EP2876297A1 - Method for controlling an electric machine for restarting a motor vehicle - Google Patents

Abstract

The invention relates to a method for controlling an electric machine (6) for starting or restarting a vehicle engine, the machine (6) rotating the engine in a direct direction when it is restarted by means of a flexible transmission element (4), the control of the machine (6) taking place during a sliding detection of the flexible element (4), when a slip is detected, inversion of the direction of rotation of the machine ( 6) or canceling the rotation of the machine (6), so that the motor is driven or recalled to a starting or new position by oscillating at least once around it, and, from this position, driving rotating in the engine's direct direction by the machine (6) for starting or restarting.

Description

The invention relates to a method of controlling an electric machine connected to a flexible transmission element for starting or restarting the engine of a motor vehicle, this driving taking place when the flexible element slides and, the if necessary, a first restart of the engine could not be performed. The electric machine may, for example, be a reversible alternator with a pulley driven or driving the flexible transmission element, this pulley being disposed on the accessory front of a housing of the engine of the motor vehicle.

Such undesired slip of the flexible transmission element connecting the thermal engine to the engine can occur, for example, when this flexible element is a belt that has been wet when driving the vehicle, which does not allow a drive effective of the engine during its startup or restart.

The present invention finds a preferential but nonlimiting application for a vehicle equipped with an automatic stop and start system and also for a hybrid vehicle having a heat engine and an electric machine for propelling the vehicle, this hybrid vehicle being equipped or not an automatic shutdown and restart system.

In fact, to reduce CO ₂ emissions and save fuel, automatic stop and start systems, also known as STT for the English name "Stop and Start", are becoming more and more common. .

Such a system provides for putting the heat engine into standby with the clutch open as soon as the vehicle speed is below a minimum speed and the brake pedal is depressed. When the brake pedal is released, the system automatically restarts the engine and when an action is exerted on the accelerator, the clutch closes.

Several technical solutions to achieve an automatic shutdown and restart system can be used but one of the most common is to use a alternator reversible to ensure the restart of the engine, this alternator is also referred to as alternator-starter. This reversible alternator can therefore be the electric machine for restarting the thermal engine within the meaning of the present invention. This is not limiting and the electric machine within the meaning of the invention can also be, for example, an electric motor equipping a hybrid vehicle.

In this type of solution with reversible alternator, the alternator can be used in generator mode to store energy but also in engine mode to start or restart the engine. To transmit the starting torque which is very important with respect to the torque in electric generator mode, a flexible element transmission system is used, most frequently a belt, this system having been redesigned and reinforced by compared to the system associated with a conventional alternator mounted on the accessory front of a crankcase of the engine.

The flexible transmission element can thus be located on the accessory facade of a thermal propulsion engine casing. Such an accessory facade, known from the state of the art, is shown in FIG. figure 1 .

In general, the facade 1 accessory of a housing of a thermal propulsion engine of a motor vehicle may have a reversible alternator 6 or alternator-starter. This reversible alternator 6 has a rotor rotating about a substantially horizontal axis of rotation.

At the end of the shaft corresponding to the axis of rotation is mounted a generator pulley 3 in revolution about said axis. This pulley 3 is part of a flexible element transmission system for driving a crankshaft of the engine or conversely being driven by the crankshaft. This pulley 3 may for example allow the reversible alternator 6 to transmit to the crankshaft the torque necessary to ensure the rotation and starting of the engine.

The alternator pulley 3 rotates during start-up or, when the vehicle is traveling, is driven by a second pulley 5 connected to one end of the crankshaft of the heat engine, this by means of a flexible transmission element 4, advantageously a smooth or notched belt or chain. This second pulley 5 is also called crankshaft pulley. The second pulley 5 rotates with its axis coincides with that of the crankshaft by driving or being rotated by the crankshaft.

Tensioning rollers 2 and 2a are also provided on the path of the flexible transmission member 4. A roller 2 may for example have an arm 8 with a cocking finger 9 cooperating with a limit stop 10a. The casing 1 accessory of the crankcase also advantageously carries an air conditioning compressor pulley 7 and a water pump carrying a pulley whose drive is provided by a secondary belt located in a plane other than that of the main belt 4, this secondary belt being classically secured to the second pulley 5 or crankshaft pulley.

The flexible transmission element 4 and the pulleys 3, 5 perform a drive by adhesion. A driving pulley, for example the second crankshaft pulley 5 or the alternator pulley 3 respectively, here causes a receiving pulley, respectively the pulleys 3 or 5, thanks to the flexible transmission element 4, frequently in the form of a pulley. belt. This belt can have several forms: flat, trapezoidal, ridged, etc.

To limit the costs and the complexity of the accessory façade 1, the range of validity of the transmission system does not take into account all the life cases, namely for example the temperature, the humidity, the wear of the element flexible transmission, etc.

Thus, in certain situations of traffic of the motor vehicle, in particular the passage of a ford or the truck monitoring projecting large amount of water, the torque capacity of the accessory facade 1 no longer allows to ensure a restart of the thermal motor. Indeed, in these cases of life, the flexible transmission element 4 advantageously in the form of a belt, undergoes significant water projections and slips.

To remedy this drawback, protection solutions by cowling of the flexible transmission element exist. However, these rollover solutions are not efficient enough.

The document US-2012/0234282 discloses a method of starting a hybrid motor vehicle engine also equipped with an electric auxiliary motor. The method comprises a step of driving in reverse rotation of the electric motor of the vehicle with consecutive drive of the shaft of the engine. This rotation drive causes the deformation of a damping element which recalls the motor shaft in the other direction of rotation causing a step of driving in rotation in the opposite direction that the reverse rotation when the application of a current on the electric motor is interrupted. This step is followed by a step of starting the heat engine by rotation other than in the opposite direction of the shaft of the electric motor and consequently of the heat engine.

However, this document does not deal with the problem caused by a flexible transmission element that does not effectively transmit the driving movement of the engine crankshaft by the reversible alternator, for any reason.

Therefore, the problem underlying the invention is to ensure a start or restart of the engine of a motor vehicle by an electric machine transmitting a rotational movement to the engine with a flexible transmission element this when the flexible transmission element does not provide effective transmission between the electric machine and the engine.

• détection d'un glissement ou d'une possibilité de glissement de l'élément souple,
• quand un glissement ou une possibilité de glissement est détecté, inversion du sens de rotation de la machine électrique ou annulation de la rotation de la machine électrique, afin que le moteur thermique soit conduit ou rappelé dans sa position de départ ou dans une nouvelle position en oscillant au moins une fois autour de celle-ci,
• à partir de la position de départ ou de la nouvelle position, entraînement en rotation en sens direct du moteur thermique par la machine électrique pour tenter un démarrage ou redémarrage.

To achieve this objective, it is provided according to the invention a method of controlling an electric machine for starting or restarting a heat engine fitted to a motor vehicle, the electric machine rotating the heat engine from a starting position in a direction said direct when starting or restarting via a flexible transmission element, the control of the electric machine taking place when the flexible element slips or is likely to slide when a start or restart, characterized by the following steps:

• detection of a sliding or sliding possibility of the flexible element,
• when a slip or a possibility of sliding is detected, reversing the direction of rotation of the electric machine or canceling the rotation of the electric machine, so that the heat engine is driven or returned to its starting position or in a new position. oscillating at least once around it,
• from the starting position or from the new position, rotating drive in the direct direction of the engine by the electric machine to attempt a start or restart.

The technical effect is to obtain a treatment of the flexible transmission element by oscillation of the heat engine around its rest position, that is to say its starting position, treatment that allows the flexible element of no longer slip and therefore perfectly fulfill its transmission function between the electric machine and the engine, for example by drying the flexible transmission element when it is wet. It is also possible to use the new stopping position as a new stitch starting, which makes it possible to use the compression energy in the opposite direction and to have a larger angular range to start the engine.

Advantageously, the reversal of the direction of rotation of the electric machine is done as long as a threshold angle of rotation of the thermal engine in the opposite direction to the forward direction is not exceeded, this threshold angle this threshold angle corresponding to the top dead center of a cylinder of the engine. Advantageously, the electric machine is driven at its maximum torque in the opposite direction so that the sliding caused dry for example the flexible transmission element.

Advantageously therefore, the method of the invention is implemented after starting or restarting the electric machine in a curative treatment of a sliding or sliding possibility of the flexible element: it is not, in the invention, to systematically consider a preventive treatment of possible slipping of the belt, before starting or restarting, but to practice a curative treatment, when the electric machine has already started / restarted, according to a dynamic mode, and not static. The invention is only implemented in dynamic mode, and only when necessary, once the machine is running, and not by seeking to pre-position the belt while the machine is stopped, this which is both more efficient and more economical in terms of movements due to the repositioning of the belt.

Advantageously, the angular range of the oscillations of the heat engine is becoming wider for consecutive oscillations.

Advantageously, the detection of a sliding of the flexible element is done according to a ratio of electric machine speed to engine speed, a ratio above a threshold value being representative of a sliding of the flexible element.

The invention relates to a set of an electric machine and a heat engine in a motor vehicle, the electric machine rotating the heat engine from a starting position in a direct direction when it is started or restarted by via a flexible transmission element, characterized in that the electric machine is driven according to such a driving method when the flexible element slips or is likely to slip during a start or restart of the engine thermal device, the assembly comprising a means for detecting a possible sliding of the flexible element, a central control unit of the electric machine with a means for controlling the direction of rotation of the electric machine.

Advantageously, the flexible transmission element is a belt.

Advantageously, the electric machine is a reversible alternator connected to a pulley intended to drive or be driven by a crankshaft pulley connected to a crankshaft of the engine, the two pulleys being carried by the accessory front of a housing of the engine.

The invention relates to a motor vehicle characterized in that it comprises such an assembly.

Advantageously, the motor vehicle is a hybrid vehicle.

Advantageously, the motor vehicle is equipped with an automatic stop and restart system.

• la figure 1 est une représentation schématique d'une façade accessoire d'un carter de moteur de véhicule automobile selon l'état de la technique comprenant une poulie reliée à un alternateur réversible et une poulie de vilebrequin, l'alternateur réversible pouvant être piloté par un procédé de pilotage conformément à la présente invention.

Other features, objects and advantages of the present invention will appear on reading the detailed description which follows and with reference to the appended drawing given by way of non-limiting example and in which:

• the figure 1 is a schematic representation of an accessory frontage of a motor vehicle engine casing according to the state of the art comprising a pulley connected to a reversible alternator and a crankshaft pulley, the reversible alternator being controllable by a method of control in accordance with the present invention.

The figure 1 has been described in the introductory part of the present application. In what follows the driving method according to the invention will be described in connection with a reversible alternator 6 as an electric machine. This reversible alternator 6 has a pulley 3 that can be driven or driven when the engine is started or restarted by the pulley 5 of the crankshaft of the engine by a belt 4 serving as a flexible transmission element, the two pulleys 3 and 5 being carried by the accessory front 1 of the thermal engine housing.

This is however not limiting although being a preferred embodiment of the present invention. Indeed, the electrical machine 6 driven by the method according to the present invention may be other than a reversible alternator, for example an electric motor, the electric motor driving the heat engine through a flexible transmission element 4 which may be other than a strap.

In general, the control method of an electric machine 6 according to the present invention is carried out to ensure the starting or restarting of a heat engine fitted to a motor vehicle, the electric machine 6 conventionally driving the thermal engine from a starting position in a direction said direct when starting or restarting via a flexible element 4 transmission. This control of the electric machine 6 takes place when the flexible element 4 slides or is likely to slip during a start or restart, which leads to a poor transmission between the electric machine 6 and the heat engine, the more frequently between the machine 6 and the crankshaft of the engine.

The control method according to the present invention comprises a step of detecting a slip or a sliding possibility of the flexible transmission element 4. This detection can be performed by following in real time the speeds of the electric machine 6 and the engine. A threshold of predetermined deviation crossed, it will be recognized a sliding situation of the flexible element 4 transmission.

This detection of a sliding of the flexible element 4 can be done for example according to an electric machine speed ratio 6 engine speed, a ratio above a threshold value being representative of a slip of the flexible element 4 and therefore a poor transmission between the electric machine 6 and the engine can prevent its starting or restart.

Other detection means may also be implemented, for example means for detecting the humidification of the flexible element 4 with detection of a humidification value capable of causing the sliding of the flexible element 4 these means may also take into account external temperature or humidity conditions.

When a slip or a possibility of sliding is detected, a step is taken to invert the direction of rotation of the electrical machine 6 or to cancel the rotation of the electric machine 6, so that the heat engine is driven or recalled in its starting position or in a new starting position close to the old one by oscillating at least once around it. Thus the electric machine 6 can rotate in the opposite direction of the forward direction or be stopped. In the latter case, it is the engine that returns itself to its starting position.

This step is based on the fact that a resistive or compression torque of the engine appears as soon as the engine starts its rotation. As long as the compression has not completely passed, if the torque coming from the electric machine 6 is released by stopping it, the heat engine, advantageously because of its crankshaft under the effect of the compression, changes direction of rotation and is recalled to its starting position and can even overtake it to take a new starting position.

This also applies during a reversal of direction of the electric machine 6, as soon as the rotation of the electric machine 6 in this inverted direction is stopped, the heat engine returns to its starting position. The dynamics of regime are known in advance by the laws of the physics of the system crank crank of the engine.

The reversal of the direction of rotation of the electric machine 6 can be done as long as a threshold angle of rotation of the thermal engine in the direction opposite to the direct direction is not exceeded, this threshold angle corresponding to the top dead center of a cylinder of the engine. By top dead center, it is defined by stopping the piston in a cylinder of the engine before starting in the opposite direction, the top dead center corresponding to the strongest compression in the cylinder.

It can be carried out several consecutive oscillations of the engine around its starting position. The angular range of the oscillations of the heat engine is advantageously more and more wide for consecutive oscillations. The purpose of these oscillations is to gradually dry the flexible transmission element 4 on an increasingly important angular sector.

For example, in the case of oscillation by stopping the electric machine 6, it can transmit a rotation in a direct direction to the engine and be stopped again, this several times in a row, the engine returning to its position. departure and may overtake it because of its inertia and then return to this position.

For example, in the case of oscillations by an electrical machine rotated in the opposite direction, this rotation in opposite direction can be reversed again so that a new rotation in the direct direction of the electrical machine 6 can be initiated again and and so on.

The last step of the control method according to the present invention is, from the old or new starting position, to cause the engine to rotate in the direct direction by the electric machine 6 to attempt a start or restart. At the end of this step, it can be returned to the detection step to know if the flexible element 4 transmission is still likely to slip or not. In case of sliding possibility, it is repeated the previous steps.

Thus, the control method of the electric machine according to the present invention makes it possible to recommit a start or restart in a short period of time following a startup failure. In the case of a flexible element 4 of wet transmission, such a control method makes it possible to dry the flexible element to make it perform its driving function effectively again.

The invention also relates to a set of an electric machine 6 and a heat engine in a motor vehicle, the electric machine 6 rotating the heat engine from a starting position in a direct direction when it starts. or restart via a flexible transmission element 4.

The electric machine 6 is then driven according to such a control method when the flexible element 4 slides or is likely to slip during a start or restart of the engine. The assembly comprises a means for detecting a possible sliding of the flexible element 4, a central control unit of the electric machine 6 with a means for controlling the direction of rotation of the electric machine 6.

A particularly advantageous application of the control method of the electric machine as described or of an assembly of such a driven electric machine associated with a heat engine is intended for a motor vehicle equipped with an automatic stop and restart system. of its engine. Thus, it is allowed to return very quickly to the motor vehicle this automatic stop and restart function even when the flexible transmission element was slippery.

Another particularly interesting application of the control method is for a hybrid vehicle, the latter being equipped or not with a system for automatically stopping and restarting the engine. Indeed, for such a vehicle, the stops and restarts of its engine are frequent and the safety aspect of rolling restarts is even more important than for vehicles equipped with an automatic stop and restart system.

Thus, for all applications and in particular for the two preferred applications mentioned above, for any type of motor vehicle, a restart is secured in specific life situations, such as for example heavy rain, fording etc.

The invention is in no way limited to the described and illustrated embodiments which have been given by way of example only.

Claims (11)

A method of controlling an electric machine (6) for starting or restarting a heat engine fitted to a motor vehicle, the electric machine (6) rotating the heat engine from a starting position in a direction said direct when starting or restarting via a flexible element (4) transmission, the control of the electric machine (6) taking place when the flexible element (4) slips or is likely to slide when a start or restart, characterized by the following steps: - detection of a sliding or sliding possibility of the flexible element (4), - when a slip or a possibility of sliding is detected, inversion of the direction of rotation of the electric machine (6) or cancellation of the rotation of the electric machine (6), so that the engine is driven or recalled in its position of departure or in a new position by oscillating at least once around it, - From the starting position or the new position, driving in rotation in the direct direction of the engine by the electric machine (6) to attempt a start or restart. Method according to Claim 1, in which the reversal of the direction of rotation of the electric machine (6) takes place as long as a threshold angle of rotation of the thermal motor in opposite direction to the forward direction is not exceeded, this threshold angle corresponding to the top dead center of a cylinder of the engine. Method according to one of the preceding claims, characterized in that it is implemented after starting or restarting the electric machine in a curative treatment of a sliding or sliding possibility of the flexible element (4). ). The method of claim 2 or 3, wherein the angular range of the oscillations of the heat engine is becoming wider for consecutive oscillations. A method according to any one of the preceding claims, wherein the detection of a sliding of the flexible element (4) is based on a ratio of electric machine (6) on engine speed, a ratio above a threshold value being representative of a sliding of the flexible element (4). Set of an electric machine (6) and a heat engine in a motor vehicle, the electric machine (6) rotating the heat engine from a starting position in a direct direction when it is started or restarted via a flexible transmission element (4), characterized in that the electric machine (6) is driven according to a control method according to any one of the preceding claims when the flexible element (4) slides or is capable of sliding during start-up or restart of the heat engine, the assembly comprising means for detecting a possible sliding of the flexible element (4), a central control unit of the electric machine (6) with means for controlling the direction of rotation of the electric machine (6). An assembly according to claim 6, wherein the flexible transmission member (4) is a belt. An assembly according to claim 7, wherein the electric machine (6) is a reversible alternator connected to a pulley (3) intended to drive or be driven by a crankshaft pulley (5) connected to a crankshaft of the heat engine, the two pulleys (3, 5) being carried by the accessory facade (1) of a housing of the engine. Motor vehicle characterized in that it comprises an assembly according to any one of claims 7 or 8. Motor vehicle according to claim 9, which is a hybrid vehicle. Motor vehicle according to claim 9 or 10, which is provided with an automatic stop and restart system.

Images