US3095536A - Relay type automotive tachometer with time delay circuitry for the relay to enable operation at high engine speeds - Google Patents

Description

June 25, 1963 v. c. WESTBERG 3,095,536

RELAY TYPE AUTOMOTIVE TACHOMETER WITH TIME DELAY CIRCUITRY FOR THE RELAY To ENABLE OPERATION AT HIGH ENGINE SPEEDS 2 Sheets-Sheet 1 Filed July 15, 1959 CRANK 59 sHAFTl IO '2 REDUCTION ix? nlsrmsurok J POINT/57'} i 23'- I2 F l I 2| Z0 2g{|]||| 63 i 3 H 6, 62 f/ U V gVlxINTOR. DWELL SPARK ERNON ESTBERG POINTS CLOSED) PomTs BY OPEN MW l/w (99? June 25, 1963 v. c. WESTBERG 3,095,536

RELAY TYPE AUTOMOTIVE TACHOMETER WITH TIME DELAY CIRCUITRY FOR THE RELAY TO ENABLE OPERATION AT HIGH ENGINE SPEEDS Filed July 15, 1959 2 Sheets-Sheet 2 F 2 I 4| L 55 INVENTOR. VERNON C. WESTBERG BY W /AM FM 494W Arrvs Patented June 25, 1963 RELAY TYPE AUTOMOTIVE TACHOMETER WITH TIME DELAY CIRCUITRY FOR THE RELAY T ENABLE OPERATION AT HIGH ENGINE SPEEDS 'Vernon C. Westherg, 520 E. Haven St., Arlington Heights, Ill. Filed July 15, 1959, Ser. No. 827,368 3 Claims. (Cl. 32470) The present invention relates to tachometers and more particularly to an electrical tachometer or the relay type.

In a conventional electrical tachometer a relay is provided which is actuated by the ignition points and which has double throw contacts which are arranged to charge a capacitor when the relay is energized and to discharge such capacitor through a microammeter or the like when the relay is dc-energized with the microammeter being directly calibrated in terms of speed. Available devices of this type have given satisfactory results at moderate engine speeds, say, on the order of 4,000 to 5,000 rpm. maximum, and with engines having moderate compression ratios. However, such devices have not been capable of reliable operation with high performance engines having extreme compression ratios and maximum speeds within the range of 8,000 to 10,000 rpm. As :a result of the failure of electrical tachometers to operate under such extreme conditions, operators of sports cars and racing cars have not had full confidence in this type of tachometer and tended to go to \other types of tachometers which are more expensive and more diflicult to install in order to achieve the necessary reliability and accuracy.

Accordingly it is an object of the present invention to provide an electrical tachometer for an automotive engine or the like Which is more accurate and reliable than conventional tachometers of this type over a wide range of engine speed. It is a related object to provide a tachometer capable of giving reliable readings for high compression engines operating at speeds of up to 8,000 or 10,000 rpm. and which is particularly suitable for use with the engines in modern sports and racing vehicles.

More specifically it is an object to provide an electrical tachometer of the relay type which is capable of making positive electrical contact during both the charge and discharge portions of the cycle free of the tentative, chattering operation generally encountered at high speeds. It is a more specific object to provide an electrical relay type of tachometer which is connected in the primary circuit of an ignition coil but which is not afiected by the high voltage transient waves induced in the primary winding during and following the spark, on the contrary, the relay armature in the present device responds only to the direct voltage of the automobile battery, remaining in perfect synchronism with the opening and closing of the ignition points.

It is another object of the present invention to provide an electrical tachometer of the relay type in which the relay contacts have an extremely long life and in which the contact characteristics remain unchanged over many millions of switching operations and even when operated at sustained high speed.

It is a further object of the invention to provide an electrical tachometer of the relay type in which the contacts are more easily adjusted than in conventional devices and in which the contact spacing may be greater and less critical of adjustment, while producing accurate results over a wide nange of engine speed.

It is still another object of the present invention to provide an electrical tachometer which is extremely simple and compact and which, in spite of its improved performance and accuracy, may be produced at a cost which does not exceed that of conventional tachometens or" the electrical type.

Other objects and advantages of the invention become apparent upon reading the attached detailed description and upon reference to the drawings in which:

FIGURE 1 is a schematic diagram of electrical tachometer constructed in accordance with the present invention shown connected to a conventional automotive ignition circuit.

FIG. 2 is a side elevation of the relay employed in the circuit of FIG. 1, with certain parts broken away to reveal the details of construction.

FIG. 3 is a front elevation of the relay shown in FIG. 2.

FIG. 4 is a top view of the relay shown in FIGS. 2 and 3.

FIG. 5 is a typical voltage wave which exists in the relay supply circuit during the sparking cycle.

While the invention has been described in connection with a preferred embodiment, it will be understood that I do not intend to be limited to the embodiment shown but intend to cover the various alternative and equivalent constructions falling within the spirit and scope of the appended claims.

Referring now to FIGURE 1 there is shown a typical ignition circuit 10 including an ignition coil 11 having a primary 12 and a secondary 13. Connected to the secondary winding is a distributor 14 for distributing the spark to the spark plugs in succession. A representative spark plug is shown at 15.

Current is supplied to the primary winding 12 from an automotive battery 20 through an ignition switch 21. The remaining terminal of the primary coil is connected to ground through the usual ignition points 22 operated by a cam 22a. Shunted across the points 22 is an ignition condenser 23. As will be apparent to one skilled in the art, closing of the points over the period of dwell causes a build up of flux in the core of the ignition coil 11. When the points are opened during the spar portion of the cycle, the sudden collapse flux induces a high voltage in the secondary winding 13 which causes a spark across the points of the spark plug depending upon the phasing of the distributor 14. The spark plugs fire in succession upon the successive openings of the ignition points 22. In a typical 8 cylinder engine four spark plugs fire during a single revolution of the crankshaft.

In practicing the present invention a relay type tachometer is provided which includes a relay 30 having a coil 31, .a core 32 and an armature 33. One side of the winding 3 1 is grounded as indicated at 34. Tthe other side of the winding is connected by a single lead '35 to the primary circuit of the ignition system. Preferably this lead is connected, as shown, to the ungrounded one of the ignition points so that the relay coil is connected across the ignition points for operation in synchronism with the latter.

The relay preferably includes single pole, double throw contacts, and means are provided for visually indicating the rate that these contacts are operated. The central contact, indicated at 40, is movable with the armature '33 and cooperates with a lower or charging contact 41 and an upper or meter contact 42. In series with the central contact 40 is a charging capacitor 45. In series with the lower or charging contact 41 is a battery or other constant potential source 46. It will be apparent that when the relay is operated, causing closure of contacts 40, 41, the battery 46 will be shunted across the capacitor 45, charging the capacitor with a charge depending upon the battery voltage. In series with the upper or meter contact 42 is a meter 50 so that the capacitor is discharged cyclically into the meter. The meter is preferably of the moving coil or DArsonval type capable only by the battery but also by the voltage resulting from the collapse of field about the primary Winding 12. This causes pull-in of the relay. Simultaneously, the capacitor 58, which, as stated, is on the order of 0.33 mfd., is charged to a value which depends upon the voltage drop through the resistor 59. Using a resistor Within the range of, say, 150 to 500 ohms, this voltage is not so great as to substantially affect the promptness of pullin of the relay. The ignition points are only open for a short space of time. It will be appreciated by one skilled in the art that in the case of an 8-cylinder four-cycle engine with points set for 60 to 80% dwell, and at a speed of 8,000 rpm, the open time during which the above series connection is maintained may be only on the order of 0.0004 to 0.00081 second which might not seem to be sufficiently long to allow the relay 30 to respond. However, upon closure of the ignition points the above series circuit is converted to a loop circuit which goes from ground, through the relay winding 31, through the paralleled capacitor and resistor 58, 59, back to ground. The charge stored in the capacitor '58 is of such polarity as to produce a flow oi current around the loop circuit which is in the opposite direction from the iiow which took place when the points were initially opened, but the reversal takes place so rapidly that the armature remains held in. In short, the relay, by reason of the continued flow, is found to be energized for an additional time interval, during discharge by the capacitor, suificiently long so that the armature 33 is enabled to complete a positive downward stroke (as viewed in FIG. 1). Thus it is seen that the relay 30 remains closed during the initial portion of the succeeding dwell period, a portion of the cycle not utilized in a conventional relay type tachometer. In the case of an engine of the type having a long dwell on the order of 60 to 80%, and rotating at an extremely high speed in excess of 8,000 r.p.m., relay closure is caused to be as positive and well defined as it is at substantially lower speeds on the order of 6,000 rpm. or less.

As one of the byproduct advantages of the scheme described above, the adjustment of the contacts 41, 42 is made considerably less critical. As previously mentioned extremely close contact spacing of a thousandth of an inch or less is generally thought necessary for synchronization at high speed. However, it is found that when employing the above combination of capacitive reactance and shading ring the contact spacing may be made several times this amount, and the adjustment becomes correspondingly less critical while maintaining perfect synchronization at 'high speed. Thus the relay is less susceptible to malfunctioning as a result of contact wear or oxidation or because of the entry of dust particles between the contacts. O-r, stated in other terms, the present invention makes it possible to go from speeds of say, 6,000 rpm. to higher speeds on the order of 10,000 rpm. with a high degree of reliability and without having to make a further reduction in the contact spacings usually used at the lower speed rating.

While I prefer to employ the shading ring and capacitive reactance in combination with one another for optimum results, nevertheless experience shows that worth while improvement may be brought about by each of these features employed singly. That is to say, the use of series capacitive reactance improves the positiveness of the relay operation even where the shading ring is not used, and the shading ring tends to avoid the double stepping, even where the series capacitance feature is not employed. Consequently my invention contemplates use of the above distinguishing features both singly and combined.

Where it is desired to employ the shading ring feature alone while permitting the adjustment required for use with dual points, the rheostat 59 may be used in units of lower speed rating without the associated capacitor to provide adjustable impedance in the circuit of the relay winding. This variable impedance makes it possible to adjust for successful operation of the unit with any ignition system regardless of the use of single or dual points,

, thus making it unnecessary to tamper with the relay adjustment.

It will be apparent that the above device is distinguished not only by its reliability under extreme conditions in which it is called upon to operate but by simplicity and low cost. Installation requires connection of only a single supply wire, with grounding through the vehicle frame.

I claim as my invention:

1. In an electrical tachometer for use with an automotive ignition system having a primary circuit including breaker points for grounding the same, the combination comprising a relay having a coil and armature, contacts on said relay including a central contact and relatively stationary charging and discharging contacts alternatively engaged therewith, a spring for biasing the armature for engagement between the central contact and the discharging contact, a charging circuit including a battery of constant voltage connected to the charging contact, a dis charging circuit including an indicating meter connected to the discharging contact, a first capacitor connected to the central contact so that the capacitor is alternatively charged across the battery and discharged through the indicating meter, a resistor connected in series with the relay coil so that an IR drop is developed across the resistor depending upon the current in the coil, means for connecting the relay coil and its series-connected resistor across the breaker points so that the relay is supplied with current from the primary circuit by direct current flow through said restrictor when the points are open and so that the relay is connected to form a slrort-circuiting loop circuit with said resistor when the points are closed during the ignition dwell period, and a second capacitor connected across said resistor so that when the points are opened current flows in a first direction through the relay coil with such capacitor acquiring a charge proportional to the IR drop in said resistor and so that when the points are closed to form said loop circuit a current flow is set up in said relay coil in the opposite direction, said relay being of the type having a single pole face and so constructed that the armature is attracted to the pole face regardless of the direction of current flow in said coil so that the relay armature is held in not only during the interval that the points are open but also during an addi tional finite interval as the second capacitor discharges during the ensuing ignition dwell period when the points are closed.

2 In an electrical tachometer for use with an automotive ignition system having a primary circuit including breaker points for grounding the same, the combination comprlsing a relay having a coil and armature, contacts on said relay including a central contact and relatively stationary charging and discharging contacts alternatively engaged therewith, a spring for biasing the armature for engagement between the central contact and the discharging contact, a charging circuit including a battery of constant voltage connected to the charging contact, a discharging circuit including an indicating meter connected to the discharging contact, a first capacitor connected to the central contact so that the capacitor is alternately charged across the battery and discharged through the indicating meter, a resistor connected in series with the relay coil so that an IR drop is developed across the resistor depending upon the current in the coil, means for connecting the relay coil and its series-connected resistor across the breaker points so that the relay is supplied with current from the primary circuit by direct current flow through said resistor when the points are open and so that the relay is connected to form a shortcircuiting loop circuit with said resistor when the points are closed during the ignition dwell period, and a second capacitor connected across said resistor so that when the points are opened current flows in a first direction through

Claims (1)

1. IN AN ELECTRICAL TACHOMETER FOR USE WITH AN AUTOMOTIVE IGNITION SYSTEM HAVING A PRIMARY CIRCUIT INCLUDING BREAKER POINTS FOR GROUNDING THE SAME, THE COMBINATION COMPRISING A RELAY HAVING A COIL AND ARMATURE, CONTACTS ON SAID RELAY INCLUDING A CENTRAL CONTACT AND RELATIVELY STATIONARY CHARGING AND DISCHARGING CONTACTS ALTERNATIVELY ENGAGEMENT BETWEEN THE CENTRAL CONTACT AND THE DISCHARGENGAGEMENT BETWEEN THE CENTRAL CONTACT AND THE DISCHARGING CONTACT, A CHARGING CIRCUIT INCLUDING A BATTERY OF CONSTANT VOLTAGE CONNECTED TO THE CHARGING CONTACT, A DISCHARGING CIRCUIT INCLUDING AN INDICATING METER CONNECTED TO THE DISCHARGING CONTACT, A FIRST CAPACITOR CONNECTED TO THE CENTRAL CONTACT SO THAT THE CAPACITOR IS ALTERNATIVELY CHARGED ACROSS THE BATTERY AND DISCHARGE THROUGH THE INDICATING METER, A RESISTOR CONNECTED IN SERIES WITH THE RELAY COIL SO THAT AN IR DROP IS DEVELOPED ACROSS THE RESISTOR DEPENDING UPON THE CURRENT IN THE COIL, MEANS FOR CONNECTING THE RELAY COIL AND ITS SERIES-CONNECTED RESISTOR ACROSS THE BREAKER POINTS SO THAT THE RELAY IS SUPPLIED WITH CURRENT FROM THE PRIMARY CIRCUIT BY DIRECT CURRENT FLOW THROUGH SAID RESTRICTOR WHEN THE POINTS ARE OPEN AND SO THAT THE RELAY IS CONNECTED TO FORM A SHORT-CIRCUITING LOOP CIRCUIT WITH SAID RESISTOR WHEN THE POINTS ARE CLOSED DURING

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