JP5152015B2 - Control device for variable compression ratio internal combustion engine - Google Patents

Description

  The present invention relates to a control device for estimating an actual compression ratio in a variable compression ratio internal combustion engine using a multi-link piston-crank mechanism.

  In order to variably control the compression ratio of an internal combustion engine, as exemplified in Patent Documents 1 and 2, a multi-link variable compression ratio device using a multi-link piston-crank mechanism is known. The piston and crankshaft of the internal combustion engine are connected via a plurality of link members, and are provided with a control link that restricts the degree of freedom of these link members. By changing the dynamic fulcrum position), the piston position is relatively displaced up and down to change the compression ratio. For example, a control shaft having an eccentric shaft to which the control link base end is connected is used to change the swing fulcrum position of the control link, and the rotational position of the control shaft is changed by an actuator such as an electric motor. It has a configuration.

  Further, in such a variable compression ratio internal combustion engine, in order to obtain a variation due to an individual difference in an actual compression ratio, that is, an actual compression ratio, and an error from a target compression ratio, Patent Document 3 uses an in-cylinder pressure sensor. It has been proposed to obtain the compression ratio with high accuracy.

JP 2000-73804 A JP 2002-215902 A JP 2005-48621 A

  However, the method using the in-cylinder pressure sensor as described in Patent Document 3 is costly, and is subject to characteristic variations due to the characteristics of the in-cylinder pressure sensor itself, changes in temperature, and the like. There is a problem that the accuracy is not high. The present invention seeks to obtain variations due to individual differences in compression ratios by a variable compression ratio mechanism with a relatively simple configuration.

  The present invention has a control link in which a piston and a crankshaft of an internal combustion engine are connected via a plurality of link members, and restricts the degree of freedom of these link members. In a variable compression ratio internal combustion engine that is swingably connected to an eccentric shaft of a shaft and whose compression ratio changes in accordance with the rotational position of the control shaft, the control shaft is in a predetermined compression ratio state during fuel cut of the internal combustion engine. It is characterized in that a peak value in a cycle of torque necessary for maintaining the pressure is obtained and an actual compression ratio is estimated from the peak torque.

  In the variable compression ratio mechanism using the multi-link type piston-crank mechanism as described above, the pressure in the combustion chamber acting on the piston acts as a reaction force on the control shaft, and this correlates with the actual compression ratio. In particular, during the fuel cut, a peak torque corresponding to the compression ratio of the engine is generated without being affected by variations in combustion, and the actual compression ratio is estimated from this.

  Preferably, in order to increase the accuracy of estimation of the actual compression ratio, the target compression ratio is controlled to the maximum compression ratio during the fuel cut, and the actual compression ratio is estimated from the peak torque in this state, or the target The compression ratio is controlled to the maximum compression ratio and the minimum compression ratio, and the actual compression ratio can be estimated from the peak torque in each state.

  According to the present invention, it is possible to easily detect variations in the compression ratio due to individual differences in the variable compression ratio mechanism without using an in-cylinder pressure sensor.

The system block diagram of one Example of this invention. Explanatory drawing which shows the input / output signal with respect to a controller collectively. The flowchart which shows 1st Example. The characteristic view which shows the relationship between the torque of a control shaft, and in-cylinder pressure. The characteristic view which shows the relationship between the cylinder pressure for every intake pressure, and a compression ratio. The characteristic view which shows the relationship between the angle of a control shaft, and compression ratio (design value). The characteristic view which shows the dispersion | variation in the cylinder pressure during combustion. The characteristic view which shows the in-cylinder pressure change correlated with the compression ratio during fuel cut. The time chart corresponding to 1st Example. The flowchart which shows 2nd Example. The time chart corresponding to 2nd Example. The flowchart which shows 3rd Example. The flowchart following FIG. The time chart corresponding to 3rd Example. The flowchart which shows 4th Example. The time chart corresponding to 4th Example.

  FIG. 1 shows an example of a basic configuration of a variable compression ratio internal combustion engine equipped with a multi-link variable compression ratio mechanism to which the control device of the present invention is applied. As shown in FIG. A piston 1 is slidably disposed in the cylinder 6, and one end of an upper link 11 is connected to the piston 1 via a piston pin 2 so as to be swingable. The other end of the upper link 11 is rotatably connected to one end portion of the lower link 13 via a first connecting pin 12. The lower link 13 is swingably attached to the crankpin 4 of the crankshaft 3 at the center thereof. The piston 1 receives combustion pressure from a combustion chamber defined above. The crankshaft 3 is rotatably supported on the cylinder block 5 by a crank bearing bracket 7.

  One end of a control link 15 is rotatably connected to the other end of the lower link 13 via a second connecting pin 14. The other end of the control link 15 is swingably supported by a part of the internal combustion engine body, and the position of the swing fulcrum can be displaced with respect to the internal combustion engine body in order to change the compression ratio. It has become. Specifically, a control shaft 18 extending in parallel with the crankshaft 3 is provided, and the other end of the control link 15 is rotatably fitted to an eccentric shaft provided eccentric to the control shaft 18. The control shaft 18 is rotatably supported between the crank bearing bracket 7 and the control bearing bracket 8, and its rotational position is controlled by an actuator mechanism using an electric motor 19. That is, when the control shaft 18 is rotationally driven by the actuator mechanism to change the compression ratio, the center position of the eccentric shaft that becomes the swing fulcrum 16 of the control link 15 moves relative to the engine body. As a result, the motion constraint condition of the lower link 13 by the control link 15 changes, the stroke position of the piston 1 with respect to the crank angle changes, and the engine compression ratio is changed accordingly.

  Here, the combustion load acting on the piston 1 of the engine acts in the direction of pulling up the control link 15 and tries to rotate the control shaft 18 to one of the rotational positions (determined by the arrangement of the eccentric shaft). Accordingly, the reaction force acts on the electric motor 19 even after reaching the target compression ratio, and the electric motor 19 needs to generate torque in order to maintain the constant compression ratio.

  The internal combustion engine includes a throttle valve 21, a fuel injection valve 22, and an intake pressure sensor 23 on the intake passage side, and an air-fuel ratio sensor 24 on the exhaust passage side. Further, it has sensors such as a knocking sensor, a water temperature sensor, a crank angle sensor, a control shaft rotation angle sensor, and an electric motor load sensor (not shown), and these detection signals are shown in FIG. Has been entered.

  The present invention is not limited to the specific type of multi-link variable compression ratio mechanism as shown in the figure, but various types of variable compression in which the actuator of the control shaft receives a reaction force related to the in-cylinder pressure. It can be applied to a ratio mechanism.

  In the above embodiment, an appropriate motor load sensor is provided to detect the holding torque necessary for the electric motor 19 when the compression ratio is in the predetermined compression ratio, but the torque is obtained from the current value applied to the electric motor 19. You may do it.

  Next, a first embodiment of compression ratio estimation will be described based on the flowchart of FIG. First, in step 1, it is determined whether or not the difference between the target compression ratio and the compression ratio indicated by the control shaft rotation angle sensor is a predetermined value or less. That is, it is determined whether or not the compression ratio variably controlled by the electric motor 19 has converged to a desired target compression ratio. In step 2, it is determined whether or not the fuel is being cut. In step 3, it is determined whether or not the intake pressure detected by the intake pressure sensor 23 is stable within a predetermined range. In step 4, it is determined whether or not the engine speed is a predetermined value or less, for example, about 2000 rpm or less. Unless all these conditions are satisfied, the actual compression ratio is not estimated.

  If these conditions are satisfied, the process proceeds to step 5 and the reaction torque of the control shaft 18, that is, the holding torque of the electric motor 19, is read every minute crank angle, for example, every 1 ° CA. Then, in step 6, a peak value is obtained from the torque data sequence for each 1 ° CA, and from this peak torque, a predetermined characteristic as shown in FIG. 4 (relationship between the reaction torque of the control shaft 18 and the in-cylinder pressure) is obtained. ) To obtain the in-cylinder pressure. This in-cylinder pressure corresponds to the peak in-cylinder pressure in the cycle.

  Next, in step 7, the compression ratio is obtained from the peak in-cylinder pressure with reference to a map of predetermined characteristics (relationship between in-cylinder pressure and compression ratio) as shown in FIG. More specifically, since the relationship between the in-cylinder pressure and the compression ratio is affected by the intake pressure upstream of the intake valve, the map in FIG. 5 is configured as a three-dimensional map with the intake pressure as one of the parameters. And the compression ratio is obtained from the intake pressure at that time.

  In the variable control of the compression ratio, the correlation between the compression ratio (target compression ratio) and the angle of the control shaft 18 as shown in FIG. 6 is used to control the target compression ratio according to the operating conditions. The shaft 18 is driven. If the actual compression ratio estimated by the above processing is deviated from the target compression ratio at that time, the subsequent compression ratio control is executed with the deviation corrected.

  Although the reaction force of a plurality of cylinders sharing the control shaft 18 acts on the control shaft 18, the actual compression ratio is estimated for each cylinder because the phases of the compression top dead center positions are different. Is possible.

  FIG. 9 is a time chart showing changes in parameters corresponding to the processing of the above embodiment. As shown in the figure, fuel cut is started when the accelerator opening or throttle opening is fully closed, but even if the target compression ratio changes stepwise to a high compression ratio, actual compression Since the ratio (control shaft angle) changes with the delay of the control system, estimation of the actual compression ratio starts when this compression ratio converges to the target compression ratio. The “compression ratio” indicated by the solid line in the lowermost stage is an apparent compression ratio indicated by the angle of the control shaft 18 and is substantially synonymous with the angle of the control shaft 18.

  In the present embodiment, the actual compression ratio can be accurately estimated by obtaining the peak torque while the fuel is being cut and the conditions of the intake pressure and the engine speed are aligned as described above. FIG. 7 shows an example of in-cylinder pressure change when ignition / combustion is accompanied (characteristic c when ignition / combustion is not performed is also added as a comparative example), and as shown as characteristics a and b, When ignition and combustion are involved, the peak value of the in-cylinder pressure and its timing change relatively greatly depending on the degree of combustion for each cycle, and the correlation with the compression ratio becomes weak. On the other hand, FIG. 8 shows an example of a change in the in-cylinder pressure without ignition / combustion. As shown by comparing the characteristic d of the low compression ratio and the characteristic e of the high compression ratio, Is correctly correlated with the value of the compression ratio.

  Next, FIGS. 10 and 11 show a second embodiment in which the target compression ratio is positively controlled to the maximum compression ratio during fuel cut in order to estimate the compression ratio.

  In FIG. 10, in step 101, it is determined whether or not the fuel is being cut. In step 102, it is determined whether or not the intake pressure detected by the intake pressure sensor 23 is stable within a predetermined range. In step 103, it is determined whether or not the engine speed is a predetermined value or less, for example, about 2000 rpm or less. In step 104, the state of a flag indicating that the calculation of the in-cylinder pressure has been completed is determined. That is, it is determined whether the calculation of the in-cylinder pressure has not been completed yet. When all these conditions are satisfied, the process proceeds to step 105, and the target compression ratio is set to the maximum compression ratio.

  Thereafter, in step 106, it is determined whether or not the difference between the target compression ratio and the compression ratio indicated by the control shaft rotation angle sensor is a predetermined value or less. That is, it is determined whether or not the position of the control shaft 18 variably controlled by the electric motor 19 has converged to a position corresponding to the maximum compression ratio.

  Steps 107 to 109 are the same as Steps 5 to 7 described above, and the reaction torque of the control shaft 18, that is, the holding torque of the electric motor 19, is read every minute crank angle, for example, every 1 ° CA, and 1 ° of these is read. The peak value is obtained from the torque data string for each CA, the peak in-cylinder pressure is obtained from the peak torque, and finally the actual compression ratio is obtained from the peak in-cylinder pressure and the intake pressure.

  In step 110, it is determined whether the actual compression ratio is estimated for all the cylinders by these processes. If all cylinders have been estimated, the flag is set in step 111 and the target compression is performed in step 112. Return the ratio to normal control.

  Thus, by estimating the actual compression ratio with the apparent compression ratio depending on the angle of the control shaft 18 being the maximum compression ratio, the actual compression ratio can be estimated more stably and accurately, and the variable compression ratio can be estimated. It is possible to reliably determine the presence or absence of variations in compression ratio due to individual differences in mechanism.

  Next, FIGS. 12 to 14 show a third embodiment in which the actual compression ratio is estimated under each condition by sequentially switching the target compression ratio to the highest compression ratio and the lowest compression ratio during the fuel cut. Show.

  Steps 201 to 211 in FIG. 12 are not particularly different from steps 101 to 111 in the second embodiment described above, and the actual compression ratio under the maximum compression ratio condition is obtained by these processes. Then, the process proceeds from step 204 to step 212 in FIG. 13, and the actual compression ratio under the minimum compression ratio condition is similarly obtained by the processes in steps 212 to 220.

  In step 220, the actual compression ratio value obtained under the high compression ratio condition is corrected using the actual compression ratio value under the minimum compression ratio condition, and the final high compression ratio condition is obtained. The actual compression ratio is obtained. The value of the actual compression ratio under the high compression ratio condition after correction is used for the subsequent correction of the compression ratio control as described above.

  That is, since the combustion chamber volume is large on the low compression ratio side, variations (individual differences) in the compression ratio are less likely to occur than on the high compression ratio side. Therefore, the variation in the estimated compression ratio on the low compression ratio side can be considered as some difference in the measurement system including torque detection, not the compression ratio itself, and this difference is used under the maximum compression ratio condition. If the estimation result is corrected, the compression ratio can be estimated more accurately. That is, the difference between the estimated compression ratio on the high compression ratio side and the estimated compression ratio on the low compression ratio side serves as an index indicating higher accuracy of variations due to individual differences.

  In step 220, for example, the average value of all cylinders of the estimated compression ratio on the low compression ratio side is obtained, and the difference between the estimated compression ratio on the maximum compression ratio side and the estimated compression ratio on the minimum compression ratio side of each cylinder is By adding the average values of all cylinders of the estimated compression ratio on the low compression ratio side, the actual compression ratio under the maximum compression ratio condition of each cylinder is finally obtained.

  As shown in the time chart of FIG. 14, the angle of the control shaft 18 changes after a change in the target compression ratio, so the period during which the compression ratio is estimated on the high compression ratio side and the low compression ratio side. It is discontinuous with the period during which the compression ratio is estimated.

  Next, FIGS. 15 and 16 show a fourth embodiment in which a variable valve mechanism that can change the valve lift characteristics of the intake valve is provided, and a change in the effective compression ratio due to the valve lift characteristics is avoided. Therefore, the actual compression ratio is estimated with the valve lift characteristic fixed to a predetermined valve lift characteristic. Various types of variable valve mechanisms are known. In this embodiment, for example, the opening timing and closing timing of the intake valve are the same by delaying the phase of the camshaft relative to the crankshaft. A type that can only be retarded or advanced is used, and the actual compression ratio is estimated with the intake valve closing timing held at the bottom dead center.

  Steps 301 to 304 are the same as Steps 1 to 4 described above. First, in Step 301, it is determined whether or not the difference between the target compression ratio and the compression ratio indicated by the control shaft rotation angle sensor is equal to or less than a predetermined value. In step 302, it is determined whether the fuel is being cut. In step 303, it is determined whether the intake pressure detected by the intake pressure sensor 23 is stable within a predetermined range. In step 304, the engine is determined. It is determined whether or not the number of rotations is a predetermined value or less, for example, about 2000 rpm or less. In step 305, the state of a flag indicating that the calculation of the in-cylinder pressure has been completed is determined. When all these conditions are satisfied, the routine proceeds to step 306, where the target intake valve closing timing (IVC) of the variable valve mechanism is set as the bottom dead center.

  Thereafter, in step 307, it is determined whether or not the difference between the target closing timing and the actual closing timing (for example, detected from the camshaft phase) is equal to or smaller than a predetermined value. That is, it is determined whether or not the variable valve mechanism that is variably controlled by hydraulic pressure or the like has converged to the target value.

  Steps 308 to 310 are the same as steps 5 to 7 described above, and the reaction force torque of the control shaft 18, that is, the holding torque of the electric motor 19, is read every minute crank angle, for example, every 1 ° CA, and these 1 ° The peak value is obtained from the torque data string for each CA, the peak in-cylinder pressure is obtained from the peak torque, and finally the actual compression ratio is obtained from the peak in-cylinder pressure and the intake pressure.

  In step 311, it is determined whether the actual compression ratio is estimated for all the cylinders by these processes. If all cylinders have been estimated, the flag is set in step 312, and then the target intake air is determined in step 313. Return the valve closing timing to normal control.

  In this way, by estimating the actual compression ratio in the state where the intake valve closing timing that affects the effective compression ratio is a predetermined position, that is, the bottom dead center position, the accuracy can be improved without being affected by the variable valve mechanism. A high actual compression ratio can be estimated.

  The above intake valve closing timing process can be applied in combination with the active control of the target compression ratio as in the second and third embodiments described above.

DESCRIPTION OF SYMBOLS 1 ... Piston 3 ... Crankshaft 11 ... Upper link 13 ... Lower link 15 ... Control link 18 ... Control shaft 19 ... Electric motor 25 ... Control unit

Claims (7)

A piston of an internal combustion engine and a crankshaft are connected via a plurality of link members, and have a control link that limits the degree of freedom of these link members, and the base end of the control link is an eccentric shaft of the control shaft. In a variable compression ratio internal combustion engine that is connected so as to be able to swing and whose compression ratio changes according to the rotational position of the control shaft,
A variable compression ratio characterized in that during a fuel cut of an internal combustion engine, a peak value in a cycle of torque necessary for holding the control shaft in a predetermined compression ratio state is obtained, and an actual compression ratio is estimated from the peak torque. Control device for internal combustion engine.   The target compression ratio is controlled to the highest compression ratio during the fuel cut to estimate the actual compression ratio, and the actual compression ratio is estimated from the peak torque in this state. A control device for a variable compression ratio internal combustion engine.   In order to estimate the actual compression ratio, the target compression ratio is controlled to the maximum compression ratio and the minimum compression ratio during the fuel cut, and the actual compression ratio is estimated from the peak torque in each state. The control apparatus for a variable compression ratio internal combustion engine according to claim 1.   In a configuration including a variable valve mechanism that can change the valve lift characteristic of the intake valve, the actual compression ratio is estimated while being fixedly held at a predetermined valve lift characteristic during the fuel cut. The control apparatus for a variable compression ratio internal combustion engine according to any one of claims 1 to 3.   5. The control device for a variable compression ratio internal combustion engine according to claim 1, wherein the torque is obtained from a current value of an electric motor that drives the control shaft.   6. The control apparatus for a variable compression ratio internal combustion engine according to claim 1, wherein the actual compression ratio is estimated on condition that the intake pressure upstream of the intake valve is within a predetermined pressure range.   The control apparatus for a variable compression ratio internal combustion engine according to any one of claims 1 to 6, wherein the actual compression ratio is estimated on condition that the engine speed is equal to or less than a predetermined value.

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