METHOD FOR SETTING A POSITION SERVO CONTROL OF AN ACTUATOR, SUCH AS A MOTOR VEHICLE ACTUATOR

Description

[0001] The invention relates generally to the field of actuator position control. More particularly, the invention relates to a computer-implemented method for adjusting the position control of an actuator, such as an actuator in a motor vehicle.

[0002] Position-controlled actuators are widely used in internal combustion engine vehicles to control their powertrain. Precise control of these actuators contributes to optimizing powertrain operation, particularly in terms of efficiency, driving pleasure, and compliance with emissions standards. Examples of actuators include those found in the air intake loop of an internal combustion engine, such as those in the exhaust gas recirculation (EGR) valve, the throttle body, the wastegate of a turbocharger, and others.

[0003] The actuators used in vehicles are manufactured in large quantities and often have relatively varied characteristics. Furthermore, they are subject to significant dry friction, fouling, temperature variations, and aerodynamic forces, making their control delicate and complex.

[0004] In the state of the art, a method known as the "tuner" approach, using trial and error, is employed to adjust the position control servo controller until the desired system response is achieved. This method requires numerous physical tests to obtain the desired performance, as well as significant expertise and practical experience. However, it does not guarantee the robustness of the performance obtained. Further validation tests with dispersed systems and varying external conditions, such as altitude and temperature, are necessary to ensure performance robustness.

[0005] Actuators are typically controlled by a computer, using control techniques derived from advanced automation, and employing modern control algorithms such as state feedback, polynomial, adaptive, or others. Implementing these advanced control algorithms usually requires a dynamic mathematical model of the system to be controlled. A common approach used by those skilled in the art is to construct a dynamic "knowledge" model by directly applying the laws of physics. This approach demands a thorough understanding of the system's components. Furthermore, it requires numerous physical tests to fine-tune the model's parameters and accurately represent the response of the actual system.Another less expensive approach is to identify a mathematical model of "behavior" based solely on knowledge of the inputs and outputs of the system to be controlled.

[0006] Identifying a dynamic model for air intake loop actuators presents inherent complexities such as a divergent open-loop response, significant dry friction, and a pure delay. In open loop, for a constant input, the actuator's divergent behavior results in an output that continuously increases until it reaches mechanical limits in the system. Dry friction prevents the mathematical model identification algorithm from converging to the correct parameters. Identifying the pure delay is essential in position control system design, as it significantly improves both performance and robustness.

[0007] Document EP3341604A1 discloses a system for controlling an actuator to a position setpoint, in which a pure delay compensator is integrated.

[0008] The invention aims to provide a solution to the problem described above of the state of the art, particularly for position-controlled actuators in the air intake loop of a thermal vehicle, by providing a computer-implemented method for adjusting the position control of an actuator, through easy and automatable identification of a behavioral dynamic model of the actuator of the second-order transfer function type with a pure delay.

[0009] According to a first aspect, the invention relates to a computer-implemented method for adjusting a position control device for an actuator, comprising a phase of identifying a mathematical model of the actuator in the form of a first second-order transfer function with a pure delay d, and a phase of calculating a controller for the position control device using the identified mathematical model. According to the invention, the identification phase comprises the steps of a) controlling the actuator in a closed-loop system with a step input and by applying an anti-friction vibration signal, the closed-loop system comprising a simple proportional controller and being mathematically modeled in the form of a second second-order transfer function with the pure delay d;b) determine static gain parameters K, damping Π, natural angular frequency Ω n and pure delay d of the second transfer function from measurements on a position signal output from the closed-loop system delivered by it in response to the control with the step setpoint and the anti-friction vibration signal applied in step a); c) identify the first transfer function with the pure delay d measured in step b) and static gain parameters k, damping ξ, and natural angular frequency ω n calculated algebraically from the static gain parameters K, damping Π and natural angular frequency Ω n determined in step b).;

[0010] According to a particular characteristic, the mathematical modeling of the closed-loop system is obtained using a second-order Taylor series approximation.

[0011] According to another particular feature, the identification phase includes a preliminary step of adjusting the anti-friction vibration signal, including an open-loop measurement of actuator hysteresis due to dry friction.

[0012] According to yet another particular characteristic, the preliminary adjustment step includes an adjustment of the anti-friction vibration signal with an amplitude at least equal to a hysteresis width and a high frequency not disturbing the operation of the actuator.

[0013] The invention also relates to a computer comprising a memory storing program instructions for implementing the method as briefly described above. In one particular embodiment, the computer is an engine control unit for a motor vehicle.

[0014] The invention also relates to an assembly comprising a heat engine and a control computer, the heat engine incorporating at least one position-controlled actuator in its air intake loop and the control computer being a computer as indicated above.

[0015] The invention also relates to a vehicle comprising an assembly as indicated above.

[0016] Other advantages and features of the present invention will become more apparent upon reading the detailed description below of a particular embodiment of the invention, with reference to the accompanying drawings, in which: [ Fig.1 ] There Fig.1 is a block diagram illustrating the implementation of the method according to the invention in a vehicle internal combustion engine. Fig.2 ] There Fig.2 is a general flowchart of different steps included in a particular embodiment of the process according to the invention. Fig.3 ] There Fig.3 is a schematic diagram relating to the measurement of hysteresis due to dry friction in a position-controlled actuator. Fig.4 ] There Fig.4 is a curve showing hysteresis due to dry friction in a position actuator. Fig.5 ] There Fig.5 is a block diagram of a closed-loop system used in the method of the invention for identifying a mathematical model of a position-controlled actuator. Fig.6 ] There Fig.6 shows mathematical equations applied in the process of the invention. Fig.7 ] There Fig.7 shows waveforms of a closed-loop control system of the Fig.5 by a step input, with an anti-friction vibration signal, and an output position signal delivered in response by the closed-loop system. Fig.8 ] There Fig.8 shows a magnification of the waveform of the position signal coming out of the Fig.7 and measurements taken on this outgoing position signal for the identification of a mathematical model of the actuator.

[0017] With reference to the Fig.1 In the particular embodiment described here, the method according to the invention is implemented in a vehicle control computer (CCM), such as an engine control computer, responsible for controlling a vehicle's internal combustion engine (MT).

[0018] As shown schematically in the Fig.1 The MT internal combustion engine includes an air intake loop with a BP throttle body, a TC turbocharger and an EGR valve with actuators controlled in position by digital servo systems.

[0019] An embedded software system (SLE) is contained in a MEM memory of the CCM computer and its function is the general control of the MT internal combustion engine. Data communications for the control of the MT internal combustion engine, between the embedded software system (SLE) and various actuators and sensors of the MT internal combustion engine, are typically carried out through a data communication network (not shown) of the vehicle, for example a CAN bus.

[0020] The SLE embedded software system comprises various software modules, including an MD_ABP software module, shown as an example in the Fig.1 implementing a digital servo system dedicated to position control of the throttle body actuator. According to the invention, the embedded software system SLE also includes an MD_R software module cooperating with the MD_ABP digital servo system. The MD_R software module is responsible for implementing the method according to the invention by executing program code instructions via a processor (not shown) in the CCM computer.

[0021] The MD_ABP digital servo device is configurable in several modes, under the control of the MD_R software module responsible for implementing the process of the invention, namely a functional configuration and adjustment configurations.

[0022] To the Fig.1 The MD_ABP digital control device is shown schematically in a closed-loop functional configuration. In this functional configuration, the mathematical, dynamic, and behavioral model of the throttle body position actuator (PB) was previously identified, as described below, using the method of the invention. Knowledge of the PB actuator model, represented by the transfer function G(s) where s is the Laplace operator, allowed for the definition of a controller C(s), typically of the PID (Proportional-Integral-Derivative) type. The controller C(s), once the transfer function G(s) has been identified, is defined using calculation methods known to those skilled in the art, which will not be described here. Typically, a pre-command function P_Cde is also integrated into the MD_ABP digital control device.In addition, an anti-friction function (not shown) can be integrated into the MD_ABP digital control device, in the form of a vibration signal of predefined frequency and amplitude.

[0023] As seen at the Fig.1 The MD_ABP digital control device receives as input a position command, denoted R(s) in Laplace space, and outputs a position command, denoted U(s) and U', respectively in Laplace space and time space. In feedback, the MD_ABP digital control device also receives as input a position feedback signal Y from the throttle body BP, denoted Y(s) in Laplace space, representing the actual position of the throttle body in the BP following the position command R(s).

[0024] As seen at the Fig.1 , the transfer function G(s) of the actuator of the BP housing, to be identified by the method of the invention, is a second-order transfer function with a pure delay, in which the parameters k, ξ, ω n and d represent respectively the static gain, the damping, the natural frequency and the pure delay of the aforementioned open-loop actuator.

[0025] Now also referring to Figs.2 à 8 , a particular embodiment of the process of the invention is described in detail, in the context of the adjustment of the MD_ABP digital servo device ensuring the position control of the actuator of the BP throttle body.

[0026] As seen at the Fig.2 The method according to the invention essentially comprises three main steps S1 to S3, the execution of which is managed by the MD_R software module. The adjustment process of the MD_ABP digital servo device is typically initiated by a human operator, responsible for fine-tuning the device, who interacts with the MD_R software module via a human-machine interface such as an ORD computer, or a test bench, hosting a dedicated software application.

[0027] Steps S1 to S3 correspond respectively to A) a first open-loop test of the BP housing actuator, with the MD_ABP digital servo device in a first setting configuration, for the definition of an anti-friction vibration signal used in the process of the invention, B) a second closed-loop test of the BP housing actuator, with the MD_ABP digital servo device in a second setting configuration, to identify the parameters k, ξ, ω n and d from measurements on a step response with anti-friction signal and algebraic calculations, and C) a third step of defining the functional configuration of the MD_ABP digital servo device, knowing the parameters k, ξ, ω n and d.

[0028] With particular reference to Figs.3 And 4In step S1, the BP housing actuator is directly controlled in open loop, under the control of the MD_R software module's processing, by a dual-slope setpoint Rdp delivered by the MD_ABP digital servo device in the first adjustment configuration mentioned above. The effective position response Ydp of the BP housing actuator, for the issued dual-slope setpoint Rdp, is read by the MD_R software module process.

[0029] The dual-slope setpoint Rdp and the effective position response Ydp of the BP housing actuator are analyzed by the MD_R software module process to identify a relationship, in the form of a hysteresis, representing the dry friction opposing the fluid motion of the BP housing actuator. The width of this hysteresis determines the required amplitude of the anti-friction vibration signal to overcome the dry friction. The frequency of the anti-friction vibration signal to be applied is typically extracted from a knowledge base; depending on the type of actuator, this frequency must be high enough not to disrupt the actuator's operation.

[0030] An example of the resulting hysteresis curve, Hdp, is shown at the Fig.4 The percentage amplitudes (%) of the double-slope setpoint Rdp and the effective position response Ydp are shown on the x and y axes, respectively, of the hysteresis curve Hdp. The hysteresis width LH is approximately 20% of the setpoint amplitude Rdp.

[0031] As seen at the Fig.2 , step S2 essentially comprises three sub-steps S20 to S22.

[0032] In substep S20, the MD_R software module process commands the MD_ABP digital servo device to be placed in the second aforementioned setting configuration, designated R_ABP at the Fig.5 .

[0033] In this control configuration, the BP housing actuator is controlled in closed loop with a proportional controller kp and the anti-friction vibration signal identified in step S1 and designated here as SAF. The closed-loop control with the proportional controller kp aims to address the divergent open-loop behavior of the BP housing actuator by forcing it to converge. The anti-friction vibration signal SAF is added to the position command Ue(s) applied to the BP housing actuator. The anti-friction vibration signal SAF counteracts the effect of dry friction, preventing the actuator from stopping in a position that does not correspond to the command, which would introduce an error in identifying the static gain of the transfer function G(s).

[0034] In this setting configuration of the Fig.5 The closed-loop system, formed by the BP housing actuator and the R_ABP device, has as its transfer function the function H(s) represented by equation E1 at the Fig.6 . In the transfer function H(s) = Ye(s) / Re(s), Re(s) and Ye(s) are respectively the input and output of the closed-loop system, namely, the position setpoint and the position response of the actuator to this setpoint, and the parameters k, ξ, ωn and d are, as above, the static gain, damping, natural frequency and pure delay to be identified of the open-loop actuator.

[0035] The transfer function H(s) remains a second-order function thanks to the use of a proportional controller kp. However, this transfer function H(s) is not rational due to the presence of the term e - ds< in the denominator of the function H(s). To perform algebraic calculations, it is necessary to eliminate the term e - ds< in the denominator of the function H(s) by replacing it with a rational function. In the invention, the choice is made to use the second-order Taylor series approximation, given by equation E2 in the Fig.6 to replace the term e -ds<. Comparative simulations, performed by the inventive entity and based on the Bode plot (magnitude and phase), between the original transfer function and the approximated transfer function, showed that the error due to this approximation is negligible in the bandwidth of the closed-loop system. The choice to approximate the term e -ds< by the second-order Taylor series allows the second order to be preserved for the approximated transfer function H(s), which would not be the case with the first-order Padé approximation commonly used for the term e -ds<.

[0036] The transfer function H(s) obtained with the Taylor series approximation is given by equation E3 at the Fig.6 This E3 equation is of the second order and includes static gain parameters K, damping Ϡ, natural angular frequency Ω n and pure delay d.

[0037] By term-by-term identification of equations E1 and E3 of the transfer function H(s), equations E4 are obtained. Fig.6 which link the parameters K, Π and Ω n to the parameters k, ξ and ω n to be identified. By inverting equations E4, equalities E5 are obtained. Fig.6 which give the parameters to be identified k, ξ and ω n as a function of the parameters K, Π, Ω n , d and kp .

[0038] Substeps S21 and S22 are respectively a substep of obtaining by measurement and calculation the parameters K, Π, Ω n and d and a substep of calculation of the parameters to be identified k, ξ and ω n as a function of the determined values ​​of K, Π, Ω n , d and the known gain kp.

[0039] With reference to the Fig.5 and to Figs.7 And 8, the parameters K, Π, Ω n and d are obtained in substep S21 from measurements taken on an outgoing position signal Ye (actuator position) delivered by the closed-loop system configured in substep S20 (R_ABP, Fig.5 ) in response to a step input Re applied to the input of the closed-loop system, with the anti-friction vibration signal SAF present in the actuator control Ue.

[0040] To the Fig.7 Examples of waveforms for the step input Re, the output position signal Ye, and the control signals Ue, SAF, and the corresponding averaged control signal Ue_moy are shown. The position P as a percentage (%) is indicated on the y-axis of these waveforms.

[0041] As seen at the Fig.8 On the output position signal Ye, the following are measured: the delay d, a peak time tp, a peak overshoot Dp, and an output delta Ds corresponding to an input delta De of the step setpoint Re. The peak time tp is the rise time of the output position signal Ye until it reaches the peak overshoot Dp measured relative to the output delta Ds. The delay d to be identified is therefore measured directly on the output position signal Ye. The parameters K, Ϡ, and Ωn are calculated using the known equalities (E6) shown in the Fig.8 , based on the values ​​of tp, Dp, Ds and De.

[0042] In substep S22, the parameters k, ξ and ωn of the transfer function G(s) are calculated using the E5 equalities shown in the Fig.6 , from the values ​​of K, Π, Ω n and d obtained in substep S21. At the end of substep S22, the different parameters of the transfer function G(s) are identified and the mathematical modeling of the actuator of the BP housing is therefore completed.

[0043] In step S3, the MD_R software module process calculates, using the transfer function G(s) identified in step S2, a suitable compensator C(s) for the MD_ABP digital servo device in its functional configuration shown in the Fig.1 The methods for calculating the correctors are known to those skilled in the art and are therefore not detailed here.

[0044] The method of the invention finds a primary, but not exclusive, application in the position control of actuators in gasoline and diesel internal combustion engines. The present invention improves the robustness and performance of actuator position control systems, as well as their implementation and validation times. The method of the invention is fully automatable, and the resulting adjustment process can be easily implemented by a relatively inexperienced person.

[0045] The invention is not limited to the particular embodiment described herein by way of example. A person skilled in the art may, depending on the applications of the invention, make various modifications and variations that fall within the scope of the invention's protection.

Claims

1. Computer-implemented method for adjusting a position control device (MD_ABP) of an actuator (BP) comprising an identification phase (S1, S2) of a mathematical model of said actuator (BP) in the form of a first transfer function (G(s)) of second order with a pure delay d and a phase of calculating (S3) a controller (C(s)) of said position control device (MD_ABP) using said mathematical model (G(s)), characterized in that said identification phase (S1, S2) comprises the steps of: a) controlling (S21) said actuator (BP) in a closed-loop system (R_ABP, BP) with a step setpoint (Re) and by applying an anti-friction vibratory signal (SAF), said closed-loop system (R_ABP, BP) comprising a simple proportional controller (kp) and being mathematically modeled in the form of a second second-order transfer function with said pure delay d (H(s)); b) determining (S22, E6) parameters of static gain K, damping Π, natural pulsation Ωn and pure delay d of said second transfer function (H(s)) from measurements (De, Ds, d, tp, Dp) on an output position signal (Ye) of said closed-loop system (R_ABP, BP) delivered by the latter in response to the control with said step setpoint (Re) and said anti-friction vibratory signal (SAF) applied in step a); and c) identifying (S23, E5) said first transfer function (G(s)) with said pure delay d measured in step b) and parameters of static gain k, damping ξ, and natural pulsation ωn calculated algebraically (E5) from the parameters of static gain K, damping Π and natural pulsation Ωn determined in step b).

2. Method according to claim 1, characterized in that the mathematical modeling of said closed-loop system (R_ABP, BP) is obtained using a second-order Taylor series approximation (E2).

3. Method according to claim 1 or 2, characterized in that said identification phase comprises a preliminary step of adjusting (S1) said anti-friction vibratory signal (SAF) comprising an open-loop measurement (Rdp, Ydp) of a hysteresis (Hdp) of said actuator (BP) due to dry friction.

4. Method according to claim 3, characterized in that said preliminary adjustment step (S1) comprises an adjustment of said anti-friction vibratory signal (SAF) with an amplitude at least equal to a width (LH) of said hysteresis (Hdp) and a high frequency not disturbing the operation of said actuator (BP).

5. Computer (CCM) comprising a memory (MEM) storing program instructions (MD_R) for implementing the method according to any one of claims 1 to 4.

6. Computer according to claim 5, characterized in that said computer is an engine control computer (CCM) of a vehicle.

7. Assembly comprising an internal combustion engine (MT) and a control computer (CCM), said internal combustion engine (MT) integrating at least one actuator (BP, EGR, TC) controlled in position in its air intake loop, characterized in that said control computer is a computer (CCM) according to claim 5 or 6.

8. Vehicle characterized in that it comprises an assembly (MT, CCM) according to claim 7.