Method and system for controlling vacuum level of a brake assist system

Abstract

A method for monitoring an internal combustion engine (1) of a motor vehicle having an exhaust gas recirculation circuit (8), the method being for monitoring a vacuum level in a brake assist system (3), the vacuum level of the brake assist system (3) being dependent on the prevailing 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 one first threshold value (NOK1), and a step of deactivating (E3) the exhaust gas recirculation in order to increase the vacuum in the air intake distributor (17).

Description

Technical Field

[0001] This invention relates to the field of brake assist systems, and particularly to the control of vacuum levels in brake assist systems.

[0002] The present invention particularly relates to motor vehicles equipped with spark-ignition internal combustion engines that are highly efficient and capable of achieving low levels of energy consumption and therefore low levels of CO2 emissions.

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

[0004] The intake system includes an intake distributor that distributes fresh air to each engine cylinder and is connected to the brake assist system.

[0005] Modern spark-ignition engines are typically equipped with mechanical vacuum pumps to ensure 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 becomes, and the greater the braking force required by the driver. To ensure comfortable braking for the driver, the vacuum level in the brake assist system must be controllable.

[0006] However, using a vacuum pump to overcome the lack of vacuum in the brake assist system is expensive and raises space issues related to its integration into the engine. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned problems, and in particular to ensure safe vehicle braking without the use of a vacuum pump.

[0008] The present invention relates to a method for controlling an internal combustion engine of a motor vehicle having an exhaust gas recirculation circuit, the method being used to control the vacuum level in a brake assist system, the vacuum level of which depends on the dominant vacuum in an air intake distributor.

[0009] The method includes at least one step of measuring a vacuum level in a brake assist system; at least one step of comparing the measured vacuum level with at least one first threshold; and at least one step of deactivating exhaust recirculation to increase the vacuum in an air intake distributor.

[0010] Advantageously, the process includes the step of closing the throttle valve of the air intake distributor to maintain a constant flow of fresh air into the air intake distributor.

[0011] Optionally, during the comparison step, the measured vacuum level is compared with a second threshold that is substantially below the first threshold.

[0012] In one embodiment, the process includes the step of modifying the timing of the engine's variable valves.

[0013] In one embodiment, the process includes the step of modifying the variable lift of the engine valves.

[0014] The present invention also relates to a control system for an internal combustion engine of a motor vehicle having an exhaust gas recirculation loop, the control system being used to control the vacuum level in a brake assist system, the vacuum level of which depends on the dominant vacuum in an air intake distributor.

[0015] The control system includes means for measuring the vacuum level in the brake assist system, means for comparing the measured vacuum level with at least one first threshold, and means for adjusting a valve in the exhaust recirculation loop to increase the vacuum in the air intake distributor.

[0016] Advantageously, the measuring device includes a sensor for the vacuum level in the brake assist system.

[0017] In one embodiment, the measuring device includes a model for predicting the vacuum level in the brake assist system.

[0018] Optionally, the comparison device compares the measured vacuum level with a second threshold that is substantially below the first threshold.

[0019] The present invention also relates to a motor vehicle including a control system as defined above. Attached Figure Description

[0020] Other objects, features, and advantages of the invention will become apparent from the following description, which is given by way of non-limiting example only and with reference to the accompanying drawings, wherein:

[0021] - Figure 1 This is a partial schematic diagram of an internal combustion engine in a motor vehicle that is associated with an engine braking assist system.

[0022] - Figure 2 The steps of a first method for implementing a process for monitoring the vacuum level in an engine brake assist system are shown;

[0023] - Figure 3 The steps of a second method for implementing a process for monitoring the vacuum level in an engine brake assist system are shown;

[0024] - Figure 4A It is a graphical view of the Miller engine cycle as the crankshaft angle changes;

[0025] - Figure 4B It is a graphical view of the Atkinson engine cycle as the crankshaft angle changes;

[0026] - Figure 5 This is a graphical view of an example of an implementation of a process for monitoring the vacuum level in a brake assist system during driver braking; and

[0027] - Figure 6 The steps of a third implementation of a method for controlling the vacuum level in an engine braking assist system are shown. Detailed Implementation

[0028] Figure 1 A portion of a three-cylinder internal combustion engine 1 for a motor vehicle and a portion of a brake assist system 3 for a motor vehicle are shown.

[0029] Engine 1 is equipped with an exhaust system 4 for combustion gases and an intake system 5 for fresh air.

[0030] The exhaust circuit 4 includes an exhaust manifold 6, a turbocharger with a turbine 7, and at least one partial exhaust gas recirculation (EGR) circuit 8. The exhaust circuit 4 may include a low-pressure EGR 8 circuit or a high-pressure EGR 8 circuit.

[0031] exist Figure 1 In the example shown, EGR circuit 8 is a low-pressure EGR and includes a valve 9 for regulating gas flow and a cooler 10 for combustion gases.

[0032] The exhaust system 4 also includes, but is not limited to, one or more pollution control devices, such as a three-way catalytic converter 11 and / or a particulate filter 12.

[0033] The fresh air intake circuit 5 includes an air filter 13, a turbocharger compressor 14, a boost air cooler 15, a throttle valve 16 for regulating the flow of gas into the engine 1, and an intake distributor 17 for distributing gas to each cylinder 2 of the engine 1. Therefore, the gas entering the engine 1 is a mixture of fresh air recovered by the intake circuit 5 and exhaust gas recirculated by the EGR recirculation circuit 8.

[0034] The intake circuit 5 is connected to the vehicle braking system, and specifically the intake distributor 17 is connected to the brake assist system 3.

[0035] The brake assist system 3 must have a satisfactory vacuum level, which depends on the dominant vacuum in the intake manifold 17. The lower the vacuum level in the brake assist system 3, the harder the brake pedal, meaning the greater the braking force required by the driver. To ensure comfortable braking for the driver, the vacuum level in the brake assist system 3 must be controlled. In particular, the vacuum in the intake manifold 17 must be increased.

[0036] In order to control the vacuum level in the brake assist system 3, the engine 1 includes a computer and a system for controlling the vacuum level in the brake assist system 3.

[0037] An ECU is an onboard system that manages the electronic functions of a motor vehicle, and specifically controls the vacuum control system.

[0038] The system for controlling the vacuum level in the brake assist system 3 includes a device 3 for measuring the vacuum level in the brake assist system 3, a device for comparing the measured vacuum level with at least one first threshold, and a device for adjusting the EGR 8 valve 9.

[0039] The apparatus for measuring the vacuum level in the brake assist system 3 includes at least one vacuum level sensor and / or a model for predicting the vacuum level in the brake assist system 3 based on various variables, such as the braking force applied by the driver. The vacuum level sensor may be located in the brake assist system 3 or in the intake manifold 17.

[0040] The comparison device allows a measured vacuum level to be compared with at least one threshold to predict whether the measured vacuum level represents a dangerous situation for the driver. In one embodiment, the comparison device compares the measured vacuum level with a first threshold and then with a second threshold that is substantially lower than the first threshold.

[0041] The device for adjusting valve 9 in the EGR 8 circuit allows control of the flow of combustion gases in the EGR 8 circuit, specifically by closing valve 9 of EGR 8. If valve 9 in the EGR circuit 8 is closed, no more recirculated gas flows in the intake circuit 5. Therefore, the flow rate of fresh air through throttle valve 16 is amplified, and the vacuum level in the intake distributor 17 is not sufficiently increased.

[0042] Therefore, the control system also includes means for adjusting the throttle valve 16, which allows the throttle valve 16 to be slightly closed, such that the fresh air flow rate circulating in the intake circuit 5 when the EGR 8 valve 9 is closed is the same as the fresh air flow rate circulating in the intake circuit 5 when the EGR 8 valve 9 is open.

[0043] Therefore, the device for adjusting the EGR 8 valve 9 and the device for adjusting the throttle valve 16 result in an increase in the vacuum in the intake distributor 17, and thus an increase in the vacuum in the brake assist system 3.

[0044] This invention also proposes a method for controlling the vacuum level in a brake assist system 3. According to three implementation methods, in Figure 2 , Figure 3 and Figure 6 The steps of the process over time t are shown in the figure.

[0045] according to Figure 2 The first method shown comprises four steps: E1, E2, E3, and E4.

[0046] The first step is step E1, which is the measurement of the vacuum level in the brake assist system 3. The vacuum level in the brake assist system 3 is specifically measured using a device for measuring the vacuum level in the control system.

[0047] The method includes a second step, E2, which compares the vacuum level measured during measurement step E1 with a threshold. A device for comparing the vacuum level measured in the control system enables these comparisons. For example, the threshold is equal to 350 mbar. If the measured vacuum level is greater than the threshold, the SUP condition is not at risk, and the process restarts at measurement step E1. On the other hand, if the measured vacuum level is less than the threshold, the condition INF1 is considered at risk, and steps E3 and E4 are executed.

[0048] The third step, E3, of the process is the deactivation step E3 of the exhaust gas recirculation. Deactivating the EGR 8 circuit increases the vacuum in the intake manifold 17. Step E3 is performed using the device for regulating the EGR 8 valve 9 of the control system.

[0049] Step E4, closing the throttle valve 16, is performed approximately simultaneously with step E3, deactivating the system. To amplify the increase in vacuum in the brake assist system 3, a constant flow of fresh air must be maintained in the air intake distributor 17 when valve 9 of the EGR circuit 8 is closed. Therefore, the throttle valve 16 is slightly closed, and in this way, the vacuum in the intake distributor 17 increases. This fourth step, E4, is implemented by means of a device that adjusts the throttle valve 16 of the control system.

[0050] To prevent driver inconvenience due to changes in pedal consistency during braking application, steps E3 and E4 are implemented when the driver releases the brake pedal. These steps are activated until the vacuum level exceeds a specific threshold ensuring that the vacuum level in the brake assist system 3 has been sufficiently increased. When the EGR 8 circuit is disconnected and the throttle valve 16 is partially closed, efficiency is temporarily reduced due to pumping losses. However, these losses are negligible because stages E3 and E4 last only a few seconds.

[0051] Once steps E3 and E4 have been completed, the first measurement step E1 of the process is executed again.

[0052] according to Figure 3 The second method shown comprises five steps: E1, E2, E3, E4, and E5.

[0053] This implementation works for engines that include variable valve timing systems, particularly variable intake and exhaust valve timing systems (VVT).

[0054] In this implementation, comparison step E2 compares the measured vacuum level with two different thresholds. The measured vacuum level is compared to a first threshold, and if the measured vacuum level is greater than the first threshold, there is no risk of a SUP (Sustainable Uptake) situation, and the process restarts at measurement step E1. On the other hand, if the measured vacuum level is lower than the first threshold, the vacuum level is compared to a second threshold. The second threshold is substantially lower than the first threshold, and for example, the first threshold is equal to 350 mbar, and the second threshold is equal to 250 mbar.

[0055] If the measured vacuum level is greater than the second threshold, then condition INF1 is considered risky. The method executes the first strategy level INF1, which corresponds to executing steps E3 and E4 as described in the first implementation.

[0056] On the other hand, if the measured vacuum level is less than the second threshold, the situation is considered to be of greater risk (INF2), and the method executes the second strategy level (INF2), which corresponds to the execution steps E3, E4, and E5.

[0057] Step E5 is a modification step for the variable valve timing of engine 1, performed simultaneously with steps E3 and E4. It allows the vacuum level in brake assist system 3 to increase more quickly.

[0058] The modification step E5 for the variable valve timing of engine 1 is to readjust the opening and closing of the intake and exhaust valves in a conventional manner when using a variable cycle (such as the Miller cycle or the Atkinson cycle).

[0059] Typically, the exhaust valves open and close at the bottom dead center and top dead center of the crankshaft, respectively, and similarly, the intake valves open and close at the top dead center and bottom dead center of the crankshaft, respectively.

[0060] Figure 4A The Miller engine cycle is shown as a function of crankshaft angle. The dashed curve represents the Miller cycle before implementing valve timing modification step E5, and the solid curve represents the Miller cycle after implementing step E5. The valves that allow fresh air into the combustion chamber close earlier in the Miller-type engine cycle than in the conventional cycle. Therefore, the workload during the intake and compression phases is reduced, which improves engine efficiency (producing greater torque for the same amount of injected fuel).

[0061] Figure 4B The diagram illustrates the Atkinson cycle of an Atkinson engine as the crankshaft angle varies. The dashed curve represents the Atkinson cycle before valve timing modification step E5, and the solid curve represents the Atkinson cycle after step E5. The valves allowing fresh air into the combustion chamber close later in the Atkinson engine cycle than in the conventional cycle. Therefore, the workload during the intake and compression phases is reduced, which improves engine efficiency (producing greater torque for the same amount of injected fuel).

[0062] Step E5 modifies the timing of these variable cycles to adjust the opening and closing of the exhaust and intake valves to the normal cycle, thereby increasing the vacuum in the intake manifold 17.

[0063] Installing the second-level INF2 results in greater pumping losses. However, these losses are negligible because stages E3, E4, and E5 last only a few seconds, and the second-level INF2 is not very common in vehicle use. The execution of the second-level INF2 in this process is primarily necessary during emergency braking by the driver. For other braking situations, the first-level INF1 in this process is generally sufficient to restore the desired vacuum level in Brake Assist System 3.

[0064] Figure 5 The implementation of the process for monitoring the vacuum level in the brake assist system 3 while driving the vehicle at time t is illustrated graphically. Figure 5 The process shown is based on the second implementation presented above.

[0065] exist Figure 5 In the diagram, the first curve d shows the evolution of the vacuum level in the brake assist system 3, measured in mbar, over time t. The second curve p shows the actions of the control processes performed during time t, which vary with the vacuum level in the brake assist system 3. Finally, the third curve f shows the different braking operations F1, F2, F3, and F4 performed by the driver over time t.

[0066] At t=0, after the vacuum level is restored by the vacuum level measuring device, the comparison device compares the vacuum level with the first threshold NOK1. The measured vacuum level is greater than the first threshold NOK1, so the situation is not serious. The driver performs the first two braking maneuvers F1 and F2, and the brake assist system 3 loses vacuum. However, the vacuum level remains above the threshold NOK1, and no action is taken.

[0067] When the driver applies the brake F3, the control system's measuring device notices that the vacuum level in the brake assist system 3 is below the first threshold NOK1 but above the second threshold NOK2. Therefore, the process executes steps E3 and E4, as described above, to deactivate EGR 8 and close the throttle body 16, because this is the critical condition for the first level INF1. As can be seen from curve p, the first level INF1 process is executed at tF3_f, corresponding to the driver releasing the brake pedal. The first level INF1 control process continues until tF3_ok (i.e., the time required for the vacuum level in the brake assist system 3 to rise above the OK threshold). The first INF1 level typically lasts for several seconds.

[0068] The OK threshold is a safety threshold that allows vacuum measuring devices to quickly assess whether the vacuum level might become critical after the next braking operation and to see if the vacuum level has returned to normal after the process has been performed. For example, the OK threshold is equal to 500 mbar.

[0069] The driver finally applies F4 braking at time tF4_d. F4 braking is particularly forceful and corresponds to emergency braking. Just before tF4_d, the vacuum in brake assist system 3 suddenly drops during F4 braking and falls below the second threshold NOK2. Therefore, the process executes the second level INF2, which corresponds to the implementation steps E3, E4, and E5 as described above.

[0070] On curve p, the second level INF2 of the process is executed at tF4_f, corresponding to the driver releasing the brake pedal. The second level INF2 of the control process continues until tF4_ok (i.e., the time required for the vacuum level in brake assist system 3 to rise until it exceeds the OK threshold). Similar to the first level INF1, the second level INF2 typically lasts for several seconds.

[0071] Alternatively, the second level of the process, INF2, is performed at tF4_d, corresponding to the moment the driver depresses the brake pedal, because the fourth braking operation, F4, is an emergency braking operation, and the driver's sensation during the application of the brakes is considered less important than the urgent need to slow the vehicle down.

[0072] The method for monitoring the vacuum level in the brake assist system 3 can also be based on... Figure 6 The third method shown is implemented within time t.

[0073] According to this implementation, the method includes a sixth step E6 of modifying the variable valve lift of engine 1. Similar to step E5 of modifying the variable valve timing of engine 1, step E6 of modifying the valve lift allows the vacuum dominating in the intake distributor 17 to be increased by modifying the valve opening degree.

Claims

1. A method for monitoring an internal combustion engine (1) of a motor vehicle equipped with an exhaust gas recirculation circuit (8), the method being used to monitor the vacuum level in a brake assist system (3), the vacuum level of the brake assist system (3) depending on the dominant vacuum in an air intake distributor (17), characterized in that, The method includes at least the following steps: - Measure the vacuum level in the brake assist system (3) described in (E1); - Compare the measured vacuum level with at least one first threshold (NOK1) (E2); and - Deactivate (E3) exhaust recirculation to increase the vacuum in the air intake distributor (17).

2. The method according to claim 1, comprising the step of closing (E4) the throttle valve (16) of the air intake distributor (17) to maintain a constant flow rate of fresh air into the air intake distributor (17).

3. The method according to any one of claims 1 and 2, wherein, In the comparison step (E2), the measured vacuum level is compared with a second threshold (NOK2) that is substantially lower than the first threshold (NOK1).

4. The method according to any one of claims 1 to 3, comprising the step of modifying the variable valve timing of the engine (1) (E5).

5. The method according to any one of claims 1 to 4, comprising the step of modifying the variable valve lift of the engine (1) (E6).

6. A system for monitoring an internal combustion engine (1) of a motor vehicle equipped with an exhaust gas recirculation circuit (8), the system for monitoring the vacuum level in a brake assist system (3), the vacuum level of the brake assist system (3) depending on the dominant vacuum in an air intake distributor (17), characterized in that, The system includes 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 (NOK1), and means for adjusting the valve (9) of the exhaust recirculation loop (8) to increase the vacuum in the intake distributor (17).

7. The system according to claim 6, wherein, The measuring device includes a vacuum level sensor in the braking assist system (3).

8. The system according to any one of claims 6 and 7, wherein, The measuring device includes a model for predicting the vacuum level in the braking assist system (3).

9. The system according to any one of claims 6 to 8, wherein, The comparison device compares the measured vacuum level with a second threshold (NOK2) that is substantially below the first threshold (NOK1).

10. A motor vehicle comprising a control system according to any one of claims 6 to 9.

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