Electricity: measuring and testing – Internal-combustion engine ignition system or device – Electronic ignition system
Reexamination Certificate
2000-02-14
2001-08-21
Metjahic, Safet (Department: 2858)
Electricity: measuring and testing
Internal-combustion engine ignition system or device
Electronic ignition system
C324S388000
Reexamination Certificate
active
06278278
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The invention relates to a measuring and diagnostic device for an ignition system of an internal combustion engine.
German Patent DE 40 39 356 C1 discloses a circuit configuration for determining the discharge voltage of an ignition system of an internal combustion engine. The circuit configuration evaluates the spark plug discharge voltage, which is transformed to the primary side of an ignition coil, through the use of a voltage converter connected as an emitter follower.
German Patent DE 27 59 155 C2 discloses a circuit configuration for detecting the spark burning duration in ignition devices for internal combustion engines. Using an integrator device and a downstream-connected trigger device, the primary-side ignition voltage profile of a transistor-controlled ignition coil is converted with a predetermined response voltage into a square-wave pulse whose duration corresponds to the spark burning duration.
U.S. Pat. No. 4,331,922 discloses a diagnostic device for an ignition system of an internal combustion engine for monitoring the battery voltage, the ignition switch and the spark head voltage. The diagnostic device has a plurality of comparators for comparing the primary voltage with different reference voltages, the comparator outputs being connected via peak value storage circuits to a logic unit which controls devices for indicating faulty conditions.
Since the primary-side ignition voltage across the ignition switch has relatively high voltage levels being above the input voltage range of standard operational amplifiers, particularly complicated clamping circuits are necessary. In addition, the task is not accomplished by the comparators alone, rather a plurality of peak value store circuits are necessary, and also an evaluation logic unit.
In the course of the development of ignition systems in internal combustion engines, it has been shown that it is necessary to protect the ignition switch (power output stage transistor) against destruction if, by way of example, the primary winding of the ignition coil has a short circuit to the positive terminal of the battery voltage source. In addition, for diagnostic purposes, it is helpful to detect the spark burning duration and take suitable measures if the duration lies outside a predetermined desired value range.
A characteristic evaluation signal from which the two phenomena mentioned above can be measured and evaluated is the primary-side profile of the ignition voltage.
With the power output stage switched on, the primary-side ignition voltage has a low level of the order of magnitude of approximately 2V and, after the current flow through the primary winding is switched off at the ignition instant, momentarily rises to approximately 300 to 400V (spark head) until a flashover occurs at the spark plugs on the secondary side. The primary-side ignition voltage then levels out at a value above the battery voltage Vbat which depends on the battery voltage, the burning voltage of the spark gap and on the transformation ratio of the ignition coil. As soon as the energy stored in the ignition coil has then dissipated, the primary-side ignition voltage swings back to a value corresponding to the battery voltage Vbat.
The primary-side ignition voltage Upr thus has relatively high voltage levels which lie above the input voltage range of integrated circuits and necessitate special clamping circuits.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a measuring and diagnostic device for an ignition system of an internal combustion engine which overcomes the above-mentioned disadvantages of the heretofore-known devices of this general type, which is suitable in particular for integrated circuits, which makes it possible for the relatively large level differences of the primary-side ignition voltage in the range of interest to be reliably detected and evaluated through the use of simple circuitry measures in a wide temperature range with a single reference voltage, and at the same time, in addition to generating a signal for measuring the spark burning duration, also monitors the ignition switch and, if a fault is identified, generates signals which, when they occur, enable the ignition switch or the internal combustion engine to be protected against destruction by being switched off.
With the foregoing and other objects in view there is provided, in accordance with the invention, for an internal combustion engine having an ignition system with an ignition coil and with an ignition switch, the ignition coil having a primary coil supplied with a battery voltage, the ignition switch connected to the primary coil via a junction point for periodically interrupting a current through the primary coil, a measuring and diagnostic device, including:
a protective resistor;
a first regulating circuit having an input to be connected, via the protective resistor, to the junction point between the primary coil and the ignition switch and having an output;
the first regulating circuit including a first linear amplifier having a non-inverting input connected to the input of the first regulating device, having an inverting input supplied with a reference voltage, and having an output connected to the output of the first regulating device;
the first regulating circuit including a first transistor having a base connected to the output of the first linear amplifier, having a collector connected to the input of the first regulating circuit, and having an emitter connected to ground;
a first comparator having a non-inverting input connected to the output of the first regulating circuit, an inverting input supplied with a first comparison voltage and having an output for outputting a diagnostic signal;
a first resistor and a second resistor;
a second regulating circuit, configured identical to the first regulating circuit, having an output and having an input connected, via the first resistor, to the battery voltage and connected to an auxiliary voltage via the second resistor;
the second regulating circuit including a second linear amplifier having a non-inverting input connected to the input of the second regulating circuit, having an inverting input supplied with the reference voltage, and having an output connected to the output of the second regulating circuit;
the second regulating circuit including a second transistor having a base connected to the output of the second linear amplifier, having a collector connected to the input of the second regulating circuit, and having an emitter connected to ground; and
a second comparator having a non-inverting input connected to the output of the second regulating circuit, having an inverting input connected to the output of the first regulating circuit and having an output for outputting a measurement signal.
In accordance with another feature of the invention, the protective resistor and the first resistor have identical resistances.
In accordance with yet another feature of the invention, the reference voltage is greater than the maximum saturation voltage of the ignition switch.
In accordance with a further feature of the invention, the first linear amplifier turns the first transistor off, if the primary voltage is less than the reference voltage, and turns the first transistor on if the primary voltage is greater than the reference voltage.
In accordance with yet a further feature of the invention, the first linear amplifier turns on the first transistor when Upr>Uref to such an extent that a first current I
1
=(Upr−Uref)/R
1
is established through the protective resistor, which effects a voltage drop Upr−Uref across the protective resistor.
In accordance with another feature of the invention, the first comparison voltage has a value of 0V<V
1
<0.7V.
In accordance with yet another feature of the invention, the first and the second resistor are dimensioned in such a way that the second current corresponding to the sum of the currents flowing through them is greater than the first current thro
Greenberg Laurence A.
Lerner Herbert L.
Metjahic Safet
Nguyen Vincent Q.
Siemens Aktiengesellschaft
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