FR2791013A1 - Command procedure for a vehicle drive train assembly, comprises of separate gearbox and engine controllers connected to one another via data transfer links - Google Patents

Abstract

The system comprises of an accelerator pedal (7) the position of which is relayed to a calculation unit (3). This is linked to an internal combustion engine and a gearbox controller (4) via two-way data links (5,8,9,10,11). The gearbox controller controls an automatic gearbox (2). The system determines the richness of the fuel mixture in relation to the accelerator pedal position and the engine speed/operation state. This enables the controllers to control the engine or gearbox accordingly.

Description

The present invention relates to a group control method

  motor-propellant of a motor vehicle. Current trends in the propulsion of motor vehicles increasingly require a reduction in pollutant emissions, combined with a reduction in

fuel consumption.

  To achieve the objectives leading to satisfying these trends, the powertrains are increasingly associated with a computer which develops the most suitable strategy for the engine of the group to operate at

  any time in the best possible conditions.

  Although there are not many motor vehicles with an automatic gearbox in Europe, European manufacturers have developed automatic gearboxes controlled by a computer. Such a gearbox makes it possible, according to several input parameters, to choose in any circumstance the gear ratio best suited to

  instant driving conditions.

  When a powertrain is composed of an internal combustion engine and an automatic gearbox, it is known to exchange information between the control units of the two units in order to best coordinate their strategies control. Thus, it is usual for the "driver's desire" parameter necessary for the engine control unit to be communicated to the automatic gearbox control unit and, for its part, the gearbox control unit to inform the engine control unit of the change in engine torque to provide and on

the gear ratio engaged.

  On the other hand, the increasingly stringent requirements in terms of pollution reduction and fuel consumption lead manufacturers to choose internal combustion engines operating on the principle of direct fuel injection and according to strategies. say lean air-fuel mixture (in English "lean burn"), in which the ratio between these two components of the mixture is less than 1. However, these so-called "clean" engines require a very refined control of their operating conditions and therefore a fairly sophisticated sophistication of the control computer. For example, in certain areas of operation, it may be preferable for consumption and / or reduction of pollution, to operate the engine in lean mixture at a higher speed (i.e. to engage the lower ratio of the gearbox; Rl ratio), rather than imposing a stoichiometric mixture on it with a R gearbox ratio and a lower speed. This is contrary to what has hitherto been generally accepted, namely that in order to reduce consumption, it was desirable to choose the higher gear ratio and thus reduce the engine speed. However, current automatic gearboxes and their control computers are still designed to operate on this principle and therefore ill-suited to

  more recent engines mentioned above.

  However, the risk of inadequacy between the choice of the transmission ratio of the gearbox and the operation of engines of this type is even greater in the case where the gearbox is of the manual type, since in this case it is up to the driver that it is up to choosing the most suitable gear, which constitutes an almost insurmountable difficulty, taking into account all the parameters which come into play and the speed of reaction which the driver should demonstrate in the appropriate choice of the gear to engage . Choosing the wrong ratio can largely neutralize or even destroy the consumption and pollution abatement advantages

get "clean" motors.

  It should also be noted that control computers for "clean" engines already exist in various forms, but so far they have not been developed to ensure coordination with the gearbox, whether manual. or automatic. The object of the invention is to propose a method for controlling a powertrain making it possible to ensure this coordination between the operation of the engine and that of the gearbox and this by modifying the design of the control computer as little as possible. of

engine of the powertrain.

  The subject of the invention is therefore such a method of controlling a powerplant for a motor vehicle, comprising an engine and a gearbox, said engine being controlled by an engine control computer connected to a sensor raising the position. of the accelerator pedal of said engine, this method consisting in - a) determining in said engine control computer, as a function of the signal delivered by said sensor, a torque value as a function of the engine speed and b) to be determined in function of this torque value, the instantaneous operating point of said engine by setting a plurality of operating parameters among which the richness value of the air / fuel mixture and the ignition advance, - this process being characterized in that 'it also consists of: - c) taking into account said instantaneous operating point, in determining a value representing a desired speed ratio leading to optimal engine operation, taking into account instant driving conditions; and - d) using said value to control the engagement of said desired ratio in said gearbox, - operations c) and d) being carried out in

  said engine control computer.

  The process that has just been defined has the advantage of being able to be implemented by a conventional engine control computer with minimal modifications to its programming and its connections. Such a computer can thus be used to control a direct injection engine and / or a lean mixture operation, while allowing

  optimizing consumption and pollution control.

  However, it can also be used to optimally control a conventional engine operating with a stoichiometric ratio of the air / fuel mixture in which case the modified parts will not be used. In both cases, the value representing the desired gear ratio can be used to arrive at making the choice of gear ratios of the gearbox coupled to the engine optimal, whether this gearbox is on command.

  manual or automatic control.

  Thus, the invention provides the important advantage of making the engine computer of a general application, possibly with small programming and / or connection modifications, to

  a whole range of engines from a manufacturer catalog.

  It should also be noted that the concept of the invention may relate both to ignition engines

controlled only with spontaneous ignition.

  According to a first mode of implementation of

  the invention, applying to cases where the moto- group

  propellant comprises an automatic gearbox associated with an automatic gearbox computer, the method consists in transmitting said desired gear ratio value to the gearbox computer and in engaging the gearbox ratio

based on this value.

  Thanks to these characteristics, it becomes possible, by using an engine control computer whose base is conventional, but which is modified according to the invention, to add to the powertrain an automatic gearbox including the control computer. requires only a slight modification of its

software.

  In this case, it is advantageous, when said gearbox control computer is able to determine a predetermined driving mode from among a plurality of driving modes, that the method of the invention also consists in examining whether said transmission mode driving is a mode ensuring fuel economy and / or pollution control, and applying said desired ratio value to said gearbox control computer only if the driving mode selected is this mode ensuring fuel economy and / or depollution. This characteristic makes it possible to maintain, at the driver's choice, operating modes usually ensured by an automatic gearbox according to predetermined criteria such as driving styles, road configuration or even the

  safety (gearbox temperature).

  According to a second mode of implementation of

  the invention, applying to cases where the moto- group

  thruster comprises a manual gearbox, the method consists in converting said desired ratio value into displayable information for the driver

of the vehicle.

  In this case, this information can usefully be used to assist the driver of the vehicle to initiate the most adequate gear ratio, with a view to optimizing the reduction in consumption and pollution. According to a particular characteristic of this second embodiment of the invention, it may then be advantageous, in view of improving this assistance to the driver, to generate displayable information for the driver relating to the instantaneous gear ratio engaged and display the two pieces of information side by side, for example on the dashboard of the motor vehicle, to prompt the driver to change gear ratio, each time the two

information does not match.

  If in this case said gearbox is of the pure manual control type, the method can advantageously also consist in generating in said engine computer a value representing the gear ratio actually engaged, this value being estimated from the speed of said engine and of the speed of

  vehicle and display this value.

  However, in the case where said gearbox is of the type with manual impulse control, the method can then consist in transmitting to said engine computer a value representing the instantaneous ratio

  engaged developed by said gearbox.

  In order to obtain an adaptation of the choice of the desired speed ratio value at the operating temperature (during heating or in hot operation), the invention advantageously proposes, according to another of its characteristics, to take up a parameter representing a duration predetermined engine operation after starting and to determine the value representing a desired speed ratio by favoring pollution control or consumption, depending on whether

  said duration has not or has already elapsed.

  Said duration parameter can be the time of

  engine operation or temperature.

  In order to avoid any "beating" of the calculated value of desired gear ratio, it may also be advantageous to change the value representative of the desired gear relative to the current value of this desired gear only if a criterion value of

  gear change exceeds a predetermined threshold.

  This criterion value is advantageously determined by comparing the specific consumption of said engine in the presence of the desired ratio value and the specific consumption of the engine in the presence of the new desired ratio value and to compare the

  difference of the two values at said threshold.

  Other features and advantages of this

  invention will appear during the description which goes

  follow, given only by way of example and made with reference to the appended drawings in which: - Figure 1 is a very simplified diagram of a powerplant and its engine and gearbox control computers for illustrate a first embodiment of the invention; - Figure 2 is a flowchart illustrating the process steps implemented in the engine computer used in the arrangement shown in Figure 1; - Figure 3 is a graph of the torque C provided by the engine as a function of its speed V to illustrate the selection of an engine torque; - Figure 4 is a graph of the torque supplied by the engine as a function of its speed showing the choice of the operating point as a function of several operating zones relating to the air-fuel ratio of the mixture supplied to it;

  - Figure 5 is a flowchart of sub-

  program developing one of the steps in the flowchart shown in Figure 2; - Figure 6 is a graph of the torque as a function of the engine speed allowing the choice of an optimized gear ratio in the sense of a compromise between consumption, pollution and approval;

  - Figure 7 is a flow diagram of a sub-

  program detailing the operations carried out during one of the stages of the flow chart illustrated in FIG. 2; - Figure 8 is a flowchart illustrating the process steps implemented in the gearbox computer used in the arrangement shown in Figure 1; - Figure 9 illustrates with a graph of a value representative of the will Vc of the driver as a function of the speed Vv of the vehicle, the selection of the speeds of the gearbox; - Figure 10 is a diagram illustrating a particular embodiment of the invention applied to the case where the gearbox is manually controlled; and - Figure 11 is a diagram similar to that of Figure 10 showing a variant of the invention applied to the case of a gearbox with control

manual impulse.

  Figure 1 is a schematic representation intended to illustrate the first mode of implementation of the method according to the invention. An internal combustion engine 1 for a motor vehicle is coupled to an automatic gearbox 2. To the internal combustion engine 1 is associated an engine computer 3 and to the gearbox 2 is associated a gearbox computer 4. The two computers 3 and 4 communicate with each other and with the engine and the gearbox via a communication system which can be produced in a manner known per se by individual wires or by a CAN type multiplexed bus. Thus, the engine computer 3 communicates with the engine 1 via a link 5 and the gearbox computer 4 communicates with the gearbox

speeds via a link 6.

  The engine computer 3 also receives from an accelerator pedal sensor 7 a driver will signal representative of the degree of depression and, where appropriate of the gradient of depression, of the accelerator pedal of the vehicle. This signal is used in the engine computer 3 which also transmits it to the gearbox computer 4, via a link 8. According to the invention, the engine computer 3 also works out, according to a process described below , a desired gear ratio signal which is transmitted to the

  gearbox computer 4 by a link 9.

  The gearbox computer 4 in turn transmits a possible torque reduction request and a gear ratio signal engaged to the engine computer 3 by

  through respective links 10 and 11.

  FIG. 2 represents a simplified flowchart of the process steps executed iteratively in the engine computer 3. At the start of a cycle in El, it is first carried out, in step E2, in reading the information relating to the accelerator pedal, read by the sensor 7 and the corresponding signal Vc is shaped to be applied to the gearbox computer 4. The pedal information is also applied, in step E3, to a cartography which contains a set of values translating a curve of torque according to the mode, for example that represented on figure 3. This cartography is in memory in the engine computer 3 and its consultation gives place to the fixing of a point of Cpp operation during

step E3.

  If it is a direct injection engine, step E4 consists, for example, in correlating with this operating point Cpp, an operating zone defined by calibration in the mapping plan {Torque, Speed} and carrying respectively on an operation in stoichiometry S, in a homogeneous lean mixture LB or even in a lean mixture laminated ULB (FIG. 4). The values of richness and advance when the point is started are thus determined from corresponding maps in memory

in the engine control unit 3.

  According to the invention, step E5 consists in determining an optimal speed ratio. This ratio can be chosen to achieve the best compromise between consumption and pollution in normal operation or to set a degraded mode in the event of a failure,

  hydraulic, for example, in the powertrain.

  As shown in Figure 5, a separate value for the optimal ratio can be determined during step E5, first by performing a test in E5.1 to examine the temperature of the engine. To this end, it is possible to measure 11 directly the temperature of the oil or of the cooling water of the engine 1 and to compare it with a predetermined threshold. As a variant, it is also possible to set an operating delay during which the engine operates in the heating phase. If the test of step E5.1 finds that the temperature threshold has not yet been crossed or if the time has not yet elapsed, the engine computer 3 chooses from a map a gear ratio favoring the depollution at the expense of consumption

  (for example to prime a catalyst more quickly).

  On the other hand, if the temperature threshold is crossed or the heating-up period has elapsed, the engine computer 3 switches to another map establishing desired speed ratios favoring fuel economy. It should be noted that advantageously, the test of step E5.l, in so far as it consists in comparing the temperature of the engine to a threshold, can also be used for thermal protection of the engine, when the vehicle is in specific driving conditions which could cause the engine to overheat, for example when climbing a pass with a caravan towed by the vehicle. If the test in step E5.1 establishes that the engine has reached the predetermined temperature, the computer searches for the ratio of the powertrain that corresponds to the minimum consumption, while respecting the constraints of emission standards and driving comfort acceptable. This ratio is determined by process step E5.2, in an optimized map on a test bench. It should be noted that taking into account constraints related to driving pleasure are important to avoid a choice of gear leading to too low (lack of recovery and buzzing) or too high (overspeed) speed. The profile of such

  mapping may be that shown in Figure 6.

  Otherwise, the engine computer 3 determines during the process step E5.3, a strategy which, by an adequate determination of the gear ratio, leads to the fastest possible rise in temperature of the engine 1, without degrading consumption and limiting harmful emissions account

  given the priming phase of the catalyst.

  Step E6 (Figures 2 and 7) consists in avoiding any

  "beat" of the value "desired ratio" Rs, that is

  say, too rapid a variation of this value over time. For this, this step E6 consists first of all in carrying out a test in E6.1 which compares the value Rs of the speed ratio which has just been determined with the previous value RS ant. If this test finds equality

  between the two values, the previous ratio is maintained.

  Otherwise, the ratio value is confronted with a predetermined criterion during an E6.2 test. If the value passes the criterion, the new report value is transmitted, as the desired report, to the gearbox calculator 4. Otherwise, the old report Rsant is suggested to this calculator. The criterion of step E6.2 is chosen to manage a compromise between driving pleasure (not too many gear changes successively quickly) and the reduction of the time during which the suggested gear does

  does not match the suggested ratio.

  An example of a criterion capable of satisfying this compromise can be based on the difference between the so-called CSE value (specific consumption reduced to the developed mechanical energy) of the current motor point for the ratio Rs ant and the desired ratio Rs according to the function fe ( t) = I ACSE (u) of> rs-Rs-_an threshold This function is reset to zero each time the Rs ratio changes. Integration is maintained as long as Rs # Rsant. Then, this part of the process ends in E8 after transfer of the value Rs of the desired ratio to

  gearbox computer 4 during step E7.

  FIG. 8 represents the process steps implemented iteratively by the gearbox computer 4. After the start in E9, it is first carried out, during step E10, in reading the driver information Vc representative of the position of the accelerator pedal. It is transmitted to it by link 8 (Figure 1). The computer 4 deduces therefrom several quantities such as the degree of depression of the pedal and the

sinking gradient.

  During the next step Ell, according to fuzzy logic rules implementing, in a manner known per se, self-adaptive strategies, the computer determines several parameters, such as the driving habits of the driver (sportsman, etc.) and parameters relating to the road profile (slope level uphill or downhill etc.) and also the water temperatures of

  engine oil and cooling 1.

  Then, as a function of the self-adaptive strategies and the data collected during the step E1, the computer 4, during the step E12, chooses an operating mode of the powerplant, adapted to all these data. Operating modes are, for example, economic, medium, sport, slope 1, slope 2, pollution control, hot box security, etc. These modes can essentially fall into two categories, namely those which allow a fuel economy and an aid to pollution control, on the one hand and the other modes mentioned above, on the other hand. The method therefore examines, during a test in E13 which of the modes has been chosen. If the test E13 establishes that an "other mode" has been chosen, the method goes to step E14 during which a passage decision is taken by the gearbox computer 4 in accordance with conventional passage laws deposited in a plan mapping {Vehicle speed, Driver's willingness}. FIG. 9 is an example of a graphic representation of such a mapping, the plain lines representing the rising passages and the

  dashed lines the descending passages.

  Then, in the course of a step E 15, are made in a conventional manner to the decision to shift gears thus taken, dynamic corrections such as downshifting under braking, gear blocking on rapid pedal lift, shifting mapping to another etc. This part of the process ends in E17 after the execution in step E16 of a safety function reacting to a possible manipulation of the gearbox selector lever when shifting into reverse or downshifting to avoid overspeeds. During step E 15, the information of the report actually engaged is transmitted to the computer

engine.

  If the test E13 establishes that the economic or depollution mode has been selected, the method awaits (step E18) the supply of the information “desired report” delivered during step E7 by the engine computer 3 and transmitted to the gearbox computer 4 via link 10 (see Figures 1 and 2). Then the program

  repeat steps E15 to E17 as previously described.

  We will now describe a second embodiment of the invention with particular reference to Figures 10 and 11. This embodiment applies specifically to cases where the motor vehicle is equipped with a gearbox manually operated. In this case, an engine computer 3 is used

  which can be the same as that of figure 1, that is to say

  say who is capable of carrying out the process phases described above with reference to FIGS. 2 to 7. This computer 3 therefore defines at all times the best speed ratio to be selected in terms of consumption and pollution control according to the processes already described. However, the “desired report” information Rs is here transmitted to a display device 11 making it possible to

  inform the driver of the value of this desired ratio.

  Advantageously, the same display 11 also displays the value relating to the gear ratio actually engaged Re, thus facilitating the perception of the driver and inviting him to change gear, if the two items of information

do not match.

  However, as in this example, the gearbox is pure manual control, the engaged gear ratio signal Re is not directly available here. According to the invention, this signal is generated by calculation in the engine computer 3 from an estimate by correlation between the vehicle speed and the engine speed. The ratio value depending on the signal thus estimated is then displayed on the display device 11 so that the driver can make the proposed ratio value coincide with the position

real from the box.

  FIG. 11 represents a variant of the embodiment which has just been described in connection with FIG. 10. This variant applies more particularly to a gearbox 2a with manual control by electrical pulses. In this case, the engine computer 3 is identical to that described above. It therefore produces a desired speed ratio signal Rs and the corresponding ratio value is transmitted to a display device 11a as information accessible to the

  driver (dashboard, for example).

  In this case, the actually engaged report signal Re is available at the output of the gearbox 2a with impulse control and it can therefore possibly be transmitted to the engine computer 3, if it is desirable for the latter to have it. It suffices in this case that the display device 2a comprises a decoder o the signal is decoded and shaped before being transmitted to the engine computer 3. Thus, the driver also perceives here side by side the two report information speed, and it is asked to match the two ratio values at any time

thus displayed.

Claims (11)

  1. Method for controlling a motor-propulsion unit (1, 2) for a motor vehicle, comprising an engine (1) and a gearbox (2), said engine being controlled by an engine control computer (3) connected to a sensor (7) recording the position of the accelerator pedal of said engine, this method consisting of - a) determining in said engine control computer (3), as a function of the signal delivered by said sensor (7), a torque value as a function of the engine speed and - b) to determine as a function of this torque value, the instantaneous operating point of said engine (1) by fixing a plurality of operating parameters among which the richness value of the mixture air / fuel and ignition advance, - this process being characterized in that it further consists of: - c) taking into account said instantaneous operating point, to determine a value representing a desired gear ratio leading optimal engine operation, taking into account instant driving conditions; and - d) using said value to control the engagement of said desired ratio in said gearbox (2), - operations c) and d) being carried out in   said engine control computer (3).   2. Method according to claim 1, characterized in that, the powertrain comprising an automatic gearbox (2) associated with an automatic gearbox computer (4), it consists in transmitting said gear ratio value desired to said gearbox computer (4) and to engage the   ratio of the box according to this value.   3. Method according to claim 2, characterized in that, said gearbox control computer (4) being able to determine a predetermined driving mode from among a plurality of driving modes, it also consists in examining whether said mode driving mode is a mode ensuring fuel economy and / or pollution control, and applying said desired ratio value to said gearbox control computer (4) only if the driving mode selected is this mode ensuring economy fuel and / or pollution control. 4. Method according to claim 1, characterized in that, the powertrain comprising a manual gearbox (2), it consists in converting said desired ratio value into displayable information for the driver of the vehicle.   5. Method according to claim 4, characterized in that it consists in generating displayable information for the driver relating to the instantaneous gear ratio engaged and in displaying the two information side by side, for example on the table on board the motor vehicle, to prompt the driver to change gear, whenever the two information does not match.   6. Method according to claim 5, characterized in that, in the case where said gearbox is of the pure manual control type, it also consists in generating in said engine computer a value representing the gear ratio actually engaged, this value being estimated from the speed of said engine (1) and the speed of the vehicle and displaying this value. 7. Method according to claim 5, characterized in that, in the case where said gearbox is of the type with manual impulse control, it also consists in transmitting to said engine computer a value representing the instantaneous engaged engaged report worked out by said gearbox.   8. Method according to any one of   previous claims, characterized in that   also consists in reading a parameter representing a predetermined duration of engine operation after it has started and in determining the value representing a desired speed ratio by favoring pollution control or consumption, depending on whether said duration is not or has already passed.   9. Method according to claim 8, said duration parameter is the operating time of the engine or its temperature.   10. Method according to any one of   previous claims, characterized in that   also consists in only changing the value representative of the desired ratio with respect to the current value of this desired ratio only if a criterion value of   gear change exceeds a predetermined threshold.   11. Method according to claim 10, characterized in that said criterion value is determined by comparing the specific consumption of said motor (1) in the presence of the desired ratio value and the specific consumption of the engine in the presence of the new ratio value desired and to confront the   difference of the two values at said threshold.