JP7722315B2 - camshaft - Google Patents

Description

The present invention relates to a camshaft.

In an internal combustion engine, the valves (intake valves and exhaust valves) are opened and closed by a camshaft, which is rotated by the crankshaft via a transmission device such as a timing chain. Positive cam torque is generated during the phase interval when the cam on the camshaft opens the valve, and negative cam torque is generated during the phase interval when the cam on the camshaft closes the valve.

When cam torque fluctuates greatly when the camshaft rotates, the tension applied to the transmission fluctuates greatly, leading to fluttering and reduced durability of the transmission. In contrast, in the internal combustion engine described in Patent Document 1, two valve lifts, a main lift and a sub-lift, are performed by a single cam in one cycle, and the camshaft is configured so that the cam torque generated by the main lift is offset by the cam torque in the opposite direction generated by the sub-lift.

Japanese Patent Application Laid-Open No. 2000-257408

However, the method described in Patent Document 1 requires the valve to be opened and closed multiple times in one cycle, reducing the degree of freedom in valve opening and closing control.

In view of the above-mentioned problems, the object of the present invention is to suppress camshaft torque fluctuations while ensuring freedom of valve opening and closing control in an internal combustion engine.

The gist of this disclosure is as follows:

(1) A camshaft in an internal combustion engine that is rotationally driven by a crankshaft via a transmission, the camshaft comprising a plurality of cams spaced apart in the axial direction of the camshaft, the plurality of cams having asymmetric lift curves, the cams being configured such that the peak position of negative cam torque generated by a first cam that opens and closes a valve located in a first cylinder is included in a phase interval in which positive cam torque is generated by a second cam that opens and closes a valve located in a second cylinder, or the camshaft being configured such that the peak position of positive cam torque generated by the first cam that opens and closes a valve located in a first cylinder is included in a phase interval in which negative cam torque is generated by a second cam that opens and closes a valve located in a second cylinder.

(2) The camshaft described in (1) above, wherein the multiple cams have asymmetric lift curves in which the maximum lift position is closer to the valve closing position than the valve opening start position, and the peak position of the negative cam torque generated by the first cam is included in the phase interval in which the positive cam torque is generated by the second cam.

(3) A camshaft as described in (1) or (2) above, wherein the plurality of cams are formed so that the peak position of the negative cam torque generated by the first cam substantially coincides with the peak position of the positive cam torque generated by the second cam.

The present invention makes it possible to suppress camshaft torque fluctuations while ensuring freedom of valve opening and closing control in an internal combustion engine.

FIG. 1 is a diagram that schematically shows an internal combustion engine provided with a camshaft according to an embodiment of the present invention. FIG. 2 is a schematic partial cross-sectional view of an internal combustion engine. FIG. 3 is a timing chart showing the valve lift amount of the intake valve and the cam torque generated in the intake camshaft. FIG. 4 is a diagram showing an example of a cam profile of an intake cam. FIG. 5 is a diagram showing the change over time in cam torque generated by a plurality of intake cams having the cam profile shown in FIG.

Embodiments of the present invention will be described in detail below with reference to the drawings. Note that in the following description, similar components will be given the same reference numerals.

Figure 1 is a diagram that schematically shows an internal combustion engine 1 provided with a camshaft according to an embodiment of the present invention. The internal combustion engine 1 includes a piston 2, a connecting rod 3, a crankshaft 4, an intake camshaft 5, an exhaust camshaft 6, an intake valve 7, and an exhaust valve 8.

In this embodiment, the internal combustion engine 1 is an in-line four-cylinder engine and has four cylinders. Each cylinder is equipped with a piston 2, two intake valves 7, and two exhaust valves 8, and a combustion chamber 9 is formed above the piston 2. The piston 2 is connected to the crankshaft 4 via a connecting rod 3. Combustion of the air-fuel mixture in the combustion chamber 9 causes the piston 2 to reciprocate in the axial direction of the cylinder, and the reciprocating motion of the piston 2 is converted into rotational motion of the crankshaft 4 by the connecting rod 3.

An intake-side timing sprocket 10 is provided at one end of the intake camshaft 5, and the intake-side timing sprocket 10 is connected to a timing sprocket 13 provided on the crankshaft 4 via a timing chain 12. The timing sprocket 13, timing chain 12, and intake-side timing sprocket 10 function as a transmission device that transmits the rotational motion of the crankshaft 4 to the intake camshaft 5. The intake camshaft 5 is rotated by the crankshaft 4 via these transmission devices.

An exhaust-side timing sprocket 11 is provided at one end of the exhaust camshaft 6, and the exhaust-side timing sprocket 11 is connected to a timing sprocket 13 via a timing chain 12. The timing sprocket 13, timing chain 12, and exhaust-side timing sprocket 11 function as a transmission device that transmits the rotational motion of the crankshaft 4 to the exhaust camshaft 6. The exhaust camshaft 6 is rotated by the crankshaft 4 via these transmission devices. Note that the internal combustion engine 1 may also be equipped with a timing belt instead of the timing chain 12 as a transmission device.

The intake camshaft 5 is provided with multiple intake cams 51 spaced apart from one another in the axial direction of the intake camshaft 5. In this embodiment, eight intake cams 51 are provided on the intake camshaft 5 to open and close a total of eight intake valves 7 arranged in four cylinders. Two intake cams 51 arranged above the two intake valves 7 arranged in cylinder No. 1 simultaneously open and close the two intake valves 7 in cylinder No. 1. Two intake cams 51 arranged above the two intake valves 7 arranged in cylinder No. 2 simultaneously open and close the two intake valves 7 in cylinder No. 2. Two intake cams 51 arranged above the two intake valves 7 arranged in cylinder No. 3 simultaneously open and close the two intake valves 7 in cylinder No. 3. Two intake cams 51 arranged above the two intake valves 7 arranged in cylinder No. 4 simultaneously open and close the two intake valves 7 in cylinder No. 4.

The exhaust camshaft 6 is provided with multiple exhaust cams 61 spaced apart from one another in the axial direction of the exhaust camshaft 6. In this embodiment, eight exhaust cams 61 are provided on the exhaust camshaft 6 to open and close a total of eight exhaust valves 8 arranged in four cylinders. The two exhaust cams 61 arranged above the two exhaust valves 8 arranged in cylinder No. 1 simultaneously open and close the two exhaust valves 8 in cylinder No. 1. The two exhaust cams 61 arranged above the two exhaust valves 8 arranged in cylinder No. 2 simultaneously open and close the two exhaust valves 8 in cylinder No. 2. The two exhaust cams 61 arranged above the two exhaust valves 8 arranged in cylinder No. 3 simultaneously open and close the two exhaust valves 8 in cylinder No. 3. The two exhaust cams 61 arranged above the two exhaust valves 8 arranged in cylinder No. 4 simultaneously open and close the two exhaust valves 8 in cylinder No. 4.

As described above, in this embodiment, internal combustion engine 1 is provided with a camshaft on each of the intake valve side and the exhaust valve side. In other words, internal combustion engine 1 is a so-called DOHC (Double Over Head Camshaft) type internal combustion engine. The intake valve side valve mechanism will be described in detail below, but the exhaust valve side valve mechanism has the same configuration as the intake valve side valve mechanism. In other words, exhaust camshaft 6 has the same configuration as intake camshaft 5.

Figure 2 is a schematic partial cross-sectional view of the internal combustion engine 1. Figure 2 shows a cross-sectional view of the intake valve 7 and its surroundings. The internal combustion engine 1 is equipped with a valve train that drives the intake valve 7. The valve train has an intake camshaft 5, a valve lifter 14, and a valve spring 15. In this embodiment, the valve train is a direct-hit (direct-acting) valve train configured so that the intake cam 51 of the intake camshaft 5 directly presses the valve lifter 14.

The valve lifter 14 has a cylindrical shape and is slidable along a guide hole 161 formed in the cylinder head 16. The end of the valve stem 71 of the intake valve 7 abuts against the inner surface of the valve lifter 14. A spring retainer 18 is attached to the end of the valve stem 71 by a cotter 17. The valve spring 15 extends axially of the valve stem 71 between the spring retainer 18 and the spring seat 19.

The valve stem 71 is slidably supported by the valve guide 20. The valve spring 15 biases the intake valve 7 toward the intake camshaft 5. As a result, the valve head 72 of the intake valve 7 closes the end of the intake port 21 that communicates with the intake passage.

The intake cam 51 is fixed to the shaft 52 of the intake camshaft 5 and converts the rotational motion of the intake camshaft 5 into linear motion of the intake valve 7. When the intake cam 51 comes into contact with the valve lifter 14 due to the rotation of the intake camshaft 5, the rotational force of the intake camshaft 5 is transmitted to the valve lifter 14 via the intake cam 51. As a result, the valve lifter 14 and intake valve 7 move linearly away from the intake camshaft 5, and the valve head 72 opens the end of the intake port 21. Therefore, the intake camshaft 5 rotates in conjunction with the rotation of the crankshaft 4, opening and closing the intake valve 7.

Figure 3 shows a timing chart of the valve lift of the intake valve and the cam torque generated on the intake camshaft. Figure 3 shows data related to the intake cam of cylinder 1 (#1) and data related to the intake cam of cylinder 3 (#3), which is next to cylinder 1, for a comparative example (dashed line) based on conventional technology and an example (solid line) based on this embodiment. The change in valve lift over time is called a lift curve.

When the intake cam opens the intake valve, positive cam torque is generated on the intake camshaft, and when the intake cam closes the intake valve, negative cam torque is generated on the intake camshaft. Positive cam torque peaks between the valve opening position, where the intake valve begins to open, and the maximum lift position, where the intake valve lift is at its maximum. On the other hand, negative cam torque peaks between the maximum lift position and the valve closing position, where the intake valve completely closes. Note that positive cam torque refers to the torque required to rotate the camshaft, and negative cam torque refers to the torque that promotes the rotation of the camshaft.

In the example shown in Figure 3, the timing at which the intake valve 7 of cylinder 3 begins to open is slightly earlier than the timing at which the intake valve 7 of cylinder 1 completes closing. As shown in Figure 3, the intake cam of the comparative example has a symmetrical lift curve in which the maximum lift position (crank angle A1) is located halfway between the valve opening start position and the valve closing completion position, and the negative cam torque generated by the intake cam of cylinder 1 peaks at the timing (crank angle A3) before positive cam torque is generated by the intake cam of cylinder 3. In this case, at the peak of the negative cam torque, the negative cam torque is not offset by the positive cam torque, resulting in large torque fluctuations in the intake camshaft. This results in increased flutter and reduced durability of transmission devices such as timing chains.

On the other hand, the intake cam of the embodiment has an asymmetric lift curve in which the maximum lift position (crank angle A2) is closer to the valve closing position than the valve opening start position, and the negative cam torque generated by the intake cam of cylinder 1 peaks at the timing (crank angle A4) when positive cam torque is generated by the intake cam of cylinder 3. In this case, the negative cam torque is offset by the positive cam torque at the peak position of the negative cam torque, resulting in smaller torque fluctuations in the intake camshaft compared to the comparative example.

In other words, in this embodiment, the multiple intake cams 51 have asymmetric lift curves in which the maximum lift position is closer to the valve closing position than the valve opening start position, and are configured so that the peak position of the negative cam torque generated by the first intake cam 51 that opens and closes the intake valve 7 arranged in the first cylinder is included in the phase interval in which positive cam torque is generated by the second intake cam 51 that opens and closes the intake valve 7 arranged in the second cylinder. This makes it possible to reduce the peak value (absolute value) of the negative cam torque. Therefore, with the intake camshaft 5 according to this embodiment, torque fluctuations of the intake camshaft 5 can be suppressed while ensuring freedom of valve opening and closing control.

In this embodiment, the multiple intake cams 51 have the following cam profile to obtain the above-mentioned lift curve. Figure 4 is a diagram showing an example of a cam profile of the intake cam 51. In this embodiment, the multiple intake cams 51 provided on the intake camshaft 5 have the same cam profile.

As shown in FIG. 4, the intake cam 51 has a valve-opening side buffer section 51a, a valve-opening side lift section 51b, a valve-closing side lift section 51c, and a valve-closing side buffer section 51d. The valve-opening side buffer section 51a and the valve-opening side lift section 51b are located on the valve-opening side (forward in the direction of rotation) of the nose top T, which corresponds to the maximum lift position, and form a valve-opening side section that contributes to opening the intake valve 7. On the other hand, the valve-closing side lift section 51c and the valve-closing side buffer section 51d are located on the valve-closing side (backward in the direction of rotation) of the nose top T and form a valve-closing side section that contributes to closing the intake valve 7. The valve-opening side buffer section 51a has a rotation angle θa, the valve-opening side lift section 51b has a rotation angle θb, the valve-closing side lift section 51c has a rotation angle θc, and the valve-closing side buffer section 51d has a rotation angle θd.

The intake cam 51 is configured so that the sum of the rotation angles θa and θb is greater than the sum of the rotation angles θc and θd. In other words, the intake cam 51 is configured so that the valve-opening side interval is longer than the valve-closing side interval. Therefore, the crank angle from the valve-opening start position to the maximum lift position is longer than the crank angle from the maximum lift position to the valve-closing end position, and the maximum lift position is biased toward the valve-closing side. Therefore, an intake cam 51 with such a cam profile achieves an asymmetric lift curve in which the maximum lift position is closer to the valve-closing end position than the valve-opening start position. Furthermore, in the intake camshaft 5, the phases of the multiple intake cams 51 are set so that the peak position of the negative cam torque generated by the first intake cam 51 that opens and closes the intake valve 7 located in the first cylinder is included in the phase interval in which positive cam torque is generated by the second intake cam 51 that opens and closes the intake valve 7 located in the second cylinder.

Figure 5 shows the time variation of the cam torque generated by multiple intake cams 51 having the cam profile shown in Figure 4. In Figure 5, the cam torque generated by the intake cams 51 of cylinders 1 (#1) through 4 (#4) is shown by a dashed line, and the composite cam torque generated on the intake camshaft 5 by these intake cams 51 is shown by a solid line. Also, for reference, Figure 5 shows the waveform of the lift curve obtained by the intake cam 51 of cylinder 1 by a dashed line.

In the data of Figure 5, the peak position of the negative cam torque generated by the intake cam 51 of cylinder 1 approximately coincides with the peak position of the positive cam torque generated by the intake cam 51 of cylinder 3, the peak position of the negative cam torque generated by the intake cam 51 of cylinder 3 approximately coincides with the peak position of the positive cam torque generated by the intake cam 51 of cylinder 4, the peak position of the negative cam torque generated by the intake cam 51 of cylinder 4 approximately coincides with the peak position of the positive cam torque generated by the intake cam 51 of cylinder 2, and the peak position of the negative cam torque generated by the intake cam 51 of cylinder 2 approximately coincides with the peak position of the positive cam torque generated by the intake cam 51 of cylinder 1. That is, the multiple intake cams 51 are configured so that the peak position of the negative cam torque generated by the first intake cam 51 that opens and closes the intake valve 7 located in the first cylinder (e.g., cylinder 1, 3, 4, or 2) approximately coincides with the peak position of the positive cam torque generated by the second intake cam 51 that opens and closes the intake valve 7 located in the second cylinder (e.g., cylinder 3, 4, 2, or 1). This reduces not only the peak value of the negative cam torque but also the peak value of the positive cam torque, thereby further suppressing torque fluctuations in the intake camshaft 5. Note that, in this specification, "approximately coinciding between the peak position of the negative cam torque and the peak position of the positive cam torque" means that the difference between the peak positions is 10° or less.

The multiple intake cams 51 may have asymmetric lift curves in which the maximum lift position is closer to the valve opening start position than the valve closing completion position, and the peak position of the positive cam torque generated by the first intake cam 51 that opens and closes the intake valve 7 arranged in the first cylinder may be configured to be included in the phase interval in which the negative cam torque is generated by the second intake cam 51 that opens and closes the intake valve 7 arranged in the second cylinder. This reduces the peak value of the positive cam torque. Therefore, even with this modification, torque fluctuations of the intake camshaft 5 can be suppressed while maintaining the degree of freedom in valve opening and closing control. In this case, for example, the intake cam 51 is configured so that the valve closing side interval is longer than the valve opening side interval. That is, in the cam profile shown in FIG. 4, the sum of the rotation angles θc and θd is greater than the sum of the rotation angles θa and θb.

Furthermore, the multiple intake cams 51 may have asymmetric lift curves in which the maximum lift position is closer to the valve opening start position than the valve closing completion position, and may be configured so that the peak position of the positive cam torque generated by the first intake cam 51 that opens and closes the intake valve 7 arranged in the first cylinder roughly coincides with the peak position of the negative cam torque generated by the second intake cam 51 that opens and closes the intake valve 7 arranged in the second cylinder. This can further suppress torque fluctuations in the intake camshaft 5.

Furthermore, when the maximum lift position is closer to the valve closing completion position than the valve opening start position, the valve opening speed can be slower than when the maximum lift position is closer to the valve opening start position than the valve closing completion position. Therefore, in the former case, deviation of the actual opening and closing operation of the intake valve 7 from the designed lift curve can be suppressed more effectively than in the latter case, thereby improving the stability of the opening and closing control of the intake valve 7.

The above describes preferred embodiments of the present invention, but the present invention is not limited to these embodiments and various modifications and variations can be made within the scope of the claims. For example, one intake valve 7 and one exhaust valve 8 may be provided per cylinder.

The valve mechanism used to open and close the intake valve 7 and exhaust valve 8 may be a rocker arm type valve mechanism in which a cam on a camshaft presses a valve lifter via a rocker arm. The internal combustion engine 1 may also be a SOHC (Single Over Head Camshaft) type internal combustion engine in which the intake valve 7 and exhaust valve 8 are opened and closed by a single camshaft.

REFERENCE SIGNS LIST 1 Internal combustion engine 4 Crankshaft 5 Intake camshaft 51 Intake cam 6 Exhaust camshaft 61 Exhaust cam 7 Intake valve 8 Exhaust valve 10 Intake side timing sprocket 11 Exhaust side timing sprocket 12 Timing chain 13 Timing sprocket

Claims (1)

1. A camshaft in an internal combustion engine that is rotationally driven by a crankshaft via a transmission,
a plurality of cams spaced apart from one another in the axial direction of the camshaft;
The camshaft has asymmetric lift curves, and the cams are formed so that a peak position of negative cam torque generated by a first cam that opens and closes a valve disposed in a first cylinder substantially coincides with a peak position of positive cam torque generated by a second cam that opens and closes a valve disposed in a second cylinder.