JP4389555B2 - Control device for variable compression ratio internal combustion engine - Google Patents

Description

  The present invention relates to a control device for a reciprocating variable compression ratio internal combustion engine capable of variably controlling the compression ratio, and more particularly to a control device for a variable compression ratio internal combustion engine for an automobile.

  For example, Patent Document 1 discloses a variable compression ratio internal combustion engine that can be variably controlled to an optimal compression ratio in accordance with engine operating conditions in order to improve the thermal efficiency of the reciprocating internal combustion engine, that is, fuel efficiency, and avoid abnormal combustion such as knocking. Is disclosed. Such a control apparatus for a variable compression ratio internal combustion engine is provided with a compression ratio map in which an optimal compression ratio is assigned in advance using the engine speed and load as parameters, so that the target compression ratio is read from this compression ratio map. In addition, the actuator of the variable compression ratio mechanism is controlled.

In general, the partial compression is controlled to a high compression ratio to improve thermal efficiency, and the high compression is controlled to a low compression ratio to avoid knocking.
JP 2002-285876 A

  However, conventionally, when setting the target compression ratio, the gear ratio of the vehicle transmission is not considered, and the same target compression ratio is set regardless of whether the gear ratio is high or low. Sudden acceleration is normally performed in a low gear ratio state, but since it is necessary to set a compression ratio that can avoid knocking during sudden acceleration at this low gear ratio, generally rapid acceleration is not performed. Under the high gear ratio condition, the compression ratio is set lower than the optimum compression ratio in at least a part of the operation region (rotation speed / load region), and the thermal efficiency is lowered accordingly, and the fuel consumption is deteriorated.

  In view of this, the present invention controls the compression ratio more optimally in consideration of the gear ratio of the vehicle transmission.

  That is, the present invention provides a variable compression ratio internal combustion engine control device that includes a variable compression ratio mechanism that can change the compression ratio and controls the compression ratio to a target compression ratio in accordance with engine operating conditions, in accordance with the gear ratio of the vehicle transmission. Further, the present invention is characterized in that a correction means for correcting the target compression ratio is provided.

  Alternatively, a plurality of target compression ratio maps having different characteristics according to the gear ratio of the vehicle transmission are provided, and the target compression ratio map is switched according to the actual gear ratio.

  Desirably, the setting of the target compression ratio at a high gear ratio has a relatively wide rotational speed / load region in which the high compression ratio is set compared to the setting of the target compression ratio at a low gear ratio. It has become.

  According to the present invention, it is possible to reliably avoid knocking at the time of sudden acceleration at a low gear ratio, and at the same time, it is possible to set a higher target compression ratio at a high gear ratio at which sudden acceleration is not generally performed, The fuel consumption can be further improved.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

  FIG. 1 is an explanatory diagram showing an example of a variable compression ratio mechanism for an internal combustion engine according to the present invention. The variable compression ratio using a multi-link type piston-crank mechanism known from the above-mentioned Patent Document 1 and the like. The mechanism is shown. This figure mainly shows the link configuration of the piston-crank mechanism, and accordingly, the dimensional ratios of the respective members are partially exaggerated.

  The variable compression ratio mechanism includes an upper link 5 having one end connected to the piston 3 via a piston pin 4, and is pivotably connected to the other end of the upper link 5 via a first connection pin 10. The lower link 2 is swingably connected to the crankpin 11 of the crankshaft 1 and one end is connected to the lower link 2 via the second connecting pin 9 and the other end is connected to the internal combustion engine body (for example, the cylinder). And a control link 6 that is swingably connected to the block) and regulates the degree of freedom of the lower link 2. The piston 3 slides up and down in a cylinder (not shown) to define a combustion chamber. More specifically, the other end of the control link 6 is swingably supported by an eccentric cam 8 of a control shaft 7 disposed at a lower portion of a cylinder block (not shown), and is controlled by a rotational position of the eccentric cam 8. The swing fulcrum position of the lower end of the link 6 is changed, and the top dead center position of the piston 3 and the compression ratio are changed accordingly. The crankshaft 1 rotates in the clockwise direction in the figure.

  For example, the lower link 2 is divided into two parts along a plane passing through the center of the crankpin 11 and assembled by bolts (not shown). In addition, the thick solid line in a figure shows each link as what is called a skeleton figure.

  The target compression ratio of the internal combustion engine by the variable compression ratio mechanism is controlled according to the operating conditions of the engine. In this embodiment, the target compression ratio is assigned with the engine speed and load as parameters. A compression ratio map is stored in advance in a control unit (not shown), and a target compression ratio is set based on the target compression ratio map. Then, a signal indicating the gear ratio of the vehicle transmission is input to the control unit, and the target compression ratio is corrected according to the gear ratio.

  FIG. 2 shows the tendency of the characteristic of the target compression ratio according to the gear ratio. As shown in the figure, the target compression ratio is a low speed with the rotational speed and load (for example, accelerator pedal opening) as parameters. High compression ratio on the low load side, low compression ratio on the high speed and high load side. And, the setting of the target compression ratio at the high gear ratio has a relatively wide rotational speed / load region where the high compression ratio is set compared to the setting of the target compression ratio at the low gear ratio. . FIG. 2 shows the compression ratio in two stages of high and low for simplification of explanation, but it goes without saying that it can be controlled in more stages.

  That is, the rapid acceleration is normally performed after the transmission is made to have a low gear ratio in order to quickly increase the engine rotation speed up to a high rotation range where the maximum torque is generated and improve the acceleration performance. Therefore, at a low gear ratio where rapid acceleration is performed, it is necessary to set a relatively low compression ratio in order to avoid knocking. On the other hand, when the gear ratio is high, sudden acceleration is not normally performed, so there is no need to set the compression ratio in consideration of avoiding knocking during sudden acceleration. Therefore, by setting the compression ratio to be relatively higher at the time of the high gear ratio than at the time of the low gear ratio, the fuel consumption can be further improved at the time of the high gear ratio. When the gear ratio is low, the acceleration performance can be improved while avoiding knocking by setting a relatively low compression ratio.

  FIG. 4 illustrates the setting of the target compression ratio when the accelerator pedal opening θa slightly changes. As shown by the solid line in FIG. 4, the change in the accelerator pedal opening θa during a predetermined time ΔT. When the amount Δθa is equal to or smaller than the predetermined amount Δθ, the compression ratio is not changed according to the accelerator pedal opening θa. In other words, the change in the accelerator pedal opening θa is ignored, and the compression ratio is kept constant. As shown by the broken line, if the accelerator pedal opening θa changes more greatly, the target compression ratio also changes according to the change in the accelerator pedal opening θa, that is, the load.

  In other words, if the compression ratio control is performed so that the compression ratio is optimized in response to a slight change in the accelerator pedal opening θa, the energy consumption of the actuator required to change the compression ratio increases, and conversely the fuel consumption deteriorates. End up. Therefore, when the change amount Δθa of the accelerator pedal opening θa is equal to or less than the predetermined amount Δθ, the energy consumption of the actuator can be reduced by preventing the compression ratio from responding sensitively according to the accelerator pedal opening θa. it can. For example, a slight variation in the accelerator pedal opening θa that is not intended by the driver, such as a change in the accelerator pedal opening when the vehicle is traveling at a substantially constant vehicle speed, is ignored for control and the compression ratio does not change. Thereby, energy consumption required for compression ratio variable control can be reduced, and fuel consumption can be improved. If the change in the accelerator pedal opening θa is large, the fuel efficiency is improved by optimizing the compression ratio even if energy is consumed for driving the actuator.

  As described above, it is desirable to change the value of the predetermined amount Δθ, which is a threshold value as to whether or not to change the compression ratio when the accelerator pedal opening θa slightly changes, according to the gear ratio of the vehicle transmission. . Specifically, as shown in FIG. 5, the larger the gear ratio, the larger the predetermined amount Δθ is set.

  That is, a high gear ratio is usually obtained in the case of high-speed steady driving. In this state, it is sufficient to increase or decrease the engine load in accordance with the road gradient in order to maintain a constant speed, and further increase the vehicle speed. Therefore, there is little need for rapid acceleration. Therefore, it becomes unnecessary to change the compression ratio more sensitively to changes in the accelerator pedal opening degree θa as the gear ratio becomes higher. Therefore, by increasing the value of the predetermined amount Δθ as the gear ratio increases and reducing the number of compression ratio variable operations, the energy consumption of the actuator can be reduced and the high compression ratio state can be maintained to the maximum while avoiding knocking. By doing so, fuel consumption can be further improved.

  The flowchart of FIG. 3 shows the flow of the compression ratio control in consideration of the gear ratio of the vehicle transmission as described above. First, in step 1, the compression ratio ε0, the engine speed N0, and the gear ratio X0 at that time are shown. , Vehicle speed V0, accelerator pedal opening degree θa, and accelerator pedal opening change amount Δθa are detected. In step 2, it is determined whether the gear ratio is large. If the gear ratio is high, the process proceeds to step 3 to correct the target compression ratio to the high compression ratio side, and in step 4, a predetermined amount Δθ serving as a threshold is set. After setting as a larger value, proceed to Step 5.

  If the gear ratio is low, the process proceeds from step 2 to step 5 as it is, so that the value of the target compression ratio map is used as it is for the target compression ratio, and the predetermined amount Δθ is a relatively small value.

  In step 5, it is determined whether the change amount Δθa of the accelerator pedal opening θa is larger than the predetermined amount Δθ. If NO, that is, if it is equal to or smaller than the predetermined amount Δθ, the change in the accelerator pedal opening θa is ignored. The ratio variable control is not performed (step 6). That is, the compression ratio is maintained as it is. If the change amount Δθa of the accelerator pedal opening θa is larger than the predetermined amount Δθ, the process proceeds to step 7, and the compression ratio is variably controlled in response to the change of the accelerator pedal opening θa.

  By the way, in consideration of the time of deceleration, if the compression ratio is set to be higher at the time of high gear ratio than at the time of low gear ratio, the pumping loss is increased, the engine brake is increased, and the amount of deceleration is increased, so that the inertia traveling can be performed The distance will decrease. Therefore, it is preferable to simultaneously change the effective compression ratio of the internal combustion engine during such deceleration. As a specific means for changing the effective compression ratio, for example, a known variable valve mechanism is provided in the valve operating device on the intake valve side of the internal combustion engine, and the closing timing of the intake valve is increased by so-called early closing or late closing. It is possible to reduce the effective compression ratio by approaching the dead center side.

  In other words, the high gear ratio is set at the time of deceleration when the engine brake is reduced and the distance that can be driven by inertia is extended to improve fuel efficiency. However, if the high compression ratio is set at this high gear ratio, the pumping loss is increased. Will increase and the engine brake will tend to increase. Therefore, when a high gear ratio is set during deceleration, the intake valve closing timing is moved to the top dead center side by the variable valve mechanism described above to reduce the effective compression ratio, thereby reducing the pumping loss and engine braking. Make it smaller. Thereby, the inertial mileage at the time of deceleration can be extended and fuel consumption can be improved.

  Further, the pumping loss can be further reduced by reducing the effective compression ratio to a region exceeding the combustion stability limit during the fuel cut at a high gear ratio during deceleration. When combustion is resumed, the combustion stability at the high compression ratio can be used to quickly return to stable combustion with a slight increase in the effective compression ratio (change to the bottom dead center side of the intake valve closing timing). Is possible. On the other hand, if the low gear ratio is set at the time of deceleration, the combustion stability deteriorates, so the effective compression ratio cannot be lowered to the region exceeding the combustion limit, but conversely, the low gear ratio is set at the time of deceleration. This is the case where the engine brake is used to increase the deceleration amount, so it is better to increase the effective compression ratio. FIG. 6 shows the relationship between the gear ratio at the time of deceleration, the target compression ratio (mechanical compression ratio), and the effective compression ratio. As the gear ratio is larger, the mechanical compression ratio is higher and the effective compression ratio is Controlled low.

  FIG. 7 shows an example of a variable valve mechanism used for variable control of the effective compression ratio. Since this variable valve mechanism is known, for example, from Japanese Patent Laid-Open No. 10-184404, only its outline will be described.

  The variable valve mechanism 61 is mainly composed of an inner cylinder 62, an outer cylinder 63, a piston 64, and the like. The inner cylinder 62 is fixed to the front end of the camshaft 65 via a mounting bolt 66. A cup-shaped outer cylinder 63 is fitted on the outer peripheral side of 62 so as to be capable of relative rotation at a constant angle. The outer cylinder 63 is provided with a sprocket portion 63a that meshes with the timing belt. Further, a ring-shaped piston 64 is provided between the inner cylinder 62 and the outer cylinder 63, and the piston 64 is provided on the outer peripheral surface of the inner cylinder 62 and the outer peripheral surface of the outer cylinder 63 via a helical thread. Each is engaged. Further, the piston 64 is constantly urged forward by a return spring 67, and a hydraulic chamber 68 is annular between the front surface of the piston 64 and the back surface of the lid portion of the outer cylinder 63 to counter this spring force. Is defined. The hydraulic chamber 68 is connected to the control hydraulic circuit via an oil passage 69 in the mounting bolt 66 and an oil passage 70 passing through the camshaft 65.

  That is, when hydraulic pressure is supplied into the hydraulic chamber 68 via the oil passage 70 or the like, the piston 64 moves in the axial direction, and this axial movement is converted into relative rotational movement between the inner cylinder 62 and the outer cylinder 63. The For this reason, the phase of the camshaft 65 and the crankshaft for opening and closing an intake valve (not shown) changes by a predetermined amount. Therefore, the phase of the valve lift characteristic of the intake valve can be continuously changed within a predetermined angle range, and the intake valve closing timing can be delayed.

  The effective compression ratio of the internal combustion engine can be changed by various types of variable valve mechanisms.

BRIEF DESCRIPTION OF THE DRAWINGS Structure explanatory drawing which shows an example of the variable compression ratio mechanism applied to this invention. The characteristic view which shows the characteristic of the target compression ratio in a low gear ratio, and the characteristic of the target compression ratio in a high gear ratio in contrast. The flowchart which shows the flow of a process of compression ratio control. The time chart which shows the change of the compression ratio with respect to the minute change of the accelerator pedal opening degree θa. The time chart which shows the relationship between gear ratio and predetermined amount (DELTA) (theta). The characteristic view which shows the relationship between a gear ratio, a mechanical compression ratio, and an effective compression ratio. Sectional drawing which shows an example of the variable valve mechanism which changes an effective compression ratio.

Explanation of symbols

1 ... Crankshaft 2 ... Lower link 3 ... Piston 5 ... Upper link 6 ... Control link 7 ... Control shaft

Claims (2)

In a control apparatus for a variable compression ratio internal combustion engine that includes a variable compression ratio mechanism capable of changing the compression ratio and controls the compression ratio to a target compression ratio according to engine operating conditions.
Correction means for correcting the target compression ratio according to the gear ratio of the vehicle transmission, and a variable valve mechanism for changing the effective compression ratio of the internal combustion engine,
In the above correction means, the setting of the target compression ratio at the high gear ratio is relatively larger than the setting of the target compression ratio at the low gear ratio. To correct
The variable valve mechanism controls the high gear ratio so that the effective compression ratio becomes smaller at the time of deceleration than the low gear ratio , and the combustion stability limit when the high gear ratio at the time of deceleration and the fuel is cut. A control apparatus for a variable compression ratio internal combustion engine, characterized in that the effective compression ratio is lowered to a region exceeding . In a control apparatus for a variable compression ratio internal combustion engine comprising a variable compression ratio mechanism capable of changing a compression ratio and controlling the target compression ratio according to engine operating conditions based on a target compression ratio map,
There are multiple target compression ratio maps with different characteristics according to the gear ratio of the vehicle transmission. These target compression ratio maps are set for the target compression ratio at the low gear ratio when the target compression ratio is set at the high gear ratio. Compared to, the rotational speed / load region where the compression ratio is high is a relatively wide characteristic, and the target compression ratio map is switched according to the actual gear ratio,
A variable valve mechanism for changing the effective compression ratio of the internal combustion engine is further provided. During deceleration, the high gear ratio is controlled so that the effective compression ratio is smaller than the low gear ratio. A control apparatus for a variable compression ratio internal combustion engine, wherein the effective compression ratio is reduced to a region exceeding the combustion stability limit when the fuel is being cut .

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