US2815082A

US2815082A - Variable pitch propeller having an acceleration sensitive device

Info

Publication number: US2815082A
Application number: US452790A
Authority: US
Inventors: James R Kessler
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1954-08-30
Filing date: 1954-08-30
Publication date: 1957-12-03
Anticipated expiration: 1974-12-03

Description

KESSLER VARIABLE PITCH PROPELLER HAVING AN Dec. 3, 1957 ACCELERATION SENSITIVE DEVICE Filed Aug. 30, 1954 United States Patent VARIABLE PITCH PROPELLER HAVING AN ACCELERATION SENSITIVE DEVICE James R. Kessler, Troy, Ohio, assignor to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application August 30, 1954, Serial No. 452,790

8 Claims. (Cl. 170-16014) This invention pertains to means for maintaining constant speed prime mover operation by varying the load, and particularly to a speed control system for variable pitch propellers.

Heretofore, speed controlling systems have embodied governing means which were both speed and acceleration sensitive. However, many systems now in use merely include speed sensitivity, which by itself does not provide adequate control. This invention pertains to a self-contained acceleration sensitive device which may be incorporated in existing servo systems for controlling speed and thereby improve their operation. Accordingly, among my objects are the provision of a self-contained acceleration sensitive device; and the further provision of an acceleration sensitive device which can be incorporated in existing servo systems having only speed sensitivity.

The aforementioned and other objects are accomplished in the present invention by providing a closed acceleration sensitive loop in one load controlling direction. Specifically, the acceleration sensitive device of this invention is adapted for use with systems of the type wherein external forces tend to adjust the load on the prime mover in one direction. In particular, the acceleration sensitive device may be incorporated in a variable pitch propeller servo system wherein the centrifugal and aerodynamic twisting moments on the blades tend to move the blades toward a predetermined pitch position. As disclosed herein, the external forces tend to rotate the blades about their longitudinal axes to a low angle position. In control systems for propellers of this type blade angle is maintained by maintaining fluid under pressure in the increased pitch chamber of a pitch changing servo-motor, by applying pressure fluid to the increase pitch chamber and permitting predetermined amounts of fluid to leak therefrom while the decrease pitch chamber is closed. Blade angle is increased during constant speed operation by applying pressure fluid to the increase pitch chamber in quantities greater than are permitted to leak therefrom while the decrease pitch chamber is connected to drain. Conversely, blade angle is decreased during constant speed operation by discontinuing the application of pressure fluid to the increase pitch chamber while permitting the predetermined leakage therefrom and supplying fluid under substantially no pressure to the decrease pitch chamber, since the external forces are effective to reduce blade angle.

The acceleration sensitive device of this invention includes a cylinder having disposed therein a reciprocable piston capable of fluid pressure actuation in either direction. The piston divides the cylinder into two chambers, the upper of which is connected to the increase pitch chamber of the pitch changing servo-motor, thereby constituting part of the acceleration sensitive loop. The piston carries a speed sensitive plunger capable of linear movement relative thereto, the plunger being urged in one direction by an adjustable spring. The lower cylin- A ICC der chamber is connected to a source of fluid pressure through a restricted orifice, and the plunger constitutes a valve for controlling flow through the lower cylinder chamber to drain. When the speed sensitive plunger is in the onspeed, or equilibrium position, the lower chamber receives pressure fluid through the restricted orifice meters an equal volume of fluid to drain, thereby maintaining equal total pressures on opposite sides of the piston, which will remain in an equilibrium position.

When an overspeed condition exists, the speed sensitive plunger will move to restrict or entirely interrupt the bleeding of fluid from the lower chamber to drain, thereby causing the piston to move upwardly and inject a volume of fluid into the increase pitch chamber in response to acceleration. At the same time, the governor valve of the pitch changing servo system is supplying flow to the increase pitch chamber. When acceleration ceases and deceleration begins, the speed sensitive plunger will move to bleed the lower chamber to drain, thus, causing the piston to move downwardly and withdraw a volume of fluid from the increase pitch chamber, while the governor valve is still supplying flow to the increase pitch chamber. Upon return to onspeed, the-piston will assume its equilibrium position.

When an underspeed condition exists, the speed sensitive plunger will move to increase the bleed of fluid from the lower chamber, thereby eiiecting downward movement of the piston. Thus, a volume of fluid is withdrawn from the increase pitch chamber while the governor valve is neither supplying pressure or flow to the increase pitch chamber, and leakage therefrom continues. When deceleration ceases and acceleration begins, the speed sensitive plunger responds and thereby restricts the bleeding of fluid to drain from the lower chamber to cause upward movement of the piston Whereby a volume of fluid is injected into the increase pitch chamber. Upon return to the onspeed condition, the piston again assumes an equilibrium position. Thus, the acceleration sensitive device operates to stabilize speed control, by minimizing hunting or overshooting during speed transients.

Further objects and advantages of the presentinvention will be apparent from the following description, reference being had to the accompanying drawing wherein a preferred embodiment of the present invention is clearly shown.

In the drawing:

Fig. 1 is a fragmentary view, in elevation, of a variable pitch propeller incorporating the acceleration sensitive device of this invention.

Fig. 2 is a schematic diagram of a servo system incorporating the acceleration sensitive device of this invention.

With particular reference to Fig. 1, a variable pitch propeller 10 is shown including a hub 11 having a plurality of radially extending sockets 12 within which propeller blades 13 are supported for rotation about their longitudinal axes to different pitch positions. The hub 11 has attached thereto and rotatable therewith a regulator assembly 14, within which a servo system for actuating the pitch changing means, is contained. The propeller 10 is adapted to be rotated by an engine driven shaft 15, and the propeller assembly and pitch changing motors may be of the type disclosed in the Blanchard et a1. Patents 2,307,101 and 2,307,102.

With reference to Fig. 2, a servo system, as modified by the acceleration sensitive device of this invention, is shown in schematic form. It is to be understood that components of the servo system, in a propeller assembly,

are disposed within the regulator 14, and subjected to 3 centrifugal force upon propeller rotation, the direction of centrifugal force being indicated by arrow 16 in Fig. 2.

The servo system includes a source of fluid pressure 20, which may take the form of a pump driven by propeller rotation, the pump 20 drawing fluid from a conduit 21 and discharging fluid under high pressure into a conduit 22. The high pressure conduit 22 connects with a pressure control valve assembly 23, which may be of the type disclosed in copending application, Serial No. 276,372, filed March 13, 1952, in the name of Richard E. Moore et al., now Patent No. 2,737,253. The pressure control valve assembly 23 regulates the pressure of fluid in conduit 24, and maintain the pressure potential of fluid therein at a value suflicient to meet the requirements of the pitch changing means, to be described.

The pitch changing means, as shown schematically, comprise a fluid motor 30 having a cylinder 31 within which a reciprocable piston 32 is disposed. The piston 32 divides the cylinder 31 into an increase pitch chamber 33 and a decrease pitch chamber 34. In addition, the piston 32 is shown schematically as including a rod 35 having formed thereon a rack 36, which engages a pinion 37 connected to rotate with the propeller blade 13. Structurally, the pitch changing motor 30 may be of the type shown in the aforementioned Blanchard et al. Patent 2,307,101, but suflice it here to say that downward movement of the piston 32, as shown in Fig. 2, will increase the pitch position of blade 13, while upward movement of piston 32 will decrease the pitch position of the blade.

The servo system is also shown including governing means 40, which may comprise a valve guide 41 having disposed therein a valve piston 42, which is located radially within the regulator 14 and, consequently, responds to the thrust of centrifugal force in the direction of arrow 16. The piston 42 includes valving lands 43 and 44, which cooperate with

ports

45 and 46 of the valve guide 41. In addition, the piston 42 is 'pivotally interconnected at 47 to a lever 48 having a fulcrum point 49, the position of which may be made adjustable, if so desired. However, for the purposes of the present invention, the fulcrum point 49 can be considered fixed, as shown. The free end of lever 48 has attached thereto a tension spring 50, which tends to move the lever 48 in a counterclockwise direction about point 49, as shown in Fig. 2. Inasmuch as centrifugal force acting on the piston 42'tends to rotate the lever 48in a clockwise direction about point 49, it will be appreciated that at a predetermined speed of propeller rotation, as evidenced by the predetermined thrust of centrifugal force in the direction of arrow 16, the opposing forces on lever 48 will be in equilibrium, thereby maintaining the piston 42 in the position-shown in Fig. 2. The position of piston 42, as shown in Fig. 2, constitutes the onspeed position thereof, from which it may be seen that fluid under pressure from conduit 24 may flow through valve guide port 51, through port 45, to conduit 53 and the increase pitch chamber 33. At the same time, conduit 54, which interconnects control port 46 and the decrease pitch chamber 34 is blocked.

Conduits

53 and 54 are shown having

branch connections

55 and 56, which connect with opposite sides of a shuttle valve 57, constituting a part of the pressure control valve assembly 23. The shuttle valve 57 merely connects the pressure control valve assembly 23 with the higher of the pressure potentials existent in either

conduits

53 or 54. The increase pitch conduit 53 is also connected with a constant leak valve assembly 59 of the type disclosed in copending application, Serial No. 273,-

806, filed February 28, 1952, in the name of Richard E.

Moore et al., now Patent No. 2,745, 500.

The constant leak valve assembly 59 permits a predetermined amount of leakage from the increase pitch chamber 33, the volume of leakage being equal to the volume of flow through the port 45 when the governor valve piston 42 is in the equilibrium position depicted in Fig. 2. This arrangement is provided inasmuch as the blades 13 are subjected to centrifugal and aerodynamic centrifugal twisting moments during rotation, which twisting moments tend to move the blades 13 to a low pitch position. Thus, in order to maintain blade angle during propeller rotation, a predetermined pressure potential must be maintained in the increase pitch chamber 33 so as to balance out the forces tending to move the blades to a low pitch position. This pressure potential is maintained by having port 45 slightly open to supply port 51 during onspeed conditions so as to maintain the holding pressure in chamber 33, while the flow supplied by the governor valve 40 is bled to drain through the constant leak valve assembly 59. Moreover, it should be noted that while the blade angle is being maintained fixed, as shown in Fig. 2, the decrease pitch chamber is blocked.

The operation of the servo system thus far described is as follows. During onspeed conditions, as previously alluded to, a predetermined pressure potential is maintained in increase pitch chamber 33, while the decrease pitch chamber 34 is blocked, and the flow supplied by the governor valve through port 45 is bled to drain by the constant leak valve assembly 59. When the propeller overspeeds, the thrust of centrifugal force in the direction of arrow 16 will overcome the force of tension spring 50 and thereby result in movement of piston 42 upwardly so that port 45 is opened wider to pressure port 51, while port 46 is connected to drain through valve port 58. At this time the flow supplied to the increase pitch charmber 33 is greater than that which can be bled to drain by the constant leak valve 59, and inasmuch as the decrease pitch chamber 34 is connected to drain, the piston 32 will move downwardly, as viewed in Fig. 2, thereby increasing the pitch position of the blade 13. Conversely, when an underspeed condition exists, the force of spring 50 will overcome the thrust of centrifugal force in the direction of arrow 16 to move the piston 42 downwardly, thereby discontinuing the application of pressure fluid to conduit 53 without connecting the conduit 53 to drain, while conduit 54 is supplied with fluid under virtually no pressure due to the restriction of port 46 by land 44. Pressure fluid is not required to effect the reduction in blade angle, since the external forces acting on the blade 13 are suflicient to move the piston 32 upwardly, as viewed in Fig. 2, and flow is only supplied to decrease pitch chamber 34 to prevent the existence of voids therein. Moreover, upward movement of piston 32 is permitted by reason of the fact that the constant leak valve assembly 59 permits a predetermined amount of leakage from the increase pitch chamber 33.

The acceleration sensitive device of this invention is designed to be connected between conduits 24 and conduits 53 and is generally indicated by the numeral 60. Inasmuch as the increase pitch chamber 33 is never connected to drain by the governor valve 40, and leakage therefrom is controlled by the constant leak valve 59, the servo system may be said to have a substantially closed loop, within which the acceleration sensitive device 60 and the increase pitch chamber 33 are connected. The acceleration sensitive device comprises a servo cylinder 61 having disposed therein a free piston 62 capable of reciprocable movement by fluid pressure. The piston 62 divides the cylinder 61 into an upper chamber 63 and a lower chamber 64. Moreover, as shown in Fig. 2, the piston 62 is formed with an annular groove 65 between its head surfaces. The lower chamber 64 of the cylinder is connected through a restricted orifice 66 to a conduit 25 having connection with the conduit 24. The upper chamber '63 of the cylinder has a port 67, which is connected by a conduit 26 to the conduit .53. In addition, an intermediate portion of the cylinder 61 has formed therein a drain port 68, which within the limits of movement of piston 62 always communicates with theannular groove 65.

The piston 62 is centrally recessed at 69 and carries a speed sensitive plunger 70. The plunger 70 includes 6 a pair of spaced lands 71 and 72 and is formed with a through passage 73 for maintaining equal pressures on opposite end surfaces of lands 71 and 72. In this manner, movement of plunger 70 is only afiected by speed changes. The plunger 70 is urged in a downward direction, as viewed in Fig. 2, by a compression spring 74, the force of which may be adjusted by movement of seat 75 having connection with a threaded device 76. In this manner, the speed to which plunger 70 will respond can be varied.

The piston 62 is formed with a passage 77, which interconnects the lower chamber 64 and recess 69 between the spaced lands 71 and 72 of the plunger. The piston 62 is further formed with a passage 78, which interconnects the recess 69 and the annular groove 65. It is to be understood that the recess 69, in effect, constitutes a valve guide for the plunger 70, with land 72 controlling the flow of fluid from the lower chamber 64 through the drain passage 68. The acceleration sensitive device 60 controls the volume of fluid within the acceleration sensitive loop. Thus, a substantially closed acceleration sensitive loop is formed by the upper chamber 63 and the increase pitch chamber 33 including

conduits

26 and 53. Accordingly, downward movement of the piston 62 relative to the cylinder 61 will withdraw fluid from the increase pitch chamber 33, while upward movement of piston 62 in cylinder 61 will add fluid to the increase pitch chamber 33. The governor valve 40 merely supplies flow to the increase pitch chamber 33 under overspeed conditions and onspeed conditions suflicient to maintain, pressure in the increase pitch chamber and supply the constant leak valve assembly 59.

The operation of the servo system, as modified by the acceleration sensitive device, is as follows. During onspeed operation of the propeller, the governor valve piston 42 will assume its equilibrium position, as shown in Fig. 2, and the speed sensitive plunger 70 will, likewise, assume its equilibrium position, as shown in Fig. 2. In the equilibrium position of plunger 70, the thrust of centrifugal force in the direction of arrow 16 is equal and opposed to the thrust of spring 74 so that land 72 will bleed fluid through passage 78 to drain in an amount equal to that flowing through calibrated orifice 66 into the lower chamber 64. Thus, the piston 62 will be maintained in the position shown in Fig. 2.

During overspeed conditions, the governor valve piston 42 will supply flow to the increase pitch chamber 33, as well as to the constant leak valve 59, while the decrease pitch chamber 34 is connected to drain. At this time, the speed sensitive plunger 70 will move upwardly, as viewed in Fig. 2, so as to restrict or entirely out ofl the bleed of fluid through passage 78 to drain, and, accordingly, fluid flowing through orifice 66 will effect upward movement of the piston 62 until the total pressures acting on opposite surfaces thereof are equal, at which time, the land 72 will be positioned so that fluid is again bled through passage 78 to drain. Upward movement of the piston 62 injects a volume of fluid into the increase pitch chamber 33 in response to acceleration. As soon as the propeller begins to decelerate and return to the onspeed condition, the speed sensitive plunger 70 will move downwardly, as viewed in Fig. 2, to increase the bleed of fluid through passage 78 to drain, and when the bleeding of fluid to drain through port 68 is greater than that supplied through orifice 66, the piston 62 will move downwardly and withdraw a volume of fluid from the increase pitch chamber 33. At this time, it should be noted that the governor valve piston 42 is still supplying flow to the increase pitch chamber 33. However, as soon as the propeller returns to the onspeed condition, the governor valve piston 42, the speed sensitive plunger 70 and the piston 62 will assume their equilibrium positions whereupon the blade 13 will be maintained at the adjusted position.

During underspeed conditions, the governor valve piston 42 will move downwardly to interrupt the flow of fluid to the increase pitch chamber 33, while fluid is supplied to the decrease pitch chamber 34 to prevent the existence of voids therein. The external blade forces will move the blades 13 to a lower pitch position, thereby effecting upward movement of the piston 32. At the same time, the speed sensitive plunger will move downwardly, as viewed in Fig. 2, thereby increasing the bleed of fluid to drain and resulting in downward movement of the piston 62, which withdraws a volume of fluid from the increase pitch chamber 33. When deceleration ceases and acceleration towards the onspeed condition begins, the speed sensitive plunger 70 will move upwardly, as viewed in Fig. 2, thereby preventing the drain of fluid through passage 78 from lower chamber 64 and resulting in upward movement of piston 62, thereby injecting a volume of fluid into the increase pitch chamber 33. When the onspeed condition is again attained, the piston 62 will be in its equilibrium position, as will the speed sensitive plunger 70 and the governor valve piston 42.

It is to be understood that during overspeed conditions, the pitch changing motor 30 is actuated to increase the angle of blades 13, while during underspeed conditions, the blades 13 will move to a lower angle position due to centrifugal and aerodynamic centrifugal twisting moments. The acceleration sensitive device 60 merely stabilizes the adjustment of pitch by the motor 30 so that the speed of propeller operation will be returned to the preselected level in the minimum time and without undesirable fluctuations, or hunting about the selected speed level. Moreover, it will further be appreciated that both the acceleration sensitive device 60 and the governor valve 40 are mounted radially within the regulator 14 so as to respond to the thrust of centrifugal force during propeller rotation.

From the aforegoing, it is apparent that the present invention provides a self-contained acceleration sensitive device, which may be incorporated in existing servo systems so as to improve and stabilize their operation. Moreover, the device of this invention is of simple construction and requires only two hydraulic connections to be incorporated in existing servo systems.

While the embodiment of the present invention as herein disclosed, constitutes a preferred form, it is to be understood that other forms might be adopted.

What is claimed is as follows:

1. The combination with a servo system for maintaining constant speed operation of a variable pitch propeller, said servo system including a source of fluid pressure, a fluid motor for adjusting the pitch of said propeller including an increase pitch chamber and a decrease pitch chamber, and governor controlled valve means for controlling the flow of pressure fluid from said source to said motor so as to maintain propeller speed substantially constant by adjusting the pitch of said propeller; of, an acceleration sensitive device for improving the speed stability of said servo system, said acceleration sensitive device including a variable volume chamber connected to the increase pitch chamber of said motor and means operatively connected with said chamber and responsive to propeller acceleration and deceleration for controlling the volume of said chamber to thereby promote speed stability by conjointly controlling the volume of fluid within the increase pitch chamber of the pitch changing .motor with said governor controlled valve means.

2. The combination with a servo system for maintaining constant speed operation of a variable pitch propeller, said servo system including a source of fluid pressure, a fluid motor for adjusting the pitch of said propeller including an increase pitch chamber and a decrease pitch chamber, and governor controlled valve means for controlling the flow of pressure fluid from said source to said motor so as to maintain propeller speed substantially constant by adjusting the pitch of said propeller; of, an acceleration sensitive device comprising a cylinder having disposed therein a reciprocable piston, said piston dividing said cylinder into two chambers, one of which is connected to said increase pitch chamber, the position of said piston within the cylinder and said governor controlled valve means conjointly controlling the volume of fluid in said increase pitch chamber, and a speed sensitive valve element carried by said piston for controlling the actuation of said piston in response to acceleration and deceleration of said propeller to thereby modify the volume of fluid in said increase pitch chamber.

3. The combination with a servo system for maintaining constant speed operation of a variable pitch propeller, said servo system including a source of fluid pressure, a fluid motor for adjusting the pitch of said propeller including an increase pitch chamber and a decrease pitch chamber, and governor controlled valve means for controlling the flow of pressure fluid from said source to said motor so as to maintain propeller speed substantially constant by adjusting the pitch of said propeller; of, an

acceleration sensitive device comprising a cylinder having disposed therein a reciprocable piston, said piston dividing said cylinder into two chambers, one of which is connected with the increase pitch chamber and the other of which is connected to the source of fluid pressure, said cylinder having a drain port, and a speed sensitive plunger carried by said piston and having a follow-up relationship therewith for controlling the flow of fluid from said other chamber to drain to thereby control the position of said piston within said cylinder and the volume of fluid in said one chamber, said acceleration sensitive device and said governor controlled valve means conjointly controlling the volume of fluid in said increase pitch chamber.

4. The combination with a servo system for maintaining constant speed operation of a variable pitch propeller, said servo system including a source of fluid pressure, a fluid motor for adjusting the pitch of said propeller including an increase pitch chamber and a decrease pitch chamber, and governor controlled valve means for controlling the flow of pressure fluid from said source to said motor so as to maintain propeller speed substantially constant by adjusting the pitch of said propeller; of, an acceleration sensitive device comprising a cylinder, at reciprocable piston disposed in said cylinder and dividing said cylinder into two chambers, means connecting one of said chambers to said increase pitch chamber, means connecting the other of said chambers to said source of fluid pressure, a valve element carried by said piston and responsive to the speed of propeller rotation, and resilient means for opposing movement of said valve element, said cylinder having a drain port cooperable with said valve element and through which said valve element controls the flow of fluid from said other chamber in response to acceleration and deceleration of said propeller to thereby control piston movement and vary the volume of fluid in said one chamber, said acceleration sensitive device and said governor controlled valve means conjointly controlling the volume of fluid in said increase pitch chamber.

5. A servo system for maintaining substantially constant speed operation of a prime mover, including in combination, a source of fluid pressure, a fluid motor for adjusting the load on said prime mover, governor controlled valve means for controlling the flow of pressure fluid from said source to said motor so as to maintain prime mover speed substantially constant, and an acceleration sensitive device connected with said system including, a cylinder, a reciprocable piston disposed in said cylinder and dividing said cylinder into two chambers, said cylinder having a drain port and a calibrated inlet orifice for one of said chambers, means interconnecting said inlet orifice and said source of fluid pressure, means interconnecting the other chamber and said motor, and a speed sensitive plunger carried by said piston and movable relative thereto for controlling the flow of. fluid between said inlet orifice and said drain port to thereby control the position of said piston Within said cylinder in response to acceleration and deceleration of said prime mover.

6. A servo system for maintaining substantially constant speed operation of a prime mover, including in combination, a source of fluid pressure, a fluid motor for adjusting the load on said prime mover, governor controlled valve means for controlling the flow of pressure fluid from said source to said motor so as to maintain prime mover speed substantially constant, and an acceleration sensitive device connected with said system including a cylinder, a reciprocable piston disposed in said cylinder and dividing said cylinder into two chambers, said cylinder having a drain port and an inlet orifice for one of said chambers, means interconnecting said inlet orifice and said source of fluid pressure, means interconnecting the other chamber and said motor, and a speed sensitive plunger carried by said piston and having a follow-up relationship therewith for controlling the flow of fluid from said one chamber to drain and thereby control the position of said piston within said cylinder in response to acceleration and deceleration of said prime mover.

7. A servo system for maintaining substantially constant speed operation of a prime mover, including in combination, a source of fluid pressure, a fluid motor for adjusting the load on said prime mover, governor controlled valve means for controlling the flow of pressure fluid from said source to said motor so as to maintain prime mover speed substantially constant, and an acceleration sensitive device connected with said system including a cylinder, a piston disposed in said cylinder and dividing said cylinder into two chambers, means connecting one of said chambers to said motor, means connecting the other of said chambers to said source of fluid pressure, the said other chamber having a drain port, and a speed sensitive plunger for controlling the flow of fluid to drain from said other chamber to thereby control the position of said piston within said cylinder in response to acceleration and deceleration of said prime mover.

8. A servo system for maintaining substantially constant speed operation of a prime mover, including in combination, a source of fluid pressure, a fluid motor for adjusting the load on said prime mover, governor controlled valve means for controlling the flow of pressure fluid from said source to said motor so as to maintain prime mover speed substantially constant, and an acceleration sensitive device connected with said system including, a cylinder having disposed therein a pressure responsive member which divides said cylinder into two chambers, means connecting one of said chambers to said motor, means connecting the other of said chambers to said source of fluid pressure, said other chamber having a drain port, and a speed sensitive plunger carried by said pressure responsive member and movable relative thereto for controlling the flow of fluid to drain from said other chamber to thereby control the position of said pressure responsive member within said cylinder, said pressure responsive member and said speed sensitive plunger being arranged so that said member will follow-up the movement of said plunger in response to acceleration and deceleration of said prime mover.

References Cited in the file of this patent FOREIGN PATENTS Holland July 15, 1946