Security circuit for a cooling fluid temperature-control device of an internal-combustion engine

The present invention relates to the regulation of the coolant temperature of the cooling circuit of an internal combustion engine.

The cooling circuit of an internal combustion engine comprises, in general, a motor fan which is powered either all or nothing, or continuous control, depending on the temperature prevailing in the coolant circuit. To this end, a temperature sensor is inserted at a predetermined location of the cooling circuit.

The over temperature operation of an internal combustion engine can cause permanent damage what the drivers of motor vehicles are often not aware. Thus, a heat engine can be severely damaged when a failure occurs in the cooling circuit. For example, when the temperature sensor is often a thermal switch is malfunctioning, the cooling system fan can not be fed properly. This leads to a very rapid increase in temperature and this increase, although it is displayed on a thermometer of the dashboard, may not be perceived by the driver so that the internal combustion engine continues to operate under conditions of excessive temperature.

If to increase the effectiveness of the control, the cooling circuit is associated with a temperature servo complex assembly comprising a large number of electronic components, the reliability of the circuit can be smaller than that of an assembly operating all or nothing, and in this case, the risk of damage to the engine increases accordingly.

US-A-3,568,648 discloses a device for regulating the coolant temperature of an internal combustion engine, in particular for use in a railroad locomotive. This device comprises several motor fan units, of which the electric motors are supplied by means of relays controlled by adjustment buckles. The installation also includes a number of additional control loops, including one that allows to excite all relays together when the temperature exceeds a value considered dangerous. However, this system is relatively complex because of the cost constraints are not the same as in the automotive art. In addition, this device allows only a discontinuous adjustment of power sent to the motor fan group.

Also known from DE-A-2 Patent 827 373 and FR-A-2455174, regulating devices for cooling circuits for engaging a fan to get the full cooling effect when a temperature threshold value measured by a single sensor system is reached.

US-A-3924101 describes, meanwhile, oven temperature detection circuit having a MOS-type transistor.

The invention aims to provide a safety circuit for a coolant fluid of the temperature control device of the cooling circuit of an internal combustion engine to significantly reduce the risk of over temperature operation of the engine, even when regulation is performed by means of a complex electronic circuit.

The invention therefore relates to a cooling device of an internal combustion engine, comprising at least a motor-fan unit which is associated with the circuit of the engine cooling heat transfer fluid and whose diet is based on a signal temperature measurement provided by a sensor mounted in said heat transfer fluid circuit, a first source of reference and a first comparator connected by one of its inputs to this source and by the other of its inputs to a point representing said signal measurement, said comparator being connected by its output to a relay which a movable contact is connected in the circuit of the engine motor fan unit in such a manner that it connects this motor directly to the power source when the fluid temperature coolant reaches a predetermined value, the cooling device comprising a second source of reference and a second comparator whose output signal is used to control a regulator also connected in the supply circuit of the electric fan assembly to determine the supply depending on the temperature, this device being characterized in that said control member is a power semiconductor intended to ensure the continuous adjustment of the motor fan unit of the power supply into a predetermined temperature range, in that the contact of said relay is connected in parallel with the power circuit of said semiconductor, and in that the set point of the first reference source is chosen at a value corresponding to the maximum temperature that the internal combustion engine can reach without deterioration.

Thanks to these features, continuous adjustment is obtained from the power sent to the motor fan group. In addition, a failure of the control device always causes excitation of the electromagnetic switching member, which supplies power to full power of the motor fan unit and the maximum cooling of the coolant cooling the engine. Of course, this means that if a failure occurs, the power absorbed by the motor fan group will be maximum, even if the conditions of the internal combustion engine speed do not require such power, but it is considered that s 'This is a lesser evil to the extent that the deterio ration or destruction of the internal combustion engine can be avoided.

The invention will be better understood using the following description of example and given solely with reference to the accompanying drawings, wherein:<ul><li>- Fig. 1 is a diagram of a safety circuit forming part of a temperature regulating device according to the invention;</li><li>- Fig. 2 shows a temperature control device according to the invention for an internal combustion engine having a motor-fan unit whose operation is slaved to a set point temperature;</li><li>- Fig. 3 shows another application of the safety circuit in a control device of the invention whose operation is similar to that of the device shown in Fig. 2;</li><li>Fig. 4 shows the connection of a power element connected in the motor supply circuit of the motor fan unit, circuit for use in a temperature control device according to the invention.</li></ul>

In the following description, the invention will be described in application to a temperature control device of a coolant for cooling an internal combustion engine mounted on a motor vehicle. In this case, a coolant is circulated in the engine through a radiator in front of which is placed a motor-fan unit whose speed is set according to the coolant temperature conditions. However, it should be noted that the invention applies égalementà air-cooled engines in which the temperature control is achieved by varying the speed of the fan that forces the air to pass around the motor. Note also that the invention is not limited to the use in a motor vehicle, any type of internal combustion engine whether stationary or mobile may be provided with a regulating device according to the invention.

Given this, Fig. 1 shows the engine 1 of a motor-fan unit is connected to the positive and negative terminals of a battery 2 which may be that supplying the motor vehicle. A working contact 3 is connected in series in this circuit. Between terminals of the battery 2 is also connected a series circuit consisting of a resistor 4 and a thermistor 5, the latter constituting a temperature sensor that can be placed in the heat transfer fluid circuit to detect its temperature and which in the case of an air-cooled engine may directly detect the internal combustion engine temperature. In the case shown, the thermistor has a negative temperature coefficient. The terminals of the battery 2 are also connected to a voltage regulator consisting of a resistor 6 and a Zener diode 7 across which appears a regulated voltage. It is applied to a voltage divider composed of resistors 8 and 9, the junction point 10 between these two resistors providing a reference voltage determining the maximum temperature of the coolant is not exceeded. The junction point 10 is connected to the inverting input of an operational amplifier 11 forming the comparator. The non-inverting input of this amplifier is connected to the junction point 12 between the resistor 4 and the thermistor 5. The output of comparator 11 is connected to the positive terminal of the voltage regulator 6.7 via a resistor 13 and via a resistor 14 to the base of the switching transistor 15 whose collector emitter path is connected firstly to the positive terminal of the battery 2 and the other hand to a diode 16. Celle- is connected with its cathode to a parallel connection of the junction point of a diode 17 connected with its anode to ground and a relay coil 18 which is coupled to the contact 3 inserted into the motor supply circuit 1.

The part of the installation as described above operates as follows.

When the temperature of the coolant rises, the resistance of the thermistor 5 decreases such that the potential of the junction point 12 is lowered. When the value of this potential decreases below that set on the junction point 10 by the resistors 8 and 9, the amplifier 11 and flip-flop makes the transistor 15 conductive so that the relay coil 18 is energized. This results in the closing of the contact 3 and the power of the engine 1.

This process takes place during the normal operation of the entire control device. However, when a failure occurs for example by a short-circuit of the thermistor 5, the potential of the junction point 12 is returned to ground and thereby latch the amplifier 11 as during normal circuit operation. In this case, the relay 18 is excited continuously and the engine 1 drives the fan continuously for cooling the coolant. However, in this case, if the temperature falls beyond the set value set by the potential of the junction point 10, the engine 1 does not stop. But, the excessive temperature of the internal combustion engine is avoided.

The safety circuit also includes a voltage divider composed of resistors 19 and 20 connected to the terminals of the voltage regulator 6.7. The junction 21 of these resistors provides a reference signal whose potential corresponds to a higher engine temperature than the potential of the divider 8 and 9. This signal is applied to the inverting input of a second operational amplifier 22 whose noninverting input is connected to the junction point 12 between the resistor 4 and the thermistor 5. the output of the amplifier 22 is connected through a resistor 23 to the voltage regulator to 6.7 and also a resistor 24 itself itself connected to the base of a transistor 25 whose emitter-collector circuit is connected firstly to the positive terminal of the battery 2 and the other hand to a 26 series resistor connected to a signali tion element 27 which, in the illustrated case is a light emitting diode connected also to ground. This LED may be placed on the dashboard of the vehicle. We can add to it other elements also powered warning by the transistor 25 such as a buzzer or similar body.

This circuit operates in the same way as the above described circuit but has a higher set point for providing a warning signal to the driver of the vehicle when a predetermined temperature set by the voltage divider 19,20 is exceeded. Thus, the vehicle operator is immediately warned of overheating in the engine cooling circuit of the vehicle. According to a variant, it is possible to connect the collector of transistor 25 to the relay coil 18 through a diode 16A (shown dotted). In those circumstances, in case of overheating of the engine, the motor fan is connected to the battery via the contact 3. This variant thus protects the internal combustion engine even in case of failure of the above described circuit (comparator 11 and transistor 15) or another element of the circuit, even if the vehicle driver is slow to respond when the diode 27 lights up.

The safety circuit also comprises a third voltage divider composed of resistors 28 and 29 connected between ground and the voltage regulator 6, 7. The junction point 30 of this voltage divider is connected to the noninverting input of an operational amplifier 31 whose inverting input is connected to the junction point 12 between the resistor 4 and the thermistor 5. the operational amplifier 31 which also functions as a comparator is connected to the voltage regulator 6, 7 by a resistor 32 and through a resistor 33 to a control transistor 34 whose collector emitter path is connected firstly to the positive terminal of the battery 2 and the other hand to a diode 35 whose cathode is connected to one end of the relay coil 18.

This part of the safety circuit has the function of providing the excitation of the relay 18 and thus the continuous operation of the motor 1 of the motor fan unit when the thermistor has to be disconnected from the circuit. Indeed, when this occurs, the potential of the junction point 12 rises abruptly so that the latch amplifier 31 making the transistor 34 which can thus energizing the coil of relay 18.

It is thus seen that the internal combustion engine is cooled, that the thermistor 5 is put in short circuit or disconnected from the assembly.

We will now refer to Fig. 2 which shows a control device used with the safety circuit as described above about Fig. 1. The mounting of this regulating device is a simplified version of that described in patent application EP-A-0042333 in the name of the Applicant. However, for clarity, will now be described briefly this circuit and the impact that on it the Fig safety circuit. 1.

Fig. 2, one recognizes the motor 1 of the motor fan unit and the battery 2 of the vehicle. A diode 52 is connected across the motor 1. Furthermore, there is shown the relay coil 18 and its working contact 3, these elements being connected in the same way as in FIG. 1 as regards the safety circuit.

The Fig regulating device. 2 cooperates with a thermistor 5 to negative temperature coefficient thermistor and this is connected between the negative pole of the battery 2 and a resistor 36 forming therewith a voltage divider which receives power from a voltage regulator consisting of a resistor 37 and a Zener diode 38 and whose junction point 39 reflects the heat transfer fluid temperature flowing in the internal combustion engine.

This junction point 12 replaces FIG. 1, the safety circuit there taking its temperature information.

The junction point 39 is also connected to the inverting input of an operational amplifier 40 operating as a comparator whose non-inverting input is connected to a reference junction point 41 provided between two resistors 42 and 43 connected across the regulator voltage 37, 38. the output of comparator 40 is connected to the noninverting input of another operational amplifier 44 described later.

The operational amplifier 40 is provided against a feedback circuit consisting of a resistor 45, a diode 46 and a potentiometer 47.

The regulating device also comprises an oscillator 48 of triangular signals whose output 49 is connected to the inverting input of the operational amplifier 44 which compares the triangular voltage output of the oscillator 48 with the output of the operational amplifier 40 to provide at its output a pulse signal whose duty cycle reflects the potential of the junction point 39 and therefore the coolant temperature.

The output of this amplifier 44 is connected through a resistor 50 to a power circuit including a transistor 51 through which is fed the engine 1 of the motor fan unit.

Have been described in the aforementioned patent application, during normal operation of the regulating device, the duty cycle of the pulses applied to the base of transistor 51 via the resistor 50 increases with the coolant temperature detected by the thermistor 5 and causes progressive speed rotation of the motor up to full voltage of the power transistor 51.

Thanks to the combination of Fig safety circuit. 1 with FIG regulating device. 2, it is possible to choose for the maximum duty cycle that can be supplied by the pulse signal of the amplifier 44, a value which is slightly less than 100%, so that in normal operation, the engine 1 will not work full speed under control of the regulating device, but under the control of the safety circuit of which the set temperature (junction point 10 of FIG. 1) may be selected to a value corresponding to the highest temperature that the engine heat can reach without deterioration. Thus, the maximum speed is reached only when the coil 18 is energized and the contact 3 is closed and greater than the maximum speed that can be obtained with the circuit described in the aforementioned patent application because the voltage drop in the power transistor to the motor is removed by the assembly according to the present application. This voltage drop may be 1.5 volts for a transistor operating with a current of 30 amps. As a result, thanks to the invention improves the overall performance of the regulation device because you can remove the inherent loss of power to the power transistor (1.5 x 30 = 45 Watts in the chosen example). The assembly of the invention also suppress the heating of the full conduction power device and reduces the size of the radiator that is associated with the power transistor.

The combination of the safety circuit and the regulating device as described above allows to obtain also the following advantages over the safety.

The drive motor 1 is supplied at its maximum power to ensure maximum cooling of the coolant fluid when the latter reaches the temperature considered to be hazardous for the internal combustion engine.

When the power stage with the transistor 51 fails the engine 1 operates at full capacity and protects the internal combustion engine.

Fig. 3 shows a variant of the regulating device in which the functions of the operational amplifiers 40, 44 and 48 of FIG. 2 are made using an integrated circuit 53. (The latter may be the integrated circuit commercially available under the designation L121 AB.) This circuit comprises sixteen terminals.

Terminal 6 delivers a constant regulated voltage.

The thermistor 5 is connected in series with a resistor 54 form a divider bridge wherein the point of junction 55 provides a signal which represents the measured temperature of the coolant. The safety circuit receives this point 55 the coolant temperature information.

The junction point 55 is connected to terminal 3 of the integrated circuit 53 via a resistor 56. The terminal 5 of the integrated circuit is connected to a voltage divider composed of resistors 57 and a predetermined portion of a potentiometer 58 to provide the integrated circuit the reference voltage which is compared to the measurement voltage applied to the terminal 3 through the resistor 56.

The integrated circuit 53 can also generate a delta voltage whose characteristics can be determined by a capacitor 59 and a resistor 60 which also sets the slope of the variation of the energy of the control signal provided on terminal 7 of the integrated circuit , control signal constituted by a train of variable duty cycle pulses as a function of the comparison between the reference signal applied to terminal 5 and said measurement signal applied to terminal 3. the resistor 60 and a diode 61 connected between terminals 2 and 5 of the integrated circuit is intended to introduce hysteresis in the internal voltage comparator at the integrated circuit and whose inputs are terminals 3 and 5. this hysteresis can be adjusted by means of a potentiometer 62.

The integrated circuit of the output signal appearing at the terminal 7 is applied to a power stage 63 consisting of two transistors in Darlington. The power transistor 64 of this stage is shunted by the contact 3 controlled by the relay coil 18 of the safety circuit.

The power transistor supplying the motor 1 is preferably an MOS transistor which is advantageously mounted according to Fig. 4 in the motor circuit 1. This assembly has the advantage of being directly attacked by the measuring signal from the integrated circuit. It comprises a MOS transistor 65 whose gate is connected to terminal 7 of the integrated circuit 53 of FIG. 3 via a resistor 66, this gate is also connected to ground via a resistor 67 and a Zener diode 68. This latter component protects the MOS transistor having the particular advantage is of not requiring a transistor of pre-amplification. On the contrary, the resistance 66 may be connected directly to the terminal 7 of the integrated circuit 53 of FIG. 3.