1. Field of the Invention
The invention relates generally to a variable valve system for an internal combustion engine, which opens and closes, using a cam, an intake valve and an exhaust valve of an internal combustion engine. More specifically, the invention relates to a variable valve system for an internal combustion engine, which uses an electric motor to obtain power to drive a cam.
2. Description of the Related Art
Japanese Patent Application Publication No. JP-A-2004-183612 describes an internal combustion engine provided with a variable valve system that can change valve opening/closing characterstics (a valve lift amount, valve opening time, valve closing time, etc.) of an intake valve and an exhaust valve. The variable valve system drives a cam using power from au electric motor instead of power transmitted from a crankshaft. Accordingly, the variable valve system can flexibly control the rotation speed and the rotation direction of the cam independently of the rotation of the crankshaft.
With the variable valve system described in Japanese Patent Application Publication No. JP-A-2004-183612, for example, the phase of the cam can be changed by increasing/decreasing the rotation speed of the cam while the intake valve or the exhaust valve is closed (phase variable control). Meanwhile, the valve-open duration can be changed by increasing/decreasing the rotation speed of the cam while the intake valve or the exhaust valve is open (valve-open duration variable control). If the rotation of the cam is reversed before the valve is maximally lifted while the valve is open, the actual valve lift amount is less than the maximum valve lift amount (valve lift amount variable control). With this variable valve system, the valve opening/closing characteristics of the intake valve and the exhaust valve can be changed with greater flexibility.
An electric motor that is used to drive the cams may be shared by all the cylinders. Alternatively, each cylinder may be provided with an electric motor. Also, the cylinders may be divided into multiple groups, and an electric motor may be provided to each group. When one group consists of two cylinders, an electric motor may drive the cams corresponding to two cylinders that are different in the rotation phase of the cams. In this case, if the cams are oscillated by alternately switching the rotation direction of the electric motor between the normal rotation direction and reverse rotation direction, the valve lift amount variable control described above can be performed simultaneously on the valves of the two cylinders. More specifically, the rotation direction of the electric motor is alternately switched such that each cam corresponding to one of the cylinders opens and closes the valve using, from among two ramp portions thereof, only the ramp portion used to open the valve during normal rotation of the arm, and each cam corresponding to the other cylinder opens and closes the valve using only the ramp portion used to close the valve during normal rotation of the cam.
However, a cam commonly employed in a valve system for an internal combustion engine is formed such that the shape of the ramp portion on the valve opening side with respect to the cam nose is different from that on the valve closing side with respect to the cam nose. The ramp portion on the valve opening side is steeply inclined in order to quickly open the valve to reduce the valve-pen duration, thereby increasing the time area (the value obtained by integrating the valve opening amount) per unit valve-open duration. In contrast, the ramp portion on the valve closing side is moderately inclined in order to gradually close the valve to reduce the speed at which the valve contacts a valve seat, thereby reducing vibration and noise that are caused when the valve contacts the valve seat.
Therefore, if the valve lift amount variable control is performed simultaneously on the valves of the two cylinders, each valve of one of the cylinders is quickly opened and closed by the steeply inclined ramp portion, and each valve of the other cylinder is gradually opened and closed by the moderately inclined ramp portion. This causes a difference in the valve lift curve between the valves of the two cylinders. As a result, the intake air amount varies between the two cylinders, causing torque fluctuation in the internal combustion engine as a whole.
The variable valve system described above can change the valve opening/closing characteristics with great flexibility. However, the flexibility in the valve opening/closing characteristics is provided under a certain degree of constraint, because alternately switching the rotation direction of the cams causes the difference in the valve lift curve between the valves of the two cylinders.
An object of the invention is to provide a variable valve system for an internal combustion engine, which can change valve opening/closing characteristics with greater flexibility.
A first aspect of the invention relates to a variable valve system for an internal combustion engine. The variable valve system includes an electric motor that can be rotated in any one of the normal rotation direction and the reverse rotation direction; a first cam that is driven by the electric motor, a second cam that has the same shape as the first cam, that is driven by the electric motor, and that differs from the first cam in the rotation phase; a first valve that is opened and closed by the first cam; a second valve that is opened and closed by the second cam; and a control unit that controls rotation of the electric motor. In the variable valve system, each of the first cam and the second cam is symmetric with respect to the straight line passing the cam center and the cam nose.
According to the first aspect, because each of the first cam and the second cam is symmetric with respect to the straight line passing the cam center and the cam nose, the same valve lift curve can be obtained regardless of whether the cam is rotated in the normal rotation direction or the reverse rotation direction. JD addition, the rotation direction and the rotation speed of each cam can be flexibly controlled by the control unit, because the electric motor is used to obtain power to drive the cams. According to the first aspect the valve opening/closing characteristics of the first valve and the second valve can be changed with greater flexibility.
In the first aspect, the control unit may alternately switch the rotation direction of the electric motor between the normal rotation direction and the reverse rotation direction such that the first valve is opened and closed using, from among two ramp portions of the first cam, the ramp portion used to open the first valve when the electric motor is rotated in a given direction (hereinafter, referred to as the “opening ramp portion”), and the second valve is opened and closed using, from among two ramp portions of the second cam, the ramp portion used to close the second valve when the electric motor is rotated in the given direction (hereinafter, referred to as the “closing ramp portion”).
As described above, the first valve is opened and closed using the opening ramp portion of the first cam, and the second valve is opened and closed using the closing ramp portion of the second cam. Opening/closing each of the valves using only one of the ramp portions of the corresponding cam enables the valve to be driven by a lift amount that is less than that when the cam is rotated in only one direction and the valve is opened and closed using the entirety of the cam. In addition, the first cam and the second cam have the same shape, and each of the first cam and the second cam is symmetric with respect to the straight line passing the cam center and the cam nose. Accordingly, opening/closing one of the valves using the opening ramp portion and the other valve using the closing ramp portion (using the opening ramp portion of the first cam and the closing ramp portion of second cam, or using the closing ramp portion of the first cam and the opening ramp portion of the second cam) does not cause a difference between the two valve lift curves.
In the first aspect, the control unit may control the rotation speed of the electric motor such that the rotation speed at the start time of the open period of the first valve is higher than the rotation speed at the end time of the open period of the first valve, and the rotation speed at the start time of an open period of the second valve is higher than the rotation speed at the end time of the open period of the second valve.
As described above, the rotation speed of the electric motor at the start time of the open period of each valve is made higher than that at the end time of the open period. Thus, the valve-pen duration of each valve can be reduced to increase the time area (the value obtained by integrating the valve opening amount) per unit valve-open duration. Accordingly, even if the ramp portions of each cam are moderately inclined to have the valve gradually contact a valve scat, the valve lift curve, according to which the valve is opened quickly and closed gradually, can be obtained.
In the first aspect, the control unit may control the rotation speed of the electric motor such that the rotation speed at the end time of the open period of the first valve is lower than the rotation speed at the start time of the open period of the first valve, and the rotation speed at the end time of the open period of the second valve is lower than the rotation speed at the start time of the open period of the second valve.
As described above, the first valve is opened and closed using the opening ramp portion of the first cam, and the second valve is opened and closed using the closing ramp portion of the second cam. Opening/closing each of the valves using only one of the ramp portions of the corresponding cam enables the valve to be driven by a lift amount that is less than that when the cam is rotated in only one direction and the valve is opened and dosed using the entirety of the cam. In addition, the first cam and the second cam have the same shape, and each of the first cam and the second cam is symmetric with respect to the straight line passing the cam center and the cam nose. Accordingly, opening/closing one of the valves using the opening ramp portion and the other valve using the closing ramp portion (using the opening ramp portion of the first cam and the closing ramp portion of second cam, or using the closing ramp portion of the first cam and the opening ramp portion of the second cam) does not cause a difference between the two valve lift curves.
In the first aspect, the variable valve system may further include a camshaft used to take air into cylinders or discharge exhaust gas from the cylinders. The camshaft is driven by the electric motor controlled by the control unit. The electric motor drives the first cam provided onto the camshaft. Also, the electric motor drives the second cam provided onto the camshaft. Thus, the camshaft is directly driven by the electric motor, and the camshaft drives the first cam and the second cam. Accordingly, the variable valve system has excellent response characteristics. As a result, the variable valve system can appropriately perform the opening/closing control for an intake valve and an exhaust valve, thereby considerably improving the operating performance of the internal combustion engine.
A second aspect of the invention relates to a variable valve system for an internal combustion engine. The variable valve system includes an electric motor that can be rotated in any one of a normal rotation direction and a reverse rotation direction; multiple cams that are provided to take air into cylinders or discharge exhaust gas from the cylinders, and that are driven by the electric motor, multiple valves that are opened and closed by the respective cams; and a control unit that controls rotation of the electric motor. Each of the cams is symmetric with respect to the straight line passing the cam center and the cam nose.
According to the second aspect, because each valve is opened and closed by the corresponding cam that is symmetric with respect to the straight line passing the cam center and the cam nose, the same valve lift curve can be obtained regardless of whether the cam is rotated in the normal rotation direction or the reverse rotation direction.
In addition, in the second aspect, the rotation direction and the rotation speed of each cam can be flexibly controlled by the control unit, because the electric motor is used to obtain power to drive the cams. According to the second aspect, the valve opening/closing characteristics of valves can be changed with greater flexibility.
In the second aspect, the control unit may alternately switch the rotation direction of the electric motor between the normal rotation direction and the reverse rotation direction such that the cam opens and closes the valve using only one of two ramp portions of the cam. Because the valve can be opened and closed using only one of the two ramp portions, the valve can be driven by a lift amount that is less than that when the valve is opened and closed by rotating the cam in only one direction and using the entirety of the cam.
In the second aspect, the control unit may control the rotation speed of the electric motor such that the rotation speed at the start time of the open period of the valve is higher than the rotation speed at the end time of the open period of the valve.
As described above, the rotation speed of the electric motor at the start time of the open period of each valve is made higher than that at the end time of the open period. Thus, the valve-open duration of each valve can be reduced to increase the time area per unit valve-open duration. Accordingly, even if the ramp portions of each cam are moderately inclined to have the valve gradually contact a valve seat, the valve lift curve, according to which the valve is opened quickly and closed gradually, can be obtained.
In the second aspect, the control unit may control the rotation speed of the electric motor such that the rotation speed at the end time of the open period of the valve is lower than the rotation speed at the start time of the open period of the valve.
As described above, the rotation speed of the electric motor at the end time of the open period of each valve is made lower than that at the start time of the open period. Thus, vibration and noise that are caused when the valve contacts the valve seat can be reduced by reducing the speed at which the valve contacts the valve seat. Accordingly, even if the ramp portions of each cam are steeply inclined to increase the time area per unit valve-open duration, the valve lift curve, according to which the valve is opened quickly and closed gradually, can be obtained.
In each of the first and second aspect, the control unit may receive data from a sensor that detects an engine operating state.
In each of the first and second aspect, the internal combustion engine may be an in-line four-cylinder engine.
In each of the first and second aspect, the power stroke may take place in the internal combustion engine in the order of a first cylinder, a third cylinder, a fourth cylinder, and a second cylinder.
In each of the first and second aspect the first cam and the first valve may constitute a valve unit for the fourth cylinder, and the second cam and the second valve may constitute a valve unit for the first cylinder. In addition, the first cam and the second cam may be arranged such that the phase of the cam nose of the fast cam and the phase of the cam nose of the second cam deviate from each other by 180 degrees in the circumferential direction of the camshaft.
The foregoing and further objects, features and advantages of the invention will become apparent from the following description of example embodiments with reference to the accompanying drawings, wherein the same or corresponding portions will be denoted by the same reference numerals and wherein:
Hereafter, a first embodiment of the invention will be described with reference to
[Structure of Variable Valve System]
In the internal combustion engine 1 shown in
Cams 50, cams 52, cams 54, and cams 56 are arranged so as to contact the upper portions of the corresponding valve lifters 16. In the first embodiment, the cams 50 denote the cams contacting the valve lifters 16 provided to the cylinder #1. The cams 52 denote the cams contacting the valve lifters 16 provided to the cylinder #2. The cams 54 denote the cams contacting the valve lifters 16 provided to the cylinder #3. The cams 56 denote the cams contacting the valve lifters 16 provided to the cylinder #4.
The cams 50 contacting the valve lifters 16 provided to the cylinder #1 and the cams 56 contacting the valve lifters 16 provided to the cylinder #4 are fixed to a camshaft 22. The cams 52 contacting the valve lifters 16 provided to the cylinder #2 and the cams 54 contacting the valve lifters 16 provided to the cylinder #3 are fixed to a camshaft 24 that is rotatable with respect to the camshaft 22 and that is arranged coaxially with the camshaft 22. In the structure shown in
A first driven gear 26 is coaxially fixed to the camshaft 22. A first output gear 28 is meshed with the first driven gear 26. The first output gear 28 is coaxially fixed to the output shaft of a first motor 30. Thus, torque of the first motor 30 can be transmitted to the camshaft 22 via the first output gear 28 and the first driven gear 26.
A second driven gear 32 is coaxially fixed to the camshaft 24. A second output gear 36 is meshed with the second driven gear 32 via an intermediate gear 34. The second output gear 36 is coaxially fixed to the output shaft of a second motor 38. With this structure, torque of the second motor 38 can be transmitted to the camshaft 24 via the second output gear 36, the intermediate gear 34, and the second driven gear 32.
As shown in
As shown in
Although not described in detail here, the cam 52 corresponding to the cylinder #2 and the cam 54 corresponding to the cylinder #3 are fixed to the camshaft 24 such that the phases of the cams 52, 54 are deviated from each other by 180 degrees. Each of the cams 52, 54 has the same shape as that of the cam 50 corresponding to the cylinder #1 and the cam 56 corresponding to the cylinder #4. Each of the cams 52, 54 is symmetric with respect to the straight line passing the cam center and the apex of the cam nose.
The operation of the variable valve system 10 is controlled by an ECU 40 (Electronic Control Unit) 40. The ECU 40 is connected to various sensors (not shown) that detect the operating state of the internal combustion engine, such as a crank angle sensor, a cam angle sensor, and an accelerator angle sensor. In addition, the ECU 40 is connected to various actuators such as an actuator for the first motor 30, and an actuator for the second motor 38, etc. Also, the ECU 40 stores programs used to control the rotations of the first motor 30 and the second motor 38. The ECU 40 processes the data transmitted from the various sensors, and control the rotations of the motors 30, 38 based on the processing result.
[Operation of Variable Valve System]
Next, the operation of the variable valve system 10 will be described with reference to
The variable valve system 10 can variously change the valve opening/closing characteristics of the valve 12 as shown in
First, the operation for changing the “phase”, shown in
The “valve-open duration” can be changed, as shown in
Next, the operation for changing the “valve-open duration and valve lift amount”, shown in FIT 4, will be described.
In the operation for changing “the valve-open duration and the valve lift amount”, first, the camshaft 22 is rotated in the clockwise direction, that is, the normal rotation direction, as shown in
Thus, the cam 56 oscillates while only the opening ramp portion 56b, from among the two ramp portions 56b, 56c, contacts the valve lifter 16 (#4). Accordingly, the valve 12 of the cylinder #4 is operated according to the valve lift curve defined by the cam lift curve of the opening ramp portion 56b of the cam 56.
Next, the camshaft 22 is further rotated in the reverse rotation direction. Then, as shown in
The cams 50, 56 are periodically oscillated by continuously performing the series of the operations described above. Accordingly, the valve lift amounts of the valves 12 of the cylinder #1 and the cylinder #4 can be simultaneously changed by the cams 50, 56 both fixed to the camshaft 22. At this time, the valve lift amounts of the valves 12 can be appropriately changed by appropriately changing the amounts of oscillation of the cams 50, 56. Also, when the cams 50, 56 are oscillated, only the “valve lift amount” can be changed, without changing the valve-open duration, as shown in
In the first embodiment described above, the valve 12 of the cylinder #4 is opened and closed using the opening ramp portion 56b of the cam 56 and the valve 12 of the cylinder #1 is opened and closed using the closing ramp portion 50c of the cam 50 by alternately switching the rotation direction of the first motor 30 to periodically oscillate the cams 50, 56.
Also, in the first embodiment, the valve 12 of the cylinder #1 and the valve 12 of the cylinder #4 are opened and closed using only the closing ramp portion 50c of the cam 50 and the opening ramp portion 56b of the cam 56, respectively. Accordingly, each of the valves 12 can be operated by a lift amount less than that when the valves 12 are opened and closed using the entireties of the cams 50, 56 by rotating the camshaft 22 only in the normal rotation direction.
As shown in
With the variable valve system 10 according to the first embodiment described above, the operation of the cams 50, 56 can be variously changed, because the rotation speed of the camshaft 22 is appropriately controlled by controlling the first motor 30 using the ECU 40. Also, each of the cams 50, 56 is symmetric with respect to the straight line passing the cam center and the apex of the cam nose. Accordingly, the same valve lift curve can be obtained regardless of whether the cams 50, 56 are oscillated in the normal rotation direction or the reverse rotation direction. Therefore, with the variable valve system 10 according to the first embodiment, the rotation direction of the camshaft 22 is not limited to a certain direction, and the operation of the cams 50, 56 can be variously changed by appropriately controlling the rotation direction of the camshaft 22. Thus, the valve opening/closing characteristics of the valve 12 can be changed with great flexibility.
In the operation for changing the valve lift amount according to the first embodiment, the opening ramp portion 56b is used in the cam 56 corresponding to the cylinder #4, and the closing ramp portion 50c is used in the cam 50 corresponding to the cylinder #1. However, the closing ramp portion 56c may be used in the cam 56 corresponding to the cylinder #4, and the opening ramp portion 50b may be used in the cam 50 corresponding to the cylinder #1. Which ramp portion, from among the opening ramp portion and the closing ramp portion, should be used may be determined depending on the rotation position of each of the cams 50, 56 when a command for staring the operation for changing the valve lift amount is issued.
In the case of the cylinder #2 and the cylinder #3, the cams 52, 54 have the same shape, and each of the cams 52, 54 is symmetric with respect to the straight line passing the cam center and the apex of the cam nose. Accordingly, the same valve lift curve can be obtained regardless of whether the camshaft 24 is rotated in the normal rotation direction or reverse rotation direction. Although not descried in detail here, the operation of the cams 52, 54 can be variously changed by appropriately controlling, using the second motor 38, the rotation speed and the rotation direction of the camshaft 24 and the angle by which the cams 52, 54 are oscillated. Thus, the valve opening/closing characteristics of the valve 12 can be changed with great flexibility.
Next, a second embodiment of the invention will be described with reference to FIG. 6.
The structure of a variable valve system according to the second embodiment is shown in
As described in the first embodiment, each of the cams 50, 52, 54 and 56 is symmetric with respect to the straight line passing the cam center and the apex of the cam nose. Accordingly, when the motors 30, 38 are rotated at a constant speed, the rotation speed at the start time of the open period of the valve 12 is equal to the rotation speed at the end time of the open period of the valve 12. However, the valve 12 is required to be quickly opened to quickly reduce the valve-open duration, thereby increasing the time area (the value obtained by integrating the valve opening amount) per unit valve-open duration. Meanwhile, the valve 12 is required to be gradually closed to reduce the speed at which the valve 12 contacts the valve seat, thereby reducing vibration and noise that are caused when the valve 12 contacts the valve seat. However, these two requirements contradict each other. Accordingly, if the shape of the cam is defined such that one of these requirements is fulfilled, the other requirement cannot be fulfilled.
The second embodiment is made to fulfill both the requirement concerning the speed at which the valve 12 is opened and the requirement concerning the speed at which the valve 12 is closed. According to the second embodiment, the valve 12 is quickly opened by appropriately selecting the shape of the cam, and the valve 12 is gradually closed by controlling the rotation speed of the motors 30, 38. More specifically, both of the opening ramp portion and the closing ramp portion of each of the cams 50, 52, 54 and 56 are steeply inclined so as to increase the time area per unit valve-open duration. In addition, the rotation speed NCclose of the motors 30, 36 at the end time of the open period of the valve 12 is made lower than the rotation speed NCopen at the start time of the open period of the valve 12.
Thus, the valve lift curve, indicated by the slid line in
The control descried above can be applied not only to the case where each of the cams 50, 52, 54 and 56 is rotated in the normal rotation direction but also to the case where the cams 50, 52, 54 and 56 are oscillated by alternately switching the rotation direction of the motors 30, 38.
Next, a third embodiment of the invention will be described with reference to
The variable valve system according to the third embodiment, as well as the variable valve system according to the second embodiment, is characterized in that both the requirement concerning the speed at which the valve 12 is opened and the requirement concerning the speed at which the valve 12 is closed are fulfilled by appropriately selecting the shape of the cam and controlling the rotation speed of the motors 30, 38.
In the third embodiment, both of the requirements are fulfilled in the approach opposite to that in the second embodiment. According to the third embodiment, the valve 12 is closed gradually by appropriately selecting the shape of the cam, and the valve 12 is opened quickly by controlling the rotation speed of the motors 30, 38. More specifically, the shape of both the opening ramp portion and the closing ramp portion of each of the cams 50, 52, 54 and 56 are moderately inclined to have the valve 12 gradually contact the valve seat. In addition, the rotation speed NCopen of the motors 30, 38 at the start time of the open period of the valve 12 is made higher than the rotation speed NCclose at the end time of the open period of the valve 12.
Thus, the valve lift curve, indicated by the solid line in
The control described above can be applied not only to the case where each of the cams 50, 52, 54 and 56 is rotated in the normal rotation direction but also to the case where the cams 50, 52, 54 and 56 are oscillated by alternately switching the rotation direction of the motors 30, 38.
[Others]
While the invention has been described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the exemplary embodiments. To the contrary, the invention is intended to cover various modifications and equivalent arrangements. For example, the invention can be realized according to the following modified examples.
In the embodiments described above, the cams corresponding to two cylinders are driven by one motor. However, the cams corresponding to one cylinder may be driven by one motor. In this case as well, the shape of each cam is symmetric with respect to the straight line passing the cam center and the apex of the cam nose. Thus, the same valve lift curve can be obtained regardless of whether the cam is rotated in the normal rotation direction or the reverse rotation direction. Accordingly, the rotation direction and the rotation speed of the cam can be flexibly set, whereby the valve opening/closing characteristics of the valves can be changed with great flexibility.
In the embodiments described above, the power stroke order of the internal combustion engine 1 is #1→#3→#4→#2. However, the invention can be applied to an internal combustion engine where the power stroke order is #1→#2→#4→#3.
Number | Date | Country | Kind |
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2005-203833 | Jul 2005 | JP | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
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PCT/IB2006/001911 | 7/11/2006 | WO | 00 | 1/2/2008 |