JP6345294B2 - Engine unit and saddle riding type vehicle - Google Patents

Description

  The present invention relates to an engine unit and a saddle type vehicle.

  Conventionally, an independent throttle type four-stroke engine that can be mounted on a motorcycle is known (for example, see Patent Document 1). The independent throttle type engine means an engine in which a throttle valve is provided for each combustion chamber (cylinder).

  The 4-cycle engine disclosed in Patent Document 1 includes a combustion chamber, an intake passage, an exhaust passage, an intake valve, an exhaust valve, and a throttle valve provided in the intake passage. The engine of Patent Document 1 has a period (overlap period) in which both the intake valve and the exhaust valve are open for high output. In addition, the volume of the intake passage is adjusted in order to improve combustion stability during low load operation of the engine. Specifically, the ratio (volume ratio) to the stroke volume (exhaust amount per cylinder) of the volume (port volume) from the combustion chamber side opening (intake valve opening) of the intake passage to the throttle valve is the overlap period. Is set based on.

Japanese Patent Laid-Open No. 10-212980 JP 2008-230535 A JP 2009-92018 A

  As described above, the volume ratio in Patent Document 1 means the ratio of the port volume to the stroke volume (the displacement per cylinder). For this reason, in order to adjust the volume ratio in an engine having a predetermined displacement, it is necessary to adjust the port volume. Therefore, when the intake passage is configured using the technique of Patent Document 1 in order to improve the combustion stability of an engine having a predetermined displacement, the port volume is determined according to the displacement of the engine.

  On the other hand, the cross-sectional area of the intake passage affects the output of the engine. Therefore, in order to achieve high engine output, it is necessary to design the intake passage so that the cross-sectional area of the intake passage has a size suitable for high engine output.

  Therefore, when improving the combustion stability of the engine using the technology of Patent Document 1 while realizing high engine output, the intake passage cross-sectional area and port volume are determined to be specific values. As described above, the port volume means the volume from the intake valve opening to the throttle valve. Therefore, the distance between the intake valve opening and the throttle valve is also determined by determining the cross-sectional area of the intake passage and the port volume.

  By the way, in a saddle riding type vehicle such as a motorcycle, there may be a case where a sufficient space for arranging the throttle body in the vicinity of the engine cannot be secured. For example, in a scooter type motorcycle disclosed in Patent Document 2, a storage box is disposed above the engine unit. In this case, it is difficult to secure a sufficient space for arranging the throttle body between the engine unit and the storage box. Therefore, in the motorcycle disclosed in Patent Document 2, the throttle body is disposed so as to be biased to one side with respect to the center of the motorcycle in the width direction of the motorcycle.

  Further, for example, in a motorcycle equipped with a V-type engine disclosed in Patent Document 3, a throttle body assembly, a front cylinder, and a rear cylinder are disposed below an air cleaner. In the motorcycle disclosed in Patent Document 3, it is difficult to ensure a sufficient space between the front cylinder and the rear cylinder. Therefore, the throttle body assembly is disposed above the front cylinder and the rear cylinder.

  Thus, in the saddle riding type vehicle, the position of the throttle body is restricted by the components such as the storage box and the cylinder. Thereby, the position of the throttle valve is also restricted. For this reason, when the above-described port volume is determined from the viewpoint of improving the combustion stability during low-load operation (including idling) of the engine, the cross-sectional area of the intake passage cannot be freely adjusted. This makes it difficult to increase the engine output. On the other hand, when the cross-sectional area of the intake passage is determined from the viewpoint of high engine output, the port volume cannot be freely adjusted. This makes it difficult to improve combustion stability during low-load operation of the engine.

  Therefore, an object of the present invention is to obtain a configuration that can achieve both high engine output and improved combustion stability during low-load operation even when the throttle valve position is limited.

  During low-load operation of the engine (including idling), the portion downstream of the throttle valve in the intake passage becomes negative pressure. For this reason, in an engine having an overlap period, the burned gas in the combustion chamber tends to flow back into the intake passage during the overlap period during low-load operation. The burnt gas that has flowed back into the intake passage again flows into the combustion chamber during the intake stroke. Thereby, combustion stability falls. In particular, when the volume of the portion downstream of the throttle valve in the intake passage increases, the above phenomenon becomes remarkable. Therefore, in order to improve combustion stability during low load operation of the engine, it is preferable to reduce the volume of the portion downstream of the throttle valve in the intake passage.

  However, as described above, the position of the throttle valve is limited in the saddle riding type vehicle. For this reason, the volume of the portion downstream of the throttle valve in the intake passage may not be reduced. Accordingly, the present inventors have made various studies in order to improve combustion stability during low-load operation of the engine without reducing the volume of the portion downstream from the throttle valve.

  As a result, it was found that the above-described backflow of burned gas occurs because the pressure in the intake passage is lower than the pressure in the exhaust passage during the overlap period during low load operation of the engine. Further, in the overlap period, the difference between the pressure in the intake passage (intake pressure) and the pressure in the exhaust passage (exhaust pressure) is reduced, or the pressure in the intake passage is made higher than the pressure in the exhaust passage. As a result, it was found that the backflow of the burned gas can be suppressed.

  While proceeding with the study based on the above findings, the present inventors tried to improve the combustion stability during low-load operation of the engine by increasing the pressure in the intake passage during the overlap period. . As a result, the following was further found out.

  If the pressure in the intake passage increases during the overlap period, the intake air amount of the engine in one cycle increases, and the engine output increases. This makes it impossible to maintain the engine operating range in a desired low-load operating range. For example, if the engine intake amount in one cycle increases when the engine is idling, the engine output cannot be maintained at an output suitable for idling.

  For this reason, in the conventional engine configuration, when the pressure in the intake passage is increased during the overlap period during low load operation, it is necessary to reduce the output by delaying the ignition timing. However, if the ignition timing is delayed during low-load operation of the engine, fuel consumption may be reduced. Therefore, it is not preferable to delay the ignition timing during low-load operation of the engine. Thus, with the conventional engine configuration, it has been difficult to increase the pressure in the intake passage during the overlap period while enabling a desired low-load operation.

  Therefore, the inventors have further studied the configuration of the engine that can increase the pressure in the intake passage during the overlap period while enabling a desired low load operation. In the research, the present inventors set the pressure in the intake passage during normal low-load operation as a reference pressure, and the region in which the pressure in the intake passage is lower than the reference pressure during one cycle (crank angle). And the characteristics of the engine having a region higher than the reference pressure were examined in detail. As a result, the pressure in the intake passage is increased in the overlap period while preventing an increase in the intake amount of the engine in one cycle by changing the pressure in the intake passage as described above with respect to the reference pressure. I found out that That is, it has been found that the pressure in the intake passage can be increased during the overlap period while enabling a desired low load operation. With this configuration, it is possible to improve the combustion stability during low-load operation of the engine regardless of the position of the throttle valve.

  Based on the above findings, the present inventors have conceived the following configuration of the engine unit.

An engine unit according to an embodiment of the present invention is a four-stroke engine unit including an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke in one cycle. The engine unit includes a combustion chamber provided with at least one intake port and at least one exhaust port, and is connected to the at least one intake port, and air in the atmosphere is connected to the at least one intake port. An intake passage that leads into the combustion chamber, an exhaust passage that is connected to the at least one exhaust port and exhausts the gas in the combustion chamber to the atmosphere via the at least one exhaust port, and an intake air that opens and closes the intake port A valve, an exhaust valve that opens and closes the exhaust port, and an adjustment valve that is provided in the intake passage and adjusts an opening area of the intake passage. The intake valve opens before the exhaust valve closes and before the exhaust valve opens during the one cycle when at least the operation range of the engine unit is a predetermined low load operation range. close up. In the adjustment valve, the intake pressure between the adjustment valve and the combustion chamber in the intake passage is expressed by the following equations (1) and (2) in the one cycle at least in the low load operation region. The opening area is adjusted so as to satisfy the relationship.
P _IC <P _VIC (1)
_PIO > _PVIO (2)

However, in the above formula (1), P _VIC is the value at the time when the intake valve is closed in the virtual fixed operation state where the opening area of the intake passage is assumed to be fixed to a constant value during the one cycle. The intake pressure. P _IC is in the adjustment operating condition in which the opening area is adjusted by the control valve in said one cycle, which is the intake pressure when the said intake valve is closed. In the adjustment operation state, the adjustment valve adjusts the opening area so that the rotation speed of the engine unit is equal to the rotation speed in the virtual fixed operation state.

In the above formula (2), P _VIO is the intake pressure when the intake valve is opened in the virtual fixed operation state. _PIO is the intake pressure when the intake valve is opened in the adjusted operation state.

  The terminology used herein is used for the purpose of defining particular embodiments only and is not intended to be limiting of the invention. As used herein, “and / or” includes any and all combinations of one or more of the associated listed components. As used herein, the terms “including”, “comprising” or “having” and the use of variations thereof are described features, steps, elements, components, and / or Identify the presence of their equivalents, but may include one or more of steps, actions, elements, components, and / or groups thereof. In this specification, “attached”, “connected”, “coupled”, and / or their equivalents are used in a broad sense, “direct and indirect” attachment, Includes both connections and couplings. Further, “connected” and “coupled” are not limited to physical or mechanical connections or couplings, and can include direct or indirect connections or couplings.

  Unless defined otherwise, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs. Terms defined in commonly used dictionaries should be construed as having a meaning consistent with the meaning in the context of the related art and disclosure, and unless explicitly defined herein. Should not be interpreted in an ideal or overly formal sense.

  In the description of the invention, it is understood that a number of techniques and processes are disclosed. Each of these has individual benefits and can also be used with one or more or possibly all of the other disclosed techniques. Therefore, for clarity, the description of the invention refrains from repeating all possible combinations of individual steps unnecessarily. However, the specification and claims should be read with the understanding that all such combinations are within the scope of the invention.

  In the following description, numerous specific examples are set forth in order to provide a thorough understanding of the present invention. However, it will be apparent to those skilled in the art that the present invention may be practiced without these specific examples.

  The following disclosure is, therefore, to be considered as illustrative of the invention and is not intended to limit the invention to the specific embodiments illustrated by the following drawings or description.

  The engine unit according to an embodiment of the present invention can achieve both high engine output and improved combustion stability during low-load operation even when the throttle valve position is limited.

FIG. 1 is a left side view showing a straddle-type vehicle. FIG. 2 is a schematic diagram showing the configuration of the engine unit. FIG. 3 is a diagram showing a pressure change in the intake passage and a pressure change in the exhaust passage. FIG. 4 is a diagram showing the relationship between the throttle opening and the crank angle during low load operation. FIG. 5 is a flowchart showing an example of the control operation of the ECU. FIG. 6 is a view showing an engine unit according to another embodiment. FIG. 7 is a diagram showing the relationship between the auxiliary valve opening and the crank angle during low-load operation.

  Hereinafter, an engine unit according to an embodiment of the present invention and a straddle-type vehicle including the engine unit will be described. In addition, the dimension of the structural member in each figure does not represent the dimension of an actual structural member, the dimension ratio of each structural member, etc. faithfully.

  In the following description, front, rear, left, and right mean front, rear, left, and right as viewed from the driver who is seated on the seat 24 of the saddle riding type vehicle 10 while grasping the handle 16. To do.

<Configuration of saddle riding type vehicle>
FIG. 1 is a left side view showing the saddle riding type vehicle 10. The saddle riding type vehicle 10 is equipped with an engine unit 100 according to an embodiment of the present invention. The engine unit 100 will be described later. An arrow F in FIG. 1 indicates the forward direction of the saddle riding type vehicle 10, and an arrow U indicates the upward direction of the saddle riding type vehicle 10.

  Referring to FIG. 1, saddle riding type vehicle 10 includes a body frame 12. A head pipe 12 a is provided at the front end of the body frame 12. A steering shaft 14 is inserted into the head pipe 12a so as to be rotatable in the left-right direction. A handle 16 is attached to the upper end of the steering shaft 14. Although a detailed description is omitted, the handle 16 is provided with an accelerator grip (not shown). The amount of operation of the accelerator grip by the driver is detected by the APS 42 described later as the accelerator opening.

  A bracket 18 is attached to the lower end portion of the steering shaft 14. An upper end portion of a pair of front forks 20 is attached to the bracket 18. A front wheel 22 is rotatably supported on the lower ends of the pair of front forks 20.

  A seat 24 is supported on the rear portion of the vehicle body frame 12. A storage portion 26 is provided below the sheet 24. For example, a helmet or the like can be stored in the storage unit 26.

  An engine 28 of an engine unit 100, which will be described later, is disposed below a substantially central portion in the front-rear direction of the body frame 12. The engine 28 is a unit swing type engine, for example, and is supported by the vehicle body frame 12 so as to be able to swing in the vertical direction.

  A transmission device 30 is disposed behind the engine 28. A rear wheel 32 is rotatably supported at the rear end of the transmission device 30. The transmission device 30 transmits the power generated by the engine 28 to the rear wheel 32. Thereby, the rear wheel 32 is driven.

<Engine unit configuration>
Next, the configuration of the engine unit 100 will be described. FIG. 2 is a schematic diagram showing the configuration of the engine unit 100. In the following, the case where the engine unit 100 includes the single-cylinder engine 28 will be described. Moreover, in FIG. 2, each component of the engine unit 100 is simplified and shown.

  Referring to FIG. 2, an engine unit 100 includes an engine 28, an air cleaner 34, an intake pipe 36a, an intake pipe 36b, an exhaust pipe 38, a throttle device 40, an accelerator position sensor (hereinafter referred to as APS) 42, and a pressure sensor. 44, a crank angle sensor 46, and an engine control device (hereinafter referred to as ECU) 48. First, components other than the engine 28 will be briefly described.

  The air cleaner 34 sucks air in the atmosphere (air outside the saddle riding type vehicle 10) and purifies the sucked air. One end of the intake pipe 36 a is connected to the air cleaner 34. The other end of the intake pipe 36a is connected to a throttle body 40c described later of the throttle device 40. One end of the intake pipe 36b is connected to the throttle body 40c of the throttle device 40. The other end of the intake pipe 36b is connected to a passage 50a formed in a cylinder head 50 described later. One end of the exhaust pipe 38 is connected to a passage 50b formed in a cylinder head 50 described later. In the present embodiment, for example, an intake passage 49a is formed by the space in the intake pipe 36a, the space in the throttle body 40c, the space in the intake pipe 36b, and the passage 50a. In the present embodiment, for example, the exhaust passage 49b is formed by the space in the passage 50b and the exhaust pipe 38. The intake passage 49a guides air in the atmosphere purified by the air cleaner 34 into a combustion chamber 70 (described later) of the engine 28 via an intake port 71a (described later). On the other hand, the exhaust passage 49b discharges the gas in the combustion chamber 70 to the atmosphere (outside of the saddle riding type vehicle 10) via an exhaust port 71b described later. The configuration of the intake passage 49a is not limited to the configuration shown in FIG. 2, and any configuration that can guide air in the atmosphere into the combustion chamber 70 described later may be used. Further, the configuration of the exhaust passage 49b is not limited to the configuration shown in FIG. 2, and may be any configuration that can discharge the gas in the combustion chamber 70 to the atmosphere. In the following description, “upstream” and “downstream” mean “upstream” and “downstream” based on the flow direction of air flowing from the air cleaner 34 to the exhaust passage 49b via the intake passage 49a and the engine 28. To do.

  The throttle device 40 includes a throttle valve 40a, a drive device 40b that drives the throttle valve 40a, and a throttle body 40c. The throttle valve 40a and the driving device 40b are provided in the throttle body 40c. For example, an electric motor can be used as the driving device 40b.

  The throttle valve 40a is driven by the drive device 40b to adjust the opening area of the intake passage 49a. That is, in the present embodiment, the throttle valve 40a is an adjustment valve that adjusts the opening area of the intake passage 49a. The drive device 40b is controlled by the ECU 48, as will be described later. In the present embodiment, when the throttle valve 40a is most open, the opening area of the intake passage 49a is defined as “1”, and when the throttle valve 40a is most closed, the intake passage 49a The opening area is defined as “0”. The throttle valve 40a can adjust the opening area of the intake passage 49a in the range of 0 to 1, for example.

  The APS 42 detects the driver's accelerator operation amount as the accelerator opening. The APS 42 outputs a signal indicating the detected accelerator opening to the ECU 48. The pressure sensor 44 detects the pressure (intake pressure) in a portion downstream of the throttle valve 40a in the intake passage 49a. That is, the pressure sensor 44 detects the pressure in the portion between the throttle valve 40a and the combustion chamber 70 described later in the intake passage 49a. In the following, the intake pressure means the pressure in the portion between the throttle valve 40a and the combustion chamber 70 in the intake passage 49a. The pressure sensor 44 outputs a signal indicating the detected pressure to the ECU 48. In the present embodiment, the pressure sensor 44 is a pressure detection unit. The crank angle sensor 46 detects a rotational position (hereinafter referred to as a crank angle) of a crankshaft 58 of the engine 28 which will be described later. The crank angle sensor 46 outputs a signal indicating the detected crank angle to the ECU 48.

  The ECU 48 includes, for example, a CPU (Central Processing Unit) and a memory. The ECU 48 adjusts the opening of the throttle valve 40a (hereinafter referred to as the throttle opening) by controlling the driving device 40b based on signals output from the APS 42, the pressure sensor 44, and the crank angle sensor 46. The control operation of the ECU 48 will be described later.

  Next, the configuration of the engine 28 will be described. Note that various known engine configurations can be adopted as the configuration of the engine 28, and thus detailed description of each component will be omitted.

  The engine 28 includes a cylinder head 50, a cylinder 52, a piston 54, a crankcase 56, a crankshaft 58, a connecting rod 60, an intake valve 62, an exhaust valve 64, a fuel injection device 66, and a spark plug 68.

  The piston 54 is provided in the cylinder 52 so as to be able to reciprocate. The crankshaft 58 is provided in the crankcase 56 so as to be capable of rotational movement. The piston 54 and the crankshaft 58 are connected by a connecting rod 60. The reciprocating motion of the piston 54 is transmitted to the crankshaft 58 via the connecting rod 60. Thereby, the crankshaft 58 rotates.

  In the engine 28, a combustion chamber 70 is formed by the cylinder head 50, the cylinder 52, and the piston 54. The combustion chamber 70 is provided with an intake port 71a and an exhaust port 71b. In the cylinder head 50, a passage 50a connected to the intake port 71a and a passage 50b connected to the exhaust port 71b are formed. In the present embodiment, the intake pipe 36b and the combustion chamber 70 are connected by the passage 50a. Further, the combustion chamber 70 and the exhaust pipe 38 are connected by the passage 50b.

  The intake valve 62 opens and closes the intake port 71a. The exhaust valve 64 opens and closes the exhaust port 71b. The intake valve 62 is driven by a known valve operating mechanism (not shown). Similarly, the exhaust valve 64 is driven by a valve operating mechanism (not shown). The fuel injection device 66 injects fuel into the intake passage 49a. The fuel supplied into the intake passage 49a is sent to the combustion chamber 70 as an air-fuel mixture together with air. The spark plug 68 ignites the air-fuel mixture in the combustion chamber 70.

<Operation of engine unit>
In the engine 28 having the above-described configuration, one cycle includes an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke. That is, the engine unit 100 according to the present embodiment is a 4-stroke engine unit. Further, in the present embodiment, when at least the operation region of the engine unit 100 is a predetermined low load operation region, the intake valve 62 opens before the exhaust valve 64 is closed during one cycle and the exhaust gas is exhausted. Close before valve 64 opens. In other words, at least in the low-load operation region, the intake stroke is started before the exhaust stroke ends. That is, in one cycle, there is an overlap period in which both the intake valve 62 and the exhaust valve 64 are open at the start of the intake stroke.

  Here, as described above, in the conventional engine having the overlap period, the burned gas in the combustion chamber easily flows back into the intake passage during the overlap period during the low load operation. The burnt gas that has flowed back into the intake passage again flows into the combustion chamber during the intake stroke. Thereby, combustion stability falls. Therefore, in the present embodiment, when the operation region of the engine unit 100 is a predetermined low load operation region, the ECU 48 switches the operation of the engine unit 100 from the normal operation to the low load operation. In the present embodiment, “low load operation” includes idling operation. The operation region determination method will be described later. Hereinafter, the low load operation of the engine unit 100 will be described together with the control operation of the ECU 48.

  First, normal operation of the engine unit 100 will be described. During normal operation, the ECU 48 controls the drive device 40b of the throttle device 40 based on the signal output from the APS 42. In the present embodiment, for example, a relationship (map) between the accelerator opening and the throttle opening is stored in advance in the memory of the ECU 48. The ECU 48 controls the drive device 40b based on the relationship stored in the memory and the accelerator opening detected by the APS 42. Thereby, the throttle opening is adjusted to an opening corresponding to the accelerator opening. In this way, during normal operation, the throttle opening is adjusted according to the accelerator operation amount of the driver.

  Next, the low load operation of the engine unit 100 will be described. As will be described in detail below, in this embodiment, during low load operation, the opening area of the intake passage 49a changes during one cycle even when the accelerator opening is fixed to a constant value. The throttle device 40 is controlled by the ECU 48. In the following description, the state of the engine unit 100 during low load operation in which the throttle device 40 is controlled as described above is referred to as an adjusted operation state. In the following description, the state of engine unit 100 that is assumed that the opening area of intake passage 49a is fixed at a constant value during one cycle during low-load operation is referred to as a virtual fixed operation state. The throttle opening of the engine unit 100 in the virtual fixed operation state is adjusted to a predetermined value according to the accelerator opening, similarly to the engine unit 100 during normal operation. Therefore, in the engine unit 100 in the virtual fixed operation state, the throttle opening is adjusted to a predetermined value determined according to the accelerator opening, and the throttle opening is fixed to the predetermined value during one cycle. This corresponds to the operating state of the engine unit 100. In the present embodiment, the throttle valve 40a adjusts the opening area of the intake passage 49a so that the rotational speed of the engine unit 100 becomes equal to the rotational speed of the engine unit 100 in the virtual fixed operation state in the adjustment operation state. . Note that, by adjusting the opening area of the intake passage 49a as described above in the adjusted operation state, the output of the engine unit 100 and the intake air amount in one cycle are substantially equal to the output in the virtual fixed operation state and the intake air amount in one cycle. Will be equal.

FIG. 3 is a diagram showing a change in pressure (intake pressure) in the intake passage 49a and a change in pressure (exhaust pressure) in the exhaust passage 49b when the engine unit 100 is in a low load operation. In FIG. 3, for comparison, an example of a change in the intake pressure in the intake passage 49a when it is assumed that the engine unit 100 is operating in the virtual fixed operation state is indicated by a broken line. Note that the intake pressure shown in FIG. 3 is the pressure in the portion between the throttle valve 40a and the combustion chamber 70 in the intake passage 49a as described above. Further, the exhaust pressure shown in FIG. 3 is the pressure in the vicinity of the exhaust port 71b in the exhaust passage 49b. In FIG. 3, “TDC” represents a top dead center, and “BDC” represents a bottom dead center. In FIG. 3, θ _IC represents the crank angle when the intake valve 62 is closed, and θ _IO represents the crank angle when the intake valve 62 is opened.

  Referring to FIG. 3, in the present embodiment, the opening area of the intake passage 49a is throttled so that the intake pressure satisfies the relationship of the following expressions (1) and (2) in the adjusted operation state during low load operation. It is adjusted by the valve 40a.

P _IC <P _VIC (1)
P _{VIC in the} above equation (1) is the intake pressure at the time when the intake valve 62 is closed (see the crank angle θ _{IC in} FIG. 3) in the above-described virtual fixed operation state. P _IC of the formula (1), in a regulating operation condition described above, a suction pressure when the intake valve 62 is closed.

_PIO > _PVIO (2)
P _VIO of the formula (2), in a virtual fixed operating condition described above, a suction pressure when the intake valve 62 is opened (see the crank angle theta _IO in Figure 3). P _IO of the formula (2), in a regulating operation condition described above, a suction pressure when the intake valve 62 is opened.

  Hereinafter, a method for adjusting the opening area of the intake passage 49a so as to satisfy the relationship of the above formulas (1) and (2) will be described with an example. FIG. 4 is a diagram illustrating an example of the relationship between the throttle opening and the crank angle in the adjustment operation state. In FIG. 4, for comparison, an example of the throttle opening in the virtual fixed operation state is indicated by a broken line as the virtual throttle opening. The rotational speed of the engine unit 100 is the same when the engine unit 100 is operated at the throttle opening indicated by the solid line in FIG. 4 and when the engine unit 100 is operated at the virtual throttle opening indicated by the broken line.

  Referring to FIGS. 2 and 4, in the adjustment operation state, for example, ECU 48 indicates that the average value of the throttle opening when intake valve 62 is closed during one cycle indicates that intake valve 62 is open. The drive device 40b is controlled to be larger than the average value of the throttle opening when More specifically, the ECU 48 determines that the average value of the throttle opening when the intake valve 62 is open is smaller than the virtual throttle opening and the intake valve 62 is closed during one cycle. The driving device 40b is controlled so that the average value of the throttle opening becomes larger than the virtual throttle opening. For example, the throttle opening when the intake valve 62 is open is set to a value about 0.5 times the throttle opening determined based on the accelerator opening in the conventional engine unit. The throttle opening when the intake valve 62 is closed is set to a value about 1.5 times the throttle opening determined based on the accelerator opening in the conventional engine unit. By adjusting the throttle opening in this way, during one cycle, the opening area of the intake passage 49a when the intake valve 62 is open is smaller than the opening area of the intake passage 49a in the virtual fixed operation state. . Further, during one cycle, the opening area of the intake passage 49a when the intake valve 62 is closed becomes larger than the opening area of the intake passage 49a in the virtual fixed operation state. As a result, the amount of air that flows into the portion of the intake passage 49a downstream of the throttle valve 40a when the intake valve 62 is open is smaller than when the engine unit 100 is operating in the virtual fixed operation state. Can be reduced. Further, compared with the case where the engine unit 100 is operating in the virtual fixed operation state, when the intake valve 62 is closed, the amount of air flowing into the portion downstream of the throttle valve 40a in the intake passage 49a is increased. can do. As a result, the intake pressure can be adjusted so as to satisfy the relationship of the above formulas (1) and (2). By adjusting the intake pressure in this way, it is possible to sufficiently increase the intake pressure during the overlap period as shown in FIG. 3 while preventing an increase in the intake amount in one cycle. Thereby, during the overlap period, the difference between the pressure in the downstream portion in the intake passage 49a and the pressure in the exhaust passage 49b can be reduced, or the pressure in the downstream portion in the intake passage 49a can be reduced in the exhaust passage 49b. It can be higher than the pressure. In the present embodiment, for example, information (map) indicating the relationship between the accelerator opening, the crank angle, and the throttle opening during low load operation is stored in advance in the memory of the ECU 48. The ECU 48 adjusts the throttle opening based on the information (map), accelerator opening, and crank angle stored in the memory.

  Next, the control operation of the ECU 48 will be described. FIG. 5 is a flowchart showing the control operation of the ECU 48. The flowchart of FIG. 5 shows an example of the control operation of the ECU 48 when the saddle riding type vehicle 10 is traveling.

  Referring to FIG. 5, ECU 48 first acquires the intake pressure based on the output signal of pressure sensor 44 (step S1).

  Next, the ECU 48 determines whether or not the operation region of the engine unit 100 is a predetermined low load operation region based on the intake pressure acquired in step S1 (step S2). In the present embodiment, for example, the ECU 48 determines that the operation region of the engine unit 100 is a predetermined low load operation region when the average value of the intake pressure in one cycle is equal to or less than a predetermined threshold value. The threshold value is appropriately set in consideration of, for example, the configuration of the saddle riding type vehicle 10 (e.g., engine 28 displacement). The threshold value is set to a value of 70 kPa or less, for example.

  In step S1, the ECU 48 may further acquire the rotational speed of the engine unit 100 (engine 28) based on the detection signal of the crank angle sensor 46. In step S2, the ECU 48 may determine whether or not the operation region of the engine unit 100 is a predetermined low load operation region based on the intake pressure and the rotational speed acquired in step S1. Specifically, the ECU 48 determines the operation region of the engine unit 100 in advance when the average value of the intake pressure is equal to or less than a predetermined threshold value and the rotational speed of the engine unit 100 is equal to or less than the predetermined threshold value. It may also be determined that this is a low load operation region. Note that, similarly to the pressure threshold, the rotational speed threshold is appropriately set in consideration of the configuration of the straddle-type vehicle 10.

  When it is determined in step S2 that the vehicle is not in the low load operation region (NO), the ECU 48 executes the above-described normal operation control (step S3). Then, it returns to step S1. In the present embodiment, the ECU 48 continues the normal operation control until it is determined in step S2 that the vehicle is in the low load operation region, for example.

  When it is determined in step S2 that the vehicle is in the low load operation region (in the case of YES), the ECU 48 executes the above-described control of low load operation (step S4). Thereby, the engine unit 100 will be in an adjustment driving state. Then, it returns to step S1. In the present embodiment, for example, the ECU 48 continues the control of the low load operation until it is determined in step S2 that it is not the low load operation region. That is, the adjusted operation state is maintained.

  In the present embodiment, for example, the ECU 48 executes the low load operation process (step S4) in one cycle following the cycle determined as the low load operation region in step S2, and then returns to the process of step S1. . However, the ECU 48 may return to the process of step S1 after executing the low load operation process (step S4) in each of the two consecutive cycles, for example. For example, the ECU 48 executes low-load operation processing in an odd-numbered cycle among a plurality of consecutive three or more cycles, and performs normal operation processing in an even-numbered cycle. You may return to processing.

<Effect of engine unit>
In the present embodiment, an overlap period is provided in the 4-stroke engine 28. Thereby, the output of the engine 28 can be improved.

  Further, in the present embodiment, the opening area of the intake passage 49a is adjusted so that the intake pressure satisfies the relationship of the above formulas (1) and (2) during low load operation. Thereby, it is possible to sufficiently increase the intake pressure during the overlap period while preventing an increase in the intake amount in one cycle. That is, it is possible to sufficiently increase the intake pressure during the overlap period while enabling a desired low load operation.

  As a result, it is possible to reduce the difference between the intake pressure and the exhaust pressure during the overlap period or to make the intake pressure higher than the exhaust pressure while enabling a desired low load operation. Thereby, it is possible to prevent the burnt gas in the combustion chamber 70 from flowing back into the intake passage 49a during the overlap period while enabling a desired low load operation. As a result, the combustion stability during low load operation of the engine 28 can be improved.

  Therefore, in the engine unit 100, it is not necessary to adjust the volume of the portion from the throttle valve 40a to the intake port 71a in the intake passage 49a in order to improve the combustion stability. That is, according to the engine unit 100, the engine 28 can be increased in output by appropriately setting the cross-sectional area of the intake passage 49a, and the opening area of the intake passage 49a can be adjusted by the throttle valve 40a. The combustion stability at the time of 28 low load driving | operation can be improved. Therefore, even when the position of the throttle valve 40a (the position of the throttle device 40) is restricted, it is possible to achieve both higher output of the engine 28 and improved combustion stability during low load operation.

  In the engine unit 100, for example, low load operation control can be executed in two consecutive cycles. In this case, the combustion stability during low load operation of the engine 28 can be sufficiently improved.

  In the present embodiment, the combustion stability can be effectively improved in the single-cylinder engine unit 100 having low combustion stability during low-load operation.

  The engine unit 100 includes an electronically controlled throttle valve 40a. Here, when the throttle valve 40a is provided in the saddle riding type vehicle 10, since the drive device 40b is provided in the throttle body 40c, the throttle body becomes larger than when a mechanical throttle valve is provided in the saddle riding type vehicle. . For this reason, when the electronically controlled throttle valve 40a is provided, the degree of freedom of arrangement of the throttle body 40c is reduced. That is, the restriction on the position of the throttle valve 40a is increased. However, in the present embodiment, as described above, even when the electronically controlled throttle valve 40a is used, both high engine output and improved combustion stability during low-load operation can be achieved.

<Other embodiments>
In the above-described embodiment, the case where the opening area of the intake passage 49a is adjusted by the electronically controlled throttle valve 40a has been described. However, the method for adjusting the opening area of the intake passage 49a is not limited to the above example. Hereinafter, an engine unit according to another embodiment of the present invention will be described.

  FIG. 6 is a view showing an engine unit 100a according to another embodiment of the present invention. Below, the part different from the engine unit 100 among the structures of the engine unit 100a is demonstrated.

  Referring to FIG. 6, engine unit 100a differs from engine unit 100 described above in that it has an intake passage 72 instead of intake passage 49a and a throttle device 74 instead of throttle device 40.

  The intake passage 72 has a main passage 72a and a sub-passage 72b. In the present embodiment, the main passage 72a corresponds to the intake passage 49a described above. The sub passage 72b communicates the upstream portion and the downstream portion of the throttle valve 74a, which will be described later, in the main passage 72a.

  The throttle device 74 includes a throttle valve 74a, an auxiliary valve 74b, and a drive device 74c. The throttle valve 74a is mechanically connected to an accelerator grip (not shown) provided on the handle 16 (see FIG. 1). That is, the throttle valve 74a is a mechanical throttle valve. The opening degree of the throttle valve 74a is adjusted according to the accelerator opening degree.

  The auxiliary valve 74b is driven by the drive device 74c to adjust the opening area of the sub passage 72b. For example, an electric motor can be used as the driving device 74c. More specifically, for example, a stepping motor can be used as the driving device 74c. The drive device 74c is controlled by the ECU 48, as will be described later. Although detailed description is omitted, for example, an ISC (idle speed control) valve can be used as the auxiliary valve 74b. In the present embodiment, the pressure sensor 44 detects the pressure (intake pressure) in the portion downstream of the throttle valve 74a and the auxiliary valve 74b in the intake passage 72. That is, the pressure sensor 44 detects the pressure in the portion between the throttle valve 74 a and auxiliary valve 74 b and the combustion chamber 70 in the intake passage 72. In the following description, the intake pressure means the pressure in the intake passage 72 between the throttle valve 74a and the auxiliary valve 74b and the combustion chamber 70.

  In the present embodiment, when the throttle valve 74a is most open, the opening area of the main passage 72a is defined as “1”, and when the throttle valve 74a is most closed, the opening area of the main passage 72a is It is defined as “0”. The throttle valve 74a can adjust the opening area of the main passage 72a in the range of 0 to 1, for example. In this embodiment, when the auxiliary valve 74b is most open, the opening area of the sub-passage 72b is defined as “1”, and when the auxiliary valve 74b is most closed, the sub-passage 72b The opening area is defined as “0”. The auxiliary valve 74b can adjust the opening area of the sub-passage 72b within a range of 0 to 1, for example. In the present embodiment, the throttle valve 74 a and the auxiliary valve 74 b are adjustment valves that adjust the opening area of the intake passage 72.

  In the present embodiment, during normal operation, the ECU 48 controls the drive device 74c so that, for example, the opening area of the sub-passage 72b becomes a predetermined constant size. Specifically, the opening area of the sub passage 72b is set to 0.5, for example. At this time, the opening area of the main passage 72a is adjusted by the throttle valve 74a according to the accelerator opening. Note that the opening area of the sub-passage 72b may vary during normal operation. For example, the opening area of the sub passage 72b may be adjusted according to the accelerator opening.

  Next, the low load operation of the engine unit 100a will be described. As will be described in detail below, in the present embodiment, during low load operation, the opening area of the intake passage 72 changes during one cycle even when the accelerator opening is maintained at a constant value. The throttle device 74 is controlled by the ECU 48. That is, the engine unit 100a enters the adjustment operation state. Specifically, as in the above-described embodiment described with reference to FIG. 3, the opening area of the intake passage 72 is adjusted so that the intake pressure satisfies the relationship of the following expressions (1) and (2). . In the present embodiment, the state of the engine unit 100a that is assumed that the opening area of the intake passage 72 is fixed to a constant value during one cycle during low load operation is referred to as a virtual fixed operation state. In the present embodiment, the auxiliary valve 74b has an opening area of the intake passage 72 so that the rotational speed of the engine unit 100a is equal to the rotational speed of the engine unit 100a in the virtual fixed operation state in the adjustment operation state. Adjust. Note that, by adjusting the opening area of the intake passage 72 as described above in the adjustment operation state, the output of the engine unit 100a and the intake air amount in one cycle are substantially equal to the output in the virtual fixed operation state and the intake air amount in one cycle. Will be equal.

P _IC <P _VIC (1)
In this embodiment, _{P VIC} and _{P IC} of the above formula (1) are respectively defined as follows. P _VIC is the intake pressure when the intake valve 62 is closed in the virtual fixed operation state. P _IC is in the adjustment operation state, which is the intake pressure when the intake valve 62 is closed.

_PIO > _PVIO (2)
In this embodiment, _{P VIO} and _{P IO} of the formula (2) are respectively defined as follows. P _VIO is the intake pressure when the intake valve 62 is opened in the above-described virtual fixed operation state. _PIO is the intake pressure when the intake valve 62 is opened in the adjusted operation state.

  Hereinafter, a method for adjusting the opening area of the intake passage 72 so as to satisfy the relationship of the above formulas (1) and (2) will be described with an example. FIG. 7 is a diagram showing an example of the relationship between the opening degree of the auxiliary valve 74b (hereinafter referred to as auxiliary valve opening degree) and the crank angle in the adjustment operation state. In FIG. 7, for comparison, an example of the auxiliary valve opening in the virtual fixed operation state is indicated by a broken line as the virtual auxiliary valve opening. In the present embodiment, the virtual auxiliary valve opening is maintained at a constant value during one cycle. The rotational speed of the engine unit 100a is different between when the engine unit 100a is operated at the auxiliary valve opening indicated by the solid line in FIG. 7 and when the engine unit 100a is operated at the virtual auxiliary valve opening indicated by the broken line. Each is equal. In FIG. 7, “TDC” represents the top dead center, and “BDC” represents the bottom dead center.

  6 and 7, in the adjustment operation state, for example, the ECU 48 determines that the average value of the opening degree of the auxiliary valve when the intake valve 62 is closed during one cycle is that the intake valve 62 is open. The driving device 74c is controlled so as to be larger than the average value of the auxiliary valve opening when More specifically, the ECU 48 determines that the average value of the auxiliary valve opening when the intake valve 62 is open is smaller than the virtual auxiliary valve opening and the intake valve 62 is closed during one cycle. The driving device 74c is controlled so that the average value of the auxiliary valve opening when the vehicle is in the middle is larger than the virtual auxiliary valve opening. For example, the ECU 48 sets the opening area of the sub-passage 72b when the intake valve 62 is open to 0.1, and the opening area of the sub-passage 72b when the intake valve 62 is closed to 0.9. The auxiliary valve opening is adjusted. By adjusting the auxiliary valve opening in this manner, the opening area of the intake passage 72 when the intake valve 62 is open during one cycle is smaller than the opening area of the intake passage 72 in the virtual fixed operation state. Become. Further, during one cycle, the opening area of the intake passage 72 when the intake valve 62 is closed is larger than the opening area of the intake passage 72 in the virtual fixed operation state. As a result, compared to when the engine unit 100a is operating in the virtual fixed operation state, when the intake valve 62 is open, it flows into the portion of the intake passage 72 downstream of the throttle valve 74a and the auxiliary valve 74b. The amount of air to be reduced can be reduced. Further, when the intake valve 62 is closed, the engine unit 100a flows into a portion of the intake passage 72 downstream of the throttle valve 74a and the auxiliary valve 74b as compared with the case where the engine unit 100a is operating in the virtual fixed operation state. The amount of air can be increased. As a result, the intake pressure can be adjusted so as to satisfy the relationship of the above formulas (1) and (2). By adjusting the intake pressure in this way, it is possible to sufficiently increase the intake pressure during the overlap period while preventing an increase in the intake amount in one cycle. Thereby, in the overlap period, the difference between the intake pressure and the exhaust pressure can be reduced, or the intake pressure can be made higher than the exhaust pressure.

  Although detailed explanation is omitted, for example, information (map) indicating the relationship between the crank angle and the auxiliary valve opening degree during low load operation may be stored in the memory of the ECU 48 in advance. During the low load operation, the ECU 48 may adjust the auxiliary valve opening based on the above information and crank angle stored in the memory. Although detailed description is omitted, particularly during idling during low load operation, for example, the ECU 48 may adjust the auxiliary valve opening degree by performing feedback control so that the target rotation speed can be maintained. . In this case, for example, the auxiliary valve opening when the intake valve 62 is closed is maintained at a preset value, and the auxiliary valve opening when the intake valve 62 is open is adjusted by feedback control. .

  As described above, also in the engine unit 100a, during the low load operation, the opening area of the intake passage 72 is adjusted so that the intake pressure satisfies the relationship of the above formulas (1) and (2). Thereby, it is possible to sufficiently increase the intake pressure during the overlap period while preventing an increase in the intake amount in one cycle. That is, it is possible to sufficiently increase the intake pressure during the overlap period while enabling a desired low load operation. As a result, it is possible to reduce the difference between the intake pressure and the exhaust pressure during the overlap period or to make the intake pressure higher than the exhaust pressure while enabling a desired low load operation. Thereby, it is possible to prevent the burnt gas in the combustion chamber 70 from flowing back into the intake passage 72 during the overlap period while enabling a desired low load operation. As a result, the combustion stability during low load operation of the engine 28 can be improved.

  Therefore, in the engine unit 100a, it is not necessary to adjust the volume of the portion from the throttle valve 74a and the auxiliary valve 74b to the intake port 71a in the intake passage 72 in order to improve the combustion stability. That is, according to the engine unit 100a, the auxiliary valve 74b achieves higher output of the engine 28 by appropriately setting the cross-sectional area of the intake passage 72 while the intake passage 72 (more specifically, the auxiliary passage 72b). ), The combustion stability during low-load operation of the engine 28 can be improved. Therefore, even when the position of the throttle valve 74a (the position of the throttle device 74) is restricted, it is possible to achieve both higher output of the engine 28 and improved combustion stability during low load operation.

  The engine unit 100a according to the present embodiment can be used in, for example, various straddle-type vehicles in which a sub passage is provided in the intake passage. Specifically, the engine unit 100a may be used, for example, in a straddle-type vehicle that performs idle speed control, or may be used in a straddle-type vehicle that includes an FID (first idle device).

<Modification>
In the above-described embodiment, the case where the engine unit has the single-cylinder engine 28 has been described. However, the engine unit may have a multi-cylinder independent throttle type engine. In this case, an intake passage and a throttle valve may be provided for each cylinder (combustion chamber), and the above-described low-load operation control may be executed for each cylinder. If the intake passage has a sub-passage, an auxiliary valve may be provided for each cylinder and the above-described low-load operation control may be executed.

  In the above-described embodiment, the case where the combustion chamber 70 is provided with one intake port 71a and one exhaust port 71b has been described, but a plurality of intake ports may be provided in the combustion chamber. A plurality of exhaust ports may be provided in the combustion chamber. When a plurality of intake ports are provided in the combustion chamber, the engine includes an intake valve that opens and closes each intake port. When a plurality of exhaust ports are provided in the combustion chamber, the engine includes an exhaust valve that opens and closes each exhaust port.

  In the above-described embodiment, whether or not the operation region is a predetermined low-load operation region is determined based on the intake pressure in step S2, but the operation region determination method is not limited to the above example. For example, a sensor for detecting the throttle opening may be provided, and the low load operation region may be determined based on the throttle opening detected by the sensor. Further, a sensor for detecting the output torque of the engine may be provided, and the low load operation region may be determined based on the output torque detected by the sensor. In addition, a sensor that detects the flow rate of air in the intake passage may be provided, and the low load operation region may be determined based on the flow rate detected by the sensor. Further, the low load operation region may be determined based on the amount of fluctuation within one cycle of the engine rotational speed. In these determination methods, a predetermined threshold value is set, and the low load operation region is determined by comparing the threshold value with the detection result of each sensor.

  In the above-described embodiment, the scooter-type straddle-type vehicle 10 on which the driver rides is described. However, the present invention is, for example, a scooter-type straddle-type vehicle in which the driver rides with the feet in the same posture, and a saddle-ride such as an ATV (All Terrain Vehicle) and a snowmobile. The present invention can also be applied to a type vehicle.

  According to the present invention, even when there is a restriction on the position of the throttle valve, it is possible to achieve both high engine output and improved combustion stability during low-load operation. Therefore, the present invention can be used in various straddle-type vehicles in order to increase engine output and improve combustion stability during low-load operation.

DESCRIPTION OF SYMBOLS 10 Saddle type vehicle 12 Body frame 14 Steering shaft 16 Handle 18 Bracket 20 Front fork 22 Front wheel 24 Seat 26 Storage part 28 Engine 30 Transmission device 32 Rear wheel 34 Air cleaner 36a, 36b Intake pipe 38 Exhaust pipe 49a, 72 Intake passage 49b Exhaust Passage 72a Main passage 72b Sub passage 40, 74 Throttle device 40a, 74a Throttle valve 40b, 74c Drive device 40c Throttle body 74b Auxiliary valve 42 APS
44 Pressure sensor 46 Crank angle sensor 48 ECU
DESCRIPTION OF SYMBOLS 50 Cylinder head 52 Cylinder 54 Piston 56 Crankcase 58 Crankshaft 60 Connecting rod 62 Intake valve 64 Exhaust valve 66 Fuel injection apparatus 68 Spark plug 70 Combustion chamber 71a Intake port 71b Exhaust port 100, 100a Engine unit

Claims (8)

A four-stroke engine unit including an intake stroke, a compression stroke, a combustion stroke, and an exhaust stroke in one cycle,
A combustion chamber provided with at least one intake port and at least one exhaust port;
An intake passage that is connected to the at least one intake port and guides air in the atmosphere into the combustion chamber through the at least one intake port;
An exhaust passage connected to the at least one exhaust port and exhausting the gas in the combustion chamber to the atmosphere via the at least one exhaust port;
An intake valve for opening and closing the intake port;
An exhaust valve for opening and closing the exhaust port;
An adjustment valve that is provided in the intake passage and adjusts an opening area of the intake passage;
The intake valve opens before the exhaust valve closes and before the exhaust valve opens during the one cycle when at least the operation range of the engine unit is a predetermined low load operation range. Close,
In the adjustment valve, the intake pressure between the adjustment valve and the combustion chamber in the intake passage is expressed by the following equations (1) and (2) in the one cycle at least in the low load operation region. An engine unit that adjusts the opening area so as to satisfy the relationship.
P _IC <P _VIC (1)
_PIO > _PVIO (2)
However, in the above formulas (1) and (2),
P _VIC is the intake pressure at the time when the intake valve is closed in a virtual fixed operation state in which it is assumed that the opening area of the intake passage is fixed to a constant value during the one cycle.
P _IC is in the adjustment operating condition in which the opening area is adjusted by the control valve in the one cycle, a the intake pressure when the said intake valve is closed,
In the adjustment operation state, the adjustment valve adjusts the opening area so that the rotation speed of the engine unit is equal to the rotation speed in the virtual fixed operation state,
P _VIO is the intake pressure when the intake valve is opened in the virtual fixed operation state,
_PIO is the intake pressure when the intake valve is opened in the adjusted operation state.   In the adjustment operation state, the adjustment valve has an average value of the opening area when the intake valve is open during the one cycle smaller than the opening area in the virtual fixed operation state, and The engine unit according to claim 1, wherein the opening area is adjusted so that an average value of the opening area when the intake valve is closed is larger than the opening area in the virtual fixed operation state. A controller for adjusting the opening of the adjusting valve;
A pressure detection unit for detecting the intake pressure,
The engine according to claim 1 or 2, wherein the control unit determines whether or not the operation region is the predetermined low-load operation region based on the intake pressure detected by the pressure detection unit. unit.   The said adjustment valve adjusts the said opening area so that the said intake pressure may satisfy | fill the relationship of said Formula (1) and (2) in each cycle of 2 continuous cycles. The engine unit described.   The engine unit according to any one of claims 1 to 4, wherein the engine unit is a single-cylinder engine unit. A plurality of the combustion chamber, the intake passage, and the adjustment valve are provided,
A plurality of intake passages are connected to the plurality of combustion chambers;
The engine unit according to any one of claims 1 to 4, wherein a plurality of the adjustment valves are respectively provided in the plurality of intake passages. It has an electronically controlled throttle valve,
The engine unit according to claim 1, wherein the throttle valve is the adjustment valve.   A straddle-type vehicle comprising the engine unit according to any one of claims 1 to 7.

Images