JP2008101520A - Mirror cycle engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce a cooling loss by heat insulation of an engine. <P>SOLUTION: This invention is characterized by a combustion chamber 143 of constituting a wall surface of a nonmetallic material having the high thermal insulation and heat storage effect, an operation state detecting means for an engine operation state, a compression ration variable means 100 capable of varying the engine compression ratio based on the detected engine operation state, and an intake valve closing timing variable means 200 changing the closing timing of an intake valve so that the actual compression ratio determined by the closing timing of the intake valve, becomes smaller than the actual expansion ratio determined by the opening timing of an exhaust valve, similarly based on the detected engine operation state. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a Miller cycle engine.

2. Description of the Related Art Conventionally, an attempt has been made to use a heat insulating engine that increases the thermal efficiency of an engine by attaching a heat insulating material such as ceramic to the wall surface of the combustion chamber to reduce cooling loss (see, for example, Non-Patent Document 1).
Papers of the Japan Society of Mechanical Engineers 1996 No. 96-1 “Combustion and combustion chamber of heat shield engine”

  However, since the heat transfer coefficient of ceramic increases at a high temperature such as during a high load, the temperature of the intake air in the combustion chamber increases, and the temperature at the end of compression increases by 200 ° C. or more. When such a temperature rise occurs, in a gasoline engine, the occurrence of knocking at a high load cannot be avoided. Therefore, in the conventional fixed compression ratio engine, the compression ratio has to be lowered at the time of high load (as a result, all operating regions). This means that the fuel efficiency effect at low load is greatly impaired. In addition, the charging efficiency of intake air is fundamentally important at high loads, and when the intake air temperature rises, a trade-off occurs in which the amount of air decreases and torque decreases.

  Therefore, the present invention insulates the combustion chamber and variably controls the engine compression ratio and the actual compression ratio, thereby achieving both improvement in thermal efficiency at low load and knock avoidance at high load, and improvement in fuel efficiency. The purpose is to plan.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

  A combustion chamber (143) having a wall surface made of a non-metallic material having a high thermal insulation and heat storage effect, an operating state detecting means for detecting an engine operating state, and a compression with a variable engine compression ratio based on the detected engine operating state Based on the ratio variable means (100) and the detected engine operating state, the intake valve is controlled so that the actual compression ratio determined by the closing timing of the intake valve is smaller than the actual expansion ratio determined by the opening timing of the exhaust valve. Intake valve closing timing varying means (200) for changing the closing timing.

  According to the present invention, in the Miller cycle engine in which the actual compression ratio is smaller than the actual expansion ratio by utilizing both the heat insulation effect and the heat storage effect by the heat insulation of the combustion chamber, the thermal efficiency is improved at the time of low load. Achieving compatibility with knock avoidance at high loads and improving fuel efficiency.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 shows an engine 100 according to the present invention.

  The engine 100 includes a variable compression ratio mechanism that changes an engine compression ratio by changing a piston stroke. In this embodiment, as the compression ratio variable mechanism, the multi-link type compression ratio variable mechanism which has been previously proposed by the present applicant and is publicly known, for example, in Japanese Patent Laid-Open No. 2001-227367 is applied. Hereinafter, an engine equipped with this multi-link type compression ratio variable mechanism is referred to as a “compression ratio variable engine”.

  The variable compression ratio engine 100 connects the piston 122 and the crankshaft 121 with two links (an upper link (first link) 111 and a lower link (second link) 112), and a control link (third link) 113. To control the lower link 112 and change the compression ratio.

  The upper link 111 has an upper end connected to the piston 122 via a piston pin 124 and a lower end connected to one end of the lower link 112 via a connection pin 125. The piston 122 is slidably fitted to a cylinder liner 129 fitted to the cylinder block 123, receives a combustion pressure, and reciprocates in the cylinder 120.

  The lower link 112 has one end connected to the upper link 111 via the connecting pin 125 and the other end connected to the control link 113 via the connecting pin 126. Further, the lower link 112 inserts the crankpin 121b of the crankshaft 121 into a substantially central connecting hole, and swings about the crankpin 121b as a central axis. The lower link 112 can be divided into left and right members. The crankshaft 121 includes a plurality of journals 121a and a crankpin 121b. The journal 121a is rotatably supported by the cylinder block 123 and the ladder frame 128. The crank pin 121b is eccentric from the journal 121a by a predetermined amount, and the lower link 112 is swingably connected thereto.

  The control link 113 is connected to the lower link 112 via a connecting pin 126. The control link 113 is connected to the control shaft 114 at the other end via a connecting pin 127. The control link 113 swings around the connecting pin 127. A gear is formed on the control shaft 114, and the gear meshes with a pinion 132 provided on the rotation shaft 133 of the compression ratio control actuator 131. The control shaft 114 is rotated by the compression ratio control actuator 131, and the connecting pin 127 moves.

  FIG. 2 is a diagram for explaining a compression ratio changing method by the variable compression ratio engine 100.

  In the compression ratio variable engine 100, the controller 300 described later controls the compression ratio control actuator 131 to rotate the control shaft 114 to change the position of the connecting pin 127, thereby changing the compression ratio. For example, as shown in FIGS. 2 (A) and 2 (C), if the connecting pin 127 is set to the position P, the top dead center position (TDC) is increased and the compression ratio is increased.

  As shown in FIGS. 2B and 2C, when the connecting pin 127 is moved to the position Q, the control link 113 is pushed upward, and the position of the connecting pin 126 is raised. As a result, the lower link 112 rotates counterclockwise about the crank pin 121b, the connecting pin 125 is lowered, and the position of the piston 122 at the piston top dead center is lowered. Therefore, the compression ratio becomes a low compression ratio.

  FIG. 3 is a diagram showing piston stroke characteristics of the variable compression ratio engine 100. FIG. 3A is an enlarged view of a solid line portion surrounded by a square in FIG.

  The variable compression ratio engine 100 has a piston near the top dead center as compared with a normal engine (hereinafter referred to as “normal engine”) in which the piston and the crankshaft are connected by a single link (connecting rod) and the compression ratio is constant. There is a characteristic that the period of stay is long.

  This point will be described with reference to FIG. In FIG. 3, the solid line indicates the piston stroke characteristic of the variable compression ratio engine 100, and in particular, the thick solid line indicates the piston stroke characteristic when the compression ratio is high. The thin solid line shows the piston stroke characteristics when the compression ratio is low. A chain line indicates a piston stroke characteristic of a normal engine. The compression ratio of the normal engine is the same as the compression ratio when the variable compression ratio engine 100 is set to a low compression ratio.

  As shown in FIG. 3, in the case of a normal engine, the piston moves fast (high acceleration) near the top dead center and dull (low acceleration) near the bottom dead center.

  On the other hand, in the case of the variable compression ratio engine 100, a piston stroke characteristic close to simple vibration can be obtained by appropriately setting the link configuration. Therefore, the vibration reduction effect that eliminates the need for the balancer shaft (four cylinders) is obtained, the piston acceleration is leveled, and the piston speed near the top dead center becomes slower than that of the normal engine. As a result, the variable compression ratio engine 100 has a longer period during which the piston stays near the top dead center than a normal engine having the same compression ratio.

  In the vicinity of the top dead center, scavenging, filling, and air-fuel mixture formation are performed by high-pressure fresh air supplied from an air supply valve, and ignition is also performed. By reducing the piston speed in the vicinity of the top dead center where the stroke is concentrated in this way, it is possible to increase the output rotational speed. However, if the piston speed near the top dead center decreases, the cooling loss increases accordingly.

  Next, an intake valve variable valve mechanism 200 of the engine 100 according to the present invention will be described with reference to FIGS. 4 and 5. FIG. 4 is a perspective view showing the intake valve variable valve mechanism 200 of the engine 100 according to the present invention. FIG. 5 is a drive shaft direction view of the lift / operating angle variable mechanism 210 constituting a part of the intake valve variable valve mechanism 200.

  The intake valve variable valve mechanism 200 includes a lift / operation angle variable mechanism 210 that changes the lift / operation angle of the intake valve 211 and a lift center angle of the intake valve 211 (a crank angle position at which the intake valve 211 reaches the maximum lift). And a phase variable mechanism 240 that advances or retards the phase. In FIG. 4, only a pair of intake valves 211 corresponding to one cylinder and related parts are simply illustrated.

  First, the configuration of the lift / operating angle variable mechanism 210 will be described.

  Each cylinder of engine 100 is provided with a pair of intake valves 211 and a pair of exhaust valves (not shown). A hollow drive shaft 213 extending in the cylinder row direction is provided above the intake valve 211. The drive shaft 213 is linked to the crankshaft 121 by a belt or chain (not shown) via a driven sprocket 241 provided at one end, and rotates around the shaft in conjunction with the crankshaft 121.

  A pair of rocking cams 220 is attached to the drive shaft 213 so as to be rotatable with respect to the drive shaft 213 for each cylinder. Although the operation will be described in detail later, the pair of swing cams 220 swings (moves up and down) around a drive shaft 213 within a predetermined rotation range, so that the valve lifter 219 of the intake valve positioned below the swing shaft is moved. Is pressed, and the intake valve 211 is lifted downward. The pair of swing cams 220 are fixed to each other in the same phase by a cylinder or the like.

  In FIG. 5, the swing cam 220 has a support hole 222 a formed through the base end portion thereof, and is rotatably supported on the outer peripheral surface of the drive shaft 213. The swing cam 220 has a pin hole 223a formed through the end of the cam nose 223. A base circular surface 224a and a cam surface 224b extending in an arc shape from the base circular surface 224a to the distal end edge side of the cam nose 223 are formed on the bottom surface of the rocking cam 220, and the base circular surface 224a and the cam surface 224b are formed. In contact with the valve lifter 219 in accordance with the swing position of the swing cam 220.

A cylindrical drive cam 215 is fixed to the outer periphery of the drive shaft 213 by press fitting or the like. The center P ₄ of the drive cam 215 is located at a position eccentric from the axis P ₃ of the drive shaft 213 by a predetermined amount. The drive cam 215 is fixed at a position away from the swing cam 220 by a predetermined distance in the axial direction. Then, the base end of the link arm 225 is rotatably fitted to the outer peripheral surface of the drive cam 215. The link arm 225 includes an annular base 225a having a relatively large diameter and a protruding end 225b that protrudes from a part of the base 225a. A pin hole 225c is formed through the protruding end 225b.

  A control shaft 216 extends in the cylinder row direction parallel to the drive shaft 213 and is rotatably supported above the drive shaft 213.

  One end of the control shaft 216 is provided with a lift amount control actuator 230 that rotates the control shaft 216 within a predetermined rotation angle range (see FIG. 4). The lift amount control actuator 230 is controlled by the first hydraulic device 301 based on a control signal from the controller 300 that detects the operating state of the engine 100.

A control cam 217 is fixed to the outer peripheral surface of the control shaft 216 by press fitting or the like. The center P ₁ of the control cam 217 is located at a position eccentric from the axis P ₂ of the control shaft 216 by a predetermined amount. A rocker arm 218 is fitted to the control cam 217 so as to be rotatable on the outer peripheral surface of the control cam 217. The rocker arm 218 swings about the axis P ₁ of the control cam 217 as a fulcrum.

  The rocker arm 218 extends in the left-right direction perpendicular to the axial direction around a central base end 218a supported by the control cam 217, and has one end 218b and the other end 218c at both ends thereof. Further, pin holes 218d and 218e are formed through the one end 218b and the other end 218c, respectively.

  The one end 218b of the rocker arm 218 and the protruding end 225b of the link arm 225 are connected by a connecting pin 221 that passes through the rocker arm 218 so that the rocker arm 218 is positioned upward.

  The other end portion 218c of the rocker arm 218 and the one end portion 226a of the link member 226 are connected by a connecting pin 228 through which both are inserted.

  The other end portion 226b of the link member 226 and the end portion on the cam nose 223 side of the swing cam 220 are connected by a connecting pin 229 that passes through both of them so that the swing cam 220 is positioned below the rocker arm 218. .

  A snap ring for restricting the movement of the link arm 225 and the link member 226 in the axial direction is provided at one end of each pin 221, 228, 229.

  Next, the configuration of the phase variable mechanism 240 will be described.

  The phase variable mechanism 240 includes a phase angle control actuator 241 and a second hydraulic device 302.

  The phase angle control actuator 241 relatively rotates the sprocket 242 and the drive shaft 213 within a predetermined angle range.

  Second hydraulic device 302 controls phase angle control actuator 241 based on a control signal from controller 300 that detects the operating state of engine 100.

  By the hydraulic control to the phase angle control actuator 241 by the second hydraulic device 302, the sprocket 242 and the drive shaft 213 are relatively rotated, and the lift center angle is advanced or retarded.

  Next, the operation of the lift / operating angle variable mechanism 210 will be described in detail.

When the drive shaft 213 rotates in conjunction with the crankshaft, the rocker arm 218 swings about the center P ₁ of the control cam 217 via the drive cam 215 and the link arm 225 that is rotatably fitted to the outer periphery of the drive cam 215 ( Move up and down). The swing of the rocker arm 218 is transmitted to the swing cam 220 via the link member 226, and the swing cam 220 swings within a predetermined angle range. As the swing cam 220 swings, that is, moves up and down, the valve lifter 219 is pressed and the intake valve 211 is lifted downward.

Here, when the control shaft 216 via the lift control actuator 230 is rotated, the center P ₁ of the control cam 217 serving as a swing fulcrum of the rocker arm 218 also rotationally displaced, the support position of the rocker arm 218 relative to the engine body As a result, the initial swing position of the swing cam 220 changes. Therefore, the initial contact position between the swing cam 220 and the valve lifter 219 also changes. Since the swing angle of the swing cam 220 per crankshaft rotation is always constant, the maximum lift amount changes as shown in FIG. 6 described below.

  6A and 6B are views of the lift / operating angle variable mechanism 210 in the drive axis direction. FIG. 6A is a diagram showing the positions of the swing cam 220 when the intake valve 211 is at the zero lift when the swing cam 220 is at the minimum swing and at the maximum swing. FIG. 6B is a diagram illustrating the positions of the swing cam 220 when the intake valve 211 is fully lifted and when the swing cam 220 is at the minimum swing.

  Here, the time of zero lift of the intake valve means that the intake valve 211 does not lift (that is, the lift amount of the intake valve is zero). In addition, when the intake valve is fully lifted, the intake valve 211 has the maximum lift amount.

As shown in FIG. 6A, when the center P ₁ of the control cam 217 is located above the axis P ₂ of the control shaft 216 and the thick portion 117a of the control cam is located above, the rocker arm 218 is positioned upward as a whole, and the end of the rocking cam 220 on the side of the connecting pin 229 is relatively lifted upward. That is, the initial position of the swing cam 220 is inclined in a direction in which the cam surface 224b is separated from the valve lifter 219 (see the left side of FIG. 6A). Therefore, when the swing cam 220 swings with the rotation of the drive shaft 213, the base circle surface 224a continues to contact the valve lifter for a long time, and the period during which the cam surface 224b contacts the valve lifter is shortened. For this reason, the maximum lift amount of the intake valve 211 is reduced (see the right side of FIG. 6A). Further, the crank angle section from the opening timing to the closing timing of the intake valve 211, that is, the operating angle of the intake valve 211 is also reduced.

On the other hand, as shown in FIG. 6B, when the center P ₁ of the control cam 217 is located below the axis P ₂ of the control shaft 216 and the thick portion 117a of the control cam is located below. The rocker arm 218 is positioned downward as a whole, and the end of the swing cam 220 on the side of the connecting pin 229 is relatively pushed down. That is, the initial position of the swing cam 220 is inclined in a direction in which the cam surface 224b approaches the valve lifter 219 (see the left side of FIG. 6B). Therefore, when the swing cam 220 swings with the rotation of the drive shaft 213, the portion that contacts the valve lifter 219 immediately shifts from the base circle surface 224a to the cam surface 224b. For this reason, the maximum lift amount of the intake valve 211 is increased (see the right side of FIG. 6B). In addition, the operating angle of the intake valve 211 is increased.

  FIG. 7 is a view for explaining the operation of the intake valve variable valve mechanism 200.

  Since the initial position of the control cam 217 described above with reference to FIG. 6 can be continuously changed, the valve lift characteristic of the intake valve 211 is continuously changed accordingly. That is, as shown by the solid line in FIG. 7, the intake valve variable valve mechanism 200 continuously increases and decreases the lift amount and the operation angle of the intake valve 211 simultaneously by the lift / operation angle variable mechanism 210. be able to. Depending on the layout of each part, for example, the opening timing and closing timing of the intake valve 211 change substantially symmetrically as the lift amount and operating angle of the intake valve 211 change.

  Furthermore, as shown by the broken line in FIG. 7, the intake valve variable valve mechanism 200 can advance or retard the lift center angle by the phase variable mechanism 240.

  In this way, by combining the lift / operation angle variable mechanism 210 and the phase variable mechanism 240, the intake valve variable valve mechanism 200 can open and close the intake valve 211 at an arbitrary crank angle position. That is, the closing timing of the intake valve 211 can be set to an arbitrary timing.

  Using this intake valve variable valve mechanism 200, it is possible to realize a Miller cycle engine in which the actual expansion ratio determined by the opening timing of the exhaust valve is increased with respect to the actual compression ratio determined by the closing timing of the intake valve.

  The Miller cycle engine stops the intake in the middle of the intake stroke, and expands and compresses the intake before and after the bottom dead center to reduce the effective stroke. Thereby, reduction of pump loss can be aimed at, and a fuel consumption improves.

  FIG. 8 shows a PV diagram (solid line) of a Miller cycle engine in which the intake valve closing timing is controlled to approximately 90 ° before bottom dead center (BBDC) by the intake valve variable valve mechanism 200 and the intake valve closing timing after bottom dead center. (ABDC) It is the figure which compared with the PV diagram (broken line) of the engine fixed to 40 degrees.

  The Miller cycle engine significantly closes the closing timing of the intake valve 211 from the bottom dead center BDC, and stops the intake in the middle of the intake stroke. Therefore, the intake air in the cylinder adiabatically expands to the bottom dead center BDC regardless of the intake stroke. As a result, the in-cylinder gas pressure decreases as shown in FIG. Along with this, the temperature in the cylinder also decreases.

  After the bottom dead center BDC, the compression stroke starts. However, up to the gas pressure in the cylinder where adiabatic expansion has started is merely a return of the gas pressure in the cylinder. Therefore, in actuality, the compression is started from the point in time when the in-cylinder gas pressure is restored (the piston position at which compression starts). Therefore, the actual compression ratio decreases as the intake valve closing timing is advanced.

  This decrease in the actual compression ratio is accompanied by a decrease in the in-cylinder gas temperature at the top dead center TDC, so that the combustion state is deteriorated and the combustion speed is decreased. Therefore, the fuel efficiency improvement effect cannot be obtained as the pump loss is reduced.

  In this way, when the intake valve closing timing is advanced by the intake valve variable valve mechanism 200, the pump loss can be reduced, but the actual compression ratio is reduced and the intake temperature at the compression top dead center is reduced, so that combustion is performed. The condition gets worse.

  FIG. 9 is a diagram showing the relationship between the intake valve closing timing and the engine compression ratio (compression ratio uniquely determined by the piston top dead center position) that is necessary to make the actual compression ratio the same.

  As described above, the actual compression ratio decreases as the intake valve closing timing is advanced. Therefore, as shown in FIG. 9, it is necessary to increase the engine compression ratio in order to keep the actual compression ratio the same when the intake valve closing timing is advanced. For example, when the engine compression ratio is 10 when the intake valve closing timing is BDC and the intake valve closing timing is set to 90 ° before the bottom dead center (BBDC), the engine compression is maintained in order to keep the actual compression ratio the same. The ratio needs to be 20.

  In the present embodiment, the compression ratio variable engine 100 can increase the engine compression ratio in accordance with the intake valve closing timing. However, when the engine compression ratio increases, the space shape of the combustion chamber at the compression top dead center position becomes flat, and the cooling loss at the compression top dead center increases. Therefore, even if the reduction in the compression temperature at the compression top dead center is improved by increasing the engine compression ratio, the cooling loss increases on the other hand, so that sufficient thermal efficiency cannot be improved.

  Therefore, in this embodiment, in order to reduce the cooling loss due to the flattening of the combustion chamber due to such high compression, a part of the combustion chamber wall surface (piston, cylinder, head, intake / exhaust valve) is insulated or heat storage. Consists of highly effective materials.

  FIG. 10 is a cross-sectional view of a normal piston and a heat insulating piston according to the present embodiment.

  In the case of a normal piston, heat from combustion escapes from the piston 122 to the cylinder 123 via the piston ring 122a.

  On the other hand, in the case of the heat insulating piston according to the present embodiment, heat transfer is blocked by a heat insulating material (such as ceramic) 122b stuck in a layered manner on the crown surface of the piston 122. Further, by providing the cylinder liner 129 and configuring the cylinder liner 129 with a heat insulating material, it is possible to more effectively prevent heat transfer to the cylinder and reduce cooling loss.

  Furthermore, a heat insulating material such as ceramic has a heat storage action for storing heat of combustion gas. Therefore, the intake air is warmed by the heat of the high-temperature heat insulating material, and the intake air temperature rises. Therefore, in the case of the Miller cycle engine, a decrease in the intake air temperature at the compression top dead center due to a decrease in the actual compression ratio can be suppressed by an increase in the intake air temperature due to the heat storage action. As a result, the variable compression ratio engine 100 can suppress a decrease in the compression temperature at the compression top dead center without extremely increasing the engine compression ratio.

  As described above, according to the present invention, the intake valve variable valve mechanism 200 is combined with the compression ratio variable engine 100 in which at least a part of the wall surface of the combustion chamber is formed of the heat insulating material.

  Thereby, the variable compression ratio engine 100 can set the compression ratio to an appropriate high compression ratio, and can greatly reduce the cooling loss during combustion when the compression ratio is increased.

  Further, the intake valve variable valve mechanism 200 can reduce the pump loss by advancing the intake valve closing timing, and also heats the intake air by actively storing heat at the time of combustion / exhaust by the heat storage action which is a side effect of the heat insulating material. Therefore, a decrease in the compression temperature at the compression top dead center can be suppressed. At this time, knocking can be avoided by lowering the compression ratio under operating conditions where the temperature of the heated intake air reaches a temperature that causes knocking.

  That is, according to the present invention, the performance of the mirror cycle engine is greatly improved by utilizing both the heat insulating effect and the heat accumulating effect by the heat insulation of the combustion chamber, and the fuel efficiency is improved by reducing the cooling loss and the pump loss. Can be achieved.

  Hereinafter, the control of the compression ratio and the intake valve closing timing by the variable compression ratio engine 100 will be described.

  FIG. 11 is a diagram showing a configuration of a control system of the compression ratio variable engine 100 in which the combustion chamber 143 is thermally insulated according to the present invention.

  The control system of the compression ratio engine 100 includes a compression ratio engine 100, a cylinder surface temperature sensor 141 that detects the temperature of the cylinder wall, a knock sensor 142 that detects knock, an intake valve variable valve mechanism 200, and a knock sensor 142. Ignition advance control device 400 for controlling the ignition timing based on the detected signal, and a controller for controlling compression ratio engine 100, intake valve variable valve mechanism 200, and ignition advance control device 400 300.

  The controller 300 includes a compression ratio control map (see FIG. 12) in which a target compression ratio is assigned in advance according to the engine operating conditions, and the intake air temperature increases based on the detection signal of the cylinder surface temperature sensor 141 and compression is performed. The compression ratio is controlled with a margin before reaching a condition where control of the ratio is inevitable. Specifically, the compression ratio is controlled by driving the compression ratio control actuator 131 to rotate the control shaft 114 and moving the position of the control link 113. In addition, an engine rotation speed signal, an engine load signal, and the like (operation state detection means) detected by sensors (not shown) are input to the controller 300.

  FIG. 12 is a compression ratio control map in which a target compression ratio is assigned in advance according to engine operating conditions. This map is set so that the target compression ratio decreases as the load increases and the speed decreases. As shown in FIG. 12 (A), under normal warm-up conditions, the cylinder wall temperature is high in the low-speed full load region, and knocking is likely to occur. Therefore, the compression ratio ε is targeted at 8. . On the other hand, as shown in FIG. 12B, if the cylinder wall temperature is equal to or lower than a predetermined temperature, such as before the warming-up with a low coolant temperature, the compression ratio is set to be higher (for example, ε = 10).

  On the other hand, knocking is unlikely to occur in the partial load region, such as when driving at the engine output required by the R / L (load necessary to drive the vehicle on a flat road without acceleration / deceleration) characteristics. Therefore, the compression ratio is set high to about 15 to improve fuel efficiency. Even if the vehicle speed becomes high even in the full load region, knocking is less likely to occur, so the compression ratio is set to a relatively high value for the purpose of increasing output by improving thermal efficiency.

  If knocking still occurs even if the compression ratio is controlled according to the engine operating conditions, the ignition timing is controlled in addition to the compression ratio to suppress knocking. FIG. 13 shows transient characteristics of compression ratio control and ignition advance control when knocking occurs.

  As shown in FIG. 13, when the detection signal of knock sensor 142 exceeds the slice level at time t1, controller 300 controls actuator 131 to be driven so as to lower the compression ratio of compression ratio variable engine 100. At the same time, the ignition advance control device 400 retards the ignition timing by a predetermined knock retard amount to quickly suppress the knock. Then, a kind of feedback control (trace) is performed in which the ignition timing is gradually advanced in accordance with the change in the compression ratio (time t1 to t2) and the optimum ignition timing is maintained so as to be in a weak knock state. Knock control).

  The controller 300 also includes an intake valve closing timing control map in which a target intake valve closing timing is assigned in advance according to engine operating conditions.

  FIG. 14 is a diagram showing control of engine operating conditions and intake valve closing timing. In this embodiment, when it is desired to advance the closing timing of the intake valve 111 such as in a low load region, the center angle is set to an advanced angle with a low lift / small operating angle as shown in FIG. Conversely, when it is desired to delay the intake valve closing timing, such as in a high load range, the center angle is set to a retarded angle at a high lift / large operating angle as shown in FIG. In the middle load range, an intermediate lift characteristic is set as shown in FIG.

  According to the present embodiment described above, the crown surface of the piston 122 and the cylinder liner 129 are made of a heat insulating material, and the heat efficiency of the combustion chamber 143 can be improved, thereby improving the thermal efficiency.

  At the same time, by variably controlling the engine compression ratio by the variable compression ratio engine 100, it is possible to maintain a high compression ratio at the time of partial load and improve the thermal efficiency by reducing the cooling loss. On the other hand, at the time of full load or when knocking is detected, the compression ratio can be relatively lowered to suppress the occurrence of knocking.

  Furthermore, the actual compression ratio is variably controlled by the intake valve variable valve mechanism 200, whereby the actual compression ratio can be lowered and the pump loss can be reduced. At this time, the heat storage action by the heat insulation of the combustion chamber can suppress the reduction of the intake air temperature at the compression top dead center due to the reduction of the actual compression ratio, thereby improving the combustion.

  The variable compression ratio engine 100 according to the present embodiment realizes a piston stroke characteristic close to simple vibration, thereby eliminating the imbalance between the piston speeds at the top and bottom dead centers and reducing the secondary vibration. Also have. In addition, the piston speed near the top dead center is slowed down, and the combustion time can be increased. Therefore, the output rotational speed can be increased. On the other hand, an increase in cooling loss caused by a slow piston speed near the top dead center can be effectively eliminated by heat insulation of the combustion chamber.

It is a figure which shows a compression ratio variable engine. It is a figure explaining the compression ratio change method by a compression ratio variable engine. It is a figure which shows the piston stroke characteristic of a compression ratio variable engine. It is a perspective view which shows an intake valve variable valve mechanism. It is a drive shaft direction view of the lift / operating angle variable mechanism that constitutes a part of the intake valve variable valve mechanism. It is a figure explaining the change of the lift amount by a lift and a working angle variable mechanism. It is a figure explaining the effect | action by an intake valve variable valve mechanism. The PV diagram of the Miller cycle engine in which the intake valve closing timing is controlled to approximately 90 ° before bottom dead center (BBDC) by the intake valve variable valve mechanism and the intake valve closing timing are fixed to 40 ° after bottom dead center (ABDC). It is the figure which compared with the PV diagram of the other engine. It is a figure which shows the relationship between an engine compression ratio required in order to make intake valve closing timing and an actual compression ratio the same. It is sectional drawing of a normal piston and the heat insulation piston by this embodiment. It is a figure which shows the structure of the control system of this invention. 3 is a compression ratio control map in which a target compression ratio is assigned in advance according to engine operating conditions. This shows the transient characteristics of compression ratio control and ignition advance control when knocking occurs. It is a figure which shows control of an engine operating condition and an intake valve closing timing.

Explanation of symbols

100 Compression ratio variable engine (Compression ratio variable means)
111 Upper link (first link)
112 Lower link (second link)
113 Control link (3rd link)
114 Control shaft 122 Piston 141 Cylinder surface temperature sensor (wall surface temperature detecting means)
142 Knock sensor (knock detection means)
200 Intake valve variable valve mechanism (Intake valve closing timing variable means)
210 Lift / Operating Angle Variable Mechanism 211 Intake Valve 240 Phase Variable Mechanism 300 Controller

Claims (9)

A combustion chamber composed of a non-metallic material having a high thermal insulation and heat storage effect on the wall surface;
An operating state detecting means for detecting an engine operating state;
A compression ratio variable means for varying the engine compression ratio based on the detected engine operating state;
Similarly, based on the detected engine operating condition, the intake valve closing time is changed so that the actual compression ratio determined by the closing timing of the intake valve is smaller than the actual expansion ratio determined by the opening timing of the exhaust valve. Time variable means,
Mirror cycle agency with. 2. The Miller cycle engine according to claim 1, wherein the intake valve closing timing varying means advances the closing timing of the intake valve as the load detected by the operating state detecting means is lower. 3. 3. The Miller cycle engine according to claim 1, wherein the compression ratio variable unit increases the engine compression ratio as the load detected by the operating state detection unit is lower. The compression ratio varying means is
A first link having one end connected to the piston via a piston pin;
A second link connected at one end to the other end of the first link and rotatably mounted on the crankshaft;
A third link having one end connected to the other end of the second link;
A control shaft that has an eccentric shaft portion that is eccentric with respect to the rotation center shaft, and is connected to the eccentric shaft portion so that the other end of the third link can swing freely;
With
4. The Miller cycle engine according to claim 3, wherein the top dead center position of the piston is changed by rotating the control shaft and moving the eccentric shaft portion up and down based on an engine operating state. 5. The mirror cycle engine according to claim 4, wherein a link configuration of the first link, the second link, and the third link is set so that a stroke characteristic of the piston is substantially simple vibration. A knock detection means,
The compression ratio varying means reduces the engine compression ratio when a knock occurrence frequency or a detected value detected by the knock detection means exceeds a predetermined value. Mirror cycle agency described in one. A wall surface temperature detecting means for detecting the temperature of the wall surface of the combustion chamber;
The compression ratio varying means reduces the engine compression ratio when the wall surface temperature detected by the wall surface temperature detecting means is equal to or higher than a predetermined value. Miller cycle agency. The intake valve closing timing variable means includes a lift / operation angle variable mechanism that changes the lift / operation angle of the intake valve, and a phase variable mechanism that advances or retards the phase of the lift center angle of the intake valve. The Miller cycle engine according to any one of claims 1 to 7, characterized in that it is characterized in that: A combustion chamber composed of a non-metallic material having a high thermal insulation and heat storage effect on the wall surface;
An operating state detecting means for detecting an engine operating state;
An internal combustion engine comprising compression ratio variable means for varying the engine compression ratio based on the detected engine operating state,
A mirror cycle engine characterized in that the closing timing of the intake valve is set so that the actual compression ratio determined by the closing timing of the intake valve is smaller than the actual expansion ratio determined by the opening timing of the exhaust valve.

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