192 clutches and power-stop control – Clutches – Operators
Reexamination Certificate
1999-10-14
2001-06-19
Lorence, Richard M. (Department: 3681)
192 clutches and power-stop control
Clutches
Operators
C192S10900B
Reexamination Certificate
active
06247570
ABSTRACT:
BACKGROUND
The present invention relates to centrifugal clutches such as are used in light vehicles, chain saws, pumps, wind mills, compressors, engine, electric motor, wind driven products and the like for variably coupling rotational power sources to driven loads.
Centrifugal clutches are disclosed, for example in U.S. Pat. Nos. 2,942,711 and 3,971,463 to the above-named inventor, which patents are incorporated herein by this reference. Typically, a plurality of radially movable shoes frictionally contact an inside surface of a drum that rotates concentrically with a hub to which the shoes are connected. Normally, the hub is fixed on a driving shaft or face plate that is coupled to an engine or power source, the drum being coupled to a driven load by means such as a belt, chain or direct coupled drive. Such clutches transmit little or no torque at low speeds, and progressively increased torque at higher speeds in proportion to centrifugal forces to which the shoes are subjected. In the above-identified patents, spring biasing elements are employed for maintaining the clutches in a disengaged condition at speeds below a predetermined threshold for permitting the engine or other power source to idle at no load.
Centrifugal clutches as previously implemented are subject to a number of problems and disadvantages. For example:
1. They are ineffective in that they fail to provide a desired torque-speed relationship to match the characteristics of the power source;
2. They are short-lived in that there is excessive slippage and consequent wear of the shoes, particularly when there is a large vibrational component or high inertia load in the torque;
3. They are unreliable in that springs used therein are subject to breakage, particularly in that they have fatigue inducing stress risers in hooks at opposite ends;
4. They are unsafe in that the shoes can fly apart in case there is structural failure of the drum; and
5. They are undesirably expensive to produce.
The clutch as disclosed in the '711 patent can be assembled in a variety of ways to selectively provide correspondingly different torque-speed relations such as straight-centrifugal with selectable speeds of engagement; relatively quick-acting; or relatively smooth-acting. However, none of the torque-speed relations is entirely satisfactory, and there are numerous possibilities for incorrect assembly. The clutch as described in the '463 patent provides driving member projections that are successively engageable with the shoes at increasing speed increments for progressively increased torque transmission. Again, none of the torque-speed relations is entirely satisfactory, particularly when it is desired to obtain initial engagement at a high percentage of the full-load speed of the clutch, and the clutch is excessively complex and expensive to produce.
It is also known to have direct metal-to-metal contact between the drum and metal shoe members of centrifugal clutches. However, the applications for such clutches are severely limited by a lower coefficient of friction, excessive wear, and galling.
U.S. Pat. No. 5,560,465 to the present inventor discloses a centrifugal clutch having an interlocking combination of shoes and compression biasing springs for preventing separation of the shoes in the event of axial disengagement or structural failure of the drum, and a spring biased wedge that smoothly transitions between low-gain and high gain orientations within a narrow speed range. Unfortunately, the clutch described in the '465 patent is not entirely satisfactory in that the drum can become damaged by direct contact with metallic shoes in the event that lining material on the shoes is worn through. Also, desired gain-speed profiles typically desired in particular applications are difficult to obtain, particularly without requiring undesirably large inventories of variantly configured components.
Thus there is a need for a centrifugal clutch that provides desired torque-speed profiles that smoothly transition from no-load to full load in an adjustable narrow speed range, that is fail-safe against lining wear-through as well as against separation of the shoes in case of failure of the drum, and that is reliable, long-lasting, and inexpensive to produce.
SUMMARY
The present invention meets this need by providing a centrifugal clutch having an interlocking combination of shoes and stop pins, and that in its preferred implementations includes compression biasing springs that are adjustable with tamper-free locking, reversible spring biased wedges that smoothly transition between selected low-gain and high gain engagements within a desired narrow speed range. In one aspect of the invention, the clutch includes a rotatable drum having a circularly cylindrical inside surface; a plurality of shoes, each shoe including a rigid metallic shoe member and a lining having an external engagement surface for frictionally contacting the inside surface of the drum; means for coupling each shoe to a rotatable hub for rotation therewith when the hub rotates concentrically with the drum; means for permitting movement of each shoe radially inwardly and outwardly relative to the drum; each shoe having a radially inwardly projecting first lock portion and a radially outwardly projecting second lock portion circumferentially spaced from the first lock portion; and a stop pin interposed between the first and second lock portions of each adjacent pair of the shoes for blocking the shoe members from moving radially outwardly into contact with the inside surface of the drum and for preventing separation of the shoes in the event of axial disengagement or structural failure of the drum during high-speed operation of the clutch.
The compression springs can have openings therein, being located by the stop pins projecting therethrough. Preferably the compression springs each include a plurality of stacked spring washers for enhanced fatigue resistance. Preferably the stop pins have respective adjustment members assembled therewith for adjustably loading the compression springs. The adjustment members can be adjustment nuts having threaded engagement with corresponding stop pins, an end portion of each stop pin having non-circular axial engagement with a respective shoe member for preventing rotation of the stop pin during adjustment of the adjustment nut.
The means for coupling and the means for permitting can include a plurality of dogs formed on the hub; a generally radially oriented slot formed on each shoe; a wedge member slidably engaging the slot of each shoe and having a wedge surface for engagement by a corresponding one of the dogs; and a wedge spring for biasing the wedge member against the corresponding dog. Preferably each wedge member is formed with an oppositely inclined pair of the wedge surfaces, the clutch being operable with torque transmission in opposite rotational directions, each of the dogs engaging one of the oppositely inclined wedge surfaces in one direction of transmitted torque and the other of the wedge surfaces during torque transmission in an opposite direction. Also, the oppositely inclined wedge surfaces can be asymmetrical, a torque-speed characteristic of the clutch being adjustable by selectively reversing the wedge members in the respective slots. The respective slots can be inclined at an angle of approximately 10 degrees from being radially oriented with corresponding ones of the dogs. Preferably the clutch can further include a plurality of keeper members, each keeper member being pivotally located relative to the hub for limiting outward movement of a respective wedge member.
Preferably the clutch further includes a guide on each shoe for circumferentially engaging an adjacent shoe, thereby radially stabilizing the shoes relative to the drum. Each guide can be formed by a pair of facing parallel-spaced guide surfaces extending from proximate one of the contact extremities of the respective shoe, a tongue portion of each shoe extending from the other of the contact extremities into engagement with the guide
Lorence Richard M.
Sheldon & Mak
LandOfFree
Fail-safe adjustable centrifugal 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 Fail-safe adjustable centrifugal clutch, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Fail-safe adjustable centrifugal clutch will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2484829