CA1179414A - Vital vehicle movement detector - Google Patents

Abstract

(Case No. 7105) ABSTRACT OF THE DISCLOSURE
The speed proportional frequency signal from the speed generator being checked is amplified and applied to a high-pass filter-rectifier with a low frequency limit corresponding to a predetermined minimum train speed. Polarity of the rec-tified output is opposite to the DC operating energy so that, with four-terminal load resistor and smoothing capacitor, the filter-rectifier operation is vital. The rectified signal activates an oscillator level detector when its level exceeds the breakdown of a Zener diode control device selected to cor-respond to minimum speed output. The level detector is coupled by a stepdown transformer to a differential amplifier biased by a signal supplied from an associated zero speed detector.
The bias signal has sufficient level to enable the differential amplifier to produce an output in response to the level detec-tor input only when the train speed is greater than zero. This output represents proper operation of the axle generator and is coupled to enable the train speed governor to respond to other train control signals. When the train is stopped, the differential amplifier is biased below operating level. How-ever, a supplemental bypass signal present only when train brakes are set is coupled through the differential amplifier output to enable the speed governor during station stops.

Description

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(Case No. 7105) VITAL VEHICLE MOVE~MEN'r DETECTOR

BACKGROU~D OF THE INVENTION
My in~ention pertains to a vehicle movement detsctor fox use with a vehicle overspeed control system. More particularly~ the inv~ntion relates to a detector which ,- checks the integrity of the vehicle speed measuring means pickup device when the vehicle is moving and provides an output signal, to enable the continued release o~ the vehicle brakes, only when a valid speed signal is registered.
Speed control systems for vehicles including railroad trains require apparatus for measuring the actual vehicle or train speed so that it may be compared with the desired speed.
Frequently, this apparatus is of the tachome~er, axle genera-tor type which produces an alternating current signal whose frequency varies in proportion with the train speed. Integ-; rity of the tachometer apparatus is very important because an unsafe condition can result if failure occurs, ~or example, if the drive shaft to the axle genexator should bxeak as the train starts to move. m er~ore, some form of movement detec-tor is required which will register the output of the tacho-meter or speed generator, to assure its integrity and reli-a~ility, at those times when other conditions indicate that the train is moving. In the absence of output from such a detector, a brake application is actuated. An alternate method is to use two speed pickup devices with a comparison for agreement of the outputsO However, this redundancy is costly and results in complex circuitry. Where the spe~d control apparatus is part of an automatic train operation system~ the use of a zero velocity detector as part of the system is required to assure that door opening occurs only when the train is fully stopped at a station platfnrm. Such zero velocity apparatus also provides a simulated tachom~ter signal to enable the train to start up from the station stop.
An example o~ vital zero motion or zero speed ~hecking appara~
tus for ~se in a train control system is disclosed in United States Patent 3,553~488, issued January 5~ 1971 to John 0. G~
Darr~w and Raymond C. Franke for a Fail-Sa~e Circuit Arrange~
ment. ~hen such zero speed checking apparatus is used with a train control system, a simple arrangement su~h as a high pass filter cannot be used to check tachometer integrity during train movement since the high ~requency electrical check signal produeed b~ the æero speed detector when the train iæ stopped i8 applied through the tachometer pickup element. This will result in output from the movement detector even if there is n~ speed signal. Since both detector arrangements are neces-sary in the complete system, an arrangement which inh~bits this incorrect response of the movement detector to the high frequen~y signal from the zero speed appaxatus is necessary.
Accordingly, an object of my invention is a vital vehicle mGvement detector for use in a speed control system in combina-tion with a zero speed detector arrangement.
Another object of the invention is a vehicle movement detector which checks the integrity of the vehicle speed measuring apparatus when the vehicle is in motion~

A further object of my invention is a vital vehicle move-ment detector in which the detection of vehicle movement to register the integrity of the speed measuring device is in-hibited if the associated zero velocity detector registers a vehicle at stop~
Still another object of the invention is a vehicle move ment detector apparatus which is responsive to various input signals to check integrity and operation of the vehicle speed measuring axle generator device only when the train should 10 be moving and has exceeded a preselected minimum speed level.
Yet another object of the invention is detector appara-tus for use in a complete train control system, which includes a zero speed detector arrangement, to assure the integrity ~ of the train speed pickup device only when the train is moving to enable the speed governor to retain train brakes released to continue the train movement.
~till a further object of the invention is to provide a vital vehicle movement detector, for assuring the integrity - of vehicle speed measuring apparatus, co~prising, input means coupled for receiving speed signals from the speed measuring apparatus and responsive for supplying corresponding output signals with characteristics representing vehicle speed, a filter-rectifier network ~oupled to the input means for pro-ducing a selected polarity output signal only in response to input signals representing at least a predetermined minimum vehicle speed, a level detector means coupled to the filter-rectifier network and operable for producing an output when ~7~

the level of the selected polarity signal indicates a vehicle speed at least equal to the predetermined minimum, a differ-ential amplifier means coupled to receive the output of the level detector means and responsive thereto for producing an output signal only when enabled by a bias signal of prese-lected characteristic and at least a predetermined minimum level, the differential amplifier means also coupled for supplylng the output signal to enable continued movement of the vehicle, and an inhibitor circuit means coupled to the differential amplifier means for supplying the bias signal having the preselected characteristic and predeter-mined level only when the vehicle speed is greater than zero.
Other objects, features, and advantages of my invention will become apparent from the following specification and ; 15 appended claims when taken in connection with the accompany-ing drawing.
SU~RY OF THE INVENTION
.
The movement detector arrangement comprises, in sequence, an amplifier network for receiving the input signals from the tachometer speed generator, a high pass filter and rectifier network, a level detector element, and a differential ampli-fier, all formed by solid-state circuit elements. In opera-tion, signals from the vehicle or train tachometer device or axle generator pickup coil are applied to the initial ampli-fier network. Specifically~ this is an alternating current - siynal with a fraquency proportional to the vehicle speed.
The same signal is applied to the zero velocity detector network of the vehicle used in the train control system, an example of which is shown in the previously cited patent.
When the train is stopped, the speed generator pickup coil i8 supplied with a signal from an oscillator element to check the elactrical integrity of the tachometer pickup, which iæ part of the circuit to enable the door opening action and to prevent an emergency brake application during a station stopO In the presently disclosed arrangement, the input signal is ampli~
fied, and then filtered and rectified by a high pass unit.
The lower limit of the filter portion of this unit represents a predetermined minimum speed level at which vehicle movement is evident. The rectifiers used are poled to pro~ide an out-put polarity opposite to that of the direct current energy source which supplies power for operation of the apparatus.
Since its load is a four-terminal resistor, and since shorting the series capacitor would cause a loss of output, operation of the filter, rectifier network is thus on a vital basis~
that is, it cannot fail so as to deliver full output at a low frequency. The rectified direct current output, smoothed in an output stage of the filter-rectifier including a vital four-terminal capacitor to prevent ripple from the rectifier from substituting for the following level detector's alterna-ting current output, is applied to an oscillator based level f~

detector element~ Circuit parameters are selected so that the level of this direct current signal is suffic~ent to trigger an oscillatory response by the level detector only if the initial input signal fxequency is high enough to pass through the filter element, that is, if the train speed is greater ~han the pre~etermined minimum speed. To inhibit the detection of the zero velocity oscillator input as a valid tachometer pickup, a differential amplifier element biased by the gating signal from the zero velocity apparatus is coupled to the le~el dete~tor via a transformer which pro~ides only a small level output signal. When the train is moving, a steady positive biasing signal is applied to the differential amplifier to enable it to pass the low level input signal pro-vided by the le~el detector output. The output of the differ~
; 15 ential amplifier complex enables t]he speed governor to produce an outputJ other conditions being 'proper, so that the train braking remains released and continued movement occurs. When the train stops at a station under normal, i. e., not emer-gencyD braking, the zero velocity oscillator signal comprises periodic pulses so that the resultant bias signal level is insufficient to enable the differential amplifier. Lack of xesponse by this element to the level detector input signal elLminates the normal output from the movement detector net-work so that the speed governor would no longer be enabled to actuate release of the brakes. In other words, no false signal of the integrity of the tachometer pickup element is produced as a result of the simulated speed signal from the zero velocity oscillator. However, when the train has stopped at a station and the brakes are set, an interim enabling signal is supplied from a separate oscillator to the speed governor so that the movement detector is effectively bypassed, for a time period, until the minim~m speed level is again reached.
The train may thus renew its movement at such time as the train control system directs.
BRIBF DESCRIPTION OF THE DRAWING
Before defining the invention in the appended claim~, I
shall describe a specific arrangement of the invention illus-/ trated in the accompanying drawing, which is a schematiccircuit diagram o* a preferred embodiment of the on-board vital movement detector as used in a train speed control system.
DESCRIPTIO~ OF THE_ILLUSTRATED ~MBODIMæNT
Referring to the drawing, the first stage or portion of the movement detector apparatus shown at the left ls the amplifier element including the faur transistors Ql to Q4.
Energy for the operation of this amplifier and for the remain-der of the detector apparatus is supplied ~rom a direct currentsource of any known type. Connections to the positive termi-nal of this source are designated by the reference +B. The negative terminal of this source is represented by the conven-tional ground symbol shown as connected to the common or ground bus of the apparatus. The input to the amplifier, that is, the base to collector electrodes of transistor Ql, is csnnected across the inductance coil 18 which is part of the speed measuring means oE the train and is wound on a permanent magnet. This speed measuring means also includes a gear wheel 22 of magnetic material which is driven by a train axle and is positioned so that it is near one end of the magnet on which is wound coil 18. The combination of these elements comprises an axle driven speed gene-rator or tachometer and is the same as the similarly de-signated elements shown in the previously cited Patent 3,553,488~ The parallel connections to the elements of the zero velocity detector of this cited patent are ill-ustrated by the conventional double arrowhead symbols.
The apparatus of the present application is designed to work in conjunction with a slightly modified version of this zero velocity detection apparatus, as will be shortly discussed.
When the train is moving, an aLternating current signal is induced in coil 18 having a frequency propor-tionaL to the speed of a train. Coil 18 is also part of ; the feedback circuit of an oscillator element 1 of the zero velocity detector which is periodically enabled by a gating signal when the train is stopped, as e~plained in the cited patentO Thus,alternating current pulses are produced across coil 18, during a train stopped condition, with a frequency predetermined by the oscillator network parameters. The pulse rate at which these signals are generated is determined by the element parameters in the zero veloci-ty detector, also as explained in the cited - 7 ~

patent, and are not pertinent here~ However, the fre~uency of the alternating current generated by -this oscillator network is within the operating fre~uen~y range of the tachometer when the train is moving so that a filter tuned to pass the signals representing txain speed will also pass the oscillator pulses produced within the zero velocity detector.
Returning to the present apparatus, the input signal from coil 18 is amplified in the initial transistor network, as pre-viously mentioned. The output of this amplifier is filtered and rectified in the next element w~ich includes capacitors &1 and C2, diodes Dl and D2, and a four terminal load resistor : R~. The values of capacitors Cl and C2 are selected in rela-tion to the value of resistor R7 so as to form a high pass filter whose lower limit is representativa of the output fre-quency of the tachometer at a predetermined minimum speed of ~he train. The diodes or half wave rectifiers Dl and D2 are poled so as to produce an output polarity across resiætor R7 that is opposite to that of the direct current enersy supply from terminal +~. Under this provision, plu5 the ~act that load resistor R7 is a four terminal vital element, the filtex-rectifier network constitutes a vital, high pas~ filter in-capable of d~livering an inappropriate output due to a com, ponent failure such as the shorting of series capacitor Cl.
The direct current output from this stage, appeaxing acros~
resistor R7, is filtered or smoothed in the network including resistor R8 and capacitor C3. It may be noted that capacitor C3 is a four terminal element in order to provide a vital smoothing filter network.
The output voltage of the filter-rectifier stage appear-ing across capacitor C3 is applied to the level detector ele-ment whose principal components are the transistor Q5, the Zener diode D3, and output transformer Tl. This level detec-tor network is similar to that disclosed in my pri~r United States Patent 3,737~806, issued June 5, 1973, for a Fail-Safe Circuit Arrangement. Re~erence is made to this patent for a full description of the operation of this level detector.
Briefly, the detector is an oscillator based on transistor Q5 (reference Tl in the patent) and a voltage breakdown device such as diode D3 (Zl in the patent~. The oscillator becomes active, i. e., sufficient feedback exists to sustain oscilla-tion, only when the DC input is of sufficient level to causediode D3 to breaX down, i. e., conduct in the reverse direc-tion, and assume a low impedance condition. In this applica-tion, the level detector is actuated, i. e., oscillation begins, when train speed is at or above the selected minimum. The re-quency of the tachometer output is then such that a sufficientsignal passes through the filter network of capacitors Cl, C2 and resistor R7 to produce a sufficient level of applied rec-tified direct current energy to break down diode D3~
In this present application, the level detector or oscil-lator output is taken from the voltage drop across the induc-tance, shown in the patent as winding Ll, by adding a secondary winding to form coupling or output transformer Tl. me added g _ secondary is wound with only a very few turns so that trans-former Tl acts to step dawn the voltage drop in producing the output signal. To further aid the cross reference to the cited patent 3,737,8060 capacitors Cl, C2, C3 o~ the patent are equivalant to c~pacitors C5, C6 J and C7, respectivsly~ of this present arrangement, with capacitor C4 and resistor R10 - herein being the same as capacitor C4 and re~istor R5 of the patent.
Normally the level detector output occurs when the speed of the train is above the predetermined minimum level. How~
ever, the oscillator level detector is also actuated when the train is stopped, by the high frequency signals from the associated zero velocity oscillator apparatus with which this arrangement cooperates in the traill control system~ The manner in which this signal is generated ~md applied is discussed in the cited prior patent 3,553,488 to which reference i~ made for exact details. What is important in the present arrange-ment is that the output of this movement detector mu~t be inhibited under this condition, ~hat is, when the train is actually stopped and the zero velocity oscillator is acti~e.
To accomplish this, the output of the level detector stage from the secondary of transformer Tl is supplied to the inpu~ of a differential amplifier element formed by transis-tors Q6 and Q7 and the associated resistor units. This input is supplemented from terminal 8 through four terminal capacitor C8 to provide a bias signal or level for the differential amplifier. Terminal 8 represents the lead 8 in the cited prior patent 3,553,4B8 which carries the gating signal pro-vided at emitter 59 of the switching transistor T6 in that patent~ In the specific zero velocity apparatus a~sociated with the movement detector disclosed herein, the zero veloci~y arrangement is modified so that the polarity of ~he signals is - reversed from that discussed in the prior patent. In other words, lead or terminal 8 has a +B signal when the vehicle i9 mo~ing at more than a predetermined minimum speed level. When the vehicle is stopped so that there is no output from the tachometer speed generator~ terminal 8 is periodically lowered to a ground level signal as the zero velocity apparatus, par-ticularly its oscillator element 1 is actuated and functions to detect this stopped condition. Said in another way, in the modified patent system, the oscillator based on transistor Tl oscillates when lead 8 from emitter 59 has a n~gative or ground signal. If the gate signal on lead 8 is at ~B, no oscillation can occur in the zero velocity detector so tha$ no signal i5 produced in coil 18 other ~han that from the tachometar gear de~ice 22.
With the input on terminal 8 at the +B lavel, a positive ~oltage appears on the upper plate of capacitor C~. The dif-ferential amplifier including transistors Q6 and Q7 is then biased so that the low level output signal from the secondary of transformer Tl is amplified and applied to tran~istor Q8.
This output amplifier element then provides an alternating current output through capacitor C9 to terminal 80 from whence it is supplied to enable the speed governor for the train control apparatus to actuate circuitxy which allows continued train movement. If the signal at lead 8 iB at ground; oscil-lations in the zero velocity apparatus occur. As explained, terminal or lead 8 periodirally switches between +B and ground potentials dur~ng this condition. The .ummed voltage developed on capacitor C8 is then at such a low level that the differen~r tial amplifier is biased outside its operating range. The output from transformer Tl is blocked and no output thus occurs from transistor Q8 to terminal 80. Thus, under any condition that the high freguency from ~he zero velocity appa-ratus could turn on the level detector, its OLItpUt will be blocked by the differential amplifier action and a signal on terminal 80 is inhibited. Thus, a final enabling output from transistor Q8 will occur only when the vehicle is moving above a predetermined speed.
The only other condition which must be considered is to provide an output ~rom the movement detector apparatus when the vehicle or train is stopped and the brakes are applied, in order that the speed governor is not shut off to inhibit a restart of train movement. This is accomplished by means of the oscillator unit shown conventionally as a dashed block in the lower part of the drawing. When active, this unit supplies its output signal through the collector resistor Rl9 of transistor Q7 to the base electrode o transistor Q8. This signal is amplified by this transistor and applied through capacitor C9 to terminal 80. This action is poss~ble since, under a train stopped condition, transistor Q7 is turned off ~ 12 ~

~L~7~

because of ~he biasing conditions ~rom terminal 8~ Whan the vehicle ~egins to ~o~e, the brake switch shown sc~ematically, which may be one of the manual ~ontrol contacts, opens. The oscillator remains activated for a brief tLme by the c~arge acro~s capacitor C10~ which must have a tLme constant long enough to overlap the time it takes the train to reach the - minimum speed at which the normal apparatus senses its move_ ment and provides the enabling output at terminal 80 through : the l~vel detector and differential amplifier, as already des-cribed.
It thus i~ seen that the enabling output ~t terminal 80 i~ obtained only if either the tachometer i8 properly oper~-ting or if the train is stopped and the br~kes applied. No failure can cause this output in th~e a~sence of one of these condition~. Thus, the failure of the tachometer element will be assuredly detected and the enabl:ing ~ignal eliminaked or inhibited so as to cause the train to be halted. This reRult is obtained in an efficient and economic m~nner by the move~
ment detector apparatus of m~ invention.
Although I have herein shGwn and described but a single e~bodiment of the vital movement detector apparatus of my invention, it is to be under~tood that changes and modiflca-tions therein within the scope of the appended claim~ may be made without departing from the spirit and scope of my inven-tion.

_ 13 -

Claims (8)

Having now described the invention, what I claim as new and desire to secure by Letters Patent, is:

1. A vital vehicle movement detector, for assuring the integrity of vehicle speed measuring apparatus. comprising, (a) input means coupled for receiving speed signals from said speed measuring apparatus and responsive for supplying corresponding output signals with charac-teristics representing vehicle speed, (b) a filter-rectifier network coupled so said input means for producing a selected polarity output signal only in response to input signals representing at least a predetermined minimum vehicle speed, (c) a level detector means coupled to said filter-rectifier network and operable for producing an output when the level of said selected polarity signal indicates a vehicle speed at least equal to said predetermined minimum, (d) a differential amplifier means coupled to receive the output of said level detector means and respon-sive thereto for producing an output signal only when enabled by a bias signal of preselected charac-teristic and at least a predetermined minimum level, (1) said differential amplifier means also coupled for supplying said output signal to enable continued movement of said vehicle, and (e) an inhibitor circuit means coupled to said differen-tial amplifier means for supplying said bias signal having said preselected characteristic and predeter-mined level only when said vehicle speed is greater than zero.

2. A vehicle movement detector as defined in claim 1 in which, (a) said speed signals are alternating current signals having a frequency characteristic proportional to vehicle speed and (b) said filter-rectifier network is tuned as a high pass filter with a low frequency limit at the fre-quency representing said predetermined minimum vehicle speed.

3. A vehicle movement detector as defined in claim 2 in which, said input means is an amplifier network operable for supply-ing amplified speed signals with frequency proportional to vehicle speed to said filter-rectifier network.

4. A vehicle movement detector as defined in claim 3 in which said filter-rectifier network comprises, (a) a vital loading element, (b) a pair of capacitors of preselected values coupled for coacting with said loading element to pass only signals having valid frequency characteristics representing at least said predetermined minimum speed level, and (c) a pair of diodes interconnected with said loading element and said capacitors for applying a voltage signal of said selected polarity across said loading element when valid speed signals are re-ceived from said input amplifier network.

5. A vehicle movement detector as defined in claim 1 in which said level detector comprises, (a) an oscillator element having an oscillatory feedback circuit, (b) a normally nonconducting voltage breakdown device coupled into said oscillatory feedback circuit for blocking feedback signals to inhibit operation of said oscillator element, (1) said voltage breakdown device connected to receive said selected polarity signal and responsive thereto when said pre-determined speed level is attained for assuming a conducting condition to com-plete said oscillator feedback circuit and enable oscillator operation, and (c) an output means coupled to said oscillator element for supplying said oscillation signal to said dif-ferential amplifier.

6. A vehicle movement detector as defined in claim 1 which further includes, (a) another output means coupled to said differential amplifier means and operable for supplying a sig-nal to enable continued movement of said vehicle when a differential amplifier output is present, and (b) a supplemental signal source active only when said vehicle is stopped and its brakes applied, (c) said supplemental source coupled to said output means for supplying an enabling output signal when said differential amplifier is biased to an in-active condition and existing vehicle conditions activate said supplemental source.

7. A vehicle movement detector as defined in claim 5 in which, (a) said voltage breakdown device is a Zener diode having a reverse breakdown voltage selected at a predeter-mined level of said selected polarity signal devel-oped when said vehicle speed equals and is greater than said predetermined minimum speed, (b) said output means is a stepdown transformer having its primary winding coupled into said oscillator feedback circuit, and (c) said bias signal is received from a separate source coupled to the input of said differential amplifier and which produces a biasing signal having said preselected characteristic and predetermined level only when said vehicle speed is greater than zero.

8. A vehicle movement detector as defined in claim 7 in which, (a) said vital loading element of said filter-rectifier network is a vital four terminal resistor, (b) said diodes are poled for producing a selected polar-ity signal across said vital resistor opposite to the polarity of the operating energy for said input ampli-fier network and said differential amplifier means, (c) whereby the operation of said high pass filter network is on a vital basis so that a valid selected polarity output signal is produced only when the input speed signal frequency is at or above the filter lower limit and no fault exists within any of said resistor, capa-citor, and diode components.