Method for controlling an air pump located in a secondary air circuit

Abstract

The present invention relates to a method for controlling an air pump disposed in a secondary air circuit extending between a connection on an air intake line and a connection on an exhaust line of a heat engine. The method comprises the steps of determining an initial flow rate setpoint (Dc) and pressure ratio (Crp) between the upstream and downstream sides of the air pump. It is characterized in that it comprises determining a corrected flow rate setpoint (Dc') and pressure ratio (Crp'), determining an initial control signal (Scp) of the air pump from characteristic curves (Ccp), determining a corrected control signal (Scp') from the initial control signal (Scp) of the air pump, and controlling the air pump using the corrected control signal (Scp'). Figure 6

Description

Title of the invention: Method for controlling an air pump arranged in a secondary air circuit

[0001] The present invention relates to the field of pollution control of internal combustion engines. More particularly, the invention relates to a method for controlling an air pump arranged in a secondary air circuit of a heat engine.

[0002] In motor vehicles equipped with an internal combustion engine, the treatment of exhaust gases is a major issue. The purpose of this treatment is to reduce the emissions of various pollutants resulting from the operation of the internal combustion engine.

[0003] It is known, for example from document FR3122215A1, an internal combustion engine equipped with an exhaust line comprising a catalyst, this catalyst incorporating an electric heating device. This heating device aims to allow the operating temperature of the catalyst to be reached quickly before starting the internal combustion engine. A device for injecting secondary air into the exhaust line of the internal combustion engine is also described. This secondary air injection circuit extends between a tapping on the air intake line of the engine and a tapping on the exhaust line of this engine. This secondary air injection circuit comprises an air pump and means for controlling the air flow. An air flow is usually injected before starting the internal combustion engine of the vehicle in order to raise the temperature of the catalyst.

[0004] However, when sending a flow control instruction to the air pump, a delay can be observed between the moment of the command and the moment when the air flow is actually established in the circuit. Thus, the response of the system to a flow instruction is therefore generally delayed due to the actual physical behavior of the pump, which penalizes the activation time and therefore ultimately the starting of the internal combustion engine.

[0005] There is therefore a need to improve the response of the air injection system when a flow rate instruction is issued.

[0006] To achieve this objective, the invention provides a method for controlling an air pump arranged in a secondary air circuit extending between a tapping on an air intake line and a tapping on an exhaust line of a heat engine, the method comprising the steps of: -determining an initial flow rate setpoint, -determining an initial pressure ratio setpoint between the upstream pressure and the pressure downstream of the air pump, characterized in that it further comprises the steps of: -determining a corrected flow rate setpoint from the initial flow rate setpoint, -determining a corrected pressure ratio setpoint between the pressure upstream and the pressure downstream of the air pump from the initial pressure ratio setpoint, -determination of an initial control signal for the air pump from characteristic curves of this pump which establish this initial control signal as a function of the corrected flow rate setpoint and the corrected pressure ratio setpoint, -determination of a corrected control signal from the initial control signal of the air pump, -control the air pump using the corrected control signal.

[0007] The technical effect is to make the response of the air pump faster and more precise, the requested air flow is available as soon as possible. The invention is particularly useful during the start-up phases of the air pump. It is used in particular to compensate for the time required to start the pump.

[0008] Various additional features may be provided, alone or in combination:

[0009] In one embodiment, the step of determining the corrected flow rate setpoint comprises a step of temporarily increasing the value of the initial flow rate setpoint from the start of this initial setpoint.

[0010] In one embodiment, this temporary increase in the initial flow rate setpoint value is maintained for a determined holding time.

[0011] In one embodiment, this step of temporarily increasing the value of the initial flow rate setpoint is followed by a step of progressive return to the value of the initial flow rate setpoint.

[0012] In one embodiment, the step of determining the corrected flow rate setpoint comprises a step of determining the air flow rate in the secondary air circuit and a step of determining a correction value for the initial flow rate setpoint based on the difference between the value of the initial flow rate setpoint and the determined air flow rate.

[0013] In one embodiment, the step of determining the corrected pressure ratio setpoint comprises: - a step of determining the effective pressure ratio between the pressure upstream and the pressure downstream of the air pump, - a step of applying a fixed pressure ratio determined for a determined duration followed by a step of convergence towards the effective pressure ratio.

[0014] In one embodiment, the step of determining the corrected flow pressure ratio setpoint comprises: - a step of determining the effective pressure ratio between the pressure upstream and the pressure downstream of the air pump, - a step of determining a correction value for the initial pressure ratio setpoint based on the difference between the value of the initial pressure ratio setpoint and the actual pressure ratio.

[0015] The invention also relates to a motorization assembly comprising a heat engine connected to an intake line and to an exhaust line, a secondary air circuit extending between a tapping on the air intake line and a tapping on the exhaust line, characterized in that the assembly comprises a computer comprising the means of acquisition, processing by software instructions stored in a memory as well as the control means required for implementing a method according to any one of the variants previously described.

[0016] The invention also relates to a vehicle comprising such a motorization assembly.

[0017] Other features and advantages will appear on reading the following description of a particular, non-limiting embodiment of the invention, given with reference to the figures in which:

[0018] [Fig.l]: this figure schematically represents a heat engine equipped with an exhaust line comprising an electrically heated catalyst and a secondary air injection line comprising a controlled air pump according to the invention.

[0019] [Fig.2]: this figure represents a method of controlling the air pump by using its characteristic curve according to the prior art.

[0020] [Fig.3]: this figure illustrates an example of obtaining the corrected flow rate setpoint according to the invention.

[0021] [Fig.4]: this figure illustrates an example of obtaining the corrected pressure ratio setpoint according to the invention.

[0022] [Fig.5]: this figure illustrates another example of obtaining the corrected pressure ratio setpoint according to the invention.

[0023] [Fig.6]: this figure represents the method of controlling the air pump using its characteristic curve according to the invention.

[0024] [Fig.l] schematically illustrates a motorization assembly 1. This assembly 1 comprises a thermal engine 2 with internal combustion with spark ignition or compression ignition. This thermal engine 2 comprises an engine block with at least one cylinder, for example here four cylinders, for combustion. Such a thermal engine 2 can equip a vehicle, for example a motor vehicle to enable it to move.

[0025] The thermal engine 2 is connected, for example via an intake manifold, to an air intake line 3 intended to direct the air necessary for its operation towards the thermal engine 2. The thermal engine 2 is also connected, for example via an exhaust manifold, to an exhaust line 4 for evacuating the combustion gases produced during the operation of the engine.

[0026] In this embodiment, the air intake line 3 is equipped with an air filter 3a for filtering the air admitted into the thermal engine 2.

[0027] The engine assembly 1 is equipped with a turbocharger, with a compressor 3b arranged in the air intake line 3 and a turbine 4a arranged in the exhaust line 4 for expanding the exhaust gases and driving the compressor 3b. The turbine 4a and the compressor 3b are connected by a drive shaft (not shown).

[0028] The air intake line 3 is also equipped with a valve 3c for metering the quantity of air admitted. This valve is conventionally referred to as a throttle body.

[0029] In this intake line 3, the air filtered by the air filter 3a then passes through the compressor 3b then through the throttle body 3c to then be admitted into the thermal engine 2.

[0030] In this embodiment, the exhaust line 4 is equipped, in addition to the turbine 4a, with a catalyst 4b. This catalyst comprises a heating element 4c. For better control of the heating power, the heating element 4c may be an electric heating grid. The exhaust line 4 may be equipped with another pollution control member 4d, such as another catalyst or a particulate filter.

[0031] In order to be able to inject air into the exhaust line 4, a secondary air circuit 5 is provided extending between a tapping on the air intake line 3 and a tapping on the exhaust line 4.

[0032] In this embodiment, the tapping of the secondary air circuit 5 is located downstream of the air filter 3a, but before the compressor 3b, so that the secondary air circuit 5 is supplied with filtered air.

[0033] This secondary air circuit 5 comprises an air pump 5f intended to draw air from the air intake line 2 and blow it into the exhaust line 4. For more flexible control, this air pump 5f can be an electric air pump. A pipe 5c connects the tapping on the air intake line 3 to the air pump 5f.

[0034] This secondary air circuit 5 may comprise an air valve 5d. This air valve 5d is positioned on the secondary air circuit 5 downstream of the air pump 5d. A pipe connects the air pump 5f to the air valve 5d of the secondary circuit.

[0035] In this embodiment, the secondary air circuit 5 is also equipped with a pressure and temperature sensor 5e of the air circulating in this circuit, arranged between the valve 5d and the air pump 5f.

[0036] The tapping of the secondary air circuit 5 to the exhaust line 4 is located upstream of the catalyst 4b equipped with the heating element 4c, but downstream of the turbine 4a.

[0037] The creation of an air flow in the secondary air circuit 5 makes it possible to transport the calories supplied by the heating element 4c to the catalyst 4b, so that the latter quickly reaches its effective temperature.

[0038] A control module 6 is also provided, for example an electronic computer. The control module 6 is configured to control the operation of the air pump 5f and the air valve 5d of the secondary circuit, and that of the heating element 4c. The control module 6 is also configured to measure the temperature and the air pressure via the sensor 5e of the secondary circuit.

[0039] This control module 6 comprises the means of acquisition, processing by software instructions stored in a memory as well as the control means required for implementing the method of controlling the air pump 5f detailed later.

[0040] As illustrated by [Fig.2], it is conventional to control the air pump 5f using characteristic curves of the pump Cep, which determine an initial signal Sep for controlling the air pump 5f of the secondary circuit from an initial flow rate setpoint De and an initial upstream pressure / downstream pressure ratio setpoint, Crp. This control signal can be a conventional RCO type control signal which controls the current intensity to be supplied to the pump 5f.

[0041] In order to reduce the response time of the air pump 5f, it is planned to carry out a correction of the set flow rate De (block Corrl in [Fig.6]). As illustrated in [Fig.3], the principle consists of starting from the start of the initial flow rate set point of the air pump 5f to temporarily increase the value of the initial flow rate set point De, by a determined factor fl. This correction makes it possible in a way to boost the set flow rate by temporarily requesting a corrected set flow rate De' higher than the initially requested flow rate set point De. By over-requesting the air pump 5f, the strategy seeks to reach the initial set flow rate De more quickly and thus to minimize the response time of the latter.

[0042] It is possible to trigger this correction, for example, when the gradient of the flow rate setpoint De is positive, which reflects a request for an increase in the flow rate. When this correction is triggered, it is possible, for example, to apply an increase factor fl to the flow rate setpoint De, to obtain the corrected setpoint flow rate De'. This increase factor fl may be, for example, +30%. It is also possible to maintain this increase factor fl for a determined duration dl. This maintenance duration dl may be between 1 and 2 seconds, for example 1.5s. It is also possible to follow this maintenance duration dl by a progressive decrease in the factor fl to +0% to return gradually to a corrected flow rate setpoint De' equal to the initial requested flow rate setpoint De. This decrease time d2 can be between 2 and 3 seconds, for example 2.5 seconds. These different parameters fl, dl, d2, can depend on the sizing of the air pump 5f and can also be a function of the requested flow rate setpoint De.

[0043] Still with the aim of reducing the response time of the air pump 5f, the strategy also provides for using a corrected setpoint Crp' of the upstream pressure / downstream pressure ratio of the air pump 5f obtained from the initial setpoint Crp of the upstream pressure / downstream pressure ratio of the air pump 5f (Corrl block in [Fig.6]).

[0044] Indeed, as illustrated in [Fig.4], during the start-up of the air pump 5f, the pressure ratio resulting from Rpm measurements starts from 1, because before the activation of the air pump 5f, the pressures at the terminals of the air pump are in equilibrium and substantially equal, and evolve according to the activation speed of the pump, to reach a stable value when the air pump 5f delivers its set flow rate. There is therefore a notion of loop between the control which depends on the pressure ratio and the pressure ratio which depends on the response of the pump and therefore on its control.

[0045] Thus, in order to temporarily free oneself from this loop which slows down the response of the air pump 5f, it is planned to apply at the start of the control of the air pump 5f, a corrected pressure ratio setpoint Crp', starting with a first part at a fixed value, Rpf, then a second part at the value of the actual measured pressure ratio, Rpm.

[0046] [Fig. 4] shows a first example in which at the start of the control of the pump 5f, the pressure ratio setpoint Crp' has a first part in which it first takes the fixed pressure ratio value Rpf. The value of this fixed pressure ratio, Rpf, is maintained for a determined holding time d3. During this holding time d3, the value of the fixed pressure ratio, Rpf, is greater than the value of the measured upstream pressure / downstream pressure ratio, Rpm. This holding time d3 is in this first example followed by a determined transition time d4 during which the pressure ratio setpoint, Crp', converges towards the value of the pressure ratio resulting from the pressure measurements, Rpm.

[0047] [Fig. 5] shows a second example in which at the start of the control of the pump 5f, the pressure ratio setpoint Crp' first takes the fixed pressure ratio value Rpf. The value of this fixed pressure ratio, Rpf, is maintained for a holding time d3'. During this holding time d3', the value of the fixed pressure ratio, Rpf, is greater than the value of the measured upstream pressure / downstream pressure ratio, Rpm.

[0048] In this second example, as soon as the value of the measured upstream pressure / downstream pressure ratio, Rpm, is considered close to the value of the fixed pressure ratio, Rpf, the holding time d3' is followed by a determined transition time d4' during which the pressure ratio setpoint, Crp', converges towards the pressure ratio value from the pressure measurements, Rpm.

[0049] In these two examples, the different parameters Rpf, d3, d3', d4, d4', can depend on the sizing of the air pump 5f and can also be a function of the requested flow rate setpoint De.

[0050] Thus, as illustrated in [Fig.6], from the corrected flow rate setpoint De' and the corrected pressure ratio setpoint Crp', the initial control signal Sep of the air pump 5f is determined from characteristic curves Cep of this pump which establish this initial control signal Sep as a function of the flow rate of the pressure ratio at the terminals of the air pump.

[0051] Still with the aim of reducing the response time of the air pump 5f, it is planned to correct the initial control signal by comparing the flow rate setpoint with a measurement of the flow rate actually provided by the air pump 5f. This strategy thus makes it possible to adjust the control according to the actual feedback from the system. This makes it possible to compensate for physical drifts of the pump, such as manufacturing dispersions, wear, fouling, etc., but also helps to reduce the response time of the pump to establishing a set flow rate in the circuit. The actual feedback required for this strategy can be a direct measurement of the flow rate Dm in the circuit if the latter is equipped with a measuring system such as a flow meter for example. But this feedback can also be an estimate of the flow rate achieved from the known Barré St Venant equation:

[0052] pQ J p \ Q = s pii

[0053] With:

[0054] S: the passage section uncovered by the valve. It is a function of the position of the valve 5d and its manufacturing characteristics which establish the relationship between the position and the section of the valve 5d. PO, the pressure upstream of valve 5d, i.e. that measured by sensor 5e. T0, the temperature upstream of valve 5d, i.e. that measured by sensor 5e. Cfe, a known function which is based on the upstream / downstream pressure ratio at the valve to determine a coefficient of pressure loss of the gases passing through the valve. P, the pressure downstream of the valve, which can be considered very close to atmospheric pressure.

[0055] As illustrated in [Fig.6], by comparing this estimate or measurement of the effective flow rate Dm with respect to the initial flow rate setpoint De, at block Corr3, the strategy will calculate and apply a corrective factor f2 to the initial command Sep of the pump at air 5f and thus determine the corrected control signal Sep' which will be applied to control the air pump 5f. This correction factor f2 can be calculated from a known control principle such as PID (Proportional-Integrator-Derivative).

[0056] The invention is not limited to the embodiment described.

[0057] In one embodiment, the corrected flow rate setpoint De' can be determined by applying a correction value to the initial flow rate setpoint De based on the difference between the value of the initial flow rate setpoint De and the air flow rate Dm determined in the secondary air circuit 5. The correction value can be obtained by PID (Proportional, Integral, Derivative) regulation, i.e.: De' = De + PID(Dc-Dm), the term PID(Dc-Dm) designating the correction value based on the PID regulation principle.

[0058] In one embodiment, the corrected pressure ratio setpoint Crp' can be determined by applying a correction value to the initial setpoint Crp based on the difference between the value of the initial pressure ratio setpoint Crp and the effective pressure ratio Rpm at the terminals of the air pump 5f of the secondary air circuit 5. This correction can be obtained by the formula: Crp' = Crp + (Crp - Rpm)

[0059] The proposed invention makes it possible to supplement a known strategy for controlling the pump by using its characteristic curve. The solution thus makes it possible to considerably improve the response time and the precision in terms of establishing the flow rate when a setpoint is issued.

Claims

Claims

1. Method for controlling an air pump (5f) arranged in a secondary air circuit (5) extending between a tapping on an air intake line (3) and a tapping on an exhaust line (4) of a heat engine (2), the method comprising the steps of: - determining an initial flow rate setpoint (De), - determining an initial pressure ratio setpoint (Crp) between the pressure upstream and the pressure downstream of the air pump (5f), characterized in that it further comprises the steps of: - determining a corrected flow rate setpoint (De') from the initial flow rate setpoint (De), - determining a corrected pressure ratio setpoint (Crp') between the pressure upstream and the pressure downstream of the air pump (5f) from the initial pressure ratio setpoint (Crp),-determination of an initial control signal (Sep) of the air pump (5f) from characteristic curves (Cep) of this pump which establish this initial control signal (Sep) as a function of the corrected flow rate setpoint (De') and the corrected pressure ratio setpoint (Crp'), -determination of a corrected control signal (Sep') from the initial control signal (Sep) of the air pump (5f), -controlling the air pump (5f) using the corrected control signal (Sep').,

2. Method according to claim 1, characterized in that the step of determining the corrected flow rate setpoint (De') comprises a step of temporarily increasing the value of the initial flow rate setpoint (De) from the start of this initial setpoint.

3. Method according to claim 2, characterized in that the temporary increase in the initial flow rate setpoint value (De) is maintained for a determined holding time (dl).

4. Method according to claim 2 or claim 3, characterized in that the step of temporarily increasing the value of the initial flow rate setpoint (De) is followed by a step of progressive return to the value of the initial flow rate setpoint (De).

5. Method according to claim 1, characterized in that the step of determining the corrected flow rate setpoint (De') comprises a step of determining the air flow rate (Dm) in the secondary air circuit (5) and a step of determining a correction value for the initial flow rate setpoint (De) based on the difference between the value of the initial flow rate setpoint (De) and the determined air flow rate (Dm).

6. Method according to any one of the preceding claims, characterized in that the step of determining the corrected pressure ratio setpoint (Crp') comprises: - a step of determining the effective pressure ratio (Rpm) between the pressure upstream and the pressure downstream of the air pump (5f), - a step of applying a determined fixed pressure ratio (Rpf) for a determined duration (d3, d3') followed by a step of convergence towards the effective pressure ratio (Rpm).

7. Method according to one of claims 1 to 6, characterized in that the step of determining the corrected flow rate pressure ratio setpoint (Crp') comprises: - a step of determining the effective pressure ratio (Rpm) between the pressure upstream and the pressure downstream of the air pump (5f), - a step of determining a correction value for the initial pressure ratio setpoint (Crp) based on the difference between the value of the initial pressure ratio setpoint (Crp) and the effective pressure ratio (Rpm).

8. Motorization assembly (1) comprising a heat engine (2) connected to an intake line (3) and to an exhaust line (4), a secondary air circuit (5) extending between a tapping on the air intake line (3) and a tapping on the exhaust line (4), characterized in that the assembly comprises a computer (6) comprising the means of acquisition, processing by software instructions stored in a memory as well as the control means required for implementing a method according to any one of the preceding claims.

9. Vehicle comprising a motorization assembly (1) according to the preceding claim.

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