Apparatus for controlling the starter in internal combustion engine

Abstract

 An apparatus for controlling the starter, in internal combustion engines, the fuel inlet circuit of which comprises an automatic starter device (17, 19, 20) for enriching the mixture; the starter device (17, 19, 20) comprises a wax type thermostatic actuator (17) having a heating resistor element (19) selectively connectable to the voltage generator (10, 15) which feeds the electrical loads (12, 13, 14) of the motor vehicle and the ignition system (11) of the engine, by thermally operated electronic switch (Q1; Q3) upon reaching an established threshold temperature, existing in a housing for the engine, which depends upon the environmental temperature and/or upon the temperature of the same engine.

Description

BACKGROUND OF THE INVENTION

[0001] This invention refers to an apparatus for controlling the starter device or rich mixture control for internal combustion engines, in particular for low-powered two-stroke engines normally used on scooters or similar two-wheels motor vehicles.

[0002] As is known, in the field of low-powered two-stroke engines, to which the invention refers, the circuit for feeding the fuel mixture to the engine comprises a carburettor normally provided with an automatic starter device which comes into operation to enrich the fuel mixture fed to the engine, thereby facilitating the starting up and smooth running of the engine itself under certain environmental conditions.

[0003] In general, an automatic starter device comprises a wax-type thermostatic actuator disposed into an auxiliary circuit for feeding the fuel mixture, which is provided with a resistor element which, when the engine is running, is constantly connected to the electric voltage generator which normally supplies power to the ignition system of the engine, in order to disconnect the auxiliary circuit feeding the fuel mixture to the engine.

[0004] In particular, the resistor element of a conventional starter, is constantly powered by the voltage generator of the vehicle, and heats the wax contained in the thermostatic actuator whose volume increases considerably with the temperature, acting on a small piston member which operates a shutter device which progressively closes the auxiliary circuit supplying fuel to the engine.

[0005] In the starters of conventional type, the resistor element is consequently powered as soon as the engine starts up, and the auxiliary circuit for feeding the mixture remains active for a certain period of time, following the start up, and is then progressively deactivated until it is shut off completely.

[0006] The duration of the transient state depends upon the structural features of the starter device, as well as upon the thermal power generated by the resistor element, the environmental temperature and the thermal resistance existing between the starter device and the outside environment. In fact, these devices are very often set by appropriately insulating their housing.

[0007] It is therefore evident from what has been described above, that in the conventional type automatic starter devices the electric heating resistor remains constantly switched on and their transient state of activation depends solely upon the functional and structural features of the device itself; this making it difficult to achieve a controlled operation of the starter device, as the temperature of the outside environment and/or of the engine changes, both during start up and running of the engine.

[0008] With the automatic starter devices presently known, there is practically no possibility of achieving a controlled operation of the auxiliary fuel mixture supply circuit, either during start up or while the engine is running, with the serious risk of the starter device not cutting in or cutting in incorrectly, particularly when operating at low environmental temperatures and with tendentially weak mixture settings, aimed at reducing harmful emissions.

OBJECTS OF THE INVENTION

[0009] The main object of this invention is to allow a controlled operation of the starter device, both during start up and the normal running of the engine in order to obviate the problems of the previously known starter devices.

[0010] A specific object of this invention is to provide a control apparatus for controlling the starter of internal combustion engines, in particular for two-stroke engines, in order to allow greater flexibility in operating or managing the starter device, both in relation to the environmental conditions and the operative conditions of the same engine.

[0011] A still further object of this invention is to provide an electronic control apparatus for controlling the starter device of an engine, as described previously, capable of self-powering by means of the same feeding voltage for the starter, without jeopardising the correct functioning of the latter.

[0012] A further object of this invention is to provide a control apparatus for controlling a starter device, which is easy to assemble onto a motor vehicle, without calling for complicated wiring operations, and which at the same time is able to operate with any ignition system and any power supply system for the engine.

[0013] A still further object of the invention is to provide a control apparatus for controlling a starter device, whereby it is possible to directly and flexibly enable the cutting in and cutting out of the auxiliary circuit supplying the fuel mixture to the engine, in such a way as to ensure the smooth running of the engine both at low environmental temperatures, and within a pre-established temperature range, thereby making it possible to reduce harmful emissions.

BRIEF DESCRIPTION OF THE INVENTION

[0014] All this can be achieved by means of a control apparatus for controlling starter devices for internal combustion engines, in particular two-stroke engines in low-powered motor vehicles, according to which the starter device comprises an electric heating resistor selectively connectable to a power source by means of a thermally controlled electronic switch capable of cutting in when a pre-established threshold temperature is exceeded.

[0015] In particular, according to the invention, the electronic switch connected in series to the electric heating resistor of the starter device, is switched on by a thermal sensor, upon reaching a pre-established threshold temperature, which senses the temperature in a housing for the sensor, regardless of the environmental temperature and the temperature of the engine.

[0016] According to a preferred embodiment, a control electrode of the electronic switch for connecting the starter device to a power supply voltage, is connected to a temperature sensing circuit which is self-powered with the same supply voltage for the electric heating resistor of the starter device, by means of a selective control circuit which senses the switched on state of the same electronic switch which connects the starter device to the power source.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] These and further features of the control apparatus for controlling a starter device of an internal combustion engine, according to this invention, will be described in greater detail hereunder, with reference to the accompanying drawings, in which:

Fig. 1 shows the general diagram of a first embodiment of a starter control apparatus, according to the invention;

Fig. 2 shows a diagram of the electronic control circuit for the starter, forming part of the apparatus of figure 1;

Fig. 3 shows the general diagram of a second embodiment of a starter control apparatus, according to the invention;

Fig. 4 shows a general diagram of the electronic control circuit for the starter, forming part of the apparatus of figure 3.

Fig. 5 shows a flow diagram illustrating the strategy for controlling the starter, according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

[0018] With reference to figures 1 and 2, a description will be given of the general features and of a first embodiment of an apparatus for controlling a starter device, according to the invention.

[0019] As shown in the example of figure 1, the apparatus as a whole comprises a voltage generator 10 having a single winding for supplying power to an ignition system 11 of the internal combustion engine of a motorvehicle, and to an alternating current load 12, as well as to a direct current load 13 and, if necessary, to an electric battery 14; the power is supplied through a voltage regulator 15 schematically shown. The ignition circuit 11 and the voltage regulator 15 may be of any suitable type, for example as shown and described in IT-A-1.270.142 of the same applicant, filed on 26.05.1994, to which reference is made and which forms an integral part of these specification.

[0020] The apparatus of fig. 1 also comprises an automatic starter device connected to an auxiliary circuit 16 for supplemental feeding of the fuel mixture to the engine, where A, B and M respectively indicate an inlet for the auxiliary air, an inlet for the fuel, and the outlet for the auxiliary flow of fuel mixture to the engine.

[0021] An automatic starter device, as shown, substantially comprises a per se known wax-type thermostatic actuator 17, having a piston member 18 designed to close the fuel inlet B when it is thrust forward by the expansion and by the increased volume of the wax caused by the heat generated by a thermally resistive element in contact with the actuator, for example by an electric resistor 19.

[0022] As also shown in figure 1, the resistor 19 for heating the thermostatic actuator 17 of the automatic starter device, is connected to the voltage generator 10, and more precisely to the alternating current outlet AC of the voltage regulator 15, through a control device 20 comprising a thermally operated electronic switch, connected in series to the supply circuit of the resistor 19. The entire control device 20 is enclosed in a casing, from which protrude only the two inlet IN e earth GND terminals, the casing being disposed in a housing for the engine.

[0023] According to a general aspect of this invention, the electronic switch of the control device 20 is thermally operatable by means of a temperature sensing circuit, upon reaching a threshold temperature appropriately preset by the manufacturer; the aforesaid sensor circuit consequently measures the temperature existing in the compartment housing the engine.

[0024] Therefore the duration of the transient state, that is to say the operating time of the thermostatic actuator 17, after the temperature sensing circuit has detected the threshold temperature has been exceeded, depends upon several factors, in particular upon the heat generated by the resistor 19 for the starter, the outside environment temperature, and the temperature of the engine with which the control device 20 is indirectly in contact; in this way it is possible to ensure the controlled operation of the starter device, both during start up and during the normal running of the engine.

[0025] A first preferred embodiment of the thermal control device 20, particularly suitable for use with a voltage generator 10 having a single winding for supplying power to an ignition system 11 and to the electrical loads 12, 13 and 14 of a motor vehicle, is shown in the diagram of fig. 2.

[0026] In this figure, the control device 20 comprises a thermally operated electronic power switch Q1, for example an MOS transistor, or other suitable electronic switch, which must have a low voltage drop when in ON condition, so as to feed the starter correctly and generate a low quantity of heat, so as not to significantly affect the value of the temperature sensed by a temperature sensed circuit; the electronic switch must also be designed in such a way as to have a low current consumption on the control electrode, and can be selectively connected to a feeding voltage, in series with the resistor 19 of the thermostatic actuator 17, by means of the IN and GND terminals.

[0027] The electronic switch Q1 is thermally operated by means of a temperature sensing circuit 21 capable of sensing the temperature in a compartment or casing which houses the device 20; such temperature, as mentioned previously, is correlated to the temperature of the outside environment and to that of the internal combustion engine.

[0028] In particular in the example of fig. 2, the temperature sensing circuit 21 comprises a first voltage comparator 22, whose outlet U1 is connected, by means of the resistor R1, to the control electrode G of the electronic switch Q1.

[0029] The non inverting inlet I1 of the voltage comparator 22, is fed with a constant voltage, for example by the voltage of the central point of a voltage divider R2 and R3 which supplies a reference voltage correlated to the value of a threshold temperature Ts, which when exceeded causes the electronic switch Q1 to switch ON and consequently supply power to the resistor 19 of the starter.

[0030] The inverting inlet I2 of the voltage comparator 22 is in turn fed with a voltage of variable value in relation to the changes in temperature sensed by the sensing circuit 21. More precisely, the inverting inlet I2 is connected to the central point of a second voltage divider R4, R5 in which the resistor R5 has a resistance of a value which varies according to the sensed temperature; in particular, the resistor R5 is of NTC type whose resistance decreases as its temperature increases. The two voltage dividers R2, R3 and R4, R5 provide a resistive bridge which together with the voltage comparator 22 define a temperature sensor for operation of the electronic switch Q1.

[0031] The starter control device 20 is self-fed with the same inlet voltage for the heating resistor 19 of the thermostatic actuator of the starter device. In this connection, as shown in fig. 2, the inlet side of the temperature sensing circuit 21, that is to say the part which supplies power to the comparator 22 and the two voltage dividers R2, R3 and R4, R5 is connected, by means of a voltage stabiliser 23, to the outlet of a direct current feeding circuit 24, comprising a diode D1 and a capacitor C1, branched from the inlet side IN of the control device 20, as shown.

[0032] More precisely, the temperature sensing circuit 21 is connected, by means of a second electronic switch Q2, for example in the form of a transistor, to the feeding circuit 24.

[0033] The base of the transistor Q2 is in turn connected to the central point between a resistor R6 and a ZENER dicde Z1; the resistor R6, the diode Z1 and the transistor Q2 together define a voltage stabiliser circuit capable of stabilising the output voltage of the feeding circuit 24 at a constant value.

[0034] In the case shown, the use of the voltage stabilizer 23 is necessary in that, even though it is regulated at a low effective value, typically at a value of 13 Volts by the voltage regulator 15, the alternated voltage applied to the inlet 12 presents a very high peak value which may be as high as 100 Volts; the capacitor C1 of the feeding circuit 24, by means of the diode D1 will consequently self-charging to this peak value, to feed the temperature sensing circuit 21. However the inlet voltage of the voltage comparator 22 and the voltage applied to the control electrode G of the electronic switch Q1, must be kept regulated at a value much lower than the above-mentioned peak value, for example at a voltage of approximately 10 Volts. This stabilising function for the inlet voltage of the temperature sensing circuit 21, is consequently carried out by the unit composed of the resistcr R6, the diode Z1, the transistor Q2 and a capacitor C2 connected in parallel to the outlet side of the voltage stabiliser circuit 23, the charge value of C2 being therefore limited to the 10 Volts required by the ZENER diode Z1.

[0035] It is obvious therefore that any other type cf voltage stabiliser or regulator suitable for the required voltages, can be used in place of the voltage stabiliser 23.

[0036] As mentioned previously, the entire control device is self-fed by means of the same circuit as the resistor 19 for heating the starter device, which is connected in series to the control switch Q1; in particular, the control device is fed with the voltage supplied by the capacitor C1 of the feeding circuit 24, appropriately stabilised by the voltage stabiliser circuit 23.

[0037] In order to maintain the output voltage of the feeding circuit 24 at an adequate value, the capacitor C1 must be periodically charged to the desired voltage value; this can take place only when the electronic switch Q1 is OFF, since under these conditions the capacitcr C1 is subjected to the entire voltage existing on the AC output of the regulator. Conversely, when the switch Q1 is ON, that is to say when the current is flowing through the resistor 19, there is practically no voltage on the inlet IN, due to the fact that the diode D1 is connected towards the earth GND through the same switch Q1.

[0038] In order to ensure the correct feeding of the entire circuit, both during the ON phases and during the OFF of the switch Q1, that is to say during the phase of activation of the starter circuit of the engine, it is necessary in any case to periodically recharge the feed-through capacitor C1.

[0039] In this connection, a special control circuit 25 is provided to control the feeding circuit 24, which when the voltage of C1 drops below a pre-established value, operates to open the switch Q1 for a very brief time instant sufficient to allow the recharging of C1, without significantly affecting the heating phase of the starter.

[0040] In the case shown, the control circuit 25 comprises a second voltage comparator 26 whose inverting inlet I3 is connected to the central point of a voltage divider R7 and R8 so as to be fed with an appropriate fraction of the output voltage of the voltage stabilising circuit 23.

[0041] In turn, the non-inverting inlet I4 of the voltage comparator 26, is connected to the central point of a further voltage divider R9, R10 so as to be fed with a fraction of the output voltage of the feeding circuit 24; a hysteresis resistor R11 is connected between the non-inverting inlet I4 and the outlet of the voltage comparator 26. In turn, the outlet of the voltage comparator 26 is connected to the cathode of a diode D2, whose anode is in turn connected to the control electrode G for the electronic switch Q1.

[0042] The apparatus operates as described briefly hereunder: at start up, when the engine is cold, or when the variable resistor R5 of the temperature sensing circuit 21 senses a Teng temperature below a pre-established threshold value Ts for controlling the starter (Teng>Ts-NO, fig. 6) Q1 is open or OFF and the resistor 19 of the starter is not powered (Starter OFF - fig. 6), and consequently the auxiliary circuit of the carburettor is open (SI), enabling a secondary flow of fuel mixture to be fed to the engine.

[0043] As the temperature of the engine increases, or as the temperature of the external environment changes, when the temperature sensor senses that the Teng temperature has reached and exceeded the threshold value Ts (Teng>Ts-SI), the electronic switch Q1 is made to close or ON, connecting the resistor 19 of the starter to the inlet voltage source (starter ON). Flowing of the current through the resistor 19 progressively heats the thermostatic actuator 17 causing expansion of the wax which, after a transitory period of time depending upon the temperature of the engine, and upon the temperature of the external environment, as well as upon the heat generated by the circulation of current through the resistor 19, gives rise to the closure of the auxiliary circuit supplying fuel to the engine.

[0044] At this point, with the engine running, and with temperature conditions remaining higher than those of the Teng threshold value Ts, since it is thermally controlled the switch Q1 will be constantly closed or OFF, (except for the brief intervals of time in which C1 is fed) and the resistor 19 of the starter fed, maintaining the auxiliary circuit of the carburettor closed.

[0045] Whenever, due to various causes, the temperature of the engine and/or the temperature of the external environment decreases, thereby causing the Teng temperature of the thermal sensor to drop below the threshold temperature Ts, the switch Q1 will be closed or ON again to feed the resistor 19 of the starter device.

[0046] A more detailed description will now be given of the operation of the apparatus with reference to the electronic control device of figure 2.

[0047] As mentioned previously, the voltage comparator 22 of the temperature sensing circuit 21 has its non-inverting inlet I1, and inverting inlet I2 connected to a resistive bridge fed with the voltage stabilised by circuit 23 comprising the voltage divider R2, R3 and the voltage divider R4 and R5, in which R5 is a thermoresistor with negative temperature coefficient (NTC) whose resistance varies as the temperature changes, that is to say it decreases as the temperature of the resistor increases.

[0048] The non-inverting inlet I1 of the comparator 22 consequently has a voltage of a constant value which defines the Ts value of the threshold temperature at which the temperature sensing circuit 21 comes into operation. Vice versa the inverting inlet I2 of the comparator 22 has a voltage which varies in relation to variations in the temperature of R5.

[0049] With the engine cold or at start up, the temperature sensed by R5 is lower than the threshold temperature Ts; under these conditions the voltage applied to the inverting inlet I2 of the comparator 22 is higher than the voltage existing on the non inverting inlet I1.

[0050] The voltage at the outlet U1 of the comparator 22 will be low and the electronic switch Q1 will be cut off or open, preventing current from being fed to the resistor 19 of the starter. In this situation, the only current flowing in the starter is the current feeding the starter control device which being very low (0.5 mA, 3mA), is unable to activate the starter which requires approximately 1.5 A to be activated, and 0.2 A to remain in the activated state.

[0051] As the temperature sensed by R5 increases, the voltage existing on the inverting inlet I2 of the comparator 22 drops below the level of the voltage present on the non-inverting inlet I1; consequently the output U1 of the voltage comparator 22 will switch from a low value to a high value by biasing, by means of the current limiting resistor R1, the control electrode G of the electronic switch Q1, which will enter into a conductive state enabling current to be supplied to the resistor 19; the starter closes the auxiliary circuit for feeding fuel to the engine after a transitory period or interval of time depending upon the operative conditions of the engine, as well as upon the temperature of the external environment.

[0052] The MOS transistor Q1 of fig. 2 or other equivalent power switch, therefore constitutes a thermally-controlled electronic switch, which, when it is conductive condition, presents a very low voltage drop. Under these conditions the capacitor C1 of the feeding circuit 24 discharges progressively to feed the entire device.

[0053] To enable the device to continue to be fed, it is necessary to periodically recharge the capacitor C1; however, since C1 is branched from the inlet terminal of the electronic device which controls the starter, and is consequently subjected the same voltage existing on the electronic switch Q1, to enable it to be recharged it is necessary for Q1 to be opened or OFF for a very brief time instant sufficient to allow the recharging of C1.

[0054] It is for this purpose that the control circuit 25 comprising the voltage comparator 26 is provided with hysteresis on the voltage existing at the terminals of the capacitor C1. By appropriately calculating the values of the resistances of the two voltage dividers R7, R8, and R9, R10, and of the feedback resistor R11, it is possible to define a minimum voltage threshold on the capacitor C1, sufficiently higher than the voltage of the ZENER diode Z1, below which the outlet U2 of the comparator 26 will switch low and by means of the diode D2 will cut off the switch Q1, which will open to allow the capacitor C1 to recharge to the voltage value corresponding to the high threshold of the hysteresis for which the voltage comparator 26 will go back to switching high.

[0055] Summarising, the switch Q1 will be cut off, or in a conductive state, depending on the condition of the outlet U1 of the comparator 22, which in turn will depend on the temperature of the variable resistor R5; if the temperature sensed by the resistor R5 is below the threshold value Ts (low temperature), then the outlet of the comparator 22 will be low and Q1 cut off, enabling the capacitor C1 to recharge, by means of the diode D1, to the voltage value existing on the inlet terminal IN.

[0056] Since the device consumes a very small amount of current, varying roughly from 0,5 mA to 3 mA in relation to the peak voltages present on the inlet terminals IN, of the resistors, and to the type of voltage comparator used, with a temperature below the threshold value Ts and consequently with Q1 open, the starter in fact is not powered since in order to be activated it would require a considerably higher current, for example of 1,5 Ampere, and a current for maintaining the conductive state of approximately 0,2 Ampere.

[0057] Conversely, when the temperature of R5 exceeds the threshold value Ts determined by the resistive divider R2 R3, then the outlet U1 of the comparator 22 will be high and will bias the switch Q1 to close. The switch Q1 will consequently choose between the conductive and cuttoff conditions, controlled by the outlet of the voltage comparator 22.

[0058] Since the charging current for the capacitor C1 is limited exclusively by the low resistance 19 of the starter, whose value is approximately 20 Ohm under normal operating conditions, the time required by C1 to recharge from the low value of the voltage threshold, to the high value, is very short, while the time in which the same capacitor C1 discharges from the high threshold to the low threshold, to feed the temperature sensing circuit 21, depends upon the current consumption of all the components. The two times "Ton" of conduction of Q1, and "Toff" of cuttoff are very different from each other, with Ton>>Toff; therefore, the voltage at the terminals of the resistor 19 of the starter differs substantially from that existing at the outlet AC of the voltage regulator 15 by a fraction, for example lower by 0,2 Volt, for an output of 13 rated Volts, without jeopardising the correct functioning of the starter.

[0059] For certain particular applications two threshold temperatures Ts1 and Ts2 may be required, with Ts1<Ts2, so that for a temperature TR of the variable resistor R5 of the temperature sensing circuit 21, there will be:

TR<Ts1 starter not fed;

Ts1≤TR≤Ts2 starter fed;

TR>Ts2 starter not fed.

[0060] All this may be achieved as shown by the phantom line in figure 2, for example by providing a third voltage comparator 27 whose non-inverting inlet I5 is connected to the central point of the resistors R4 R5, while its inverting inlet I6 is connected to the central point of a further voltage divider R12, R13 fed with the stabilised output voltage of the circuit 23; R12, R13 define the second temperature threshold Ts2 as required. The outlet of the voltage comparator 27 on the contrary is connected to the cathode of a diode D3, while the anode of D3 is connected to the control electrode G for controlling the electronic switch Q1, as shown.

[0061] In the case of figures 1 and 2, the starter control apparatus comprises a single thermally-operated electronic switch, in that the voltage regulator 15 used supplies only positive half waves as its AC outlet.

[0062] Whenever use is made of a commercial-type ignition and load input system, as shown in figure 3 and as described in the introductory part of the patent IT-A-1.270.142, mentioned previously, in which the AC output of the voltage regulator 15 presents positive and negative half waves, use must be made of two thermally-controlled electronic switches, for the control device 20, for example according to the diagram of figure 4.

[0063] In figure 3 and in figure 4 the same reference numbers as the previous figures have been used to indicate similar or equivalent parts, to which reference is made.

[0064] The device of figure 4 differs from the device of figure 2 in that the voltage comparator 22 must alternatively cut off or put into conductive state both the electronic switch Q1 and the electronic switch Q3 to allow or cut-off the circulation of the current through the resistor 19 of the starter, during both the half waves.

[0065] Consequently, also in figure 4, reference 24 has been used to indicate a self-feeding circuit, reference 23 a voltage stabiliser, and reference 25 a feeding control circuit, as explained previously. Again in figure 4, phantom lines have been used to indicate the use of a voltage comparator 27 whenever two threshold temperatures Ts1 and Ts2 are required.

[0066] The circuit of figure 4 differs from the circuit of figure 2, due to the presence of two thermally-controlled electronic switches Q1 and Q3, and due to the fact that the feeding circuit 24 is connected to the inlet terminal IN and to the earth GND, by means of two diodes D1, D4 with the cathode in common, designed to allow the charging of the capacitor C1 both during the positive half waves, and during the negative half waves of the voltage existing at the AC outlet of the voltage regulator 15. For all the remainder, the circuit of figure 4 operates in a substantially similar way to the circuit of figure 2.

[0067] In the case shown in figure 4, since the two power MOSS Q1 and Q3 present an internally integrated diode, with the anode connected to the source and the cathode connected to the drain, for this reason use has been made of two MOSFET connected to the source and the gate in common, which are simultaneously piloted onto the gate and are capable of blocking the current in both directions. The charging of the capacitor C1 takes place by bridge, by means of the diodes D1 and D4 and those integrated inside Q1 and Q3. The negative pole of the power supply which in figure 2 is referred to the earth voltage, now refers to the source shared in common by the two switches Q1 and Q3, in such a way that by connecting their gate in parallel, they can be controlled simultaneously.

Claims

1. Apparatus for controlling a starter device (17, 19) in a feeding circuit (16) for feeding a fuel mixture to an internal combustion engine, in which the starter device (17, 19) comprises a wax-type thermostatic actuator (17) having a resistive heating element (19) connectable to a voltage source (AC), characterised in that:

- the resistive heating element (19) of the starter device (17, 19) is selectively connectable to the voltage source (AC), by means of an electronic control device (20) comprising an electronic switch (Q1; Q3) connected to an inlet terminal (IN) and to an outlet terminal (GND) of the control device, in series with the resistive heating element (19);

- in that it comprises a temperature sensing circuit (21) connected to a control electrode (G) of the electronic switch (Q1; Q3); and

- in that it comprises a self-feeder circuit (24) branched off between the inlet terminal (IN) and the outlet terminal (GDN) of the electronic control device.

2. Apparatus as claimed in claim 1, characterised in that the temperature sensing circuit (21) comprises a heat sensitive resistor (R5) for sensing the temperature existing in a housing for the engine.

3. Apparatus as claimed in claim 2, characterised in that the temperature sensing circuit comprises a voltage comparator (22) a non-inverting inlet (I1) of which is fed with a voltage of a constant value proportional to a first threshold temperature, and an inventing inlet (I2) of which is fed with a variable voltage which depends on the temperature sensed by the heat-sensitive resistor (R5), and in which the outlet (U1) of the voltage comparator (22) is connected to the control electrode (G) of the electronic switch (Q1; Q3).

4. Apparatus as claimed in claim 3, characterised in that the inverting (12) and non-inverting (I1) inlets of the voltage comparator (22) are connected to a resistive bridge (R2, R3; R4, R5) whose branch (R4, R5) connected to the inverting inlet (I2) comprises a temperature sensitive resistor (R5) having a negative temperature coefficient (NTC).

5. Apparatus as claimed in claim 1, characterized in that the self-feeding circuit (24) comprises a capacitor (C1) connected to the voltage source (IN) for the resistive heating element (19) of the starter device (17, 19), and by comprising a control circuit (25) for controlling the charge state of capacitor (C1) of the self-feeding circuit (24), comprising a second voltage comparator (26) whose outlet (U2) is connected to the control electrode (G) of the electronic switch (Q1, Q3 ; in which the inverting inlet (I3) of the second voltage comparator (26) is fed with the output voltage of a voltage stabiliser circuit (23); in which the non-inverting inlet (I4) of the second voltage comparator (26) is fed with the voltage existing on the capacitor (C1) of the self-feeding circuit (24), and in which the second voltage comparator (26) comprises a hysteresis circuit (R11) for the voltage of the capacitor (C1) of the self-feeding circuit (24), defining a first threshold voltage during the discharge phase of the capacitor (C1), higher than the output voltage of the voltage stabiliser circuit (23), and a second threshold voltage higher than the first one during the charging phase of said capacitor (C1).

6. Apparatus as claimed in claim 5, characterised in that, during the feeding phase of the resistive heating element (19) of the starter device (17, 19), the control circuit (25) of the capacitor (C1) of the self-feeding circuit (24) is preset to cut off the electronic switch (Q1; Q3), for a length of time much shorter than the conductive time of the same electronic switch (Q1; Q3) during the aforesaid feeding phase.

7. Apparatus as claimed in claims 1 and 3, characterised in that the temperature sensing circuit (21) comprises a further voltage comparator (27) whose outlet (U3) is connected to the control electrode (G) of the thermally-actuated electronic switch (Q1; Q3), a non-inverting inlet (I5) of which is fed with said variable voltage depending on the temperature sensed by the same sensing circuit (21), and the inverting inlet (I6) of which is fed by a voltage divider (R7, R8) with a constant voltage proportional to a second threshold temperature higher than the first one.

8. Apparatus as claimed in claims 1 and 3, characterized in that the resistive heating element (19) of the starter device (17, 19) is fed in alternating current (AC) with positive and negative half waves from said voltage source (10); in that the electronic control device comprises a first and a second thermally-operated electronic power switches (Q1; Q3 , both connected in series to the resistive heating element (19), of the starter device (17, 19);
   in that the outlet of the first voltage comparator (22) is connected to control electrodes (G) of both the electronic switches (Q1; Q3); and
   in that one side having negative polarity of the self-feeding circuit (24) is connected to a central point of the power circuit of both the electronic switches (Q1; Q3).

Drawing