Title: Simplified method and apparatus for assuring periodic control of the timing of an internal combustion engine

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Abstract: Method and apparatus for periodically controlling the timing of an internal combustion engine in which two voltages are generated, one of which corresponds to a selected portion of one complete rotation of the engine shaft whereas the other is a function of time. A control signal is generated when the second voltage becomes equal to the first. The first voltage is of the form aq+b+ce.sup. -.gamma.q, in which a, b, and c may be any constants and .gamma. is a positive constant, while the second voltage is of the form d+ ge.sup. -.alpha.t, in which d and g may be any constants and .alpha. is a positive constant. SUMMARY OF THE INVENTION It is known to be necessary in order to insure the satisfactory operation of a reciprocating internal combustion motor, such as the motor of an automotive vehicle, for example, to ignite the combustible gas in advance of the moment at which the piston reaches the top dead center point in the cylinder in question. In devices of a conventional type, the ignition is advanced by means of a centrifugal advance device and by means of a vacuum operated advance device, these two devices constituting mechanical controls which determine the relative position of a cam and a switch, the cam being driven in rotation by the motor and the switch being inserted in the primary circuit of an ignition coil. In this type of apparatus the presence of several mechanical parts is a by no means negligible cause of engine trouble and, moreover, rapid opening and closing of the switches leads to a progressive deterioration of their contacts during use, so that good operation requires frequent maintenance. In order to avoid the disadvantages resulting from the use of a switch it has already been proposed, for example in applicant's U.S. Pat. Application Ser. No. 562,844, filed Mar. 27, 1975, U.S. Pat. No. 4,066,968, to provide analogous devices making it possible to control the timing of an internal combustion engine by utilizing only electronic components, thus eliminating the mechanical devices customarily required. These electronic component devices make it possible to initiate the ignition with an advance the representative curve of which is a straight line, as a function of the speed of rotation. When the advance curve takes the form of a succession of connected straight line segments, it is necessary either to provide a relatively complex speed discriminating circuit to select those of the electronic circuits which should be used in the speed zone in which one is operating, or utilize a group of circuits functioning simultaneously, one of which is selected by comparison on the assumption that the advancement curve is a monotone or straight line in the working interval. These prior art electronic devices work on the principle of comparing two voltages, the first of which is a linear function of the inverse of the speed of rotation of the motor with which the device is associated, and the second is a linear function of time. This comparison makes it possible to generate a control signal which results in producing, for the ignition of the internal combustion motor of an automotive vehicle, a linear curve of ignition advancement as a function of the speed of rotation. This linearity, as has been explained above, makes it necessary, in order to obtain a curve consisting of several different straight segments, to add a certain number of electronic components to the circuits generating the first and second voltages, so as to permit a change in straight segments when shifting from one range of speeds of rotation to another range of speeds of rotation. It is the object of the present invention to provide an analog electronic device which makes it possible to obtain an ignition advance curve as a function of the speed of rotation which has a finite radius of curvature which differs in dependence on the points of the curve. In this way it is possible, over the entire range of rotational speeds which must be taken into consideration, to obtain a single curve by comparing two voltages, one of which is a function of the inverse of the speed of rotation and the other of which is a function of time. It is thus no longer necessary to have available supplementary electronic components for changing the straight curve segment in dependence on the portion of the total operating range within which one is working, as is the case in the devices of the prior art. This results not only in a simplification of the electronic device and consequently a decrease in its cost, but also in an improved response to the needs of the motors. The device according to the invention receives information from a certain number of sensors, and in particular from a speed detector, which indicates the speed of rotation of a shaft which, in the case of a control for the ignition of an internal combustion motor, may be a shaft connected to the crankshaft or cam shaft of the motor. The device according to the invention is an analog assembly which transforms the information received into control signals which are supplied either to the ignition coil or to other means controlled by the device from, for example, a fuel pump, a starter, a fuel injection device, a carburetor, an air pump, or an automatic transmission. It will be appreciated that this list of possible applications is representative and not exhaustive. In accordance with the invention at least one of the two voltages compared is an asymptotic exponential function which may be simply provided by the charging or discharging of a circuit comprising a condenser and a resistance. It has already been proposed in the prior art that, in order to control the ignition of an internal combustion motor, two voltages be compared, one of which is an exponential function of time and the other of which is proportional to the speed of rotation of the shaft of the motor (see the article by B. J. Hoetink, in the Dutch Review, "de Ingenieur", Volume 76, No. 22, pages W95 to W99). However, this prior art device is not satisfactory because the curve which represents the ignition advance as a function of the speed of rotation is an exponential asymptotic curve in which the position of the asymptote is a function of the structure of the sensor for the speed of rotation which is used. It follows that, for a given sensor, the position of the asymptote is determined, which makes it impossible to modify the curve as a function of the values of parameters other than the speed of rotation and, in particular, as a function of the vacuum. On the contrary, the device according to the invention makes it possible to obtain an ignition advance the curve of which, as a function of the speed of rotation, is an exponential asymptotic curve, the position of the asymptote being essentially a function of the characteristics of the electronic circuits used and, in particular, of the value of the resistances and the capacitances which are included in the circuits generating the exponential voltages compared. It follows that one may easily introduce parameters other than the speed of rotation of the motor and, in particular, the value of a vacuum, so as to modify the ignition advance curve obtained, by simply changing the value of a resistance or a capacitor. It is therefore an object of the present invention to provide a process for insuring the periodic control of at least one function dependent upon one or more parameters, and in particular, on the speed of rotation of a shaft, which control must be initiated with a phase displacement with respect to the instant of passage of an indicator connected to the shaft before a stationary mark, the displacement being a function of the speed of rotation of the shaft. In this process a signal P is generated, the duration q of which corresponds to passage of a rotating sector having a constant angle .phi. in front of a stationary mark, the angle (2.pi.-.phi.) corresponding to the absence of this signal for a time q. A complementary signal P may be generated throughout the period q. After having generated a signal P, there is generated, during a subsequent period q or q, a first voltage which is a function of q. During one of the subsequent periods q, a second voltage is generated as a function of the time t from the beginning of the period q of the signal P under consideration. A control signal is generated when the second of the aforesaid voltages becomes equal to the first, said control signal being used to initiate the control step in question. The process is characterized by the fact that the first voltage is of the form q+b+ce.sup. -.gamma.q ; a, b and c being any constants and .gamma. being a positive constant, and that the second voltage is of the form d+ge.sup. -.alpha.t, d and g being any constants and .alpha. being a positive constant. In a preferred embodiment of the process according to the invention the first voltage is generated during the period q following a period q of the signal P. This first voltage is stored and the second voltage is generated during the following period q. The second voltage is generated at the terminals of a condenser which is charged through a charging resistance. In a simple and advantageous embodiment, the first voltage is a linear function of q. In this case the first voltage is obtained by utilizing an integrator which operates during the period of the signal P or P. The return to the initial state of the first and second voltages preferably occurs at the moment at which the trailing edge of the signal P occurs. In the case in which it is desired to utilize parameters other than the speed of rotation of the shaft, for example the value of the vacuum in an intake line, the characteristics of the components of the circuits permitting the generation of the first and/or second voltage are modified as a function of the parameter to be used. The value of the process according to the invention comes from the fact that the electronic circuits making it possible to generate the first and second voltages which are to be compared are particularly simple since the linear functions may be generated without difficulty by means of an integrator and the asymptotic exponential functions may be generated without difficulty by charging a condenser. If this process is used for the ignition of an internal combustion motor it is arranged so that the top dead point corresponds to the end of the passage of the sector having an angle of rotation .phi. is in front of the stationary mark associated therewith, that is to say, at the end of the signal P. The time t.sub.o at which equality between the first and second voltages occurs is counted, beginning with the beginning of the signal P and the ignition advance is thus equal to the difference between the duration of the signal P and the time t.sub.o. If the angular rotation of the shaft is equated to time by designating by N the angular speed of rotation expressed in revolutions per minute, one may write ##EQU1## a formula in which .theta. represents the advance of the ignition in degrees, .phi. is in degrees, N is in RPM, and the quantity ##EQU2## so that t.sub.o is in seconds. It will, moreover, be seen that, if the second voltage never becomes equal to the first, and the ignition is fired at the end of the signal P, there is no advance of the ignition. If an initial setting is desired in which there is an advance or a lag in firing, it suffices to displace the rotating angular sector of the sensor with respect to the fixed mark so that the end of the passage of the rotating sector by the fixed mark is angularly displaced with respect to the top dead point. Taking into account the form of the equations representing the first and second voltage and allowing, on the other hand, for the relationship, above indicated, which exists between .theta. and t.sub.o, it may be easily deduced that, when the ignition is fired because the first and second voltages have become equal, the expression of .theta. as a function of N is of the form: .theta.=.phi.+KN Log (1+(A/N)+Be.sup.-.beta./N). In this formula K, A, B and .beta. are constants which are essentially a function of the characteristics of the components of the electronic circuits which generate the first and second voltages. One may therefore, for example, by adjusting the value of a resistance, modify the ignition curve obtained as a function of the value of a parameter such as the vacuum in the intake line of the motor. A further object of the present invention is to provide the new article of manufcture which consists of a device adapted to carry out the above defined process and particularly adapted to assure the timing of the ignition of a reciprocating internal combustion motor with respect to the top dead point of the stroke of each piston, said device comprising a stationary sensor which cooperates with a rotating sector having the angle .phi. and associated with the shaft, the speed of rotation of which determines the command to fire, said sensor supplying, during the passage of the sector having the angle .phi. aforesaid, a signal P of duration q, characterized by the fact that it comprises, in the first place, a circuit which generates a first voltage of the form aq+ b+ce.sup.-.gamma.q ; a, b, and c being any constants and .gamma. a positive constant; in the second place, a circuit which generates a second voltage of the form d+ge.sup. -.alpha.t, in which formula d and g are any constants, .alpha. is a positive constant and t represents the time counted from the beginning of the signal P; and, in the third place, a comparator supplied by the two above circuits and capable of generating a control signal when the second voltage becomes equal to the first voltage. When the second voltage does not become equal to the first voltage before the end of the signal P during which it is generated and when it is desired to initiate the control signal at the moment at which the signal P ends, the output of the comparator and the signal P is connected to an OR gate permitting the delivery of a control signal. In a preferred embodiment of the invention the control signal emitted at the moment at which ignition must occur is supplied to the input of a monostable, the output of which controls two transistors associated in a "Darlington" pair, said pair making it possible to cut off the supply to the primary coil of the ignition coil associated with the device at the moment at which emission of the control signal takes place. When the first voltage is a linear function of q, that is to say in the case in which c=o, the circuit generating the first voltage is an integrator functioning for the duration of the signal P, the output voltage of said integrator being maintained during the following signal P by means of a condenser connected between an input and the output of the integrator. The output voltage of the integrator is returned to zero by supplying a reverse voltage pulse to the integrator input connected to the condenser at the moment at which the trailing edge of the signal P occurs. This pulse is provided by a monostable multivibrator in response to the trailing edge of the signal P. The integrator, which generates the first voltage, has its input other than the one which is connected to the condenser supplied during the signal P and connected to ground during the signal P through a transistor. The circuit generating the second voltage consists of a condenser associated with a charging resistance. The charging resistance of the circuit generating the second voltage is continuously or discontinuously modified as a function of the value of a parameter such as the vacuum in the intake line of the motor which is associated with the device.


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