JP2004190590A - Reciprocating variable compression ratio engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve high speed output in a setting state of the low compression ratio. <P>SOLUTION: This reciprocating variable compression ratio engine has a lower link 2 rotatably installed on a crank pin 1a of a crankshaft 1, an upper link 5 for linking this lower link 2 and a piston 3 and a variable compression ratio means for variably controlling the engine compression ratio by changing a motion restricting condition of the lower link 2. When a crank angle until the piston becomes a maximum lowering speed from the upper dead center is set to θ1H in a setting state of the high compression ratio, and a crank angle until the piston becomes a maximum lowering speed from the upper dead center is set to θ1L in a setting state of the low compression ratio, θ1H≥θ1L is realized. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an improvement of a multi-link reciprocating variable compression ratio engine capable of changing an engine compression ratio.
[0002]
[Prior art]
In the field of reciprocating internal combustion engines suitably used for automobiles, various variable compression ratio engines capable of changing the engine compression ratio have been proposed in order to make the engine compression ratio appropriate in accordance with the operating state. ing. For example, Patent Literature 1 discloses a multi-link variable compression ratio engine in which a piston and a crankpin are linked by a plurality of links, and an engine compression ratio can be changed by changing a motion constraint condition of the link. ing.
[0003]
[Patent Document 1]
JP 2000-73804 A
[Problems to be solved by the invention]
In such a multi-link variable compression ratio engine, by changing the link geometry, in addition to the engine compression ratio, piston stroke characteristics, which greatly affect engine operation performance such as output performance and fuel consumption performance, especially piston speed Can be set from a wide range. However, a sufficient study has not been made on the pattern of the piston speed according to the setting state of the engine compression ratio.
[0005]
SUMMARY OF THE INVENTION It is a main object of the present invention to optimize the setting of the piston stroke characteristics, particularly the maximum piston rising speed and the maximum descending speed according to the setting state of the engine compression ratio, and to effectively improve the engine operation performance.
[0006]
[Means for Solving the Problems]
A reciprocating variable compression ratio engine according to the present invention includes a plurality of links that link a piston and a crankpin of a crankshaft, and can variably control an engine compression ratio by changing a motion constraint condition of the link. . Then, in a setting state of the high compression ratio, the crank angle until the piston reaches the maximum descent speed from the top dead center is θ1H, and in a setting state of the low compression ratio, the crank angle until the piston reaches the maximum descent speed from the top dead center. Assuming that the crank angle is θ1L, a feature is that θ1H ≧ θ1L.
[0007]
【The invention's effect】
According to the present invention, since θ1H ≧ θ1L, for example, in a setting state of a low compression ratio used in a high load region, the volume efficiency on the high-speed side can be focused on and the maximum output can be effectively improved. it can.
[0008]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0009]
FIG. 1 is a schematic configuration diagram showing a reciprocating variable compression ratio engine according to an embodiment of the present invention. The variable compression ratio engine includes an upper link 5 and a lower link 2 as a plurality of links that link the piston 3 and the crankpin 1a of the crankshaft 1. The lower link 2 is rotatably attached to the crank pin 1a. One end of the upper link 5 is connected to the piston 3 by the piston pin 4, and the other end is connected to the lower link 2 by the first connection pin 10. Further, a variable control means for variably controlling the engine compression ratio by changing the motion constraint condition of the lower link 2 is provided. The variable control means includes a control shaft 7 extending in the cylinder row direction parallel to the crankshaft 1, an eccentric cam 8 eccentrically provided on the control shaft 7, and a control for linking the eccentric cam 8 and the lower link 2. A link 6. The control link 6 has one end connected to the lower link 2 by the second connection pin 9 and the other end swingably mounted on the eccentric cam 8. When the control shaft 7 is rotationally driven by a hydraulic or electric actuator 12 as a driving means, the other end position of the control link 6 attached to the eccentric cam 8, that is, the position of the swing center of the control link 6 is adjusted. Change. Thereby, the engine compression ratio can be variably controlled by changing the motion constraint condition of the lower link 2.
[0010]
2 to 4 show an example of a link geometry of a reciprocating variable compression ratio engine satisfying the following settings (1) to (6). 2 shows a setting state of a low compression ratio, and FIG. 3 shows a setting state of a high compression ratio. Points P0 to P5 denote a rotation center P0 of the crankshaft 1, a center P1 of the crankpin 1a, and a piston by the piston pin 4, respectively. 3, a connection center P2 between the upper link 5 and the first connection pin 10, a connection center P3 between the upper link 5 and the lower link 2, a connection center P4 between the lower link 2 and the control link 6 by the second connection pin 9, and a control link 6. (The center of the eccentric cam 8) P5. In FIG. 4, trajectories PH1 to PH5 indicate trajectories of points P1 to P5 in a high compression ratio setting state, and trajectories PL1 to PL5 indicate trajectories of points P1 to P5 in a low compression ratio setting state. .
[0011]
As shown in FIG. 4, the piston reciprocation axis (PH2, PL2) is offset to one side (right side in FIG. 4) with respect to a reference line Y1 extending in the cylinder axis direction through the rotation center P0 of the crankshaft 1. The upper link-lower link connection center locus PH3, PL3 is located on the offset side. On the other hand, the swing center P5 (PH5, PL5) of the control link 6 and the link center locus PH4, PL4 of the lower link-control link are on the opposite side (left side in FIG. 4) from the offset side with respect to the reference line Y1. To position.
[0012]
The swing center P5 of the control link is set so as to be farther from the reference line Y1 in the low compression ratio setting state PL5 than in the high compression ratio setting state PH5. That is, when the engine compression ratio is increased, the swing center P5 is set so as to approach the reference line Y1.
[0013]
In addition, by controlling the control shaft 7 to rotate in multiple steps or steplessly including the setting state of the low compression ratio and the setting state of the high compression ratio, the compression ratio can be variably controlled in multiple steps or steplessly. Can be.
[0014]
With reference to FIG. 5, definitions of symbols used in this specification will be described. In FIGS. 5 and 6 to 11, high CR corresponds to the setting state of the high compression ratio by the variable compression ratio means, and low CR corresponds to the setting state of the low compression ratio.
[0015]
(Equation 1)
Vmax1: Maximum descending speed of the piston (mm / rad)
Vmax1H: Vmax1 in the setting state of the high compression ratio
Vmax1L... Vmax1 in a low compression ratio setting state
Vmax2: Maximum ascent speed of the piston (mm / rad)
Vmax2H: Vmax2 in a high compression ratio setting state
Vmax2L: Vmax2 in the setting state of the low compression ratio
θ1 ... Crank angle (°) from top dead center to Vmax1
θ1H: θ1 in a high compression ratio setting state
θ1L: θ1 in the setting state of the low compression ratio
θ2: crank angle (°) from Vmax2 to top dead center
θ2H: θ2 in a high compression ratio setting state
θ2L: θ2 in a low compression ratio setting state
As is well known, in a general four-stroke internal combustion engine, the intake stroke and the expansion stroke are the piston downstrokes, and the exhaust stroke and the compression stroke are the piston upstrokes. Therefore, the maximum descending speed is the maximum piston speed in the intake stroke and the expansion stroke, and the maximum rising speed is the maximum piston speed in the exhaust stroke and the compression stroke.
[0016]
In a single-link reciprocating engine in which a crankpin and a piston are linked by a single connecting rod, both θ1 and θ2 are uniquely determined by a crank radius-conrod length ratio, and the crank radius and the connecting rod length are determined by a piston side force, a piston and a crank. Since there is a restriction due to interference avoidance with the shaft, inertial weight of the connecting rod, and the like, both θ1 and θ2 are substantially limited to the range of about 72 to 76 °.
[0017]
On the other hand, in the multiple link type variable compression ratio engine as in the present embodiment, θ1, θ2, Vmax1, etc. can be set from a wide range depending on the setting of the geometry of the plurality of link parts. The influence on the sound vibration performance, the maximum low-speed torque, the maximum high-speed torque, the fuel efficiency, and the like by the setting is increased. Preferably, in a high load range (output range), control for lowering the compression ratio, that is, setting of a low compression ratio, is used to improve the maximum output by taking the optimum ignition timing while avoiding knocking. In a low load region including the load fuel consumption region, control for increasing the compression ratio, that is, setting of a high compression ratio is used in order to improve thermal efficiency and improve fuel efficiency.
[0018]
In this embodiment, as will be described later, the maximum output (torque) on the high speed side in the setting state of the low compression ratio used in the high load region can be effectively improved. In order to improve the maximum output described above, it is only necessary to increase the volumetric efficiency and reduce the pump loss. However, since the values of θ1 and θ2 at which the volume efficiency becomes maximum are different from the values of θ1 and θ2 at which the pump loss becomes minimum (specifically, a value on the maximum volume efficiency side is a small value, and a value on the minimum pump loss side is a large value). In the present embodiment, the following characteristic settings (1) to (6) are performed in consideration of both the volume efficiency and the pump loss.
(1) θ1H ≧ θ1L
That is, the crank angle θ1H until the piston reaches the maximum descending speed Vmax1H from the top dead center in the setting state of the high compression ratio, and the crank angle θ1H until the piston reaches the maximum descending speed Vmax1L from the top dead center in the setting state of the low compression ratio. Above the crank angle θ1L.
[0019]
As shown in FIG. 6, the smaller the value of θ1 is (the closer the maximum descent speed is to the top dead center), the greater the inertia effect during the intake stroke, which is the piston ascending stroke, on the high speed side, and the more the volume efficiency is improved. On the low speed side, the inertia effect during the intake stroke is reduced, and the volume efficiency is reduced. Conversely, as θ1 is increased (the timing of the maximum descent speed is moved away from the top dead center), the volume efficiency decreases on the high speed side, and improves on the low speed side. Therefore, by setting the piston speed characteristics so that the above θ1H ≧ θ1L, in a high load range using a low compression ratio setting, the high speed side can be used as compared with a case using a high compression ratio setting. Volumetric efficiency is improved, and its maximum output can be improved. In addition, in the high-speed and low-load region using the high compression ratio setting, the piston descending speed in the early stage of the intake stroke is smaller than in the case where the low compression ratio setting is used, and the air inflow speed at the time when the intake valve starts to open. And the pump loss is reduced. Further, since the inertia effect is reduced and the volumetric efficiency is reduced, the throttle opening required for inhaling the same amount of air can be further increased, and the pump loss is further reduced, and the effect of improving fuel efficiency is obtained.
(2) | θ1H−θ1L | ≧ | θ2H−θ2L |
That is, the absolute value | θ1H−θ1L | of the value obtained by subtracting θ1L from θ1H is set to be equal to or greater than the absolute value | θ2H−θ2L | of the value obtained by subtracting the crank angle θ2L from θ2H.
[0020]
As shown in FIG. 7, the volume efficiency is improved as θ1 becomes smaller in the entire region at least in the range of 50 ≦ θ1 ≦ 130. The volume efficiency is highest when θ2 is around 80 °, and the volume efficiency decreases as the angle deviates from around 80 °. Therefore, it is better that θ2 does not greatly deviate from a value near 80. Accordingly, by setting | θ1H−θ1L | ≧ | θ2H−θ2L | in addition to the above-described setting of θ1H ≦ θ1L, the rate of change of θ2 accompanying a change in the compression ratio becomes relatively small, and Irrespective of the setting of the ratio, it is possible to keep θ2 close to 80 and suppress a decrease in volumetric efficiency. In addition, the rate of change of θ1 with the change of the compression ratio becomes relatively large, and the volume efficiency can be sufficiently increased and improved with the reduction of the compression ratio.
[0021]
Further, in order to change the compression ratio, it is necessary to rotate the control shaft 7 by the actuator 12 and move the eccentric cam 8 serving as the swing center of the control link 6 with respect to the engine body. In order to reduce the energy required for rotationally driving the control shaft 7 and the control time, the amount of movement of the eccentric cam 8 with respect to the engine body is suppressed to the minimum necessary, and the change in the compression ratio is reduced. It is better to reduce the amount of change in θ2 (the amount of movement in the direction of the vertical axis θ2 in FIG. 7). | Θ1H−θ1L | ≧ | θ2H−θ2L |, and by suppressing the rate of change of θ2 with a change in the compression ratio to be relatively low, the energy required for rotationally driving the control shaft 7 can be reduced. In addition, the control time can be reduced.
(3) Vmax1H ≦ Vmax1L
That is, the maximum lowering speed Vmax1H of the piston in the setting state of the high compression ratio is equal to or less than the maximum lowering speed Vmax1L of the piston in the setting state of the low compression ratio.
[0022]
Increasing the piston maximum descent speed increases the inertial effect during the intake stroke, which greatly contributes to the improvement of volumetric efficiency. Therefore, as shown in FIG. 8, by setting θ1H ≧ θ1L and Vmax1H ≦ Vmax1L, it is possible to effectively improve the volumetric efficiency in a high load region using a low compression ratio setting. In addition, in a low load region using a high compression ratio setting, the piston maximum descent speed is relatively low, reducing pump losses and improving fuel economy.
(4) | θ1H-90 | ≧ | θ1L-90 |
That is, the absolute value | θ1H−90 | of the value obtained by subtracting 90 (°) from the crank angle θ1H between the top dead center and the maximum descent speed in the setting state of the high compression ratio is calculated as the upper value in the setting state of the low compression ratio. The absolute value | θ1H−90 | of the value obtained by subtracting 90 (°) from the crank angle θ1L between the dead center and the maximum descending speed is equal to or more than the absolute value | θ1H−90 |.
[0023]
When the setting for increasing the output on the high-speed side is made as in (1) to (3) above, the sound and vibration performance in this high-speed output region relatively decreases. Compared with a conventional general single-link type internal combustion engine, in a multiple-link type variable compression ratio engine as in the present embodiment, the number of link parts is increased, and the friction in the bearing portion is increased, so that the high-speed range is reduced. It is important to secure output and control vibration. Therefore, as shown in FIG. 9, by setting | θ1H-90 | ≧ | θ1L-90 |, the piston descending stroke in the setting of the low compression ratio used in the high-speed and high-load region is relatively close to a simple vibration, At the same time as improving the volumetric efficiency, the sound and vibration performance can be mainly improved, and the high-speed output can be improved by reducing the friction.
(5) | θ2H-90 | ≧ | θ2L-90 |
For the same reason as the above (4), as shown in FIG. 10, assuming that | θ2H-90 | ≧ | θ2L-90 |, the piston ascending stroke at a low compression ratio setting used in a high load region is simply set. By approaching the vibration, the sound and vibration performance in a high-speed and high-load region can be improved, and the output can be improved with a reduction in friction. In particular, by setting | θ2H-90 | ≧ | θ2L-90 | and | θ1H-90 | ≧ | θ1L-90 |, sound vibration performance in a high-speed output range can be sufficiently improved.
(6) θ2H ≦ θ2L
That is, the crank angle θ2H between the maximum piston speed and the top dead center when the high compression ratio is set is equal to or less than the crank angle θ2H between the maximum piston speed and the top dead center when the low compression ratio is set.
[0024]
In a high-speed, high-load range, when θ2 is small (the timing at which the piston reaches its maximum ascending speed is close to the top dead center), the pump loss increases near the top dead center at which the intake start / exhaust ends, and the output decreases. Therefore, it is desirable to increase θ2 (make the timing of the maximum piston rise speed away from the top dead center) to reduce the pump loss. Therefore, as shown in FIG. 11, by setting θ2H ≦ θ2L, pump loss in a high-speed and high-load region using a low compression ratio setting can be mainly reduced, and the output and fuel efficiency can be improved. However, in order to further improve the high-speed output, it is necessary to set θ2L so as to improve the volume efficiency. Therefore, it is preferable that 80 ≦ θ2 ≦ 90 and θ2H ≦ θ2L.
[0025]
As described in (1) to (6) above, not only θ1H, θ2H, θ1L, θ2L, etc. are optimized according to the setting state of the compression ratio, but also the setting of the variable ranges of θ1 and θ2, that is, the upper dead By defining the angle range with respect to the point, the output on the low-speed side and the high-speed side can be more effectively increased.
[0026]
For example, by setting θ1 ≧ 90, as compared with the case of θ1 ≦ 90, both the low compression ratio and the high compression ratio are improved, the volume efficiency on the low speed side is improved, and the low speed torque is improved. Thus, an effect of improving fuel economy by reducing pump loss can be obtained.
[0027]
When θ1L ≧ θ1H is satisfied in such an area where θ1 ≧ 90, the output on the low speed side can be mainly improved. On the other hand, when θ1L ≧ θ1H in the range of θ1 ≦ 90, the output on the high-speed side can be improved while the decrease in the low-speed torque is kept small.
[0028]
Considering volume efficiency and pump loss, the high-speed torque becomes maximum when θ2 is around 80 °, and decreases as θ2 deviates from around 80 °. On the other hand, the maximum torque on the low speed side is not very sensitive to the change of θ2. Therefore, by setting θ2 to be close to 80 °, it is possible to effectively increase the high-speed torque while suppressing a decrease in the low-speed torque.
[0029]
The volumetric efficiency decreases with substantially the same tendency when θ2 shifts from around 80 ° to either the top dead center side or the bottom dead center side. The sound vibration performance tends to decrease as θ2 goes away from 90 ° (corresponding to simple vibration). Therefore, by setting 80 ≦ θ2 ≦ 90, it is possible to achieve both improvement in high-speed / low-speed torque and improvement in sound vibration performance. In addition, by expanding the valve overlap, the optimum timing of θ2 can be set to be closer to the top dead center.
[0030]
In order to averagely improve the torque over the entire range without causing excessive reduction in either the low-speed torque or the high-speed torque, the region where the sum of the low-speed torque improvement rate and the high-speed torque improvement rate is the maximum (θ1 = 115 ° ± 10 °, θ2 = 80 ° ± 10 °), it is possible to improve the maximum torque in the entire speed range from high speed to low speed.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing a reciprocating variable compression ratio engine according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram showing a link geometry of a variable compression ratio engine in a setting state of a low compression ratio.
FIG. 3 is an explanatory diagram showing a link geometry of a variable compression ratio engine in a setting state of a high compression ratio.
FIG. 4 is an explanatory diagram showing trajectories of link connection points and rotation centers of the variable compression ratio engine.
FIG. 5 is a characteristic diagram showing piston speed characteristics in a set state of a low compression ratio and a high compression ratio.
FIG. 6 is a diagram illustrating setting of θ1H ≧ θ1L and its operation.
FIG. 7 is a diagram illustrating the setting of | θ1H−θ1L | ≧ | θ2H−θ2L | and the operation thereof.
FIG. 8 is a diagram illustrating the setting of Vmax1H ≦ Vmax1L and the operation thereof.
FIG. 9 is a diagram illustrating the setting of | θ1H-90 | ≧ | θ1L-90 | and the operation thereof.
FIG. 10 is a diagram illustrating the setting of | θ2H-90 | ≧ | θ2L-90 | and its operation.
FIG. 11 is a diagram illustrating setting of θ2H ≦ θ2L and its operation.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Crank shaft 1a ... Crank pin 2 ... Lower link 3 ... Piston 4 ... Piston pin 5 ... Upper link 6 ... Control link 7 ... Control shaft 8 ... Eccentric cam 12 ... Actuator

Claims (7)

Multiple links linking the piston and the crankpin of the crankshaft,
A variable compression ratio means that variably controls the engine compression ratio by changing the motion constraint condition of the link,
In the setting state of the high compression ratio, the crank angle until the piston reaches the maximum descending speed from the top dead center is θ1H,
In a setting state of a low compression ratio, assuming that the crank angle until the piston reaches the maximum descending speed from the top dead center is θ1L,
A reciprocating variable compression ratio engine, wherein θ1H ≧ θ1L. In the setting state of the high compression ratio, the crank angle from the state where the piston reaches the maximum ascending speed to the top dead center is θ2H,
In a setting state of a low compression ratio, when a crank angle from a state where the piston reaches the maximum ascending speed to a point where the piston reaches the top dead center is θ2L,
The variable compression ratio engine according to claim 1, wherein | θ1H-θ1L | ≧ | θ2H-θ2L |. In the setting state of the high compression ratio, the maximum descending speed of the piston is set to Vmax1H,
When the maximum lowering speed of the piston is Vmax1L in the setting state of the low compression ratio,
3. The reciprocating variable compression ratio engine according to claim 1, wherein Vmax1H ≦ Vmax1L. The reciprocating variable compression ratio engine according to any one of claims 1 to 3, wherein | θ1H-90 | ≧ | θ1L-90 |. In the setting state of the high compression ratio, the crank angle from the state where the piston reaches the maximum ascending speed to the top dead center is θ2H,
In a setting state of a low compression ratio, when a crank angle from a state where the piston reaches the maximum ascending speed to a point where the piston reaches the top dead center is θ2L,
The reciprocating variable compression ratio engine according to any one of claims 1 to 4, wherein | θ2H-90 | ≧ | θ2L-90 |. In the setting state of the high compression ratio, the crank angle from the state where the piston reaches the maximum ascending speed to the top dead center is θ2H,
In a setting state of a low compression ratio, when a crank angle from a state where the piston reaches the maximum ascending speed to a point where the piston reaches the top dead center is θ2L,
The reciprocating variable compression ratio engine according to claim 1, wherein θ2H ≦ θ2L. The plurality of links are configured by a lower link rotatably attached to a crankpin of a crankshaft, and an upper link that cooperates with the lower link and a piston,
The variable compression ratio means drives a control shaft extending in the cylinder row direction, an eccentric cam provided eccentrically to the control shaft, a control link that links the eccentric cam and the lower link, and a rotational drive of the control shaft. The reciprocating variable compression ratio engine according to any one of claims 1 to 6, further comprising a driving unit.

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