BR112020021988A2 - speed control method for an internal combustion engine - Google Patents

Abstract

A control method for an internal combustion engine is described, carried out by means of feedback control of the engine speed, based on an error (Err) of said engine speed, calculated between a reference value ( Ref) and a measured value (Vel) of the speed, with said control comprising a sum (S2) of a proportional contribution (P) and an integral contribution (I); the method comprises a step of adding a derivative contribution (D) only when a first sign of the aforementioned error and a second sign of a derivative of the motor rotation are mutually consistent.

Description

SPEED CONTROL METHOD FOR A COMBUSTION ENGINE INTERNAL CROSS REFERENCE WITH RELATED PATENT APPLICATIONS

[001] This patent application claims the priority of Italian patent application No. 102018000004932 filed on 04/27/2018, the entire content of which is incorporated herein by reference.

TECHNICAL FIELD OF THE INVENTION

[002] The present invention relates to the field of control methods to control the point of operation of internal combustion engines.

STATE OF ART

[003] It is known that the accelerator pedal allows the driver to cause a variation in the rotation speed of the internal combustion engine.

[004] Evidently, this is a consequence of a variation in the torque distributed by the internal combustion engine.

[005] The accelerator pedal can therefore be related to the point of operation of the internal combustion engine, that is, the speed / torque of the engine, representing, with a relative inclination of the said pedal, a required torque value or a desired speed the engine.

[006] The speed and torque of the motor are evidently interrelated parameters; however, speed control implies very rapid responses from the internal combustion engine.

[007] The speed control in the internal combustion engine is particularly delicate due to the intrinsic delay in the engine response, due to several factors, including the capacitive effect of the intake manifold, which presents a slow response.

[008] During a gear change or a maneuver, or the sudden insertion of a load, carried out by a pump or a vehicle compressor, or during a sudden variation in the inclination of the road, maximum speed and accuracy of response are required from the speed control.

[009] A speed control method is based on the calculation of a speed error in relation to a reference value, consequently calculating the necessary control variable (torque) of the controlled system, in order to vary the motor response internal combustion to reduce or cancel this error. Obviously, this is a feedback control.

[010] A typical controller used in the known state of the art to control motor speed is of the PI (proportional, integral) type. In other words, the error is corrected, between a reference value and the measured or estimated value of the system output, by means of a proportional controller and an integral controller that, based on the referred error, generate respective control signals. The sum of the respective outputs, that is, the respective control signals generated, is applied to the system input to make the system output converge with the reference value, which in this case is a motor speed reference.

[011] It would be extremely advantageous to also use a derivative contribution, providing a complete PID (proportional, integral, derivative) control, since the derivative contribution would allow an immediate reaction, since the derived term is a component of anticipated control. Unfortunately, the derived term usually introduces high frequency dynamics into the system, making control unstable.

[012] In a complete PID controller, the outputs of controllers P, I and D are added and the result is applied to the input of the system to be controlled.

[013] Due to the instability mentioned above, the derivative contribution is generally not used.

SUMMARY OF THE INVENTION

[014] The purpose of the present invention is to provide a method of controlling an internal combustion engine that allows the implementation of a fast speed control, but which, at the same time, is stable and fluid.

[015] The basic idea of the present invention is to provide a speed control with feedback through a PID controller, comprising a proportional, integral and derived contribution only when a motor speed error is caused by a variation in the value speed reference, otherwise the controller is PI, that is, it comprises only a proportional contribution and an integral contribution.

[016] In other words, when the aforementioned operational condition occurs, a complete PID controller is used, in which the sum of the respective outputs, that is, the respective control signals generated, is applied to the internal combustion engine input for make the motor output converge with the speed reference value.

[017] This means that when the speed error is caused by an external disturbance, for example, a rapid variation in the inclination of the road or the activation of a device connected to an engine PTO, etc., the derivative contribution does not is added to the proportional and full contributions.

[018] To discriminate the case in which the error depends on a variation of the reference signal or a variation of the load, it is sufficient to compare a signal of the aforementioned motor rotation speed error with a signal of a rotation speed derivative. the engine. In particular, if the signals are inconsistent, then the speed error is caused by a change in load.

[019] Below, "speed" means "engine rotation speed".

[020] When the speed derivative is detected as positive and the error is negative, this means that the motor is accelerating beyond the reference value. This usually occurs when a load is suddenly removed.

[021] Vice-versa, when the speed derivative is negative and the speed error is positive, this means that the torque distributed by the motor is not sufficient to deal with the applied load, for example, suddenly.

[022] Therefore, according to the present invention, the derivative contribution is added to the proportional and integral control outputs when the derivative and error signals are in agreement.

[023] Vice-versa, when the signs are inconsistent, the derivative contribution is not added to the full and proportional contributions.

[024] Regarding the specific implementations of the invention, the use of the derivative contribution can be decided when the signs mentioned above are concordant and positive, or concordant and negative.

[025] The fact of using the derivative contribution according to the present invention makes the engine extremely fast, but at the same time it is avoided the introduction of a high frequency dynamics in the control system, which could make the control unstable.

[026] “Controller” indicates the general revolution control performed on the internal combustion engine.

[027] According to a preferred variation of the invention, not only must the signals be concordant, but the absolute value of the speed error must exceed a first predetermined limit, and the absolute value of the speed derivative must exceed a second predetermined limit.

[028] According to a preferred variation of the invention, which combines with the previous ones, when only proportional and integral contributions are used, the derivative of the motor rotation speed (which is normally multiplied by a predetermined parameter that defines the derivative contribution above), this is used to modify an operational parameter of the integral controller in order to compensate for sudden variations due to loads.

[029] In particular, the integral controller comprises a saturator, which saturates the control signal that goes to the internal combustion engine, based on a speed error and the speed derivative of said internal combustion engine.

[030] The derivative contribution responds much more quickly than the other proportional and integral contributions, but its contribution is used to intervene in the integral contribution, minimizing the excessive and scarce responses of the internal combustion engine, without affecting its stability.

[031] From the above, it is clear that a signal is not generated that is added to the proportional and integral contributions to minimize the excesses; instead, the derivative contribution is used to deal with sudden load changes.

[032] Preferably, the signal obtained from the sum of the full, proportional and derived contributions is not saturated.

[033] The claims describe preferred variations of the invention, forming an integral part of the present description.

BRIEF DESCRIPTION OF THE FIGURES

[034] Other objectives and advantages of the present invention will become clear from the following detailed description of an exemplary embodiment of the invention (and its variations), and from the accompanying drawings, provided for purely non-limiting purposes illustrative, in which: - Figure 1 shows a control diagram based on an example of implementation of the present invention; Figures 2a and 2b show two equivalent control diagrams used in a mutually exclusive manner according to another example of implementation of the present invention; - Figure 3 shows in detail a block of the control diagram in figure 2b.

[035] The same numbers and reference letters in the figures identify the same elements or components.

[036] In the context of the present description, the term “second” component does not imply the presence of a “first” component. These terms are used for clarity purposes only and should not be construed in a limiting manner.

DETAILED DESCRIPTION OF EXEMPLIFICATIVE FORMS OF INCORPORATION

[037] Figure 1 shows, using a block diagram, an exemplary control.

[038] The control is performed recursively in discrete time, according to the frequency of operation of the UCM processing unit that controls the internal combustion engine.

[039] The internal combustion engine is shown in figure 1 with the Engine block.

[040] A revolution sensor, such as a phonic wheel applied to the transmission shaft, provides a measurement of the speed of the internal combustion engine.

[041] In addition, the accelerator pedal or any suitable vehicle device to transmit a reference speed, such as a robotic transmission or a power take-off, generates the reference signal Ref in terms of the desired engine speed.

[042] The measured speed, Vel, is subtracted from the desired speed, Ref, generating an error Err (of speed) through the first adding node S1, on the left in figure 1.

[043] The same error value (speed) is transmitted to the input of blocks P and 1, while a speed signal is transmitted to the input of block D, providing a PID control.

[044] The outputs of controllers P, I and D converge at the adding node S2, on the right in figure 1, to control the internal combustion engine. Generally, controllers receive speed signals at the input and generate control signals relative to the percentage of torque that the motor must distribute, in relation to the relative nominal torque.

[045] The derivative contribution D is given by the derivative of the rotation speed of the AVel motor multiplied by a fixed or adjustable KD parameter.

[046] The signal block receives, at the input, the error mentioned above, and also the derivative of the speed AVel coming from the derivative block D, and compares the relative signals, allowing or not, through the Switch, that the output of the derivative block D flow to the adding node S2.

[047] Therefore, when the switch enables the derivative output, a complete PID control is obtained, otherwise, a PI type control is obtained.

[048] Preferably, the Signal block allows the contribution of the derivative controller when both signals are positive and also when both signals are negative.

[049] According to a preferred variation of the invention, the Signal block not only compares the signals, but also verifies that, when both are positive, the speed error exceeds a predetermined positive positive limit, and the derivative exceeds a second positive limit predetermined. When both conditions, of agreement of the signs and exceeding the respective thresholds, are satisfied, then the derivative contribution is used.

[050] Therefore, the verification that the limits have also been exceeded (positively and / or negatively) represents a more restrictive condition than just the agreement of the signs.

[051] Vice-versa, when both signs are negative, the Sign block checks whether the speed error is below a third predetermined negative limit, and whether the derivative contribution is below a fourth predetermined negative limit. When both conditions, of agreement of the signs and exceeding the respective thresholds, are satisfied, the derivative contribution is used.

[052] When the modules (absolute values) of the first and third limits are equal, and the second and fourth limits are identical, then the Signal block allows the referred derivative control, when the above mentioned signs are in agreement, the absolute value of the error velocity exceeds a first predetermined limit, and the absolute value of the velocity derivative exceeds a second predetermined limit.

[053] Consequently, a first interval is defined between the first and third limits, and a second interval varies between the second and fourth limits, with the derivative controller being disconnected from the adding node S2.

[054] In an error / derivative of the 3 x 3 revolution matrix, a so-called “dead band” is therefore defined, in which the derivative controller is disconnected from the adding node S2.

[055] The following table shows an example of the application of the mechanism for activating the derivative contribution based on signs and limits. NEGATIVE <| BAND | POSITIVA> post | o a mo moment esmas | ro a | The

[056] The presence of a "1" indicates that the derivative contribution is added in the adding node S2, while a "O" indicates that the derivative contribution is not added and, therefore, is disconnected from the adding node S2.

[057] According to another preferred variation of the invention, which combines with any of the previous variations, when the Signal block disconnects the first output of derivative control D from the second adding node S2, and connects a second output of derivative control D to the controller integral, in particular to the Sat 1 saturator, with reference to figure 3, which limits the contribution of the integral controller 1, the first output of the derivative control provides KD x AVel, while the second output provides only AVel.

[058] Thus, figures 2a and 2b correspond to the existing equivalent arrangements when the Signal block respectively enables or disables the connection of the derivative control output with the second adding node S2.

[059] Therefore, the integral contribution is saturated according to a function F (Err, AVel) of the Err velocity error and the velocity derivative. NEGATIVE <| BAND | POSITIVE> [put OQ o eme e e e sema sms Da o |

[060] The presence of a “-1” indicates that the derivative contribution is not used to control the engine, according to the present variation, and a second output of the derivative block, which generates the derivative of the rotation speed of the AVel engine. , interacts with the saturator of the integral controller as described below.

[061] In addition, to allow the interaction of the derivative block (AVel) with the saturator in the integral controller, limits can be established that the speed error and the speed derivative must exceed (both positively and negatively), with the above mentioned dead band being defined symmetrical in relation to the two main and secondary diagonals of the square matrix.

[062] An integral controller 1 (discrete time), according to a preferred variation of the present invention, can be diagrammed, with reference to figure 3, as a memory containing an Int-1 value generated by the same integral controller 1, as in the previous step (therefore, the value "Int-1" indicates that it is generated in "step-1"), to which the current value of the Err velocity error is added iteratively, through the adding node S3, and conveniently multiplied by the integral coefficient KI, through the multiplier node M1. The result of the sum realized by the adding node S3 represents the output of the integral controller 1, that is, the control signal mentioned above, and simultaneously the Int-O input of the memory (that is, in "step-0", that is, the current step), which stores it for the subsequent integration step.

[063] The Sat 1 saturator, according to the present invention, is arranged between the adding node S3 and the input of the memory block, so that the limitation is performed not only at the output of the integral controller, but also in the memory block contained therein.

[064] According to a preferred variation of the present invention, the Sat 1 saturator performs a symmetric saturation with respect to zero, and the saturation modulus is given by the following formula: | Saturation | = | K x RadQ f [exp (-JErr] / A)] x [exp (-JAVeI | / B) IX]

[065] Where: RadQ represents the square root operator; Exp represents the exponential; | Err | represents the Err error module described above; | AVeI | represents the module of the speed derivative of the AVel engine; K, A and B represent constant values.

[066] The derivative of the motor speed can be expressed using Newton's equation: AVel = Cost x [(Torque distributed by the motor) - (Torque resistant due to external loads)]

[067] Where Cost is usually the reciprocal of the moment of inertia J] of the internal combustion engine.

[068] External loads include, for example, the inclination of the road traveled by the vehicle guided by the internal combustion engine, or the resistant torque offered by an electric generator, a compressor or a pump connected to a related TF (PTO) .

[069] The CALC block is based on the inputs: - Err speed error - AVel speed derivative

[070] And apply the aforementioned formula by calculating the saturation module | Saturation |.

[071] The CALC block has two outputs, each addressed to the two inputs: high and low of the Sat 1 saturator.

[072] A positive or negative saturation is applied only when the Err and AVel signals are discordant, otherwise the signal is saturated at + 100% of the actuator's authority.

[073] A second sat 2 saturator is preferably arranged between the multiplier node M1 and the adding node S3, to limit the control signal to + 100% and -100% of the so-called "actuator authority". The reasons for implementing saturations for the actuator authority are already known to a person skilled in the art, and are substantially intended to avoid an unnecessary demand for actuator (motor) performance exceeding the relative rating characteristics. In this case, the actuator is the internal combustion engine, which cannot supply more than the relative rated torque on the relative speed / rated torque map.

[074] According to a preferred variation of the invention, the aforementioned formula is implemented in the CALC block by means of a Lookup Table, with the advantage of greater flexibility, as it allows the modification of the table's own coefficients, introducing deviations to from the output of the aforementioned formula, which are most suitable for the specific internal combustion engine. In addition, the Lookup Table allows the reduction of computational work.

[075] An example of the Lookup Table is shown below, having | AVel | and | Err | as inputs. [Too | 200 | 300 | 00 | Lo o oo | 6 | 37 [22 | 1) With 7 vv 6) [Er »Ene

[076] The values shown in the matrix, for example 5 x 5, in the preceding table, are those considered optimal for implementing the present invention. However, they can be suitably varied.

[077] Said values are positive when the error Err is negative and AVel is positive, while each of the values shown in the table are multiplied by "-1" when Err is positive and AVel is negative.

[078] In other words, the Sat 1 saturator is symmetrical with respect to zero, and when the error is negative and AVel is positive, this indicates manipulation of the upper (positive) portion of the saturator (upper limitation); vice versa, when Err is positive and AVel is negative, this indicates manipulation of the lower (negative) part of the saturator (lower limitation).

[079] The present method can be advantageously implemented through a UCM processing unit (Engine Control Unit) to control the internal combustion engine, which processes information about the engine speed and pressure in the accelerator pedal, or requests for revolutions or torque coming from other devices, and consequently controls the internal combustion engine as described above.

[080] The present invention can advantageously be carried out by means of a computer program comprising means of encoding for carrying out one or more steps of the method, when such a program is executed on a computer. It should therefore be understood that the scope of protection extends to said computer program and also to computer-readable means, which comprise a recorded message, with said computer-readable means comprising means of program coding for the realization of one or more method steps, when that program is run on a computer.

[081] Variations of the exemplary non-limiting embodiment described above are possible, without departing from the scope of the present invention, comprising all equivalent embodiments for a person skilled in the art.

[082] From the above description, a person skilled in the art is able to produce the object of the invention without introducing other details of construction. The elements and features illustrated in the various preferred embodiments, including the drawings, can be combined with each other without departing from the scope of the present patent application. What is described in the section on the state of the art is provided only for a better understanding of the invention, and does not represent a declaration of the existence of what is described. In addition, if it is not specifically excluded from the detailed description, what is described in the state of the art section should be considered as an integral part of the detailed description.

Claims (11)

Claims 1. METHOD OF CONTROL FOR AN INTERNAL COMBUSTION ENGINE, performed by means of a control by feedback of the speed of the motor itself, based on an error (Err) of the aforementioned motor speed, calculated between a reference value (Ref) and a measured value (Vel) of the speed, characterized in that said control comprises a sum (S2) of a proportional contribution (P) and an integral contribution (1), with the method comprising a step of also adding a derivative contribution (D) , only when at least a first sign of the aforementioned error and a second sign of a derivative of the said motor rotation are in agreement with each other. 2. METHOD according to claim 1, characterized in that said derivative contribution (D) is added when said speed error exceeds a first predetermined positive limit, and said motor speed derivative exceeds a second predetermined positive limit, and / or when said speed error is less than a third predetermined negative limit, and said derivative contribution is less than a fourth predetermined negative limit. METHOD according to claim 2, characterized in that a module of said first limit and a module of said third limit coincide, and a module of said second limit and a module of said fourth limit coincide. 4. METHOD, according to any one of claims 1 to 3, characterized in that the method comprises a saturation step of said integral contribution according to [F (Err, AVel)]: - a derivative (AVel) of the said measured value the engine speed (Vel); and - said speed error (Err); when said first sign of said error and said second sign of said derivative contribution are at least inconsistent with each other. 5. METHOD, according to claim 4, characterized in that said integral contribution (1) consists of the sum (S3) of: - an error value (Err) calculated in the current stage, and multiplied by an integral coefficient (KI) ; and - a full contribution amount (Int-1) generated in the immediately preceding step; in which the said saturator (Sat 1) is applied to the sum mentioned. 6. METHOD, according to either of claims 4 or 5, characterized in that an absolute value of said saturation is given by the following formula: ISaturation | = | K x RadQ f [exp (- | Err] / A)] x [exp (- | AVel | / B) X | where RadQ represents the square root operator; Exp represents the exponential; | Err | represents the Err error module described above; | AVeI | represents the module of the speed derivative of the AVel engine; K, A and B represent constant values. 7. METHOD, according to any one of the preceding claims, characterized in that the mentioned absolute value of said saturation is given by a query table, in which the relative values are included, in absolute values, between 0 and 100% of a torque internal combustion engine rating. 8. COMPUTER PROGRAM, characterized by comprising program coding means adapted to carry out all the steps as described in any one of claims 1 to 7, when said program is executed on a computer. 9. COMPUTER-LEGIBLE MEANS, comprising a registered program, said computer-readable means being characterized by comprising program coding means adapted to carry out all the steps as described in any of claims 1 to 7, when said program is executed on a computer. 10. INTERNAL COMBUSTION ENGINE, comprising: a device for measuring a relative speed; a processing unit (UCM) configured to control the aforementioned internal combustion engine based on a speed reference signal (Ref); characterized in that said processing unit is configured to carry out the control method as defined in any one of claims 1 to 7. 11. VEHICLE OR FIXED INSTALLATION, characterized by comprising the internal combustion engine as defined in claim 10.