JP2019019675A - Variable compression ratio device for internal combustion engine - Google Patents

Abstract

To provide a variable compression ratio device for an internal combustion engine that can prevent breakage of components in reverse operation.SOLUTION: A friction screw mechanism 33 changes a rotational position of a control axis 13 of a variable compression ratio device by converting turning force of an electric motor 18 into thrust force of a plate 20. The friction screw mechanism has reverse efficiency characteristic that reverse efficiency declines as a stroke amount of the plate 20 on a high compression ratio side is small.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a variable compression ratio device for an internal combustion engine.

  In Patent Document 1, a plurality of driven rollers are pressed against a driving roller at a predetermined crossing angle, and a stroke member that supports the driven roller by using an axial motion accompanying a rotational motion generated in the driven roller by the rotation of the driving roller. A so-called twist roller type power conversion mechanism that performs the feed operation is disclosed.

JP 2004-197864 A

When the conventional power conversion mechanism is applied to a reduction gear of an electric motor in a variable compression ratio mechanism of an internal combustion engine, if the electric motor fails, the stroke member is struck by a stopper when the reverse operation is caused by an external force, and the parts are damaged. There was a risk of it occurring.
An object of the present invention is to provide a variable compression ratio device for an internal combustion engine that can prevent component damage during reverse operation.

  In the variable compression ratio device for an internal combustion engine in an embodiment of the present invention, the power conversion mechanism has a reverse efficiency characteristic in which the reverse efficiency is lower when the engine compression ratio is low than when it is high.

  Therefore, it is possible to prevent component damage during reverse operation.

1 is a configuration diagram of a variable compression ratio mechanism 1 according to Embodiment 1. FIG. FIG. 3 is a longitudinal sectional view of the actuator 16 according to the first embodiment. FIG. 3 is a cross-sectional view taken along line S3-S3 in FIG. FIG. 4 is a diagram showing the relationship between the rotation axis O1 of the drive roller 22 and the rotation axis O2 of the driven roller 23. FIG. 4 is a diagram showing a relationship between a stroke amount of a plate 20 and a thrust reaction force received from the variable compression ratio mechanism 1. FIG. 3 is a diagram showing a usage area in a compression ratio of the engine 2. FIG. 6 is a characteristic diagram of reverse efficiency η _t with respect to the stroke amount of the plate 20 in the friction screw mechanism 33 of the first embodiment. FIG. 6 is a characteristic diagram of the design pressing force of the driven roller 23 with respect to the stroke amount of the plate 20 in the friction screw mechanism 33 of the first embodiment. FIG. 10 is a characteristic diagram of reverse efficiency η _t with respect to the stroke amount of the plate 20 in the friction screw mechanism 33 of the second embodiment. FIG. 10 is a characteristic diagram of the design pressing force of the driven roller 23 with respect to the stroke amount of the plate 20 in the friction screw mechanism 33 of the second embodiment. FIG. 10 is a characteristic diagram of reverse efficiency η _t with respect to the stroke amount of the plate 20 in the friction screw mechanism 33 of the third embodiment. 4 is a time chart of external force input to the friction screw mechanism 33 when the engine 2 is operated at high speed and low torque. FIG. 10 is a characteristic diagram of reverse efficiency η _t with respect to the stroke amount of the plate 20 in the friction screw mechanism 33 of another embodiment.

Embodiment 1
FIG. 1 is a configuration diagram of a variable compression ratio mechanism 1 according to the first embodiment.
The variable compression ratio mechanism 1 of the first embodiment is a multi-link variable compression ratio mechanism, and changes the engine compression ratio of an engine (internal combustion engine) 2 mounted on a vehicle. The piston 3 of the engine 2 is disposed in a cylinder 4a formed in the cylinder block 4. The piston 3 slides in the cylinder 4a. One end of the upper link 5 is connected to the piston 3 via a piston pin 3a so as to be swingable. The other end of the upper link 5 is rotatably connected to one end of the lower link 7 via a first connecting pin 6. The lower link 7 is swingably attached to the crankpin 8a of the crankshaft 8 at the center thereof. The piston 3 receives combustion pressure from a combustion chamber defined above it. The crankshaft 8 is rotatably supported on the cylinder block 4 by a crank bearing bracket 9.

One end of the control link 10 is rotatably connected to the other end of the lower link 7 via a second connecting pin 11. The other end of the control link 10 is swingably supported by a part of the engine 2 main body, and the position of the swing fulcrum 12 can be displaced with respect to the engine 2 main body in order to change the engine compression ratio. is there. Specifically, a control shaft 13 extending in parallel with the crankshaft 8 is provided, and the other end of the control link 10 is rotatably fitted to an eccentric shaft 14 provided eccentric to the control shaft 13. The control shaft 13 is rotatably supported between the crank bearing bracket 9 and the control bearing bracket 15.
Therefore, when the control shaft 13 is rotationally driven by an actuator 16 (see FIG. 2), which will be described later, in order to change the engine compression ratio, the center position of the eccentric shaft 14 serving as the swing fulcrum 12 of the control link 10 is moved to the engine 2 body. Move against. As a result, the motion constraint condition of the lower link 7 by the control link 10 changes, and the stroke position of the piston 3 with respect to the crank angle changes, whereby the engine compression ratio is changed.

2 is a longitudinal sectional view of the actuator 16 according to the first embodiment, and FIG. 3 is a sectional view taken along line S3-S3 in FIG.
The actuator 16 changes the rotational position of the control shaft 13. The actuator 16 includes a housing 17, an electric motor 18, a friction screw mechanism 33, and a plate 20.
The housing 17 is fixed to the cylinder block 4. The housing 17 is formed in a substantially cylindrical shape, and has a motor housing portion 17a and a friction screw housing portion 17b inside. The motor housing portion 17a and the friction screw housing portion 17b are separated by a partition wall 17c.
The electric motor 18 is accommodated in the motor accommodating portion 17a. The electric motor 18 is, for example, a brushless motor. The motor drive shaft 19 passes through the partition wall 17c, and one end portion 19a projects into the friction screw housing portion 17b. The vicinity of one end 19a of the motor drive shaft 19 is supported by a ball bearing 20a fixed to the partition wall 17c so as to be rotatable around the rotation axis O1 of the motor drive shaft 19. The other end 19b of the motor drive shaft 19 is supported by a ball bearing 20b fixed to the bottom 17d of the housing 17 so as to be rotatable around the rotation axis O1. A resolver 21 that detects the rotation angle of the motor drive shaft 19 is provided in the motor housing portion 17a. The resolver 21 outputs rotation angle information to a control unit (not shown).

Hereinafter, the X axis is set in the direction along the rotation axis O1, and the direction from the other end 19b side to the one end 19a side in the X axis direction is defined as the X axis positive direction. The direction around the rotation axis O1 is referred to as a circumferential direction, and the radial direction of the rotation axis O1 is referred to as a radial direction.
The friction screw mechanism 33 is housed in the friction screw housing portion 17b. The friction screw mechanism 33 is a power conversion mechanism that converts the rotational force of the electric motor 18 into the thrust of the plate 20. The friction screw mechanism 33 includes a driving roller 22 and a driven roller 23.
The drive roller 22 is a cylindrical member extending in the X-axis direction, and rotates integrally with the motor drive shaft 19. One end 22a of the drive roller 22 is splined to one end 19a of the motor drive shaft 19. The other end portion 22b of the driving roller 22 protrudes toward the X axis positive direction side from the friction screw housing portion 17b. The rotation axis of the drive roller 22 coincides with the rotation axis O1 of the drive roller 22.
Three driven rollers 23 are located on the outer peripheral side of the driving roller 22 and are arranged at equal intervals in the circumferential direction. The driven roller 23 is in rolling contact with the drive roller 22 while being pressed against the drive roller 22 by a set pressing force. As shown in FIG. 4, the driven roller 23 has a rotation axis O2 that is inclined with respect to the rotation axis O1 of the drive roller 22 by a predetermined crossing angle (lead angle) θ. Journal portions 23a and 23b are provided at both ends of the driven roller 23 in the X-axis direction. Both journal portions 23a and 23b are supported so as to be rotatable about the rotation axis O2 with respect to the plate 20.

The plate 20 is linked to the tip of the arm 26 fixed to the control shaft 13 via an intermediate link 27. The plate 20 has a front plate 28 and a rear plate 29. The front plate 28 is arranged with a predetermined gap on the X axis positive direction side of the rear plate 29. One end of the intermediate link 27 is connected to the front plate 28 via a connecting pin 30 so as to be swingable. A through hole 28a through which the drive roller 22 passes is formed at the center of the front plate 28. A radial bearing 24a and a thrust bearing 25a that support the journal portion 23a of the driven roller 23 are fixed to the front plate 28.
A radial bearing 24b and a thrust bearing 25b that support the journal portion 23b of the driven roller 23 are fixed to the rear plate 29. At the center of the rear plate 29, a through hole 29a through which the drive roller 22 passes is formed. A spacer 31 is interposed between the plates 28 and 29. The spacer 31 is formed in a cylindrical shape, and a screw 32 for fastening both the plates 28 and 29 passes through the spacer 31.

  The friction screw mechanism 33 according to the first embodiment presses the three driven rollers 23 against the driving roller 22 at a predetermined crossing angle θ, and performs the movement in the X-axis direction accompanying the rotational movement generated in the driven roller 23 by the rotation of the driving roller 22. This is a so-called twist roller type power conversion mechanism that uses the plate 20 to make a stroke. As the plate 20 strokes, the arm 26 swings and the rotational position of the control shaft 13 changes, whereby the engine compression ratio changes. In the variable compression ratio mechanism 1 of the first embodiment, when the plate 20 strokes in the positive direction of the X axis, the control shaft 13 rotates in a direction to increase the engine compression ratio. On the other hand, when the plate 20 strokes in the positive direction of the X axis, the control shaft 13 rotates in a direction to lower the engine compression ratio. Hereinafter, the stroke of the plate 20 in the positive X-axis direction is referred to as the stroke toward the high compression ratio, and the stroke in the negative X-axis direction is referred to as the stroke toward the low compression ratio. The control unit basically decreases the engine compression ratio as the load on the engine 2 is lower, and increases the engine compression ratio as the load on the engine 2 is higher. Thereby, coexistence with fuel consumption performance and output performance is realizable. The stroke of the plate 20 in the negative direction of the X axis is regulated by the interference with the partition wall 17c. That is, the partition wall 17c functions as a stopper that defines the stroke range of the plate 20. In addition, you may provide another component as a stopper.

  FIG. 5 is a diagram showing the relationship between the stroke amount [mm] of the plate 20 and the thrust reaction force [N] received from the variable compression ratio mechanism 1. The external force (thrust reaction force) input to the plate 20 is uniquely determined according to the stroke amount due to the characteristics of the variable compression ratio mechanism 1. In FIG. 5, the stroke amount when the plate 20 is at the low compression ratio side end in the stroke possible range, that is, at the position corresponding to the lowest compression ratio, is 0, and the stroke amount toward the high compression ratio side is a positive value. . As shown in FIG. 5, the thrust reaction force has a characteristic that the maximum is obtained when the stroke amount is the median value and becomes smaller as the stroke amount is farther from the median value. The thrust reaction force when the stroke amount is 0 and the thrust reaction force when the stroke amount is the maximum (when the plate 20 is in a position corresponding to the maximum compression ratio) are almost the same.

Here, when the electric motor 18 fails in a state where the plate 20 is stroked to the maximum compression ratio or a high compression ratio in the vicinity thereof, the following problems are concerned.
When the friction screw mechanism 33 reversely operates (straight line → rotation) due to an external force from the variable compression ratio mechanism 1, the plate 20 rapidly strokes and is struck against the partition wall 17c, resulting in component damage.
On the other hand, when the reverse operation of the friction screw mechanism 33 is impossible, the engine compression ratio is fixed to the maximum compression ratio or a high compression ratio in the vicinity thereof. FIG. 6 is a diagram showing a use area in the compression ratio of the engine 2. As shown in FIG. 6, the usable range of the engine 2 becomes smaller as the engine compression ratio becomes higher. For this reason, if the engine compression ratio is fixed at the maximum compression ratio or a high compression ratio in the vicinity thereof, the operating range of the engine 2 is limited, and there is a high possibility that a desired output cannot be obtained.

In the first embodiment, aiming to solve the above problem, the reverse efficiency characteristic according to the stroke amount of the friction screw mechanism 33 is set so that the reverse efficiency is lower when the engine compression ratio is low than when it is high. . Reverse efficiency [%] is the efficiency at the time of reverse operation (ratio of output to input). FIG. 7 is a characteristic diagram of the reverse efficiency η _t with respect to the stroke amount of the plate 20 in the friction screw mechanism 33 of the first embodiment. In FIG. 7, the reverse efficiency η _t has a characteristic of increasing in proportion to the stroke amount. The reverse efficiency characteristic of FIG. 7 can be realized by making the design pressing force of the driven roller 23 inversely proportional to the stroke amount of the plate 20, as shown in FIG. At this time, the design pressing force on the high compression ratio side should not be less than the necessary minimum pressing force. The required minimum pressing force is the minimum pressing force required for making the plate 20 stroke, and is proportional to the thrust reaction force shown in FIG. As shown in FIG. 8, a linear design pressing force characteristic in which the design pressing force increases as the engine compression ratio is lower is in contact with the curve representing the required minimum pressing force characteristic on the high compression ratio side. The reverse efficiency characteristics shown can be realized.
In the first embodiment, in order to change the design pressing force according to the stroke amount of the plate 20, a method of changing the outer diameter of the driving roller 22 in contact with each driven roller 23 according to the stroke amount of the plate 20 is adopted. ing. Specifically, in the rotation axis O1 direction (X-axis direction) of the drive roller 22, the outer diameter of the drive roller 22 is a driven roller corresponding to the highest compression ratio from the contact position with the driven roller 23 corresponding to the lowest compression ratio. The linear taper shape gradually decreases in diameter toward the contact position with 23.

As described above, the friction screw mechanism 33 according to the first embodiment has reverse efficiency characteristics in which the reverse efficiency decreases as the engine compression ratio decreases, that is, as the stroke amount of the plate 20 toward the high compression ratio decreases. Therefore, the reverse operation resistance value, which is a force necessary for reversely operating the friction screw mechanism 33, increases as the engine compression ratio decreases. For this reason, even if the electric motor 18 fails when the plate 20 is stroked to the maximum compression ratio or a high compression ratio in the vicinity thereof, the reverse operation resistance value is relatively small, so the friction screw mechanism 33 can operate in reverse. The plate 20 receives an external force and strokes toward the low compression ratio side. Thereby, the operation region of the engine 2 is excessively limited, and it is possible to suppress the output from reaching the desired output.
Further, even if the plate 20 rapidly strokes toward the low compression ratio side due to an external force, the plate 20 receives a relatively large reverse operation resistance on the low compression ratio side and decelerates. For this reason, the collision between the plate 20 and the partition wall 17c can be avoided or the collision energy can be reduced. As a result, it is possible to prevent component damage during reverse operation.
In the friction screw mechanism 33 of the first embodiment, the lower the engine compression ratio, that is, the smaller the stroke amount of the plate 20 toward the high compression side, the higher the pressing force of each driven roller 23 against the drive roller 22. As a result, it is possible to easily realize the reverse efficiency characteristic in which the reverse efficiency is lowered as the engine compression ratio is lower.

[Embodiment 2]
Next, the second embodiment will be described. Since the basic configuration of the second embodiment is the same as that of the first embodiment, only the differences from the first embodiment will be described.
FIG. 9 is a characteristic diagram of the reverse efficiency η _t with respect to the stroke amount of the plate 20 in the friction screw mechanism 33 of the second embodiment. In FIG. 9, the reverse efficiency η _t is 0 in the range from the lowest compression ratio to the desired engine compression ratio, and is proportional to the compression ratio in the range from the desired engine compression ratio to the predetermined high compression ratio. In the range from the ratio to the maximum compression ratio, a constant maximum value is set. The reverse efficiency characteristic of FIG. 9 is realized by using a method of changing the outer diameter of the drive roller 22 that contacts each driven roller 23 according to the stroke amount of the plate 20 so that the set pressing force as shown in FIG. 10 is obtained. it can.

In the friction screw mechanism 33 of the second embodiment, the pressing force of each driven roller 23 against the driving roller 22 is a constant maximum value when the engine compression ratio is equal to or less than a desired engine compression ratio. As a result, the reverse efficiency η _t on the lower compression ratio side than the desired engine compression ratio becomes the minimum value, so that when the electric motor 18 fails, the collision between the plate 20 and the partition wall 17c can be avoided or the collision energy can be reduced. In addition, a desired operation region can be used.
In Embodiment 2, since the reverse efficiency η _{t in} the range from the lowest compression ratio to the desired engine compression ratio is 0, the electric motor 18 is operated in a state where the plate 20 is stroked to the highest compression ratio or a high compression ratio in the vicinity thereof. In the case of failure, when the friction screw mechanism 33 is reversely operated, the plate 20 cannot make a stroke toward the lower compression ratio side than the desired engine compression ratio. Therefore, it is possible to reliably prevent the plate 20 from being hit against the partition wall 17c. Further, since the plate 20 can be stroked to a desired engine compression ratio during reverse operation, a desired operating region can be used.

[Embodiment 3]
Next, the third embodiment will be described. Since the basic configuration of the third embodiment is the same as that of the first embodiment, only portions different from the first embodiment will be described.
FIG. 11 is a characteristic diagram of the reverse efficiency η _t with respect to the stroke amount of the plate 20 in the friction screw mechanism 33 of the third embodiment. In FIG. 11, the reverse efficiency η _t is proportional to the compression ratio in the range from the desired engine compression ratio to a predetermined high compression ratio in the range L from the lowest compression ratio to the desired engine compression ratio, In the range from the predetermined high compression ratio to the maximum compression ratio, the constant maximum value is set. The range L is a movement amount (stroke amount) when the plate 20 is returned to the high compression ratio side when the engine 2 is operated at high speed and low torque. The calculation method of the minimum value of the reverse efficiency η _t and the movement amount L is shown below.

  FIG. 12 is a time chart of the external force input to the friction screw mechanism 33 when the engine 2 is operated at high speed and low torque. In FIG. 12, the sign of the external force is reversed in the section from time t1 to t2. This is because, when the engine 2 is under a low load, the external force acting on the friction screw mechanism 33 is mainly an alternating load due to the operating inertia (inertial force) of the variable compression ratio mechanism 1. By the way, when the engine 2 is heavily loaded, the external force acting on the friction screw mechanism 33 is caused by the variable compression ratio mechanism 1 receiving the explosive force of the engine 2 because the explosive force in the expansion stroke increases. The swinging load input to the screw mechanism 33 is mainly used. A portion indicated by hatching in FIG. 12 is energy for returning the plate 20 from the low compression ratio side to the high compression ratio side, and this energy × reverse efficiency is an external force input to the electric motor 18. From there, the movement amount L is obtained.

In the section from time t1 to time t2, the equation of motion of the external force that returns the plate 20 from the low compression ratio side to the high compression ratio side is the following expression (1).
Here, I _e is the inertia on the combustion chamber side on the link shaft, A is the vibration amplitude, and ω is the vibration period.
The relationship between the external force and the friction screw mechanism 33 is expressed by the following equation (2) from the law of conservation of momentum.
Here, η _t is the reverse efficiency, m is the mass of the plate 20, and v is the moving speed of the plate 20.
When the equation (2) is transformed, the movement amount L of the plate 20 becomes the following equation (3).
Therefore, the minimum value of the reverse efficiency η _t is obtained by setting the movement amount L to a desired engine compression ratio and substituting it into the equation (3).

In the third embodiment, the reverse efficiency η _t in the range L from the lowest compression ratio to the desired engine compression ratio is a certain minimum value, and is higher than the desired engine compression ratio when the engine 2 is operated at high speed and low torque. The plate 20 that has been stroked to the low compression ratio side can be stroked to the desired engine compression ratio by an external force. Here, in Embodiment 2, since the reverse efficiency η _{t in} the range from the lowest compression ratio to the desired engine compression ratio is 0, the plate 20 is in a state of being stroked to the higher compression ratio side than the desired engine compression ratio. When the electric motor 18 breaks down, the friction screw mechanism 33 cannot be reversely operated even when the engine 2 is operated at a high speed and a low torque, so there is a concern that the fuel efficiency may deteriorate. On the other hand, in the third embodiment, the plate 20 can be returned to the high compression ratio side by the external force during the high rotation / low torque operation, so that the fuel efficiency performance of the engine 2 during the high rotation / low torque operation can be improved. Since the minimum value of reverse efficiency η _t is sufficiently smaller than the maximum value, when the plate 20 rapidly strokes toward the low compression ratio due to an external force, the collision between the plate 20 and the partition wall 17c is avoided, or the collision Energy can be reduced.

[Other Embodiments]
As mentioned above, although the form for implementing this invention was demonstrated based on embodiment, the concrete structure of this invention is not limited to embodiment, The design change of the range which does not deviate from the summary of invention And the like are included in the present invention.
The variable compression ratio mechanism is not limited to the multi-link variable compression ratio mechanism shown in the embodiment, and the present invention can be applied as long as the engine compression ratio is determined by the rotational position of the control shaft.
The method of changing the set pressing force characteristics of each driven roller in accordance with the stroke amount of the stroke member is arbitrary, and for example, a piezoelectric element as described in JP-A-2004-197864 may be used. In this case, as shown in FIG. 13, it is possible to set a reverse efficiency characteristic such that the reverse efficiency η _t changes stepwise at a desired engine compression ratio.

1 Variable compression ratio mechanism
2 Engine
13 Control axis
16 Actuator
18 Electric motor
20 Plate (Stroke member)
22 Drive roller
23 Followed roller
33 Friction screw mechanism (power conversion mechanism)

Claims (5)

A variable compression ratio mechanism that changes the engine compression ratio according to the rotational position of the control shaft;
An actuator for changing the rotational position of the control shaft;
With
The actuator is
A stroke member linked to the control shaft;
An electric motor;
A power conversion mechanism that converts the rotational force of the electric motor into the thrust force of the stroke member,
A drive roller that is rotationally driven by the electric motor;
The shaft is rotatably supported by the stroke member, has an axis that is inclined with respect to the axial direction of the drive roller, is in rolling contact with the drive roller in a state of being pressed against the drive roller, and the stroke member is connected to the drive roller. A plurality of driven rollers that generate thrust to stroke in the axial direction;
A power conversion mechanism;
With
A variable compression ratio device for an internal combustion engine, wherein the power conversion mechanism has a reverse efficiency characteristic in which the reverse efficiency is lower when the engine compression ratio is low than when the engine compression ratio is high. The variable compression ratio device for an internal combustion engine according to claim 1,
The reverse efficiency when the engine compression ratio is less than or equal to a predetermined compression ratio is lower than when the engine compression ratio exceeds the predetermined compression ratio, and is higher than the predetermined compression ratio when the power conversion mechanism is reversely operated. A variable compression ratio device for an internal combustion engine in which the stroke member at a position corresponding to the engine compression ratio on the low compression ratio side is a value that can be stroked to a position corresponding to the predetermined compression ratio by an external force input to the stroke member . The variable compression ratio device for an internal combustion engine according to claim 1,
The power conversion mechanism is a variable compression ratio device for an internal combustion engine having a reverse efficiency characteristic in which the reverse efficiency becomes zero when the engine compression ratio is equal to or less than a predetermined compression ratio. The variable compression ratio device for an internal combustion engine according to any one of claims 1 to 3,
The power conversion mechanism is a variable compression ratio device for an internal combustion engine in which the pressing force of the plurality of driven rollers against the drive roller is higher when the engine compression ratio is low than when the engine compression ratio is high. The variable compression ratio device for an internal combustion engine according to claim 4,
The power conversion mechanism is a variable compression ratio mechanism of an internal combustion engine in which the pressing force is a constant maximum value when the engine compression ratio is equal to or less than a predetermined compression ratio.