US2785367A - Dynamometer control - Google Patents

Description

March 12, w ROMAN ET AL 2,785,367

DYNAMOMETER CONTROL 6 SheetsSheet 2 Filed April 5, 1954 sum 'dwv so e INVENTORS Walter G. Romon,Frcnk Slomur and Joseph F. Kovolsky WC W WITNESSES:

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ATTORN EY March W G, ROMAN ET AL DYNAMOMEITER CONTROL 6 Sheets-Sheet 3 Filed April 5, 1954 INVENTORS Walter 6. Roman Frank Slomor 0nd BJYoseph F. Kovolsky.

WITNESSES:

ATTORNEY March 12, 1957 w, ROMAN ET AL 2,785,367

DYNAMOMETER CONTROL 6 Sheets-Sheet 4 Filed April 5, 1954 m m a in a m 32H wi. 6 n nTbs. 6.: m nTE 1 3 in zmv h Q m .E 22m 2m Lu l F ZN nC. ow. T I wo l l rllll I|.|.| l I I l I l I I ll illllll l I I I I I I I l I I l I I I III lllll-l I I I I I I III I 6 3 z: 68

INVENTORS 0 N .2 LL

WITNESSES:

ATTORNEY March 12, 1957 w ROMAN ETAL 2,785,367

DYNAMOMETER CONTROL 6 Sheets-Sheet 5 Filed April 5, 1954 sobo 4600 5600 R.P. M. Fig.4.

Engine Torque Engine Tut Governor Action I l I I l I l Characteristic With Gurnni Limit loooauoo mu $1 m s m m Rwb m w ko E K V m n9 1 m Y OMB. R Z d Gm w r m f O W 7 i .l F

WITNESSES:

ATTORNEY Sim March 12, 1957 w ROMAN ET AL 2,785,367

DYNAMOMETEIR CONTROL Filed April 5, 1954 6 Sheets-Sheet 6 I00 C:f Dynamarnatcr Characteristic Required for Governor Test 90 Absorbing g 70 so K E 50 Q 40 b w 30 l J 20 f 10 4: r 0 .fi'

moo 2000 5000 400a 5000 6000 R. P. M. Fig. 6.

Slope Control Characteristic G.) I E E E G.) O w I 0 Engine Characteristic i A I000 2000 3000 4000 500a 5000 R. P. M.

- Fig. 8. I WITNESSES: INVENTORS 6%, Walter G. Romon,Frank Slamar M and Joseph F. Kovalsky.

ATTORN EY nited States Patent DYNAMOMETER CONTRQL Walter G. Roman, Pittsburgh, Pa., and Frank Siamar, East Aurora, and Joseph F. Kovaisky, Buffalo, N. Y., assignors to Westinghouse Electric nrporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application April 5, 1754, Serial No. 421,046

24- Ciaints. (Cl. 318-498} This invention relates generally to systems of control for electric motors and more particularly to such systems wherein the motor is employed as a dynamometer used in motoring and load absorbing modes of operation.

A dynamometer is a device that measures either the torque delivered by an engine or motor or the torque required to drive such an engine or motor or more generally any rotating piece of machinery.

The usual electric dynamometer is a D. C. or A. C. motor having its frame mounted on trunnion bearings so it is free to rotate. Free rotation is prevented in some instances by means of a lever arm, the free end of which is spring loaded as by a conventional calibrated coil spring assembly, or more commonly a platform scale, which measures the force required to restrain the end of the lever which, with the length of the lever arm to the center of rotation, indicates torque. Horsepower determinations are made from the product of torque and speed. Since all measurements must be accurate, an accurate speed indicating tachometer is connected to the dynamometer for this purpose. When special speed regulating control is required, the usual practice is to use a tachometer or pilot generator belted or otherwise suitably connected to the dynamometer shaft to be driven at a speed proportional to shaft speed. The signal generated by this generator is then fed back into the system to regulate the speed. Dynamometers which are to be used over a broad speed range are usually of the direct current motor type, because of the ease of controlling such devices through armature voltage control and field voltage control. The alternating current types are primarily adapted for single speed special purpose applications.

The invention as herein disclosed illustrates a control arrangement for a direct current type of electric motor dynamometer and in the interest of simplicity, in repr resenting the arrangement in the drawings, the mechanical details of the dynamometer, such as the rotatably mounted frame, lever arm and platform scale are not shown. Such details are simple in nature and are readily appreciated from the discussion above.

Typical of the expanding applications of dynamometers are those presently found in the automotive industry, which employs the dynamometer for a wide variety of engineering and development tests. Although the device is by no means new to the industry, the modern dynamorneter with its reliable, accurate and sensitive control has measurably advanced the art of automotive testing. Also the ability of the dynamo-meter and its associated equipment to simulate road conditions such as automobile inertia, wind resistance and road grades has made it possible to move automotive proving grounds indoors for many tests.

The advantages of laboratory testing of new or eX- perimental designs is obvious. Laboratory tests can be conducted under controlled conditions permitting tests to be performed always to the same reference or stand ard. Variables encountered in outdoor testing such as temperature, wind and rain cannot affect indoor test results. The more accurate test results obtained with these indoor tests enable test engineers to detect and evaluate incremental improvements in design.

Another advantage of conducting tests under controlled conditions in a laboratory rather than on an outdoor proving ground is the savings in time. Identical conditions of previous tests can be reproduced at any time in the laboratory while wind or road conditions may delay outdoor tests for days at a time.

A dynamometer employed in automotive testing must be a versatile device. It must be capable of testing all of the components of the vehicle which affect its performance and its serviceability. For example, the dynamometer must be capable of testing the engine for friction loading, for output torque, for horsepower and if a governor is employed, for the governor characteristics. It must be capable of testing transmissions and axles as well as the vehicle chassis. In accomplishing this the requirements of the dynamometer are that it be capable of operating in both motoring and load absorbing control modes, for example in regard to engine tests it is necessary to crank the engine with the dynamometer in order to start the engine when load absorbing tests are to be made, to determine engine output torques and horsepower. This means that the dynamometer must first be operated as a motor to drive and crank the engine and thereafter operated as a load absorbing generator to apply torques of predetermined character to the engine. These torques may be constant in nature or they may vary in some suitable manner to simulate conditions such as ascending or descending grades and acceleration conditions. In the motoring mode the dynamometer is also used to drive the engine to determine the friction drag of the engine from the torque required to drive it. In transmission testing two dynamometers are required, one operated in the motoring mode connected to the input shaft of the transmission and one operated in the load absorbing mode connected to the output shaft of the transmission. By this arrangement accurate information relating to friction losses and, in general, the torque transmission capabilities of the transmission at various speeds are readily determined. The foregoing represents but a few of the applications of the dynamometer in vehicle component test procedures.

One object of this invention is to provide a dynamometer which is simple with respect to operational requirements and accuracy.

Another object of this invention is to provide a dynamometer arrangement which is adjustable for constant torque control.

Yet another object of this invention is to provide a dynamometer suitable for internal combustion engine testing which is capable of maintaining constant speed over the full torque range of the engine being tested.

Another object of this invention is to provide a dynamometer with which variable torque characteristics over the operating speed range are obtainable.

Further to the preceding object, it is an object of this invention to provide a dynamometer which selectively provides both positive and negative slopes to the speedtorque characteristic.

Another object of this invention is to provide a dynamometer capable of simulating effects of windage in the speed-torque characteristic.

A further object of this invention is to provide a novel arrangement of current limit and torque control for an electric motor type of dynamometer.

Further to the preceding object, it is an object of this invention to provide a control for a direct current electric motor including torque and current limit control of the motor derived from motor armature current wherein the torque and current limit signals are effectively isolated.

In the application of apparatus according to the preceding object to dynamometers, it is an object hereof to provide selective separately adjustable motoring and load absorbing current limit protection.

The foregoing statements are merely illustrative of the various aims and objects of this invention. Other objects and advantages will become apparent from a study of the following specification when considered in conjunction with the accompanying drawings in which:

Figure 1 is a block diagram of a dynamometer apparatus embodying the principles of this invention;

Figs. 2a, 2b and 20 together diagrammatically illustrate the details of the control arrangement of this in vention;

Fig. 3 graphically illustrates the characteristics of a magnetic amplifier employed in producing the system current cue;

Fig. 4 shows the dynamometer speed characteristic for difierent values of field current, that is, the full load curve;

Fig. 5 illustrates the current limit characteristics of the dynamometer system for both motoring and absorbing operation. These are typical curves, and do not represent the only curves obtainable in the respective modes of operation;

Fig. 6 shows the substantially constant torque characteristics of the direct current dynamometer under current limit control in the absorbing mode of operation, such characteristics being needed, for example, in testing performance of the governor on the test engine;

Fig. 7 relates the test engine torque characteristic to constant torque characteristics of the dynamometer de picting system characteristics in the absorbing mode of operation during tests of the speed governor on the test en ine;

Fig. 8 shows speed-torque slope control characteristics of the dynamometer system; 7

Fig. 9 shows a tachometer generator arrangement employing direct current machines for obtaining a voltage proportional to the square of the operating soeed: and

Fig. 10 shows an alternating current tachometer generator and associated circuit for obtaining a voltage proportional to the square of the tachometer speed.

The dynamometer system illustrated in block form in Fig. 1 comprises a dynamometer D which includes a direct current motor having an armature winding and a field windisw. the l tter betas riesiomfltfirl DP. As noted in the opening statements hereof, the motor frame (not shown) is journaled in bearings and suitably restrained shaft of the dynamometer is connected to a rotatable device such as the test unit TU indicated in block outline. For example, such a device may be an internal combustion engine, a shaft of transmission assembly, a shaft of an axle assembly or it may be a rotatable drum assembly adapted to receive the rear Wheels of a vehicle for cha ssis tests. Such devices are not shown in detail in the interest of simplicity.

An induction motor I drives a generator G having a bias field winding GBF and a re ulating-field winding GRF. The armature winding of the generator is connected in a series loop with the armature winding of the dynamometer forming a variable voltage motor drive. The generator is driven at constant speed by the induc tion motor I which is supplied from a suitable source of three-phase alternating current voltage. The armature circuit of the dynamometer and generator is controlled by a switch generally designated M1 which is adapted for automatic control by suitable controls appearing in the detailed showing of the system yet to be described.

As noted earlier, in automotive testing versatility is required. The dynamometer must be adaptable for both motoring and load absorbing operation in internal comvoltage.

current limit potentiomoters 5? and bustion engine testing. In this capacity, in one test phase, it must be capable of holding the speed of the test engine constant regardless of variations in test engine output torque. In another test phase, it must be capable of holding torque constant as the test engine speed is varied for governor esting. For still other test phases, it must be capable of introducing a speed-torque slope to simulate acceleration both upgrade and downgrade and it must also be capable of selectively introducing non-linear torque variations with speed to simulate windageeifects on the automobile body for adequate chassis testing. At the same time, the system must be self-protecting to obviate overload damage.

Generator bias field .13? is provided to reduce the genera-tor residual voltage to zero in the absence of other excitation. The generator regulating field GRP provides excitation as required to properly control the dynamometer.

To this end generator field is controlled by the output of a controllable generator field rectifier GER which in turn is controlled by an amplifier A. The input circuit of the amplifier is subjecte to several voltages adapted to give motor operation of the character required depending upon the manner of their combination and their individual magnitudes.

One of the amplifier input voltages is a speed error This voltage is derived from the difierence be tween an adjustable reference voltage and a voitage produced by a tachometer generator T driven by the dynamometer D. The adjustable reference voltage is derived across a tapped portion of a potentiometer 21 on ergizcd by a speed reference circuit SR, which is a regulated supply of direct current voltage, and is combined in series opposition with the tachometer voltage in the amplifier input circuit. Thus adjustment of the tap of potentiometer 2? establishes the speed which is to be maintained by the dynamometer to pr uce the n cos sary tachometer voltage to attain equ'libipum in the speed regulating loop. By this means selected constant dynamometer speeds are ootained for both motoring and load absorbing operation.

System protection is achieved by current limiting through the production or" a current i' iit voitage derived from motor armature current. The curr. limit voltage is applied across the input circuit of A. A magnetic amplifier MA which is controlied by the dynamometer armature current produces the current limit voltage.

This amplifier comprises an alternating current main winding MW, a bias winding 5W, a concol winding CW, which latter, as shown, is connected in series in the motor armature circuit. The characteristic of the magnetic amplifier is shown in 3, wherein the sloping line indicates the substantially line" port on of the saturation curve. The ampere turns oi bias win BW bias the amplifier to a given point along the ch cteristic. For example, this point may be apprc midpoint of the linear portion of the characteristic. ampere turns of the control winding CW reverse with reversal of motor armature current. In the motoring mode of operation, the control ampere turns are in opposition to the ampere turns of the bias winding and drive the output current downwardly by decreasing the saturation of the core material. in the load absorbing mode of operation the control Winding ampere turns add to the bias winding 4i and 51 are energized with constant voltage produced by a current limit reference circuit CLR, the output of which is applied in parallel with series connected potentiometers 4F and 5? across a potentiometer 1? which is employed to initially calibrate the current limit loop when the armature current of the dynanometer is zero. in this circuit resistor 12R is connected in series with parallel circuit branches including the tapped portions of potentiometer IF, the taps of potentiometer 4P and SP respectively and the respective sections 4TU1 and 4TU2 of double triode tube 4TU which is used as a diode. This series parallel circuit is connect ed across the input cir cult of amplifier A.

For the purpose of this invention proper function of the current limit circuit is achieved by adjusting potentiometer lP so that for zero armature current in the armature circuit of the dynamometer and generator, no current will flow in either direction in the current limit circuit, even through the absorbing and motoring potentiometers 4P and 5? are set at their minimum values which correspond to zero load current in the armature circuit for both load absorbing and motoring operating modes. With poteutiometers 4P and SP set to provide the desired degree of current limit, absorbing and motoring armature currents respectively increase and decrease the voltage across resistor 12R about that value of voltage which exists at zero armature current. When this voltage changes from the value existing when the armature current is zero, it amounts to, or, has the effect of, a polarity reversal in the circuit. When increasing, if it exceeds that value of voltage set by the tap of potentiometer 4P for absorbing current limit, the diode 4TU1 conducts. When it decreases to a value below the initial value an amount exceeding the voltage set by the tap of potentiometer 5? for motoring current limit control, the diode #lTUZ becomes conducting. The current signal thus produced for either mode of operation swamps all other signals in the amplifier input circuit, limiting the output of the generator to that current level set at either potentiometer 4P or potentiometer 5P. This will be explained in greater detail in regard to the detailed circuits of Figs. 2a, 2b and 2c. The characteristics obtained with the current limit control described above are illustrated in Fig. 5 for both motoring and absorbing modes of operation. These characteristics may be varied at will, that is, any value of current limit up to maximum rated current may be set for either mode of operation, and the established limit is maintained over the system speed range in the presence of torque loading which drives the armature current to the selected limit. Since the dynamometer torque is a function of load current it will be appreciated that the dynamometer torque characteristic may be established by this method. The torque characeteristics are plotted in Fig. 6 along with the dynamometer full load characteristic which appears in dotted outline. The dynamometer characteristic plotted as a function of field current against dynamome-ter speed appears in Fig. 4.

n the dynamometer characteristic shown in Fig. 4, the base speed with maximum fixed field current and maximum armature voltage is about 2500 revolutions per minute. The dynamometer speed over this speed range is controlled by armature voltage variation. Beyond base speed the characteristic is obtained by weakening of the dynamometer field. Excitation for the dynamometer field is provided by a dynamometer field rectifier DFR controlled by respective potentiometers ZAP and 3A1, which in turn are mechanically ganged with respective pot ntionieters 2? and 3?, the latter of which provides slope control or" the speed-torque characteristics yet to be described. While not so indicated, the pairs of potentiometers 2P, ZAP and 3P, 3A? may be suitably blanked to provide speed control by armature voltage variation up to base speed and beyond base speed by dynamometer field control. In the present arrangement a negative bias on a tube section 18TU1, shown in Fig. 2b, prevents field weakening over the range of armature voltage control.

Fig. 7 plots the test engine torque against representative constant dynamometer torques, as explained in connection with Figs. 5 and 6. T his characteristic of operation is used in testing the test engine governor which, to function properly, must regulate test engine speed for any torque loading within system limits which may be selected, as shown by the intersection between the test engine and dynamometer torque characteristics. Further governor testing referred to as governor surge may be made with this arrangement by a procedure known as load dumping. In this, the dynamometer torque is suddenly reduced to some low value, or zero, and then just as suddenly reapplied. The resulting load surge tests the governor behavior under dynamic conditions.

Sl pe control of the speed-torque characteristic, for example, to give a more stable operating point when the equipment under test exhibits relatively constant speed characteristics, is achieved by adding a voltage proportional to motor torque to the speed reference voltage in the tachometer generator loop. In the absorbing mode of operation under straight speed regulation, the dynamometer operates to hold the speed of the test engine constant. As the engine throttle is advanced and the output power increased, the dynamometer torque loading rises, which increases the load current responsive torque voltage. This voltage when added to the speed reference voltage of potentiometer 2P requires more tachometer generator voltage for equilibrium which, in turn, requires a higher speed of the test engine. Thus when the torque voltage is combined with the speed reference voltage, a slope is introduced in the speed-torque characteristic, that is, the speed increases as the absorbed load increases. In the motoring mode the torque voltage reverses and subtracts from the tachometer generator voltage. This slope control may also be used in simulating upgrade and downgrade load conditions. In short, the slope control can be used to cover the range of test characteristics between constant torque and constant speed conditions.

This control is accomplished by means of a potentiometer 3P which is energized by the differential of the voltages appearing across the output resistor 20R of the torque signal circuit TS and resistor assembly 31R, 35R, here shown as one resistor for drawing convenience. As illustrated, resistor assembly 31R, 35R is connected in series opposition with the resistor 20R across the potentiometer SP, and is energized with a selected constant value of voltage derived from the speed reference circuit SR. Since the torque signal varies with dynamometer armature current, it will be appreciated that the voltage drop across resistor 20R may be greater than or less than the constant voltage drop across resistor assembly 31R, 35R and hence the voltage drop across potentiometer 3]? will reverse, depending upon the conditions. In practice, since the magnetic amplifier due to its bias has an output current when the dynamometer armature current is Zero, the voltage across resistor ZfiR at zero armature current is balanced against the fixed reference voltage across resistor assembly 31R, 353. Thus at Zero armature current the actual torque signal which is the sum, in an algebraic sense, of these voltage drops is zero. When the current increases in the absorbing direction, the voltage drop across potentiometer 3? increases in a sense adding to the speed reference voltage. When the armature current increases in the motoring direction, the voltage drop across potentiometer 3P increases in a reverse sense and subtracts from the speed reference voltage. With this arrangement the polarity and magnitude of the voltage across potentiometer 3P respectively indicate the direction and magnitude of the torque. As noted earlier, potentiometer 3P is mechanically ganged with potentiometer SAP which is used to control the dynamometer field rectifier DFR. This arrangement extends grid of and varies the conduction of the tube STU.

the range of slope control over the higher speed ranges.

A better understanding of this invention will be had 'from the basic control principles, outlined hereinabove in connection with the block diagram of Fig. 1; by refer ence to the detail circuit system of Figs. 2a, 2b and 2c. in this detail circuit the induction motor I is connected to a three-phase circuit comprising conductors L1, L2 and L3 which in turn are connected to supply conductors 1L1, 1L2 and 11.3 by means of respective switches 1M4, EMS and 1M6 of a power supply contactor TM. in this illustration the generator G'ineludes a series field winding 08?. The use of such a winding epends upon the requirements of the system. The magnetic amplifier MA is shown in greater detail indicating a closed loop core MAC on which the respective windings are disposed. Additionally the bias winding is controlled by a rhcostat 85R connected in series therewith to provide the required degree of bias voltage to obtain the desired output characteristic at Zero armature current discussed in connection with Fig. 3.

The tachometer generator T which is driven by the dynamometer is connected in a circuit including the polarity reversing switches F1, F2 and R1, R2, which are provided for the purpose of reversing the connection of the armature terminals of the tachometer across a resistor 37R forming part of the input circuit to the amplifier A. This provision is made in the event it is desired to reverse the direction of operation of the dynamometer for certain tests.

The speed reference circuit SR is a regulated D. C. supply of the required voltage. This regulated supply is connected to a direct current supply source and includes a very stable reference tube designated ltlTU, two stages of amplification in tube sections 9TU1 and 9TU2 of a tube 9TU and a series impedance tube 8TU, the grid of which is controlled by the output of the two stage amplifier 9T U. Any change in line voltage is reflected as a change in grid voltage on tube section 9TU1. The variation in output of tube section 9TU1 correspondingly controls the grid of tube section 9TU2 which in turn controls the In this manner the series impedance afforded in the circuit by tube STU is varied and the voltage drop thereacross is varied in such a manner as to maintain the voltage across conductors 145 and 135 substantially constant. This voltage is applied across the speed reference potentiometer 2P.

"grease Isolation of the torque signal circuit from the current signal circuit is achieved by respective transformers ST and 9'1 and the circuits of the torque signal and current signal channels. The primary windings 3TP and 9T? of transformers 8T and 9T of which are connected in series with the alternating current main winding MW of the magnetic amplifier. The secondary winding )TS of the transformer 9T is connected as the input to a full wave rectifier circuit including a double diode tube 6TU, the output of which is filtered by a capacitor 4C and applied across the torque signal resistor 29R. Since alternating current flows in the main winding circuit of the magnetic amplifier including conductors 155 and T59 when there is zero armature current in the dynamorneter armature circuit, a voltage will appear across the output of the torque signal circuit from 133 to 125, that is, across the resistor ZtiR. This output voltage corresponding to zero armature current is balanced against a fixed reference voltage appearing across resistors 31? and 35R connected in series in a circuit paralleling speed potentiometer 2? across conductors 145 and 135 in the speed reference circuit SR. Thus under the condition of zero armatur current, the actual torque signal which is the algebraic sum of these voltage drops is zero. The algebraic sum of these two voltages appears across the speed-slope control potentiometer 3P. This circuit is traceable from the upper terminal of potentiometer 3P through conductor through the torque signal output resistor 29R to conductor 133 to terminal 156 through resistors 31R and 35R to conductor 135 and back to the other side of the potentiometer 3P.

With this arrangement when the armature current increases in the absorbing direction, the voltage drop across potentiometer 3]? increases in such a direction that the lower side of potentiometer 3? connected to circuit 135 is positive with respect to the upper side. of potentiometer 3? at 125. When the armature current increases in the motoring direction, the voltage drop across potentiometer 3? increases, but in this instance in such a direction that the upper side at circuit 125 becomes positive with respect to the lower side at circuit 135. The polarity and magnitude of the voltage appearing across potentiometer 3? is therefore indicative of the direction and magnitude of the torque.

The current signal for the system is derived in the current signal circuit CS from the rectified voltage of the secondary winding 8T5 of transformer 8T. A full-wave rectified output voltage is produced by means of a double diode STU. The output of rectifier 5TU is filtered and applied across resistor 12R. This circuit produces a voltage across resistor 12R between circuits 149 and it) when there is zero armature current and this voltage increases when the current increases in the absorbing direction and decreases when the armature current increases in the motoring direction.

The current limit reference circuit CLR is connected to a regulated supply of direct current which is not shown, but may conventionally include a rectifier tube for rectifying an alternating current supply and one or more voltage re ulating tubes for providing the required magnitude of regulated direct current voltage at the indicated direct current terminals of the current limit reference circuit. This circuit, which as earlier noted, in cludes the current signal output resistor in series and is provided with respective parallel branches including in series respective tapped portions of potentiometer 1P, respective taps of potentiometers ll and 5? and respective tube sections 4TH and ETUZ of the rectifier tube STU.

Tube 4TU is shown as a double triode operated as a diode with the grids of the respective sections connected to the plates thereof. Tube section TUlt is selectively connected to the tap of potentiometer 4P or to a point 189 between potentiometers 4P and 5P by means of respective manually operated switches Al and B1 As noted earlier, this circuit is used for testing the speed governor on the test engine. Since potentiometer 4? is used to set the current limit values in the absorbing mode of operation, it will be appreciated that when switch Al is closed, selected constant values of torque, through current limit operation, are obtained by different settings of the tap of potentiometer 4-1 from posi tions between circuit 193 and point 169, which latter corresponds to minimum torque. By this expedient, therefore, the control of engine speed by the governor as shown in Fig. 7 for any value of torque within the system limits may be obtained.

For governor surge testing, switch Ai is open and switch B1 is selectively opened and closed. Also switch AZ is opened and switch B2 closed. This applies a fixed low speed reference voltage in the tachometer generator loop which provides low speed regulation. Potentiometer 2? no longer controls speed. However, operation of the speed control drives potentiometer ZAP which weakens the dynamometer field which unloads the drive and permits higher speeds. When switch E1 is open the current limit effect is removed and there is no control of engine torque, but when switch B1 is closed the minimum absorbing torque loading is applied to that closing of Bl. in effect dumps the load and opening B1 in efiect picks it up. Thus a wide variation in loading of the test engine is available by this control to test the dynamic characteristics of the governor in regulating the speed of the test engine.

In practice with zero armature current the tap of potentiometer IP is adjusted so that the potential of circuit 149 is equal to the potential of point It between potentiometers 41 and SP. If the maximum absorbing current control at potentiometer 4P is set at its minimum value which corresponds to movement of the tap of potentiometer 4P to point N9, the voltage drop across the tube section dTUl is zero. Any increase in dynamometer armature current in the absor ing direction will then cause this tube section to conduct and override any signal to the amplifier A, with the result that the current in the armature circuit is held to approximately zero. As the tap of potentiometer i? is moved in the direction towards circuit 1&3, the positive bias on the cathode of tube section 4TU1 is increased, which increases the negative bias on this tube. Therefore no voltage will appear across circuits 149 to .12 until the current in the absorbing direction reaches a value that will give a voltage change equal to and exceeding the negative bias voltage on tube section 4TH Thus the voltage between the tap of potentiometer 4P and point 109 determines the maximum absorbing current.

When the armature current is in the motoring direction, the voltage across circuits 149 to 119 will decrease. As this voltage decreases, it tends to make the voltage across the other tube section dTUZ more positive. The negative bias on this latter tube section corresponds to the voltage between the tap of potentiometer SP and point Therefore the tube section 4TU2 conducts when the voltage across the circuits 1:29 to 119 decreases in an amount sufiicient to overcome the negative bias. When this second tube section conducts it will apply a voltage across circuits 145 and 112 which will override any signal therein and will limit the armature current in the motoring direction to the value set by the potentiometer 5?.

As will be seen by reference to Figs. 2a and 2b, the circuits i 39 and 11?. are connected across a potentiometer i i-P, which constitutes one input circuit to the double triode tube llTU of the amplifier A. In this circuit a signal limiter is provided to limit the voltage across conductors M9 to 112 due to the speed si nals which appear therein so that the current limit circuits have a smaller voltage to overcome, resulting in a more constant current characteristic. This limiter circuit includes resistors 17R, 21R, 38R and 39R, and a pair of blocking rectifiers BRl and SR2. This limiter circuit is connected across potentiometer i4? and resistor 17R and is supplied with a supply of direct current which is poled in opposition to blocking rectifiers BR and BRZ. This blocking voltage is selected of a value corresponding to the limit of signal voltage which is to be permitted to appear across tile potentiometer MP. The signal voltage is so poled as to pass through the blocking rectificrs BRl and BRZ selectively, depending upon its instant polarity whenever its magnitude exceeds the magnitude of the blocking bias on the rectifiers.

The voltage amplifier A which controls the generator field rectifier GPR comprises two stages of voltage plification represented in double triodes llTU and IZTU respectively. The output of the first stage is the output of a coupling transformer MT, and power for the plate supply of this tube is provided by a secondary winding 411% of a transformer 4T having a primary winding TP. Primary winding 4T1 is connected to conductors 425 and 560 connected to a supply transformer 181 by contacts 1M1 of a contactor IM. A predetermined portion of the voltage of the secondary winding 4TS2 is connected between a midpoint of the primary winding IOTP of transformer NT and to a common point 100 in the circuit including resistor 51R and potentiometer 151 for the cathodes of the two tube sections llTUl and 1G 11TU2. The primary Winding lllTP has its respective ends connected to the respective plates of the tube sections 11TU1 and 11TU2.

When the grids of the respective tube sections of the first stage are at the same potential, each section conducts an equal amount of current. Thus the current from X to Y in lilTP will be equal to the current from X to Z in IOTP. Since these ampere turns are in opposition, the net fiuX in the core of tarnsformer will be zero. This will result in zero voltage across the secondary winding lfiTS from Y1 to Z1.

if the grid of the first section llTUl should be at a higher potential than the grid of tube section llTUZ, the current in the primary winding of the coupling transformer from X to Y will be greater than the current from .f to Z. This will result in a net flux in the core of transformer iii? and will produce an A. C. voltage ap pearing across the secondary winding terminals Yi to 2?. The polarity of tris A. C. voltage across the secondary winding of transformer WT will be such as to be in phase with the A. C. voltage supplying the second stage from 1-11 to H2. Since the voltage Y1 to Xi on the secondary winding of tarnsformer is in phase with the anode voltage to the second stage and the voltage Z1 to X1 is out of phase with the anode voltage, then tube section TZTUT. will conduct more current than tube section IZTUZ, producing a greater current throu h resistor sea than is produced through resistor Consequently the output of the voltage amplifier measured between circuits Z li and 149 will be such that circuit 241 will be negative with respect to circuit 349.

If on the other hand the potential of the grid of 11TU1 is made more negative than the grid of tube 11TU2, the voltage at the secondary ifiTS of the coupling transformer ldT will be of opposite phase and the ouipr' of the voltage transformer will be of such polarity as to cause tube section IZTUZ to conduct more current than tube section 12TU1, making circuit 241 positive with respect to circuit 149.

Potentiometer 14F across which all of the control voltages are combined for speed, torque, slope and current limiting purposes is a sensitivity control and adjustment of its tap determines how much of the input signal coming from the above named sources is to be used. Potentiometer 15?, the tap of which is common to the cathode circuits of both tube sections llTUl and HTUZ, is a balance control and is used to adjust the output of the voltage amplifier to the proper value with zero input signal.

Since all of the input signals are combined in potentiometer 14P which controls tube section 1.1T U1 of the first stage of amplification, the tube section H UZ of this first stage is used for feedback control, and to this end has applied thereto a feedback signal or antihunt signal proportional to the rate of change of generator field current, which is applied in such a manner as oppose the changing input signal. This serves to stabilize the system and to prevent oscillation.

This is accomplished by connecting a resistor Still in series in the field circuit of the generator regulating field GRF. The voltage developed across resistor which is proportional to the generator field current. is difierentiated by means of a capacitor 24C which is connected in series with the potentiometer 12? across the resistor 38R. The voltage appearing across the potentiometer 12? is therefore proportional to the rate of change of voltage across the resistor 83R. The setting of the tap of potentiometer 12P determines the magnitude of the feedback signal which is applied to the grid of tube section TFLTUZ. If desired, a filter circuit may be employed to eliminate the generator field current ripple frequency in the grid circuit of tube lllTUl.

The generator field rectifier which is the power supply for the generator regulating field GR? is a three-phase rectifier comprising three gas-filled grid controlled tubes 13TU, 14TU and 15TU. These tubes are respectively provided with alternating current plate voltage from a three-phase transformer, the respective Y-connected secondary windings of which are connected to the respective plate circuits of the three rectifier tubes. The cathode circuits of these tubes are connected to a common circuit 149 and the generator regulating field circuit is completed through resistor 88R and the generator regulating field back to the common terminal of the i-connected secondary winding system of the three-phase transformer MT. The output voltage of this generator field rectifier circuit is determined by the time at which each grid is triggered with respect to the anode voltage during any particular positive half cycle of anode alternating current. It the grid is triggered earlier in the half cycle the output voltage will be high because the tube will conduct over a longer period of the positive half cycle of alternating current. As the time of firing is retarded the average output voltage becomes less.

The triggering voltage on each grid is the sum of a fixed alternating current voltage and a direct current voltage which is the output of the voltage amplifier. The alternating current component for each grid is derived from respective voltage divider circuits VDL VDZ and V133, and the respective voltages are applied to the rectifier grids by means of coupling capacitors 32C, 33C and 34C which connect the respective alternating current voltage divider circuits to respective direct current voltage divider circuits W34, VDS and VD6.

The alternating current voitages are obtained in each case from a transformer secondary phase which follows the phase voltage of the plate for that particular tube. This A. C. component lags the anode voltage on its particular tube by approximately 120". Therefore, when the output voltage from the voltage amplifier is zero, the output of the rectifier will be that corresponding to triggering of the respective rectifier tubes at approximately 120 on the anode cycle. As the output voltage from the voltage amplifier is increased, this direct current component is added to the alternating component at the respective grids of the gas filled rectifiers. This combination is such that earlier firing of each gas filled rectifier occurs and consequently higher rectifier output is obtained. When the polarity of the direct current component is reversed the angle of firing of the respective tubes is retarded and the output decreases. Therefore, when circuit 241 is positive with respect to circuit 149, the output of the generator field rectifier system is increased, and when circuit 241 is negative with respect to circuit 1 3, the output of the generator field rectifier is decreased. 7

The dynarnometer field control rectifier includes a three-phase rectifier supply supplying the AC excitation for the dynamometer field DF, and includes a control circuit comprising a triode llfiTU connected as a diode for controlling the output of the rectifier. The arrangement of this rectifier DFR is similar to that for the generator field supply. It functions in eifect as a low gain regulator which regulates the field current of the dynaniometer field. The regulating signal is the voltage drop across a resistor 129R which is connected in series in the dynamometer field circuit and the reference voltage is the voltage between circuits 375 and 371. The control circuit includes a regulated direct current supply,

here indicated by the positive and negative terminals across the potentiometer 17?, which maintains the voltage across conductors 311 and 371 at a suitable constant voltage. The details of this voltage regulator circuit are conventional and are therefore not shown. Potentiomcter ZAP which is connected in series with calibrating potentiometers 221 and 211 across the regulated supply of voltage is mechanically ganged with the speed potentiometer 2F, and its purpose as described in connection with Fig. 1 is to weaken the dynamometer field above base speed. Potentiometer SAP which is connected between the tap of potentiometer ZAP and a tap of potentiometer ZtlP, which latter is connected in parallel with potentiometer ZIP, is mechanically coupled to the speed slope control potentiometer 3P, and its purpose is to further weaken the field as required by adjustment of potentiometer SF in order to obtain the required rising speed characteristic over a wide speed range.

If the speed slope control potentiometer 3P is set at zero, point 319, that is the tap on potentiometer BAP, will be connected directly to the tap on potentiometer ZAP, that is, point 320. If the tap of potentiometer 17? is adjusted so that its potential is equal to the potential of the tap of potentiometer ZAP when the speed control is at base speed, then the voltage across the tube lfiTU will be negative when the speed control is at zero. With the speed control at zero, tube ISTU will not conduct so there will be no voltage drop across resistor 1636K. Consequently the reference voltage will be the voltage be tween the tap of potentiometer l7? and circuit 371, and the current will adjust itself until the voltage across resistor 129R is equal to this voltage, representing full excitation.

As the tap of speed control potentiometer 2P is advanced in the direction of increasing speed and its volt age increased, the potential of the tap of potentiometer ZAP will approach the potential of the tap of potentiometer 17F, and will be equal to it at base speed. During this entire travel of the tap of potentiometer ZAP, the voltage across tube 18TU will be negative and consequently the same current will flow through the dynamometer field, because no change in tube conduction has yet occurred.

As the speed control is increased above base speed,

the potential of the tap of potentiometer ZAP goes below the potential of the tap of potentiometer 17?, which puts a positive voltage on the tube ISTU. This will result in a voltage drop across resistor 196R by reason of conduction of the diode ISTU. The voltage across resistor 106R subtracts from the previous reference voltage, and therefore the voltage across resistor 129R must fall in order to restore equilibrium. This condition is realized through a change in grid potential on the dynarnometer field rectifiers 19TU, 2iiTU and 21'I'U, as a result of the change in the direct current bias on each due to conduction of tube section 18TU which causes a drop in voltage in circuit 375 which supplies the direct current voltage dividers for the respective dynarnometer field rectifier tubes. If desired, sections of the potentiometer ZAP over that range in which it causes conduction of the tube 18TU may be shunted by suitable resistor arrangements which introduce a degree of non-linearity required to approximate the constant horsepower characteristics of the dynamometer above base speed. For any particular setting of field current for the dynamometer, further reductions may be realized by adjustment of the speed slope control potentiometer 3? which drives potentiometer tap 3A1 in a sense to increase the speed slope characteristic. Since potentiometer 3A? is slaved to the tap voltage of potentiometer ZAP, it will be appreciated that its efiect on slope control will be limited to speeds above base speeds.

The potentiometer IMP constitutes essentially element of a diagonal of a bridge circuit having for one pair of adjacent legs the tapped sections of potentiometer 2?, the remaining adjacent legs of which include, respectively, potentiometer 9? in series with resistor 36R and series resistors 31R and 35R. The output diagonals of the bridge circuit are represented in the tap of poten tiorneter 2F and point 156, the bridge being energized by the regulated voltage supply between circuits and 135. The output diagonal of this bridge circuit includes the tap of potentiometer 2P, a switch AZ which is normally closed, excepting when governor speed control tests are to be made when switch B2 is closed in its place, a resistor 34R, a resistor 37R across which the 36119-1 eter generator voltage is applied, the potentiometer 14? at the amplifier input, resistors 17R and HR in series,

the tapped portion of potentiometer 3?, the torque signal output resistor 20R to terminal 156. The regulating system is set up in such a manner that the input voltage to the amplifier through circuits 149 and 112 connected across potentiometer MP is always essentially zero. This means that the summation of all of the input signals to this circuit will be essentially zero at dynamic equilibrium.

if the speed slope potentiometer 3P is set at Zero, that is, the tap on potentiometer 3P is set at its lower terminal so that its potential corresponds to the potential of circuit 1135, then the input voltage to the amplifier across potentiometer M? will be the sum of the voltage drops across resistor 37R from terminal 170 to circuit 135. That is, the tachometer voltage will be compared only with the voltage rep across the tapped portion of potentiometer 2?. Hence the speed of the dynamometer will be regulated so as to maintain the voltage across resistor 37R equal to the setting of the speed control potentiometer.

"i'o make the voltage between circuits 149 and 112 zero so that no voltage appears across potentiometer 14?, the voltage across resistor 37R must be such that terminal 166 is positive with respect to 149. When the dynamometer is operating in the load absorbing mode, the voltage drop across potentiometer 3P will be of such polarity that circuit 135 will be positive with respect to circuit 125.

if the slope control is increased from Zero, the voltage 135 to 134 at the tap of potentiometer 3P will be included in the input to the amplifier. Since this voltage is in series aiding relation with the reference voltage, the tachometer voltage will have to be higher for higher loads than for lower loads, because at the higher loads the current cue will be higher and consequently the torque signal will be higher. In this manner the slope control is obtained, that is, for a given speed setting if the load is increased the speed will be increased by reason of the addition of this voltage.

If at any time in the operation of the regulator the current should exceed the value set by the maximum current settings at potentiometers 4? and SP, the voltage input to the amplifier will be controlled exclusively by the current limit circuit, with the result that the output of the regulator loop will be such as to maintain this current limit regardless of the other signals.

if the dynamometer is operated in the opposite direction of rotation, the tachometer connections are reversed at switches F1, F2 and R1, R2 so that the same polarity holds for both directions of rotation.

For emergency stop operation the reference voltage is quickly changed to zero, and at the same time the current limit is recalibrated to its maximum value. This is accomplished by means of emergency stop switch EMS2 which shunts the tapped portion of potentiometer 2P, and by switch EMS which shunts potentiometer 4P in the current limit circuit applying maximum negative bias to the absorbing current limit tube section 4TU1. in this manner the dynamometer speed is forced to zero at a current equal to the maximum rated current of the machine.

in the circuits herein described it will be appreciated that numerous control and protectivedevices have been eliminated from the system in the interest of drawing simplicity. However, sufiicient control has been shown to illustrate the automatic control aspects of this system.

in order to start the motor generator set comprising the induction motor I and generator G, the operator depresses the Start pushbutton, which closes contacts STE and 5T2. This completes a circuit from alternating current supply conductor 45% through the closed contacts SP1 of the Stop pushbutton through the closed contacts T1 of the Start pushbutton through the coil of contactor 1M and back to conductor 46% representing the other side of the alternating current supply circuit from transformer 131". When contactor 1M closes, it connects the siternating current induction motor to line conductors 1L1, 1L2 and 1L3 through its contacts 1M4, 1M5 and 2M6. At the same time 2 holding circ for the coil of contactor 1M which shunts the contac i of the Start puslibutton is formed by closed. contacts EMZ. Qlosure of. contacts 1M1 of contactor 1M completes an energizing circuit for conductor 425 which energizes both coils of a time delay relay TD, one coil of which is energized through the normally closed contacts TDI. of this relay. After predetermined time interval the time delay relay picks up. When it picks up its contacts TDZ close, completing an energizing circuit across conductors 425 and 460 which includes the coil of the contactor 2M. contactor 2M at its contacts 2M3, 2M4 and 2M5 connects the primary windings of three-phase transformers MT and 15T for rator field rectifier dynamometer field rectifier cuits respectively to the supply of alternating current represented in conductors 1L1, 1L2 and 1L3. An auxiliary set of contacts 2M1 operated by contactor 2M completes a holding circuit for the coil of this contactor across conductors 525 and 466'. Provision may be made for opening the contactor 2M by means of a toggle operated circuit breaker, not shown, so that tests and adjuston the electronic regulator circuits may be made without having to go through the time delay period required by the time delay relay before checking the circuits. However, on each initial start-up of the equipment with this arrangement, the time delay will be efiective.

Now that the auxiliary circuits have been established the operator may start the dynamometer. in order to start the dynamometer the speed control potentiometer 2? must be in its zero speed position. This potentiomstar, as will be noted from mechanical connections provided, controls set of contacts designated 2P1 which are closed in the zero speed position of potentiometer 21. When the Start pushbutton is depressed, contacts 8T2 are closed. Contacts ST?- in practice are controlled from a separate dyna nometer Start pushbutton but again in the interest of simplicity, are shown combined with the Start pushbutton described. An energizing circuit is therefore completed for the coil of the low voltage relay LV beginning at the contacts VRXZ connected to a positive supply or" direct current and including the contacts SP2, the now closed contacts 8T2, the closed contacts 2P1, either set of contacts PR2 or R112, depending upon the position of the selector switch SW which controls the forward and reverse relays PR and RR, either set of contacts of switch .tSW of selector switch SW, closed contacts 1M3, closed contacts 2M2, and the closed contacts VRI of the voltage relay VR through the coil of the low voltage relay LV to the negative side of the direct current supply. The low voltage relay now picks up, closing its contacts LVl, 1V2, and U14 and opening contact LV3. Contact LVi connects the coil of contactor M through circuit 21 across a supply of direct current. Energization of contactor M closes contacts M1 in the armature circuit of the dynamometer applying the voltage of the generator thereto. Contacts LVd of the low voltage relay shunt the Start pushbutton contacts ST2 and the speed potentiometer contacts 2P1 to form a holding circuit for the coil or". the low voltage relay which is independent of the position of the named contacts. In addition, contact LVZ is closed and contact LV3 is opened. Contact LV3, which is normally closed, in conjunction with emergency stop contacts EMSd shunts the output of the two-stage amplifier A from the direct current voltage divider circuits, closing the direct current grid circuits of the gas filled rectifiers BTU, MTU and lS'l'U in a loop including a resistor 53R having a sufiiciently high ohmic value that with the occurrence of grid current tiow in the grid circuits of the gas filled rectifiers during conduction, a sufiiciently high voltage drop occurs across resistor 58R to bias the respective gas filled rectifiers to complete cutoff. Hence during the starting operation the generator 15 field rectifier circuit output is zero due to the self-biasing action at resistor 58R.

When contacts LV2 close, resistor 58R is shunted from the grid circuits of the gas filled rectifiers, and contacts LVS upon opening open the closed grid circuit loop decribed above. Thus the regulator may begin to operate.

Up to this point the regulator has been regulating for zero voltage out of the generator. It now becomes a speed regulator taking its one from the speed potentiometer 2P and the dynamometer-driven tachometer generator T.

An overvoltage relay VR is provided to protect the system against overvoltage. The coil system of this relay is connected through conductors DP and DN across the dynamometer armature circuit. Upon the occurrence of suficient voltage in the circuit, voltage relay VR picks up, opening its normally closed contacts VRi which deenergizes the low voltage relay. When the low voltage relay 'is deenergized cont-acts LVZ open and contacts LV3 close,

which closes the gas filled rectifier direct current grid circuit loop including the resistor 58R therein, quickly biasing the output of the generator field rectifier to zero as described.

For emergency stop operation the emergency stop contacts are actuated. Closure of emergency stop contacts EMSS completes an energizing circuit for Voltage relay VRX, the windings of which are connected across the dynamometer armature circuit by switch EMS5. Energization of voltage relay VRX closes contacts VRXl which shunt the low voltage relay contacts LVl normally used to maintain the coil of contactor M energized. As a consequence the armature circuit of the dynamometer remains connected to that of the generator. Emergency stop contacts EMS3 shunt low voltage relay contacts LV2 and close, shunting the resistor 55R from the grid circuit of the gas filled rectificrs of the generator field rectifier. Opening of emergency switch contacts EMSd prevents closing of the rectifier grid circuit loop, should low voltage contacts LV3 close during the emergency stop operation.

Closure of emergency stop contacts EMSZ shunts the speed reference voltage from the input to the amplifier A. As a consequence the system is regulated to zero speed by the negative biasing effect on the amplifier of the tachometer generator T, the voltage of which drops with the speed of the dynamometer and contacts EMS} recalibrate the current limit for maximum absorbing current limit control by shunting potentiometer 4P and applying maximum negative bias to the tube section iTUl.

In some tests such as chassis tests where wind loading must be simulated, the torque must vary as the square of the speed. To accomplish this two direct current tachometer generators may be employed. Both are coupled to the dynamometer to be driven thereby. An arrangement for producing a voltage proportional to the square of the speed is illustrated in Fig. 9. Here tachometers T1 and T2 are connected to the dynamometer. The output of tachometer generator T1 is connected to the field winding T2F of tachometer generator T2. The output of tachometer generator T2 is therefore proportional to the square of the dynamometer speed. Tachometer T2 may be connected across resistor 37R as is tachometer T in Fig. 2A. The speed squared voltage thus obtained is compared to a current signal from the slope control determined by the setting of potentiometer 3P. This results in a torque proportional to the square of the speed. A constant torque can be added to or subtracted from this characteristic by including a fixed signal. The rising torque characteristic thus obtained is approximately parabolic.

Another arrangement whereby the speed squared signal may be obtained is illustrated in Fig. 10. In this an A. C. tachometer generator is employed. Such a generator may be provided with fixed excitation through the medium of a constantly excited winding for producing 16 a magnetic field or it may involve a simple permanen magnet rotor arrangement in which the rotor is spot magnetized to have at least two poles, one north pole and one south pole. The output of such a generator is a voltage which varies with the speed of rotation, and the frequency of the output voltage is a function of the speed of rotation. The speed squared voltage is produced in a simple resistor-capacitor network comprising a resistor 9MP. and a capacitor C connected in series across the output circuit of the A. C. tachometer generator. For a particular speed range, for example speeds between zero and 6,000 revolutions per minute, which are the usual speeds encountered in this type of testing, it is possible to relate the capacitor impedance to the resistor impedance over the frequency range such that the voltage across the resistor is approximately proportional to the square of the speed of rotation of the dynamometer. For this speed range it has been found that the capacitor impedance should be made approximately five times as high as the impedance of the resistor at maximum operating speed. The voltage developed across resistor WR may be rectified and if necessary filtered and applied across a resistor such as 37R in the input circuit to the amplifier A. As in the discussion with regard to Fig. 9, the slope control is introduced at potentiometer 3?, the combined voltages giving a rising torque characteristic which varies as the square of the speed.

One of the most common uses of the dynamometer is the testing of internal combustion engines. In this test thespeed torque curve of the engine is obtained. Also data on such items as optimum spark setting, carburetor adiustment and fuel consumption is obtainable. Engine variables such as water, oil and carburetor temperatures,

' il and exhaust pressures are held at fixed values during these tests. These tests are performed with the constant speed characteristic of the dynamometer. In these tests,

as described in detail in connection with Figs. 2a, 2b, and 2c, the dynamometer is started and brought up to some low speed with the speed control. Under these conditions the dynamometer is motoring as it cranks the engine. When the fuel and ignition are turned on and the engine starts, the dynamometer becomes a generator and absorbs the engine power at speeds determined by the setting of the dynamometer speed control. After all data is taken at full throttle, the fuel and ignition are cut off, causing the dynamometer to motor but at the same speed as under full throttle due to the control adored by the speed control of the dynamometer system. The torque reading then is the frictional torque at that operating speed. The speed is then increased with the speed con trol and the test repeated. By this means a family of curves is obtained indicating engine performance over the full speed range.

in testing the governor of the test engine, the dynamometer is operated with its constant torque characteristic in the absorbing mode of operation. Since the speed of the engine is fixed by the governor, the speed control of the dynamometer is at a low value determined by the drop across resistor 35R, it being recalled that in this test switch A2 is opened and switch B2 closed. When the maximum absorbing load limit established at potentiometer 41 is reduced to some value below the maximum torque available from the engine, the engine accelerates with constant torque determined by the dynamometer loading until the engine governor limits the speed. The

en ine then remains at that speed and torque. As the maximum absorbing load limit is changed through adjustment of potentiometer 4P, the torque changes While the speed of operation is determined by the engine governor. The load can be changed from maximum engine torque to zero torque, giving the complete behavior of the governor under various load conditions.

A mechanical failure such as a broken shaft can be simulated by means of switch B1 in the current limit reference circuit. For this test the switch A1 is opened and the switch B1 is used to simulate the mechanical condition. When switch B1 is closed the system is regulated for minimum current limit and, hence, minimum load torque. When the switch is opened the torque limiting is completely removed and the torque rises. Thus the effect of a mechanical failure is simulated by closing of switch B1. By repeating this test with various governor settings a family of curves is obtained, giving governor surge performance at various speeds.

In testing transmissions the information required includes wear under specified speeds and loads, eiliclency and life. For automatic transmissions, additional infor mation, such as output speed, torque and slippage under various load conditions is important. For this test two dynamometers such as herein disclosed are employed. The input dynamometer connected to the input shaft of the transmission is operated with a constant speed characteristic, while the output dynamometer fixes the load by operating with a substantially constant torque characteristic. In testing the transmission characteristics of automatic transmissions, the input speed is fixed and the output torque is increased until the input torque corre sponds to the maximum engine torque developed at that speed. The acceleration characteristic of the transmission can also be determined by coupling a calibrated inertia to the output of the transmission.

In testing axles the information usually desired includes such items as wear under various speeds and loads, efficiency, life and deflections of the various members of the assembly. This test requires three dynamometer systems, one input and two output. The input dynamometer operates at constant speed while the two output dynamometers operate at constant load. By adjusting the loads on the output shafts and the speed on the input shaft, a variety of output speeds and loads can be ob tained for testing wear, life and other factors. By setting the input dynamometer speed to a very low value, through adjustment of potentiometer 2P and loading the output connections, the deflections in the various elements of the axle assembly can be measured from noload to the rated load of the axle.

Chassis tests involve testing the complete automobile. Thistest is designed to collect data, in a laboratory, where road testing waspreviously required. The equipment for this test involves a large rotating cylinder to which the dynamometer is connected. The rear wheels of the car ride on this cylinder or roll. The inertia of this rotating system is adjustable to correspond to the inertia of the car under test. The front of the car is supplied with a flow of air to provide cooling corresponding to the motion ofthe car at a given speed. -In this test the dynamometer is operated in its load absorbing mode. With this arrangement the overall performance of the car can be obtained by conducting a test similar to the engine test.

For acceleration testing, a load in addition to the car inertia must be included. This corresponds to the wind resistance. To simulate this the torque proportional to the speed squared characteristic of the dynamometer is used, as discussed in connection with Figs. 9 and 10. To simulate a car accelerating uphill the speed torque curve is displaced by a fixed amount corresponding to the steepness of the hill. If downhill acceleration is desired, the speed torque curve is displaced in the opposite direction as discussed hereinbefore.

It will'be appreciated from the foregoing detailed considerations of the system herein disclosed that various modifications of this invention may be made, both as to its details and as to the organization of such details, without departing from the spirit and scope hereof. For example, the unique arrangement for obtaining current limiting and constant torque control by the expedient of a single magnetic amplifier biased to the midpoint of .its characteristic, may be replaced with an arrangement involving two magnetic amplifiers respectively biased into their minimum output ranges, and arranged to respond to opposite polarities of motor armature current, to selectively control respective current limiting channels, for motoring and absorbing operation, involving respective diode sections such as 4TU2 and 4TU1. Such an arrangement, however, is more complicated than that herein illustrated. Additionally, under some circum stances, in applications other than that herein discussed, it may be desirable to operate a rectifier arrangement such as the generator field rectifier between maximum and minimum output conditions. This can easily be accomplished with the system disclosed by reducing the ohmic value of resistor 58R to such level that grid current flow therethrough will not bias the gas filled rectifiers of the rectifier circuit to cutoff. Under these conditions operation of a switching arrangement such as the emergency stop switches EMS3 and EMS4 will alternately shunt and insert resistor 58R in the direct current grid circuit loop to alternately switch the rectifier between maximum and minimum output levels. Such an arrangement is desirable in printing press or paper mill controls, for instance, wherein it is necessary to inch the roll system for the purpose of threading a new paper web through the press. Other obvious variations in the system will be readily apparent to those skilled in the art.

Accordingly it is intended that the foregoing disclosure and the showings made in the drawings shall be considered only as illustrative of the principles of this invention and not construed in a limiting sense.

We claim as our invention:

1. A control for a direct current motor comprising, a current signal circuit responsive to motor current for producing a voltage which increases in reponse to increasing armature current of one polarity and which decreases in response to increasing armature current of a reverse polarity, a pair of oppositely poled polarized circuit's, circuit means connected with each polarized circuit for biasing each polarized circuit, circuit means connecting said current signal circuit to both polarized circuits, and means responsive to the output of said polarized circuits for controlling said motor.

,2. A current limit control for a direct current motor comprising, a current signal circuit adapted for connection with the armature circuit of said motor to respond to motor armature current, said current signal circuit producing an output voltage which increases with increasing armature current of one polarity and which decreases with increasing armature current of a reversed polarity, a pair of oppositely poled parallel connected polarized circuits, circuit means connected with each polarized circuit for applying a negative biasing voltage thereto, circuit means connecting said current signal circuit to said polarized circuits to apply said output voltage thereto, and electrical means responsive to conduction of said polarized circuits for controlling said motor.

3. A current limit control for a direct current motor comprising, a saturable core device having a bias winding biasing said device to a given point along its linear characteristic, a control winding for biasing said device above and below said point and connected to the armature circuit of said motor, and an output winding; 21 pair of oppositely poled parallel connected polarized electrical circuits, circuit means connecting said output winding to said polarized circuits, and motor control means responsive to conduction of said polarized circuits for controlling said motor.

4. A current limit control for a direct current motor comprising, a saturable core device having a polarized output circuit, a bias winding circuit biasing said device to a given level of output and a control winding adapted for connection to the armature circuit of said motor; a pair of negatively biased parallel connected polarized circuits, circuit means connecting said polarized output circuit to said parallel connected polarized circuits, and

ray 185,367

I circuits for controlling said motor.

5. A variable voltage control for a direct current motor comprising, a variable voltage motor supply circuit having an input circuit, a magnetic amplifier having a polarized output circuit, a bias winding circuit biasing said amplifier to a given point on its output characteristic and a control winding circuit adapted for connection to the armature circuit of said motor for biasing said amplifier above said point with increasing armature currents of one polarity and for biasing said amplifier below said point with increasing armature currents of reversed polarity, a pair of parallel connected oppositely poled rectifiers, a supply of biasing voltage connected with each rectifier and negatively biasing each rectifier, circuit means connecting said polarized output circuit of said magnetic amplifier with said pair of rectifiers,

and circuit means connecting said pair of rectifier circuits to said input circuit of said variable voltage supply circuit.

6. A variable voltage control for a direct current motor comprising, a variable Voltage motor supply circuit having an input circuit, a magnetic amplifier having a polarized output circuit, a bias winding circuit biasing said amplifier to a given point on its output characteristic and a control winding circuit adapted for connection to the armature circuit of said motor for biasing said amplifier above said point with increasing armature currents of one polarity and for biasing said amplifier below said point with increasing armature currents of reversed polarity, a supply of reference voltage, a first potentiometer connected across said supply of reference voltage and having an adjustable tap, a pair of biasing potentiometers connected in series across said supply of reference voltage and each having an adjustable tap, a pair of diodes connected in parallel opposed relation, the cathode of one being connected to the tap of one biasing potentiometer and the anode of the other being connectedto the tap of the other biasing potentiometer, said polarized output circuit of said magnetic amplifier being connected to the tap of said first potentiometer, and circuit means connecting saiddiodes to said input circuit of-said variable voltage motor supply circuit;

7. A controlsystem for controlling a directcurrent motor comprising, a variable voltage device having an output circuitradapted for connection to the armature V Winding of said motor and having an input control-circuit,

a' reference voltage circuit, electrical means connected with said motor for producing a voltage proportional to motor speed, circuit means differentially combining said reference and said speed voltage in said input control circuit, current responsive circuit means connected with the armature winding of said motor for producing a voltage proportional to armature load current, a second reference voltage circuit, an impedance device connecting said current responsive circuit means and said second reference voltage circuit in differential, and circuit means connecting said impedance device in said input control circuit.

8. A control system for controlling a direct current motor comprising, a variable voltage device having an input circuit and an output circuit adapted for connection to the armature winding of said motor, means for pro ducing a speed reference voltage, means responsive to motor speed for producing a speed indicating voltage, circuit means difierentially combining said speed voltage and said speed reference voltage in said input circuit, means responsive to motor armature current for producing a torque indicating voltage, means for producing a torque reference voltage, and circuit means differentially combining said torque reference voltage and said torque indicating voltage in said input circuit.

9. A control system for controlling a direct current motor comprising, a variable voltage device having an input circuit and an output circuit adapted for connection to the armature winding of said motor, means for producing a speed reference voltage, means responsive to 'motor speed for producing a speed indicating voltage,

circuit means differentially combining said speed voltage and said speed reference voltage in said input circuit, means responsive to'motor armature current for producing a load current indicating voltage, means responsive to said load current indicating voltage for producing a voltage indicative of motor torque, means for produc ing a motor torque reference voltage, circuit means dif ferentially combining said torque indicating voltage and said torque reterence voltage in said input circuit, impedance means responsive to said load current indicating voltage, a pair of oppositely poled, negatively biased, parallel connected rectifier circuits, circuit means connecting said impedance means in series with said parallel connected rectifiers, and circuit means conductively connecting said rectifiers to said input circuit.

10. A control system for controlling a direct current motor comprising, a variable voltage device having an input circuit and an output circuit adapted for connection to the armature winding of said motor, said input circuit comprising an impedance device, means for pro ducing a speed reference voltage, means connected with said motor for producing a motor speed voltage, circuit means difierentialy combining said speed reference voltage and said speed voltage across said impedance device, and a limiter circuit connected across said impedance device and becoming conductive with the occurrence of a predetermined voltage across said impedance device.

11. A control system for controlling a direct current motor comprisnig, a variable voltage device having an input circuit and an output circuit connected to the armature Winding of said motor, said input circuit comprising an impedance device, condition responsive means connected to said motor for producing a voltage corresponding to an operating characteristic of said motor, a source of adjustable reference voltage, circuit means differentially connecting said condition responsive means and said source of reference voltage across said impedance device, and a limiter circuit connected across said impedance device and becoming conductive with the occurrence of a predetermined voltage across said impedance device.

12. A control system for controlling a direct current motor comprising, a variable voltage device having an input circuit and an output circuit connected to the annature winding of said motor, said input circuit comprising an impedance device, condition responsive means connected to said motor for producing a voltage corresponding to an operating characteristic of said motor, a source of adjustable reference voltage, circuit means differentially connecting said condition responsive means and said source of reference voltage across said impedance device, and a limiter circuit comprising negatively'biased rectifier means connected across said impedance device and becoming conductive upon the occurrence of a voltage across said impedance device exceeding said negative bias.

13. A control system for controling a direct current motor comprising, a variable voltage device having an input circuit and an output circuit connected to the armature winding of said motor, said input circuit comprising an impedance device, condition responsive means connected to said motor for producing a voltage corresponding to an operating characteristic of. said motor, a source of adjustable reference voltage, circuit means differentially connecting said condition responsive means and said source of reference voltage across said impedance device, a limiter circuit comprising a pair of parallel connected oppositely poled rectifiers connected across said impedance device, and means for applying a negative bias voltage to each rectifier.

14. A control for controlling a direct current motor comprising, a variable voltage device having an input circuit and having an output circuit connected to the armature winding of said motor, said input circuit comprising an impedance device, a current responsive circuit connected to the armature winding of said motor, a rectifier, means for applying a negative bias voltage to said rectifier, means connecting said current responsive circuit to said rectifier to apply a positive voltage thereto which when greater than said negative bias voltage causes said rectifier to conduct, circuit means connecting said rectifier and said current responsive means across said impedance device, a negatively biased rectifier circuit con nected across said impedance device to conduct when the voltage of said impedance device exceeds said negative bias of said last named rectifier, and circuit means connected with said impedance device for applying a control voltage thereto.

15. A control for controlling a direct current motor comprising, a variable voltage device having an input circuit and having an output circuit connected to the armature winding of said motor, a current responsive circuit connected to the armature winding of said motor and producing an output voltage which increases with increasing armature current of one polarity and which decreases with increasing armature current of a reversed polarity, a pair of parallel connected, oppositely poled, negatively biased rectifiers; means for establishing a reference point of potential between the negative bias voltages of said rectifiers, circuit means connecting said current responsive means in series with said parallel connected rectifiers, said voltage of said current responsive means causing one rectifier to conduct when increasing and reaching a value above said reference potential greater than the negative bias on said one rectifier and causing the other rectifier to conduct when decreasing and reaching a value below said reference potential greater than said negative bias on said other rectifier, and circuit means connecting said current responsive means and said parallel connected rectifiers to said input circuit.

16. A control for controlling a direct current motor comprising, a variable voltage device having an input circuit and having an output circuit connected to the armature winding of said motor, a current responsive circuit connected to the armature winding of said motor and producing an output voltage which increases with increasing armature current of one polarity and which decreases with increasing armature current of a reversed polarity, a pair of parallel connected, oppositely poled, negatively biased rectifiers; means for establishing a reference point of potential between the negative bias voltages of said rectifiers, circuit means connecting said current responsive means in series with said parallel connected rectifiers, said voltage of said current responsive means causing one rectifier to conduct when increasing and reaching a value above said reference potential greater than the negative bias on said one rectifier and causing the other rectifier to conduct when decreasing and reaching a value below said reference potential greater than said negative bias on said other rectifier, circuit means connecting said current responsive means and said parallel connected rectifiers to said input circuit, and a limiter circuit comprising a pair of oppositely poled, parallel connected, negatively biased rectifiers connected across said input circuit.

17. Dynamometer apparatus comprising, a direct current motor having an armature winding and a field winding and adapted for connection to a rotatable device to be tested for selective motoring and absorbing operation, amplifier means having an output circuit connected to said armature winding and having an input circuit, means for producing a speed reference voltage, means connected with said motor for producing a voltage indicative of motor speed, circuit means differentially combining said speed reference voltage and said speed indicating voltage in said input circuit, means responsive to motor armature current for producing a torque reference voltage, and circuit means differentially combining said torque indicating voltage and said torque reference voltage in said input circuit.

l8. Dynamometer apparatus comprising, a direct current motor having an armature winding and a field Winding and adapted for connection to a rotatable device for selective motoring and absorbing operation, amplifier means having an output circuit connected to said armature d. having an input circuit, means for producing a speed reference voltage, means connected with said motor for producing a voltage indicative of motor speed, circuit means difierentially combining said speed reference voltage and said speed indicating voltage in said input circuit, means responsive to motor armature current for producing a voltage indicative of motor torque, means for producing a torque reference voltage, circuit means differentially combining said torque indicating voltage and said torque reference voltage in said input circuit, and a pair of parallel connected, oppositely poled, negatively biased rectifiers connected across said input circuit.

19. Dynamometer apparatus comprising, a direct current motor having an armature winding and a field winding and adapted for connection to a rotatable device to be tested for selective motoring and absorbing operation, amplifier means having an output circuit connected to said armature winding and having an input circuit, means for producing a speed reference voltage, means connected with said motor for producing a voltage indicative of motor speed, circuit means differentially combining said speed reference voltage and said speed indicating voltage in said input circuit, means responsive to motor current for producing a voltage indicative of motor torque, means for producing a torque reference voltage, circuit means differentially combining said torque indicating voltage and said torque reference voltage in said input circuit, means responsive to motor current for producing a voltage indicative of motor current, a pair of negatively biased, parallel connected oppositely poled rectifiers, means connected with said rectifiers for establishing a reference voltage intermediate the negative biases thereon, s motor current indicating voltage increasing with increasing motor current during absorbing operation of said motor and decreasing with increasing motor current during motoring operation, and circuit means connecting said means responsive to motor current and said parallel connected rectifiers in a series circuit across said input circuit.

20. A direct current circuit for reversibly energizing an electrical device comprising, an electrical device, a direct current supply circuit, a control potentiometer connected across said supply circuit, said control potentiometer having an adjustable tap, a pair or" biasing potentiometers connected in series across said supply circuit, each biasing potentiometer having an adjustable tap, a pair of rectiers each having an anode and a cathode, a common circuit connecting the anode of one rectifier to th cathode of the other rectifier, the cathode of said one rectifier being connected to the adjustable tap of one biasing potentiometer, the anode of said other rectifier being connected to the adjustable tap of the other of said biasing potentiometer, a supply of adjustable direct current voltage, and circuit means connecting said electrical device and said supply of adjustable direct current voltage in series between said common circuit and said adjustable tap of said control potentiometer.

21. A direct current circuit for reversibly energizing an electrical device in dependence of variations of a variable direct current voltage above and below a given value comprising, a direct current energized electrical bridge circuit comprising a control potentiometer having an adjustable tap, the tapped portions of said control potentiometer forming adjacent legs of said bridge circuit, a pair of biasing potentiometers forming the remaining adjacent legs of said bridge circuit, each biasing potentiometer having an adjustable tap, an electrical device to be controlled, circuit means for producing a variable direct current voltage, and a circuit connecting said electrical device and said circuit means in series with the adjustable tap of said control potentiometer and having parallel oppositely poled rectifier branches connectedwith the respective taps of said bias potentiometers, said adjustable tap of said control potentiometer being so adjusted that for a' given value of direct current voltage of said circuit means the potential of the circuit point between said circuit means and said electrical device substantially equals the potential of the circuit point between said bias potentiometers.

22. An electrical circuit comprising, a direct current energized electrical bridge circuit including a tapped impedance device having tapped sections forming one pair of adjacent bridge legs and including a pair of impedance devices respectively forming the remaining adjacent bridge legs, an electrical device to be controlled, a variable supply of direct current voltage, a circuit connecting said electrical device and said variable voltage supply of direct current voltage in series with the tap of said first named impedance device and including a pair of oppositely poled parallel rectifier branches respectively connected at predetermined points on said pair of impedance devices.

23. A circuit for controlling the speed torque characteristic of a direct current electric motor comprising, an amplifier device having an output circuit connected to V 24 7 energize said motor and having an input circuit, a circuit for producing a motor speed reference voltage, circuit means connected to said motor for producing a voltage indicative of the instant speed of said motor, a circuit for producing a motor torque reference voltage, circuit means connected to said motor and responsive to motor current for producing a voltage indicative of instant motor torque, an impedance device differentially combining said torque reference voltage and said motor torque voltage, and a series circuit including said input circuit to said amplifier, differentially combining said speed reference voltage and said motor speed voltage and including a tapped portion of said impedance device.

24. A speed square control for a direct current motor comprising, a permanent magnet rotor alternating current generator having an output circuit and having said rotor mechanically connected to be driven by the motor, a capacitor and a resistor connected in series across said output circuit, the impedance of said capacitor for the highest generator frequency being approximately of the order of five times the impedance of said resistor.

References Cited in the file of this patent UNITED STATES PATENTS 2,021,753 Suits Nov. 19, 1935 2,301,689 Edwards et al Nov. 10, 1942 2,450,484 Palmer et a1. Oct. 5, 1948 2,632,139 Bloodworth Mar. 17, 1953

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