JP7610450B2 - Engine System - Google Patents

Description

The present invention relates to an engine system having an engine.

For example, Patent Document 1 discloses an engine combustion chamber structure in which multiple fine grooves extending radially are formed on the piston crown surface in order to reduce engine cooling loss.

JP 2018-087506 A

However, knocking can occur in engines. One way to suppress engine knocking is to reduce the inner diameter of the cylinder and lengthen the piston stroke instead. However, it can be difficult to lengthen the piston stroke due to space constraints on the engine. For this reason, it is desirable to suppress engine knocking without reducing the inner diameter of the cylinder.

Therefore, the present invention aims to provide an engine system that can suppress engine knock.

In order to solve the above problems, an engine system of the present invention includes a piston accommodated in a cylinder, a cylinder head disposed on the cylinder, and an ignition control unit, and when the piston is positioned at top dead center, a small-diameter combustion chamber, which is a combustion chamber with a radius smaller than the inner radius of the cylinder, is formed between a central area of the crown surface of the piston and a central area of the inner surface of the cylinder head where an ignition plug is disposed, and a squish, which is a gap between a peripheral area around the central area of the crown surface of the piston and a peripheral area around the central area of the inner surface of the cylinder head, is formed at a position close to the center of the piston when the piston is positioned at top dead center. The radius of the small-diameter combustion chamber is equal to or less than the value obtained by multiplying the time during which the squish, which varies according to the reciprocating motion of the piston, is equal to or less than the quenching distance by the flame propagation speed due to ignition of the spark plug , and the ignition control unit controls the ignition timing of the spark plug so that combustion of the mixed gas in the small-diameter combustion chamber is terminated within the time during which the squish is equal to or less than the quenching distance, and also controls the ignition timing of the spark plug so that the flame reaches the inner surface of the small-diameter combustion chamber before the unburned mixed gas compressed by the expansion of the flame generated by ignition of the spark plug satisfies the conditions for self-ignition .

The area of the piston crown that forms the squish may have a first plane facing the intake valve and a second plane facing the exhaust valve, and the first and second planes may form a pent roof type crown.

The peripheral area of the piston crown surface that forms the squish may further include a third plane that is located on one side of the longitudinal ridge of the pent roof-shaped crown surface formed by the first and second planes and intersects with the first and second planes, and a fourth plane that is located on the other side of the longitudinal ridge and intersects with the first and second planes, and the first, second, third and fourth planes form a pyramidal crown surface that is inclined in four directions.

In addition, the area of the third plane may be smaller than the areas of the first plane and the second plane, and the area of the fourth plane may be smaller than the areas of the first plane and the second plane .

Also, a recess may be formed in a central area of the inner surface of the cylinder head, and the small diameter combustion chamber may include the recess .

The present invention makes it possible to suppress engine knock.

FIG. 1 is a schematic diagram showing a configuration of an engine system according to a first embodiment. FIG. 2 is a perspective view of the engine. FIG. 3 is a perspective plan view of the engine as seen from the cylinder head side. FIG. 4 is a diagram showing the relative relationship between the position of the inner surface of the cylinder head and the position of the crown surface of the piston. FIG. 5 is a diagram for explaining the ignition timing. FIG. 6 is a perspective view showing a piston of an engine of the engine system according to the second embodiment. FIG. 7 is a perspective plan view of the engine according to the second embodiment, as viewed from the cylinder head side. FIG. 8 is a schematic perspective plan view illustrating an example of an operation of the engine according to the second embodiment. FIG. 9 is a schematic perspective plan view illustrating another example of the operation of the engine according to the second embodiment. FIG. 10 is a schematic diagram showing a configuration of an engine system according to the third embodiment. FIG. 11 is a schematic diagram showing a configuration of an engine system according to the fourth embodiment.

The following describes in detail an embodiment of the present invention with reference to the attached drawings. The dimensions, materials, and other specific values shown in the embodiment are merely examples to facilitate understanding of the invention, and do not limit the present invention unless otherwise specified. In this specification and drawings, elements that have substantially the same function and configuration are given the same reference numerals to avoid duplicated explanations, and elements that are not directly related to the present invention are not illustrated.

First Embodiment
1 is a schematic diagram showing a configuration of an engine system 1 according to a first embodiment. The engine system 1 is applied to, for example, a hybrid vehicle or an internal combustion engine vehicle. The engine system 1 includes an engine 10 and an engine control unit 12. The engine 10 includes a cylinder block 20, a piston 22, a cylinder head 24, an intake valve 26, and an exhaust valve 28.

The cylinder block 20 has multiple cylinders 30 formed therein. The pistons 22 are slidably housed within the cylinders 30. The pistons 22 are connected to a crankshaft (not shown) through connecting rods 32. The crankshaft rotates in accordance with the reciprocating motion of the pistons 22.

The cylinder head 24 is provided on the cylinder block 20 on the opposite side to the crankshaft. The cylinder head 24 is disposed on the cylinder 30 so as to close the cylinder 30, and is connected to the cylinder block 20. An intake port 34 and an exhaust port 36 are formed in the cylinder head 24. The intake port 34 and the exhaust port 36 communicate with a space surrounded by the inner surface of the cylinder 30, the inner surface 38 of the cylinder head 24, and the crown surface 40 of the piston 22. Hereinafter, the space surrounded by the inner surface of the cylinder 30, the inner surface 38 of the cylinder head 24, and the crown surface 40 of the piston 22 may be referred to as a gas storage space for convenience.

The intake valve 26 is provided in the intake port 34 and opens and closes the intake port 34. When the intake port 34 is opened by the intake valve 26, air is sent through the intake port 34 to the gas storage space. The exhaust valve 28 is provided in the exhaust port 36 and opens and closes the exhaust port 36. When the exhaust port 36 is opened by the exhaust valve 28, gas in the gas storage space is sent out through the exhaust port 36.

The cylinder head 24 is provided with an injector 42 and a spark plug 44. The injector 42 and the spark plug 44 are located near the central axis of the cylinder 30. The injector 42 is arranged with its nozzle facing the gas storage space. The injector 42 injects fuel, such as gasoline, into the gas storage space at a predetermined timing. The spark plug 44 is arranged with its electrode facing the gas storage space. The spark plug 44 ignites a mixture of air and fuel at a predetermined timing to cause combustion. This combustion causes the piston 22 to reciprocate within the cylinder 30.

The engine control unit 12 is composed of a semiconductor integrated circuit including a central processing unit, a ROM in which programs and the like are stored, and a RAM as a work area. The engine control unit 12 functions as an ignition control unit 46 by executing a program. The ignition control unit 46 controls the ignition timing of the spark plug 44. The ignition control unit 46 will be described in detail later.

Figure 1 shows the piston 22 at top dead center. A hemispherical recess 50 is formed in the central area of the crown surface 40 of the piston 22. A spark plug 44 is disposed in the central area of the inner surface 38 of the cylinder head 24. When the piston 22 is at top dead center in the engine 10, a small diameter combustion chamber 52 is formed between the central area of the crown surface 40 of the piston 22 and the central area of the inner surface 38 of the cylinder head 24 where the spark plug 44 is disposed. The small diameter combustion chamber 52 is a combustion chamber with a radius smaller than the inner radius of the cylinder 30. In other words, the inner surface of the recess 50 becomes the inner surface of the small diameter combustion chamber 52.

In addition, a first plane 54 and a second plane 56 are formed in the peripheral area of the crown surface 40 of the piston 22 around the central area. In other words, the first plane 54 and the second plane 56 indicate the area around the recess 50 in the crown surface 40. The first plane 54 faces the intake valve 26. The second plane 56 faces the exhaust valve 28.

Figure 2 is a perspective view of the engine. As shown in Figure 2, the first plane 54 and the second plane 56 form a so-called pent roof type crown surface 40. In addition, the first plane 54 and the second plane 56 are uniformly flat, and no valve recesses are formed.

Returning to FIG. 1, in the engine 10, when the piston 22 is at top dead center, both the intake valve 26 and the exhaust valve 28 are closed. When the intake valve 26 is closed, the surface of the intake valve 26 facing the first plane 54 is approximately flush with the inner surface 38 of the cylinder head 24. When the exhaust valve 28 is closed, the surface of the exhaust valve 28 facing the second plane 56 is approximately flush with the inner surface 38 of the cylinder head 24.

As shown in FIG. 1, the gap between the peripheral area around the central area of the crown surface 40 of the piston 22 and the peripheral area around the central area of the inner surface 38 of the cylinder head 24 is sometimes called the squish 60. The squish 60 indicates the relatively narrow gap between the piston 22 and the cylinder head 24 when the piston 22 is located near the top dead center.

Specifically, a squish 60 is formed between the first plane 54 on the crown surface 40 and the inner surface 38 of the cylinder head 24 and the surface of the intake valve 26 facing the first plane 54. Also, a squish 60 is formed between the second plane 56 on the crown surface 40 and the inner surface 38 of the cylinder head 24 and the surface of the exhaust valve 28 facing the second plane 56. In other words, the peripheral area of the crown surface 40 of the piston 22 that forms the squish 60 has the first plane 54 and the second plane 56.

Figure 3 is a perspective plan view of the engine 10 as seen from the cylinder head 24 side. As shown in Figure 3, in the engine 10, two intake ports 34 and two exhaust ports 36 are formed for each cylinder 30. Although not shown, an intake valve 26 is provided for each intake port 34 opening surface, and an exhaust valve 28 is provided for each exhaust port 36 opening surface. The first plane 54 faces both of the two intake valves 26, and the second plane 56 faces both of the two exhaust valves 28.

When the piston 22 moves toward the top dead center, the mixed gas in the gas storage space is compressed. At this time, the gap between the first plane 54 and the inner surface 38 of the cylinder head 24, i.e., the squish 60, causes the mixed gas present on the first plane 54 to flow upward along the first plane 54 from the bottom dead center side to the top dead center side. In other words, the mixed gas on the first plane 54 flows in the direction from the first plane 54 toward the small diameter combustion chamber 52, as shown by arrow A10.

In addition, due to the gap between the second plane 56 and the inner surface 38 of the cylinder head 24, i.e., the squish 60, a flow occurs in the mixed gas present on the second plane 56 that ascends the second plane 56 from the bottom dead center side to the top dead center side. In other words, the mixed gas on the second plane 56 flows in a direction from the second plane 56 toward the small diameter combustion chamber 52, as shown by arrow A12. The flow of mixed gas as shown by arrows A10 and A12 is generated by the squish 60, and is therefore sometimes called a squish flow.

In the engine 10, this squish flow causes the mixed gas to be concentrated in the small diameter combustion chamber 52 formed by the recess 50. In addition, since the engine 10 does not have a valve recess, the squish flow is not obstructed by the valve recess, and the mixed gas can be appropriately concentrated in the small diameter combustion chamber 52.

Figure 4 is a diagram showing the relative relationship between the position of the inner surface 38 of the cylinder head 24 and the position of the crown surface 40 of the piston 22. In Figure 4, the horizontal axis indicates the time when the piston 22 moves, and the vertical axis indicates the position of the crown surface 40 of the piston 22. More specifically, the position of this crown surface 40 indicates the relative positions of the first plane 54 and the second plane 56 with respect to the inner surface 38 of the cylinder head 24.

When the piston 22 moves toward the top dead center, the first plane 54 and the second plane 56 approach the inner surface 38 of the cylinder head 24, forming a squish 60. The squish 60 becomes shorter as the piston 22 moves toward the top dead center. In other words, the squish 60 varies according to the reciprocating motion of the piston 22.

When the piston 22 is at top dead center, the squish 60 becomes shorter than the quenching distance. The quenching distance indicates the distance over which the flame cannot propagate and is extinguished. The quenching distance is set to, for example, 2 mm, but may be appropriately set through experiments or simulations. When the quenching distance is 2 mm, the squish 60 when the piston 22 is at top dead center is set to, for example, between 0.5 mm and 1 mm. Note that the specific numerical value is not limited to this example and may be set as appropriate.

As shown in FIG. 4, timing T1 indicates the boundary timing at which the squish 60, which has a value longer than the quenching distance, changes to a value below the quenching distance as the piston 22 moves toward top dead center. Timing T2 indicates the boundary timing at which the squish 60, which is less than the quenching distance, changes to a value longer than the quenching distance as the piston 22 moves toward bottom dead center. Therefore, the time Tqd from timing T1 to timing T2 indicates the time during which the squish 60, which fluctuates in accordance with the reciprocating motion of the piston 22, is less than the quenching distance. In other words, time Tqd indicates the time during which the squish 60 is maintained below the quenching distance.

In the engine 10, the radius of the small-diameter combustion chamber 52 is equal to or smaller than the value obtained by multiplying the time Tqd during which the squish 60, which varies in accordance with the reciprocating motion of the piston 22, is equal to or smaller than the extinction distance by the flame propagation speed due to ignition of the spark plug 44. In other words, assuming that the radius of the small-diameter combustion chamber 52 is R and the flame propagation speed is Vf, the following formula (1) is satisfied. The flame propagation speed indicates the speed at which a flame generated by ignition propagates through the small-diameter combustion chamber 52.
R≦Tqd×Vf...(1)

Because the radius of the small diameter combustion chamber 52 satisfies the above formula (1), in the engine 10, the flame caused by ignition can reach the inner surface of the small diameter combustion chamber 52 before the squish 60 becomes longer than the quenching distance. Then, when the flame reaches the inner surface of the small diameter combustion chamber 52, the squish 60 is below the quenching distance, so the flame is not propagated to the squish 60. As a result, in the engine 10, combustion does not occur in the entire gas storage space, but in the small small diameter combustion chamber 52 formed by the recessed portion 50.

Therefore, in the engine system 1 of the first embodiment, it is possible to suppress knocking in the engine 10 without reducing the inner diameter of the cylinder 30.

In addition, the engine 10 of the first embodiment has a smaller volume of the small diameter combustion chamber 52 compared to conventional engines in which the entire gas storage space is used as the combustion chamber, so it is possible to achieve a high compression ratio while suppressing knocking in the engine 10. As a result, the engine system 1 of the first embodiment can further improve combustion efficiency.

In addition, in the engine system 1 of the first embodiment, knocking of the engine 10 can be further suppressed by controlling the ignition timing in addition to the radius of the small diameter combustion chamber 52.

Figure 5 is a diagram explaining the ignition timing. In Figure 5, the time progression of the squish 60 and an example of the ignition timing are shown on a common time axis.

In ignition example A, ignition begins at the timing of the black circle PA1, the generated flame propagates, and the leading edge of the flame reaches the inner surface of the small-diameter combustion chamber 52 at the timing of the black square PA2, before timing T2 when the squish 60 is below the quenching distance. However, in ignition example A, the combustion of the mixed gas continues even after the flame reaches the inner surface of the small-diameter combustion chamber 52, and the combustion of the mixed gas ends at the timing of the white circle PA3 after the squish 60 becomes longer than the quenching distance.

In the case of ignition example A, the squish 60 becomes longer than the quenching distance, and there is a risk that the burning flame will propagate to the mixed gas present in the squish 60. If this happens, after timing T2, the unburned mixed gas in the squish 60 may be compressed by the expansion of the flame propagated to the squish 60, and the unburned mixed gas in the squish 60 may self-ignite. As a result, there is a risk that the engine 10 may knock.

In contrast, in ignition example B, ignition begins at the timing of the black circle PB1, the leading edge of the flame reaches the inner surface of the combustion chamber at the timing of the black square PB2, and combustion of the mixed gas ends at the timing of the white circle PB3, which is before timing T2 when the squish 60 is below the quenching distance.

In the case of ignition example B, the combustion in the small diameter combustion chamber 52 ends before the squish 60 becomes longer than the extinction distance, so the flame does not propagate to the mixed gas in the squish 60 after timing T2. This makes it possible to suppress spontaneous ignition of the unburned mixed gas in the squish 60.

In light of this, the ignition control unit 46 controls the ignition timing of the spark plug 44 so that the combustion of the mixed gas in the small diameter combustion chamber 52 ends within the time that the squish 60 is equal to or less than the quenching distance. In other words, the ignition control unit 46 starts ignition of the spark plug 44 before the ignition timing at which the timing at which the combustion of the mixed gas in the small diameter combustion chamber 52 ends is the boundary timing T2 at which the squish 60 goes from being equal to or less than the quenching distance to being longer than the quenching distance. This ignition start condition corresponds to the later threshold value in the appropriate range Ts of ignition timing.

In ignition example C, ignition is started at the timing of black circle PC1, which is a relatively early timing based on the timing when the piston 22 reaches the top dead center. In ignition example C, the generated flame propagates, and the front of the flame reaches the inner surface of the small-diameter combustion chamber 52 at the timing of black square PC2, and the combustion of the mixed gas ends at the timing of white circle PC3. However, in ignition example C, the unburned mixed gas in the small-diameter combustion chamber 52 is compressed by the expansion of the generated flame, and before the front of the generated flame reaches the inner surface of the small-diameter combustion chamber 52, the unburned mixed gas compressed in the small-diameter combustion chamber 52 satisfies the conditions for autoignition and autoignition occurs. The conditions for autoignition are, for example, the pressure of the unburned mixed gas is equal to or higher than a predetermined pressure, and the temperature of the unburned mixed gas is equal to or higher than a predetermined temperature. If autoignition occurs, there is a high possibility that the engine 10 will knock as a result.

In contrast, in ignition example D, ignition begins at the timing indicated by the black circle PD1, which is later than the ignition timing indicated by the black circle PC1 in ignition example C. In ignition example D, the generated flame propagates, and before the unburned mixed gas in the small-diameter combustion chamber 52 meets the conditions for self-ignition, the leading edge of the flame reaches the inner surface of the small-diameter combustion chamber 52 at the timing indicated by the black square PD2, and the combustion of the mixed gas ends at the timing indicated by the white circle PD3.

In consideration of this, the ignition control unit 46 controls the ignition timing of the spark plug 44 so that the flame reaches the inner surface of the small-diameter combustion chamber 52 before the unburned mixed gas, compressed by the expansion of the flame generated by ignition, meets the conditions for self-ignition. In other words, the ignition control unit 46 starts ignition of the spark plug 44 later than the ignition timing at which the unburned mixed gas meets the conditions for self-ignition when the leading edge of the flame reaches the inner surface of the small-diameter combustion chamber 52. This ignition start condition corresponds to the earlier threshold value in the appropriate range Ts of ignition timing.

The ignition control unit 46 controls the ignition so as to satisfy either or both of the above-mentioned later ignition start conditions and the above-mentioned earlier ignition start conditions. This allows the engine system 1 to further suppress knocking of the engine 10.

Furthermore, the flame propagation speed may vary depending on operating conditions such as intake air temperature. Therefore, when the engine system 1 is introduced, reference operating conditions that indicate standard or typical operating conditions are set, and the radius of the small diameter combustion chamber 52 is designed using the flame propagation speed at the reference operating conditions.

When the engine system 1 is in operation, the radius of the small-diameter combustion chamber 52 is fixed, so the ignition control unit 46 adjusts the ignition timing within the appropriate range Ts of the ignition timing described above in accordance with fluctuations in the actual operating conditions. This makes it possible to more reliably suppress knocking of the engine 10.

For example, a reference ignition timing is set in advance, which indicates the ignition timing corresponding to the radius of the small-diameter combustion chamber 52 designed based on the reference operating conditions. The ignition control unit 46 acquires the current operating conditions and derives the amount of shift of the ignition timing from the reference ignition timing based on the current operating conditions. The ignition control unit 46 determines the ignition timing corresponding to the current operating conditions from the reference ignition timing and the amount of shift of the ignition timing. Then, when the determined ignition timing is reached, the ignition control unit 46 starts ignition of the spark plug 44.

Second Embodiment
6 is a perspective view showing a piston 122 of an engine 110 of an engine system 100 according to the second embodiment. The piston 122 of the second embodiment has a recess 50 formed in a central area of the crown surface 40, similar to the piston 22 of the first embodiment. In the engine 110, when the piston 122 is located at top dead center, a small diameter combustion chamber 52 is formed between the central area of the crown surface 40 of the piston 122 and a central area of the inner surface 38 of the cylinder head 24 where the ignition plug 44 is disposed.

In the peripheral area around the central area of the crown surface 40 of the piston 122, a first plane 154, a second plane 156, a third plane 170, and a fourth plane 172 are formed. The first plane 154 corresponds to the first plane 54 of the first embodiment and faces the intake valve 26. The second plane 156 corresponds to the second plane 56 of the first embodiment and faces the exhaust valve 28. The plane extending from the first plane 154 and the plane extending from the second plane 156 form a so-called pent roof. In addition, the first plane 154 and the second plane 156 are uniformly flat, and no valve recess is formed.

Figure 7 is a perspective plan view of the engine 110 of the second embodiment, seen from the cylinder head 24 side. The dashed line in Figure 7 indicates the ridgeline 174 of the pent roof formed by the plane extending from the first plane 154 and the plane extending from the second plane 156.

As shown in FIG. 7, the third plane 170 is disposed on one side of the longitudinal direction of the ridge 174 of the pent roof-shaped crown surface 40 formed by the first plane 154 and the second plane 156. Meanwhile, the fourth plane 172 is disposed on the other side of the longitudinal direction of the ridge 174. The third plane 170 and the fourth plane 172 are formed so as not to overlap with the projection plane of the opening surface of the intake port 34 and the opening surface of the exhaust port 36 onto the crown surface 40.

6 and 7, the third plane 170 is inclined with respect to the ridge line 174 so as to proceed from one end of the ridge line 174 in the longitudinal direction toward the periphery of the crown surface 40 toward the crankshaft side. The third plane 170 is formed so as to intersect with the first plane 154 and the second plane 156. The fourth plane 172 is inclined with respect to the ridge line 174 so as to proceed from the other end of the ridge line 174 in the longitudinal direction toward the periphery of the crown surface 40 toward the crankshaft side. The fourth plane 172 is formed so as to intersect with the first plane 154 and the second plane 156.

In this way, in the piston 122, the first plane 154, the second plane 156, the third plane 170, and the fourth plane 172 form a pyramidal crown surface 40 that is inclined in four directions. In other words, the first plane 154, the second plane 156, the third plane 170, and the fourth plane 172 roughly correspond to each side of a pyramid with a missing apex.

Although not shown, the inner surface 38 of the cylinder head 24 is formed to face the first plane 154, the second plane 156, the third plane 170, and the fourth plane 172, respectively. The first plane 154, the second plane 156, the third plane 170, and the fourth plane 172 form a squish 60 between themselves and the inner surface 38 of the cylinder head 24. When the piston 122 is located at top dead center, the squish 60 becomes shorter than the quenching distance.

7, the squish 60 generates a squish flow in the direction from the first plane 154 to the small-diameter combustion chamber 52 as shown by the arrow A20 in the mixed gas on the first plane 154. The squish 60 generates a squish flow in the direction from the second plane 156 to the small-diameter combustion chamber 52 as shown by the arrow A22 in the mixed gas on the second plane 156. The squish 60 generates a squish flow in the direction from the third plane 170 to the small-diameter combustion chamber 52 as shown by the arrow A24 in the mixed gas on the third plane 170. The squish 60 generates a squish flow in the direction from the fourth plane 172 to the small-diameter combustion chamber 52 as shown by the arrow A26 in the mixed gas on the fourth plane 172. In this way, in the engine 110 of the second embodiment, the squish flow flows in from all four sides of the small-diameter combustion chamber 52, so that the mixed gas can be more appropriately concentrated in the small-diameter combustion chamber 52.

Also, as in the first embodiment, the radius of the small diameter combustion chamber 52 of the engine 110 is equal to or less than the value obtained by multiplying the time Tqd during which the squish 60, which varies according to the reciprocating motion of the piston 122, is equal to or less than the quenching distance by the flame propagation speed due to the ignition of the spark plug 44. Therefore, in the engine system 100 of the second embodiment, as in the first embodiment, it is possible to suppress knocking of the engine 110 without reducing the inner diameter of the cylinder 30.

In addition, in the engine system 100 of the second embodiment, the ignition control unit 46 controls the ignition timing in the same manner as in the first embodiment, thereby further suppressing knocking of the engine 110 in the same manner as in the first embodiment.

Figure 8 is a schematic perspective plan view illustrating an example of the operation of the engine 110 according to the second embodiment. In Figure 8, arrows A24 and A26 indicate the squish flow on the third plane 170 and the squish flow on the fourth plane 172. Also, arrow A30 indicates an example of the flow of intake air introduced into the gas storage space through the intake port 34.

The intake air is introduced so that it becomes a tumble flow of vertical vortices in the gas storage space. However, in some cases, the vertical vortices may spread horizontally and collapse, as shown by arrow A30.

In contrast, in the engine 110, the squish flow on the third plane 170 and the squish flow on the fourth plane 172 flow in such a way as to push the intake air vertical vortex in a direction toward the central axis of the cylinder 30. This suppresses the collapse of the vertical vortex in the lateral direction.

Therefore, in the second embodiment of the engine system 100, the intake tumble flow can be maintained as an appropriate vertical vortex, which can improve the combustion efficiency.

Figure 9 is a schematic perspective plan view illustrating another example of the operation of the engine 110 according to the second embodiment. In Figure 9, arrows A24 and A26 indicate the squish flow on the third plane 170 and the squish flow on the fourth plane 172. Also, arrow A40 indicates another example of the flow of intake air introduced into the gas storage space through the intake port 34.

The intake air is introduced so that the flow speed is faster the closer it is to the central axis of the cylinder 30, in order to form a vertical vortex in the gas storage space. However, in some cases, the flow speed of the intake air near the inner surface of the cylinder 30 may become too fast.

In contrast, in engine 110, the squish flow on third plane 170 and the squish flow on fourth plane 172 impede the flow of intake air close to the inner surface of cylinder 30, suppressing the flow velocity of intake air close to the inner surface of cylinder 30. As a result, the flow velocity of intake air becomes relatively faster closer to the central axis of cylinder 30. Note that in FIG. 9, the thicker the arrow A40, the faster the flow velocity.

Therefore, in the engine system 100 of the second embodiment, the distribution of the intake flow velocity can be appropriately achieved, and as a result, it is possible to appropriately form longitudinal vortices.

Third Embodiment
10 is a schematic diagram showing a configuration of an engine system 200 according to a third embodiment. In an engine 210 of the engine system 200, the central area of the crown surface 40 of the piston 22 does not have a recess 50 as in the first embodiment, but has a flat surface 250a. In addition, a recess 250b is formed in the central area of the inner surface 38 of the cylinder head 24. In the engine 210, when the piston 22 is located at the top dead center, the flat surface 250a of the crown surface 40 of the piston 22 and the recess 250b of the inner surface 38 of the cylinder head 24 form a small diameter combustion chamber 52. Note that the peripheral area around the central area of the crown surface 40 of the piston 22 may be a pent roof type as in the first embodiment, or a pyramidal type as in the second embodiment.

The radius of the small diameter combustion chamber 52 of the engine 210 is equal to or less than the value obtained by multiplying the time Tqd during which the squish 60, which varies according to the reciprocating motion of the piston 22, is equal to or less than the quenching distance by the flame propagation speed due to the ignition of the spark plug 44, as in the first embodiment. Therefore, in the engine system 200 of the third embodiment, it is possible to suppress knocking of the engine 210 without reducing the inner diameter of the cylinder 30, as in the first embodiment.

Fourth Embodiment
11 is a schematic diagram showing a configuration of an engine system 300 according to a fourth embodiment. In an engine 310 of the engine system 300, a recess 350a is formed in a central area of a crown surface 40 of a piston 22. In addition, a recess 350b is formed in a central area of an inner surface 38 of a cylinder head 24. In the engine 310, when the piston 22 is located at the top dead center, a small diameter combustion chamber 52 is formed by the recess 350a in the crown surface 40 of the piston 22 and the recess 350b in the inner surface 38 of the cylinder head 24. Note that the peripheral area around the central area of the crown surface 40 of the piston 22 may be a pent roof type as in the first embodiment, or a pyramidal type as in the second embodiment.

The radius of the small diameter combustion chamber 52 of the engine 310 is equal to or less than the value obtained by multiplying the time Tqd during which the squish 60, which varies according to the reciprocating motion of the piston 22, is equal to or less than the quenching distance by the flame propagation speed due to the ignition of the spark plug 44, as in the first embodiment. Therefore, in the engine system 300 of the third embodiment, it is possible to suppress knocking of the engine 310 without reducing the inner diameter of the cylinder 30, as in the first embodiment.

Although an embodiment of the present invention has been described above with reference to the attached drawings, it goes without saying that the present invention is not limited to such an embodiment. It is clear that a person skilled in the art can come up with various modified or revised examples within the scope of the claims, and it is understood that these also naturally fall within the technical scope of the present invention.

For example, the shape of the peripheral area around the central area of the crown surface 40 of the piston 22, 122 is not limited to the pent roof type of the first embodiment or the pyramidal type of the second embodiment. For example, the peripheral area around the central area of the crown surface 40 of the piston 22, 122 may be formed into a dome-shaped crown surface 40 such as a hemisphere.

1, 100, 200, 300 Engine system 10, 110, 210, 310 Engine 22, 122 Piston 24 Cylinder head 26 Intake valve 28 Exhaust valve 38 Inner surface 40 Crown surface 44 Spark plug 46 Ignition control unit 52 Small diameter combustion chamber 54, 154 First plane 56, 156 Second plane 60 Squish 170 Third plane 172 Fourth plane 174 Ridge line

Claims (5)

A piston housed within the cylinder;
a cylinder head disposed on the cylinder;
An ignition control unit;
Equipped with
When the piston is at the top dead center, a small-diameter combustion chamber having a radius smaller than the inner radius of the cylinder is formed between a central area of the piston crown surface and a central area of the inner surface of the cylinder head where an ignition plug is disposed,
a squish, which is a distance between a peripheral area around a central area of the piston crown surface and a peripheral area around the central area of an inner surface of the cylinder head, becomes shorter than a quenching distance when the piston is located at a top dead center;
a radius of the small-diameter combustion chamber is equal to or smaller than a value obtained by multiplying a time during which the squish, which varies in accordance with the reciprocating motion of the piston, is equal to or smaller than the quenching distance by a flame propagation speed due to ignition of the spark plug,
The ignition control unit is
controlling an ignition timing of the spark plug so as to terminate combustion of the mixed gas in the small-diameter combustion chamber within a time period during which the squish is equal to or shorter than the quenching distance;
and controlling the ignition timing of the spark plug so that the flame reaches the inner surface of the small-diameter combustion chamber before the unburned mixed gas compressed by the expansion of the flame generated by the ignition of the spark plug satisfies the condition for self-ignition.
Engine system. The peripheral area of the piston crown surface that forms the squish is
a first plane facing the intake valve;
a second plane facing the exhaust valve;
having
The engine system of claim 1 , wherein the first planar surface and the second planar surface form a pent roof type crown surface. The peripheral area of the piston crown surface that forms the squish is
a third plane disposed on one side of a ridge line of the pent roof-shaped crown surface formed by the first plane and the second plane in a longitudinal direction and intersecting the first plane and the second plane;
a fourth plane disposed on the other side of the ridge line in the longitudinal direction and intersecting the first plane and the second plane;
and
The engine system according to claim 2 , wherein the first plane, the second plane, the third plane, and the fourth plane form a pyramidal crown surface inclined in four directions. The area of the third plane is smaller than the areas of the first plane and the second plane,
The area of the fourth plane is smaller than the areas of the first plane and the second plane.
The engine system according to claim 3. A recess is formed in a central area of the inner surface of the cylinder head,
The small diameter combustion chamber includes the recessed portion.
The engine system of claim 1 .

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