JP4092476B2 - Reciprocating variable compression ratio engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an improvement of a multi-link type reciprocating variable compression ratio engine capable of changing an engine compression ratio.
[0002]
[Prior art]
In the field of reciprocating internal combustion engines that are preferably used in automobiles, various variable compression ratio engines that can change the engine compression ratio have been proposed in order to make the engine compression ratio appropriate according to the operating conditions. ing. For example, Patent Document 1 discloses a multi-link variable compression ratio engine in which an engine compression ratio can be changed by connecting a piston and a crankpin through a plurality of links and changing a motion constraint condition of the links. ing.
[0003]
[Patent Document 1]
Japanese Patent Laid-Open No. 2000-73804
[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, the piston stroke characteristics, particularly the piston speed, which greatly affect the engine operating performance such as output performance and fuel consumption performance. The pattern can be set from a wide range. However, sufficient studies have not been made so far on the piston speed pattern and the like according to the set state of the engine compression ratio.
[0005]
The main object of the present invention is to optimize the piston stroke characteristics, particularly the settings relating to the piston maximum ascending speed and the maximum descending speed, according to the set state of the engine compression ratio, and to effectively improve the engine operating performance.
[0006]
[Means for Solving the Problems]
The 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 the engine compression ratio by changing the motion constraint condition of the links. . Then, the crank angle until the piston reaches the maximum lowering speed from the top dead center in the high compression ratio setting state is θ1H, and the piston until the piston reaches the maximum lowering speed from the top dead center in the low compression ratio setting state. When the crank angle is θ1L, it is characterized by θ1H ≦ θ1L.
[0007]
【The invention's effect】
According to the present invention, since θ1H ≦ θ1L, the volume efficiency on the low speed side can be improved and the maximum output can be effectively improved in a low compression ratio setting state used in, for example, a high load region.
[0008]
DETAILED DESCRIPTION OF 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 together. The lower link 2 is rotatably attached to the crankpin 1a. The upper link 5 has one end connected to the piston 3 by the piston pin 4 and the other end connected to the lower link 2 by the first connection pin 10. In addition, 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 in parallel with the crankshaft 1, an eccentric cam 8 provided eccentric to the control shaft 7, and a control for linking the eccentric cam 8 and the lower link 2. And a link 6. One end of the control link 6 is connected to the lower link 2 by the second connection pin 9, and the other end is attached to the eccentric cam 8 so as to be swingable. By rotating and driving the control shaft 7 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 determined. Change. As a result, the motion constraint condition of the lower link 2 can be changed and the engine compression ratio can be variably controlled.
[0010]
FIGS. 2-4 has shown an example of the link geometry of the reciprocating variable compression ratio engine which satisfy | fills setting (1)-(6) mentioned later. 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 are respectively a rotation center P0 of the crankshaft 1, a center P1 of the crankpin 1a, and a piston by a piston pin 4. 3 and the connection center P2 of the upper link 5, the connection center P3 of the upper link 5 and the lower link 2 by the first connection pin 10, the connection center P4 of the lower link 2 and the control link 6 by the second connection pin 9, and the control link 6 The center of swing (center of the eccentric cam 8) P5 is shown. The trajectories PH1 to 5 in FIG. 4 indicate the trajectories of the points P1 to P5 in the high compression ratio setting state, and the trajectories PL1 to 5 indicate the trajectories of the points P1 to P5 in the low compression ratio setting state. .
[0011]
As shown in FIG. 4, the piston reciprocating 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 connection center locus PH4, PL4 of the lower link-control link are on the side opposite to the offset side (left side in FIG. 4) with respect to the reference line Y1. To position.
[0012]
The swing center P5 of the control link is set to be closer to 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 move away from the reference line Y1.
[0013]
Including the low compression ratio setting state and the high compression ratio setting state, the control shaft 7 is rotationally driven in multiple steps or steplessly to variably control the compression ratio in multiple steps or steplessly. Can do.
[0014]
With reference to FIG. 5, the definition of symbols used in this specification will be described. 5 and 6 to 11, high CR corresponds to a high compression ratio setting state by the variable compression ratio means, and low CR corresponds to a low compression ratio setting state.
[0015]
[Expression 1]
Vmax1: Maximum descending speed of the piston (mm / rad)
Vmax1H: Vmax1 in a high compression ratio setting state
Vmax1L: Vmax1 in a low compression ratio setting state
Vmax2: Maximum rising speed of the piston (mm / rad)
Vmax2H: Vmax2 when the high compression ratio is set
Vmax2L: Vmax2 in a low compression ratio setting state
θ1 ... Crank angle from top dead center to Vmax1 (°)
θ1H: θ1 in a high compression ratio setting state
θ1L: θ1 in a low compression ratio setting state
Crank angle (°) from θ2 to 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-cycle internal combustion engine, the intake stroke and the expansion stroke are the piston lowering stroke, and the exhaust stroke and the compression stroke are the piston rising stroke. Accordingly, the maximum descending speed is the maximum piston speed in the intake stroke and the expansion stroke, and the maximum ascent speed is the maximum piston speed in the exhaust stroke and the compression stroke.
[0016]
In a single-link reciprocating engine in which the crank pin and piston are linked by a single connecting rod, both θ1 and θ2 are uniquely determined by the crank radius-connecting rod length ratio. The crank radius and connecting rod length are determined by the piston side force, piston Since it is restricted by the avoidance of interference with the shaft and the inertia weight of the connecting rod, both θ1 and θ2 are substantially limited to a range of about 72 to 76 °.
[0017]
On the other hand, in the multi-link 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 a plurality of link parts. The effect on sound vibration performance, low speed maximum torque, high speed maximum torque, fuel consumption, etc. by the setting becomes large. Preferably, in the high load range (output range), in order to improve the maximum output by taking the optimal ignition timing while avoiding knocking, control using a low compression ratio, that is, a low compression ratio setting is used. In the low load range including the fuel efficiency range of the load, 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 low 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 above maximum output, it is only necessary to increase the volume efficiency and reduce the pump loss. However, the values of θ1 and θ2 at which the volumetric efficiency is maximized are different from the values of θ1 and θ2 at which the pumping loss is minimized (specifically, the volumetric efficiency maximum side is a small value and the pumping loss minimum side is a large value) In the present embodiment, the following characteristic settings (1) to (6) are performed in consideration of both volumetric efficiency and pump loss.
(1) θ1H ≦ θ1L
That is, when the high compression ratio is set, the crank angle θ1H until the piston reaches the maximum lowering speed Vmax1H from the top dead center until the piston reaches the maximum lowering speed Vmax1L from the top dead center when the low compression ratio is set. Of the crank angle θ1L or less.
[0019]
As shown in FIG. 6, as θ1 becomes smaller (the timing of the maximum lowering speed approaches the top dead center), the inertial effect during the intake stroke, which is the piston ascending stroke, increases on the high speed side, and the volume efficiency improves. On the low speed side, the inertial effect during the intake stroke is reduced and the volumetric efficiency is lowered. On the other hand, as θ1 increases (the time of the maximum descending speed moves away from the top dead center), the volume efficiency decreases on the high speed side, and the volume efficiency increases on the low speed side. Therefore, by setting the above θ1H ≦ θ1L, in the high load region using the low compression ratio setting, the volume efficiency on the low speed side is improved as compared with the case where the high compression ratio setting is used. The maximum output can be improved. In other words, the maximum output in the low speed and high load range can be intensively improved.
[0020]
For example, immediately after the start of rapid acceleration from the low speed and low load range, when performing control to reduce the compression ratio in order to avoid knocking, in general, it tends to cause torque reduction due to thermal efficiency reduction or acceleration performance decline, When the setting of θ1H ≦ θ1L is applied as in this embodiment, the volumetric efficiency on the low speed side in the setting state of the low compression ratio is improved, so that the reduction in the acceleration performance accompanying the reduction in the compression ratio is effectively suppressed and avoided. be able to.
[0021]
Immediately after the start of slow acceleration from the low-speed and low-load region, the throttle opening is reduced in order to reduce the intake air amount in accordance with the low load, so the pump loss tends to increase. For such a problem, in this embodiment, by setting θ1H ≦ θ1L, the volumetric efficiency is lower in the high compression ratio setting state used in the low speed and low load region than in the low compression ratio setting state. The throttle opening required for introducing the same amount of air can be increased as compared with the setting state of the low compression ratio. For this reason, it is possible to effectively reduce the pump loss in the low speed and low load range immediately after the start of the slow acceleration, and to improve the fuel efficiency.
(2) | θ1H−θ1L | ≧ | θ2H−θ2L |
That is, the absolute value | θ1H−θ1L | obtained by subtracting θ1L from θ1H is set to be equal to or larger than the absolute value | θ2H−θ2L | obtained by subtracting the crank angle θ2L from θ2H.
[0022]
As shown in FIG. 7, in the low speed range, the change in θ1 has a larger influence on the volumetric efficiency than the change in θ2. That is, the sensitivity of the change in volumetric efficiency with respect to the change in θ2 is relatively low. Further, at least in the range of 50 ≦ θ1 ≦ 130, volume efficiency is improved as θ1 is reduced in the entire region. Therefore, in addition to the above-described setting of θ1H ≦ θ1L, it is set so that | θ1H−θ1L | ≧ | θ2H−θ2L |, and the change rate of θ1 due to the change of the compression ratio is set to the value of θ2 associated with the change of the compression ratio. By setting it as the change rate or more, the volume efficiency in the high load region using the setting of the low compression ratio can be effectively increased / improved.
[0023]
Further, in order to change the compression ratio, it is necessary to rotate the control shaft 7 by the actuator 12 and to 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 shorten 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 prevented. 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). The energy required for rotationally driving the control shaft 7 can be reduced by setting | θ1H−θ1L | ≧ | θ2H−θ2L | In addition, the control time can be shortened.
(3) Vmax1H ≦ Vmax1L
That is, the maximum lowering speed Vmax1H of the piston in the high compression ratio setting state is set to be equal to or lower than the maximum lowering speed Vmax1L of the piston in the low compression ratio setting state.
[0024]
As shown in FIG. 8, when Vmax1 is increased, the inertial effect during the intake stroke is increased and the volume efficiency can be improved. Therefore, in addition to the above setting of θ1H ≧ θ1L, by setting Vmax1H ≦ Vmax1L, it is possible to effectively improve the volume efficiency of the high load region using the setting of the low compression ratio. In addition, in a low load range using a high compression ratio setting, the maximum piston lowering speed is relatively low, and fuel efficiency can be improved by reducing pump loss.
(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 lowering speed in the high compression ratio setting state is set to the upper value in the low compression ratio setting state. The absolute value | θ1H−90 | of the value obtained by subtracting 90 (°) from the crank angle θ1L between the dead center and the maximum lowering speed is set to be equal to or less.
[0025]
As in (1) to (3) above, when θ1 is set so that the output on the low speed side is emphasized, sound vibration and friction are not reduced on the low speed side compared to the high speed side. In addition, it is difficult to achieve the effect of lowering friction and improving output by improving sound vibration performance. Therefore, in the high load range that uses the low compression ratio setting, emphasis is placed on volumetric efficiency improvement over the low-speed sound vibration performance improvement, and in the low load range that uses the high compression ratio setting, the fuel efficiency range is low It is better to set so that the sound vibration performance of the sound is improved. Therefore, as shown in FIG. 9, in addition to the setting of θ1H ≦ θ1L in (1) above, | θ1H−90 | ≦ | θ1L−90 | is set, and the setting of the high compression ratio is set as compared with the setting of the low compression ratio. By making the piston lowering stroke close to simple vibration, the sound vibration performance in the low speed and low load region using the high compression ratio setting can be improved while suppressing and avoiding the output decrease in the high load region.
(5) | θ2H-90 | ≦ | θ2L-90 |
That is, the absolute value | θ2H−90 | of the value obtained by subtracting 90 (°) from the crank angle θ2H between the maximum piston rising speed and the top dead center in the setting state of the high compression ratio is set in the setting state of the low compression ratio. The absolute value | θ2H−90 | of the value obtained by subtracting 90 (°) from the crank angle θ2L between the maximum piston rising speed and the top dead center is set to be equal to or smaller than |
[0026]
Since the torque sensitivity to the change in θ2 is small on the low speed side, the influence of the output decrease in the low speed and high load region due to the change in θ2 is small. Therefore, it is preferable to set θ2 so as to further enhance the sound vibration performance improvement effect in the low speed and low load region of (4). Therefore, as shown in FIG. 10, as | θ2H−90 | ≦ | θ2L−90 |, the piston lowering stroke in the setting state of the high compression ratio is made close to simple vibration, thereby reducing the output in the low speed and high load range. The sound vibration performance in the low speed and low load range can be effectively improved while being suppressed and avoided.
(6) θ2H ≧ θ2L
That is, the crank angle θ2H between the piston maximum ascent speed and the top dead center when the high compression ratio is set is set to be equal to or greater than the crank angle θ2H between the piston maximum ascent speed and the top dead center when the low compression ratio is set.
[0027]
The effect on volumetric efficiency and pump loss with respect to changes in θ2 tends to increase on the high speed side. In the high speed and high load range where the compression ratio is lowered, increasing the volume efficiency is more effective for improving the output than reducing the pump loss. Therefore, θ2 is set to increase the volume efficiency preferentially. Is good. On the other hand, in the high speed and low load range using the high compression ratio setting, it is preferable to set θ2 so that the pump loss is reduced. If θ2 is small (the time when Vmax2 is close to the top dead center side), the pump loss near the top dead center that is the exhaust end / intake start timing may increase, leading to a decrease in output and fuel consumption. It is desirable to reduce the pump loss by setting θ2 at a time far from top dead center. Therefore, as shown in FIG. 11, by setting θ2H ≧ θ2L, the output is improved in the high speed and high load region using the low compression ratio setting, and the fuel efficiency is improved in the high speed and low load region using the high compression ratio setting. Can be achieved.
[0028]
As described in the above (1) to (6), not only θ1H, θ2H, θ1L, θ2L, etc. are appropriately set according to the compression ratio setting state, but also θ1 that changes according to the rotation of the control shaft 7. , Θ2, the output range on the low speed side and the high speed side can be effectively increased by defining the variable range of θ2, that is, the angle range with respect to the top dead center.
[0029]
For example, by setting θ1 ≧ 90, as compared with the case of θ1 ≦ 90, both the high compression ratio and the low compression ratio are set, so that the volume efficiency on the low speed side is improved and the low speed torque is improved. The pump loss reduction rate can be improved and fuel consumption can be improved.
[0030]
When θ1L ≦ θ1H in such a region of θ1 ≧ 90, low-speed torque can be improved while suppressing a decrease in output in the high-speed output region. On the other hand, when θ1L ≦ θ1H is set in the region of θ1 ≦ 90, the output on the high speed side can be intensively improved.
[0031]
In consideration of volumetric efficiency and pump loss, the high-speed torque becomes maximum when θ2 is near 80 °, and decreases as θ2 deviates from the vicinity of 80 °. On the other hand, the maximum torque in the low speed region is not very sensitive in the θ2 direction. Therefore, by setting θ2 in the vicinity of 80 °, the high-speed torque can be effectively improved while sufficiently suppressing the decrease in the low-speed torque.
[0032]
The volumetric efficiency decreases with a similar tendency regardless of whether θ2 shifts from near 80 ° to either the top dead center side or the bottom dead center side. The sound vibration performance tends to decrease as θ2 moves away from 90 ° (corresponding to simple vibration). Therefore, by setting 80 ≦ θ2 ≦ 90, it is possible to achieve both improvement in high-speed torque and improvement in sound vibration performance. Further, by expanding the valve overlap, it is possible to set the optimum time of θ2 closer to the top dead center side.
[0033]
In order to improve the torque on average throughout the entire region without causing excessive reduction of either the low speed torque or the high speed torque, a region where the sum of the low speed torque improvement rate and the high speed torque improvement rate is maximized (θ1 = 115 ° ± 10 ° and θ2 = 80 ° ± 10 ° as a center), the maximum torque can be improved in a wide speed range from a high speed range to a low speed range.
[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 low compression ratio setting state.
FIG. 3 is an explanatory diagram showing a link geometry of a variable compression ratio engine in a high compression ratio setting state.
FIG. 4 is an explanatory diagram showing a link connection point and a rotation center locus of the variable compression ratio engine.
FIG. 5 is a characteristic diagram showing the speed characteristics of a piston in a setting state of a low compression ratio and a high compression ratio.
FIG. 6 is a diagram illustrating the setting of θ1H ≦ θ1L and its operation.
FIG. 7 is a diagram illustrating the setting of | θ1H−θ1L | ≧ | θ2H−θ2L | and its operation.
FIG. 8 is a diagram illustrating the setting of Vmax1H ≦ Vmax1L and its operation.
FIG. 9 is a diagram illustrating the setting of | θ1H−90 | ≦ | θ1L−90 | and its operation.
FIG. 10 is a diagram illustrating the setting of | θ2H−90 | ≦ | θ2L−90 | and its operation.
11 is a diagram illustrating the setting of θ2H ≧ θ2L and its operation. FIG.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Crankshaft 1a ... Crankpin 2 ... Lower link 3 ... Piston 4 ... Piston pin 5 ... Upper link 6 ... Control link 7 ... Control shaft 8 ... Eccentric cam

Claims (7)

A plurality of links linking the piston and crankshaft crankpin;
A reciprocating variable compression ratio engine having variable compression ratio means for variably controlling the engine compression ratio by changing the motion constraint condition of the link,
With the high compression ratio used in the low load range set, the crank angle until the piston reaches the maximum lowering speed from top dead center is θ1H,
When the crank angle from the top dead center to the maximum lowering speed is θ1L in the low compression ratio setting state used in the high load range ,
A reciprocating variable compression ratio engine characterized by θ1H ≦ θ1L. With the high compression ratio set, the crank angle from the state where the piston reaches the maximum ascending speed to the top dead center is θ2H,
When the crank angle from the state where the piston reaches the maximum ascending speed to the top dead center in the low compression ratio setting state is θ2L,
The reciprocating variable compression ratio engine according to claim 1, wherein | θ1H−θ1L | ≧ | θ2H−θ2L |. With the high compression ratio set, the maximum descending speed of the piston is Vmax1H,
When the maximum lowering speed of the piston is Vmax1L in the low compression ratio setting state,
The reciprocating variable compression ratio engine according to claim 1, wherein Vmax1H ≦ Vmax1L. The reciprocating variable compression ratio engine according to claim 1, wherein | θ1H−90 | ≦ | θ1L−90 |. With the high compression ratio set, the crank angle from the state where the piston reaches the maximum ascending speed to the top dead center is θ2H,
When the crank angle from the state where the piston reaches the maximum ascending speed to the top dead center in the low compression ratio setting state is θ2L,
The reciprocating variable compression ratio engine according to claim 1, wherein | θ2H−90 | ≦ | θ2L−90 |. With the high compression ratio set, the crank angle from the state where the piston reaches the maximum ascending speed to the top dead center is θ2H,
When the crank angle from the state where the piston reaches the maximum ascending speed to the top dead center in the low compression ratio setting state is θ2L,
The reciprocating variable compression ratio engine according to claim 1 , wherein θ2H ≧ θ2L. The plurality of links include a lower link that is rotatably attached to a crankpin of a crankshaft, and an upper link that links the lower link and the piston,
The variable compression ratio means includes a control shaft extending in the cylinder row direction, an eccentric cam provided eccentric to the control shaft, a control link linking the eccentric cam and the lower link, and rotating the control shaft. The reciprocating variable compression ratio engine according to any one of claims 1 to 6, further comprising a drive unit.

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