EP0987434B1 - Current control device for an electrical engine starter motor and starter motor having such a device - Google Patents

Description

The present invention relates to the control of the power supply an electric motor of a vehicle starter, in particular an automobile.

Conventionally, the power supply of the electric motor of a starter is controlled by an electromechanical power contact (relay to winding) which is actuated according to the state of the contact switch of the vehicle, either directly or via electronic management integrated or not to the starter.

However, the power contacts of the vehicle starters may cause excessive voltage drops in starter electric motor terminals. The reasons for these falls can be various: corrosion of contacts, oxidation by arcs, short circuit by the copper dust deposits generated by the arcs, bouncing during closing, premature closing of contacts even before the pinion is sufficiently engaged in the crown of startup, etc.

An object of the invention is to solve this problem.

For this purpose, the invention proposes a device starting motor, in particular a vehicle, comprising a electric motor, a management unit, power switches, and an electromagnet coil for controlling the displacement of a gear wheel, characterized in that said motor and said coil are independently powered by a parallel electrical connection, a first branch comprising, in series assembly, said engine, a first controllable electronic component of power and power, a second branch comprising, in series assembly, said coil, a second controllable electronic component of power and power supply.

• le premier composant électronique commandable de puissance est un transistor de puissance.
• ce composant est commandé par une unité de gestion.
• le déplacement du pignon du démarreur est commandé par un électro-aimant dont le bobinage est monté en série avec le deuxième composant électronique qui est lui-même commandé par l'unité de gestion et qui commande l'alimentation dudit bobinage.
• le deuxième composant électronique commandable de puissance est un transistor de puissance.
• ce composant est commandé par l'unité de gestion.
• le deuxième composant électronique commandable de puissance est commandé par un signal cyclique à impulsions à largeurs modulées.
• l'unité de gestion reçoit en entrée la tension aux bornes du bobinage et comporte des moyens pour détecter la stabilisation de cette tension, ainsi que des moyens pour modifier le rapport cyclique dudit signal à impulsions à largeur modulée lorsque cette stabilisation est détectée.
• l'unité de gestion comporte des moyens pour commander le passage à l'état passant du composant de puissance qui commande l'alimentation du moteur électrique lorsque cette stabilisation de tension est détectée.
• le (ou les) transistor(s) de puissance est (sont) de type MOFSET.

This device is advantageously completed by the following different characteristics taken alone or in all their technically possible combinations:

• the first controllable electronic power component is a power transistor.
• this component is controlled by a management unit.
• the displacement of the starter gear is controlled by an electromagnet whose winding is connected in series with the second electronic component which is itself controlled by the management unit and which controls the supply of said winding.
• the second controllable electronic power component is a power transistor.
• this component is controlled by the management unit.
• the second controllable electronic power component is controlled by a cyclic pulse signal with modulated widths.
• the management unit receives as input the voltage across the winding and comprises means for detecting the stabilization of this voltage, as well as means for modifying the duty cycle of said modulated-width pulse signal when this stabilization is detected.
• the management unit comprises means for controlling the transition to the on state of the power component which controls the supply of the electric motor when this voltage stabilization is detected.
• the power transistor (s) is (are) of the MOFSET type.

The invention also relates to a vehicle starter in particular an automobile comprising an electric motor, a pinion intended to to be driven by said motor, means for moving said pinion from a rest position to a position where it meshes with a crown of thermal engine, a device for controlling the power supply of its electric motor, characterized in that this device is of the aforementioned type.

Other features and advantages of the invention will emerge still of the description which follows. This description is purely illustrative and not limiting. It must be read in conjunction with the attached single figure which is a schematic representation of a device conforming to a possible embodiment of the invention.

This figure shows a motor M of a starter D.

This motor M is mounted with a power switch T2 between the ground and a B + power terminal to the battery voltage of the vehicle.

The switch T2 is constituted not by a contact electromechanical but by a power transistor that is powered by a management unit 2.

This management unit 2 is for example a microcontroller whose an input e1 is connected to the voltage terminal B + via the vehicle's ignition switch (ignition switch or other switch, referenced by 1 in the figure) and whose output s2 controls the switch T2. The microcontroller 2 is also directly connected to the terminal B + by an input e2 supply.

The power transistor T2 is for example a transistor of the type MOFSET, whose gate is attacked by a voltage generated by said micro-controller 2, at its output s2 supra.

The management unit that constitutes this microcontroller 2 command also the supply of a coil B of an electromagnet which itself controls the movement of the starter gear.

For this purpose, the winding B is mounted between the ground and the terminal B + supply voltage to the battery with a T1 power transistor ordered by the management unit 2.

The transistor T1 is for example a MOFSET transistor whose gate is attacked by a voltage generated by the management unit 2 on one of its outputs (referenced by 1 in the figure).

This management unit 2 also receives two inputs e3, e4 on the one hand the voltage at a point between the winding B and the switch T1 and on the other hand the voltage at a point between the motor M and the transistor T2.

The supply sequence of winding B and motor M is the next.

Closing the contact switch 1 sets the microcontroller 2 in activation state.

It implements different initialization operations, such as checking that the armature of the motor M is not rotating (absence induced voltage across the motor M), that the winding B is not not fed, or such as a temperature control of the starter

Once these operations have been performed, the microcontroller 2 controls the transistor T1 so that the winding B is supplied with a current to Pulse Width Modulation (PWM or Pulse Width Modulation) Anglo-Saxon terminology generally used). For this purpose, PWM modulation can itself be generated by the microcontroller 2 on the control voltage of the gate of the transistor T1, other modes of realization being of course possible (in particular, PWM modulation the winding supply current B could be generated by a specific mounting disposed in the supply circuit of said winding B).

The control thus carried out on transistor T1 makes it possible to ensure low-speed approach of the starter gear against the crown of the thermal motor.

The voltage received on the input e3 makes it possible to monitor the evolution of the voltage across the coil B. As long as the mobile core of the electromagnet controlled by the winding B moves, the voltage at the terminals of said winding varies. It only stabilizes when the nucleus has finished his race.

When this stabilization is detected by the microcontroller 2, the voltage on output s2 goes high and unblocks the transistor from T2 power that powers the electric motor M.

At the same time, the duty cycle of the PWM voltage controlling the transistor T1 changes in value so that the intensity the supply current of the coil B goes to a holding value.

This value is chosen high enough to hold the electromagnet closed, but also weak enough not to provoke excessive heating of the winding B or the transistor T1.

In a variant, the transistor T1 may be powered according to a law of predetermined voltage as a function of time. At the end of this period, the output 2 goes high and unlocks the power transistor T2.

At the end of the start - that is when the ignition key is released or when the microcontroller 2 commands the automatic termination of start - microcontroller 2 switches voltages on outputs s1 and s2 in the low state to block the transistors T1 and T2.

Such power supply control of the electric motor of a starter has many advantages.

It performs a static switching avoiding all phenomena known oxidation of contact, wear, corrosion, rebounds of contact, etc.

It allows the reduction of costs, size and weight, the contactor having no more effort to exert when closing contacts power.

Claims (9)

1. Starter device (D) for an engine, in particular that of a vehicle, comprising an electric motor (M), a management unit, power switches (Ti) and an electromagnetic coil (B) permitting to command the movement of a gear wheel, characterised in that said motor (M) and said coil (B) are independently powered by an electrical assembly in parallel, a first branch comprising, in series connection, the said motor (M), a first electronic component (T2) that may be commanded in power and the power supply, a second branch comprising, in series connection, the said coil (B), a second electronic component (T1) that may be commanded in power and the power supply.
2. Device of claim 1, characterised in that the first component (T2) is a power transistor.
3. Device of claim 1, characterised in that the second electronic power component (T1) is a power transistor.
4. Device of any of the previous claims, characterised in that the first and second components are commanded by a management unit (2).
5. Device of any of the previous claims, characterised in that the second power component (T1) is commanded by a cyclic pulse signal of modulated width.
6. Device of claim 5, characterised in that the management unit (2) receives at the voltage its inputs of the terminals of (B) and comprises means to detect the stabilisation of this voltage, as well as means of modifying the cyclic ratio of the said modulated width pulse signal when this stabilisation is detected.
7. Device of claim 6, characterised in that the management unit (2) comprises means to command the passage to the passing state of the power component (T2) that commands the power supply of the electric motor when the stabilisation of the voltage is detected.
8. Device of any of claims 2 and 3, characterised in that the power transistor(s) (T1, T2) is/are of the MOFSET type.
9. Starting device for a vehicle, in particular an automobile, comprising an electric motor (M), a gear wheel designed to be driven by the said motor (M), means of moving the said gear wheel from a rest position to a position where it meshes with a crownwheel of the combustion engine, a device for commanding the power supply of its electric motor (M), characterised in that this device is of the type of any of the previous claims.

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