EP1521901A1

EP1521901A1 - Control structure for the adjusting motor of an electric camshaft adjuster

Info

Publication number: EP1521901A1
Application number: EP03740391A
Authority: EP
Inventors: Jens Schäfer; Martin Steigerwald; Martin Overberg
Original assignee: INA Schaeffler KG
Current assignee: Schaeffler Technologies AG and Co KG
Priority date: 2002-07-11
Filing date: 2003-07-01
Publication date: 2005-04-13
Anticipated expiration: 2023-07-01
Also published as: WO2004007919A1; DE10251347A1; JP2005532502A; US7152561B2; US7059285B2; US20060124095A1; EP1521901B1; US20050103298A1; AU2003280981A1; JP4662765B2

Abstract

The invention relates to a control structure for the adjusting motor (8) of an electric camshaft adjuster (6) in an internal combustion engine (1). Said control structure comprises a controller (19) which processes measuring signals of the internal combustion engine (1) to control data for the adjusting motor (8). A controller (19) which has meaningful values for the adjusted setpoint rotational speed of the adjusting motor (8) even when the input differential signal has a zero value, is obtained by applying the signal of an uncontrolled rotational speed (21) to the output signal (20) of a controlled setpoint rotational speed.

Description

Name of the invention

Control structure for the adjustment motor of an electric camshaft adjuster

description

Field of the Invention

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

Background of the Invention

One of the main requirements for an ideal camshaft adjuster is to ensure that the camshaft is adjusted to the desired angle. In reality, however, there are deviations between the target and the actual adjustment angle curve. These are due to mechanical and electrical inertia and the influence of disturbance variables such as camshaft torque.

A reduction in the deviations from the target adjustment angle curve of the camshaft leads to a reduction in pollutant emissions and fuel consumption, an increase in engine power and torque as well as a reduction in the electrical system load and the high emission values in the starting phase. The latter assumes that the camshaft adjuster can be controlled before or during engine start. This requirement is only through one electrical camshaft adjuster, because hydraulic adjusters are inoperable before and during the starting phase due to a lack of lubricating oil pressure.

An electric camshaft adjuster requires minimal energy consumption of the electric variable motor by appropriately training the controller. The quality of the controlled system is determined by the target-actual adjustment angle curve of the camshaft. It is increased by minimizing the deviations from the target adjustment angle.

US Pat. No. 5,787,848 B1 discloses a control structure for reaching the target adjustment speed of an adjustment motor of an electrical adjustment device of the camshaft of an internal combustion engine, the camshaft adjuster having at least one controller which generates control signals for the adjustment motor from measurement signals of the internal combustion engine. This pressure step is about controlling an internal exhaust gas recirculation by changing the valve timing. The exhaust gas recirculation reduces 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 means of which a partial overshoot or undershoot of the original torque curve is to be avoided.

Object of the invention

The invention has for its object to provide a control structure for the electric adjustment motor of a camshaft adjuster, which has the smallest possible deviation of the actual adjustment angle from the desired 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 achieved by the features of patent claim 1. Since the input signal is a differential signal, it approaches size 0 with increasing agreement between the actual value and the setpoint. This also applies to the output signal, which supplies a regulated setpoint speed of the servomotor, which then comes to a standstill. However, if the camshaft is to be held in a certain angle of rotation, the adjustment motor must rotate at the camshaft speed. A stationary adjustment motor leads to an adjustment of the angular position of the camshaft, the adjustment speed of which increases with the speed of the internal combustion engine.

According to the invention, by adding the uncontrolled speed signal, which is therefore independent of the difference signal, the required target speed is predetermined for the adjusting motor during the operating time of the internal combustion engine. As a result, the position of the camshaft relative to the crankshaft can be maintained.

For a high control quality, it is advantageous that a position control, which relates to the camshaft adjustment angle, and additionally a speed control, which relates to the adjustment motor speed, are provided. In this way, the parameters of the camshaft adjustment angle and the servomotor speed which are relevant for the angular position of the camshaft are taken into account.

It is advantageous that P, PI, PID, prediction or observer controllers can be used as controllers for position and speed control. Combinations of the above-mentioned controllers depending on the operating point are also possible. For example, a Pl controller is advantageous in the case of small setpoint / actual adjustment angle deviations and a P controller in the case of large setpoint / actual adjustment angle deviations. Fuzzy logic controllers are also conceivable.

One advantage of the prediction controller is that, depending on the respective adjustment angle jump of the camshaft, this adjustment speed is just decelerable by the adjustment motor in the period available for this pretends. In this way, the overshoot of the angle of rotation of the camshaft is avoided and adjustment energy is saved.

With an observation controller, it is advantageous that a model of the control strategy is calculated in parallel with the controller. This model uses the controller output variable 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 consists in that when the prediction controller is in position control, the difference signal between an actual adjustment angle and a set adjustment angle of the camshaft as the input signal and a regulated set adjustment speed for the adjustment motor as the output signal, and that the added speed is the camshaft speed. The added-up camshaft speed prevents the servomotor from coming to a standstill in the entire operating range of the internal combustion engine and thus prevents faulty control.

It is also 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 target adjustment speed of the adjustment motor and as an output signal a regulated set adjustment speed for the adjustment motor in the form of a voltage value or a duty cycle modulated voltage, and that the added speed is the unregulated and voltage-converted setpoint speed of the variable motor. Here, too, the added, uncontrolled setpoint adjustment speed of the adjustment motor, in which the camshaft speed is contained, prevents the adjustment motor from coming to a standstill and the associated faulty regulation.

An advantageous development of the invention consists in the fact that when the prediction controller and the PID controller are connected in series, the output signal of the Prediction controller with added camshaft speed in voltage-converted form also serves as an activation signal for the output signal of the PID controller. Since the camshaft speed is added to the output signals of both controllers, standstill of the servomotor is also reliably prevented in this case.

It serves the durability of the controller that preferably the PID controller of the speed control has a current limiting function, preferably a two-point current controller. When the specified current limit value is exceeded, the current regulator takes back the voltage or the duty cycle-modulated voltage, as a result of which the current drops. If the current falls below the current limit, the current control acts in the opposite direction.

A cost saving results from the fact that the angular position of the camshaft cannot be measured by a camshaft sensor but by a Hall sensor of the variable motor. Since the stator of a brushless DC motor has at least one Hall sensor anyway, a special camshaft sensor is therefore unnecessary.

Brief description of the drawings

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

Figure 1 is a schematic of an electrical camshaft adjuster with control electronics and separate camshaft sensor;

FIG. 2 shows the diagram from FIG. 1, but with a Hall sensor of the adjusting motor instead of the camshaft sensor;

FIG. 3 shows a camshaft adjuster with a stator of the electric adjusting motor fixed to the housing; FIG. 4 shows a control structure of a position control with a PID controller and an addition of the camshaft speed to its output signal;

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

FIG. 6 shows a control structure of a speed control with a PID controller and the addition of a voltage or duty cycle-modulated voltage of a non-regulated target adjustment speed of the adjustment motor to the output signal of the PID controller;

Figure 7 shows a control structure of a position and speed control with a

Prediction and a PID controller and with a speed and a voltage connection to the respective output signal;

Figure 8 is a flow chart for engine start and driving.

Detailed description of the drawings

In Figure 1, an internal combustion engine 1 is shown schematically. Its crankshaft 2 drives a camshaft drive wheel 4 of a commercial vehicle via a crankshaft drive wheel 3 by means of a chain or a toothed belt (not shown)

Camshaft 5 in a 2: 1 ratio. The camshaft 5 has an nNW electric camshaft adjuster 6 with an adjustment gear 7 and an electric adjustment motor 8. The angular position of the crankshaft 2 is measured by means of a crankshaft sensor 9, and the angular position of the camshaft 5 is measured by means of a camshaft sensor 10. The signals from the sensors 9,

10 reach a via a control unit 11 of the internal combustion engine 1 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 from FIG. 1, but the camshaft sensor 10 has been replaced by a Hall sensor 13 of the adjusting motor 8 which is present in any case in the case of brushless DC motors.

In Figure 3, the camshaft adjuster 6 is shown schematically. The adjusting gear 7 is designed as a three-shaft gear, with an input shaft connected to the camshaft drive wheel 4, an output shaft connected to the camshaft 5 and an adjusting shaft 14 which are connected in a rotationally fixed manner to a rotor 15 of the adjusting motor 8. The adjusting motor 8 has a stator 16 which is designed to be fixed to the housing.

FIG. 4 shows the control structure according to the invention. A difference signal 17 ± 18 of an actual adjustment angle 17 and a target adjustment angle 18 between the crankshaft 2 and the camshaft 5 is the input signal of a PID controller 19. Its output signal 20 contains a regulated target adjustment speed for the Adjusting motor 8.

When the actual and target adjustment angles 17, 18 approach, the difference signal 17 + 18 approaches the value 0. As a result, the output signal 20 and thus the regulated target adjustment speed of the servomotor 8 also approaches this value.

If the angular position of the camshaft 5 is to be maintained, the rotor 15 of the adjusting motor 8 must rotate at the camshaft speed. Deviations from this speed have the effect of considerable control position deviations, especially at higher speeds of the internal combustion engine 1.

This is prevented by the fact that, according to the invention, the camshaft speed 21 is added to the output signal 20 of the controller 19 and is thus given to the adjusting motor 8 as the target adjusting speed 20 + 21. In this way The adjusting motor 8 rotates at least at the camshaft speed 21, as a result of which the control position of the camshaft 5 is maintained.

Despite the improved control behavior due to the connection of the camshaft speed 21 to the output signal 20 of the PID controller 19, there is a large overshoot of the adjustment angle at the end of each speed jump of the adjustment motor 8. This is essentially due to the fact that it adjusts to the specifications of the target Adjustment speed cannot follow quickly enough, because acceleration and deceleration processes cannot be carried out quickly enough due to its limited torque capacity.

This behavior can be improved with a so-called prediction controller 22, which FIG. 5 shows in the control structure of a position control. Depending on the jump size of the adjustment angle, this specifies an adjustment speed that is just decelerable in the available time by the adjustment motor 8.

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 target adjustment angle 18 in FIG. 4. Depending on this change in the adjustment angle, the prediction controller 22 specifies that regulated target adjustment speed as the output signal 20 ^′ . which can be decelerated by the adjusting motor 8 within the available time in order to overcome the predetermined angular deviation.

The current camshaft speed 21 is applied to the output signal 20 ^'of the prediction controller 22 and the sum 20 ^' + 21 is given to the servo motor 8 as the target adjustment speed. The overshoot of the actual adjustment angle is avoided by the prediction controller 22 and at the same time the power consumption of the adjustment motor 8 is considerably reduced.

The regulators 19, 22 described above are used to control the position of the camshaft 5. For optimal control results, an inner control circuit with a speed control or alternatively a current or torque control of the adjusting motor 8 is also necessary. The relevant control structure is shown in FIG. 6. The input signal of the PID controller 19 ^' is the difference signal 23 + 24 between a target adjustment speed 24 and an actual adjustment speed 23 of the adjustment motor 8. A voltage is obtained as the output signal 20 ^" which is used to control the adjustment motor 8 To prevent a voltage 0 from being given if the target and actual adjusting speeds 24, 23 match, the voltage corresponding to the target adjusting speed 24 of the adjusting motor 8 is added to the output signal 20 ^" via a voltage converter 25. This ensures that the actuator 8 is always given a voltage corresponding to the target adjustment speed 24 during operation. In addition to the PID controller, P, Pl and prediction controllers can also be used as controllers.

With 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 adjustment motor 8 with a position control according to FIG. 4 and a speed control according to FIG. 6 connected in series. The position control has a prediction controller 22, the input signal as a difference signal 17 ± 18 between the actual adjustment angle 17 and the setpoint Adjustment angle 18 is formed and processed to the output signal 20 ^'of a regulated target adjustment speed. The camshaft speed 21 is added to this, which together form the target adjustment speed 20 ^′ + 21 of the adjustment motor 8.

The difference signal 20 ^′ + 21 + 23 from the target adjusting speed 20 ^′ + 21 and the actual adjusting speed 23 forms the input signal of the PID controller 19 ^{′ of} the speed control, the output signal 20 ^{″ of} which is added to the target adjusting speed 20 converted in a voltage converter 25 ^' + 21 is processed to the voltage 20 ^" + 20 ^' + 21 which drives the adjusting motor 8. In addition to the prediction and PID controllers 22, 19 ^'shown , other controllers such as P and PI controllers can also be used. Furthermore, it is conceivable to at least integrate a current limiting function, for example a two-point current regulator, into the PID controller 19 ^'of the speed control to protect the adjusting motor 8 and control electronics, which reduces the voltage or the duty cycle when the predetermined current limit value is exceeded.

FIG. 8 shows a flow diagram in which it is shown how the adjustment motor 8 is regulated when the internal combustion engine 1 starts and when it is operated. In position 26 the ignition lock is actuated, in position 27 the starter starts and ends the starting process. In position 28 the angular position of the camshaft 5 is recognized, in position 29 the adjustment angle comparison is made, the result of which leads to the actuation of the adjustment motor 8 in position 30. Driving can mean stopping according to position 31, early adjustment according to position 32 or late adjustment according to position 33. The respective result is reported back to position 28 via the return line 34, with which a new run begins.

LIST OF REFERENCE NUMBERS

internal combustion engine

crankshaft

Kurbelwellenantriebsrad

camshaft drive wheel

camshaft

Phaser

variator

adjusting

crankshaft sensor

camshaft position sensor

control unit

Hall sensor

adjusting

rotor

stator

Actual Verste II angle

Target adjustment angle, 19 ^' PID controller, 20 ^' , 20 ^" controlled output signal

Camshaft speed

Prädiktionsregler

Actual Verstelldrehzahl

Target Verstelldrehzahl

DC converter

"Turn ignition switch" position

Position "starter turns up"

Position "Angle of rotation of the camshaft"

Position "target / actual adjustment angle comparison"

Position "control of the adjustment motor" 31 "Hold" position

32 position "advance adjustment"

33 position "late adjustment"

34 return line

Claims

claims

1. Control structure for reaching the target adjustment speed of an adjustment motor (8) of an electric camshaft adjuster (6) of the camshaft (5) of an internal combustion engine (1), the camshaft adjuster (6) having 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), characterized in that the controller (19, 22, 19 ^' ) as an input signal a difference signal from setpoint and actual values and as an output signal one for the adjustment motor ( 8) has a specific, regulated target adjustment speed signal to which an uncontrolled speed signal is added.

Control structure according to claim 1, characterized in that a position control, which relates to the camshaft adjustment angle, and additionally a speed control, which relates to the adjustment engine speed, are provided.

Control structure according to claim 2, characterized in that, among other things, P, PI, PID, prediction or observer controllers can be used as controllers for position and speed control.

4. Control structure according to claim 3, characterized in that a prediction controller (22), depending on the respective adjustment angle jump of the camshaft (5), specifies an adjustment speed which is just retardable by the adjustment motor (8) in the period available for this purpose.

5. Control structure according to claim 4, characterized in that for the position control preferably the prediction controller (22) and for the speed control preferably the PID controller (19 ^' ) are provided, which can be used individually or in series.

6. Control structure according to claim 5, characterized in that with position control of the prediction controller (22) as the input signal, the difference signal (17 + 18) between an actual adjustment angle (17) and a target adjustment angle (18) of the camshaft (5) and as an output signal (20 ^' ) has a regulated target adjustment speed for the adjustment motor (8) and that the added speed is the camshaft speed (21).

7. Control structure according to claim 5, characterized in that with speed control the PID controller (19 ^' ) as the input signal, the difference signal

(23 + 24) between an actual adjusting speed (23) and a target adjusting speed (24) of the adjusting motor (8) and as an output signal (20 ^" ) a regulated target adjusting speed for the adjusting motor (8) in the form of a voltage value or a has duty cycle modulated voltage and that the added speed the unregulated and voltage converted

Desired adjustment speed (24) of the adjustment motor (8).

8. Control structure according to claim 5, characterized in that when the prediction controller (22) and the PID controller (19 ^' ) are connected in series, the output signal (20 ^' ) of the prediction controller (22) with added camshaft speed (21) in voltage-converted form at the same time as an activation signal (20 ^' + 21) for the output signal (20 ^" ) of the PID controller (19 ^' ) is used.

9. Control structure according to claim 8, characterized in that preferably the PID controller (19 ^' ) of the speed control has a current limiting function, preferably a two-point current controller.

10. Control structure according to claim 1, characterized in that the angular position of the camshaft (5) by a camshaft sensor (10) or by a Hall sensor (13) of the adjusting motor (8) is measurable.