CN114790941A - Method and device for controlling position of eccentric shaft of variable compression ratio mechanism - Google Patents

Abstract

The invention provides a method and a device for controlling the position of an eccentric shaft of a variable compression ratio mechanism. The control method can improve the accuracy of the position adjustment of the eccentric shaft, thereby being beneficial to realizing the accurate adjustment of the compression ratio of the engine.

Description

Method and device for controlling position of eccentric shaft of variable compression ratio mechanism

Technical Field

The invention relates to the technical field of engines, in particular to a method for controlling the position of an eccentric shaft of a variable compression ratio mechanism, and meanwhile, the invention also relates to a device for controlling the position of the eccentric shaft of the variable compression ratio mechanism.

Background

In order to cope with the increasingly stringent emission regulations of automobiles, research and development of new technologies have been actively conducted in various vehicle companies, and thus HCCI technology, LP-EGR technology, PDI technology, VCR technology, and the like have come into play. The VCR technology, namely the variable compression ratio technology, refers to the technology that can adjust the compression ratio of the engine in the running process of the engine, and can ensure that the engine obtains a proper compression ratio in the whole working range from low load to high load by adjusting the compression ratio along with the change of the load of the engine so as to improve the running performance of the engine.

In a variable compression ratio engine, a multi-link variable compression ratio mechanism which adopts the matching of an eccentric shaft and a multi-link mechanism so as to drive the eccentric shaft to rotate through the multi-link mechanism and further realize the change of the top dead center of an engine piston has become the research and development direction of many vehicle enterprises. In order to ensure that the engine can realize accurate control of the compression ratio in the whole working condition range, the actual position of the eccentric shaft is required to be consistent with the target position or within an allowable error range. However, in the current variable compression ratio mechanism, the accurate control of the position of the eccentric shaft still has defects, thereby influencing the accuracy of the adjustment of the compression ratio of the engine.

Disclosure of Invention

In view of the above, the present invention is directed to a method for controlling the position of an eccentric shaft of a variable compression ratio mechanism, so as to improve the accuracy of adjusting the position of the eccentric shaft.

In order to achieve the purpose, the technical scheme of the invention is realized as follows:

a position control method of an eccentric shaft of a variable compression ratio mechanism, which is applied to an engine having the variable compression ratio mechanism including the eccentric shaft and a motor that drives the eccentric shaft to rotate, a first detecting unit that detects an angle of the eccentric shaft being provided on the engine, the control method comprising:

a1. acquiring a target angle Des _ Ang of the eccentric shaft according to a target compression ratio, and acquiring the number of rotation turns N of the motor according to the target angle Des _ Ang, wherein N | Des _ Ang-Act _ Ang | Tra _ Rat/360 °, Act _ Ang is the current angle of the eccentric shaft detected by the first detection unit, and Tra _ Rat is the transmission ratio from the motor to the eccentric shaft;

a2. and controlling the motor to rotate, and fixing the rotating position of the motor after the motor rotates for N circles.

Further, the control method further includes:

a3. obtaining a current angle Act _ Ang 'of the eccentric shaft through the first detection unit, and judging whether the Del _ Ang-Act _ Ang' | is not greater than a first preset angle threshold value;

a4. if | Des _ Ang-Act _ Ang '| is less than or equal to a first preset angle threshold, ending the execution of the strategy, and if | Des _ Ang-Act _ Ang' | > the first preset angle threshold, entering a 5;

a5. obtaining the number of turns N 'of the motor according to the current angle Act _ Ang', wherein N '| Des _ Ang-Act _ Ang' | Tra _ Rat/360 degrees;

a6. controlling the motor to rotate, and fixing the rotating position of the motor after the motor rotates for N' circles;

a7. the a3-a6 is repeated until the | Des _ Ang-Act _ Ang' | is less than or equal to a first preset angle threshold value.

Furthermore, the engine further comprises a second detection unit, the second detection unit is used for detecting the number of turns of the motor, the first detection unit comprises a first rotary transformer sensor arranged at the eccentric shaft, and the second detection unit comprises a second rotary transformer sensor arranged at the motor.

Further, the second rotation sensor is located inside the motor.

Furthermore, one end of the eccentric shaft is connected with a harmonic reducer, and the motor is in transmission connection with the harmonic reducer through a belt.

Further, before executing the control method, whether the first detection unit and the second detection unit are in failure is detected, and the control method is executed only when neither the first detection unit nor the second detection unit is in failure.

Further, if the first detection unit is detected to be faulty, the control method includes:

b1. respectively obtaining a current angle Act _ Ang and a target angle Des _ Ang of the eccentric shaft according to a current compression ratio and a target compression ratio, and obtaining the number of rotation turns N of the motor according to an | Des _ Ang-Act _ Ang |;

b2. and controlling the motor to rotate, and fixing the rotating position of the motor after the motor rotates for N circles.

Further, the control method further includes:

b3. and repeating b1-b2 until the gas _ Des _ Ang-Act _ Ang _ Oc is less than or equal to a second preset angle threshold value.

Furthermore, the engine further comprises a second detection unit, wherein the second detection unit is used for detecting the rotation number of turns of the motor, if the second detection unit is detected to be in fault, the control method comprises the steps of obtaining a target angle Des _ Ang of the eccentric shaft according to a target compression ratio, obtaining a current angle Act _ Ang of the eccentric shaft by the first detection unit, and controlling the motor to rotate until | Des _ Ang-Act _ Ang | is not more than a second preset threshold angle.

Compared with the prior art, the method for controlling the position of the eccentric shaft of the variable compression ratio mechanism has the following advantages:

according to the method for controlling the position of the eccentric shaft of the variable compression ratio mechanism, the position of the eccentric shaft is detected, and the accuracy of the rotation control of the motor and the eccentric shaft can be ensured by utilizing the common detection of the two detection units, so that the accuracy of the position adjustment of the eccentric shaft can be improved, and the accurate adjustment of the compression ratio of an engine can be realized.

In addition, the two detection units respectively positioned at the eccentric shaft and the motor are arranged, and when one detection unit fails, the other detection unit is utilized to adjust the position of the eccentric shaft, so that the defect that the compression ratio cannot be accurately adjusted due to the failure of a detection part can be avoided, and the safety coefficient of the running of the engine can be further guaranteed.

Another objective of the present invention is to provide a position control device for an eccentric shaft of a variable compression ratio mechanism, the control device comprises a controller, a first detecting unit for detecting the angle of the eccentric shaft, and a second detecting unit for detecting the number of turns of a motor for driving the eccentric shaft, and during the operation of the engine, the following control method is implemented:

a1. acquiring a target angle Des _ Ang of the eccentric shaft according to a target compression ratio, and acquiring the number of rotation turns N of the motor by using the target angle Des _ Ang, wherein N | Des _ Ang-Act _ Ang | Tra _ Rat/360 °, Act _ Ang is the current angle of the eccentric shaft detected by the first detection unit, and Tra _ Rat is the transmission ratio from the motor to the eccentric shaft;

a2. and controlling the motor to rotate, and fixing the rotating position of the motor after the motor rotates for N circles.

The control device of the invention has the same beneficial effects as the control method, and is not repeated herein.

Drawings

The accompanying drawings, which are included to provide a further understanding of the invention, illustrate embodiments of the invention and together with the description serve to explain the invention and do not constitute a limitation of the invention. In the drawings:

fig. 1 is a schematic structural view of a variable compression ratio mechanism according to an embodiment of the present invention;

fig. 2 is an overall schematic view of a variable compression ratio mechanism according to the embodiment of the invention;

FIG. 3 is a schematic diagram of an embodiment of an eccentric shaft position control scheme;

FIG. 4 is a diagram showing an example of the comparison between the compression ratio and the eccentric shaft angle according to the embodiment of the present invention;

FIG. 5 is a diagram illustrating a comparison between an angle of an eccentric shaft and a number of turns of a motor according to an embodiment of the present invention;

description of reference numerals:

1. a piston; 2. an execution connecting rod; 3. a crankshaft; 4. adjusting the connecting rod; 5. a drive link; 6. an eccentric shaft; 7. an eccentric wheel; 8. a motor; 9. a harmonic speed reducer; 10. a belt; 11. a first detection unit.

Detailed Description

It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.

In the description of the present invention, it should be noted that, if terms indicating orientation or positional relationship such as "upper", "lower", "inside", "outside", etc. appear, they are based on the orientation or positional relationship shown in the drawings and are only for convenience of describing the present invention and simplifying the description, but do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus, should not be construed as limiting the present invention. Furthermore, the appearances of the terms first, second, etc. in this specification are not necessarily all referring to the same order, but are to be construed as referring to the same order.

The present invention will be described in detail below with reference to the embodiments with reference to the attached drawings.

The present embodiment relates to a position control device for an eccentric shaft of a variable compression ratio mechanism, wherein the variable compression ratio mechanism is specifically a multi-connecting-rod type variable compression ratio mechanism which adopts an eccentric shaft 6 to cooperate with a multi-connecting-rod mechanism so as to be driven by the multi-connecting-rod mechanism when the eccentric shaft 6 is driven to rotate, thereby realizing top dead center change of an engine piston 1.

As shown in fig. 1, an exemplary structure of the multi-link type variable compression ratio mechanism of the present embodiment is integrally constituted by a piston 1, an actuating connecting rod 2 having one end hingedly connected to the piston 1, a driving connecting rod 5 having one end rotatably connected to an eccentric 7 on an eccentric shaft 6, and an adjusting connecting rod 4 rotatably provided on a crankshaft 3 and having both ends rotatably connected to the actuating connecting rod 2 and the driving connecting rod 5, respectively.

The adjusting connecting rod 4 is rotatably mounted on a connecting rod journal of the crankshaft 3, the actuating connecting rod 2 and the piston 1, and the actuating connecting rod 2 and the adjusting connecting rod 4 of the driving connecting rod 5 are rotatably connected through connecting rod pins, and the crankshaft 3 is rotatably arranged in an engine cylinder body through a main journal thereof.

In the present embodiment, the overall structure of the variable compression ratio mechanism when it includes a driving portion is shown in fig. 2, in this case, the driving portion includes a motor 8 and a harmonic reducer 9, and the harmonic reducer 9 is installed at one end of the eccentric shaft 6, and the motor 8 is connected to the harmonic reducer 9 through a belt 10, so as to drive the rotation of the eccentric shaft 6 by the motor 8.

When the variable compression ratio mechanism of the embodiment is in operation, the engine ECU sends a control command to the motor 8 according to the current engine load, and the motor 8 rotates to drive the eccentric shaft 6 to rotate through the belt 10 and the harmonic reducer 9. The rotation of the eccentric shaft 6 is transmitted via the driving connecting rod 5, the adjusting connecting rod 4 and the actuating connecting rod 2, so that the top dead center of the piston 1 is changed, thereby achieving the adjustment of the engine compression ratio.

Based on the above description of the variable compression ratio mechanism, the eccentric shaft position control device of the variable compression ratio mechanism of the present embodiment includes a controller, and a first detecting unit 11 for detecting the angle of the eccentric shaft 6, and a second detecting unit for detecting the number of turns of the motor 8.

The above-mentioned controller may be, for example, the engine ECU, or alternatively, a separate control unit may be provided for the compression ratio adjustment, while, as a preferred embodiment, the first detection unit 11 includes a first rotation sensor provided at the eccentric shaft 6, and the first rotation sensor may be provided at the other end of the eccentric shaft 6 with respect to the end to which the harmonic reducer 9 is connected. The second detection unit includes a second rotation sensor disposed at the motor 8, and the second rotation sensor may be disposed inside the motor 8.

The present embodiment is applicable to a resolver sensor having two detecting units, and the present invention can be applied to any sensor device of this type, and the arrangement of the sensor device at the eccentric shaft 6 and the motor 8 is also applicable to the prior art. In addition, it should be noted that, instead of using a rotation sensor, the present embodiment can also use other sensor structures to detect the angle of the eccentric shaft 6 and the number of turns of the motor 8. Meanwhile, it should be noted that, when a resolver sensor or other sensor structure is adopted, the number of revolutions of the motor 8 is generally obtained by the controller, which is referred to the prior art means.

The eccentric shaft position control device of the variable compression ratio mechanism of the present embodiment, which is mainly included in the engine operation in the control method for the position of the eccentric shaft, executes the following control method:

a1. obtaining a target angle Des _ Ang of the eccentric shaft 6 according to the target compression ratio, and obtaining the number of rotation turns N of the motor 8 from the target angle Des _ Ang, where N | Des _ Ang-Act _ Ang | Tra _ Rat/360 °, Act _ Ang is the current angle of the eccentric shaft 6 detected by the first detection unit 11, and Tra _ Rat is the transmission ratio between the motor 8 and the eccentric shaft 6. Wherein normally, if (Des _ Ang-Act _ Ang) > 0, the motor 8 rotates forward, otherwise the motor 8 rotates backward.

a2. Under the detection of the second detection unit, after controlling the motor 8 to rotate for N circles, the rotation position of the motor 8 is fixed.

In the above-described strategy, the target angle Des _ Ang of the eccentric shaft 6 is obtained based on the target compression ratio, which is generally obtained by looking up the correspondence relationship between the target compression ratio and the eccentric shaft angle. And the correspondence relationship between the target compression ratio and the eccentric shaft angle is preset in the controller, and an example thereof may be as shown in fig. 4. Fig. 4 shows only an exemplary trend of the relationship between the target compression ratio and the eccentric shaft angle, and in specific implementation, a specific numerical value proportional relationship between the target compression ratio and the eccentric shaft angle, and a corresponding relationship diagram of the target compression ratio and the eccentric shaft angle matched with the proportional relationship between the target compression ratio and the eccentric shaft angle can be obtained through calibration of multiple tests, which are not repeated in this embodiment.

In addition, the belt transmission structure for the transmission connection of the motor 8 and the harmonic reducer 9 in the variable compression ratio mechanism may have a risk of gear skipping, and inevitably, component abrasion occurs after a long time operation, resulting in deterioration of the transmission precision of the mechanism.

For this reason, preferably, on the basis of the steps a1 and a2, the embodiment further includes the following policies:

a3. the current angle Act _ Ang 'of the eccentric shaft 6 is obtained through the first detection unit 11, and whether the | Des _ Ang-Act _ Ang' | is not greater than a first preset angle threshold value is judged.

a4. If the | Des _ Ang-Act _ Ang '| is less than or equal to a first preset angle threshold value, execution of the strategy is finished, and if the | Des _ Ang-Act _ Ang' > the first preset angle threshold value, the operation enters a5.

a5. The number of turns N ' of the motor 8 is obtained from the current angle Act _ Ang ', wherein N ' | Des _ Ang-Act _ Ang ' | Tra _ Rat/360 °, and wherein normally the motor 8 is rotated in the forward direction if (Des _ Ang-Act _ Ang ') > 0, otherwise the motor 8 is rotated in the reverse direction.

a6. Under the detection of the second detection unit, after controlling the motor 8 to rotate for N' turns, the rotation position of the motor 8 is fixed.

a7. Repeating a3-a6 until the agent Des _ Ang-Act _ Ang' | ≦ the first preset angle threshold.

In a specific embodiment, the first preset angle threshold may be 1 °, so that, through a closed-loop control process of multiple cycles, when the deviation between Des _ Ang and Act _ Ang' is within the first preset angle threshold range, the compression ratio deviation corresponding to the deviation of 1 ° on the position of the eccentric shaft 6 is 0.01, and the eccentric shaft 6 can be considered to reach the required target position within an acceptable range. Of course, it is better to make Des _ Ang match Act _ Ang ', i.e., Des _ Ang-Act _ Ang' ═ 0, than within the deviation range of 1 °.

In this embodiment, through the detection of first detecting element 11 to eccentric shaft 6 position to and the second detecting element is to the detection of motor 8 rotation number of turns, the accuracy of motor 8 and eccentric shaft 6 rotation control is guaranteed in usable two detecting element's common detection from this, can improve the accuracy of eccentric shaft 6 position control, and is favorable to realizing the accurate regulation of engine compression ratio.

It should be noted, however, that when two detection units are provided, both detection units may fail due to the effects of various uncontrollable factors and as the usage time increases. At this time, for this situation, the control method of this embodiment further includes detecting whether the first detecting unit 11 and the second detecting unit are failed before executing the policy, and executing the policy only when neither the first detecting unit 11 nor the second detecting unit is failed.

As shown in fig. 3, before executing the strategy, it is detected whether the first detecting unit 11 and the second detecting unit are failed, specifically, when performing the compression ratio adjustment, the determination of the eccentric shaft position control mode is performed first. When both the detection units are normal, the control of the position of the eccentric shaft 6 is performed by using the above-mentioned strategy, and when one of the two detection units fails, the following control method can be used.

Specifically, if the first detecting unit 11 is detected to be faulty, the control method of the embodiment includes:

b1. the current angle Act _ Ang and the target angle Des _ Ang of the eccentric shaft 6 are respectively obtained according to the current compression ratio and the target compression ratio, and the number of turns N of the rotation of the motor 8 is obtained according to the De _ Ang-Act _ Ang. And wherein normally the motor 8 rotates forward if (Des _ Ang-Act _ Ang) > 0, otherwise the motor 8 rotates backward.

b2. Under the detection of the second detection unit, after controlling the motor 8 to rotate for N circles, the rotation position of the motor 8 is fixed.

In the above b1, similarly to the aforementioned obtaining of the target angle Des _ Ang of the eccentric shaft 6 based on the target compression ratio, obtaining the current angle Act _ Ang and the target angle Des _ Ang of the eccentric shaft 6 according to the current compression ratio and the target compression ratio can also be obtained by inquiring the correspondence relationship between the compression ratio and the eccentric shaft angle.

The number of turns N of the motor 8 can be obtained according to the corresponding relationship between the angle of the eccentric shaft and the number of turns of the motor 8, and at this time, the corresponding relationship between the angle of the eccentric shaft and the number of turns of the motor 8 is also preset in the controller, and an example thereof can be as shown in fig. 5. Fig. 5 also only shows an exemplary variation trend of the relationship between the angle of the eccentric shaft and the number of turns of the motor 8, and in specific implementation, the specific numerical value proportional relationship between the two and the corresponding relationship diagram between the angle of the eccentric shaft and the number of turns of the motor 8, which are fit for the specific numerical value proportional relationship, can also be obtained by calibration of multiple tests, and further description is omitted for this embodiment.

Similar to the foregoing strategy, when the first detecting unit 11 fails, the control method of this embodiment further includes:

b3. and repeating b1-b2 until the agent Des _ Ang-Act _ Ang _ agent is less than or equal to a second preset angle threshold value.

In practical applications, the second predetermined angle threshold may also be 1 °. With such an arrangement, the present embodiment can also make the position deviation of the eccentric shaft 6 within the acceptable range through the multi-cycle closed-loop control process, and thus the eccentric shaft 6 can be considered to reach the required target position.

In this embodiment, if a failure of the second detecting unit is detected, the control method includes obtaining a target angle Des _ Ang of the eccentric shaft 6 according to a target compression ratio, obtaining a current angle Act _ Ang of the eccentric shaft 6 by the first detecting unit 11, and controlling the motor 8 to rotate until | Des _ Ang-Act _ Ang | is less than or equal to a second preset angle threshold, where normally, if (Des _ Ang-Act _ Ang) > 0, the motor 8 rotates forward, otherwise, the motor 8 rotates backward.

Therefore, when the second detection unit fails, the rotation number of the motor 8 is not acquired any more, but the motor 8 is directly driven to rotate, and as long as the actual position of the eccentric shaft 6 does not reach the target position, the motor 8 is controlled to continue to rotate until the position of the eccentric shaft 6 reaches the required target position.

The position control method of the eccentric shaft 6 of the embodiment can improve the accuracy of position adjustment of the eccentric shaft 6, and through the arrangement of the two detection units, when one detection unit breaks down, the other detection unit can be used for adjusting the position of the eccentric shaft 6, so that the defect that the compression ratio cannot be accurately adjusted due to the failure of a detection part can be avoided, the safety factor of engine operation can be guaranteed, and the method has good practicability.

The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents, improvements and the like that fall within the spirit and principle of the present invention are intended to be included therein.

Claims (10)

1. A position control method of an eccentric shaft of a variable compression ratio mechanism, which is applied to an engine having the variable compression ratio mechanism, characterized in that: the variable compression ratio mechanism comprises an eccentric shaft (6) and a motor (8) for driving the eccentric shaft (6) to rotate, a first detection unit (11) for detecting the angle of the eccentric shaft (6) is arranged on the engine, and the control method comprises the following steps:

a1. acquiring a target angle Des _ Ang of the eccentric shaft (6) according to a target compression ratio, and acquiring the number of rotation turns N of the motor (8) from the target angle Des _ Ang, wherein N | Des _ Ang-Act _ Ang | Tra _ Rat/360 °, Act _ Ang is the current angle of the eccentric shaft (6) detected by the first detection unit (11), and Tra _ Rat is the transmission ratio from the motor (8) to the eccentric shaft (6);

a2. and controlling the motor (8) to rotate, and fixing the rotating position of the motor (8) after the motor (8) rotates N circles.

2. The eccentric shaft position control method of a variable compression ratio mechanism according to claim 1, characterized in that: the control method further comprises the following steps:

a3. obtaining a current angle Act _ Ang 'of the eccentric shaft (6) through the first detection unit (11), and judging whether an | Des _ Ang-Act _ Ang' is not greater than a first preset angle threshold value;

a4. if the | Des _ Ang-Act _ Ang '| is less than or equal to a first preset angle threshold value, ending the execution of the strategy, and if the | Des _ Ang-Act _ Ang' > the first preset angle threshold value, entering a 5;

a5. obtaining a number of rotations N 'of the motor (8) according to the current angle Act _ Ang', wherein N '| Des _ Ang-Act _ Ang' | Tra _ Rat/360 °;

a6. controlling the motor (8) to rotate, and fixing the rotating position of the motor (8) after the motor (8) rotates N' turns;

a7. the a3-a6 is repeated until the | Des _ Ang-Act _ Ang' | is less than or equal to a first preset angle threshold value.

3. The method of controlling the position of the eccentric shaft of the variable compression ratio mechanism according to claim 1, characterized in that: the engine further comprises a second detection unit, the second detection unit is used for detecting the number of rotation turns of the motor (8), the first detection unit (11) comprises a first rotation change sensor arranged at the eccentric shaft (6), and the second detection unit comprises a second rotation change sensor arranged at the motor (8).

4. The eccentric shaft position control method of a variable compression ratio mechanism according to claim 3, characterized in that: the second rotation variation sensor is located inside the motor (8).

5. The method of controlling the position of the eccentric shaft of the variable compression ratio mechanism according to claim 1, characterized in that: one end of the eccentric shaft (6) is connected with a harmonic reducer (9), and the motor (8) is in transmission connection with the harmonic reducer (9) through a belt (10).

6. The variable compression ratio mechanism eccentric shaft position control method according to any one of claims 1 to 5, characterized in that: before executing the control method, whether the first detection unit (11) and the second detection unit are in failure or not is detected, and the control method is executed only when neither the first detection unit (11) nor the second detection unit is in failure.

7. The method of controlling the position of the eccentric shaft of the variable compression ratio mechanism according to claim 6, characterized in that: if the first detection unit (11) is detected to be faulty, the control method comprises:

b1. respectively obtaining a current angle Act _ Ang and a target angle Des _ Ang of the eccentric shaft (6) according to a current compression ratio and a target compression ratio, and obtaining the number of turns N of the motor (8) according to an | Des _ Ang-Act _ Ang |;

b2. and controlling the motor (8) to rotate, and fixing the rotating position of the motor (8) after the motor (8) rotates N circles.

8. The eccentric shaft position control method of a variable compression ratio mechanism according to claim 7, characterized in that: the control method further comprises the following steps:

b3. and repeating b1-b2 until the gas _ Des _ Ang-Act _ Ang _ Oc is less than or equal to a second preset angle threshold value.

9. The eccentric shaft position control method of a variable compression ratio mechanism according to claim 6, characterized in that: the engine further comprises a second detection unit, wherein the second detection unit is used for detecting the number of rotation turns of the motor (8), if the second detection unit is detected to be faulty, the control method comprises the steps of obtaining a target angle Des _ Ang of the eccentric shaft (6) according to a target compression ratio, obtaining a current angle Act _ Ang of the eccentric shaft (6) through the first detection unit (11), and controlling the motor (8) to rotate until an | Des _ Ang-Act _ Ang | is not more than a second preset threshold angle.

10. A position control device for an eccentric shaft of a variable compression ratio mechanism is characterized in that: the control device comprises a controller, a first detection unit (11) for detecting the angle of the eccentric shaft (6) and a second detection unit for detecting the rotation number of a motor (8) for driving the eccentric shaft (6), and the following control method is executed during the operation of the engine:

a1. acquiring a target angle Des _ Ang of the eccentric shaft (6) according to a target compression ratio, and acquiring the number of rotation turns N of the motor (8) according to the target angle Des _ Ang, wherein N | Des _ Ang-Act _ Ang | Tra _ Rat/360 °, Act _ Ang is the current angle of the eccentric shaft (6) detected by the first detection unit, and Tra _ Rat is the transmission ratio from the motor (8) to the eccentric shaft (6);

a2. and controlling the motor (8) to rotate, and fixing the rotating position of the motor (8) after the motor (8) rotates N circles.

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