WO2009083408A1

WO2009083408A1 - Control device for solenoid, electric starter including same, and corresponding control methods

Info

Publication number: WO2009083408A1
Application number: PCT/EP2008/066986
Authority: WO
Inventors: Herve Couetoux
Original assignee: Renault S.A.S.
Priority date: 2007-12-26
Filing date: 2008-12-08
Publication date: 2009-07-09
Also published as: EP2232049A1; FR2925977B1; FR2925977A1

Abstract

The invention relates to a control device for a solenoid (1) electrically powered by a voltage source (2), the device being preferably intended for integration into an electric starter for a combustion engine. The control device includes a main switching means (3) controlled by a calculation means (4) so as to hash the power supply of the solenoid (1), and an auxiliary switching means (5) arranged in parallel with the solenoid (1) and permitting a current flow in the solenoid (1) when the power supply is cut off by the main switching means (3). Furthermore, the device includes an additional switching means (6) arranged in series with said auxiliary switching means (5) as well as a voltage clipping means (7) arranged in parallel with the solenoid (1) and with the additional switching means (6), wherein said additional switching means (6) enables a selection between at least two current flow paths when the power supply is cut off by the main switching means (3). The invention also relates to an electric starter for a combustion engine integrating such a device, and to a control method for actuating such a device for a starter.

Description

CONTROL DEVICE FOR SOLENOID, ELECTRIC STARTER INCORPORATING THE SAME, AND METHODS

OF ORDER CORRESPONDING

The present invention relates to a control device for a solenoid electrically powered by a voltage source, the device being preferably intended to be integrated in an electric starter for a combustion engine, this device comprising a main switching means controlled by calculating means for chopping the power supply of the solenoid and auxiliary switching means in parallel with the solenoid and allowing current flow in the solenoid when its power supply is cut off by the switching means main; it also relates to an electric starter for a combustion engine incorporating such a device and a control method for the actuation of such a device respectively of such a starter.

This invention is in the context of the current automotive technology, particularly in the context of electric motor starters. This kind of starter can be coupled to the crankshaft of the engine to drive it and start its start. In particular, recently, starters have been proposed that have a feature commonly called "Stop & Start". This feature is to automatically shut down the engine when the vehicle speed is zero, for example when stopped at a red light or in any other situation requiring the stopping of the vehicle, the engine is then restarted automatically when the user ask him again. This is to reduce the consumption of the vehicle and the pollution it generates. To achieve this function "Stop & Start" also called "S & S" on a vehicle with a combustion engine, especially on a car, while maintaining a simple on-board electrical network, normally a 14V grid, there are currently two main possibilities based on electromagnetic motor starting devices. Either we use an alternator-starter which is a reversible machine placed on the belt of the engine or we use a

SUBSTITUTE SHEET (RULE 26) starter adapted to the S & S function at the power, noise, wear, etc. This last type of starter ensures, during the starting phase up to the autonomy of the engine by the combustion cycles, the crankshaft drive of the thermal engine by means of a pinion which meshes with the toothing of a ring gear mounted on the periphery of the flywheel, the engagement of the pinion in the ring being controlled by a solenoid arranged in the starter.

The use of an S & S starter mentioned above offers a very clear potential for cost reduction compared to an alternator-starter and is interesting especially for general car manufacturers, concerned about the cost-benefit ratio of their products. This kind of starter has been improved in the past, for example in the control of the current of its solenoid, for which an electronic chopper as stated in documents DE 10 034 779 and US 5,818,679 has been proposed, in order to proceed to a progressive engagement of the pinion in two stages, see for example the documents US 6,104,157 and US 6,323,562. Similarly, a solenoid having a two-stage mono-coil, that is to say having two stable powered positions of its mobile core, has been proposed for this kind of starters.

A specific control circuit intended to be integrated in such a starter has also been developed by the applicant and is the subject of a French patent application. This control device limits the power consumed by the electric starter when starting the combustion engine, this by performing a clipping of the current when powering the starter. Moreover, this kind of "Stop &Start" starters is the subject of other improvements in its functionality, particularly with regard to an additional function called "reflex-start". This function consists of restarting the engine by the starting device while the crankshaft of the engine, unlike the case of a usual start, has not yet stopped, following a fast succession of orders, for example following a stop then a restart in less than one second. In addition, this type of situation may occur in the event of a car being stopped at a red light that has just turned green, when it changes gears when entering a roundabout or when the-passage, etc.

The aforementioned alternator-starter system makes it possible to perform the "reflex-start" function in a simple way, because the coupling of the reversible electric machine with the crankshaft of the motor naturally ensures the synchronization of the rotational speed of the machine. with the crankshaft, at the drive ratio near. It is therefore sufficient to power the electric machine to provide immediately, that is to say, as soon as the currents in the electric machine, a driving torque to the engine. But, as mentioned above, the cost of an alternator-starter remains high compared to an S & S starter, thus pushing car manufacturers to find an alternative solution.

S & S starters for performing such a "reflex-start" function have recently been proposed, in particular by the applicant. Such a starter may, in particular, be equipped with a two-stage starter solenoid mentioned above. This kind of solenoid, having two stable powered positions of its movable core, makes it possible to control, on the one hand, in its first stable powered position, the engagement of the starter pinion in the toothing of said ring gear mounted on the periphery of the flywheel as well as, secondly, in its second stable powered position, powering the starter and thus driving the crankshaft of the engine, while in the rest position of the movable core, the pinion is not engaged in the crown and the starter's power supply is cut off. Alternatively, it is for example possible to provide two conventional solenoids to perform these steps, the engagement of the pinion with said crown and the switching a relay causing said starter to be energized independently of each other.

In order to achieve a power supply control of such solenoids, it is currently known to use a chopper with a transistor controlled as the main switch in combination with a second switch in parallel with the solenoid, which may preferably consist in a diode or another transistor, as an auxiliary switch to provide the so-called "free-wheel" function, that is to say, allowing the flow of current in the coil of the solenoid when the power supply of the solenoid is turned off by the main switch. Alternatively, it is known to use for the control of the solenoid power supply a conventional H bridge with four controlled transistors. The chopper solution is more economical, but does not reverse the voltage across the solenoid coil to quickly cancel the current in the solenoid, while the more expensive H bridge has this feature to cancel as fast as possible the current. In this context, it should be noted that in general the coil of such a solenoid is characterized by its inductive property, this normally causing a relatively slow response of the actuator under a given voltage.

It follows from what has been said above, on the one hand, that this kind of electric starters, especially those with "Stop &Start" and / or "reflex-start" features, respectively their solenoids must have a great flexibility of use, particularly in their order, to be able to match the level of their performance alternator-starter, and, secondly, that currently available solutions for their order remain perfectible. It would be particularly desirable to improve the control at the starting speed, at the level of the noise generated by the starter, or at the level of wear of the parts, in particular between the starter gear and the ring gear of the engine. , all these parameters being able to be influenced by the solenoid control of the starter. Therefore, the object of the present invention is to improve the current thermal engine starting systems and to provide, on the one hand, a control device for a solenoid having a great flexibility of use as well as in particular, a reduced reaction time, and, secondly, an electric starter integrating such a control device, and a corresponding control method for such a device respectively such a starter, this having recourse to simple technical means, remaining compatible with a motor vehicle equipped with a conventional electrical distribution architecture, and offering a lower cost compared to an alternator-starter.

The control device for a solenoid according to the present invention is distinguished for this purpose by the characteristics listed in claim 1, in particular in that the device comprises an additional switching means in series with said auxiliary switching means and voltage clipping means connected in parallel with the solenoid through the auxiliary switching means and with the additional switching means, this additional switching means making it possible to choose between at least two current flow paths when the power supply solenoid is cut off by the main switching means. By this structure of the control of the solenoid it is possible to proceed to a rapid shutdown of the current and thus to improve the response time of the solenoid respectively of its mobile core.

Preferably, said main switching means is provided by a controlled switch and said auxiliary switching means is provided either by a self-controlled switch or by a controlled switch whose conduction is alternately carried out with that of the main switch. The main switching means can in particular be realized by a transistor, preferably by a field effect transistor, in particular by an N-type MOSFET, and the auxiliary switching means can be realized by a diode, preferably a diode with a fast response and a small direct voltage drop, for example of the Schottky type.

In a preferred embodiment, said additional switching means is constituted by a controlled switch, this switch being controlled by said calculating means. In particular, the additional switching means may consist of a transistor, preferably a field effect transistor, in particular a P or N-type MOSFET.

In another embodiment, said voltage clipping means is constituted by a self-controlled switch, preferably a diode, in particular a deletion diode type diode.

In particular, it is possible in one embodiment of the device that the main switching means is constituted by an N-type MOSFET connected on the negative side of the solenoid voltage source and that said additional switching means is constituted by a P-type or N-type MOSFET. The main switching means may also consist of an N-type MOSFET connected on the positive side of the solenoid voltage source, said additional switching means being in this case favorably constituted by a MOSFET of type N.

In another embodiment, the main switching means is constituted by a field effect transistor adapted to measure the current flowing through it, preferably by a SenseFET type transistor, which makes it possible to obtain information on the current level in the coil of the solenoid, this information can be used when ordering.

In yet another embodiment, the solenoid positive supply rail is placed downstream of a protection relay to protect the device from accidental inversion of the voltage source.

The present invention also provides an electric starter for a combustion engine which comprises a solenoid controlled by such a control device. In particular, this starter preferably comprises a solenoid which is chosen so as to have a rated electrical voltage lower than the electric voltage supplying the starter, in particular so that the nominal voltage of the solenoid is in the range of 4 to 12. V for a voltage supplying the starter in the range of 12 to 16 V. This complements the starter equipped with a control device allowing a rapid power cut in the coil of the solenoid in the sense that this choice makes it possible to obtain a rapid rise in current. The starter then has a fast reaction time for the application as well as for the current removal in the solenoid, thus allowing a commitment and a quick and controlled disengagement of its mobile core in a stable powered position.

In one embodiment of such a starter, the solenoid may be constituted by a two-stage starter solenoid having two stable positions of its movable core, defined as a function of the current flowing through the coil.

The present invention also proposes a control method for the actuation of such a control device respectively of such a starter.

The control method of the device comprises, in current setting or current holding mode in the solenoid, the steps of - switching the main switching means or keeping it in the switching state and

- switching the additional switching means to allow the flow of current through the auxiliary switching means, and, in the fast-off mode of the current in the solenoid, it comprises the steps

to interrupt the main switching means and

interrupting the additional switching means so as to interrupt the flow of current through this switching means additional, a flow of current through the voltage clipping means remaining possible.

The control method for actuating a corresponding starter comprises, in slow engagement mode of the mobile solenoid core in a stable powered position, the steps

- switching the main switching means by chopping the current with a reduced duty cycle so as to moderately increase the current through the solenoid and to obtain a slow movement of its movable core, - after the movement of the solenoid movable core in the desired position, chopping the current through the main switching means with a duty cycle corresponding to the holding current of the solenoid movable core so as to obtain the maintenance of its movable core in a stable powered position, and, in the operating mode, fast engagement of the mobile solenoid core in a stable powered position, the method comprises the steps

- switching the main switching means by applying a full voltage wave to the solenoid so as to rapidly increase the current through the solenoid and to obtain a rapid movement of its movable core,

interrupting either only the main switching means, the latter and the additional switching means so as to rapidly decrease the current through the solenoid and to slow down the movement of the mobile core, and - after the movement of the mobile core of the solenoid in the desired position, to switch the main switching means again by chopping the current with a duty cycle corresponding to the holding current of the movable core of the solenoid so as to obtain the maintenance of its mobile core in a stable powered position. It is thus possible to have a control device respectively of an electric starter having a great flexibility of use and in particular a reduced reaction time whether it is up or down the current, which allows to better control the kinematics of the mobile core.

Other advantages emerge from the features expressed in the dependent claims and from the description which sets forth the invention in more detail with the aid of drawings.

The accompanying drawings illustrate schematically and by way of example three embodiments of the invention.

FIG. 1 represents an electronic diagram of a control device using a main switching means consisting of an N-type MOSFET connected on the negative side of the solenoid voltage source and an additional switching means constituted by a MOSFET. of type P.

FIG. 2 shows an electronic circuit diagram of a control device using a main switching means consisting of an N-type MOSFET connected on the negative side of the solenoid voltage source and an additional switching means constituted by a MOSFET. N-type FIG. 3 shows an electronic diagram where the main switching means is constituted by an N-type MOSFET connected on the positive side of the solenoid voltage source and the additional switching means is constituted by a MOSFET of the type NOT.

The invention will now be described in detail with reference to the accompanying drawings which will illustrate, by way of example, several embodiments of the invention.

The electronic diagram represented in FIG. 1 shows an embodiment of a control device according to the present invention adapted to to control a solenoid 1 powered electrically by a voltage source 2.

The solenoid may be a conventional single-stage solenoid solenoid, that is, whose movable core has a stable rest position and a single stable position at the end of travel of the movable core when the solenoid is energized. It may also consist of a two-stage starter solenoid with two stable powered positions. The control device according to the present invention is particularly adapted to be integrated in an electric starter for a combustion engine, as required in an automobile, but may be used in any other suitable application. This device is based on the known control solution using an electronic chopper, instead of an H bridge with four transistors, and comprises a main switching means 3 controlled by a calculating means 4 so as to allow the chopping of the chopper. solenoid power supply 1. The main switching means 3 makes it possible to cut or to introduce the power supply of the solenoid or even of its coil as well as of the other components downstream in the electric circuit. An auxiliary switching means 5 is connected in parallel with the solenoid 1 and allows a current flow in the solenoid 1 when its power supply is cut off by the main switching means 3. Preferably, said main switching means 3 is realized by a controlled switch and said auxiliary switching means 5 is made either by a self-controlled switch or by a controlled switch whose conduction is alternately carried out with that of the main switch 3. It is particularly favorable to realize the means of main switching 3 by a transistor, in particular by a field-effect transistor, in particular by an N-type MOSFET (Metal Oxide Semiconductor Field Effect Transistor). Said auxiliary switching means 5 is preferably produced by a diode, in particular by a Schottky type diode.

In the electrical circuit illustrated in FIG. 1, the main switching means 3 consisting of an N-type MOSFET is connected to the negative side of the voltage source 2 of the solenoid 1, which is known as a "low side" electronic chopper, unlike the "high side" type where the main switching means 3 is connected to the positive side of the source of the solenoid voltage 2 1. In the preferred case where the auxiliary switching means 5 takes the form of a diode as a self-controlled switch ensuring the continuity of the flow of current in the solenoid coil of the solenoid 1 by presenting a weak voltage drop when the current flows in a loop in the coil, that is to say when its power supply is cut by the main switching means 3, this component is commonly called "freewheel diode".

Due to the preferred application of a control device according to the present invention in the context of an electric starter for a heat engine, particularly for an automobile, the transistors used are preferably of the field effect transistor type, in particular of the MOSFET type, as mentioned above. Indeed, these transistors are particularly suitable for low voltages such as in a car edge network of about 14V encountered in the automobile. Preferably, a main N-channel MOSFET 3 is used, simply because these are more widespread than the P-channel type. In the case of a "low side" chopper, a main N-channel type MOSFET 3 is appropriate. by its positive gate control referenced to the ground of the electrical circuit, which simplifies the realization of the gate control circuit of the main MOSFET 3. A MOSFET is typically controlled at frequencies f higher than the human audible range, ie f > 15-2OkHz, with a conductive state "on" and an open state "off". If the acoustic stress is lower, the frequency can be lowered to a few kHz. The duration of the states on and off are therefore short, generally less than 100 μs. The current level in the coil of solenoid 1 can be adjusted by the value of the closing duty ratio of main MOSFET 3, this parameter being controlled by said calculating means 4. Based on this known configuration of an electronic chopper for controlling the power supply of a solenoid 1, the present invention proposes that the control device further comprises an additional switching means 6 connected in series with said switching means. auxiliary 5 as well as a voltage clipping means 7 connected in parallel with the solenoid 1 and with the additional switching means 6. This additional switching means 6 then makes it possible to choose between at least two current flow paths when the The power supply of the solenoid 1 is cut off by the main switching means 3. The additional switching means 6 can be constituted by a controlled switch, this switch being preferably also controlled by said calculating means 4. In a form of FIG. preferred embodiment, the additional switching means 6 is constituted by a transistor, preferably a tra a field effect nsistor, in particular by a P or N type MOSFET. In the configuration illustrated by way of example in FIG. 1, where the main switching means 3 is an N-type MOSFET, the additional switching means 6 is made by a P-type MOSFET. In fact, a P-type MOSFET is preferably used as an additional switching means 6, since the control of the gate of this transistor can then be carried out in a simpler way with respect to an N-type MOSFET, that is to say without using a driver circuit with a charge pump. In this case, it is possible to use a single open-collector NPN transistor on the gate of the MOSFET P. With regard to the voltage clipping means 7, it can favorably be constituted by a self-controlled switch responsive to a voltage threshold preferably fixed a diode, in particular a diode-type suppression diode or for example a resistor whose high value, strongly decreases from a certain threshold voltage applied to its terminals (also known under the name of VDR: Voltage Depends Resistor). To simplify the terminology, reference will be made hereinafter also of main switch or main MOSFET for the main switching means 3, freewheeling diode for the auxiliary switching means 5, additional switch or additional MOSFET for the additional switching means 6, and suppressor diode for the voltage clipping means 7.

Referring to the embodiment of FIG. 1 of a control device according to the present invention, it is possible to illustrate the operation and improvement according to the present invention of the known chopper adapted to driving the solenoid coil of a starter. By adding an additional switching means 6 in series with the auxiliary switching means 5 which is normally the freewheeling diode and a voltage clipping means 7 in parallel with the solenoid 1 and with the additional switching means 6, it is it becomes possible to choose between two current flow paths in the phases where the main switching means 3 does not drive (off state).

In current setting or current holding mode in the solenoid 1 coil of the starter, when the main switching means 3 is in its conductive state, the freewheeling diode 5 is used by switching the additional switching means 6 which is thus in its state of continuous conduction, which minimizes losses. Then, when it is desired to rapidly decrease the current in the solenoid 1, for example for the purpose of limiting the movement of the movable core of the solenoid 1 to its first engagement position or limit the impact speed of the core in end of its stroke, which reduces the noise and wear of the parts concerned, or for the purpose of quickly canceling the current in the solenoid, which allows for example to achieve a rapid disengagement of the starter gear of the toothed crown of the heat engine, the additional switching means 6 is used in the following manner. First, the main switching means 3 is put in its non-conducting state off and, simultaneously, the switching means additional 6 is also interrupted. The current flowing through the coil of the solenoid 1 can only then pass through the voltage clipping means 7 and thus finds a passage with a greater voltage drop, which accelerates the speed of current reduction, this phase realizing and the function of rapid shutdown of the current flowing through the solenoid 1. This phase is later also called "fast switch-off". If it is desired that the current in the solenoid 1 decreases normally respectively more slowly, simply do not interrupt the additional switching means 6 when the main switching means 3 is put in its non-conducting state off, the current can then pass through the additional switch 6.

In order to detail these explanations, it should be noted that for use on a typical automotive edge network of approximately 14V, the typical values of the characteristics of the electronic components used are approximately U _{MCP / MCS} = 40 to 60V with respect to relates to the voltage for the main switching means 3 and additional 6 and about U _D s = 35 to 55V with respect to the voltage for the suppression diode 7, this satisfying the condition U _DS <U _{MCP / MCS} - The rate of change of the current is equal to the ratio of the voltage in the loop traversed by the current divided by the inductance. This is expressed by the equation Δl / δt = U / L, where U is the counter-voltage encountered by the current in the loop and L is the inductance of the coil of solenoid 1. The inductance L varies as a function of the position of the mobile core in the coil. The counter-voltage U therefore depends on the on or off state of the additional switch 6: In the freewheel diode chopper mode 5, where the additional switch 6 is in the conductive state, it follows to the counter-tension U = r ^* l + U _DRL , where r is the resistance of the loop traversed by the current, mainly equal to the resistance of the coil of solenoid 1, and U _DRL being the voltage applied to the free-wheeling diode . In the "fast switch-off" mode, where the switch additional 6 is in the non-conductive state, the dependency reads U = r ^* l + U _DS +

UDRL-

In free-wheel diode chopper mode, with a solenoid starter solenoid 1 of a resistor of r = 1 Ω, traversed by a maintenance current of about 5 A in the initial state, one can estimate, by taking a freewheeling diode with a low Schottky voltage drop with U _DRL = approximately 0.3 V, that the counter-tension is approximately U = 5 V initially and decreases with the decrease of the current I. neglecting the term U _DRL , the decay of the current follows an exponential law, with a time constant T = L / r. In the "fast switch-off" mode with a suppression diode, U _DS = 55V is considered. The counter-tension is then approximately U = 60V initially and decreases slightly with the fall of the current I. By approximating U to a constant value, the decay of the current follows a linear law. The decay factor is therefore of the order of ten times faster in the latter case than in the freewheel diode chopper mode, which justifies the name "fast switch-off". The decay factor approximately ten times faster reflects the ratio of the counter-tensions of approximately U = 5.4V and U = 60V in both cases. In comparison, a more complex coil driving structure, such as an H bridge requiring four switches, makes it possible to obtain a counter-voltage of approximately U = 19V, since one can consider U = r ^* l + V _Rd B with V _Rd B = 14V, which corresponds to a decay factor of the current approximately three times less than in fast switch-off mode. Therefore, the gain on the decay rate of the current in the solenoid coil 1 provided by the "fast switch-off" mode of a control device according to the present invention is significant.

With reference to FIG. 2, another embodiment of a control device according to the present invention can be illustrated, according to which the switch chopper is again of the "low-side" type, that is to say say that the main switch 3 which is again an N-type MOSFET is connected the negative side of the power supply of the solenoid 1, but, alternatively, the additional switching means 6 is made by an N-channel MOSFET, unlike the case shown in Figure 1. The additional MOSFET 6 has the voltage its gate brought to a positive potential with respect to the positive power supply rail thanks to a discrete load pump circuit realized with two capacities 8.1, 8.2 and two diodes 8.3, 8.4, which allows the continuous closing of the additional N MOSFET 6 since the main MOSFET 3 chops the solenoid 1 coil voltage. An open collector NPN transistor on the additional MOSFET N gate 6 makes it possible to have a simple interface with the reference logic referred to the ground.

Another alternative is shown in FIG. 3, which shows the case where it is required to control the coil of the starter solenoid 1 with a "high side" switch, that is to say that the main switch 3 which remains an N-type MOSFET is connected on the positive side of the voltage source 2 of the solenoid 1, so as to have the minus side of the coil connected to ground. In the case illustrated, the additional control means 6 is again an N type MOSFET. The control of the main MOSFET 3 then requires a driver circuit 9 with a charge pump. This driver 9 must also tolerate significant negative voltages, up to -U _D s, on its output connected to the source of the main MOSFET 3.

According to another embodiment of the device, protection of the circuit against an accidental inversion of the battery is ensured by placing the positive supply rail downstream of a protection relay 10 known as the "More After Contact" ( + APC). This configuration makes it possible to provide protection against the permanent connection of the coil of solenoid 1 to the positive potential of the battery, for example following a short-circuit, corrosion, etc., in the case of mounting of the main switch 3 according to the "low-side" diagram. This also ensures safety against accidental activation of the starter by inserting two means of interruption in series in the electrical supply circuit of the coil of solenoid 1. It should be noted here that in the case where a reverse voltage is however applied to the power supply of the chopper, unlike a conventional chopper where the current flows directly through the parasitic reverse diode of the main MOSFET and in series the freewheeling diode, which leads to the certain destruction of the semiconductors before the fusion of a fuse protection, the present concept provides a passing the current through the parasitic reverse diode of the main MOSFET and in series winding the coil of the solenoid. The resistance of the latter tends to limit the current undergone by the inverse diode of the MOSFET. The current does not flow in the freewheeling diode since the auxiliary diode of the auxiliary MOSFET is mounted upside down with the freewheeling diode, thus blocking the current flow in parallel with the coil.

According to yet another embodiment of the control device according to the present invention, said main switching means 3 may advantageously be constituted by a field effect transistor adapted to measure the current flowing through it, preferably by a transistor of the SenseFET type. . These components exist in particular for N-type MOSFETs and deliver a measurement current which is the image of the drain current divided by an intrinsic ratio to the component. This avoids the current measurement by shunt which requires an additional component and, moreover, generates dissipative losses. The use of a conventional shunt or any other device ensuring a current measurement obviously remains compatible with the device according to the present invention. By cons, the use of a MOSFET for measuring the current flowing through it is particularly favorable in the scheme of a chopper "low-side", as shown in Figures 1 and 2. In this case, the main switch 3 is referenced to the ground which simplifies the current signal processing circuitry. In the case of a "high side" chopper, the potential of the source varies rapidly between two values close to ground voltages and the on-board network at the frequency of the division, which makes more complex the current image signal processing circuit, because the current mirror output is referenced to the potential of the source. This signal is normally a square wave of the same duty cycle and frequency as the control of the main MOSFET. The processing circuit housed in the calculation means 4 converts it into a non-pulsed value, based on the value of the signal in the conduction phase of the main switch 3. This continuous signal thus follows the evolution of the current in the coil of the solenoid, since the duty cycle is not totally zero, that is to say while there is no closure of the main MOSFET for measuring the current. The exploitation of this current information in the coil makes it possible to improve the control of the coil, in particular through the following aspects.

On the one hand, the availability of this information concerning the current flowing through the coil of solenoid 1 makes it possible to ensure better independence of the current with respect to the supply voltage and the temperature. Indeed, it is known that the voltage of an automotive edge network varies according to various conditions, among which the state of the battery, the temperature, the consumers switched on, or the setpoint voltage of the regulator. the alternator, especially if it is controlled by an external computer, as is the case on many new vehicles that optimizes the voltage level of the onboard network, while the current in the solenoid coil depends mainly on the voltage applied by the chopper and the internal resistance of the coil. It is also known that the resistance of the copper winding of the coil increases substantially with the temperature, in particular about 4% per 10 ^° C. increment of temperature increase. The electromechanical behavior of the coil is directly related to the current that creates the magnetic field acting on the moving core.

Therefore, by using current control through the coil of solenoid 1, it is possible to act directly on the control of the force that sets in motion its mobile core. Information about the current in the coil allows thus to achieve servo control of the coil current and not voltage.

On the other hand, the information regarding the current flowing through the coil of solenoid 1 allows the thermal monitoring of the coil, necessary or at least desirable because the resistance r (T) = U / l of the winding is a function of the ambient temperature, as mentioned above. Indeed, in the main application envisaged, the coil solenoid launcher 1 is located in a hot and constraining thermal environment, especially under the bonnet of a vehicle, the starter is normally mounted on the engine. In addition, the solenoid of a Stop & Start starter ensures the pre-engagement function of the pinion, which involves the power supply of solenoid 1 over the duration of the Stop phase which can last several tens of seconds or even exceed one minute. The current flowing through the coil is a holding current, of reduced value with respect to a inrush current, but which remains sufficient to cause dissipative losses that may be significant according to the sizing choices made for the solenoid, that is to say ie the number of turns, the section of the wire, etc. The heating of the coil by Joule effect thus varies its internal resistance and can bring the copper wire of the coil to critical temperatures, in particular in case of intensive use of the Stop & Start function in a very hot environment. In the case of equipping a control device according to the present invention with a SenseFET main switch, it has the information of the average voltage applied to the coil and the current flowing through the coil, which makes it possible to determine the value of the resistance with Ohm's law. It is then possible to estimate the temperature of the copper wire from the calculated resistance. If the temperature reaches a level too high, the controller may apply a predefined procedure that interrupts, under certain conditions, the pre-commitment to protect the integrity of the coil. The control system of the Stop & Start entity is informed of this situation and takes this into account during the next execution of a startup operation.

In addition, this information makes it possible to carry out a feedback by means of calculation 4, for example on the position and speed of the mobile core. Indeed, the displacement of the mobile core in the magnetic circuit varies the reluctance, the value of the current is affected transiently. The dynamic current monitoring then makes it possible to detect information on the movement of the core. For example, a criterion on dl (t) / dt makes it possible to identify the transient current trough, an index of the displacement of the mobile nucleus preceding the attainment of the first stable position of the nucleus of a two-stage solenoid. The adjustment of the chopper duty ratio can be based on this information, to improve the control of the solenoid launcher. The control of the mobile core of a solenoid can thus be improved by the exploitation of the current signal during its movement, or to verify the achievement of a given position in relation to a given reluctance value: for example the first stable position of a two-stage solenoid.

In addition, given the main application envisaged for the control device of a solenoid according to the present invention, it obviously also relates to an electric starter for a combustion engine which comprises a solenoid 1 and a control device as described above.

Furthermore, it is particularly favorable to choose a solenoid 1 integrated in the starter so that it has a nominal voltage lower than the voltage supplying the starter. Preferably, the nominal voltage of the solenoid 1 is in the range of 4 to 12 V, typically 6 to 10V, for a voltage supplying the starter in the range of 12 to 16 V. Indeed, it is very interesting to provide the use of a nominal voltage coil lower than the voltage of the onboard network which is normally 14V, because with such a coil having fewer turns, which is therefore less inductive and less resistive, the rise time of the current under a given voltage can be improved according to the law δl / δt = U / L with a value of the inductance L smaller.

This characteristic on the rise time is the corollary of the improvement of the current drop time provided by the control device equipped with a chopper having a "fast switch-off" mode. The duty cycle values are adjusted according to the ratio of the nominal voltage of the solenoid 1 coil to the on-board system voltage so as not to "burn" the coil by excessive currents, this by adjusting the voltage of the coil. power supply of the coil with the chopper. For example, if the nominal voltage of the coil is 7V and the voltage of the on-board network is 14V, to simplify the ratio which is in this example of 50%, it will be necessary, to ensure a holding current corresponding to 60% of the nominal voltage, apply a duty cycle of 60% ^* 50% = 30% to the chopper of the control device. The combination of a control device having a "fast switch-off" mode with a starter having a solenoid with a nominal voltage coil lower than the voltage of the on-board power supply network that supplies the chopper then constitutes a choice of relevant design by offering a powerful control over the reaction times of the solenoid launcher and / or auxiliary relay or any other element using a solenoid used in the starter of a Stop & Start system.

As already mentioned in the introduction, the solenoid 1 integrated in the electric starter can be constituted by a two-stage solenoid having two stable powered positions of its movable core or by a conventional solenoid with a stable powered position. It is also obvious that the starter could comprise several solenoids each controlled by a corresponding control device. It can further be noted in this context that the electronic circuit as well as the means for calculating the chopper of the control device according to the present invention can be integrated either directly on the starter or in an existing computer on the vehicle, which can notably be constituted by the injection computer of the engine or by a unit of load switching mounted under the bonnet. The choice is made according to technical and economic considerations. In particular, if it is necessary to realize a starter as described here and integrating the Stop & Start function with a low cost, it may be relevant to host the chopper in a calculator available in the vehicle architecture. In this case, the long link between the solenoid and the electronic circuit can be the source of electromagnetic disturbances and thus pose the known problem of distance. As a countermeasure, it is then possible to operate the chopper at lower frequencies, which may be included in the audible band and thus constitute a compromise at the generated noise level, and reduce the stiffness of the switching edges chopper and use contiguous connecting cables, which is a compromise with the dissipation of switching losses.

According to another aspect of the present invention, a control method for the actuation of such a control device or such a starter respectively are proposed.

The above explanations relating to the control device for a solenoid establish in particular that the control method of the device according to the present invention comprises, in current setting mode or maintaining the current in the solenoid 1, the steps of switching the solenoid 1. main switching means 3 or keeping it in the switching state and switching the additional switching means 6 so as to allow the flow of current through the auxiliary switching means 5. In fast-off mode of the current in the solenoid the method comprises the steps of interrupting the main switching means 3 and interrupting the additional switching means 6 so as to interrupt the flow of current through this additional switching means 6, a flow of current through the means voltage clipping 7 remaining possible. With regard to the use of a corresponding electric starter, the control method for the actuation of such a starter comprises, in the slow engagement mode of the mobile core of the solenoid 1 in a stable powered position, the steps to switch the main switching means 3 by chopping the current with a reduced duty cycle so as to moderately increase the current through the solenoid 1 and to obtain a slow movement of its moving core, and, after the movement of the movable core of the solenoid 1 in the desired position, chopping the current through the main switching means 3 with a duty cycle corresponding to the holding current of the movable core of the solenoid 1 so as to obtain the maintenance of its movable core in a stable powered position. In fast engagement mode of the solenoid movable core in a stable powered position, the method comprises the steps of switching the main switching means 3 by applying a full voltage wave to the solenoid so as to rapidly increase the current through the solenoid 1 and to obtain a fast movement of its movable core, then to interrupt either only the main switching means 3 or the latter and the additional switching means 6 so as to rapidly decrease the current through the solenoid 1 and to brake the movement of the movable core, and then, after the movement of the movable core of the solenoid 1 in the desired position, to switch the main switching means 3 again by chopping the current with a duty ratio corresponding to the core holding current mobile of the solenoid 1 so as to obtain the maintenance of its mobile core in a stable powered position. These control methods make it possible to have a control device or an electric starter, respectively, which has a great flexibility of use and in particular a reduced reaction time whether it is a rise or a break in the current. In particular, these methods make it possible to have greater flexibility in controlling the starter solenoid solenoid, in particular a Stop & Start starter. This makes it possible to improve the operation of several driving operations of the solenoid launcher or of a solenoid in general, even if this description refers to the example of a starter of a heat engine.

First, starter gear engaging operations in a ring gear of the engine can be facilitated and improved. These engagement operations are much more numerous with a Stop & Start starter compared to a conventional starter which intervenes only at the beginning of the journey for the initial startup of the engine. For Stop & Start starts during the journey, it is known to pre-engage the pinion during the stopping phase of the engine. Typically, the pinion is engaged in the final phase of immobilization of the crankshaft, at speeds of the order of 100 rpm or less. This makes it possible to have a mechanical connection already established between the starter gear and the crown of the engine during the restart operation, which must be the fastest, secure and quiet possible.

With the control device according to the present invention and the corresponding control method, it is in particular possible to practice two types of engagement for the restart in the Stop & Start mode.

On the one hand, a slow commitment can be made. Most of the commitments are made at the beginning of a sustainable phase of Stop. It is in particular this configuration that minimizes the acoustic effects caused by the impact between the gear teeth and the teeth of the flywheel ring. Furthermore, the highest number of commitments on a vehicle equipped with a Stop & Start starter increases the wear speed of the teeth. Slow engagement reduces noise and mechanical wear. To achieve this, the control device is used, in current setting mode or maintaining the current in the solenoid 1, with a moderate current level, that is to say with a reduced duty cycle, to obtain a relatively slow movement of the mobile core. Typically, the movable core moves in this case 1/1 o ^ιeme second to the desired engaging position. On the other hand, a quick commitment can be made. Indeed, it is necessary in certain situations to restart as soon as possible the engine, while it has not finished completely to stop. For example, if a vehicle stops at a red light that then turns green, a Stop order has been given to the engine and in the wake he must restart it, this situation is called "reflex-start". When the rotation speed of the crankshaft has dropped sufficiently, but without the crankshaft has completely stopped, it is the starter to help the engine to restart, otherwise, at higher speeds, the engine can restart on his inertia. It is then necessary to engage the gear on the ring gear which is still in motion, this operation to be performed quickly because the speed of the crankshaft oscillates strongly. It is interesting in this case to be able to engage the pinion as soon as possible via the first stable fed position of a two-stage solenoid, but then to observe whether a restart of the engine on its inertia takes place before decide to supply the starter via the second stable powered position of such a solenoid or to start by supplying the starter by an auxiliary supply channel not passing through the main contactor of the two-stage solenoid. Similarly, when using a conventional one-stage solenoid, it is desirable to be able to quickly engage the pinion via the single stable fed position of the solenoid, and then independently be able to use an alternating starter switch channel. In these cases, it is necessary to drive the solenoid so as to quickly reach the first respectively stable fed position, corresponding to the commitment of the pinion, without going to the end of stroke in the case of a two-stage solenoid, which would correspond to the closing of the main power contactor.

This objective can be achieved by applying the aforementioned control method for the control device. In detail, a full voltage wave is first applied across the solenoid coil in order to grow the current as fast as possible. The duration of this phase is of the order of a few tens of milliseconds, with a closing ratio of the main MOSFET 3 of 100% or close to 100%. This gives an initial impetus to the mobile core. Since it is desired to stabilize the mobile core as quickly as possible in the first and only stable fed position, the rise of the current is then interrupted either by opening the main MOSFET 3, corresponding to a zero duty cycle, or by briefly activating that is, in the order of 1 ms or less depending on the need and the characteristics of the coil, the chopper fast-switch-off mode at the beginning of this phase of zero duty cycle. It is thus possible to quickly modulate the force that governs the movement of the nucleus. This control strategy is also useful for achieving a smooth approach in engaging the pinion teeth in the crown toothing in order to obtain a reduced impact force. At the end of this second control phase of a duration of 10 to 20 ms depending on the characteristics of the coil, a moderate current is applied again to maintain the nucleus of the solenoid launcher in a stable position.

Furthermore, a known method for the choppers of the state of the art makes it possible to adjust the holding current to a lower value. This function can be combined with the proposed method and is particularly particularly advantageous in the case of pre-engagement of the pinion on a vehicle equipped with a starter of the Stop & Start type. It is thus possible to limit the electrical consumption and heating of the solenoid launcher during the Stop phase. Secondly, in the case of the use of a two-stage solenoid as discussed above, the complete stroke operations of the movable core without first maintaining it on the intermediate position of the solenoid may also be required, by example in the case of a "reflex-start" where the confirmation of the need to supply the starter by the power contactor arrives immediately, that is to say in the wake of the gear engagement operation by via the first stable powered position of the movable core. This is also the case for example of an initial startup operation. In these cases, it is possible to modulate the speed of movement of the mobile nucleus of the launcher solenoid in the same manner as for the pre-commitments described above. Similarly, the control applies a full voltage wave, then reduces the current level by a zero duty cycle phase by being able to use the "fast switch-off" mode of the control device to accelerate the decay rate of the current, and finally applies a holding current to keep the mobile core at the end of the race. Similarly, it is also possible to manage the force and the impact speed of the mobile core at the end of the race, in order to mitigate, if necessary, the impact of closure of the power contactor of the power supply, to increase the longevity of the contactor.

Thirdly, the fast disengagement operations of the gear gear of the ring gear of the engine can be facilitated and improved. At the end of the drive phase of the engine by the starter, concluding by the start of the motor becomes independent, the pinion must actually be disengaged. By rapidly removing the solenoid holding current by using the "fast switch-off" mode of the control device, the movable core of the solenoid respectively the pinion follows with a reduced latency time the disengagement order. This reduces the driving time of the pinion by the engine and the mechanical stresses on it and the freewheel of the starter. Finally, in the case of using a conventional one-stage solenoid for pinion engagement in combination with an auxiliary relay and a corresponding solenoid for the power supply, the rapid opening of this auxiliary starter relay can also be facilitated and improved. In particular, an auxiliary relay and a corresponding independent solenoid can be used for powering the starter to create a second activated power path independent of that through the solenoid starter contactor. The control method can then also be applied to the control device of the solenoid coil of this auxiliary relay. The control of the starter power supply is thus improved by reducing the reaction time of the contactors implemented.

It is clear that the control device for a solenoid as well as the control method according to the present invention are likely to find many other applications in all fields involving the use of a solenoid and which could likewise require a greater flexibility of use and improved control of the solenoid.

The present invention then provides a control device for a solenoid having a great flexibility of use as well as a reduced reaction time and an electric starter incorporating such a control device, as well as a control method. corresponding for such a device respectively such a starter, this by using simple technical means, remaining compatible with a motor vehicle equipped with a conventional electrical distribution architecture, and offering a lower cost compared to an alternator-starter . The corresponding starter has in particular a fast reaction time for the application as well as for the removal of the current in the solenoid, thus allowing a commitment and a rapid disengagement of its mobile core in a stable powered position.

Claims

claims

A control device for a solenoid (1) electrically powered by a voltage source (2), the device preferably being adapted to be integrated in an electric starter for a combustion engine, the device comprising a main switching means ( 3) controlled by a calculating means (4) so as to allow the electric supply of the solenoid (1) to be chopped together with an auxiliary switching means (5) placed in parallel with the solenoid (1) and allowing circulation current in the solenoid (1) when its power supply is cut off by the main switching means (3), characterized in that the device comprises an additional switching means (6) connected in series with said auxiliary switching means ( 5) and voltage clipping means (7) in parallel with the solenoid (1) through the auxiliary switching means

(5) and with the additional switching means (6), this additional switching means (6) for choosing between at least two current flow paths when the power supply of the solenoid (1) is cut by means of main switching (3).

2. Device according to the preceding claim, characterized in that said main switching means (3) is formed by a controlled switch and said auxiliary switching means (5) is achieved either by a self-controlled switch or by a controlled switch whose conduction is alternately carried out with that of the main switch (3).

3. Device according to the preceding claim, characterized in that said main switching means (3) is formed by a transistor, preferably by a field effect transistor, in particular by an N-type MOSFET, and that said auxiliary switching means (5) is formed by a diode, preferably a Schottky type diode.

4. Device according to one of the preceding claims, characterized in that said additional switching means (6) is constituted by a controlled switch, the switch being controlled by said calculating means (4).

5. Device according to the preceding claim, characterized in that said additional switching means (6) is constituted by a transistor, preferably by a field effect transistor, in particular by a P or N type MOSFET.

6. Device according to one of the preceding claims, characterized in that said voltage clipping means (7) is constituted by a self-controlled switch, preferably a diode, in particular a deletion diode type diode.

7. Device according to one of the preceding claims, characterized in that said main switching means (3) is constituted by an N-type MOSFET connected on the negative side of the voltage source (2) of the solenoid (1) and said additional switching means (6) is constituted by a P or N type MOSFET.

8. Device according to one of the preceding claims 1 to 6, characterized in that said main switching means (3) is constituted by an N-type MOSFET connected on the positive side of the voltage source (2) of the solenoid ( 1) and that said additional switching means (6) is constituted by an N-type MOSFET.

9. Device according to one of the preceding claims, characterized in that said main switching means (3) is constituted by a field effect transistor adapted to measure the current flowing therethrough, preferably by a SenseFET type transistor.

10. Device according to one of the preceding claims, characterized in that the positive supply rail of the solenoid (1) is placed downstream of a protective relay (10).

11. Electric starter for a combustion engine, characterized in that it comprises said solenoid (1) and a control device according to one of the preceding claims.

12. Starter according to the preceding claim, characterized in that said solenoid (1) is chosen to have a rated voltage lower than the voltage supplying the starter, preferably that the nominal voltage of the solenoid (1) is in the range from 4 to 12 V for a voltage supplying the starter in the range of 12 to 16 V.

13. Device according to one of the preceding claims 11 to 12, characterized in that said solenoid (1) is a two-stage starter solenoid having two stable powered positions of its movable core, defined as a function of the current flowing through the coil .

14. Control method for actuating a control device according to one of the preceding claims 1 to 10, characterized in that, in current setting or current holding mode in the solenoid (1), it comprises the steps o of switching the main switching means (3) or keeping it in the switching state and o switching the switching means further (6) so as to allow flow of current through the auxiliary switching means (5), and that, in the fast-off mode of the current in the solenoid (1), it comprises the steps of interrupting the main switching means (3) and o interrupting the additional switching means (6) so as to interrupt the flow of current through this additional switching means (6), a flow of current through the clipping means voltage (7) remaining possible.

15. Control method for actuating a starter according to one of the preceding claims 11 to 13, characterized in that, in slow engagement mode of the movable core of the solenoid (1) in a stable fed position the method comprises the steps of switching the main switching means (3) by chopping the current with a reduced duty cycle so as to moderately increase the current through the solenoid (1) and to obtain a slow movement of its core mobile, after the movement of the movable core of the solenoid (1) in the desired position, chopping the current through the main switching means (3) with a duty ratio corresponding to the holding current of the movable core of the solenoid (1) in order to obtain the maintenance of its mobile core in a stable position, and that, in the fast engagement mode of the movable core of the solenoid (1) in a stable powered position, the method comprises the steps of switching the main switching means (3) by applying a full voltage wave to the solenoid (1 ) so as to rapidly increase the current through the solenoid (1) and to obtain a fast movement of its mobile core, o to interrupt either only the main switching means (3), or the latter and the switching means further (6) so as to rapidly decrease the current through the solenoid (1) and to slow the movement of the movable core, and o after the movement of the movable core of the solenoid (1) in the desired position, to switch again the main switching means (3) by chopping the current with a duty cycle corresponding to the holding current of the movable core of the solenoid (1) so as to maintain its movable core in a position stable power supply.