EP1316722A1 - Electronic command circuit for an automotive engine starter - Google Patents

Abstract

The vehicle starter motor control circuit includes an electromagnetic contactor (CT) whose coil (L) is controlled by power transistors (T1, T2). The power stage (10) includes a diode (D1) which prevents the flow of current in the reverse direction, in the event of the inversion of polarity of the battery. <??>The electronic control circuit for a vehicle starter motor comprises an electromagnetic contactor (CT) whose coil (L) is excited via an electronic switch with power transistors (T1, T2). A management unit (G) co-operates with the electronic switch in order to control the excitation current through the coil. A free-wheeling diode (D2) is connected in parallel with the terminals of the coil. The power stage (10) includes a diode (D1) which prevents the flow of current in the reverse direction, in the event of the inversion of polarity of the battery. The electronic switch comprises a first transistor (T1) controlled by the management unit, and a second transistor (T2) mounted in series with the first, controlled in all-or-nothing mode by a logic gate (ET) sensitive to the open/closed state of the starter switch (K).

Description

The invention relates to a control circuit motor vehicle starter electronics.

Such a starter, described for example in the document FR A 2 795 884, comprises a rotary electric motor connected to a output shaft equipped with a launcher with a hub and a pinion mobile intended to cooperate with a starting gear ring to start the internal combustion engine of the motor vehicle. The pinion is generally mounted at sliding on the output shaft between a rest position, in which it is disengaged from the ring gear, and a active working position in which it meshes with said crown, which is rigidly linked in rotation or elastic to the crankshaft of the vehicle engine.

In one embodiment the output shaft is confused with the output shaft of the electric motor. Alternatively a planetary gear reducer is arranged between these two shafts output (see figure 1 of document FR A 2 795 884).

The electric motor is associated with an electromagnet contactor arranged above the engine and comprising a coil actuation of a movable core capable of acting on a contact of power to close this one and electrically supply the electric motor. This contactor has a dual function supply of electric motor with current and displacement of the movable pinion between the two rest and working positions.

The movable core is mechanically connected by a lever, such that a fork, to the launcher comprising a free wheel, in variant a conical clutch described for example in the document FR A 2 826 696, inserted axially between the pinion and the hub of the launcher. The lever is pivotally mounted and the hub of the launcher is internally provided with helical splines in taken with complementary teeth carried by the shaft of exit. The launcher and pinion assembly is thus animated by a helical movement when moving the lever to come in taken with the starter gear. The excitement of contactor is controlled by actuation of the ignition key, which closes the electrical circuit to the battery.

In FIG. 1, an electronic control device for a electromagnetic starter contactor CT, has a well known manner a management unit G formed by a microcontroller cooperating with an electronic switch, by example a transistor T1 of the MOSFET type, electrically connected in series with the contactor actuating coil L electromagnetic CT. A freewheeling diode D2 is connected in parallel to the terminals of the coil L, the cathode being connected to the positive pole of battery B, and the anode to transistor T1.

The contact C of power of the contactor CT, when it is closed, connects the electric motor M of the starter to the positive pole of battery B. Management unit G controls the grid of the transistor T1 in pulse mode, for example by modulation of PWM pulse width, allowing a variation of the duty cycle of control pulses to adjust current effective in coil L of contactor CT depending on different parameters.

The management unit G is also used to manage other functions, including automatic starter stop after starting, overcurrent protection, over overheating in the event of repeated starting attempts, and the start-up protection during false operations. She is either integrated in the starter, or housed outside the starter in a specific case. Such a device is described in the document FR-A-2 770 349.

In the event of intervention on the vehicle battery during a overhaul or troubleshooting, for example when setting up the battery or its replacement, or when starting by an auxiliary backup battery, incorrect connection of battery terminals may cause reverse polarity on the starter. In Figure 1, such a reverse polarity causes circulation of a first reverse current Ic in the power stage of the transistor T1 through the coil L, and of a second reverse current Im in the motor M.

• d'une part des problèmes de qualité et de fiabilité, car le courant inverse Ic de plusieurs centaines d'ampères, circule dans la diode roue libre D2, et provoque sa destruction. La bobine L du contacteur CT est alors excitée sous un courant de 50A, ce qui entraíne la fermeture du contact de puissance C et l'alimentation du moteur M électrique. Le sens de rotation est inversé pour un moteur M ayant un inducteur à aimant permanent. Le sens de rotation est normal pour un inducteur bobiné.
• d'autre part des problèmes de sécurité, car pour un démarreur à inducteur bobiné, la rotation du démarreur provoque l'entraínement de la couronne dentée par le pignon. Si une vitesse est restée enclenchée dans la boíte de vitesse, il sera alors possible de déplacer le véhicule avec des risques d'accident ou de collision, et des risques d'incendie du démarreur si l'inversion de polarité est maintenue.

The disadvantages of a poor electrical connection (reverse polarity) are twofold:

• on the one hand, quality and reliability problems, because the reverse current Ic of several hundred amperes, flows in the freewheeling diode D2, and causes its destruction. The coil L of the contactor CT is then energized under a current of 50A, which causes the closing of the power contact C and the supply of the electric motor M. The direction of rotation is reversed for an M motor having a permanent magnet inductor. The direction of rotation is normal for a wound inductor.
• on the other hand safety problems, because for a starter with a wound inductor, the rotation of the starter causes the drive of the ring gear by the pinion. If a gear remains engaged in the gearbox, it will then be possible to move the vehicle with risk of accident or collision, and risk of fire from the starter if the reverse polarity is maintained.

The object of the invention is to provide a circuit for electronic control of a vehicle starter switch automobile which is protected against the risk of reversal of polarity, likely to be caused by connections battery errors.

This problem is solved, in accordance with the invention, by characterizing part of claim 1.

In the case of a bad battery connection where the positive pole would be mistakenly connected to ground, the presence of the unidirectional semiconductor element blocks the passage of the current in the power stage when the switch startup is closed. Any reversal of the current is thus rendered impossible, and the coil is not energized. Contactor stays open by prohibiting the rotation of the electric motor of the starter so that the vehicle cannot move even if a speed remains engaged. Any risk of fire is avoided.

Advantageously, a second safety transistor is arranged in series with the first transistor and is controlled by all or nothing by a logic gate And sensitive to the open state or closed the start switch.

It will be appreciated that the second transistor is a transistor of safety to avoid any risk of contactor fire especially when the first transistor is short-circuited.

The unidirectional semiconductor protection element in reverse polarity is advantageously formed by a diode.

The first transistor and the second transistor of the switch are advantageously formed by transistors of power of the MOSFET type. These transistors can operate in battery polarity reversal, but in this case abnormally heat which can cause destruction of the starter. Thanks to the invention these transistors are protected in battery polarity reversal.

The first transistor is in one embodiment controlled in pulse mode by the management unit which allows properly control the supply of the coil and therefore the displacement of non-noisy way of the moving core of the contactor, supply the contactor coil in two phases as described in the aforementioned document FR A 2 795 884 to which reference will be made for more details.

In one embodiment, a TOPFET type transistor provides polarity control and allows combined thermal overcurrent and overvoltage protection.
This transistor is controlled by an AND gate like the safety transistor.

• la figure 1 représente schématiquement le circuit de commande électronique d'un démarreur conforme à l'état de la technique;
• la figure 2 montre le circuit de commande électronique d'un démarreur conforme à l'invention ;
• les figures 3 à 9 illustrent différentes variantes de réalisation du circuit de commande selon l'invention.

Other advantages and characteristics will emerge more clearly from the description which follows of an embodiment of the invention given by way of nonlimiting example, and represented in the appended drawings in which:

• Figure 1 schematically shows the electronic control circuit of a starter according to the state of the art;
• Figure 2 shows the electronic control circuit of a starter according to the invention;
• Figures 3 to 9 illustrate different alternative embodiments of the control circuit according to the invention.

In FIG. 2, the power stage 10 of the electronic control of the contactor actuation coil L Electromagnetic CT, includes a first transistor T1 controlled in PWM modulation by the management unit G, here formed by a microcontroller generating other functions as in the case of Figure 1. The output S1 of the management unit G is connected to the gate of transistor T1 by a resistive divider R1-R2. A freewheeling diode D2 is connected in parallel to the terminals of the coil L and in series with transistor T1.

A second safety transistor T2 is inserted between the first transistor T1 and ground, and is controlled in all or nothing by a logic gate AND receiving on a first input a first control signal from output S2 of the control unit management G, and on a second input a second signal representative of the open or closed state of the switch K of the ignition key. The potential of the gate of transistor T2 is fixed by a resistor R3 connected between the output of the door AND and the mass. Unit G monitors the state of the transistors.

The two transistors T1 and T2 are transistors of power and are connected in series. They are constituted as examples using N channel MOSFET type power transistors logical, which are reliable over time and which do not penalize starter efficiency. Such mounting allows control safe starting at low current. MOSFET transistors have the particularity of having a diode in parallel between the drain and source, said diode being reverse biased, this is to say the cathode in electrical connection with the positive terminal of battery B.

According to the invention, a unidirectional semiconductor element designated by the general reference 12, is connected in the circuit power stage 10 to prevent the passage of the current when the polarity of battery B has been reversed. This element 12 is advantageously constituted by a diode D1 mounted in series with transistor T1 and connected between the battery and the freewheeling diode D2. The anode of diode D1 is connected electric with the positive terminal of the battery, while its cathode is connected to the cathode of diode D2.

The two diodes D1 and D2 are for good integration advantageously housed in the same double Schottky diode box with common cathodes, thanks to which the diode D1 provides protection in reverse polarity, and diode D2 provides the wheel function free of current in coil L of contactor CT. Use of a single component incorporating the two diodes D1 and D2 allows obtain a reduction in the size and cost of the card electronic carrying, advantageously in the contactor, the diodes, transistors and the management unit.

• Dans le cas d'une polarité correcte de la batterie B comme représentée à la figure 2, une commande de démarrage normale intervient suite à la fermeture de l'interrupteur K de la clé de contact. Les deux transistors T1 et T2 sont commutés dans l'état conducteur autorisant la circulation du courant depuis le pôle positif de la batterie B vers la masse à travers respectivement la diode D1, la bobine L, le premier transistor T1, et le deuxième transistor T2. L'excitation de la bobine L provoque la fermeture du contact de puissance C du contacteur CT, et l'alimentation du moteur électrique M du démarreur.
• Dans le cas d'une mauvaise connexion de la batterie B où le pôle positif serait branché par erreur à la masse (inversion de polarité), la présence de la diode D1 bloque le passage du courant dans l'étage de puissance 10 lorsque l'interrupteur K est fermé. Toute inversion du courant est ainsi rendue impossible, et la bobine L n'est pas excitée. Le contacteur CT reste ouvert en interdisant la rotation du moteur M.

The operation of the power stage 10 of the electronic starter control circuit follows from the preceding description:

• In the case of correct polarity of the battery B as shown in FIG. 2, a normal start-up command intervenes following the closing of the switch K of the ignition key. The two transistors T1 and T2 are switched to the conductive state allowing current to flow from the positive pole of the battery B to ground through the diode D1, the coil L, the first transistor T1, and the second transistor T2, respectively. . The excitation of the coil L causes the closing of the power contact C of the contactor CT, and the supply of the electric motor M of the starter.
• In the case of a bad connection of the battery B where the positive pole would be mistakenly connected to ground (reverse polarity), the presence of the diode D1 blocks the passage of current in the power stage 10 when the switch K is closed. Any reversal of the current is thus made impossible, and the coil L is not energized. The CT contactor remains open, preventing rotation of the motor M.

For simplicity we have not shown in the other figures 3 to 9 the power contact C of the electromagnetic contactor CT nor the electric motor visible in Figures 1 and 2. The connection of terminals of contact C on the coil and on the motor electrical connection to ground is done in the same way.

In the variant of FIG. 3, the diode D1 which ensures the reverse polarity protection, is inserted, here connected, between the coil L and the first transistor T1. The anode of the diode D1 is connected for this purpose to the anode of the wheel diode D2 free, and the cathode of D1 is connected to the drain of the transistor T1. Compared to the circuit of Figure 2, we simplify the internal connection of the contactor, because the positive poles of the coil L and battery B are common, which requires a only connection at this location on the electronic card. The diodes D1 and D2 are formed in this case by components individual, because an integrated double diode box does not exist in common anode version.

In the diagram of FIG. 4, the power stage 10 is conforms to that of FIG. 2, but the diode D1 which ensures the reverse polarity protection, is positioned, i.e. connected, between transistor T2 and ground. The anode of the diode D1 is electrically connected to the source of transistor T2, and the grounded cathode. The operation is identical to that of the diagram in Figure 2 but the mass reference on the source of the transistor T2 is floating because of the threshold voltage (from the order of 1V) from diode D1.

In the other variant of FIG. 5, the diode D1 which provides reverse polarity protection, is connected between the battery B and coil L, the anode of D1 being connected electrically to the cathode of the freewheeling diode D2, and to the positive terminal of battery B. Reverse protection of polarity provided by diode D1 only prohibits the current flow in coil L.

Referring to Figure 6, the control circuit is conforms to that of the assembly of FIG. 4, but the diode D1 of reverse polarity protection is replaced by a auxiliary transistor T3 of the MOSFET type channel N. The potential of gate of transistor T3 is adjusted by a bridge comprising a Zener D5 diode with the anode connected to ground, and a resistor R4 electrically connected to the positive terminal of the battery B. The voltage drop in transistor T3 will be more weak than in the case of diode D1, but the ground reference will nevertheless remain offset by a value of the order of 0.1V to 0.3V.

In FIG. 7, the auxiliary transistor T3 of the MOSFET type channel P is connected between the positive terminal of battery B and the cathode of the freewheeling diode D2. In this case, the transistor T2 is connected directly to ground, as well as the gate of the auxiliary transistor T3. The voltage drop in the transistor T3 will also be weaker than in the case of diode D1 in figure 2.

In FIG. 8, the transistor T1 is formed by a transistor IGBT arranged between the coil L and the transistor T2. This transistor is connected between the anode of the diode D2 and the transistor T2. The T1 IGBT transistor does not have a diode in parallel between the drain and source, and will therefore block current in case of reverse polarity. Diode D1 in Figure 2 is not no longer needed but the voltage drop in the IGBT transistor will be more important than in a MOSFET. In addition, the order of the T1 IGBT transistor requires the insertion of an amplifier stage 14 to provide sufficient control current. upstairs amplifier 14 is of a type known per se, for example with two amplifier stages with transistors Q1 and Q2 and a Zener diode Z1 whose anode is connected to ground and the cathode is connected to the collector of transistor Q2 and to the gate of transistor T1 IGBTs.

In FIG. 9, the transistor T1 is constituted by a TOPFET transistor connected between the positive terminal of battery B and the freewheeling diode D2 in parallel on the coil L. This transistor T1 is connected between the battery and the cathode of the diode D2 The TOPFET transistor, on the one hand, is fully controlled or nothing by a logic gate AND receiving on a first input a first control signal from output S2 of the control unit management G and on a second input a second signal representative of the open or closed state of the switch K of the ignition key like the transistor T2 of figure 2, and other hand, does not have a diode in parallel between the drain and the source, and as in the assembly of figure 8, there is no potential problem when reversing polarity. Number of components is reduced and the TOPFET transistor, in addition to its polarity control function, allows combined protection thermal, overcurrent and overvoltage. The potential of gate of this TOPET transistor is fixed by a resistor R3 connected between the second input of the AND gate and the ground and by a resistor R2 connected between this second input of the AND gate and switch K. Resistors R1, R2 form as in Figure 1 a resistive divider.

It is clear that any other means of protection against reverse polarity can be used in the device electronic control of the starter contactor CT.

It will be appreciated that the management unit G is well protected.

In Figures 2 to 9 there is thus provided an AND gate of safety so that the transistor T1 is on only when the ignition key switch is closed. The vehicle cannot therefore start unintentionally even if the polarity.

Claims (14)

Electronic control circuit of a motor vehicle starter, comprising an electromagnetic contactor (CT) for supplying the electric motor (M) of the starter from the energy of the battery (3), and control means comprising : an electronic switch electrically inserted in series in the power stage (10) with the coil (L) of the contactor (CT), a management unit (G) cooperating with the electronic switch for adjusting the excitation current of the coil (L), and a freewheeling diode (D2) connected in parallel to the terminals of said coil (L), characterized in that the power stage (10) further comprises a unidirectional semiconductor element intended to prevent the flow of current in the event of the battery polarity reversal (B). Control circuit according to Claim 1, characterized in that the electronic switch comprises a first transistor (T1) controlled by the management unit (G), and a second transistor (T2) arranged in series with the first transistor (T1) and controlled in all or nothing by a logic gate (ET) sensitive to the open or closed state of the start switch K. Control circuit according to Claim 2, characterized in that the first transistor (T1) is controlled in pulse mode by the management unit (G). Control circuit according to Claim 2 or 3, characterized in that the unidirectional semiconductor element for reverse polarity protection is formed by a diode (D1). Electronic control circuit of a starter according to claim 4, characterized in that the protective diode (D1) is connected between the battery (B) and the freewheeling diode, the cathodes of the two diodes (D1, D2) being common. Control circuit according to Claim 4, characterized in that the protective diode (D1) is connected between the coil (L) and the first transistor (T1), the anodes of the two diodes (D1, D2) being common. Control circuit according to claim 4, characterized in that the protective diode (D1) is connected between the second transistor (T2) and the ground. Control circuit according to Claim 4, characterized in that the protective diode (D1) is connected between the battery (B) and the coil (L), the anode of the protective diode (D1) being in electrical connection with the cathode of the freewheeling diode (D2). Control circuit according to one of Claims 2 to 8, characterized in that the first transistor (T1) and the second transistor (T2) of the electronic switch are formed by MOSFET transistors. Control circuit according to Claim 9, characterized in that the unidirectional semiconductor element is formed by an auxiliary transistor (T3) of the MOSFET type. Control circuit according to claim 10, characterized in that the auxiliary transistor (T3) is connected between the second transistor (T2) and the ground. Control circuit according to Claim 10, characterized in that the auxiliary transistor (T3) is connected between the battery (B) and the cathode of the freewheeling diode (D2). Control circuit according to Claim 1, characterized in that the first transistor (T1) consists of an IGBT transistor connected between the anode of the freewheeling diode (D2) and the second transistor (T2). Control circuit according to Claim 1, characterized in that the electronic switch consists of a TOPFET transistor connected between the battery (B) and the cathode of the freewheeling diode (D2).

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