US2203871A

US2203871A - Radio traffic control

Info

Publication number: US2203871A
Application number: US105357A
Authority: US
Inventors: Winfield R Koch
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1936-10-13
Filing date: 1936-10-13
Publication date: 1940-06-11
Anticipated expiration: 1957-06-11

Description

June 11, 1940. w R oc 2,203,871

RADIO TRAFFI C CONTROL Oct. 13, 5 s s t 1 ZSnventqr Zach Gttorneg June 11, 1940. w. R. KOCH 1mm TRAFFIC common Filed Oct. 15, 1936 5 Sh t -Sh et 2 A/GHT con/max. G

M0701? DRIVE June 11, 1940. w. R. KOCH RADIO TRAFFIC CONTROL Filed Oct. 13, 1936 5 s am-sh et 5 Zjfocib (Ittomeg June 11, 1940. w. R. KOCH 2,203,871

RADIO TRAFFIC CONTROL Oct. 13, 5 sheets-Sheet 5 l'moentqr Patented June 11, 1940 UNITED STATES PATENT OFFICE RADIO TRAFFIC CONTROL tion of Delaware Application October 13, 1936, Serial No. 105,357

11 Claims.

My invention relates to radio traffic control and more particularly to a mobile radio transmitting system which may be used on a moving vehicle to assume a remote temporary control of an automatically operated tralllc signal, including a suitable radio receiver, and to restore the automatic control after exercising the aforementioned temporary control.

Substantial numbers of trafiic accidents have been caused by vehicles, such as fire apparatus, ambulances, police cars, and the like, which, because of the emergency nature of their calls, often disregard the traffic signal lights and operate contrary to the conventional traffic stop and go signals. I propose to equip such vehicles with a radio control which will assume remote temporary control of traffic signals. Under such circumstances, the vehicles, so equipped, can operate the traffic signals as they are approached not only to facilitate their own progress but also to protect other traffic. After the period of temporary control, automatic control is restored. By means of a novel arrangement of the transmitters and receivers unauthorized interference with the traffic control lights is prevented.

One of the objects of my invention is to provide means for controlling traflic signals from a mobile vehicle.

Another object is to provide means for temporarily controllin an automatically controlled traffic signal light by means of a radio frequency wave which is suitably modulated to prevent unauthorized interference with said traflic lights.

Another object is to provide means for selectively controlling radio trafiic signal lights from a mobile position.

A further object is to provide means for automatically assuming temporary control of traffic signals to facilitate the safe movement of authorized vehiclw and to signal other vehicles to stop.

Other objects will be apparent from the accompanying specification and drawings in which Fig. 1 is the schematic diagram of the transmitter, and Fig. 2 is the schematic diagram of the receiver of one embodiment of my invention.

Fig. 3 is a circuit diagram of a transmitter and Fig. 4 is a circuit diagram of a receiver for a modification of the radio traffic control of Figs. 1 and 2.

Figs. 5 and 6 represent, respectively, the circuit diagrams of a transmitter and a receiver which may be used in a further modification of my invention. and

Fig. 'l is a schematic circuit diagram of a modification of the receiver of Fig. 2.

For convenience, throughout the specification, it may be understood that the traffic signal lights are the conventional red, amber, and green lights which are usually employed at cross streets, and such streets will be assumed to extend in a north and south, and east and west direction. It may also be understood that I prefer to employ ultra high frequency waves of a length of the order of a meter as such waves have a limited sphere of propagation, are readily received and transmitted with small antennas, are not generally subject to atmospheric and other interference and are especially suited to the solution of the problems involved in radio traflic control.

Referring to Fig. 1 which is a schematic diagram of a radio transmitter, an ultra high frequency thermionic oscillator l is connected to a suitable amplifier 3 which is coupled to an antenna 5. The antenna 5 may be a small dipole which is suitably mounted, along with the balance of the transmitter; on the vehicle from which traffic control is to be exercised. The amplified carrier is modulated by a control grid 1 or the like which is coupled to a pair of generators 9, II.

These generators are arranged to give two different audio or supersonic frequencies A and B when the switch 13 is open. Either of these frequencies may be changed to a third frequency C when the switch is connected to include the capacitors l5, I1 in the respective oscillator circuits as shown. Thus the transmitter radiates an ultra high frequency wave which may be modulated by tone frequencies A and B, A and C or B and C by an appropriate manual adjustment of the switch l3.

A circuit diagram of a suitable device for receiving the modulated carrier wave, radiated from the transmitter of Fig. 1, is shown in Fig. 2. The receiver is preferably located at or near the traflic signal. An antenna I9 is located at approximately the intersection of the streets protected by the trafllc signal. Theantenna I9 is coupled to a radio frequency amplifier 2| which is also coupled to a detector and audio frequency amplifier 23. Three

filters

25, 21 and 29, respectively tuned to pass the modulation frequencies A, B, and C, are serially connected in the output circuit of the audio, or modulation frequency, amplifier. Each of the filters includes a

suitable rectifier

3i, 33, 35 and a

relay

31, 39, 4|. Each relay is arranged with a pair of contacts which are open circuited when no audio or other modulation frequency is impressed on the carrier wave.

In the operation of this system, hereinafter known as the first system, it will first be assumed that currents of modulation frequencies A and B are being rectified to create currents which close

relays

31 and 39. One of the contacts of relay 31, through a serial connection with one of the contacts of relay 39, completes the circuits of a two position triple contact relay 43 and a relay 45 which completes the power circuit 41 to the trafllc signal 49. The two position multiple contact relay 43, in the position shown, disconnects the normal automatic light control 5| and its motor drive 53 from the traffic signal 49. The relay 45, completing the circuit from the power source 41, energizes the east-west red trafllc light .55 and the north-south green trafilc light 51.

It will be observed that the circuits to the north-south red tramc light 59, and the east west green traific light GI, controlled by relay 93, are open. The amber lights 55, 61 are also open circuited by their control relay 59. .If desired, additional set of contacts 54 may be included in the relay 43 to operate a sound alarm signal 56 whenever the normal automatic control is disconnected and the remote control in operation.

If the transmitter is modulated by frequencies A and instead of A and B, the rectifiers 3|, 35 derive currents for energizing relays 31, 4I, connected respectively to these rectifiers, while the relay 39 connected to the remaining rectifier 33 is open circuited. The two position relay 43 is operated, as in the previously described operation by frequencies A-B, to remove the automatic control SI and connect the relay 59 which operates the amber lights 65. Both sets of red and green lights are not energized because the

relays

39, 45 and 53 are open circuited.

The modulation of the carrier wave by audio frequencies B-C is received, demodulated and rectified by the radio receiver and

reetifiers

33, 35. The rectified currents close the relays 39, H which complete the circuits of the two position relay 43 and the relay 53 which controls the north-south red light 59 and the east-west green light SI. Since no audio currents of frequency A are received, the relay 31 will be de-energized which in turn opens the circuits of

relays

45 and 69 which respectively control the

amber lights

55, 51, the north-south green light 51 and the east-west red light 55.

In the illustration of Fig. 2, and in corresponding figures through the specification, the traffic signal is shown with signal lights on the southerly and easterly portions of the signal, these lights are also visible in the northerly and westerly portions of the signal. From the foregoing description it can be seen that the radio transmitter is manually controlled by three modulation frequencies. The modulation frequencies A, B and C are operated in pairs A, B; or A, C; or B, C.

The carrier waves, modulated by a pair of said frequencies, are used to interrupt the automatic control of a traffic signal light, and temporarily establish a manual remote control for east-west, north-south or amber caution signals. The foregoing system is not readily subject to unauthorized control because of the several combinations of carrier frequency and modulation frequencies which are required and which are interlocking as previously described.

While the foregoing system offers a desriable means for remotely and manually controlling tranic signals, in many cases an automatic remote control is preferable. Such a system, hereinafter called the second system, is schematically illustrated by the circuit diagrams of the transmitter, Fig. 3, and the receiver, Fig. 4. In the second system means are provided for the automatic remote control of east-west or north-south traffic from a vehicle with authorized equipment.

The transmitter for the second system is illustrated schematically in Fig. 3 in which an ultra high frequency oscillator MI is connected to a radio frequency amplifier I03, which is coupled to a horizontally positioned dipole antenna I05. The amplifier I03 includes a control electrode I01 which is connected to a pair of generators I09, III through coupling coils H3, H5. The generators each develop alternating currents of audio or supersonic frequencies A, B, which continuously modulate the ultra high frequency carrier currents. The waves radiated by these currents are horizontally polarized by the orientation of the dipole antenna. The entire apparatus is installed on the vehicle, or the like, from which remote control of traflic signals is to be exercised.

The receiver for the second system is schematically illustrated in Fig. 4. A horizontally positioned dipole antenna II1, which may be pointed north and south, and preferably arranged in a plane parallel to the plane including the controlling transmitting antenna, is connected through a radio frequency amplifier II9, to a detector I2I and a low or modulation frequency amplifier I23. The output circuit of the amplifier I23 is connected to a pair of filters I25, I21 which respectively pass currents oi frequencies A and. B. The filters I25, I21 are respectively serially connected to rectifiers I29, I3I and relays I33, I35.

A second dipole antenna I31, horizontally positioned and pointing east-west in a plane which is at right angles to the plane of the first dipole antenna I I1, is connected through a second radio frequency amplifier I39 to a detector I4I and a low or modulation frequency amplifier I43. The output circuit of the low frequency amplifier- I43 includes a pair of filters I45, I41 which respectively pass currents of the two modulation frequencies A, B. The filters I45, I41 are respectively serially connected to rectifiers I49, I 5|, and relays I53,I55.

The relays I33, I35 have contacts which are serially connected to the movable contact of a biased relay I51. The relays I53, I55 have contacts which are serially connected to the movable contact of a second biased relay I59. The energizing coil of the first I51 of the two biased relays is connected across the cast-west red light NH and the north-south green light I53 of a trailic signal I65. The energizing coil of the second biased relay I59 is connected across the northsouth red light I61 and the east-west green light I69 of the traffic signal I65. The fixed contacts III, I13 of relays I51, I59 are connected together and through the energizing coil of a relay I which open circuits the motor drive I11 which controls the normal automatic operation of the lights. The other pair of fixed contacts I19, I8I are connected together and to a relay I83 which short circuits a series resistance I05 in the motor drive I11 circuit to increase the motor speed. An audible alarm signal I80 may be operated to audibly indicate operation of the remote automatic trafiic control. The alarm is actuated by the signal light power supply which is connected to the alarm by auxiliary contacts I82, I34 which are respectively incorporated in relays I15, I83.

The operation of the second system is as follows: Assume that the north-south oriented receiving antenna I I1 is energized by the modulated carrier waves radiated by a transmitting antenna I85 disposed parallel to the receiving antenna and carried by an east-west bound vehicle.

, The modulated carrier will be amplified, demodulated, and the demodulated currents amplified by the receiving system H1, H9, I2I, I23. The amplified demodulated currents will be filtered and rectified to thereby energize relays I33 and I35 whose contacts will be closed as shown.

If the traffic signal I65 happens to be on red for east-west traflic, the relay I51 will be energized because it is connected to the east-west red light IGI. Thus energized, the relay coil will overcome the force exerted by the biasing spring I81 and contact I19 closed to complete the circuit from the local battery I89 through the coil of the relay I83 which then short circuits the resistance I85 and speeds up the motor drive to turn on the green light which signals go to the east-west bound vehicle.

During this operation the relay I59, which is connected to the second radio receiver I31, I39, I4I, etc., through relays I53, I55, has no effect because these relays are open circuited, as shown, when the receiver is not actuated by a control signal. After the east-west green light I69 is energized the biasing spring I81 will cause contact Hi to be engaged which in turn completes the relay circuit I15 to open circuit the motor drive I11 and maintain the east-west green signal light for the east-west bound vehicle. The range of the radio transmitter is preferably limited to a relatively short distance so that the remote control will have no effect after the vehicle has driven a short distance beyond the trafiic light. After the transmission is thus reduced in its effect, the trafiic signal will be automatically restored to its normal control.

If the east-west bound vehicle is approaching a green light I89, the relay I51 will not be energized but the biasing spring I81 will cause the contact "I, which is connected to the relay I15, to be completed. The relay I15 is thus energized from the local battery I89 and open circuits the motor drive I11. With the motor drive open, the traffic signal will be maintained green for the east-west vehicle until it passes beyond the signal and beyond its range of control. The relay I59, connected to the north-south red light, will be energized during the maintenance of the east-west green light I69 because this relay I59 is connected thereto but the connection will not be effective because the receiver relays I53, I55 are open circuited.

Just as the operation for east-west bound traflic has been described, so may the operation for north-south bound traffic be traced; In the latter case the relays I33, I35 are opened, and

the relays I53, I55 are controlled by reception over the receiver I31, I39, I4I, etc. The amber or caution light is preferably adjusted for a time interval which is so short that it will offer substantially no delay to the automatic remote control, or the amber signal may be eliminated. If two vehicles, each equipped with remote control, are approaching the signal on east-west and north-south courses, one of the vehicles will assume control by operating the relay to stop the motor. That is, the vehicle which has the "green or go signal will have control andthe other vehicle must obey the "red" or stop" signal. As in the case of the first system, the present system offers secrecy provisions in that a combination of carrier and modulation frequencies are required to operate the traffic signal.

Circuit diagrams for a transmitter, Fig. 5, and a receiver, Fig. 6, illustrate another modification, hereinafter called the third system, of my invention. In Fig. 5 an ultra high frequency oscillator 20I is coupled to a high frequency amplifier 283 which is in turn coupled to a dipole antenna 205. A parasitic reflecting antenna 201 is suitably positioned with respect on the dipole to direct the waves radiated therefrom. The carrier.currents are modulated by an intermediate frequency oscillator 289 which is in turn modulated by a low frequency oscillator 2. Thus the transmitter radiates waves of ultra high frequency which are modulated by a modulated intermediate frequency amplifier. This apparatus is suitably installed on the vehicles which are to automatically and remotely control traflic signals.

The receiver for the third system is schematically illustrated in Fig, 6. This receiver is preferably located adjacent the traffic signal which is to be remotely controlled. In any event the dipole antennas 2I3, 2I5 should be located near the traffic signal. One of these dipoles 2I3 is made selectively responsive to signals from transmitters on north-south bound vehicles. The other is made selectively responsive to signals from transmitters on east-west bound vehicles. These antennas 2I3, 2I5 are alternately connected to an ultra high frequency amplifier 2" by means of a two position relay 2I9 which is actuated in synchronism with the normal automatic low speed signalcontrol motor Hi. The ultra high frequency amplifier is coupled through an intermediate frequency transformer 223 to a demodulator, low frequency amplifier and rectifier 225.

The output of the low frequency amplifier is filtered by a filter 221 which passes current of frequencies equal to the low frequency modulating curents from the transmitter. The rectified currents actuate a two position relay 229 which includes two fixed contacts 23I, 233 and a movable contact 235. The movable contact 235 is connected to the common lead 231 of the power source 239. The first fixed contact 23I is connected to the contact 2 of a relay 243 which controls the operation of a high speed motor 245. The second fixed contact 233 is connected to the low speed motor 22I.-

The low speed motor 22I is mechanically coupled through a ratchet, or "free wheeling device 241 to a shaft 249. The high speed motor 245 is also connected through a ratchet ,25I to the shaft 249. A rotating connector 253 is arranged to be driven by the shaft. The connector 253 makes contact with the commutators 255-251 which respectively operate the eastwest red stop lights 259, north-south green go lights 26I and the east-west green go lights 263, north-south red stop lights 265. The amber lights 261 are controlled by the commutators 289.

The N-S signal antenna 2I3 is connected when the connector 253 connects with the commutator 21I whereby the relay 2I9 is energized. The biasing springs 213 operate to connect the E-W signal antenna 2I5 when the relay 2I9 is not energized. A pair of commutators 215 are arranged to disconnect the relay 243 for a brief moment before the normal amber or "caution signal 251 is flashed. The

ratchet connections

241, 25! are arranged so that either of the two motors 22!, 245 may be operated without interiering with each other. A warning bell 243 may be included to give out warning signals whenever the automatic remote control is functioning.

The operation of the third system is as follows: With the connector 253 in the position shown, the east-west light 259 is red, and the north-south light 25! is green. The E--W signal antenna is in operative connection. If a vehicle bound eastwest with the transmitter of Fig. is approaching the red or stop signal, the waves from the transmitter will operate the receiver to thereby close the contact 23! of relay 223 as shown. The contact 24! of the relay 243 is likewise closed and therefore power will be applied to the high speed motor 245 which will quickly turn the connector 253 to just before the amber signal commutator 215 position where the high speed motor relay 243 will be energized to stop the motor; at the same time the N-S signal antenna 2!3 will be connected. This will shut off the received signal and contact 233 of relay 229 will be completed to restore to normal control the slow speed motor 22! which will operate the east-west green signal to permit the vehicle to pass.

Had the east-west signal been on green, the connector 253 would have been on the

commutators

251 and 21! which establish connections to the east-west green light 253, and the connection to the two position relay 2l9. This relay 2!!! would disconnect the EW signal antenna 2! 5 so that the remote control transmitter approaching on the east-west course would have no effect on the signal which is already green and in the desired go position. The normal low speed motor control 22! would turn the connector 253, continuing the east-West signal light 263. At the instant when the connector 253 leaves the commutator 21! the EW signal antenna 2I5 will be connected, the signals will disconnect the low speed motor 22! but the high speed motor 245 will be prevented from operating because relay 243 will be energized by the connector 253 completing contact with one of the small commutators 215.

Thus it may be seen that the third system provides means for remotely and automatically speeding up the operation of a traffic signal which is set red or stop with respect to an approaching vehicle. Through suitable means the same traffic signal, if set green or go with respect to the approaching vehicle, may be held on green by the same automatic remote control until the vehicle has passed the signal light. While I have only described the operation of the third system for vehicles on east-west courses, it should be understood that the operation is similar for north-south traffic control. If two vehicles are approaching from east-west and northsouth directions, and each is equipped with automatic control, the vehicle which is approaching on the green or go signal will maintain control and the other vehicle will be confronted with the stop or red signal light.

While I prefer to operate the signal lights to show red and green in the conventional manner and speed up or delay such lights by automatic or manual remote control, there may be instances when it is preferable to turn the signal to display red lights for both north-south and eastwest bound traffic. Slight modifications in the receiver connections of the several systems may be made to accomplish such type of remote control. By way of example, Fig. '1 shows a modification of the receiver used in the first system whereby the trafilc signals are remotely operated to the stop" or red light positions for traffic bound both north-south and east-west.

In Fig. 7 an antenna 33! is coupled to a radio frequency amplifier 303 which is in turn coupled .to a demodulator and a low frequency amplifier 305. A pair of filters 301, 333 designed to respectively pass modulation frequencies A, B are connected in the output circuit of the low frequency amplifier. The outputs of the filters, respectively, include rectifiers 3! 3!3 and relays 3!5, H1.

The contacts M9, 32! of these relays are serially connected to include a local battery 323 and the energizing coil 325 of a three contact relay 321. The first contact 323 of this relay is in the common lead from the power supply 32! and light control box 333 to the amber 335 and green 331 lights. One red signal light 333 is through the second set of contacts 34! of the relay 321 to the power source 33!. The other red signal light 343 is connected through the third set of contacts 345 of the relay 321 to the power source 33!.

The operation of this receiver is as follows: A modulated wave from the transmitter is received, amplified, demodulated, and amplified. The amplified demodulated currents are passed through filters 301, 303 and rectifiers 3! I, 3|3 to close the relays 3!3, 32!, as shown. The closing of relays 3H, 32! completes the circuit through the coil 325 of the three contact relay 321. The two contacts 34!, 345 of this relay connected to the red lights 339, 343 complete the circuits to energize the red lights. The other contact 323 opens, as shown, and breaks the circuits to the green 331 and amber 335 lights. After the remote control device has passed beyond the control area, normal automatic control is restored to the light control box 333 and its associated driving motor 341.

While I have described three systems for remote control of traffic signals from vehicles, my invention is not to be limited to any type of vehicle as the systems may be used by airplanes, vessels, or may in fact be carried by a traffic oflicer. Likewise, the system is not limited to the remote control of traffic signal lights but may be applied to semaphores, audible signals, guard gates, or the like. Although I prefer to operate the several systems with two or more modulation frequencies to assure freedom from unauthorized use, the several systems may be used without such double modulation provisions.

I claim as my invention:

1. A remote traffic-control system comprising means for signaling drivers of vehicles to proceed or stop their vehicles, a mobile transmitter including means for radiating radio frequency waves, means for modulating said waves with combinations of currents of different frequencies, means for varying said combinations, means for receiving and demodulating said waves, means for separately selecting said currents of different frequencies, means for separately rectifying said selected currents, and a plurality of separate means selectively responsive to said rectified currents to control said proceed or stop signals in accordance with said variations in said combinations.

2. A remote traffic-control system comprising means for signaling drivers of vehicles to stop, go, or proceed with caution, a mobile transmitter including means for radiating a radio frequency wave, means for selectively modulating said wave with a plurality of different frequencies, means for receiving said wave, means for demodulating said wave, means for deriving a plurality of different currents from said difl'erent modulation frequencies, and means controlled by said diflerent currents to selectively operate said stop, go and caution signals.

3. In a device of the character of claim 2, means for automatically controlling said stop, go, and caution signals when said remote control is not in operation.

4. A trailic-control signal comprising means for automatically signaling in prearranged sequences stop, so and caution signals, a remote radio frequency wave source, means for selectively impressing a plurality of different pairs of modulation signals on said wave, means for receiving and demodulating said wave, means controlled by said demodulated waves for temporarily interrupting said automatic control, and means controlled by currents derived from said different pairs of demodulated waves for selectively operating said stop, go, and caution signals.

5. A remote traflic signal control comprising means for automatically establishing in predetermined sequences stop and go signals, means for generating and radiating a polarized radio frequency carrier, means for modulating said carrier, selective means for receiving said modulated carrier and deriving currents from the modulation components thereof, and means controlled by said currents for delaying or advancing the automatic operation of said stop and go signals.

6. A remote signal control comprising means forautomatically controlling the trafllc at intersecting paths by alternate'stop and go signals, means mounted on selected vehicles for generating and radiating a radio frequency wave, means for modulating said radio frequency wave, means for receiving said wave, means for deriving controlling currents from the modulation components thereof, means for receiving waves from a transmitter in the other of said paths, means for deriving controlling currents from the modulation component thereof, means operated by either one of said derived currents for automatically increasing the rate of the operation changing said signal from stop to go to allow said vehicle to proceed in said path, for automatically thereafter interrupting said alternate operation and maintaining said signal on go upon approach of a vehicle containing said radio frequency generator and radiator.

7. In a tramc signal system including means for the normal operation of stop and go signals, the method of providing a right of way for a selected vehicle which comprises radiating radio waves from said vehicle, selectively receiving said waves according to the orientation of said vehicle, obtaining demodulated currents from said waves, utilizing said current to speed up the normal operation of said light so as to give a 8 signal for said vehicle, and thereafter automatically interrupting the normal operation of said light once a, "go" signal has been established and until the control by said vehicle has been removed. L I

8. A tramc-control system which includes a trams-signal mechanism disposed so as to provide traflic-reg'ulating signals for intersecting trailic lanes, means normally operating said signal mechanism to allow the alternate flow of traflic in said lanes, and means selectively responsive to a radio control signal originating in a vehicle traversing one of said lanes for interrupting said normal operation of said signal mechanism during the application of said radio signals to said selectively responsive means.

9. A traiilc-control system which includes a traiiic-signal mechanism disposed so as to provide traflic-regulating signals for intersecting tramc lanes, means normally operating s'aid mechanism to allow the alternate flow of tratlic in said lanes, means selectively responsive to radio control signals originating .in vehicles traversing one of said lanes, other means selectively responsive to radio control signals originating in vehicles traversing the other of said lanes, means operable by said responsive means for interrupting said normal operation of said signal mechanism during the reception of a radio signal from one of said vehicles, and means for conditioning said traflic signal during the interruption of said normal operation to allow the passage of tramc in the traflic lane which said one vehicle is traversing.

10. A traflic-control system which includes a traiflc-signal mechanism disposed so as to-provide tramc-regulating "stop" and "go signals for intersecting trafllc lanes, means normally operating said signal mechanism to allow the alternate flow of traflic in said lanes, means selectively responsive to a radio control signal originating in a vehicle traversing one of said lanes, means operable by said selectively responsive means for accelerating said normal operation to change a "stop" signal to a go" signal in the traiiic lane traversed by said vehicle, and means for interrupting said normal operation to maintain said "go" signal during the reception of said radio control signals.

11. A traffic-control system comprising signalling means adapted to control traflic in intersecting lanes, means including a switch actuated by a low-speed motor for automatically controlling the traflic at said intersection, arhighspeed motor, means responsive to a signal for operably connecting said high-speed motor to and disconnecting said low-speed motor from said switch for temporarily speeding up the operation of said system to accelerate a predetermined condition, and means thereafter stopping said automatic control to maintain said predetermined conditiomduring the application of said signal.

WINFIELD R. KOCH.