ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN ANN ARBOR PRELIMINARY SURVEY OF LITERATURE PERTINENT TO AUTOMOTIVE CLOCKS... COLWELL Project 2325 HURD LOCK AND MANUFACTURING COMPANY DETROIT, MICHIGAN January, 1955

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ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN TABLE OF CONTENTS Page OBJECT iii I. A BRIEF HISTORY OF CLOCKS 1 II. THE NATURE OF TIME 2 III. TE IDEAL CLOCK 3 IV. PRACTICAL CLOCKS A.s MAGNETICALLY IMPULSED, BALANCE-WHEEL CLOCK 6 B. OTHER TYPES OF TIME BASE 7 V. SUARY 8 VI, GENERAL RECOMMENDATIONS 9 VII. BIBLIOGRAPHY 10 FIGURES 11 ____________..ii~.._._...,ii

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN OBJECT The objective of this survey was to search literature on clocks and timing devices in general and to reconsider time-dependent phenomena as a basis for establishing a program for the development of a substantially new automotive clock} A cheek of library records indicated that there were no publications devoted specifically to automotive clocks. It is generally known, however, that all automotive clocks manufactured in quantity in the United States up to the present time have consisted of three types as follows: 1. manually wound, balance-wheel-controlled clocks, 2. electrically wound, balance-wheel-controlled clocks, and 3. electromagnetically impulsed, balance-wheel clocks. In the absence of specific useful publications directly concerned with automotive clocks, a general survey was made of publications devoted to timing devices in general. Such publications in addition to others pertinent to the problem are listed among the fifteen items of the bibliography at the end of the report. No specific citations are made to references in the bibliography since they were substantially descriptive except on the subject of accuracy of precision astronomical clocks. i-iii ~~

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN I. A BRIEF HISTORY OF CLOCKS Mankind has been aware of the time dependency of many natural phenomena for longer-than-recorded history, and the development of civilization has undoubtedly seen most of these utilized in one way or another to provide information on the elapse of time. Museums contain many examples of mankind.s efforts to harness time-dependent occurrences. As civilization developed, and in particular as man began navigating the Seven Seas, demands for greater accuracy in timing increased. One by one, the earlier timing devices fell by the waysid.e, and it is significant that only the mechanical clock and the hour glass survived the nineteenth century. Of these two, the hourglass was little more than a novelty. The first half of the twentieth century has witnessed a tremendous expansion in the use of the mechanical clock in various forms of clocks and watches both of the pendulum and balance -wheel types. This same period has witnessed -certain other developments that appear to be pertinent to the objective of this survey. These will be discussed in sequence of occurrence rather than in any sequence of alleged importance. One type of true clock used throughout the civilized world, and yet not recognized as such, is the common ordinary watt-hour or electric-power meter used by electric utilities to measure the power used by industry and the home* If a constant rate of power is introduced to these devices, they.give a true indication of elapsed time only. Another modern development is the so-called electric clock which has been developed in several forms, but which has settled down to two basic types. One is the electrically wound lock commonly found on automobiles, and the other is the synchronous electric clock commonly found in the home. The first of thesthe the electrically wound clock is essentially a mechanical clock of either the pendulum or balance-wheel type with the latter predominating. The- synchronous electric clock is not a clock at all, but simply an indicator or counter. Such a device counts cycles of alternating current and to the extent that the frequency of the alternations remains constant with time, then the indication will also be an accurate measure of elapsed time. Actually the number of cycles of alternating current generated by a central power plant is checked against and corrected to a master clock which may be a precision ~-~ 1 -~-,..

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN mechanical clock or one of the more modern precision quartz-crystal clocks. The quartz-crystal clock is probably the most significant timingdevice development in the past century or more. Its precision is many times greater than the best astronomical clock of the pendulum type. The significance of the quartz-crystal clock for the purposes of this survey is not so much in its precision as it is in the fact that it does not involve a mechanical mass acted upon by either gravity or a spring force, In other words, this is a departure from the mass-spring combination that has characterized practically all useful clocks developed up to this time. Certain components of electrical circuits possess the same relative properties of springs and mechanical mass so that the desirable properties of the mass-spring relationship can be obtained from electrical circuits, However, these analogous quantities are not influenced by variations in gravitational or other so-called mechanical forces. Consequently, these important sources of error with mechanical clocks have no effect on the quartz-crystal clock. Temperature variation, pressure variations and some other physical phenomena do affect electrical circuits, but compensation for these effects is accomplished to a greater extent than has been possible with the mechanical clock. Even now, the quartz-crystal clock has been exceeded in precision timekeeping on a laboratory basis by the application of nuclear energy. However, this development is in its infancy and the great precision attained by this means is not pertinent to the problem of the development of automotive clocks, since the precision required in such clocks does not even approach that obtainable with a relatively cheap mechanically or manually wound watch. The most significant conclusion to be drawn from this preliminary survey is that electrical circuits made up of physically small components are capable of at least equaling the precision of the common mechanical clock. Thus, the only question remaining to be answered in regard to the possible use of an electronic circuit as an automotive clock is whether sufficient accuracy can be obtained at a competitive cost. I. THE NATURE OF TIME The next section of this report will be devoted to the several components common to any type of clock, their relationship to each other and to external sources of error. The basis for that discussion will be the essential characteristics of an ideal clock. A brief review of the nature of time itself will aid in understanding the various points which will be discussed in that section. 2..

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN One of the common uses made of the iications of elapsed time is to denote various parts of the day such as noonday, midnight, and all the various intervals between. These elements of time, of course, are related to the earth's rotation about its axis, oe day corresponding to e revoltion of the earth. If this rate of rotation were to decrease or slow down, the corresponding time intervals would still have the same meaning; that is, noonday would be the same, midnight would be the same, and the time interval from one o*alock to two otelock would have the same relative meaning although on another or absolute basis the time intervals would actually be longer. One expects when driving in an automobile that if he continues at a speed of thirty miles per hour for one hour that he will have traveled a distance of thirty miles. This is a time.-dependent quantity; thus, if time were tied only to the rotation of the earth about its axis, and if such.rotation should slow down, then traveling at a speed of thirty miles per hour for an hour corresponding to the reduced speed of the earth about its axis would result in traveling a distance greater than thirty miles., Similar and entirely unrelated correlations can be cited for the rotation of the earth about the sun which is the basis for the calendar year. The quantity of flow of a liquid through' an orifice, the extent of a chemical reaction, or the speed of a falling object are all recognized as time. dependent phenomena. Any connection between these time-dependent quantities and sidereal time apparently is a mere coincidence. Obviously the common use for clocks, particularly automotive clocks, is related to "the time of day." Furthermore, the common use of automotive clocks would appear to be subordinate to the ordinary wrist or pocket watch carried by practically everyone who would drive an automobile and who would have some desire for an indication of the time of day without consulting his watch. Therefore, it seems reasonable at the outset to assume that the cumulative error in any automotive clock might be permitted to be as great as five minutes per day on the assumption that few would object to correcting such a clock at least once a day. This corresponds to a steady-state error of plus or minus 0.3 percent. III. THE IDEAL CLOCK In the literature survey, one significant characteristic was found to be common to all scientific analyses of timekeeping devices. This was the practice of subdividing all locks int essentr ess ial and functionally dis: tinct components* Those components are as follows:,~ *.

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN 1. time base 2. energy souree 3 energy valve or gate 4. time indicator or counter The relationship of these components to each other is illustrated 1she3matictally in Fig, -1 The time base establishes the frequeney of oscillation and opens and closes the energy gate* The energy source provides a ready supply at the gate at all times. The gate releases only enough energy to operate the time indicator an amount appropriate to the time interval. Based on accuracy only, any clock would be ideal that possessed the following characteristics: 1* a time base with a frequency of oscillation completely insensitive to its environment and to its function of opening and closing the energy gate, and 2. an energy gate that always released precisely the amount of energy appropriate to the time interval. The latter condition is relatively easy to satisfy while the former appears to be impossible. The degree to which the first condition is approached de termines the relative accuracy of the clock. The nature of the components illustrated in Fig 1 can be further clarified by comparing them to the common mechanical clocka The energy supply or source is ustally a spring, but may consist of iron weights as in the case of the well-known cuckoo clock. The time indicator consists principally of the hour and minute hands along with all the gears common to the familliar clock. The time bas in a mechanical clock is either a pendulum or a balance wheel. The valve or energy gate is the escapement mechanism common to all mechanical watches and clocks. The ideal mechanical clock must also have a stable time base. This objective has been characterized in technical literature as thei"free penduluml" The term "free pendulm" recognizes the fact that no pendulum can be completely free. In the ordinary pendulum clock the swing of the pendulm is resisted by the atmosphere and by friction in its support or bearings. Even if a pendulum clock were to be suspended in a vacuum, there would still be some resist ance to motion from the pendulum support. Furthermore, the physical mass which determines the period or frequency of the pendulm is affected by temperature. Increases in temperature cause the metals to expand, thus increasing the length of the pendulum and reducing its frequency. 14~

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN ITv PRACTICAL CLOCKB The discussion under this heading is devoted to an analysis and explaintation of five schematic diagrams designated as Figs* 2 througl- 6* The first three of these concern automotive clocks already in existence, while the last two represent arrangements using hydraulic, pneumatic, or thermal time bases. Figure 2 is a schematic arrangement of the pertinent components of the commn electrically wound balance-wheel automotive clock. As in the case of the ideal clock, it consists of an energy source, a time base, time indicator, and energy gate. In this case the energy source is shown to consist of several elements. These begin with the-automotive battery shown at the extreme left of the region enclosed by a dashed line. Electrical energy flows through an electrical gate consisting of contact points into an electromagnet. The electromagnet conerts electrical energy into mechanical motion, thUs storing mechanical energy in a spring This usually is a siple helical extension spring in most clocks of this type. The spring then proceeds to operate the clock in the same manner as any manally wound, mechanical clock, the difference being that the spring in the eleetrically wound clock stores much less energy making it neesssary to replenish the supply at more frequent intervals of the magnitude of one to five minutes, Near the end of the spring travel the electrical contact points are closed, thus once more releasing and convert-| ing electrical energy for- storage purposes. It should be emphasized that the frequency of rewinding bears no necessary relationship to the time base. Several arrows extending either up or down in Fig. 2 represent what could be called lateral movements of energy. These are significant either because they are energy losses which reduce the efficiency of the system or because they have some influenee on the frequency of the time base. Thus in Fig. 2, arrows a, b, and d are friction losses. Arrow a represents the hysteresis loss in the spring; arrows b and d are due to rubbing or conventional friction losses in the bearings of the escapement mechanism and balance wheel, respectively* The arrow designated as e represents the energy which the escapement mechanism feeds into the balance wheel. The amount of this energy is determined by at least two factors. The first of these is the energy required to overcome friction in the balance staff and hair spring. The second is the additional energy exchange with the balance wheel due to variations in the force exerted by the escapement mechanism in reaction with the balance wheel. This latter quantity is very important to the accuracy of the clock.. Thus, the energy quantity, designated as c, is influenced by both friction in the balance wheel and by the actual instantaneous force exerted by the driving spring* Other things bei ng equal, a mantually wound clock wound. mo re fre^ ~.... ~,

- ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN quently than is necessitated by the capacity of the spring would be more accurate. Thus, the significant difference between the schematics shown in Figs, 1 and 2 is the presence of the arrow c acting between the time base and the energy gate. These characteristics apply qualitatively to practically all automotive clocks in existence today. A. MAGNETICALLY IMPULSED, BALANCE-WEEL CLOCK A notable exception in the automotive clock field is the electrically impulsed, balance-wheel clock manufactured by the Jaeger Watch Company for the Kaiser-Frazer Company. This clock carries the UI.S patent number 1911062, A schematic diagram of the flow of energy in the Jaeger clock is shown in Fig. 3 The energy proceeds from the battery through an energy gate in the form of electrical contacts to an electromagnet where some of the energy is lost through electrical resistance heating. The remainder of the energy becomes an electromagnetic field which acts directly upon the balance wheel which in turn drives all of the time-indicating mechanism. This is a significant departure from the ideal clock in that all of the energy required to drive the time indicator must pass through the time base. Thus, it would appear that maximum error could result from this arrangement to the extent that any energy fed into the time base reacts to influence the frequency of that base. Once more the lateral arrows indicate energy lossesi The dashed line connecting the energy gate with the balance wheel simply indicates that the balance wheel alternately opens and closes the electrical contacts. Figure 4 is a schematic drawing of the physical details of the Jaeger clock. It will be noted that the balance wheel is literally a three-pole rotor of an oscillating electric motor. In its free position one of the three poles is symmetrical, relative to the two poles of the electromagnet* In this position a small dowel projecting from the hub of the balance wheel is in contact with a small, flat leaf spring. The dowel and leaf spring constitute the electrical contacts which complete the circuit from the battery through the coil of the electromagnet back to the battery. A flow of current at this time causes the poles of the rotor to be displaced due to a very slight eccentrice ity. This displacement is unstable and takes place at increasing velocity eventually breaking contact between the dowel and the spring. At this time a condenser connected in parallel with the coil discharges. This causes the current to contine to flow through the coil in the same direction and gives the balance wheel a additional "kick." During this period, the rotation of the balance wheel has been against the hair spring so that eventually it slows down stops, and begins to rotate in the opposite direction, once more bringing the dowel and leaf spring.into contact thus repeating the same half cycle on the opposite side of the free position. ~.,'-~ 6'~'

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN In the absence of any actual test data on the accuracy and energy consumption of this clock, it is unfair to condemn this particular design even though it violates to the extreme a rule that is alleged to be basic if a clock is to operate accurately. There is significance in the fact that such a radical departre from the ideal clock apparently has met the requirements for accuracy. It must be said tha the mechanical details of this clock are compact and ingenious. B. OTHER TYPES OF TINE BASE Figure 5 is a feasible energy-flow diagram for a clock involving either a hydraulic or pneumatic time base. In this case a fluid in the form of a liquid or a gas would be caused to flow through an orifice. The quantity of fluid would be constant and the rate of flow would be a function of the orifice size and the pressure difference across the orifice. In general, pressure would be created by a spring which literally would run down as in the case of the electrically wound mechanical clock. Similarly an electromagnet would be used to convert battery energy into mechanical energy stored in the spring. Electrical energy required to operate the time indicator could be taken off either before or after the electromagnet. It is significant in contrast to Fig. 2 that the frequency of the titme base and. of the "'rewinding" of the spring is identically equal and in phase. In general, a hydraulic or pneumatic time base is susceptible to errors arising from temperature variation. It was pointed out that an essential characteristic of this time ba1se is a constant quantity of fluid. The space occupied by the fluid would increase with increases in temperature due to the expansion of the material containing the fluid. Similarly, the area of an orifice would increase with increases of temperature. These are dimensional changes peculiar to the material of construction. In addition, the ability of the fluid to flow through the orifice, particularly in the case of liquids, is affected by temperature. The fluid itself would either increase in volume in the case of liquid or increase in pressure and volume in the case of a gas. It is a difficult design job to predict and to compensate for these errors, Another different and yet feasible time base is the one illustrated in Fig. 6 as a thermal time base Here the frequency of the base would be used to open and close two energy gates, one to drive the time indicator and the other to store energy as heat in the time base mechanism so that the sub8 sequent flow or radiation of this heat would determine the time interval. There is a ommon precedent for this type of design in the familiar thermal, time-delay relay. Highly developed commercial relays are indicated to be in error in time by as much as plus or minus 15 pereent even in the ab7

ENGINEERING RESEARCH'INSTITUTE ~ UNIVERSITY OF MICHIGAN sence of voltage variations Thus, at the outset it is pretty well established that the errors inherent in the thermal time base are too great to be considered for an automotive clock.. V. SUMMARY In summarizing the discussion presented in the preceding sections, it is the opinion of the author of this report that it is dangerous to assign too much significance to accuracy in an automotive clock. One consequence of this would be the elimination of various design objects which would -otherwise be quite desirable. Thus, as a general guide for future activity in the development of the substantially new automotive clock, the author suggests the following list of general specifications or objectives in sequence of deereasing importance: 1I uninterrupted operation 2. low power consumption 3. long life 4., accuracy in time keeping Most of the complaints which the author has received in connection with automotive clocks have been to the effect that they "won't runt" The ability to operate uninterrupted would seem to take precedence over all other objectives since the other objectives or qualities have no significance unless the clock operates continually. Low power consumption obviously is desirable to prevent unnecessary drain of the battery. No data were available as to the upper limit on power consmption although this can be determined for existing clocks with little difficulty. Long life for an automotive- clock probably means something beyond five years and possibly as mch as eight years. Once more no data were available in regard to this specifically, and it would be difficult to design an accelerated life test. The author expressed the opinion herein to the effect that the average automobile driver probably would not obJect to an error of as much as five minutes per day in an automotive elock. It would require a mrket survey to determine the degree of accuracy expected by the buying public for the different price levels of cars. It would also take a market survey to confirm the relative importance of the general specifications listed above. It is rela~~ 8.-~ -.

ENGINEERING RESEARCH INSTITUTE: UNIVERSITY OF MICHIGAN tively simple, however, to evaluate the accuracy of existing types of automotive clocks. Based on the overall impression obtained in the literature survey, it is the author's opinion that the feasibility of meeting the qualities listed in the sequence listed above in the same economic level are about as follows 1 mechanical time base 2* electronic time base 3. hydraulic or pneumatic time base VIx GENERAL RECOMMENDATIONS Based on the evidence accumulated in this survey, the author makes the following recomendations as an experimental approach to the development of a new automotive clock: 1. Evaluate present clocks as to power consmption and accuracy. 2. Consider the many possible electrical circuits and screen them on the basis of low power, accuracy, and economic feasibility. 5. Consider the combination of a mechanical time base with electrical elements for the other components of a clock. The activities suggested above could be carried out separately or concurrently. The specific details of procedure are not part of this report, particularly since the program for electrical circuits could involve a great many combinations and. requires the guidance of electronic experts, It is the opinion of the author that activities 2 and 3 above could very well be carried on concurrently until the accumulated evidence indicated that efforts should be concentrated on one or the other. The first activity is necessary oily to the extent that it is desirable to give some quantitative expression to the limits for power consumption and accuracy......'~' 9 ~..:...

ENGINEERING RESEARCH INSTITUTE ~ UNIVERSITY OF MICHIGAN VII. BIBLIOGRAPHY 1. Brooks, H. B., "Timing Circuits", Transactions of IRE on Instrumentation, PGI-3, 11-14 (April, 1954). 2. "Diode Amplifiers", Technical News Bulletin, 38, No. 10, U.S. Department of Commerce, National Bureau of Standards, (October, 1954). 3. Felker, J. H., "The Transistor", Proceedings, IRE, AIEE, Bell Telephone Laboratories (February, 1954). 4. Fowler, F. E., "Accurate Time for Scientific Observations", Electronics, 25, No. 1 (January, 1952). 5. Garner, Louis E., Jr., "Transistors", Education Book Publishing Division, Coyne Electrical School, Chicago, 1953. 6. Hope-Jones, Frank, Electric Timekeeping, N.A.G. Press, London, 1949. 7. Krugman, Leonard, Fundamentals of Transistors, John F. Rider, New York, 1954. 8. Morgan, E. D., "Simple Time-Delay Relay", Electronics, 27, No. 4, 178-9 (April, 1954). 9. Pearlman, Alan R., "Transistor Power Supply for Geiger Counters", Electronics, 37, No. 8 (August, 1954). 10. Philpott, S. F., Modern Electric Clocks, Pitman, New York, 1949. 11. Prugh, Thomas A., "Junction Transistor Switching Circuits", Electronics, 28, No. 1 (January, 1955). 12. Rawlings, Arthur Lionel, The Science of Clocks and Watches, Pitman Publishing Corporation, London, 1948. 13. Schenkerman, Stanley, "Feedback Simplifies Transistor Amplifiers", Electronics, 27, No. 11 (November, 1954). 14. Shea, R. F., Principles of Transistor Circuits, John Wiley and Sons, New York, 19535 15. Wise, S. J., Electric Clocks, Heywood and Company Ltd*, London, 1948. 10

TIME BASE I Fig. 1. Ideal Clock. d BALANCE WHEEL BATTERY -GATE GATE SPRING INOGATE ELECTROMAGNET a I ENERGY SOURCE I o b a d= FRICTION LOSSES Fig. 2. Electrically Wound, Balance-Wheel Clock. 11

\ I ELECTRO- BALANCE TIME BATTERY MAGNET WHEEL INDICATOR A 8 C As RESISTIVE LOSSES BS FRICTION LOSSES Ca POTENTIAL ENERGY STORED & LOST IN CONTACTOR SPRING Fig. 3. Jaeger Watch Company (K-F) Clock. BALANCE WHEEL / I/T / LEAF SPRING 1' / nDAMPING SLEEVE ACTS THROUGH ACTS THROUGH pi NOT ELECTRICAL HAIR SPRING a GROUND Fig. 4. Jaeger Watch Company Clock. 12

ENGINEERING RESEARCH INSTITUTE * UNIVERSITY OF MICHIGAN TIME ^ ~ ~r~ —- BASE I'c ENERGY E LE CTRO ~GATfE S;~SPRING SOURCE MAGNET TIME INDICATOR aoc= FRICTION LOSSES- LARGE FRICTION LOSSES- SMALL d ALTERNATE SOURCE FOR OPERATING TIME INDICATOR Fig. 5. Hydraulic or Pneumatic Time-Base Clock. DISSPATE AS- -TIMEB aig_ 6~ NErE NOTBEIBAS E SO URCE E I~ HDICATO oa b NEED NOT BE IN PHASE c ~ ENERGY STORED AS HEAT B DISSIPATED AS TIME BASE Fig.6, Therl Tiae-Base Clock. ~~ 13 ~

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