Internal-combustion engines – Igniters – Incandescent
Patent
1997-06-16
1998-10-20
Nelli, Raymond A.
Internal-combustion engines
Igniters
Incandescent
F02B 908
Patent
active
058231552
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a glow pin control circuit for controlling the electrical heating energy of a glow pin that may be used for igniting fuel, in particular for auxiliary heating apparatus in vehicles, the control circuit comprising a direct voltage source delivering the heating energy and having a supply voltage terminal on the high potential side and a ground terminal on the low potential side, and a switch means that is connected in series with the glow pin between the supply voltage terminal and the ground terminal and alternatingly turns on and off the supply voltage supplied to the glow pin, in a modulated and clocked manner.
BACKGROUND OF THE INVENTION
Glow pins of auxiliary heating apparatus of vehicles are usually controlled in clocked manner with the aid of relays. Due to the inertia of the relay contacts, such clocked control can only take place with very low frequency, usually with a clock frequency of about 1 Hz. With such a low relay switching frequency, temperature fluctuations of the glow pin result, since the glow pin cools down during switching off periods. These temperature fluctuations cannot be prevented by supplying pulse width modulated switching control pulses to the relay. Such pulse width modulated switching control pulses in fact may be used for compensating voltage fluctuations of the direct voltage source delivering the heating energy, which as a rule is the vehicle battery, but the voltage value thereof may change depending on the load condition. However, the switching-off periods occurring when the switching relay is controlled with a pulse frequency of 1 Hz, are too long for being overcome by the temperature inertia of the glow pin.
It would thus be desirable to use switching control pulses of considerably higher frequency, for example in the range of 50 Hz. With such high switching control pulses the temperature inertia of the glow pin bridges the switching-off periods so that temperature fluctuations due to the clocked control of the glow pin do not occur any more. Such high switching frequencies, however, cannot be realized with relays due to the mechanical inertia of the relay contacts.
Moreover, relays are opposed to the trend of integrating control apparatus for auxiliary heating apparatus in vehicles in the heating apparatus housings. Relays thus constitute a hindrance with such integrated control apparatus.
SUMMARY AND OBJECTS OF THE INVENTION
It is an object of the invention to make available a glow pin control circuit of the type indicated at the beginning, which is suited better for integrated control apparatus and results in an as constant as possible glow temperature of a glow pin and an as high as possible safety of the glow pin operation.
A glow pin control circuit of the type indicated at the outset is improved according to the invention in that the switch means is composed with a semiconductor power switch connected between the supply voltage terminal on the high potential side and the glow pin. The semiconductor power switch selectively connects and disconnects the supply voltage to the glow pin or incandescent means in accordance with a switching control signal. A pulse modulation circuit or means is provided feeding a control terminal of the semiconductor power switch with switching control pulses forming the switching control signal. The pulses are of such high pulse frequency and are modulated in accordance with the currently present voltage value or magnitude of the direct voltage source in such manner that the glow temperature of the glow pin remains substantially constant, irrespective of fluctuations of the currently present voltage value of the direct current source and despite the switching-off periods due to the clocked operation.
The use of a semiconductor power switch instead of the relay common so far, on the one hand, leads to smaller space requirements of the glow pin control circuit, which more easily permits the integration of control apparatus, and in addition thereto allows operation with almost arbitra
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J. Eberspacher GmbH & Co.
Nelli Raymond A.
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