METHOD AND SYSTEM FOR CONTROLLING THE VACUUM LEVEL OF A BRAKE ASSISTANCE SYSTEM

Abstract

A method for controlling an internal combustion engine (1) of a motor vehicle equipped with an exhaust gas recirculation circuit (8), for controlling the vacuum level in a brake assist system (3) whose vacuum level depends on the vacuum in an air intake distributor (17). The method comprises at least one step of measuring (E1) the vacuum level in the brake assist system (3), a step of comparing (E2) the measured vacuum level with at least a first threshold value (NOK1), and a step of deactivating (E3) the exhaust gas recirculation, so as to increase the vacuum in the air intake distributor (17). Figure for the abstract: Fig 1

Description

Title of the invention: METHOD AND SYSTEM FOR CONTROLLING THE DEPRESSION LEVEL OF A BRAKE ASSISTANCE SYSTEM Technical field

[0001] The present invention relates to the field of brake assist systems, in particular the control of the vacuum level of brake assist systems.

[0002] The invention particularly relates to motor vehicles equipped with spark-ignition internal combustion engines with high effective efficiency, making it possible to have low levels of consumption and therefore CO2 emissions.

[0003] A spark-ignition engine is associated with a fresh air intake circuit and an exhaust circuit for the combustion gases of the engine.

[0004] The intake circuit includes an intake manifold which distributes fresh air to each cylinder of the engine, and which communicates with a brake assist system.

[0005] Today, spark-ignition engines are generally equipped with a mechanical vacuum pump which ensures a satisfactory vacuum level in the brake assist system, under all driving conditions. The lower the vacuum level in the brake assist system, the harder the brake pedal and the greater the braking effort required by the driver. In order to guarantee comfortable braking for the driver, it is necessary to be able to control the vacuum level in the brake assist system.

[0006] However, the use of a vacuum pump to solve the lack of depression in the brake assist system is expensive and poses space problems linked to its integration into the engine. Statement of the invention

[0007] The present invention aims to overcome the aforementioned problems and, in particular, to ensure safe braking of the vehicle without using a vacuum pump.

[0008] The subject of the invention is a method for controlling an internal combustion engine of a motor vehicle equipped with an exhaust gas recirculation circuit, for controlling the vacuum level in a brake assist system whose vacuum level depends on the vacuum prevailing in an air intake distributor.

[0009] The method comprises at least one step of measuring the depression level in the brake assist system, at least one step of comparing the measured depression level with at least one first threshold value and at least one step deactivation of exhaust gas recirculation, so as to increase the depression in the air intake distributor.

[0010] Advantageously, the method comprises a step of closing the throttle body of the air intake distributor, so as to maintain a constant flow of fresh air in the air intake distributor.

[0011] Optionally, during the comparison step, the measured depression level is compared with a second threshold value substantially lower than said first threshold value.

[0012] According to one embodiment, the method comprises a step of modifying the variable timing of the engine valves.

[0013] According to one embodiment, the method comprises a step of modifying the variable lift of the engine valves.

[0014] The invention also relates to a system for controlling an internal combustion engine of a motor vehicle provided with an exhaust gas recirculation circuit, for controlling the vacuum level in a braking assistance system whose vacuum level depends on the vacuum prevailing in the air intake distributor.

[0015] The control system comprises means for measuring the depression level in the brake assist system, means for comparing the measured depression level with at least a first threshold value, and means for regulating a valve of the exhaust gas recirculation circuit, so as to increase the depression in the air intake distributor.

[0016] Advantageously, the measuring means comprise a sensor of the depression level in the braking assistance system.

[0017] According to one embodiment, the measuring means comprise a model for predicting the level of depression in the braking assistance system.

[0018] Optionally, the comparison means compare the measured depression level with a second threshold value substantially lower than said first threshold value.

[0019] The invention also relates to a motor vehicle comprising a control system as defined above. Brief description of the drawings

[0020] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example and made with reference to the appended drawings in which:

[0021] - [Fig.l] is a partial schematic view of an internal combustion engine of a motor vehicle associated with an engine braking assistance system;

[0022] - [Fig.2] illustrates the steps of a first mode of implementation of a method of control of the vacuum level in an engine brake assist system

[0023] - [Fig.3] illustrates the steps of a second mode of implementation of a method controlling the vacuum level in an engine braking assistance system;

[0024] - [Fig.4A] is a graphical view of a Miller type engine cycle as a function of the crankshaft angles;

[0025] - [Fig.4B] is a graphical view of an Atkinson type engine cycle in operation crankshaft angles;

[0026] - [Fig.5] is a graphical view of an example of implementation of the method of control of the vacuum level in a brake assist system, during braking by a driver;

[0027] and

[0028] - [Fig.6] illustrates the steps of a third mode of implementation of a method control of the vacuum level in an engine braking assistance system. Detailed description

[0029] In [Fig. 1], a part of a three-cylinder internal combustion engine 1 2 of a motor vehicle and a part of a braking assistance system 3 of a motor vehicle are shown.

[0030] The engine 1 is equipped with an exhaust circuit 4 for the combustion gases, and a fresh air intake circuit 5.

[0031] The exhaust circuit 4 for the combustion gases comprises an exhaust manifold 6, a turbocharger equipped with a turbine 7, and at least one circuit for partial recycling of the exhaust gases 8 to the intake, with the acronym “EGR” (“Exhaust Gas Recirculation”, in English). The exhaust circuit 4 may comprise a low-pressure EGR circuit 8 or a high-pressure EGR circuit 8.

[0032] In the example illustrated in [Fig.l], the EGR circuit 8 is a low pressure EGR and comprises a valve 9 for regulating the flow of gases and a cooler 10 for the combustion gases.

[0033] The exhaust circuit 4 also comprises, without limitation, one or more pollution control devices such as a three-way catalyst 11 and / or a particle filter 12.

[0034] The fresh air intake circuit 5 comprises an air filter 13, a compressor 14 of the turbocharger, a supercharged air cooler 15, a throttle body 16 for regulating the flow of gases entering the engine 1, and a distributor intake 17 which distributes the gases in each cylinder 2 of the engine 1. The gases which enter the engine 1 are therefore a mixture of fresh air recovered by the intake circuit 5, and exhaust gases recycled by the EGR recirculation circuit 8.

[0035] The intake circuit 5 is connected to a braking system of the motor vehicle, more particularly, the intake distributor 17 communicates with the braking assistance system 3.

[0036] The brake assist system 3 must have a satisfactory level of vacuum, this level of vacuum depending on the vacuum prevailing in the intake distributor 17. The lower the level of vacuum in the brake assist system 3, the harder the brake pedal, i.e. the greater the braking force to be provided by the driver. To ensure comfortable braking for the driver, it is necessary to control the level of vacuum in the brake assist system 3. In particular, it is necessary to increase the vacuum prevailing in the intake distributor 17.

[0037] In order to control the level of depression in the brake assist system 3, the engine 1 comprises a computer and a system for controlling the level of depression in the brake assist system 3.

[0038] The calculator is an on-board system which allows the electronic functions of the motor vehicle to be managed, and in particular allows the vacuum level control system to be controlled.

[0039] The system for controlling the depression level in the brake assist system 3 comprises means for measuring the depression level in the brake assist system 3, means for comparing the measured depression level with at least a first threshold value, and means for regulating the valve 9 of the EGR 8.

[0040] The means for measuring the depression level in the brake assist system 3 comprise at least one depression level sensor and / or a model for predicting the depression level in the brake assist system 3 according to different variables, such as the force of the braking carried out by the driver. The depression level sensor may be positioned in the brake assist system 3, or in the intake manifold 17.

[0041] The comparison means make it possible to compare a measured depression level with at least one threshold value, in order to predict whether the measured depression level represents a risk situation for the driver. According to one embodiment, the comparison means compare a measured depression level with a first threshold value and then with a second threshold value, said second threshold value being substantially lower than said first threshold value.

[0042] The means for regulating the valve 9 of the EGR circuit 8 make it possible to control the flow rate of combustion gases in the EGR circuit 8, in particular by closing the valve 9 of the EGR 8. If the valve 9 of the EGR circuit 8 is closed, there are no more recycled gases circulating in the intake circuit 5. Consequently, the flow rate of fresh air circulating through the throttle body 16 is amplified and the depression level in the intake distributor 17 does not increase sufficiently.

[0043] Thus, the control system also comprises means for regulating the throttle body 16 which make it possible to slightly close said throttle body 16, so that the flow of fresh air which circulates in the intake circuit 5 when the valve 9 of the EGR 8 is closed, is the same as the flow of fresh air which circulates in the intake circuit 5 when the valve 9 of the EGR 8 is open.

[0044] The means for regulating the valve 9 of the EGR 8 and the means for regulating the throttle body 16 therefore lead to an increase in the depression in the intake distributor 17 and, consequently, in the braking assistance system 3.

[0045] The invention also proposes a method for controlling the depression level in the braking assistance system 3. The steps of the method are illustrated over time t by figures 2, 3 and 6 according to three modes of implementation.

[0046] According to the first mode of implementation illustrated by [Fig.2], the method comprises four steps E1, E2, E3, E4.

[0047] The first step is a step E1 of measuring the depression level in the brake assist system 3. The measurement of the depression level of the brake assist system 3 is carried out in particular by the means for measuring the depression level of the control system.

[0048] The method comprises a second step E2 of comparing the depression level measured during the measurement step E1 with a threshold value. The means for comparing a measured depression level of the control system make it possible to carry out these comparisons. Without limitation, the threshold value is equal to 350 mbar. If the measured depression level is greater than the threshold value, the situation SUP is not at risk, and the process resumes at the measurement step E1. On the other hand, if the measured depression level is lower than the threshold value, the situation INF1 is considered to be risky, and the steps E3, E4 are executed.

[0049] The third step E3 of the method is a step E3 of deactivation of the recirculation of exhaust gases. The deactivation of the EGR circuit 8 makes it possible to increase the depression in the intake manifold 17. Step E3 is carried out using the means of regulation of the valve 9 of the EGR 8 of the control system.

[0050] A closing step E4 of the throttle body 16 is carried out substantially at the same time as the deactivation step E3. Indeed, in order to amplify the increase in the depression in the brake assist system 3, it is necessary to keep a constant flow of fresh air in the air intake distributor 17 when the valve 9 of the EGR circuit 8 is closed. The throttle body 16 is therefore slightly closed and, in this way, the depression increases in the intake distributor 17. This fourth step E4 is implemented by the regulation means of the throttle body 16 of the control system.

[0051] In order not to disturb the driver by a change in the consistency of the pedal during brake application, steps E3, E4 are implemented at the time the brake pedal is released by the driver. These steps are active until the vacuum level exceeds a specific threshold ensuring that the vacuum level in the brake assist system 3 has increased sufficiently. The efficiency is temporarily degraded due to pumping losses when the EGR circuit 8 is cut and the throttle body 16 is partially closed. These losses are however negligible because steps E3, E4 last only a few seconds.

[0052] Once steps E3, E4 are completed, the first measurement step E1 of the method is implemented again.

[0053] According to the second mode of implementation illustrated by [Fig.3], the method comprises five steps E1, E2, E3, E4, E5.

[0054] This mode of implementation is functional for engines comprising variable distribution systems, and in particular variable timing systems for the intake and exhaust valves, with the acronym “VVT” (“Variable Valve Timing”, in English).

[0055] In this embodiment, the comparison step E2 compares the measured depression level with two different threshold values. Indeed, the measured depression level is compared to a first threshold value, and if the measured depression level is greater than said first threshold value, the situation SUP is not at risk, and the process resumes at the measurement step EL. On the other hand, if the measured depression level is lower than the first threshold value, the depression level is compared to a second threshold value. The second threshold value is substantially lower than said first threshold value, and by way of non-limiting example, the first threshold value is equal to 350 mbar and the second threshold value is equal to 250 mbar.

[0056] If the measured depression level is greater than the second threshold value, the situation INF1 is considered risky. The method executes the first strategy level INF1 corresponding to the execution of steps E3, E4 as described in the first embodiment.

[0057] On the other hand, if the measured depression level is lower than the second threshold value, the situation INF2 is considered more risky and the method executes the second level INF2 of the strategy corresponding to the execution of steps E3, E4, E5.

[0058] Step E5 is a modification step E5 of the variable valve timing of the engine 1, implemented simultaneously with steps E3, E4. It makes it possible to increase the vacuum level in the brake assist system 3 more quickly.

[0059] The modification step E5 of the variable valve timing of the engine 1 consists of retiming the opening and closing of the intake and exhaust valves in a conventional manner, when using variable cycles such as the Miller or Atkinson cycles.

[0060] Conventionally, the opening and closing of the exhaust valves are carried out respectively at the bottom dead center of the crankshaft angle and at the top dead center of the crankshaft angle and, in the same way, the opening and closing of the intake valves are carried out respectively at the top point of the crankshaft angle and at the bottom dead center of the crankshaft angle.

[0061] [Fig.4A] represents the cycle of a Miller type engine as a function of the crankshaft angle. The dotted curve represents the Miller cycle before the implementation of the valve timing modification step E5, and the solid curve represents the Miller cycle after the implementation of step E5. The fresh gas intake valves in the combustion chamber are closed earlier in the case of a Miller type engine cycle than in the case of a conventional cycle. The resistive work in the intake and then compression phases is therefore reduced, which makes it possible to increase the engine efficiency (more torque generated for the same quantity of fuel injected).

[0062] [Fig.4B] represents the cycle of an Atkinson-type engine as a function of the crankshaft angle. The dotted curve represents the Atkinson cycle before the implementation of the valve timing modification step E5, and the solid curve represents the Atkinson cycle after the implementation of step E5. The fresh gas intake valves in the combustion chamber are closed later in the case of an Atkinson-type engine cycle than in the case of a conventional cycle. The resistive work in the intake and then compression phases is therefore reduced, which makes it possible to increase the engine efficiency (more torque generated for the same quantity of fuel injected).

[0063] Step E5 modifies the timing of these variable cycles to time the opening and closing of the exhaust and intake valves to a conventional cycle and thus increase the depression prevailing in the intake distributor 17.

[0064] The implementation of the second level INF2 generates greater pumping losses. However, they are also negligible because the steps E3, E4, E5 last only a few seconds, and the second level INF2 is a low-risk case. common in the use of a vehicle. Indeed, the execution of the second level INF2 of the process is especially necessary during emergency braking carried out by the driver. For other braking cases, the first level INF1 of the process is generally sufficient to restore a desirable level of depression in the brake assist system 3.

[0065] [Fig. 5] graphically illustrates the implementation of the method for controlling the depression level in a brake assist system 3 during the driving of a vehicle over time t. The method illustrated in [Fig. 5] is based on the second implementation mode presented above.

[0066] In [Fig.5], a first curve d shows the evolution of the depression level in mbar in the brake assist system 3 over time t. A second curve p illustrates the actions of the control method carried out over time t, as a function of the evolution of the depression level in the brake assist system 3. Finally, a third curve f illustrates the different braking operations F1, F2, F3, F4 carried out by the driver over time t.

[0067] At t equal to 0, the comparison means compare the depression level with a first threshold N0K1, after having recovered the depression level measured by the depression level measuring means. The measured depression level is greater than the first threshold N0K1 so the situation is not critical. Two first braking operations F1, F2 are carried out by the driver, and the brake assist system 3 loses depression. However, the depression level remains greater than the threshold N0K1 and no action is taken.

[0068] When the driver applies braking F3, the measuring means of the control system note that the vacuum level in the brake assist system 3 is lower than the first threshold N0K1 but higher than a second threshold N0K2. The method therefore executes the steps E3, E4 of deactivating the EGR 8 and closing the throttle body 16 as described above, because this is a critical situation of first level INF1. As can be seen on the curve p, the first level of the method INF1 is carried out at tF3_f corresponding to the release of the brake pedal by the driver. The first level INF1 of the control method is carried out until tF3_ok, the time necessary for the vacuum level in the brake assist system 3 to rise again, until it is higher than an OK threshold. The first level INF1 generally lasts a few seconds.

[0069] The OK threshold is a safety threshold allowing the vacuum measuring means to quickly assess whether the vacuum level may become critical following the next braking or not, and to see whether the vacuum level has become correct again after the execution of the method. By way of non-limiting example, the OK threshold is equal to 500 mbar.

[0070] The driver finally performs braking F4 at a time tF4_d. Braking F4 is particularly violent and corresponds to emergency braking. The vacuum present in the brake assist system 3 just before tF4_d suddenly drops during braking F4 and goes below the second threshold N0K2. The method therefore executes the second level INF2 which corresponds to the implementation of steps E3, E4 and E5 as described above.

[0071] On curve p, the second level INF2 of the method is carried out at tF4_f corresponding to the release of the brake pedal by the driver. The second level INF2 of the control method is carried out until tF4_ok, the time necessary for the vacuum level in the brake assist system 3 to rise again, until it is greater than the OK threshold. Like the first level INF1, the second level INF2 generally lasts a few seconds.

[0072] Alternatively, the second level INF2 of the method is carried out at tF4_d corresponding to the moment when the driver presses the brake pedal because the fourth braking F4 is emergency braking and the driver's sensation during the brake application is considered less important compared to the urgent need to slow down the vehicle.

[0073] The method for controlling the depression level in the braking assistance system 3 can also be implemented according to a third mode of implementation illustrated by [Fig.6] over time t.

[0074] According to this embodiment, the method comprises a sixth step E6 of modifying the variable valve lift of the engine 1. Like the step E5 of modifying the variable valve timing of the engine 1, the step E6 of modifying the valve lift makes it possible to increase the depression prevailing in the intake distributor 17 by modifying the amplitude of opening of the valves.

Claims

Claims

1. Method for controlling an internal combustion engine (1) of a motor vehicle provided with an exhaust gas recirculation circuit (8), for controlling the vacuum level in a brake assist system (3) whose vacuum level depends on the vacuum prevailing in an air intake distributor (17), characterized in that it comprises at least the following steps: - measuring (El) the vacuum level in the brake assist system (3); - comparing (E2) the measured vacuum level with at least a first threshold value (NOK1) and a second threshold value (NOK2) substantially lower than said first threshold value (NOK1); and - deactivating (E3) the exhaust gas recirculation, so as to increase the vacuum in the air intake distributor (17).

2. Method according to claim 1, comprising a step of closing (E4) the throttle body (16) of the air intake distributor (17), so as to maintain a constant flow of fresh air in the air intake distributor (17).

3. Method according to one of claims 1 and 2, comprising a step (E5) of modifying the variable timing of the valves of the engine (1).

4. Method according to any one of claims 1 to 3, comprising a step (E6) of modifying the variable lift of the valves of the engine (1).

5. Control system for an internal combustion engine (1) of a motor vehicle provided with an exhaust gas recirculation circuit (8), for controlling the vacuum level in a brake assist system (3) whose vacuum level depends on the vacuum prevailing in the air intake distributor (17), characterized in that it comprises means for measuring the vacuum level in the brake assist system (3), means for comparing the measured vacuum level with at least a first threshold value (NOK1) and a second threshold value (NOK2) substantially lower than said first threshold value (NOK1), and means for regulating a valve (9) of the circuit

6.

7.

8. exhaust gas recirculation (8), so as to increase the depression in the air intake distributor (17). System according to claim 5, wherein the measuring means comprise a sensor of the depression level in the brake assist system (3). System according to one of claims 5 and 6, in which the measuring means comprise a model for predicting the level of depression in the braking assistance system (3). Motor vehicle comprising a control system according to any one of claims 5 to 7.