FR2784944A1 - Hybrid drive for motor vehicles has combined internal combustion engine and electric motor - Google Patents

Abstract

The hybrid motor vehicle drive has an internal combustion engine (12) and an electrical machine (14) which can operate as a generator or as a motor. The internal combustion engine operates with a variable air/fuel ratio, and during transitions in the air/fuel ratio the electric machine compensates for torque fluctuations, producing smooth torque variation in the drive train.

Description

Hybrid powertrain
The invention relates to a hybrid powertrain in which the electric machine is used to compensate for a difference in torque of the thermal engine during a change of operating mode of the latter.

 The invention relates more particularly to a powertrain for a motor vehicle, of the type comprising an internal combustion engine capable of driving at least one drive wheel of the vehicle and an electric machine which is capable of being used in a generator mode or according to an engine mode in which it participates in driving the vehicle, and of the type in which the combustion engine operates with a fuel mixture whose air / fuel ratio is variable.

The invention will more particularly be described in the context of a particular hybrid powertrain. This powertrain consists of an internal combustion engine fitted with an electric machine integrated into the flywheel. In such a group, the electric machine can deliver only a very small part of the maximum power of the heat engine which therefore remains the main source of driving power for the vehicle. The machine is linked to the flywheel of the heat engine, that is to say that the flywheel is actually essentially constituted by the rotor of the electric machine. The latter is therefore directly trusted to
The engine shaft of the heat engine, and it is generally interposed between the heat engine and a transmission member such as a gearbox.

 In this context, the electric machine is generally a machine which can be used either in motor mode or in generator mode. In generator mode, the electric machine then replaces the alternator to supply an electric current intended to be used in the electrical circuit of the vehicle or to be stored in a storage battery. On the contrary, in engine mode, the electric machine is supplied with current previously stored in the storage battery and it supplies an engine torque on the engine shaft, this engine torque therefore adding to that of the heat engine to be transmitted. to the drive wheels of the vehicle.

 Up to now, it has been known to use the electric machine in engine mode to start the heat engine, to reduce the cycles of the heat engine when it is operating at idle speed, or to provide, for a short period of time, a supplement torque allowing for example to facilitate a hill start or to facilitate overtaking.

 However, the invention is in no way limited to such a powertrain, and could therefore be applied in all cases of hybrid powertrain in which the heat engine is capable of driving the vehicle by itself.

 The invention is intended to apply in particular to powertrains in which the internal combustion is capable of operating in lean mixture. When the engine is in lean mixture mode, when the driver's torque demand is not too great, fuel consumption can be limited.

 However, under certain conditions, in particular when the torque demand is too high, it is no longer possible to supply the engine with a lean mixture because it could not, for example, provide sufficient torque. In this case, it is necessary to switch the operation of the engine to a mode in which it is supplied with a fuel mixture having the stoichiometric ratio of air and fuel, or even even having an excess of fuel.

 However, as will be seen in the description, this change in operating mode is accompanied by a transient mode during which the efficiency of the combustion engine is significantly deteriorated. In a spark-ignition engine, this deterioration comes in particular from the fact that it is necessary to vary the advance on ignition so that the switching operation mode is not accompanied by a sudden variation in the torque supplied by engine.

 Thus, each change of operating mode is at the origin of an overconsumption of fuel which is not justified by a modification of the service provided to the driver.

 Also, to provide a solution to this problem, the invention provides a powertrain of the type described above, characterized in that when the air / fuel ratio of the mixture varies discontinuously from a first value to a second value, the machine Electric is controlled to compensate for variations in the torque supplied by the combustion engine so that the torque supplied by the powertrain varies continuously to correspond to a torque demand from the driver.

According to other characteristics of the invention:
-when the air / fuel ratio varies discontinuously, the combustion engine is supplied, during a transient phase, with a fuel mixture such that it is capable of supplying a torque greater than the torque requested by the driver, and the electric machine is controlled so as to absorb the additional torque and produce an electric current stored in an accumulator battery;
when the air / fuel ratio varies discontinuously in the direction of an increase, the transient phase during which the electric machine is controlled to absorb an increase in torque occurs after the discontinuous variation of the air / fuel ratio; and
-when the air / fuel ratio varies discontinuously in the direction of a decrease, the transient phase during which the electric machine is controlled to absorb an additional torque occurs after the discontinuous variation of the air / fuel ratio.

Other characteristics and advantages of the invention will appear on reading the following detailed description for the understanding of which reference will be made to the appended drawings in which:
FIG. 1 is a schematic view illustrating a powertrain according to the invention;
FIGS. 2A to 2E are graphs illustrating the operation of an engine according to the state of the art; and
FIGS. 3A to 3E are graphs illustrating, under the same conditions, the operation of a powertrain according to the invention.

 FIG. 1 shows schematically a powertrain 10 of the hybrid type, more particularly a powertrain 10 consisting of a heat engine 12, for example an internal combustion engine with alternating pistons, which is provided with a machine electric 14 integrated into its flywheel. The rotor 16 of the electric machine 14 is therefore integral in rotation with the motor shaft 18 of the heat engine 12 so that the electric machine 14 is interposed between the heat engine 12 and a transmission member 20 which can for example be a gearbox fitted with a clutch.

 A central management unit 22 controls the operation of the heat engine 12 and of the electric machine 14 as a function of various parameters and in particular as a function of a torque Cd requested by the driver.

 The driver of the vehicle manifests his request for torque by acting on an interface member such as an accelerator pedal.

The heat engine 12 provides a motor torque Cmot while the electric machine 14 imposes on the motor shaft
This is positive when the electric machine is used as a motor and negative when the electric machine is used as a generator. Thus, the powertrain 10 supplies the transmission device with a torque Cgmp which is equal to the algebraic sum of the torques
Cmot and Cme.

 When used as a generator, the electric machine 14, whose rotor 16 is then rotated either by the motor shaft 18 or by the transmission 20, produces current which is likely to be used by a vehicle's electrical system or to be stored in a storage battery.

 In accordance with the teachings of the invention, the heat engine 12 is an engine capable of operating with a lean mixture, that is to say a fuel mixture in which the air is in excess relative to the quantity of fuel. Of course, the engine is used in lean mixture only for relatively low loads, that is to say relatively low torque demands of the driver, the maximum power of the engine can only be obtained with higher richnesses. or equal to the unit richness, that is to say when the fuel mixture has an excess of fuel relative to the stoichiometric equilibrium of the combustion reaction.

 In the preferred embodiment of the invention, the internal combustion engine 12 is a spark-ignition engine with direct fuel injection.

 Direct fuel injection makes it possible to use particularly poor carbide mixtures, the ignition of the mixture being favored by the fact that direct injection makes it possible to supply the engine with a stratified lean load, that is to say a charge in which the fuel which is injected into the cylinder is not homogeneously distributed therein at the time of ignition, the fuel then being combined as much as possible in the vicinity of the spark plug, so to present a sufficient local concentration for the initiation of combustion. Compared to a homogeneous lean mixture, a layered lean mixture can therefore allow correct operation of the engine with even less fuel, this to the benefit of the consumption of the powertrain.

 FIGS. 2A to 2E show a series of graphs which illustrate the operation of an internal combustion engine controlled in a conventional manner when the driver requests from it a relatively large torque, exceeding at least the threshold torque Cs corresponding to the maximum torque likely to be supplied by the heat engine 12 when it is supplied with a lean mixture.

 We will for example be placed in the situation illustrated in FIG. 2A. On this graph, we can see that the driver requests constant torque from the motor C1 until time t1.

Then, from time t1 to time t4, the torque demand Cd emanating from the driver increases to reach a maximum torque C2. Between instants t1 and t4, at time t2, the torque Cd requested by the driver therefore reaches the threshold torque Cs, then passes over it.

 We are going to take the hypothesis in which the heat engine is capable of delivering the torque C1 by being supplied with a lean mixture stratified and that, beyond the torque Cs, we switch directly from an operating mode in lean mixture stratified to a mode of operation in stoichiometric mixture.

 In this way, as illustrated in FIG. 2B, in the context of a conventional motor, it can be seen that, from the instant t2, when the torque demand Cd becomes greater than the threshold torque Cs, it is necessary to switch the engine operating mode from a lean laminate mode to a stoichiometric mode.

 However, it has been illustrated in FIGS. 2C, 2D and 2E various operating parameters of the engine which it is necessary to modify to allow such a switching of the operation of the engine.

 Is illustrated in Figure 2C the injection time At, that is to say the opening time of the injector, which of course controls the amount of fuel introduced into the cylinder. As long as we are in the stratified lean mixture operating mode, we see that the injection duration At is proportional to the torque demand, this up to an injection duration Ats corresponding to the threshold torque Cs.

 FIG. 2D illustrates the apap opening angle of the throttle inlet valve for the heat engine 12. Until time t2, the throttle valve is wide open so as to allow a maximum of air to enter the cylinder. each cycle.

 From time t2, to switch to stoichiometric mode, we therefore begin to close the throttle valve to limit the intake air, but this partial closure does not have an immediate effect due to the column of air which is present between the intake throttle and the cylinder itself. In this way, as can be seen in FIG. 2C, it is necessary, at time t2, to suddenly increase very significantly the quantity of fuel injected into the cylinder, this in order to respect the proportions of the stoichiometry of the reaction.

 However, supplied with such a fuel mixture, the heat engine would be required to deliver a particularly large torque, so that this would result in a jerk which would be felt by the driver. Also, to avoid this feeling of jerk, one modifies at the instant t2, at the time of the changeover in stoichiometric mode, the value of the advance to the ignition, that is to say that one shifts the instant at which the spark is produced at the spark plug in relation to the movement of the piston in the cylinder. More particularly, an ignition advance withdrawal is carried out, by delaying the latter, so as to reduce the energy efficiency of the engine so that, although it is supplied with a load with a particularly significant energy potential, the the torque actually delivered by the combustion of this charge in the cylinder is not too different from the torque delivered the previous instant.

Of course, from time t2 to time t3, as the operation of the engine stabilizes, and in particular as the effect of closing the throttle becomes really effective, we are brought to reduce the withdrawal in advance as well as the injection time. In the example illustrated, it is considered that from time t3, the engine has reached its optimum efficiency in stoichiometric mode.
Also, from this instant, the throttle opening angle and the injection time increase in proportion to the torque demand Cd.

 FIGS. 3A to 3E have illustrated the operation of a powertrain in accordance with the teachings of the invention, under the same conditions of use as what has just been seen in relation to FIGS. 2A to 2E.

 Thus, FIGS. 3A to 3D which respectively illustrate the torque requested by the driver Cd, the engine operating mode, the injection time and the apap opening angle apap of the throttle valve as a function of time, resume the corresponding curves 2A to 2D without modification. This means that, for the same torque demand of the driver Cd, the powertrain according to the invention will be controlled identically with regard to the injection time and the opening of the throttle valve, which it will of course result in the same switchover at time t2 from an operating mode with a lean stratified mixture to an operating mode with a stoichiometric mixture.

 However, unlike the state of the art, the powertrain according to the invention will make it possible to rationally use the additional torque likely to be produced between times t2 and t3 due to the switching of mode operation.

 Thus, instead of compensating for the risk of overcutting by a withdrawal in advance, detrimental to the performance of the engine, it can be seen in FIG. 3E that the management unit 22 of the powertrain will control, from time t2, the electric machine 14 so that the latter absorbs a torque Cme corresponding to the additional torque supplied at that time by the internal combustion engine 12.

 In FIG. 3E, it has therefore been considered that the electric machine 14 was controlled to "supply" a negative torque.

 Of course, the electric machine 14 converts the torque thus taken from the motor shaft 18 into an electric current which is stored in the storage battery.

 In this way, the additional fuel which is injected into the engine at the time of the changeover of the operating mode is not gross in pure loss but, on the contrary, transformed by the electric machine into electric energy which is stored and which is likely to be returned at other times when the vehicle is in operation.

 In FIG. 3E, an operating state of the motor 10 has been illustrated in which, outside the acceleration period, the electric machine 14 is at rest.

However, for other operating states of the engine, the electric machine 14 could be used as a generator, for example to recharge the storage battery, or even be used as an engine, depending on other parameters of vehicle operation. In such a case, the management unit would therefore have to modify the control of the electric machine 14 when the engine operating mode changes.

 In the example above, we have just described the case where, following a tilting of engine operation, the engine is supplied with a fuel mixture having a first air / fuel ratio, then with a second air / fuel ratio, weaker. In terms of richness of the fuel mixture, this changeover therefore corresponds to a sudden increase in richness at time t2. In this case, the switching of the operating mode made it necessary to absorb an excess torque after the switching moment.

 On the contrary, when we switch the operating mode in the direction of a sudden increase in the air / fuel ratio, or even a sudden decrease in the richness of the fuel mixture, we are led on the contrary to absorb an increase in torque before the actual changeover, the latter of course having to be anticipated by the central management unit 22.

Claims (4)

 1. Powertrain for a motor vehicle, of the type comprising an internal combustion engine (12) capable of driving at least one drive wheel of the vehicle and an electric machine (14) which is capable of being used in a generator mode or according to an engine mode in which it participates in driving the vehicle, and of the type in which the combustion engine (12) can operate with a fuel mixture whose air / fuel ratio is variable, characterized in that, when the ratio air / fuel of the mixture varies discontinuously from a first value to a second value, the electric machine (14) is controlled to compensate for variations in the torque supplied by the combustion engine so that the torque supplied by the powertrain varies continuously to match a torque demand (Cd) from the driver.  2. Powertrain according to claim 1, characterized in that when the air / fuel ratio varies discontinuously, the combustion engine (12) is supplied, during a transient phase, with a fuel mixture such that it is capable of supplying a torque greater than the torque requested (Cd) by the driver, and in that the electric machine is controlled so as to absorb the additional torque and to produce an electric current stored in a storage battery.  3. Powertrain according to claim 2, characterized in that when the air / fuel ratio varies discontinuously in the direction of an increase, the transient phase during which the electric machine (14) is controlled to absorb an additional torque occurs after the discontinuous variation of the air / fuel ratio.  4. Powertrain according to claim 2, characterized in that when the air / fuel ratio varies discontinuously in the direction of a decrease, the transient phase during which the electric machine (14) is controlled to absorb an additional torque occurs after the discontinuous variation of the air / fuel ratio.