EP1521901B1 - Control structure for the adjusting motor of an electric camshaft adjuster - Google Patents

Description

Field of the invention

The invention relates to a control structure for achieving the desired adjustment speed of an adjusting motor of an electric adjusting device of the camshaft of an internal combustion engine according to the preamble of patent claim 1.

Background of the invention

A major requirement of an ideal camshaft adjuster is to ensure an exact compliance with the desired Verstellwinkelverlaufs the camshaft. In reality, however, there are deviations between the desired and the actual Verstellwinkelverlauf. These are due to mechanical and electrical inertia as well as the influence of disturbances such as the camshaft torque.

A reduction in the deviations from the desired displacement curve of the camshaft leads to a reduction in pollutant emissions and fuel consumption, to increase engine power and torque and to a reduction of the on-board network load and the high emission values in the starting phase. The latter requires that the camshaft adjuster is adjustable before or during engine start. This requirement can only be met by an electric camshaft adjuster, since hydraulic adjusters are inoperative before and during the starting phase for lack of lubricating oil pressure.

To an electric camshaft adjuster there is the demand for minimal energy consumption of the electric adjusting motor by appropriate design of the controller. The quality of the regulated system is determined by the Target-actual displacement curve of the camshaft determined. It is increased by minimizing the deviations from the desired adjustment angle.

In the US-5,787,848 B1 is a control structure for achieving the desired adjustment speed of an adjustment of an electric adjusting the camshaft of an internal combustion engine disclosed, wherein the camshaft adjuster comprises at least one controller which generates control signals for the adjusting motor from measuring signals of the internal combustion engine. This document deals with the control of an internal exhaust gas recirculation by changing the valve timing. The exhaust gas recirculation lowers the torque of the internal combustion engine. In order to achieve a torque curve similar to that of an internal combustion engine without exhaust gas recirculation, a low-pass filter is provided in the controller, by which a partial overrun or underrun of the original torque curve is to be avoided.

A control structure according to the preamble of claim 1 is in DE 100 38 354 A1 disclosed.

Object of the invention

The invention has for its object to provide a control structure for the electric variable displacement motor of a camshaft adjuster, which has a lowest possible deviation of the actual adjustment angle of the target adjustment angle of the camshaft and a low power consumption of the adjustment motor in the entire operating range of the internal combustion engine.

Summary of the invention

According to the invention, the object is solved by the features of patent claim 1.

Since the input signal is a difference signal, it approaches the actual and setpoint of size 0 with increasing agreement. This also applies for the output signal, which supplies a controlled setpoint adjustment speed of the variable displacement motor, which then comes to a standstill. However, if the camshaft is to be held in a specific angle of rotation position, the variable displacement motor must rotate with the camshaft speed. A stationary adjusting motor leads to an adjustment of the rotational angle position of the camshaft whose adjusting speed increases with the rotational speed of the internal combustion engine.

According to the invention, the required setpoint speed is predetermined to the adjusting motor during the operating time of the internal combustion engine by adding up the uncontrolled speed signal, which is thus independent of the differential signal. As a result, the position of the camshaft can be held to the crankshaft.

For a high control quality, a position control, which relates to the camshaft adjustment angle, and additionally a speed control, which refers to the variable engine speed, provided. In this way, the relevant parameters for the rotational angle position of the camshaft of the camshaft adjustment angle and the Verstellmotordrehzahl be considered.

It can be used as a controller for the speed control, inter alia, P, PI, PID, prediction or observer controller. The position control is performed by a prediction controller. There are also operating point-dependent combinations of the above controller possible, So, for example, for small target-Ist-Verstellwinkelabweichungen a PI controller and for large target-Ist-Verstellwinkelabweichungen a P controller advantageous. Fuzzy logic controllers are also conceivable.

The advantage of the prediction controller is that, depending on the respective displacement angle jump of the camshaft, it predetermines an adjustment speed which can be delayed by the adjusting motor in the period available for this purpose. In this way, the overshooting of the angle of rotation of the camshaft is avoided and thereby saves adjustment energy.

In the case of an observation controller, it is advantageous that a model of the control strategy is calculated parallel to the controller. This model uses the controller output and tries to follow the real route. This improves the control quality and also saves adjustment energy.

Depending on the required control quality, the prediction controller of the position control and the PID controller of the speed control are used individually or in series.

An advantageous embodiment of the invention is that with position control of the prediction as an input signal, the difference signal between an actual displacement and a target displacement angle of the camshaft and output as a controlled target adjustment speed for the adjusting and that the added speed is the camshaft speed. The added camshaft speed prevents the entire operating range of the engine standstill of the variable displacement motor and thus a faulty control.

Likewise, it is advantageous that, in the case of speed control, the PID controller has as input signal the difference signal between an actual adjustment speed and a desired adjustment speed of the adjustment motor and as output signal a regulated desired adjustment speed for the adjustment motor in the form of a voltage value or a duty-modulated voltage the added speed is the uneven and spannunsgewandelte desired adjustment speed of the variable displacement motor. Again, the added up unregulated desired adjustment speed of the adjusting motor, in which the camshaft speed is included, prevents a stoppage of the adjusting motor and the associated faulty control.

An advantageous development of the invention is that, when the prediction controller and the PID controller are connected in series, the output signal of the prediction controller with added camshaft rotational speed in voltage-converted form also serves as a connection signal for the output signal of the PID controller. Since the output signals of both controllers, the camshaft speed In this case, a standstill of the adjusting motor is reliably prevented even in this case.

It is the durability of the controller that preferably the PID controller of the speed control has a current limiting function, preferably a two-point current regulator. When the preset current limit value is exceeded, the current regulator decreases the voltage or the duty cycle modulated voltage, as a result of which the current drops. When the current limit value is undershot, the current regulation acts in the reverse direction.

A cost saving results from the fact that the angular position of the camshaft is not measured by a camshaft sensor but by a Hall sensor of the adjusting motor. Since the stator of a brushless DC motor anyway has at least one Hall sensor, thus eliminating a special camshaft sensor.

Brief description of the drawings

Figur 1

ein Schema eines elektrischen Nockenwellenverstellers mit Steuerelektronik und separatem Nockenwellensensor;

Figur 2

das Schema von Figur 1, jedoch mit einem Hallsensor des Verstellmotors anstelle des Nockenwellensensors;

Figur 3

einen Nockenwellenversteller mit einem gehäusefesten Stator des elektrischen Verstellmotors;

Figur 4

eine nicht erfindungsgemäße Regelstruktur einer Lageregelung mit einem PID-Regler und einer Aufaddierung der Nockenwellendrehzahl auf dessen Ausgangssignal;

Figur 5

die Regelstruktur einer Lageregelung mit einem Prädiktionsregler und einer Aufaddierung der Nockenwellendrehzahl auf dessen Ausgangssignal;

Figur 6

eine Regelstruktur einer Drehzahlregelung mit einem PID-Regler und der Aufaddierung einer spannungs- bzw. tastverhältnismodulierten Spannung einer nicht geregelten Soll-Verstelldrehzahl des Verstellmotors auf das Ausgangssignal des PID-Reglers;

Figur 7

eine Regelstruktur einer Lage- und Drehzahlregelung mit einem Prädiktions- und einem PID-Regler und mit einer Drehzahl- sowie einer Spannungsaufschaltung auf das jeweilige Ausgangssignal;

Figur 8

ein Ablaufdiagramm für den Motorstart und den Fahrbetrieb.

Further features of the invention will become apparent from the following description and the drawings, in which several embodiments of the invention are shown schematically. Show it:

FIG. 1

a schematic of an electric camshaft adjuster with control electronics and separate camshaft sensor;

FIG. 2

the scheme of FIG. 1 , but with a Hall sensor of the adjusting motor instead of the camshaft sensor;

FIG. 3

a camshaft adjuster with a housing-fixed stator of the electric adjusting motor;

FIG. 4

a non-inventive control structure of a position control with a PID controller and a summation of the camshaft speed to the output signal;

FIG. 5

the control structure of a position control with a prediction controller and an addition of the camshaft speed to its output signal;

FIG. 6

a control structure of a speed control with a PID controller and the summation of a voltage or tastverhältnismodulierten voltage unregulated target adjustment speed of the variable displacement motor to the output of the PID controller;

FIG. 7

a control structure of a position and speed control with a prediction and a PID controller and with a speed and a voltage on the respective output signal;

FIG. 8

a flow chart for the engine start and driving.

Detailed description of the drawings

an. Die Nockenwelle 5 weist einen elektrisehen Nockenwellenversteller 6 mit einem Verstellgetriebe 7 und einem elektrischen Verstellmotor 8 auf. Die Drehwinkellage der Kurbelwelle 2 wird mittels eines Kurbelwellensensors 9, die Drehwinkellage der Nockenwelle 5 mittels eines Nockenwellensensors 10 gemessen. Die Signale der Sensoren 9, 10 gelangen über ein Steuergerät 11 des Verbrennungsmotors 1 zu einem Steuergerät 12 des Verstellmotors 8. Dort werden sie zu Steuersignalen für den Verstellmotor 8 umgewandelt.In FIG. 1 an internal combustion engine 1 is shown schematically. Whose crankshaft 2 drives a Nockenwellenantriebsrad 4 a camshaft 5 in the ratio 2: 1 via a Kurbelwellenantriebsrad 3 by means of a chain, not shown, or a toothed belt $\frac{\mathit{nKW}}{\mathit{NNW}}$

at. The camshaft 5 has an electrical camshaft adjuster 6 with an adjusting gear 7 and an electric adjusting motor 8. The rotational angle position of the crankshaft 2 is measured by means of a crankshaft sensor 9, the rotational angle position of the camshaft 5 by means of a camshaft sensor 10. The signals of the sensors 9, 10 pass through a control unit 11 of the internal combustion engine 1 to a control unit 12 of the adjusting motor 8. There they are converted into control signals for the adjusting motor 8.

FIG. 2 shows the diagram of the internal combustion engine 1 of FIG. 1 However, the camshaft sensor 10 has been replaced by an existing in brushless DC motors without Hall sensor 13 of the adjusting motor 8.

In FIG. 3 the camshaft adjuster 6 is shown schematically. The adjusting 7 is designed as a three-shaft gear, with a drive shaft connected to the Nockenwellenantriebsrad 4, an output shaft connected to the camshaft 5 and a Verstellwelle 14, which are rotatably connected to a rotor 15 of the adjusting 8. The adjusting motor 8 has a stator 16 is formed on the housing fixed.

FIG. 4 A differential signal 17 ± 18 of an actual displacement angle 17 and a desired displacement angle 18 between the crankshaft 2 and the camshaft 5 is the input signal of a PID controller 19. Its output signal 20 includes a controlled Sollverstelldrehzahl for the adjusting motor eighth ,

When the actual and desired adjustment angles 17, 18 are approaching, the difference signal 17 ± 18 approaches the value 0. As a result, the output signal 20 and thus the controlled setpoint adjustment speed of the adjustment motor 8 also approaches this value.

If the rotational angle position of the camshaft 5 is to be held, the rotor 15 of the adjusting motor 8 must rotate at camshaft speed. Deviations from this speed affect, especially at higher speeds of the internal combustion engine 1 as significant rule position deviations.

This is prevented in that according to the invention, the camshaft speed 21 is added to the output signal 20 of the controller 19 and set as the setpoint speed 20 + 21 the adjusting motor 8, in this way, the adjusting motor 8 rotates at least with the camshaft speed 21, whereby the control position the camshaft 5 is maintained.

Despite the improved control behavior by the connection of the camshaft speed 21 to the output signal 20 of the PID controller 19, there is a strong overshoot of the adjustment at the end of each speed jump of the adjusting 8. This is essentially because it does not meet the specifications of the target adjustment speed fast enough, because acceleration and deceleration can not be performed fast enough because of its limited torque capacity.

This behavior can be improved with a so-called prediction controller 22, the FIG. 5 in the rule structure of a position control shows. This is dependent on the jump size of the adjustment angle of the adjusting motor 8 in the available time just delayable adjustment speed.

The size of the input signal 17 ± 18 of the prediction controller 22 corresponds to the difference between the actual adjustment angle 17 and the desired adjustment angle 18 of FIG FIG. 4 , Depending on this Verstellwinkelsprung is given by the prediction controller 22 as an output signal 20 'that regulated target adjustment speed, which can be delayed to overcome the predetermined angular deviation within the available time of the adjusting motor 8.

The output signal 20 'of the prediction controller 22, the current camshaft speed 21 is switched on and the sum 20' + 21 set as the desired adjustment speed to the adjusting motor 8. By the prediction controller 22, the overshooting of the actual adjustment angle is avoided and thereby at the same time the power consumption of the adjusting motor 8 is lowered considerably.

The previously described regulators 19, 22 serve to control the position of the camshaft 5. For optimum control results, an inner control loop with a speed control of the adjusting motor 8 is still necessary. The relevant rule structure shows FIG. 6 , The input signal of the PID controller 19 'is the difference signal 23 ± 24 between a setpoint adjustment speed 24 and an actual adjustment speed 23 of the adjustment motor 8. The output signal 20 "is a voltage which serves to control the adjustment motor 8. To prevent this . that a voltage 0 is specified if the setpoint and actual adjustment speeds 24, 23 are in agreement, the voltage corresponding to the setpoint adjustment speed 24 of the adjustment motor 8 is added to the output signal 20 "via a voltage converter 25. This ensures that the adjustment motor 8 in FIG Operation always a voltage is specified according to the target adjustment speed 24. As a controller in addition to the PID controller among other P and PI and prediction in question.

With a speed control, there are no permanent control deviations. In addition, the adjustment speeds are higher than with the position control.

FIG. 7 shows the control structure of a complete control system for the adjusting motor 8 with series connection of a position control accordingly FIG. 4 and a speed control accordingly FIG. 6 , The position control has a prediction controller 22 whose input signal is formed as a difference signal 17 ± 18 between the actual displacement angle 17 and the desired displacement angle 18 and processed to the output signal 20 'of a controlled target adjustment speed. This is added to the camshaft speed 21, which together form the desired adjustment speed 20 '+ 21 of the adjusting motor 8.

The difference signal 20 '+ 21 ± 23 from the target adjustment speed 20' + 21 and actual adjustment speed 23 forms the input signal of the PID controller 19 'of the speed control, the output signal 20 "with the added, in a voltage converter 25 voltage-converted desired adjustment speed 20th '+ 21 to the adjusting motor 8-driving voltage 20 "+ 20' + 21 is processed. In addition to the illustrated prediction and PID controllers 22, 19 ', other controllers such as P and PI controllers can also be used.

Furthermore, it is conceivable, at least in the PID controller 19 'of the speed control to protect the adjusting motor 8 and control electronics to integrate a current limiting function, for example, a two-point current controller, which takes back when exceeding the predetermined current limit, the voltage or duty cycle.

In FIG. 8 a flowchart is shown in which it is shown how the control of the adjusting 8 takes place at the start of the internal combustion engine 1 and during its operation. In position 26, the ignition switch is actuated, in position 27, the starter is running high and thus ends the starting process. In position 28, the rotational angle position of the camshaft 5 is detected, in position 29 of the Verstellwinkelvergleich is made, the result leads to driving the Verstellmotors 8 in position 30. Activation may mean holding according to item 31, advancing according to item 32 or retarding according to item 33. The respective result is returned via the return line 34 to position 28, whereby a new pass begins.

LIST OF REFERENCE NUMBERS

1

internal combustion engine

2

crankshaft

3

Kurbelwellenantriebsrad

4

camshaft drive wheel

5

camshaft

6

Phaser

7

variator

8th

adjusting

9

crankshaft sensor

10

camshaft position sensor

11

control unit

12

control unit

13

Hall sensor

14

adjusting

15

rotor

16

stator

17

Actual displacement

18

Target displacement

19.19 '

PID controller

20, 20 ', 24 "

regulated output signal

21

Camshaft speed

22

Prädiktionsregler

23

Actual Verstelldrehzahl

24

Target Verstelldrehzahl

25

DC converter

26

Position "turn ignition lock"

27

Position "Starter turns up"

28

Position "angular position of the camshaft"

29

Position "Target-actual displacement angle comparison"

30

Position "Actuation of the adjustment motor"

31

Position "Hold"

32

Position "advance"

33

Position "retard"

34

return

Claims (9)

1. Control structure for reaching the setpoint adjustment rotational speed of an adjustment motor (8) of an electric camshaft adjuster (6) of the camshaft (5) of an internal combustion engine (1), wherein the control structure has at least one controller (19, 22, 19') which generates control signals for the adjustment motor (8) from measurement signals of the internal combustion engine (1), wherein the controller (19, 22, 19') has, as an input signal, a difference signal composed of a predefined setpoint adjustment angle of the camshaft and an actual adjustment angle which differs from the latter as a result of mechanical and electrical inertia or as a result of the influence of interference variables, and has as an output signal a controlled setpoint adjustment rotational speed signal which is intended for the adjustment motor (8) and to which an uncontrolled rotational speed signal is added, characterized in that a position control process relating to the camshaft adjustment angle and in addition a rotational speed control process relating to the adjustment motor rotational speed are provided, wherein a prediction controller is used as a controller for the position control process, wherein the prediction controller (22) predefines, as a function of the respective adjustment angle jump of the camshaft (5), an adjustment rotational speed which can just still be decelerated by the adjustment motor (8) in the time period available therefor.
2. Control structure according to Claim 1, characterized in that the prediction controller (22) is provided for the position control process and the PID controller (19') is provided for the rotational speed control process, which prediction controller (22) and PID controller (19') can be used individually or connected in series.
3. Control structure according to Claim 2, characterized in that in the case of a position control process the prediction controller (22) has as an input signal the difference signal (17 ± 18) between an actual adjustment angle (17) and a setpoint adjustment angle (18) of the camshaft (5), and as an output signal (20') a controlled setpoint adjustment rotational speed for the adjustment motor (8), and in that the added rotational speed is the camshaft rotational speed (21).
4. Control structure according to Claim 2, characterized in that in the case of a rotational speed control process the PID controller (19') has as an input signal the difference signal (23 ± 24) between an actual adjustment rotational speed (23) and a setpoint adjustment rotational speed (24) of the adjustment motor (8), and as an output signal (20") a controlled setpoint adjustment rotational speed for the adjustment motor (8) in the form of a voltage value or a pulse-duty-factor-modulated voltage, and in that the added rotational speed is the uncontrolled and voltage-converted setpoint adjustment rotational speed (24) of the adjustment motor (8).
5. Control structure according to Claim 2, characterized in that in the case of a series connection of the prediction controller (22) and of the PID controller (19') the output signal (20') of the prediction controller (22) with added camshaft rotational speed (21) in a voltage-converted form serves at the same time as a connection signal (20' + 21) for the output signal (20") of the PID controller (19').
6. Control structure according to Claim 5, characterized in that the PID controller (19') of the rotational speed control process has a current-limiting function.
7. Control structure according to Claim 5, characterized in that the current-limiting function is formed by a two-level current controller.
8. Control structure according to Claim 1, characterized in that the rotational angle position of the camshaft (5) can be measured by a camshaft sensor (10) or by a Hall sensor (13) of the adjustment motor (8).
9. Control structure according to one of Claims 1 or 8, characterized in that a P controller, Pi controller, PID controller or observer controller is used as the controller for the rotational speed control process.

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