop control
Clutches
Operators
C192S10700R
Reexamination Certificate
active
06250449
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The invention relates to a centrifugal multiplate clutch with a pot-type clutch drum and a rotor which shows several disk shaped plates, fixed on a motor shaft, for which respectively the hub and the centrifugal weight are connected over a rocker bar so that, when the no-load number of revolutions is considerably exceeded, the centrifugal weight is radially moved outwards and is frictionally put against the clutch drum.
The power transfer of a motor shaft of small hand-operated implements driven by an internal combustion engine mostly takes place over a centrifugal clutch to the driven shaft which is connected with the tool. The function of this centrifugal clutch is to separate the motor shaft from the driven shaft in the no-load r.p.m. range of the engine in order to guarantee an immobilization of the tool and to connect the motor shaft and the driven shaft in the load r.p.m. range of the engine with as little slippage as possible in order to allow a complete torque transfer to the tool. Especially in the transition area between these two modes of operation of the engine, undesired states appear for which, due to a slippage between the movable clutch parts and the clutch drum, it is not the full torque which is transferred to the driven shaft so that the full power of the engine is not available on the tool. Therefore, for centrifugal clutches the aim is to maintain this transition area as small as possible to be able to meet legal requirements which allow the rotation of the tool only in an upper no-load r.p.m. range as well as to avoid a slippage in the lower load r.p.m. range, to avoid mechanical as well as thermal damages of the clutch, especially of the clutch drum and the clutch bearings and to be able to transfer the desired torque to the tool.
2. Prior Art
According to the prior art, two types of centrifugal clutches are used at present. According to a first type, centrifugal segments which are maintained at no load at a distance from the clutch drum by means of retaining springs are used. By an increase of the number of revolutions, the centrifugal force of said segments exceeds the resilience of the springs so that the centrifugal segments are radially moved outwards and are frictionally put against the clutch drum. As an alternative, centrifugal multiplate clutches are used according to the prior art for which several separate disk shaped plates are put in a row on the motor shaft. For increasing the number of revolutions of the motor shaft, the centrifugal weights placed at the end of the plates are radially moved outwards until they frictionally engage with the clutch drum. Compared with the clutch working with centrifugal weight segments, the centrifugal multiplate clutch has, to begin with, the advantage of a more constant load of the clutch parts so that a deformation of the clutch drum is avoided because of several offset bearing spots of the individual plate parts. This can be achieved in particular by the offset mounting of the individual plate parts. Moreover, the clutch mounting is easier to manipulate, especially also for service cases. Finally centrifugal multiplate clutches are cheaper to manufacture because namely several congruent plates, which can be manufactured in a corresponding simplified way, can be used for the centrifugal multiplate clutch.
Multiplate clutches are used in particular for hand operated implements such as, for example, clutches for two-cycle lawn trimmers.
SUMMARY OF THE INVENTION
The aim of this invention is to improve the above mentioned centrifugal multiplate clutch. It must be reliably guaranteed on the one hand that a torque transfer from the motor shaft to the driven shaft takes place only after a number of revolutions is reached which is 25% over the no load number of revolutions. On the other hand, for reducing wear, the slipping free area must be configured as big as possible, i.e. a slipping through or a simultaneous slipping of the clutch parts between the operating states clutched in and disengaged must be avoided as far as possible.
This aim is achieved by the centrifugal multiplate clutch which is characterized according to the invention in that the plate contour is continuously tapered in its width starting from the hub to the transition of the rocker bar into the centrifugal weight. This construction guarantees that the plate is elastically deformable only in the area of the rocker bar so that the permanently elastic properties of the centrifugal clutch are kept over a long time. Through the enlarged rocker bar configuration close to the hub—compared with the embodiments known by the prior art—the result achieved is in particular that approximately the same bending stresses are reached over the whole rocker bar cross section.
So the width of the rocker bar is tapered at least in the area of its radial extension substantially square with increasing hub center distance. This almost parabolic configuration of the rocker bar which turns to an approximate arc of a circle into the centrifugal weight avoids local tension peaks. The rocker bar length is approximately double the biggest hub diameter, the taper proportion being approximately 50%.
The centrifugal weight outer shell shows at least substantially the same curvature as the clutch drum inner side in order that the outer surface of the radially excursed centrifugal weight adheres as fully as possible, i.e. on the whole surface to the inner diameter of the clutch drum. Moreover, when disengaged, the circle center defined by the centrifugal weight outer shell must be offset inwards with respect to the hub center. This taper which is defined by the gauge for recessing creates a safe distance between the centrifugal weights and the clutch drum inner shell.
Preferably a step with continuous transitions is formed in the transition area from the rocker bar to the centrifugal weight in the plate outer shell so that in the clutched state the rocker bar is at a distance from the clutch drum, i.e. only the centrifugal weight outer shell adheres to the clutch drum inner shell.
A further improvement is obtained when each plate possesses two centrifugal weights and the transition areas from the hub to the rocker bar form with their diagonals a sharp angle with the axis to which the centrifugal weights are placed symmetrical, the diagonal being inclined against the positive sense of rotation which is defined by the clockwise direction. An angle of 20 degrees +/−10 degrees is chosen as an optimal measure.
The centrifugal multiplate clutch is provided with several plates. For the arrangement of the different plates, the free ends of the centrifugal weights can be orientated against the direction of rotation which results in a certain self-reinforcing effect (servo-effect) of the centrifugal weights. For an arrangement of the plates for which the free ends of the centrifugal weights are orientated in the same direction as the direction of rotation of the clutch (towed arrangement), there results a pressing depending on the developing centrifugal force. Two plates are now preferably placed in the direction generating a self-reinforcing effect and one plate in the opposite direction (towed arrangement). Both plates placed in the “servo” direction cause a self-reinforcement which can result in the fact that the plates become bent out of their basic plane and are placed transversely. Through the third opposite plate, a support of the two other plates takes place so that the operating safety is increased.
In order to reduce the notch effect at particularly high stressed spots of the plates and in order to guarantee an all over bearing of the centrifugal weight as complete as possible on the clutch drum inner side, fine cut stampings are used as plates, the pull off surface being approximately ≦30% of the material thickness.
According to an improvement of the invention, the plates consist of a material, preferably a steel, with an apparent limit of elasticity R
p
≧750 N/mm
2
, preferably ≧850 N/mm
2
and/or a tensile s
Bonck Rodney H.
Dolmar GmbH
McCormick Paulding & Huber LLP
LandOfFree
Centrifugal multiplate clutch does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Centrifugal multiplate clutch, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Centrifugal multiplate clutch will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2465643