FR2749451A1 - Control of starter motor for motor vehicle - Google Patents

Abstract

The process involves reducing the potential supplied to the starter motor at the beginning of the starting process, reducing the initial angular acceleration of the starter motor, making it easier for the starter pinion to engage the ring gear. The supply to the starter motor is chopped over a predetermined time by a MOSFET switch (T) that controls the current in the holding coil (10c) of the starter solenoid. A time delay circuit (14) controls the MOSFET switch, delaying the activation of the holding coil of the starter solenoid so the supply to the starter motor is interrupted then restored as the engagement coil of the solenoid releases and recloses the main contacts (10a).

Description

 The present invention relates to methods and devices for controlling motor vehicle starters.

 An example of a motor vehicle starter has been illustrated in FIG. 1.

 Such a starter conventionally comprises an electric motor M, the output shaft of which carries a pinion 1, as well as a contactor 2.

 The pinion 1 is intended to cooperate with the gear of the starter ring of the heat engine. it is slidable on the shaft of the motor M between a position where it is disengaged relative to said starter ring and a position where it meshes therewith.

 The contactor 2 comprises a coil 2a and a plunger core 2b.

 It controls the supply of the electric motor M by displacement of a movable contact 3 between an open position and a closed position, said contact 3 being pushed by said plunger core 2b.

 The contactor 2 also controls the movement of the pinion 1 from one position to the other. Its plunger core 2b is connected to the pinion 1 by mechanical means referenced by 4 as a whole.

 These mechanical means 4 include in particular a spring 5, which is mechanically interposed between the plunger core 2b and the pinion 1, and which allows the plunger core 2b to continue its travel to ensure the closing position of the movable contact 3, even if the pinion 1 is locked in abutment against the teeth of the crown of the heat engine, in a position where it does not mesh with said crown.

 However, given the speed of movement of the movable core 2b and the elasticity of the mechanical connecting means 4, due to the presence of the spring 5, there may be significant phase shifts between the translation of the pinion 1 and the closing of the contact. 3.

Particularly at low temperature, one can observe a rotation of the electric motor M, and therefore of the pinion 1, before the latter has had time to penetrate the crown. The electric motor M being supplied at full voltage, the speed of the pinion 1 increases very quickly, thus preventing the pinion from engaging with the crown. It follows a rapid destruction of the crown and the pinion.

 The object of the invention is to overcome this drawback.

 To this end, it proposes a method for controlling an electric motor of a starter motor vehicle, characterized in that the supply voltage of the electric motor of the starter motor is reduced at the start of start-up, so as to avoid an excessively rapid rise the speed of rotation of said electric motor.

 This allows time for the pinion to penetrate the crown of the engine, when the pinion teeth pass in front of the recesses in the crown.

 With such a method, the deterioration of the starter ring and the starter pinion is avoided.

 In addition, this process improves the longevity of the starter by a more progressive supply than in conventional systems (reduction of electric arcs, brush wear, mechanical shock, ...).

 Advantageously, the supply voltage at the start of startup is a chopped voltage whose peak value corresponds to the value of the supply voltage in nominal mode.

 The reduction of the supply voltage can take place during a period of a predetermined duration or during a predetermined number of slots of the chopped voltage.

 The invention also relates to a device for controlling the electric motor of a motor vehicle starter, characterized in that it comprises means for reducing the supply voltage of said electric motor at the start of starting.

 These means are advantageously means for chopping the supply voltage of said electric motor.

 In an advantageous variant, the supply of the electric motor being controlled by a contactor comprising a call winding and a holding winding, the supply of which is itself controlled by the contact switch of the vehicle, the means for chopping of the supply voltage of the electric motor include means for inhibiting the supply of the holding winding at the start of start-up, the call winding being short-circuited by closing the movable contact of the contactor.

 In another advantageous variant, the power supply to the electric motor being controlled by a coil contactor (s), the chopping means comprise a slot generator which, at the start of start-up, choppily controls the opening and closing of a switch which controls the supply of the contactor winding (s).

 In yet another advantageous variant, the supply of the electric motor being controlled by a coil contactor (s), the device comprises a switch which controls the supply of the coil (s) of the contactor, as well as a timer unit which controls the opening of the switch on closing of the movable contact of the contactor, as well as means for controlling the closing of the switch in the absence of the opening command by the timing unit.

Other characteristics and advantages of the invention will emerge from the description which follows. This description is purely illustrative and not limiting. It should be read in conjunction with the accompanying drawings on which
- Figure 1, already analyzed, is a sectional view of a motor vehicle starter
- Figure 2 is a diagram of a starter control system according to a possible embodiment for the invention
- Figures 3a, 3b and 3c are time graphs which illustrate a sequence of control signals from the system of Figure 2
- Figure 4 is a diagram of a system according to another possible embodiment for the invention
- Figures 5a to 5d are time graphs illustrating the sequences of control signals of the system of Figure 4
- Figure 6 is a diagram of another possible alternative embodiment for the system according to the invention
- Figures 7a to 7e illustrate a sequence of control signals from the system of Figure 6.

 There is shown diagrammatically in FIG. 2 an electric motor M of a starter motor vehicle D, as well as a contactor 10, consisting of a movable contact 10a, a call winding 10b and a holding winding 10c .

 The motor M is connected on the one hand to ground and on the other hand to a terminal B + supplying the battery voltage via the contact 10a.

 At a common end, the windings 10b and 10c are connected to said terminal B + by a switch 11 which is the ignition key switch.

 At its opposite end, the switch 10b is connected on the one hand to a point between the contact 10a and the electric motor M and on the other hand, by means of a diode 12 in series with a resistor 13, to the input e of a timer unit 14.

 Said diode 12 is passed from the winding 10b to the input e.

 The input e is also connected to a capacitor 15, the other end of which is connected to ground.

 The output s of the timing unit 14 controls a switch T mounted between ground and the end of the winding 10c which is opposite to the winding 10b.

 In the particular example illustrated in FIG. 2, the transistor T is of the bipolar type. Its base is connected to the output s of the unit 14 via a resistor 16, while its emitter is connected to ground and its collector to the holding winding 10c.

 Furthermore, the output s of the timer unit 14 is also connected to ground via a resistor 17.

 The operation of this circuit will now be described with reference to Figures 3a, 3b and 3c.

 FIG. 3a shows the voltage at the end common to the windings 10b and 10c.

 When the contact switch 11 is closed, the voltage on the input e of the timing unit 14 goes to its high level.

The voltage of the output s which controls the transistor T (FIG. 3b) does not pass at its high level until after a period of duration tb following the closing of the switch 11. The duration tb is for example a few tenths of a second
During this entire period, the switch T, the base of which is grounded, is blocked and no current flows through the holding coil 10c.

 When the contact switch 11 is closed, a current flows through the winding 10b, so that the movable core of the contactor moves the contact 10a to its closed position.

 However, closing the switch îOa short-circuits the coil lOb and eliminates the magnetic attraction forces which were exerted on the movable core, so that the latter returns to its rest position and opens said contact lova. This opening then restores an inrush current in the winding 10b.

 Consequently, as illustrated in FIG. 3c, the starter is supplied with a chopped voltage, which reduces its apparent supply voltage and consequently the angular acceleration of the electric motor M.

 The period of chopped current is a function of the masses, the springs and the inductances present.

 The supply of the motor M by a chopped voltage ends at the end of the period of time tb, when the output s of the timing unit 14 goes to its high level. With the transistor T closed, a current flows through the vioc holding winding.

 The contact 10a is then kept closed by the magnetic attraction exerted on the core of said contactor by the supply of said winding 10b and the motor M is continuously supplied.

 The diode 12 and the RC circuit that constitute the resistor 13 and the capacitor 15 at the input of the timer unit 14, make it possible to smooth the input voltage of said unit, so as not to disturb its operation.

 Reference is now made to FIG. 4. In the diagram illustrated in this figure, the supply of the electric motor M of the starter is controlled by a contactor 20 comprising a movable contact 20A, a call winding 20b and a holding winding 20c .

 The windings 20b and 20c are supplied with voltage at a common end connected to a terminal B + supplying the battery voltage by a controlled switch T and a contact switch 21.

 At its other end, the coil 2Ob is connected to a point between the motor M and the movable contact 2Oa. The winding 20c is in turn connected to ground.

 The switch T is controlled by a timer unit 22 and a slot generator 23 mounted in parallel.

 This unit 22 and this generator 23 are connected at the input to the terminal B + of supply to the battery voltage by means of a switch 21.

 The output of the unit 22 is connected by a diode 24 at a point to the output of the generator 23 which controls the switch T in voltage. Said diode 24 conducts from the unit 22 to the switch T.

 More particularly, the switch T is a bipolar transistor, the base of which is connected to said common point.

 Said base is also connected to the neutral via a resistor 26.

 FIG. 5a shows the input voltage of the unit 22 and of the generator 23 and in FIG. 5b, the output of the timing unit 22.

 This output goes high after a time tb after the ignition key switch 21 is closed.

 Consequently, when the ignition key 21 is closed, the output of the timer unit 22 is initially at its low level and therefore has no effect on the operation of the switch T.

The generator 23, whose output voltage has been illustrated in FIG. 5c, supplies the base of the transistor
T by slots causing a succession of blockages and conductions of said transistor.

 Contactor 20 closes and opens at the same rate, resulting in an average supply voltage to the motor proportional to the duty cycle of the generator.

 This duty cycle is adjusted so as to obtain the desired average voltage for the electric motor M.

 Of course, the conduction and blocking times are chosen to be greater than the mechanical response time of the contactor to ensure the operation of the system.

 At the end of the period of duration tb, the timer unit switches to high output and turns on the transistor T permanently. The contactor 20 remains closed and thus supplies the motor at full voltage for starting.

 The supply voltage of the electric motor M has been illustrated in FIG. 5d.

 Of course, the starter control carried out by the unit 22 and the generator 23 can complement a unit 27 for electronic control and protection of the starter comprising, in a manner known per se, automatic starter stop functions , thermal protections, starter interlock when the heat engine is running, ...

 In FIG. 4, this unit 27 is mounted in parallel with the unit 22 and the generator 23. As a variant, the outputs of the timing unit 22 and of the generator 23 can act directly on this control unit 27 instead of d '' attack the base of transistor T.

 In addition, the timer unit 22 can be replaced by a pulse counter making it possible to inhibit, after a predetermined number of chops of the motor supply.

 Reference is now made to FIG. 6 in which another possible variant for the embodiment of the invention has been illustrated.

 The supply of the electric motor M illustrated in this figure 6 is controlled there by a contactor 30, a switch T and a contact switch 31, mounted in the same way as the contactor 20, the switch T and the contact switch 21 in Figure 4.

 The movable contact and the call and holding windings of the contactor 30 have been referenced respectively by 30a, 30b and 30c.

 In the variant illustrated in this FIG. 6, the switch T is controlled by the voltage at a point connected to the switch 31 by a resistor 32 and to the output of a timer unit 33, via a diode which is passed from resistor 32 to said unit 33.

 The input of the unit 33 is connected to the end of the call winding 30b connected to the electric motor M.

 Furthermore, this timer unit 33 is connected to a unit 34, the output of which inhibits, when it is at a high level, the passage to a low level of the output of the unit 33.

 This unit 34 is for example also a timer unit, the input of which is connected to the terminal B + of supply to the battery voltage by means of the switch 31.

 In FIG. 7a, the voltage at the common point between the resistor 32 and the switch 31 is shown.

 When the contact switch 31 is flipped, the transistor T is turned on by the bias resistor 32.

 The voltage of the output s of the timer unit 33 has been illustrated in FIG. 7b.

 Said output s is high as long as the input of the unit 33 is low, which is the case when the movable contact 30a is open and the contact switch 31 closes.

 After closing the switch 31, the movable contact 30a closes after a time "tf" which represents the electromechanical response time of the contactor 30.

 This closure immediately brings the output s of the unit 33 to its low level, which causes the transistor T to block and allows the contactor to reopen after a time "to" which represents the electromechanical response time of the contactor 30.

 The transistor T remains blocked as long as the timing unit has not switched back to its high voltage after a predetermined timing time "tb.

 The transistor T then becomes on again and a new cycle takes place.

 The contactor 30 thus operates in a choppy fashion, with a closing time which is a function of its response time.

 Compared to the variant embodiment illustrated in FIG. 4, this variant makes it possible to reduce the contactor closing time to a minimum, and to have a higher chopping frequency.

 Then, at the end of the delay time of the unit 34, the delay unit 33 is inhibited and its output remains permanently at the high level, which eliminates the chopping effect.

 The voltage at the output of the timer unit 15 has been illustrated in FIG. 7c, the control voltage of the transistor T and the supply of the motor M having been shown in FIGS. 7d and 7e.

 Of course, in the same way as in the case of the device in FIG. 4, the means 32 to 34 which control the transistor T can supplement a conventional unit for managing the power of the motor M (management unit 35 in the figure 6).

 In addition, the timer unit 34 can be replaced by a pulse counter making it possible to inhibit the unit 33 after a predetermined number of chops of the motor supply.

Claims (9)

 1. Method for controlling an electric motor (M) of a motor vehicle starter, characterized in that the supply voltage of the electric motor (M) of the starter is reduced at the start of starting, so as to avoid a rise too fast the speed of rotation of said electric motor (M).  2. Method according to claim 1, characterized in that the supply voltage at the start of startup is a chopped voltage whose peak value corresponds to the value (B +) of the supply voltage in nominal mode.  3. Method according to one of the preceding claims, characterized in that the reduction of the supply voltage occurs during a period (tb) of a predetermined duration.  4. Method according to claim 2, characterized in that the reduction of the supply voltage occurs during a predetermined number of slots of the chopped voltage.  5. Control device for the electric motor (M) of a motor vehicle starter, characterized in that it comprises means (12 to 17; T, 22 to 27; T, 32 to 35) for reducing the voltage d supply of said electric motor (M) at the start of starting.  6. Device according to claim 5, characterized in that these means (12 to 17; T, 22 to 27 T, 32 to 35) include means for chopping the supply voltage of said electric motor (M).  7. Device according to claim 6, characterized in that, the supply of the electric motor (M) being controlled by a contactor (10) comprising a call winding (lOb) and a holding winding (vioc) including supply is itself controlled by the contact switch (11) of the vehicle, the means for chopping the supply voltage of the electric motor (M) include means (14) for inhibiting the supply of the holding winding at the start of startup, the call winding being short-circuited by closing the movable contact (lova) of the contactor (10).  8. Device according to one of claims 5 or 6, characterized in that, the supply of the electric motor (M) being controlled by a contactor (20) with winding (s) (20b, 20c), the chopping means comprise a slot generator (23) which at the start of start-up controls the opening and closing of a switch (T) which controls the supply of the winding (s) (20b, 20c) of the contactor (20).  9. Device according to one of claims 5 or 6, characterized in that the supply of the electric motor (M) being controlled by a contactor (30) with winding (s) (30b, 30c), it comprises a switch ( T) which controls the supply of the winding (s) (30b, 30c) of the contactor (30), as well as a timer unit (33) which controls the opening of the switch (T) when the movable contact closes (30a) of the contactor (30), as well as means (32) for controlling the closing of the switch (T) in the absence of the opening command by the timing unit (33).