US 4,320,822 AGrant
Clutch-Brake System for Rotary Mower
Issue Date:1982-03-23
•14 Claims
•5 Drawing Sheets
Abstract
A combination blade clutching and braking mechanism for insuring the safer operation of rotary lawn mowers. The clutching and braking safety mechanism automatically disengages a power clutch while the brake is being engaged. Conversely, when the mower is to be operated, the mechanism automatically disengages the brake and engages the clutch. There is a provision for a dead man control wherein the brake engages automatically and the clutch is disengaged automatically should the operator accidentally lose control of the mower.
Metadata
Assignee
- J. A. Masterson & Company
Inventors
- Robert D. Meldahl
- Robert J. Borel
Application Information
Application Number:US 146101&
Filing Date:1980-05-02
Priority Date:1977-06-20
Art Unit:352
Classifications
IPC:
F16D 6702
Field of Search:
1925614;15;16;18 R;12 R;8 R;48.3;52;105 CD;105 CE;105 CF;6611.3
Patent Drawings (5 sheets)
Description
Background of the Invention
Rotary power lawn mowers have been manufactured for many years. Their usefulness is well-known and their usage is widespread. Also known, unfortunately, are the still existing hazards inherent with the use of rotary power mowers, namely the ever present danger of accidents and possible injuries to an operator.
The whirling blade of a rotary power mower becomes potentially dangerous when the operator for any reason leaves his normal position behind the mower or other persons, especially children, are near the mower.
Innumerable attempts have been made to develop a safe and reliable mechanism to minimize and preferably eliminate the causes responsible for the unnecessary and sometimes tragic accidents, mishaps and injuries.
One of the improvements contained in the present invention is directed to an articulated clutch shoe which makes it possible to generate greater force while using smaller flyweights because this shoe can exert greater leverage from the centrifugal force acting on the flyweight.
This invention provides an improved combination of a clutch and brake mechanism which automatically disengages the source of prime power supply, such as an engine, from the cutting blade and simultaneously applies positive braking that stops the whirling blade whenever the mower handle is released intentionally or inadvertently.
The importance and significance of this invention becomes more apparent and can better be appreciated when it is realized that the blade control handle is predisposed to be in the blade stopping position under various predictable circumstances; e.g. when the operator is busy starting the mower engine, is removing the grass catcher to empty it or attach it back to the mower, is clearing debris, such as sticks from the vicinity of the mower or is adjusting cutting heights, etc. Additionally, when a child approaches the mower, when the mower is pushed across a gravel driveway or when any other hazardous condition arises, the blade is stopped by simple release of the blade control handle. There are numerous recorded accidents which have occurred under these and other circumstances.
During the occasion of any of the aforementioned events, it is of paramount importance for obvious reasons of safety that two events take place simultaneously and instantly to insure against injury: (1) that the mower blade be disengaged at once from its source of power and (2) that it be stopped positively at once and be held immobile.
Such safe operation is achieved through the use of this improved combination of clutching and braking mechanism which disconnects the power supply from the mower blade while at the same time engages a positive braking mechanism whenever the blade control handle is not in its normal operation position. Conversely, this invention releases the brake and engages the clutching mechanism whenever the blade control handle is moved to its normal operating position.
It is an object of this invention to provide on a rotary power mower effective, foolproof and convenient means for disengaging the blade from its driving power source.
It is another object of this invention to provide safe, effective and reliable braking means for stopping the mower blade in a positive manner.
It is still another object of this invention to provide means for stopping the mower blade by automatically and simultaneously disengaging a clutching mechanism while engaging a braking mechanism.
It is still another object of this invention to stop the rotating blade of the mower by disengaging a friction type clutch mechanism while at the same time engaging a braking mechanism when a dead man control is released.
It is further another object of this invention to stop the rotating blade of a power mower by disengaging the friction type clutch mechanism and engaging a braking mechanism within a time span ranging from 1 to 3 seconds from the moment the dead man control mechanism is released.
It is still another object of this invention to disengage the power source of the mower from the blade and to stop the blade by means of greatly improved and highly reliable clutch and brake designs.
It is still another object of this invention to use a new design of an articulated clutch shoe to provide a better distribution of forces on the clutch drum assembly, thus resulting in reduced stress in the friction material of the drum with less wear.
It is still another object of this invention to automatically disengage the blade when cutting is too heavy for the engine and thereby prevent engine stall.
Another object of this invention is an improved clutching mechanism design to improve the stress distribution in the clutch through the use of a hub member in the clutch assembly.
Still another object of this invention is a new and improved clutch mechanism which includes a friction member which is both cylindrical and cone-shaped on the outside and hexagonally shaped on the inside.
Still another object of this invention is to provide a new concept in clutch shoe and friction drum design which substantially improves the life of the clutch, improves dissipation of heat and simplifies construction.
It is another object of this invention to provide the clutch mechanism with unlined counterweighted clutch shoes which pivot about shoulder bolts.
It is still another object of this invention to provide shouldered bolts in the blade retaining assembly to insure that the clamp load of the blade fastening nuts do not distort the clutch or brake components. These shoulder bolts also serve as pivots for the flyweight clutch shoes, transmit engine torque from the flyweights to the blade and help transmit braking torque from the brake disc to the blade.
Summary of the Invention
This invention is directed to improved conical and centrifugal clutch mechanisms and associated braking mechanism designed to take clamp loading from the clutch mechanism by means of an intermediate sleeve member.
Instead of having metal shoes lined with friction material engaging a metal drum, as is the case with conventional drum clutches, the drum is made of friction material and the metal shoes are not lined. The friction material in the drum contains just enough abrasive to insure that the shoes wear at approximately the same rate as the drum so there will always be maximum contact area between the drum and shoe. This minimizes the wear rate of both the drum and the shoe. The arrangement thus provides a much larger surface of friction material to wear than existed when only the shoes were lined and also greatly extends clutch life.
Improved heat dissipation is another important feature of this invention. Because of the heat insulating qualities of the clutch facing material and because of the good heat conducting qualities of the metallic shoes, the engine shaft is shielded from the heat generated by clutch engagement, and this heat is conducted away from the shaft by the metallic clutch shoes. Clutch friction heat is no longer added to the combustion heat which must be dissipated by the engine.
This design also makes it possible to eliminate the conical clutch facing which previously lined the conical inner flange of the brake disc. The upper end of the friction drum now extends upwardly to conform to and engage the conical internal flange of the steel brake disc. Near the bottom inside of the clutch drum is a cylindrical spacer which extends from the end of the engine shaft to a clutch support washer.
In this improved design the clamping stresses generated by the pilot screw which retains the clutch friction member are not transmitted through the clutch drum but through the spacer. This isolates the pilot screw from the reversing rotational forces transmitted by the clutch drum which would otherwise tend to loosen the pilot screw.
A further improvement consists of unlined counterweighted clutch shoes which are simpler and more econonical.
Another improvement is the use of shoulder bolts which serve to hold the clutch and brake disc together, serve as pivots for the clutch shoes and serve to transmit torque from the clutch shoes to the blade. The use of shoulder bolts confines the clamping stresses of the blade attaching nuts to the bottom of the clutch housing to thereby prevent distortion of the brake disc and clutch which otherwise would result from excessive tightening of the blade attaching nuts. A through bolt surrounded by a sleeve would function in a similar manner.
The clutch housing now serves the additional function of providing an enclosed support for the pilot bearing.
The brake compression plate and springs were redesigned to prevent cooking of the compression plate when the brake is released, to guard the brake disc from mowing debris and to simplify manufacture.
Brief Description of the Drawings
FIG. 1 is a side elevational view showing one embodiment of the combination clutch and brake assembly;
FIG. 1A is a more detailed view of part of the control mechanism for the clutch and brake assembly;
FIG. 1B is a vertical cross-sectional view of the clutch drum assembly;
FIG. 1C is a horizontal cross-sectional view of the clutch drum assembly;
FIG. 2 shows a cross section of the clutch and brake mechanism with the clutch released and the brake engaged;
FIG. 3 illustrates the clutch and brake mechanism in partial cross section showing the clutch engaged and the brake released;
FIG. 4 is a section taken on line 4--4 of FIG. 2;
FIG. 5 is a section taken on line 5--5 of FIG. 2;
FIG. 5A is a section taken on line 5A--5A of FIG. 5;
FIG. 6 is a section taken on line 6--6 of FIG. 4 showing the springs that engage the brakes;
FIG. 7 is a section taken on line 7--7 of FIG. 6;
FIG. 8 is the same as FIG. 5 but with the clutch shoes reversed;
FIG. 9 is a partial alternative view of FIG. 5 showing the articulated clutch shoe design; and
FIG. 10 is an alternate modification of the clutch drum assembly of FIG. 1B .
Description of the Preferred Embodiment
Referring to the drawings which accompany this specification, FIG. 1 illustrates a side elevation of a rotary type power mower, shown generally at 10. The power mower 10 has a power supply source, such as an engine 11, a mower blade 12, which is suspended from a combination multi-purpose member shown generally at 14, a mower shroud 16 and a mower control handle 18, which is pivotally connected to the mower shroud at a point 20.
A pivotable control lever 22 is attached to the upper portion of the control handle 18, as seen in FIGS. 1 and 1A. A slidable, flexible connection 24 is secured at one end to the control lever 22 and at the other end to a pivotable actuating lever assembly generally seen at 26 in FIG. 1. The pivotable control lever mechanism 22 includes a slotted link 28, a mounting bracket 30, an anchoring coupling 32 and an actuating plate 34, which swings the actuating lever assembly 26 through an arc, as from the non-engaged position 48b to an engaged position 48a.
The actuating lever assembly shown at 26 in FIG. 1 has a generally M-shaped configuration, best seen in FIG. 4. The actuating lever 26 has two lobes 36 and 38 located on either side of an interconnecting section 40. At its extremities, lever 26 has a pilot end 42 at one end and an actuating end 44 at the other. The actuating end 44 extends vertically to form an actuating arm portion 46 and an actuating pilot end 48 which is engaged in the actuating plate 34 in FIGS. 2 and 3.
Partially surrounding member 14 is a generally circular compression plate seen at 50 in FIG. 2. The compression plate 50 has an inwardly disposed circular flange section 52 which is continuously connected to a vertical wall section 54. Extended portions of the wall 54 make up a plurality of brake releasing ears, such as 56 and 58 and spring lugs 72. Friction-type braking material 53 is attached to the topside of the flange section 52.
A circular spring housing generally seen at 60 is disposed above the brake housing 50. The spring housing 60 is comprised of a wall section 62 and a generally horizontal bottom section 64. In the center of the bottom section 64 is an opening 66, defined by a circular flange 67. A drive shaft 68, which is rotated by the engine 11, protrudes through the opening 66. Between the wall section 62 and the opening 66 is a concentric brake section 70.
Projecting through the bottom section 64 of the spring housing 60 is a plurality of spring lugs projecting from the compression plate 50, one of which is illustrated at 72. Each spring lug 72 retains a spring, one of which is shown at 74. While four lugs and springs are shown in the preferred embodiment, the number of lugs and springs is by no means limited to the numbers illustrated.
Friction material is attached to the underside of the brake section 70. Between the spring housing wall section 62 and the concentric brake section 70 are disposed two kidney-shaped slots 69 and 71, FIG. 4, located at 180 degrees from one another and through which protrude the brake releasing ears 56 and 58.
Member 14 is comprised of three interconnected sections: a vertical clutch housing 78 which is continuously connected to a blade mounting hub 80, which in turn is continuously connected to a pilot bearing cup 82. The blade mounting hub 80 has a plurality of holes, such as 84 and 86, which are best shown in the preferred embodiment illustrated in FIG. 2.
A combination clutch cone cup and brake flange 88 is comprised of a conical clutch flange portion 90 and a horizontally disposed brake disc portion 92, which contains a plurality of holes, such as shown at 94 and 96. The conical flange portion 90 has an internal face 91, which is disposed at a slight inward angle about 15.degree. to the vertical and which defines an opening 89.
Protruding downwardly from the brake disc are four driving lugs 63 which engage mating slots 65 in the flange of the clutch housing 78. Extending upwardly astride each of the shoulder bolt heads are lugs which prevent the shoulder bolts from turning.
The holes 84 and 86 in the blade mounting hub 80 are disposed to be in centerline alignment with the holes 94 and 96 in the brake disc 92. A plurality of shoulder bolts, such as shown at 75 have a head section 77 connected to a body section 79, a portion of which terminates in a threaded section 81 which is of smaller diameter than the body portion 79. One end of this smaller diameter is threaded. Near the other end is a retaining ring groove 79a for a retaining ring 79b. At the juncture of the body section 79 and the threaded section 81 is formed a shoulder 83.
The bolt 75, which fits through the aligned holes 94 and 84 is designed so the bolt head 77 will rest on the top surface of the brake disc 92, while at the same time the shoulder 83 rests on the top surface of the blade mounting hub 80. After the mower blade 12 is positioned in place, it is secured to the underside member 14 by means of lock washers 85 and nuts 87, making members 12, 14 and 88 one "solid" assembly. Projections pierced from the brake disc engage the hexagonal head of the shoulder bolts preventing them from turning.
A clutch drum assembly is shown at 98, FIGS. 1B and 1C. It is also seen fully in FIG. 2 and partially in FIGS. 3 and 6. The clutch drum assembly 98 comprises a drum and cone portion 100, FIG. 1B, assembled to a hexagonal hub 102, a support washer 104, and a sleeve 106, which abuts against the top side of the washer 104. A portion 103 of the cone 100 is disposed at a slight angle which matches the angle of the internal face 91 of the conical flange portion 90. A longitudinal slot 108 in the hub 102 serves as a keyway for locking the clutch assembly 98 to the drive shaft 68 by means of a key member 101.
A pilot screw bushing 110 in FIG. 2, which is pressed into the pilot bearing cup 82, receives the head 112 of a pilot screw 114. The pilot screw 114, which retains the washer 104 and sleeve 106, screws into a mating tapped hole 107 which is in the end of the drive shaft 68.
This design permits the sleeve 106 to absorb the axial clamping load that develops when the pilot screw 114 is tightened. Since it does not exert a clamping force against the clutch friction member or the hub, the pilot screw is relieved of any torsional loads that may be transmitted between the drum 98 or hub 102 and the drive shaft 68.
The torsional acceleration and deceleration forces transmitted by the hub are high in magnitude and frequency. If the pilot screw clamped through the hub as in concentional construction, the pilot screw would too frequently work loose and render the clutch inoperable.
The counterweighted clutch shoes are not lined with clutch facing material. They are disposed at 180 degrees from one another.
The clutch shoes pivot about shoulder bolts 75 which also serve to hold the clutch assembly together, hold the blade onto the clutch and transmit torque from the clutch shoes to the blade.
When the blade 12 is stopped by an obstruction, the flyweights no longer experience any centrifugal force that would urge them into engagement with the drum. As a result, the centrifugal portion of the clutch assembly is released and the engine therefore no longer rotates the blade.
When the cutting blade impacts a solid object, the drive shaft 68 is deflected. Contact with flange 67 of the spring housing prevents permanent set in the drive shaft.
In use, the operator first starts the engine 11, which at once begins to spin the drive shaft 68 and the clutch cone assembly 98 which is keyed to the drive shaft by means of the key 101. When the operator moves the control lever 22 from a non-engaged position, as shown at 22a in FIG. 1A, to an engaged position 22b, the slidable flexible connector 24 moves in a generally upward direction, retracting plate 34 in a generally rearward direction, and thus pivoting the actuating arm 46 from a non-engaged position as shown at 48b to an engaged position as shown at 48a.
Two events take place simultaneously inside of the combination brake compression plate member 50. As the operator moves the control lever 22 from its non-engaged to its engaged position, the actuating arm 46 swings rearwardly, causing the two lobes 36 and 38 to exert a downward force on the two brake releasing ears 56 and 58, pushing them downwardly, FIG. 3. This action has the effect of eliminating the frictional forces that the braking materials 53 and 76 are exerting on the bottom and top sides respectively of the brake disc 92.
As the brake disc 92 is being released, the clutch cone cup 88 moves downwardly and the internal face 91 of the conical clutch flange 90 engages the rotating clutch assembly 98. Friction between these conical members creates a light driving force to rotate the blade. As the rotation occurs, centrifugal force acting on the clutch shoes 95 causes them to pivot on the shoulder bolts 75. The toes 93 of the shoes grip the clutch drum. This creates a substantial driving force pivoted on as at 97 or shoulder bolt 75.
Conversely, when the operator releases the control lever, the reverse events occur. The action of the compression springs 74 moves the clutch cone and brake disc 88 upwardly, disengaging the conical clutch cone 90 from the clutch assembly 98 and at the same time engaging the braking materials 53 and 76 against the braking disc 92. The rotary blade is stopped and held positively locked out. Centrifugal force ceases to activate the clutch shoes. Lobes 36 and 38 rotate actuating arm 46 from its engaged position 48a to its disengaged position 48b. This in turn moves the cable 24 downwardly and moves the control lever 22 from its engaged position 22b to its disengaged position 22a.
The operator must hold the control lever 22 in its engaged position 22b against the mower control handle 18 for the mower blade to rotate. Should the operator let go of the control handle 22, either accidentally or intentionally, this constitutes a dead man control which immediately disconnects the engine drive shaft from the blade, stopping the blade. Thus, should the operator carelessly put his hand in the vicinity of the mower blade, an accident would be avoided because the blade will no longer be rotating.
When extremely heavy cutting pulls down the engine near its stall speed, the centrifugal force acting on the flyweights does not develop sufficient force to drive the blade and the grass will stop the blade, eliminating the centrifugal force entirely. With only the cone clutch engaged, the engine will resume speed instead of stalling. The clutch will automatically re-engage when the mower is pulled out of the uncut grass.
FIG. 8 shows the clutch shoes in mirror image position which provides a different set of forces and a different cutout speed.
The improved clutch drum assembly is shown at 140 in FIGS. 9 and 10.
The clutch drum assembly shown at 140 comprises a drum and cone portion 142 assembled to a hexagonal hub 144 and a support washer 146. A necked down portion 148 of the hexagonal hub 144 abuts against the top side of the support washer 146.
A portion 150 of the drum and cone 142 is disposed at a slight angle which matches the angle of the internal face of a cooperating conical flange 91. A longitudinal slot 152 in the hexagonal hub 144 serves as a keyway for locking the clutch assembly 140 to the mower drive shaft 154 and 68 by means of a key member 156 and 101.
As the brake disc 92 is being released, the clutch cone cup 88 moves downwardly and the internal face 91 of the conical clutch flange 90 engages the rotating clutch assembly 140. Friction between these two mating conical members generates a light driving torque that rotates the mower blade.
As the blade begins to rotate, centrifugal force acting on the articulate clutch shoe swings the flyweight body 158 outwardly, pivoting it about an integral cylindrical projection serving as pivot pin 160. The integral pivot pin obviates the need for pivot pins and pin retention means, at the same time forcing the toe 162 of the flyweight 158 inwardly.
The toe 162 engages a cylindrical socket 164 in the clutch shoe member 166, which thus partially wraps around the toe or cylindrical projection of the flyweight. The curved surface 168 of the articulated pivoted clutch shoe 166 automatically aligns itself with the friction drum 142 and the contact force between the curved surface 168 and the friction material surface 98 is spread uniformly over the contact area of these two members thus avoiding any concentration of high stresses on any part of the shoe 166 and permitting a higher total force to be transmitted while developing lower stresses at any given point.
Thus, the use of this articulated clutch shoe makes it possible to generate greater forces while using a smaller flyweight because the articulated shoe can exert greater leverage from the centrifugal force acting on the flyweight.
Because the stresses in the friction material are reduced, the friction drum experiences less wear. With an integral design, substantial clearance between the flyweight and the clutch housing must be provided to allow the flyweight to swing out as the shoe swings inwardly to compensate for wear of the friction drum. Some of the clearance space is now used to increase the size of the flyweight, enough to enable the clutch to transmit the torque of a more powerful engine even if the engine is operating at slower speeds.
The new articulated design has made it possible to reduce the engagement speed and the release speed of the clutch from 2200 rmp to 1500 rpm and by using a heavier flyweight, to use the clutch with a 4-horsepower engine as well as the more popular 31/2-horsepower engine.
The invention has been described in great detail sufficient to enable one of ordinary skill in the art to make and use the same. Obviously, modifications and alterations of the preferred embodiment will occur to others upon a reading and understanding of the specification, and it is our intention to include all such modifications and alterations as part of our invention insofar as they come within the scope of the appended claims.
Claims
What is claimed is:
1. A brake clutch mechanism for a rotary power mower having a cutting blade member comprising: a clutch assembly including a brake disc; a pivotal control lever for operating such clutch assembly and brake disc; said clutch assembly having a cylindrical drum and tapered cone of frictional material forming a cone clutch and operating in association with a mating tapered metal clutch cone cup fixed to said brake disc; said brake disc including means which simultaneously transfer power from the clutch assembly to the cutting blade member. wherein actuation of the pivotable control lever causes the clutch assembly and brake disc to gradually engage, and further wherein the tapered cone produces a gradual acceleration in the cutting blade member; a plurality of flyweight pivotally mounted on said brake disc outwardly of said clutch drum which are pivotally connected to clutch shoes permitting the contact forces between the clutch shoes and drum to be distributed uniformly, thereby transmitting power to the cutting blade member.
2. A brake clutch mechanism for a rotary power mower having a cutting blade member comprising: a clutch assembly including a brake disc; a pivotable control lever for operating said clutch assembly and brake disc; said clutch assembly having a cylindrical drum and tapered cone of frictional material forming a cone clutch and operating in association with a mating tapered metal clutch cone cup fixed to said brake disc; said brake disc including means which simultaneously transfer power from the clutch assembly to the cutting blade member, wherein actuation of the pivotable control lever causes the clutch assembly and brake disc to gradually engage, and further wherein the tapered cone produces a gradual acceleration in the cutting blade member; a plurality of articulated counterweighted flyweight clutch shoes pivotally mounted on said brake disc outwardly of said clutch drum, thereby transmitting power to the brake disc and to the cutting blade member.
3. The mechanism of claim 1 in which the flyweights include integral cylindrical projections which serve as pivots for the clutch shoes thereby eliminating the need for pivot pins and pin retention means.
4. The mechanism of claim 1 in which the clutch shoes include projections which partially wrap around the cylindrical projections of the flyweights providing a pivotal connection with the flyweight.
5. The mechanism of claim 1 in which the flyweights and the clutch shoes are of uniform cross section making them suitable for manufacture with powered metal technology.
6. The mechanism of claim 1 in which the cylindrical drum periphery is entirely of frictional material which is generally a poor heat conductor.
7. The mechanism of claim 1 in which the cylindrical drum has a strong hub member and a weaker clutch facing material, which distributes the forces, thereby minimizing stresses in the clutch facing material.
8. The mechanism of claim 1 in which there is a brake pressure plate enclosing the brake disc and connecting means between said control lever and said plate to actuate said plate, said plate having an upturned flange outwardly thereof to strengthen the plate and to protect the brake disc from thrown debris.
9. The mechanism of claim 8 in which there are more than two symmetrically spaced projections which are part of and extend upwardly from the upturned flange of the brake pressure plate and are engaged by springs which raise the pressure plate into a braking relationship with the brake disc when the pivotal control lever is not actuated, the symmetrical spacing of the spring projections providing equal release of the brake pressure plate when the pivotal control lever is actuated.
10. The device of claim 1 in which the taper in the cone clutch is 15 degrees so that wear is minimal and there is still adequate frictional force on the cone.
11. The mechanism of claim 1 in which a spring housing surrounds and is in close proximity to a drive shaft, whereby it provides momentary support for the drive shaft when, as a result of the blade impacting some solid object, the drive shaft is deflected until contact with the spring housing occurs, thereby assisting in avoiding permanent set in the drive shaft.
12. The mechanism of claim 1 wherein the friction material is sufficiently abrasive to insure the clutch shoes will wear as fast or slightly faster than the cylindrical drum, thereby maintaining maximum area of contact between the two and minimizing the wear of both.
13. The mechanism of claim 1 wherein the combination brake disc and clutch housing have locking lugs to prevent turning the housing under stress conditions, such as when the cutting blade member hits an object.
14. The mechanism of claim 1 wherein the clutch assembly and cylindrical drum are retained by a socket head cap screw which serves as a pilot which centers the cutting blade member and forming a pilot guide on the end of the drive shaft which fits slidably inside of a pilot bearing cup.
Patent Citations (11)
| Patent | Date | Inventor | Cited By |
|---|---|---|---|
| US682591 | 1901-09-01 | Harrison | |
| US699461 | 1902-05-01 | Dysterud | |
| US725617 | 1903-04-01 | Eisenhart | |
| US2260770 | 1941-10-01 | Brownlee | |
| US2333680 | 1943-11-01 | Schneider et al. | |
| US3253391 | 1966-05-01 | Meldahl | |
| US3420343 | 1969-01-01 | Stiepel | |
| US4213521 | 1980-07-01 | Modersohn | |
| FRX501984 | 1920-02-01 | ||
| FRX2406126 | 1979-06-01 | ||
| GBX933615 | 1963-08-01 |