US2836670A - Governor with switch control - Google Patents

Description

M y 1958 E. LAAS 2,836,670

GOVERNOR WITH SWITCH CONTROL Filed April 26, 1957 2 Sheets-Sheet 1 INVENTOR. l5 EUGENE LAAS AGENT.

May 27, 1958 E. LAAS 2,836,670

GOVERNOR WITH SWITCH CONTROL Filed April 26, 1957 2 Sheets-Sheet 2 INVENTOR.

EUGENE LAAS Em; ism/ AGENT.

United States Patent f GOVERNOR WITH SWITCH CONTROL Eugene Laas, West Hartford, Conn., assignor to Kahn and Company, Inc., Hartford, Conn., a corporation of Connecticut Application April 26, 1957, Serial No. 655,276

' 6 Claims. (Cl. 200-450) This invention relates to governors with circuit controlling means adapted to open, or close, or transfer cir cuits at predetermined speeds of rotation of an engine or other rotating element. The invention is an improvement of copending application for U. S. Letters Patent entitled Thermally Compensated Governor With Switch Control, Serial No. 607,800, filed September 4, 1956, now U. S. Patent No. 2,810,032, issued October 15, 1957. This invention furthermore, has particular reference to a governor construction in which the speed differential necessary for switch actuation, i. e., the speed difference between the switch on and off condition is reduced to a minimum value.

The general construction of governor mechanisms which produce a straight line movement of the control member in response to increasing or decreasing speeds of rotation in combination with the operation of a switch or circuit control means is well known in the art. The use of modern high speed combustion engines, particularly aircraft engines, requires exceedingly accurate and precise control of speeds. The most important considerations are (1) thermal stability, i. e. little or no drift of switch actuation with change in temperature, and (2) as small a speed differential for causing a change in switch condition as possible.

The instant design'incorporates features which minimize both of the foregoing factors thereby obtaining a 2,836,670 Patented May 27, 1958 2 Figure 3 is a portion of Figures 1 and 2 respectively, showing a further modification of one of the elements;

Figure 4 shows another modification of one of the 3 elements, and

Figure 5 is a diagram illustrating the direction of certain frictional forces.

Referring now to Figure 1 and numeral 11 in particular, a governor housing is identified which supports nearly all of the components to be described hereinafter. It may be pointed out that in the following description only the more important elements are described in view of the fact that the general design and operation of this type of governor mechanism is well known and clearly described in the prior art. Rotatably mounted within the governor housing 11 by means of ball bearings 12 and 13, there will be found a spider 14 which is engaged by a driven shaft 15 secured to the spider by coupling pin 10. Spider 14 supports a set of fly weights 16, each mounted for pivotal motion about a pin 17. It will be found that fiy weights 16 are equipped with a large aperture 18 in order to reduce the inertia of the fly weights and the mechanism in general. A radial extension 19 on each fly weight 16 is adapted to engage a sleeve cap 20 attached to a ball bearing 21. The inner race of the ball bearing 21 engages a washer 22 supporting a spring seat 23. Spring seat 23 is press-fitted to a vertical plunger 24, the upper end thereof being adapted to engage the actuating mechanism 25 of an electrical circuit switch 26 which, by means of angle brackets 27 and screws 28, is fastened to a support 29. A connector 30 and wires 31 establish electrical circuit connection from the exterior of the governor to circuit switch 26.

Plunger 24 is surrounded by an externally threaded bushing 32 the thread of which is engaged by an internally threaded hub of spur gear 33. The teeth of gear 33 are engaged by a pinion gear 34 which is fastened to a stud 35 protruding through an upper casing 36 and cotter pin 37 rotatably secures the stud in the casing. A

speed responsive switch which is usable in many new applications and which is adapted to control speeds with a higher degree of accuracy and precision.

One of the objects of this invention is the provision of a governor with electrical circuit control means which avoids one or more of the disadvantages of prior art devices.

Another object of this invention is the provision of a governor in which the speed differential necessary to cause a change in condition is of minimum value.

Another object of this invention'is the provision of a switch in which the frictional losses are greatly reduced.

Another object of this invention is to provide a governor which is substantially unaffected by the temperature rise normally experienced in and around combustion engines.

A further object of this invention is the provision of a governor type switch in which switch actuation is achieved at a predetermined setting which will remain substantially unaffected by temperature and repetitive actuation. v

Additional objects, advantages and features of the present invention will be apparent from the following description taken in combination with the accompanying drawings, in which:

Figure 1 is a vertical section of the governor with circuit controlling means embodying features of temperature compensation; a I

Figure 2 is a partial view of Figure 1,'but incorporates features to reduce the frictional losses thereby increasing accuracy of the governor;

circular recess in the underside of gear 33 serves as upper support for helical compression spring 38, the lower end of which is supported on spring seat 23.

It will be noted that by turning stud 35 and consequently pinion 34, spur gear 33 is moved vertically with respect to spring seat 23 thereby achieving a selectable force ad justment for helical spring 38.

The operation of the instant device may be visualized as follows:

When shaft 15 is driven, spider 14 rotates in unison therewith and fly weights 16 swing radially outwardly about pins 17 in response to the rotation. As the fly weights swing outwardly, projections 19 of the fiy weights tend to lift sleeve cap'20 which in turn tends to raise washer 22, spring seat 23 and plunger 24 fastened thereto to cause actuation of element 25 of circuit switch 26 which is the condition depicted in the figure. Helical spring 38 by virtue of one, of its ends resting'uponspring seat 23 is used as a biasing means to counteract the force of the fly weights. As explained above this force is adjustable by means of stud 35 and the elements in engagement therewith. The actuating speed of switch 26 therefore is the result of the force exerted by the fly weights and the counter force exerted byspring 38. Plunger 24 is designed so that it moves freely in axial direction in order to obtain a precise control. The design described thus far is fairly conventional, but as will be explained hereinafter, provisions have been made to obtain stability of operation irrespective of the infiuencesof temperature and thermal expansion.

An ordinary spring, for instance steel, will introduce large speed errors due to changes in temperature. In order to achieve stability of operation a spring is employed which has a substantially constant modulus of elasticity. In this type of spring the increase of wire length clue to thermal expansion is combined with an adjusted decrease in modulus of elasticity to give a combined thermo-elastic coefficient of substantially zero. As an example, a nickel-chromium-iron-titanium alloy marketed under the trade name of Ni-Span-C manufactured by the H. A. Wilson Company of Union, New Jersey, having a nominal composition of 42% Ni, 2.5% Ti, 5.5% Chr, and 0.03% C, may be used advantageously to obtain a substantially constant modulus o f-elasticity. In this manner the force of the spring can be kept substantially constant over temperature ranges from 50 to +150 degrees F.

The next problem is the maintaining of the working space of the spring, that is the space between the lower end of the spring hereinafter referred to as I and the upper end of the spring, hereinafter referredto as H. The following calculations used for illustrative purposes are based upon a temperature rise of 230 degrees F., materials and governor dimensions as found on the actual embodiment of the present invention and depicted in the figure.

Considering the underside of bearing 13 as a base, hereinafter referred to as A, then spring seat J rises 1.56 inches 65 10 230 degrees F., that is; length A to J temperature coefficient for steelxtemperature rise, or 0.0023 inch.

At the actuating point of circuit switch 26, the elongation of the plunger 24 from point D (upper end) to f the lower end of spring (I) will have the opposite effect, tending to lower point I by 0.0022 inch, as'the dimension A to J is substantially equal to the dimension Jto 'D.

It will be apparent, that the elongation of the aluminum housing 11 has no effect upon the working spaceof the spring. The length from the top of the support 29 (point B) to the top of the spring (H) williexpand with temperature, tending to decrease the spring working space. For /2 inch length of steel this will be: /2 inch 65 l0 230 degrees F.=0.00075 inch.

The total effect on the spring working space, assuming spring compressive force positive, is then: 0.0023 minus 0.0022 inch plus plus 0.00075 equals 0.00085 inch. Using a spring rate of pounds per inch, the net change in spring force is 0.017 lb. Using a force level of 7 pounds at 4500 R. P. M., the net shift in spring force is plus 0.017/7 100 equal 0.24% or an increasein speed of 0.12% or 5.4 R. P. M. out of the 4500 R. P. M. nominal speed setting.

The above, as it will be apparent, produces almost a perfect score since errors of this magnitude are zero and negligible for all practical purposes. The compensation shown above illustrates that thealuminum housing expansion has no effect upon spring length and thatdis tances A to J, D to I, and B to H can be selected in such a manner as to be self-compensating thereby maintaining an almost constant working space for the spring.

It can readily be shown by calculation that the shift of the fly weights due to thermal expansion and the elongation of the switch actuating mechanism do not substantially affect the results developed above and produce an additional shift of about one R. P. M., but in a direction so as to lower the speed deviation from 5.4 R. P. M. to 4.5 R. P. M.

In comparison to the above favorable results it may be well to note that if theconstant modulus of elasticity spring is replaced by an ordinary steel spring, a shiftof 60 R. P. M. minus is obtainedfor the same condition, namely 230 degrees F. temperature rise and .4500 R. P. M. It will furthermore be readily apparent'that by proportioning distances A to J, D to J and B' to'H so that the self-compensating thermal expansions are lost, this shift ofspeed will greatly increase beyond the value of60-R. P; M;

Although the instant switch is stabilized as far as temperature is concerned, there still is a speed differential of 20 R. P. M. or more between the point of contact closing and opening or vice versa in switch 26. Extensive testing has shown that this speed differential is caused primarily by the frictional forces of the engaging surface of fly weight extension 19 on the underside of sleeve cap 20. As the speed of the spider 14 increases or decreases, the contact making surface of extension 19 is urged to move radially along the underside of sleeve cap 20. The pressure exerted by the fly weights is so great and the radial motion so small, that frictional forces effectively block this radial motion. At a first glance, it would appear that this problem could be solved by providing antifriction bearings, such as roller, ball, or needle hearings on the fly weights in such a manner, that the bearings roll radially along the underside of the cap. This, however, does not produce the desired result. It is far more advantageous to shift the bearing mounting by ninety degrees as shown in Figure 2;

The fly weights have been changed to have a radially extending stud 51 upon which are mounted antifriction bearings 52, the outer races of the bearings engaging the underside of the sleeve cap 20, and the bearings mounted being oriented in such a manner that their own rotational axis intersects the axis of rotation of the spider 14.

Assuming now, for example, a speed of 4,500 R. P. M. for the spider, plunger 24 and inner race of bearing 21 do not turn, being held stationary by friction of the spring 38. If outer race of bearing 21 turns at 4,500 R. P. M., then the antifriction bearings 52 will not turn on their own axis of rotation, because there is zero rela-' tive surface speed between bearings 21 and 52. In this case one would expect normal frictional sliding resistance in the X-direction (radial, Figure 5) between the outer race of bearing 52 and the underside of sleeve cap'20. The movement in the X-direction is probably in the order of 1/ 100,000 inch.

However, the bearing 21 turns at less than 4,500 R. P. M. due to its own internal friction and drag. As a consequence, bearings 52 must turn about their own axis at some speed which is a function of this slip and the dimensions of both sets of bearings. As soon as bearing 52 rolls on the sleeve cap 20, the friction in the X-direction is reduced to a negligible value thus eliminating rubbing or sliding motion. Actually, for small movements of the plunger 24 (Y-direction) between the on and off conditions of the switch, bearings 52 will tend to move on a spiral track while they are attempting to move in the X-direction.

It will be apparent that a predetermined line contact of bearing 52 with the sleeve cap is desired in orderto maintain accuracy and stability. To achieve this, bearings 52 in Figure 2 are inclined with respect to the under side of the sleeve cap, causing the edge of the bearings to establish contact. In Figure 3, as an alternate, bearin 53 has an outer race which is equipped with an annular raised rim, and in Figure 4, the bearing has a conventional inner race 56 but the outer race 55 is of convex shape.

Tests have proven conclusively that by virtue'of the foregoing arrangement the speed differential can be reduced to such an amount that the friction of the governor mechanism is negligible and the speed differential is. determined only by the force vs. motion condition of the electrical switch assembly itself.

While there have been described and illustrated certain embodiments of the present invention, it will be apparent to those skilled in the art, that various modifications and variations may be made therein without departing'from the spirit'and field of the invention which should be limited only by the scope of the appended claims.

What is claimed is:

l. The combination of a governor-housing; a driven shaft mounted therein; said shaft engaging a spider which is driven thereby; a plurality of fly weights pivotally fastened to said spider to swing radially outwardly in response to rotation of said shaft and spider; each of said fly weights equipped with an antifriction bearing mounted so that the axes of rotation of said bearings intersect the axis of rotation of said spider; a sleeve cap mounted for rotation about the rotational axis of said shaft and spider and being engaged by said antifriction bearings which are in rolling contact with said sleeve cap when said spider rotates; one end of an axially floating plunger extending through said cap and being urged in axial movement in response to the rotation of said fly weights; the other end of said plunger adapted to engage the actuating mechanism of an electrical circuit switch and causing operation thereof as a result of the plungers axial movement; a helical compression spring surrounding a portion of said plunger and supported to oppose the axial motion of said plunger toward said switch and thereby opposing also the outward motion of said fly weights.

2. The combination as set forth in claim 1 wherein said antifriction bearings in contact with said sleeve cap comprise ball bearings.

3. The combination as set forth in claim 1 wherein said antifriction bearings in contact with said sleeve cap comprise roller bearings.

4. The combination as set forth in claim 1 wherein said antifriction bearings in contact with said sleeve cap comprise needle bearings.

5. The combination as set forth in claim 1 wherein each of said antifriction hearings in contact with said sleeve cap comprises an inner race and an outer race and said outer race is substantially in line contact with said sleeve cap.

6. The combination of a governor housing; a driven shaft mounted therein; said shaft engaging a spider which is driven thereby; a plurality of fly weights pivotally fastened to said spider to swing radially outwardly in response to rotation of said shaft and spider; each of said fly weights equipped with an antifriction bearing mounted so that the axes of rotation of said bearings intersect the axis of rotation of said spider; a sleeve cap mounted for rotation about the rotational axis of said shaft and spider and being engaged by said antifriction bearings which are in rolling contact with said sleeve cap when said spider rotates; one end of an axially floating plunger extending through said cap and being urged in axial movement in response to the rotation of said fly weights; the other end of said plunger adapted to engage the actuating mechanism of an electrical circuit control means and causing operation thereof as a result of the plungers axial movement; a helical compression spring surrounding a portion of said plunger and supported to oppose the axial motion of said plunger toward said control means and thereby opposing also the outward motion of said fly weights; said spring having a substantially constant modulus of elasticity between minus 50 and plus 150 degrees F., and said plunger and spider being proportioned to maintain the working space of said spring substantially constant in response to thermal expansion.

References Cited in the file of this patent UNITED STATES PATENTS 2,793,023 Gaubatz May 21, 1957

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