US2748182A - Overspeed device - Google Patents

Description

OVERSPEED DEVICE Filed Dec. 5, 1950 Figl.

TO CONTROL ClRCUlT Inventor- Carl H.Er-icson,

His Attorney.

United States harem OVERSPEED DEVHCE Carl H. Ericson, Buffalo, N. Y, assignor to General Electric Company, a corporation of New York Application December 5, 1950, Serial No. 199,282

9 Claims. (Cl. 123-148) This invention relates to speed responsive devices, and more particularly to electrically actuated overspeed devices.

It is an object of the invention to provide an improved and simplified speed responsive device for a machine which provides a pulsating voltage substantially proportional to its speed or for any machine which is capable of producing a pulsating voltage because it rotates, oscillates, reciprocates, vibrates or the like.

A more specific object of my invention is the provision of an electrically actuated overspeed device which need not be connected to the shaft of the machine which is to be protected.

Other objects and advantages of the invention will be apparent from the detailed description given hereinafter, while the scope of the invention is defined in the appended claims.

In carrying out my invention in one form, I provide an overspeed device having two impedances serially connected to a source of pulsating electrical potential whose frequency is proportional to the speed of the machine to be protected. One of the impedances is a capacitor, the impedance of which varies inversely with frequency, and the other is a resistor, the impedance of which is substantially unaffected by frequency, with the former being of considerably larger impedance than the latter over the normal operating range so that the amplitude of the current through the series circuit is approximately proportional to the frequency. A voltage responsive device connected in shunt with the resistance is arranged to operate when the current through the resistance reaches a value sufficient to produce a predetermined voltage drop thereacros-s.

For a clearer and more complete understanding of my invention, reference should be had to the accompanying drawing in which Fig. l is a schematic diagram of one preferred embodiment thereof, while Fig. 2 depicts schematically an embodiment of more general adaptability than Fig. 1.

Referring to Fig. l of the drawing, there is shown a form of the invention adaptable for use with a machine, such as an automobile engine for example, which provides a pulsating voltage proportional to its speed. In this embodiment the overspeed device is actuated by the pulsating potential produced by the engines ignition system.

There is shown in Fig. l a portion of a conventional automobile engine ignition system. The battery, which may be a six volt battery for example, is designated by the numeral 10 and one terminal of the battery, which may be the negative terminal, is grounded at 11. A switch, which maybe a conventional automobile ignition switch or other similar switch, is shown at 12, while the primary circuit breaker which periodically interrupts the primary ignition circuit at a frequency proportional to the speed of the engine to produce a pulsating voltage which is also proportional in frequency to the speed of the engine, is represented schematically by switch 13.

This circuit breaker has acondenser connected in shunt therewith in the conventional manner and this condenser is designated by the numeral 14. The primary circuit interrupter is connected to the primary winding 15 of an ignition transformer, and winding 15 is grounded at 16. The secondary winding of the ignition transformer, the distributor and the spark plugs are not shown in order to simplify the drawing, these parts of the ignition system not being necessary to an explanation of the invention.

There is connected to the ungrounded side of the ignition transformer primary winding, in a suitable manner such as by a spring clip 17, a series circuit comprising a capacitor 18 and an adjustable potentiometer resistance 19 having a slider 19a. The negative terminal of the resistor is grounded at 20. Connected in shunt between the slider 1% of the adjustable resistance and the grounded terminal is a voltage responsive device. This is illustrated as a dArsonval type contact making microammeter 21 having an operating coil Zia. This coil is connected in shunt with the effective portion of resistor 19 through a bridge type rectifier 21c which is preferably an integral part of instrument 21. The contact making microammeter is provided with contacts Zlb which are connected to shunt the coil of a solenoid 2.2 when the contacts close.

The solenoid 22 operates a pair of switches 23 and24 and forms one element of a typical control circuit which may be used with the present invention in the testing of an automobile engine. This control circuit also includes a momentary contact push button switch 25 and a resistor 26. Current for the operation of the control circuits may be supplied by any conventional source, and in this instance is. indicated as being supplied at volts 60 cycles by conductors 2'7 and 28. The closing of push button switch 2.5 energizes solenoid 22 through resistor 26 and closes switches 23 and 24. The closing of switch 23 completes a hold-in circuit for solenoid 2.2, permitting the release of switch 25 without deenerg'izing the solenoid. The closing of switch 24 completes :the ignition circuit of the engine, as is subsequently discussed in greater detail in connection with the operation of Fig. 1.

In accordance with my invention, the impedance of capacitor i8 is preferably considerably greater than the impedance of resistor 19 over the frequency range which is to be utilized. Inone typical device used for testing six cylinder, 4 cycle automobile engines operating between 500 and 4,000 R. P. M., a capacitor having value of .l microfarad was used for element 13 while a resistance having a value of 10,000 ohms was used for element 19; With this combination, a contact making microammeter having a range of 0-200 microamperes was used as element-Zl.

This arrangement resulted in a capacitor impedance which varied from approximately 65,000 ohms at the lower speed of 500 R. P. M. to approximately 8,000 ohms at 4,000 R. P. M. engine speed. The impedance of the capacitor in the upper portion of the operating range'thus was slightly less than the total impedance of the resistor. Nevertheless, the overspeed device operated entirely satisfactorily.

In general, it is desirable to have the impedance of the capacitor greater than the impedance of the resistor over the entire frequency range. The greater the ratio by which the capacitor impedance exceeds the resistor impedance the more linear is the variation of the current through the resistor with variations in frequency. Greater linearity in the resistor current produces greater linearity in voltage drop across the resistor, and makes it possible toobtain satisfactory results from the overspeed device withavoltage responsive device of minimum accuracy and cost.

It will be understood, of course, that other voltage responsive devices, such as solenoid operated contactors, relays, and other similar devices for example, may be used instead of the contact making microammeter illustrated without departing from my invention. It will be readily understood also that a potentiometer resistor, such as is illustrated by element 19 on the drawing, is not an essential part of the invention, and that a less expensive fixed resistor can be substituted in many cases when extreme accuracy is not required.

With the connection illustrated in Fig. 1, the signal presented to the primary of the ignition coil is essentially a square wave of constant amplitude and variable frequency, the value of the frequency depending upon the speed of the engine. Therefore, if the impedance of 13 is appreciably greater than the impedance of 19 at the highest frequency used, the amplitude of the current flowing through the capacitance-resistance series circuit is approximately proportional to the frequency and, therefore, approximately proportional to the speed of the engine. This is because the impedance of capacitor 18 varies inversely with the frequency, and this impedance being larger than the impedance of resistor 19 predominates in determining the value of current in the series circuit.

The circuit illustrated in Fig. l, as previously stated, may be utilized to provide overspeed protection for an engine which is to be tested. In operation, ignition switch 12 is first closed and then push button switch 25 is operated. Closing switch 25 energizes the coil of solenoid 22 through resistor 26 and closes switches 23 and 24. The closing of switch 23 provides a hold-in circuit for solenoid 22 when momentary contact switch 25 is released. The closing of switch 24 completes the ignition circuit of the engine from the battery through the primary winding of the ignition coil and permits operation of the engine at various speeds in the usual manner. To adjust the microammeter 21, the engine is set at the desired maximum safe speed and resistance 19 is then adjusted until, by visual inspection, it is determined that the contacts of microammeter 21 are just about to close. Thus, no accurate calibration of the overspeed device is necessary.

During subsequent tests of the engine, if it should run away for any reason, such as a coupling breaking between the engine and a dynamometer being used to load it for example, the frequency of the ignition circuit would increase and thereby increase the current through the series circuit formed by capacitor 18 and resistor 19. When the voltage drop across the effective portion of the latter increases suificiently to provide enough current to operate microammeter 21 and close contacts 21b, the engine is immediately shut down. The closing of contacts 21b shunts the coil of solenoid 22 causing the solenoid to drop out and open switches 23 and 24. The latter opens the ignition circuit of the engine while the former opens the control circuit. The engine will then remain inoperative until the control circuit again is actuated by depressing push button switch 25.

From the foregoing it will be apparent that this invention provides an overspeed protective device which need not be connected to the shaft of the machine, and which makes unnecessary any of the usual electrical, liquid, centrifugal or other tachometer devices. It will be appreciated that it is of great advantage to have an overspeed protective device which need not be connected to the shaft of the machine because of the inaccessibility of the shafts of many machines, such as the crank shafts of automobile engines for example.

In Fig. 2 of the drawing, there is illustrated an embodiment of the invention of more general adaptability than Fig. 1. in this figure, like parts bear like numerals with the corresponding parts in Fig. 1. The form of the invention illustrated in Fig. 2, may be used for any machine that rotates, reciprocates, oscillates or vibrates, or has any periodic motion by means of which it is capable of producing an alternating or pulsating voltage.

A portion of such a machine, which may, for example,

be a portion of a piston rod, valve arm, cam, rocker arm or other moving part is illustrated at 29 in Fig. 2. The two arrows extending up and down from element 29 indicate schematically that this point on the machine has a periodic motion so that a movable contact 30 which is connected to point 29 and pivoted about a point 31 contacts alternately fixed contacts 32 and 33.

In Fig. 2, two sources of potential, such as a pair of batteries ltia and 1652, are used, With two terminals of opposite polarity joined to form a midpoint and with the lower terminal of resistance 19 connected to this midpoint. The other terminals of the batteries are connected to contacts 32 and 33 respectively whereby an alternating voltage results from the alternate engagement of movable contact member 38 with fixed contact members 32 and 33. This alternating voltage, impressed on the series circuit including capacitor 13 and resistor 19, operates in the same manner as described for Fig. 1; that is, the amplitude of the current through the series circuit varies approximately proportionally with the frequency of the alternating potential. The voltage responsive device 21 is then set so that when the current through the effective portion of resistance 19 reaches a certain predetermined value corresponding to a selected speed of the machine being protected, the device 21. operates to close its contacts and energize a control circuit to discontinue operation of the machine or perform any other desired operation. Thus, a speed responsive device is provided for any machine having a periodic motion which can be translated into an alternating or pulsating potential.

While I have illustrated and described in detail certain preferred embodiments of my invention, many modifications thereof may be made by those skilled in the art, and it should be understood, therefore, that I intend to cover by the appended claims all such modifications which fall within the true spirit and scope of my invention.

What i claim as new and desire to secure by Letters Patent of the United States is:

l. A control system for a machine comprising means for deriving a pulsating voltage having a frequency proportional to the speed of the machine comprising a source of direct voltage and a circuit supplied from said source including make and break contacts opened and closed in response to the speed of the machine, a first impedance whose value varies with frequency connected to be energized by said voltage, a second impedance whose value is relatively unaffected by frequency connected to be energized in series with said first impedance, said first impedance being larger than said second impedance over at least most of the operating range of said speed responsive device whereby the amplitude of the current in said series circuit is responsive principally to the value of said first impedance, and a voltage responsive device connected in shunt with said second impedance and arranged to perform a control operation in connection with said machine when the voltage drop across said second impedance reaches a predetermined value corresponding to a selected speed of said machine.

2. A control system for a machine comprising means for deriving a pulsating voltage having a frequency substantially proportional comprising a source of direct voltage and a circuit supplied from said source including make and break contacts opened and closed in response to the speed of a machine, a capacitor of relatively large impedance and a resistor of relatively small impedance serially connected and arranged to be energized by said pulsating voltage, and a voltage responsive device connected in shunt with said resistor and arranged to perform a control operation in connection with said machine when the voltage drop across said resistor reaches a predetermined value.

3. A speed responsive device for an engine having an ignition circuit providing a pulsating voltage whose frequency is substantially proportional to the speed of the engine, comprising a first impedance Whose value varies inversely with frequency connected to be energized by said ignition voltage, a second impedance Whose value is substantially unaffected by frequency connected in series with first impedance, said first impedance being appreciably larger than said second impedance Whereby the amplitude of the current in said series circuit is approximately proportional to the speed of said engine, and a voltage responsive device connected in shunt with said second impedance and arranged to perform a control operation in connection with said engine when the voltage drop across said second impedance increases to a predetermined value corresponding to a selected speed of said engine.

4. A speed responsive device for an engine having an ignition circuit providing a pulsating voltage whose frequency is substantially proportional to the speed of the engine, comprising a capacitor of relatively large impedance and a resistor of relatively small impedance serially connected and arranged to be energized by said ignition voltage, and a voltage responsive device connected in shunt with said resistance and arranged to perform a control operation in connection with said engine when the voltage drop across said resistor increases to a predetermined value corresponding to a selected speed of said engine.

5. A speed responsive device for a machine having a periodically moving part whose period is proportional to the speed of the machine comprising, movable contact means connected to be operated by said moving part, fixed contact means associated with said movable contact means and arranged to be periodically engaged thereby at a frequency corresponding to the movement of said moving part, connections for applying an electrical potential between said fixed and movable contact means whereby a pulsating voltage having a frequency proportional to the speed of said machine is provided by the periodic engagement of said fixed and movable contact means, a capacitor of relatively large impedance and a resistor of relatively small impedance connected in series and arranged to be energized by said pulsating voltage, and a voltage responsive device connected in shunt with said resistor and arranged to perform a control operation in connection with said machine when the voltage drop across said resistor increases to a predetermined portion of the total voltage drop across the capacitor and the resistor.

6. A speed responsive device for a machine having a periodically moving part Whose motion is responsive to the speed of said machine, comprising movable contact means connected to said moving part and arranged to be moved by the motion thereof, fixed contact means associated with said movable contact means and arranged for periodic engagement with said movable contact means at a frequency corresponding to the period of motion of said moving part, electrical connections for applying an electrical potential between said fixed and movable contact means whereby a pulsating voltage is produced having a frequency corresponding to the frequency of engagement of said contacts, a first impedance Whose value varies with frequency connected to be energized by said pulsating voltage, a second impedance whose value is substantially unaffected by frequency connected in series with first impedance, said first impedance being considerably larger than said second impedance whereby the amplitude of the current in said series circuit is determined principally by the value of said first impedance, and a voltage responsive device connected in shunt with said second impedance and arranged to perform a control operation in connection with said machine when the voltage drop across said second impedance reaches a predetermined value corresponding to a selected speed of said machine.

7. An overspeed device for a machine having a periodically moving part whose frequency is proportional to the speed of the machine, comprising a pivoted movable contact member connected to said moving part, a pair of fixed contact members oppositely disposed in operative relation with said movable contact member and arranged to be contacted alternately by said movable contact memher, a source of unidirectional potential connected to said fixed contact members, said source of potential having a point of intermediate potential connected to said movable contact member whereby an alternating voltage is produced having a frequency proportional to the speed of said machine, a capacitor and a resistor serially connected in the circuit between said intermediate point and said movable contact, said capacitor having a considerably larger impedance than said resistor whereby the amplitude of the current through said series circuit is approximately proportional to the impedance of said capacitor, and a contact making voltage responsive device connected in shunt with at least a portion of said resistor, said voltage responsive device being arranged to close its contacts upon the occurrence of a predetermined amplitude of current in said resistor producing a predetermined voltage drop thereacross.

8. A speed responsive device for an engine having an ignition circuit providing a pulsating voltage Whose frequency is proportional to the speed of the engine, comprising a capacitor connected to be energized by said ignition voltage, a resistor connected in series with said capacitor, the impedance of said capacitor being larger than the impedance of said resistor whereby the amplitude of the current in said series circuit is determined principally by the impedance of said capacitor, and a contact making voltage responsive device connected in shunt with at least a portion of said resistor, said voltage responsive device being arranged to close its contacts upon the occurrence of a predetermined current in said resistor producing a predetermined voltage drop thereacross.

9. An overspeed device for an engine having an ignition circuit providing a pulsating voltage whose frequency is proportional to the speed of the engine, comprising a capacitor and a potentiometer resistor having an adjustable intermediate terminal connected in series for energization by said pulsating voltage, said capacitor having a considerably greater impedance than said resistor whereby the amplitude of the current in said series circuit is approximately proportional to said frequency and said speed, a contact making voltage responsive device connected between the adjustable terminal and one fixed terminal of said potentiometer resistance, said voltage responsive device being arranged to close its contacts upon the occurrence of a selected voltage drop across said potentiometer resistor corresponding to a predetermined current through said resistor which corresponds to a predetermined engine speed, and control circuit means responsive to the closing of said contacts to deenergize said ignition circuit and stop the operation of said engine upon the occurrence of said predetermined speed.

References Cited in the file of this patent UNITED STATES PATENTS 1,029,480 Tirrill June 11, 1912 2,010,960 Pogue Aug. 13, 1935 2,108,014 Jones Feb. 8, 1938 2,161,146 Echlin et al. June 6, 1939 2,251,436 Bentley et al. Aug. 5, 1941 2,301,115 Gilbert Nov. 3, 1942 2,349,992 Schrader May 3, 1944 2,377,591 Taylor June 5, 1945

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