FR2817916A1 - Method of controlling a vehicle and maintaining the minimum level of vacuum necessary for proper functioning of the brake assistance unit, when the vehicle is negotiating a gradient - Google Patents

Abstract

During the issuing of the provisional stopping step (EAPA), there is a step of deciding about the re-starting (ERDM) the engine, during the course of which, the ECU initiates a test (COND2) for controlling the starting of the engine, especially in order to re-establish a minimum negative pressure in the reservoir of a braking servomotor in order to ensure the proper functioning of the brake assistance unit. The method involves a step (EFMT) of engine rotating functioning, and a step (EAPA) of automatic provisional stopping when the engine is automatically stopped by an Electronic control unit (ECU), when the vehicle is stationary for a long time.

Description

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"Method for controlling a heat engine of a motor vehicle"
The invention relates to a method for controlling a heat engine of a motor vehicle.

 The invention relates more particularly to a method for controlling a thermal engine of a motor vehicle which comprises at least one operating step with the engine running and an automatic temporary stopping step during which the thermal engine is automatically stopped by an electronic unit. when the vehicle is stationary for an extended period of time.

 Many examples of such control methods are known, which are commonly known as "stop and go" methods.

 The VALEO patent application number 99.08531 describes and represents a device of this type comprising a particular improvement relating to protection against excessive discharge of the battery.

 A vehicle provided with a heat engine operating according to such a method has a major drawback which manifests itself when the vehicle is in a traffic jam on a sloping track and the engine is stopped.

 In fact, in known manner, a braking assistance system comprises a booster intended to amplify the forces exerted on the brake pedal and which uses the vacuum prevailing in an intake manifold of the engine. Such a booster generally comprises a vacuum chamber forming a vacuum tank.

 However, in the configuration mentioned above, if the circulation is carried out discontinuously, that is to say in the form of a succession of stops and short advances, the driver will tend to advance his vehicle by releasing the brake and letting it move by itself along the slope rather than restarting and engaging a gear.

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 Therefore, each time the driver releases the brake pedal to move forward, then actuates it to stop, he will exhaust the reserve of vacuum contained in the reservoir of the brake booster, so that at the end a determined number of pedal actuations, the vacuum reserve of the servomotor will be exhausted, rendering the brake assist system inoperative.

 Therefore, if the slope on which the vehicle is steep enough, the driver will not have the force necessary to apply the braking, then devoid of assistance, and his vehicle will crash into the vehicle in front.

 To overcome this drawback, it has been proposed to replace the vacuum source of the booster previously mentioned by an electric vacuum pump intended to ensure in all circumstances a minimum level of vacuum in the tank of the booster. This solution turns out to be expensive.

 To overcome this drawback, the invention proposes a control method which is intended to restart the engine as soon as the vacuum level in the reservoir of the booster risks falling below a determined risk threshold.

 To this end, the invention proposes a control method of the type described above, characterized in that it comprises, at the end of the automatic temporary stopping step, at least one step of deciding to restart the engine at during which the electronic control unit is capable of carrying out at least one test to control the restarting of the engine, in particular in order to restore a minimum vacuum in a reservoir of a brake booster of the vehicle in order to ensure the operation of '' a brake assist device.

 According to other characteristics of the invention: - the decision step comprises at least a first test representative of the driver's desire to leave the stop step

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 automatic provisional to return to the engine running stage, - if the first test is validated, the electronic unit controls the return to the engine running stage., - if the first test is not validated, l the electronic unit establishes at least a second risk test, - during the second risk test, the electronic unit compares the value of a pressure measured in a brake booster with a threshold pressure value, and it controls the return to the engine running stage if the value of the measured pressure is greater than the threshold pressure value, or else keep it in the automatic provisional stop stage otherwise, - during the second risk test , the electronic unit compares the value of a vehicle speed measured by means of a speed sensor with a threshold speed value, and it commands the return to the engine running stage if the value of the measured speed is greater than the value of the threshold speed, or else maintains it at the automatic provisional stop step otherwise.

 - during the second risk test, the electronic unit compares a state variable of a brake pedal with a zero value of the inactive state of the brake pedal, - if the value of the state variable is equal to the zero value of the inactive state of the pedal, the electronic unit stores a zero value in an intermediate counter, then commands the maintenance in the automatic temporary stop step, and if the state variable is equal to an active pedal unit value, the electronic unit positions itself on a third risk test.

 - during the third risk test, the electronic unit compares the value stored in the intermediate counter with a zero reference value of the counter, then:. if the value stored in the intermediate counter is equal to the zero value, the unit

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 electronics increments a final counter by one unit then stores the unit value in the intermediate counter, then positions itself on a fourth risk test, if the value stored in the intermediate counter is equal to the unit value, the electronic unit controls the maintains the automatic provisional shutdown step.

 - during the fourth risk test, the electronic unit compares the value displayed by the final counter to a reference value of the final counter corresponding to a number of authorized actuations of the pedal, then: if the value displayed by the counter final is different from the reference value of the final counter corresponding to the number of authorized actuations of the pedal, the electronic control unit maintains it in the automatic provisional stop step,. if the value displayed by the final counter is equal to the reference value of the final counter corresponding to the number of authorized actuations of the pedal, the electronic unit assigns the zero value to the intermediate counter and to the final counter then commands the return to l 'engine running step.

 Other characteristics and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the appended drawings in which: - Figure 1 is an overall schematic flow diagram of a method of control according to the invention, FIG. 2 is a detailed flowchart of a first embodiment of the step for deciding to restart the engine,

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 - Figure 3 is a detail flow diagram of a second embodiment of the engine restart decision step, and - Figure 4 is a detail flow diagram of a third embodiment of the decision step engine restart.

 In the following description, identical reference numerals denote elements which are identical or have similar functions.

 FIG. 1 shows a flow diagram of a method for controlling a thermal engine of a motor vehicle.

 In known manner, the method comprises at least one step EFMT of operating the engine running and an EAPA step of automatic provisional stop during which the heat engine is automatically stopped by an electronic control unit (not shown) when the vehicle is stationary at a prolonged standstill.

 The EAPA step is likely to occur if a SAG operating mode "stop and go" is selected by the driver of the vehicle, as illustrated by the test COND1 which is intermediate between the step EFMT of running engine running and the step Automatic provisional shutdown EAPA.

 The automatic provisional EAPA stop step is likely to trigger the automatic shutdown of the vehicle engine under certain conditions. Since such an EAPA step of automatic provisional shutdown is known from the state of the art, this step will not be described in more detail in the present description.

 According to the invention, the method comprises, at the end of the step EAPA of automatic provisional stop, at least one step EDRM of decision to restart the engine during which the electronic control unit is capable of perform at least one test to order the restart of the

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 engine, in particular in order to restore a minimum vacuum in a reservoir of a vehicle brake booster in order to ensure the operation of a brake assist device.

 More particularly, as illustrated in FIG. 1, the step EDRM of decision to restart the engine can intervene, as illustrated by the arrow SI, at the end of the step EAPA of automatic provisional stop, or can also, as illustrated by arrow S2, precede a return to the EAPA step of automatic provisional stop, or alternatively, as illustrated by arrow S3, command a return to the step EFMT of running engine running.

 The details of the operation of the method during the EDRM step of restarting the engine will now be described according to three embodiments shown respectively in FIGS. 2 to 4.

 In each of the embodiments described below, the information transmitted by the sensors is scanned according to a time base, or period, which can vary for example between 1 ms and 500 ms.

 Similarly, in each of these embodiments, the engine restart decision EDRM step comprises at least a first test COND2 which is representative of the driver's desire to leave the EAPA step of automatic provisional stop to return to the 'EFMT engine running step.

 This first COND2 test includes the analysis of information transmitted by sensors which are for example capable of detecting an action by the driver on a vehicle accelerator pedal, on a lever for controlling the vehicle gearbox, or on a vehicle clutch pedal (not shown).

 In all the embodiments, if the first test is validated, that is to say if one of these sensors is activated, the electronic unit controls the return according to the arrow S3 in step

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 Engine running EFMT, i.e. restarting the engine.

 Otherwise, if the first COND2 test is not validated, the electronic unit establishes at least a second risk test.

 According to a first embodiment which is represented in FIG. 2, during the second COND3A risk test, the electronic unit compares the value of a pressure PF measured in the reservoir of a brake booster with a pressure value PFS threshold determined. If the value of the pressure PF measured is greater than the value of the pressure PFS of threshold, the electronic unit controls, as illustrated by arrow S3, the return to the step EFMT of operating engine running, it is at say restarting the engine,. Otherwise, the electronic unit controls, as illustrated by arrow S2, the maintenance of the vehicle in the EAPA step of automatic provisional stop.

 According to a second embodiment which is represented in FIG. 3, during the second risk test COND3B, the electronic unit compares the value of a speed V of the vehicle measured by means of a speed sensor with a threshold speed VS value. If the value of the measured speed V is greater than the value of the threshold speed VS, the electronic unit controls, as illustrated by arrow S3, the return to the step EFMT of engine running operation. Otherwise, the electronic control unit, as illustrated by the arrow S2, maintains it at the step EAPA of automatic provisional stop.

 According to a third embodiment which is represented in FIG. 4, during the second COND3C risk test, the electronic unit compares a state variable F of a brake pedal (not shown), capable of taking the value zero 0 or unit 1, to a zero value 0 of the brake pedal inactive state.

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 If the state variable F is equal to the zero value 0 associated with the inactive state of the pedal, the electronic unit stores a zero value 0 in an intermediate counter A during a storage sub-step STO, then control, as illustrated by the arrow S2 maintains it at the step EAPA of automatic provisional stop.

 Thus, in the absence of actuation of the brake pedal, the value assigned to the intermediate counter A is always equal to the zero value 0.

 If the state variable F is equal to a unit value 1 of active state of the pedal, the electronic unit positions itself on a third COND4 risk test.

 During the third COND4 risk test, the electronic unit compares the value stored in the intermediate counter A with a zero reference value 0 of the counter.

 If the value stored in the intermediate counter A is equal to the zero value 0, this means that the process has previously passed through the inactive state of the pedal corresponding to the zero value 0 of the state variable F. As elsewhere the third COND 4 test is only activated if the variable F is equal to a unit value 1, this means that the variable F has changed state to go from the zero value 0 to the unit value 1. In this case, the electronic unit increments a final counter CF by one unit and then stores the unit value 1 in the intermediate counter A. The value assigned to the CF counter is therefore representative of the number of actuations of the brake pedal carried out by the driver of the vehicle . The electronic unit then positions itself on a fourth COND5 risk test which will be described later.

 If the value stored in the intermediate counter A is equal to the unit value 1, this means that there has been no actuation of the brake pedal, and the electronic unit controls, as illustrated by the arrow S2, maintaining the automatic provisional shutdown step EAPA.

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Au cours du quatrième test de risque COND5, l'unité électronique compare la valeur affichée par le compteur final CF à une valeur de référence CFR du compteur final correspondant à un nombre d'actionnements autorisés de la pédale. La valeur CFR de ce nombre d'actionnement est par exemple déterminée par la capacité du réservoir du servomoteur et par la quantité de dépression absorbée par chaque actionnement de la pédale de frein.

During the fourth risk test COND5, the electronic unit compares the value displayed by the final counter CF with a reference value CFR of the final counter corresponding to a number of authorized actuations of the pedal. The CFR value of this number of actuations is for example determined by the capacity of the booster tank and by the amount of vacuum absorbed by each actuation of the brake pedal.

 If the value displayed by the final counter CF is different from the reference CFR value of the final counter corresponding to the number of authorized actuations of the pedal, this means that the vacuum reservoir of the actuator still benefits from a vacuum reserve sufficient to actuation of the braking assistance system, and consequently the electronic unit controls the maintenance via the arrow S2 in the step EAPA of automatic provisional stop.

 If on the contrary, the value displayed by the final counter CF is equal to the reference CFR value of the final counter corresponding to the number of authorized actuations of the pedal, this means that the vacuum reserve is exhausted, and therefore the electronic unit initializes the counters, that is to say assigns the zero value 0 to the intermediate counter A and to the final counter CF, then commands, as illustrated by arrow S3, the return to the step EFMT of operation with the engine running, this is ie restarting the engine.

 The method therefore makes it possible to benefit from a vehicle whose engine operates according to a "stop and go" method while having a high level of safety.

Claims (10)

1. A method of controlling a thermal engine of a motor vehicle which comprises at least one step (EFMT) of running engine running and one step (EAPA) of automatic provisional stop during which the thermal engine is stopped automatically by a unit electronic control when the vehicle is stationary for an extended period of time, characterized in that it comprises, at the end of the step (EAPA) of automatic provisional stop, at least one step (EDRM) of decision of restarting the engine during which the electronic control unit is capable of performing at least one test (COND2) to control restarting of the engine, in particular in order to restore a minimum vacuum in a reservoir of a brake booster of the vehicle to ensure the operation of a brake assist device.  2. Control method according to the preceding claim, characterized in that the decision step (EDRM) comprises at least a first test (COND2) representative of the driver's desire to leave the step (EAPA) of provisional automatic stopping. to return to the engine running stage (EFMT).  3. Method according to the preceding claim, characterized in that, if the first test (COND2) is validated, the electronic unit controls the return to the step (EFMT) of running engine operation.  4. Method according to the preceding claim, characterized in that, if the first test (COND2) is not validated, the electronic unit establishes at least a second risk test (COND3A, COND3B, COND3C).  5. Method according to the preceding claim, characterized in that, during the second risk test (COND3A), the unit <Desc / Clms Page number 11>  electronics compares the value (PF) of a pressure measured in a brake booster with a value (PFS) of threshold pressure, and in that it commands the return to the step (EFMT) of engine running if the value (PF) of the measured pressure is greater than the value (PFS) of the threshold pressure, or else maintains it at the step (EAPA) of automatic provisional stop otherwise.  6. Method according to claim 4, characterized in that, during the second risk test (COND3B), the electronic unit compares the value (V) of a vehicle speed measured by means of a sensor speed at a threshold speed value (VS), and in that it commands the return to the step (EFMT) of engine running if the value (V) of the measured speed is greater than the value (VS) of the threshold speed, or else maintains it at the automatic provisional stop (EAPA) stage otherwise.  7. Method according to claim 4, characterized in that, during the second risk test (COND3C), the electronic unit compares a state variable (F) (0,1) of a brake pedal with a zero value (0) inactive state of the brake pedal.  8. Method according to claim 7, characterized in that: - if the value of the state variable (F) is equal to the zero value (0) of inactive state of the pedal, the electronic unit stores a value zero (0) in an intermediate counter (A), then commands it to be maintained at the step (EAPA) of automatic provisional stop, - if the state variable (F) is equal to a unit value (1) of active state of the pedal, the electronic unit positions itself on a third risk test (COND4).  9. Method according to claim 8, characterized in that, during the third risk test (COND4), the electronic unit compares the value stored in the intermediate counter (A) with a zero value (0) of the counter reference , then: <Desc / Clms Page number 12>  - if the value stored in the intermediate counter (A) is equal to the zero value (0), the electronic unit increments a final counter (CF) by one unit and then stores the unit value (1) in the intermediate counter ( A), then positions itself on a fourth risk test (COND5), - if the value stored in the intermediate counter (A) is equal to the unit value (1), the electronic control unit maintains it in step ( EAPA) automatic provisional shutdown.  10. Method according to claim 9, characterized in that, during the fourth risk test (COND5), the electronic unit compares the value displayed by the final counter (CF) with a reference value (CFR) of the final counter corresponding to a number of authorized actuations of the pedal, then: - if the value displayed by the final counter (CF) is different from the reference value (CFR) of the final counter corresponding to the number of authorized actuations of the pedal, the electronic unit controls the maintains at the automatic temporary stop (EAPA) stage, - if the value displayed by the final counter (CF) is equal to the reference value of the final counter corresponding to the number of authorized actuations of the pedal, the electronic unit assigns the null value (0) to the intermediate counter (A) and to the final counter (CF) then commands the return to the step (EFMT) of engine running operation.