JP6828461B2 - Variable valve gear for internal combustion engine - Google Patents

Description

The present invention relates to a variable valve gear of an internal combustion engine, and more particularly to a variable valve gear for making the operating characteristics of a valve, which is an intake valve or an exhaust valve, variable.

In an internal combustion engine, a variable valve gear for changing operating characteristics such as lift and operating angle of a valve which is an intake valve or an exhaust valve is known (see, for example, Patent Document 1).

Japanese Unexamined Patent Publication No. 2013-217249

In this type of variable valve device, the first cam and the second cam provided on the cam shaft, the rocker shaft, and the rocker shaft are rotatably provided around the axis of the rocker shaft and are brought into contact with the first cam. 1 Rocker arm, a second rocker arm rotatably provided around the axis of the rocker shaft and abutted on the second cam, a valve driven by the first rocker arm, and a valve that can appear and disappear on the first rocker arm. It is conceivable that the engagement pin is provided on the second rocker arm and the engagement pin is provided with an engagement hole that can be engaged by insertion.

According to this, by giving different cam profiles to the first cam and the second cam, it is possible to change the operating characteristics of the valve according to the engaged state of the engaging pin.

Here, the cam lift amount of the first cam nose portion of the first cam and the second cam nose portion of the second cam are made equal, and the second cam nose portion is extended rearward in the camshaft rotation direction from the first cam nose portion. When the valve is opened with the mating pin engaged, it is conceivable to extend the maximum valve lift section of the valve while maintaining the maximum valve lift amount by the first cam nose portion.

On the other hand, in order to allow the engaging pin to be easily and surely inserted into the engaging hole, it is conceivable to provide a clearance of a predetermined size between the engaging pin and the engaging hole.

In this case, according to the research results of the present inventor, when the valve is opened with the engaging pin engaged, the cam that drives the valve near the end of the first cam nose is from the first cam to the first cam. When switching to 2 cams, it was found that the valve lift amount decreased and there was an event in which the maximum valve lift amount by the 1st cam nose portion could not be maintained.

Therefore, the present invention was conceived in view of the above circumstances, and an object thereof is an internal combustion engine capable of suppressing a decrease in the valve lift amount when the cam for driving the valve is switched from the first cam to the second cam. The purpose is to provide a variable valve gear.

According to one aspect of the invention
The first cam and the second cam provided on the camshaft,
With the rocker shaft
A first rocker arm that is rotatably provided around the axis of the rocker shaft and is in contact with the first cam.
A second rocker arm that is rotatably provided around the axis of the rocker shaft and is in contact with the second cam.
The valve driven by the first rocker arm and
An engaging pin provided on one of the first rocker arm and the second rocker arm so as to appear and disappear,
An engaging hole provided on the other side of the first rocker arm and the second rocker arm and to which the engaging pin can be engaged by insertion.
With
A clearance of a predetermined size is provided between the engaging pin and the engaging hole.
The first cam has a first cam nose portion and has a first cam nose portion.
The second cam has a second cam nose portion and has a second cam nose portion.
The second cam nose portion is formed so as to extend the first cam nose portion rearward in the camshaft rotation direction.
The second cam nose portion is provided with a variable valve gear of an internal combustion engine, which has a cam lift amount larger than that of the first cam nose portion.

Preferably, the second cam nose portion has a cam lift amount larger than that of the first cam nose portion by a predetermined increase amount.
The amount of increase is set based on the rocker ratio of the first rocker arm.

Preferably, the increase is set based on the rocker ratio of the first rocker arm and the decrease in maximum valve lift.
The decrease in the maximum valve lift amount is based on the assumption that the maximum cam lift amount of the first cam nose portion and the second cam nose portion are equal and the valve is opened with the engagement pin engaged. The valve lift amount is reduced when the cam that drives the valve is switched from the first cam to the second cam near the end of the first cam nose portion.

Preferably, the increase amount is set to a value obtained by dividing the decrease amount of the maximum valve lift amount by the rocker ratio of the first rocker arm.

Preferably, the cam profile of the second cam lob portion uses the second cam lift amount of the second cam lob portion as the first cam lift amount of the first cam lob portion from the phase position before the phase position of the first cam nose portion. On the other hand, it is set to gradually increase.

According to the present invention, it is possible to suppress a decrease in the valve lift amount when the cam that drives the valve is switched from the first cam to the second cam.

It is an exploded perspective view which shows the variable valve gear of the internal combustion engine which concerns on embodiment of this invention. It is an assembly perspective view which shows the variable valve gear. It is a vertical sectional view which shows the variable valve gear. It is a figure which shows the 1st cam and the 2nd cam in the camshaft of this embodiment. It is a figure which shows the 1st cam and the 2nd cam in the camshaft of the comparative example. It is a figure which shows the valve lift curve which was planned in the comparative example. It is a figure which shows the valve lift curve actually obtained in the comparative example. It is the schematic for demonstrating the subject of the comparative example. It is a figure which shows the valve lift curve and the cam lift diagram of this embodiment. It is a figure which compared the cam lift amount of the 2nd cam lob part between the comparative example and this embodiment. It is a figure which shows the 1st rocker arm. It is a figure which shows the maximum valve lift amount and the maximum cam lift amount. It is the schematic for demonstrating the subject of the comparative example which concerns on other embodiments.

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

1 to 3 show a variable valve gear of an internal combustion engine according to an embodiment of the present invention. FIG. 1 is an exploded perspective view, FIG. 2 is an assembled perspective view, and FIG. 3 is a vertical sectional view. The variable valve gear of the present embodiment is applied to an internal combustion engine for a vehicle. The vehicle is a large vehicle such as a truck, and the internal combustion engine (engine) as a vehicle power source is a diesel engine. However, the types and uses of the vehicle and the internal combustion engine are not particularly limited. For example, the vehicle may be a small vehicle such as a passenger car, and the engine may be a gasoline engine.

The variable valve gear 1 is a device for making the operating characteristics of the valve 2 which is an intake valve or an exhaust valve variable. Here, the "operating characteristic" includes at least one of lift, operating angle, and valve timing (open and closed timing). The variable valve gear 1 shown in the figure is for driving one valve 2 of one cylinder. However, the variable valve gear 1 shown may be used to simultaneously drive a plurality of (typically two) valves 2 of one cylinder. When the valve operating characteristics are variable in a plurality of cylinders, a variable valve gear 1 is provided in each cylinder.

The variable valve gear 1 includes a valve 2, a camshaft 3, and a rocker shaft 4 arranged parallel to and spaced apart from the camshaft 3. Further, the variable valve device 1 is rotatably provided around the shaft C1 of the rocker shaft 4 and the first cam 5A and the second cam 5B provided on the cam shaft 3, and is brought into contact with the first cam 5A. It includes a first rocker arm 6A and a second rocker arm 6B that is rotatably provided around the axis C1 of the rocker shaft 4 and is in contact with the second cam 5B. Further, the variable valve gear 1 is provided with an engaging pin 7 provided on the first rocker arm 6A so as to appear and disappear, and an engaging hole 8 provided on the second rocker arm 6B and to which the engaging pin 7 can be engaged by insertion (FIG. FIG. 3) and.

The valve 2 is constantly urged by a valve spring (not shown) in a valve closing direction (upward in FIG. 1) to close the port 9. Here, the port 9 is an intake port or an exhaust port. On the other hand, when the valve 2 receives a force from the drive arm 9 of the first rocker arm 6A in the valve opening direction (downward in FIG. 1) that exceeds the force of the valve spring, the valve 2 is opened or lifted to open the port 9. Open. The amount of valve opening from the closed position of the valve 2 is called the valve lift amount.

The first cam 5A and the second cam 5B are arranged at intervals in the axis C2 direction of the cam shaft 3. Correspondingly, the first rocker arm 6A and the second rocker arm 6B are arranged adjacent to each other in the rocker shaft axis C1 direction.

The first rocker arm 6A includes the drive arm 9, a first shaft hole 10A into which the rocker shaft 4 is slidably inserted, and a first roller bearing 11A forming a contact portion with the first cam 5A. The first roller bearing 11A is arranged at a position farther from the valve 2 than the rocker shaft 4. Further, the first rocker arm 6A has an adjusting screw 17 that is screwed and attached to the tip end portion of the drive arm 9 and faces the shaft end surface of the valve 2, and a lock nut 18 that fixes the position of the adjusting screw 17.

The second rocker arm 6B has substantially the same configuration as the first rocker arm 6A, except that the drive arm 9 is not provided. The outer shape is almost the same. The second rocker arm 6B has a second shaft hole 10B into which the rocker shaft 4 is slidably inserted, and a second roller bearing 11B forming a contact portion with the second cam 5B.

As shown in FIG. 3, the first rocker arm 6A is provided with a pin support hole 12 through which the engaging pin 7 is slidably inserted. The cross-sectional shape of the engaging pin 7 and the pin support hole 12 is circular. These engaging pins 7 and pin support holes 12 are arranged coaxially with the pin shaft C3 parallel to the rocker shaft shaft C1.

The engagement hole 8 of the second rocker arm 6B also has a circular cross section and can be arranged coaxially with the pin shaft C3. Inside the engaging hole 8, a return spring 13 that constantly urges the engaging pin 7 on the non-engaging side, that is, in the direction in which the engaging pin 7 is disengaged from the engaging hole 8 (toward the left in FIG. A pressing body 14 that is interposed between the 13 and transmits the urging force of the return spring 13 to the engaging pin 7 is housed. The pressing body 14 is formed in a bottomed cylindrical shape with the engaging pin 7 side closed, accommodates the return spring 13 inside, and prevents the return spring 13 from directly hitting the engaging pin 7. The pressing body 14 is slidable in the engaging hole 8 in the axial direction of the engaging hole 8. The return spring 13 is formed by a coil spring. The engaging hole 8 is formed in a bottomed cylindrical shape in which the opposite side of the engaging pin 7 is closed. The bottom of the engaging hole 8 is provided with a breather hole 15 that allows air that is compressed and expanded as the pressing body 14 slides to and from the outside.

FIG. 3 shows a state when the tip end portion of the engaging pin 7 is engaged with the engaging hole 8, that is, when engaged. At this time, the engaging pin 7 receives a pin driving force F in the engaging direction (rightward in FIG. 3) based on hydraulic pressure or mechanical force from the outside, and is inserted into the engaging hole 8 by this pin driving force F. To. As a result, the pressing body 14 is also moved in the engaging direction, the return spring 13 is compressed, and the first rocker arm 6A and the second rocker arm 6B are in a connected state.

On the other hand, when the pin driving force F is released, the engaging pin 7 is pushed by the return spring 13 and moved from the illustrated position in the disengaging direction (toward the left in FIG. 3) and disengaged from the engaging hole 8. As a result, the pressing body 14 is also moved in the detaching direction, and the return spring 13 is extended to its natural length. As a result, the first rocker arm 6A and the second rocker arm 6B are not connected. At this time, the tip end surface, that is, the right end surface of the engaging pin 7, is positioned substantially on the same surface as the right end surface of the first rocker arm 6A, and the tip end surface, that is, the left end surface of the pressing body 14, is substantially the same as the left end surface of the second rocker arm 6B. It is located on the surface and allows relative rotational movement of both rocker arms 6A and 6B around the rocker shaft axis C1.

As shown in FIG. 3, when the engaging pin 7 is engaged, a clearance 16 is provided between the engaging pin 7 and the engaging hole 8. The reason for providing such a clearance 16 is to facilitate and ensure the insertion of the engaging pin 7 into the engaging hole 8. The clearance 16 has a predetermined size S in the radial direction with respect to the pin axis C3. Due to the presence of the clearance 16, when the engaging pin 7 is engaged in the assembled state as shown in FIG. 2, there is a slight rattling in the rotation direction between the first rocker arm 6A and the second rocker arm 6B. Occurs.

In addition, other sliding portions, that is, the sliding portion between the engaging pin 7 and the pin support hole 12, the sliding portion between the rocker shaft 4 and the first shaft hole 10A, and the rocker shaft 4 and the second shaft hole. Clearances are also provided in the sliding portions between 10B, but since the size of these clearances is smaller than the size S of the clearance 16, these clearances are ignored here and the size of these clearances is set to zero. handle.

Next, the first cam 5A and the second cam 5B in the camshaft 3 will be described. Since both cams have similar configurations, the first cam 5A will be described first, and then the differences between the second cam 5B will be described.

As shown in FIG. 4, the first cam 5A protrudes outward in the radial direction with respect to the camshaft axis C2 from the first base circle portion 21A defining the first base circle BA and the first base circle portion 21A. It has a first cam lob portion 22A and the like. The amount of protrusion of the first cam lob portion 22A from the first base circle BA in the radial direction is referred to as the first cam lift amount CL1. The first cam lob portion 22A includes a first cam nose portion 23A which is a portion where the first cam lift amount CL1 is maximum (CL1max). The first cam nose portion 23A of the present embodiment is a point-shaped portion having an extremely short phase section in the camshaft rotation direction R, but may be extended so as to extend over a predetermined phase section. The first cam lob portion 22A gradually increases the first cam lift amount CL1 as it rotates in the camshaft rotation direction R, reaches the maximum first cam lift amount CL1max in the first cam nose portion 23A, and then reaches the first cam lift amount CL1. Has a cam profile that gradually decreases.

In the camshaft rotation direction R, the first cam lob portion 22A starts from the start position θ1 and gradually increases the first cam lift amount CL1 between the start position θ1 and the phase position θ3 of the first cam nose portion 23A. It has a section 24A. The first cam lob portion 22A has a descending section 25A that ends at the end position θ5 and gradually reduces the first cam lift amount CL1 between the phase position θ3 and the end position θ5.

In FIG. 4, the second cam 5B is partially invisible because it is arranged on the back side of the first cam 5A, but the second cam 5B also has the second base circle portion 21B that defines the second base circle BB and the second cam 5B. It has a second cam lob portion 22B that protrudes outward in the radial direction with respect to the cam shaft shaft C2 from the two base circular portion 21B. The amount of protrusion of the second cam lob portion 22B from the second base circle BB in the radial direction is referred to as the second cam lift amount CL2. The radius of the second base circle BB is equal to the radius of the first base circle BA. Therefore, the second base circle portion 21B appears to overlap with the first base circle portion 21A.

The second cam lob portion 22B includes a second cam nose portion 23B which is a portion where the second cam lift amount CL2 is maximum (CL2max). The second cam nose portion 23B is formed so as to extend the first cam nose portion 23A rearward in the camshaft rotation direction R, and is extended in the camshaft rotation direction R over a phase section α longer than the first cam nose portion 23A. There is. The second cam lob portion 22B gradually increases the second cam lift amount CL2 as it rotates in the camshaft rotation direction R, reaches the maximum second cam lift amount CL2max at the second cam nose portion 23B, and then reaches the maximum second cam lift amount CL2max. It has a cam profile such that the amount CL2max is maintained for the phase interval α and then the second camlift amount CL2 is gradually reduced.

In particular, the second cam nose portion 23B has a cam lift amount larger than that of the first cam nose portion 23A. In the present embodiment, the maximum second cam lift amount CL2max of the second cam nose portion 23B is larger than the maximum first cam lift amount CL1max of the first cam nose portion 23A by a predetermined increase amount ΔCL. As will be described in detail later, the increase amount ΔCL is set to a size that suppresses a decrease in the maximum valve lift amount when both rocker arms 6A and 6B are connected.

As shown in FIG. 4, in the camshaft rotation direction R, the second camlob portion 22B starts from the same phase position as the start position θ1 of the first camlob portion 22A, and for a while, the first camlob portion 22A It has the same cam profile as the ascending section 24A. However, the second cam lob portion 22B gradually starts to increase the second cam lift amount CL2 with respect to the first cam lift amount CL1 from the increase start position θ2 set in the middle of the ascending section 24A of the first cam lob portion 22A. In the present embodiment, the second cam nose portion 23B starts at the phase position θ3 of the first cam nose portion 23A, and the amount of increase reaches ΔCL. The area from the start position θ1 to the phase position θ3 is the ascending section 24B of the second cam lob portion 22B.

The second cam nose portion 23B ends at the phase position θ4 behind the phase position θ3 by the phase section α. In the present embodiment, the phase position θ4 is set immediately before the end position θ5 of the first cam lob portion 22A. The second cam lob portion 22B ends at the end position θ6 set behind the end position θ5 of the first cam lob portion 22A. The second cam lob portion 22B has a descending section 25B that gradually reduces the second cam lift amount CL2 between the phase position θ4 and the end position θ6.

Although not shown, in the present embodiment, a pressing spring for constantly urging the second rocker arm 6B is provided so as to lightly press the second rocker arm 6B, which is free when the engaging pin 7 is not engaged, against the second cam 5B. Has been done.

Next, the advantages of the present embodiment will be described in comparison with the comparative examples. Regarding the comparative example, the same or corresponding parts as those in the present embodiment will be omitted by using the same reference numerals, and the differences from the present embodiment will be mainly described.

FIG. 5 shows the first cam 5A and the second cam 5Ba in the camshaft 3a of the comparative example. The first cam 5A of the comparative example is the same as that of the present embodiment, but the second cam 5Ba of the comparative example is different from the second cam 5B of the present embodiment.

In the second cam 5Ba of the comparative example, the second cam lob portion 22Ba includes the second cam nose portion 23Ba. The second cam nose portion 23Ba is also formed so as to extend the first cam nose portion 23A rearward in the camshaft rotation direction R, and has a phase section αa longer than that of the first cam nose portion 23A. However, the second cam nose portion 23Ba has a cam lift amount equal to that of the first cam nose portion 23A. In other words, the maximum second cam lift amount CL2maxa of the second cam nose portion 23Ba is equal to the maximum first cam lift amount CL1max of the first cam nose portion 23A and is not increased.

Based on the cam profile of these cam lobs, a valve lift curve as shown in FIG. 6 was initially planned. In the figure, the line a (broken line) is a valve lift curve that is independently provided only by the first cam lob portion 22A when the engaging pin 7 is disengaged or disengaged, that is, when both rocker arms 6A and 6B are not connected. .. The line b (solid line) is a valve lift curve provided by the cooperation of the first cam lob portion 22A and the second cam lob portion 22Ba when the engaging pin 7 is engaged, that is, when both rocker arms 6A and 6B are connected. The valve lift amount is represented by VL. Since the shapes of both cam lobs are the same in front of the camshaft rotation direction R from the first cam nose portion 23A, both valve lift curves overlap before reaching the maximum valve lift amount VLmax.

As shown in the figure, initially, when both rocker arms 6A and 6B are connected, the maximum valve lift amount VLmax brought about by the first cam nose portion 23A is equally maintained by the second cam nose portion 23Ba, and the maximum valve lift of the valve 2 is maintained. It was planned that the section would simply be extended to the cam phase larger side (camshaft rotation direction R rear side).

However, according to the research results of the present inventor, it has been found that a valve lift curve as shown in FIG. 7, which is actually different from this, can be obtained. In the figure, the line a (high broken line) is a valve lift curve provided only by the first cam lob portion 22A when both rocker arms 6A and 6B are not connected. The line b (high solid line) is a valve lift curve provided by the cooperation of the first cam lob portion 22A and the second cam lob portion 22Ba when both rocker arms 6A and 6B are connected. The line c (low broken line) represents the first cam lift amount CL1 of the first cam lob portion 22A, and the line d (low solid line) represents the second cam lift amount CL2a of the second cam lob portion 22Ba.

As can be seen in line b, the valve lift amount when both rocker arms 6A and 6B are connected is decreased from the maximum valve lift amount VLmax immediately after the cam phase exceeds the phase position θmax at which the maximum valve lift amount VLmax is reached. It was found that it decreased by ΔVL and was maintained at the decreased value (VLmax-ΔVL). This decrease in the maximum valve lift amount is also called lift loss. It was found that the lift loss was caused by the clearance 16 between the engaging pin 7 and the engaging hole 8.

This will be described with reference to FIG. 8 (A) and 8 (B) schematically show a state when the valve 2 is opened (with the engaging pin 7 engaged) when both rocker arms 6A and 6B are connected. Here, for the sake of simplicity, the first rocker arm 6A and the second rocker arm 6B are shown by simple rectangles, and only the periphery of the cam nose portions 23A and 23Ba of the first cam 5A and the second cam 5Ba is shown. Valve 2 is also shown briefly. In this figure, the valve spring 30 is also shown. The dimensions of each part are exaggerated.

FIG. 8A shows the moment when the first cam nose portion 23A of the first cam 5A comes into contact with the first rocker arm 6A. Prior to this time, substantially only the first cam 5A opens the valve 2 via the first rocker arm 6A. That is, the cam driving force f1 from the first cam 5A is transmitted through the first rocker arm 6A to give the valve opening driving force f2 to the valve 2.

At this time, although the second rocker arm 6B is rotated by the second cam 5Ba, it is only rotated (carried) in the same manner as the first rocker arm 6A, and a substantial valve opening driving force is applied to the valve 2. Do not give. Also, basically, the engaging pins 7 are held coaxially in the engaging holes 8 and the clearance 16 between them is constant around the pin shaft C3 (see FIG. 3). In the state of FIG. 8A, the second cam 5Ba also comes into contact with the second rocker arm 6B at the starting point of the second cam nose portion 23Ba.

Next, FIG. 8B shows a state immediately after the state shown in FIG. 8A. At this time, the second cam 5Ba still abuts on the second rocker arm 6B at the second cam nose portion 23Ba, and the second rocker arm 6B is held at the same position. The phase of the first cam 5A is ahead of the phase of the first cam nose portion 23A. Therefore, if there is no clearance 16 (if the size S of the clearance 16 is zero), the first rocker arm 6A and the valve 2 are held at the same position, and the maximum valve lift amount VLmax is maintained. The first rocker arm 6A is separated from the first cam 5A.

However, since there is actually a clearance 16 (because the size S of the clearance 16 is larger than zero), this is not the case, and the state shown in FIG. 8B is obtained. That is, the first rocker arm 6A is pushed by the valve spring 30 with respect to the second rocker arm 6B located at a position corresponding to the maximum valve lift amount VLmax, and rotates relative to the valve lift amount reduction direction T. Then, the engaging pin 7 moves relative to the engaging hole 8 so as to eliminate the clearance 16 (so that the size S of the clearance 16 is zero). The first rocker arm 6A is urged toward the first cam 5A by the valve spring 30. As a result, the cam driving force f3 from the second cam 5Ba is transmitted to the first rocker arm 6A through the engaging pin 7 and the engaging hole 8, and the valve opening driving force f2 is applied to the valve 2.

That is, the cam that drives the valve 2 is switched from the first cam 5A to the second cam 5Ba near the end portion (or end point) of the first cam nose portion 23A, and more specifically, immediately after the end portion is exceeded. Here, since the first cam nose portion 23A of the present embodiment has only an extremely short point-shaped phase section, the start end portion (or start point) and the end portion thereof are substantially the same, but the first cam nose portion 23A is relatively large. Even when having a long phase section, such cam switching occurs near the end of the first cam nose portion 23A.

At this time, since the first rocker arm 6A rotates relative to the second rocker arm 6B in the valve lift amount reduction direction T, the valve lift amount is reduced by the reduction amount ΔVL from the maximum valve lift amount VLmax, and a lift loss occurs. To do.

When such a lift loss occurs, when the valve drive cam is switched, a momentary shear stress is applied to the engaging pin 7, the wear of the engaging pin 7 is promoted, and there is a possibility that the variable valve gear 1 may malfunction. Further, the effective opening area of the valve 2 is reduced by the amount of the lift loss, which may cause an increase in pumping loss and the like.

Therefore, in the present embodiment, as shown in FIG. 4, the maximum second cam lift amount CL2max of the second cam nose portion 23B is made larger than the maximum first cam lift amount CL1max of the first cam nose portion 23A. More specifically, the maximum second cam lift amount CL2max of the second cam nose portion 23B is made larger than the maximum first cam lift amount CL1max of the first cam nose portion 23A by a predetermined increase amount ΔCL. As a result, the second rocker arm 6B is rotated relative to the first rocker arm 6A so as to reduce or eliminate the clearance 16 by increasing the maximum second cam lift amount CL2max, and the decrease in the maximum valve lift amount is the maximum second. It can be compensated or supplemented by an increase in the cam lift amount CL2max, and a decrease in the maximum valve lift amount, that is, a lift loss can be suppressed or eliminated. Then, it is possible to suppress or prevent wear of the engaging pin 7 and an increase in pumping loss due to lift loss.

FIG. 9 shows a valve lift curve and a cam lift diagram in the case of the present embodiment. Similar to FIG. 7, line a (high broken line) is a valve lift curve provided only by the first cam lob portion 22A when the rocker arms 6A and 6B are not connected. The line b (high solid line) is a valve lift curve provided by the cooperation of the first cam lob portion 22A and the second cam lob portion 22B when both rocker arms 6A and 6B are connected. The line c (low broken line) represents the first cam lift amount CL1 of the first cam lob portion 22A, and the line d (low solid line) represents the second cam lift amount CL2 of the second cam lob portion 22B.

As seen in line b, the valve lift amount when both rocker arms 6A and 6B are connected is the maximum valve lift amount VLmax for a while even after the cam phase exceeds the phase position θ3 of the first cam nose portion 23A. Is maintained at. That is, in the present embodiment, the increase amount ΔCL is set so as to eliminate the decrease in the valve lift amount with respect to the maximum valve lift amount VLmax, that is, the lift loss, and to make the decrease amount ΔVL zero. As a result, as originally planned (see FIG. 6), the maximum valve lift amount VLmax brought about by the first cam nose section 23A is maintained equally by the second cam nose section 23Ba, and the maximum valve lift section of the valve 2 is maintained. Can simply be extended to the larger cam phase side.

FIG. 10 is a diagram comparing the cam lift amounts of the second cam lob portions 22Ba and B between the case of the comparative example (broken line) and the case of the present embodiment (solid line). As shown in the figure, in the second cam nose portion 23B of the present embodiment, the cam lift amount is increased by the increase amount ΔCL with respect to the second cam nose portion 23Ba of the comparative example.

Further, in the present embodiment, as shown in FIG. 4, the phase position before the phase position θ3 of the first cam nose portion 23A, specifically, the increase start position set in the middle of the ascending section 24A of the first cam lob portion 22A. The cam profile of the second cam lob portion 22B is set so that the second cam lift amount CL2 is gradually increased with respect to the first cam lift amount CL1 from θ2. Therefore, when both rocker arms 6A and 6B are connected and when the valve 2 is opened, the second rocker arm 6B rotates relative to the first rocker arm 6A from the stage before reaching the phase position θ3 of the first cam nose portion 23A. The clearance 16 can be gradually reduced. Therefore, when the phase position θ3 of the first cam nose portion 23A is reached, the clearance 16 is suppressed from suddenly disappearing, and a momentary shear stress is applied to the engaging pin 7 to promote wear of the engaging pin 7. Can be suppressed.

The increase start position θ2 can be arbitrarily set as long as it is a phase position before the phase position θ3 of the first cam nose portion 23A. For example, the phase position may be set in the middle of the ascending section 24A of the first cam lob portion 22A and before the illustrated example. Alternatively, it may be set at the same phase position as the start position θ1 of the first cam lob portion 22A, or may be set at a phase position before the start position θ1.

Next, a method of setting the optimum increase amount ΔCL such that the decrease amount ΔVL of the maximum valve lift amount is set to zero will be described.

In the present embodiment, the increase amount ΔCL is set based on the rocker ratio of the first rocker arm 6A. In the case of the present embodiment, since only the first rocker arm 6A gives the valve opening driving force f2 to the valve 2, the optimum increase amount ΔCL can be obtained by considering the rocker ratio which is a typical characteristic value of the first rocker arm 6A. It becomes possible to set.

In particular, the increase amount ΔCL is set based on the rocker ratio of the first rocker arm 6A and the decrease amount ΔVL of the maximum valve lift amount as shown in FIG. 7 in the case of the comparative example. By also considering the valve lift decrease amount ΔVL in the case of the comparative example, it is possible to set a more optimum increase amount ΔCL.

FIG. 11 shows the first rocker arm 6A. Strictly speaking, the rocker ratio of the first rocker arm 6A changes according to the valve lift amount. The reason is that the geometry of the first rocker arm 6A changes with the rotation of the first cam 5A. Therefore, the rocker ratio usually means a nominal rocker ratio, and its value is represented by L1 / L2. L1 is the length from the rocker shaft shaft C1 to the center of the first roller bearing 11A. L2 is the length of the perpendicular line from the rocker shaft shaft C1 to the center of the adjusting screw 17.

However, the rocker ratio that is important in this embodiment is the value in the first cam nose portion 23A. Therefore, as shown in FIG. 12, the rocker ratio RR of the present embodiment is set to a value obtained by dividing the maximum valve lift amount VLmax corresponding to the first cam nose portion 23A by the maximum first cam lift amount CL1max. That is, the rocker ratio RR is defined by the formula (1): RR = VLmax / CL1max. RR> 1.

By the way, the relationship between the maximum first cam lift amount CL1max and the maximum valve lift amount VLmax is expressed by the equation (2): VLmax = CL1max · RR which is a modification of the equation (1). An object of the present embodiment is to increase the maximum second cam lift amount of the second cam nose portion 23B from the maximum first cam lift amount CL1max of the first cam nose portion 23A to eliminate the lift loss. Therefore, the increase amount ΔCL of the present embodiment is set to a value obtained by dividing the decrease amount ΔVL of the maximum valve lift amount by the rocker ratio RR. Here, the amount of decrease ΔVL is a value obtained by actual measurement or the like. By setting the increase amount ΔCL in this way, the object can be surely achieved.

Although the preferred embodiments of the present invention have been described in detail above, various other embodiments of the present invention can be considered. For example, the following other embodiments are possible.

(1) The arrangement of the engaging pin 7 and the engaging hole 8 may be reversed, and the engaging pin 7 may be provided on the second rocker arm 6B and the engaging hole 8 may be provided on the first rocker arm 6A. This is because even in this case, the same problems as those in the above embodiment can occur, and the problems can be solved by the present invention. Regarding the problem, in the comparative example with respect to the above embodiment, the clearance 16 on the lower side (second cam 5Ba side) disappeared as shown in FIG. 8 (B), but in the comparative example with respect to the other embodiment, FIG. 13 ( As shown in B), the clearance 16 on the upper side (opposite side of the first cam 5A) disappears.

(2) The relative arrangement of the first and second roller bearings 11A and 11B and the rocker shaft 4 may be reversed, and the first and second roller bearings 11A and 11B are arranged on the side closer to the valve 2 and far from the valve 2. The rocker shaft 4 may be arranged on the side.

(3) At least one of the first and second rocker arms 6A and 6B does not necessarily have to be directly supported by the rocker shaft 4 as in the above embodiment. For example, one rocker arm (for example, 6A) directly supported by the rocker shaft 4 is provided with a cylindrical portion for extending a shaft hole (for example, 10A) so as to project, and the other rocker arm (for example, 6B) is provided on the outer peripheral side of the cylindrical portion. ) May be rotatably supported.

(4) In the above-described embodiment, two cams and two rocker arms are provided, and the valve lift pattern can be switched in two stages as shown by lines a and b in FIG. However, it is possible to increase the number of switching stages. For example, when the number of switching stages is set to 3 and the maximum valve lift section is further extended, the number of cams and rocker arms is increased by one, and a third cam and a third rocker arm are additionally provided. Then, the second rocker arm and the third rocker arm can be connected with an additional pin. At this time, the relationship between the second cam and the third cam is the same as the relationship between the first cam and the second cam, and the relationship between the second rocker arm and the third rocker arm is the same as the relationship between the first rocker arm and the second rocker arm. The same applies when the number of switching stages is further increased. By providing three or more cams and rocker arms in this way, it is possible to set the number of switching stages to three or more.

The embodiment of the present invention is not limited to the above-described embodiment, and all modifications, applications, and equivalents included in the idea of the present invention defined by the scope of claims are included in the present invention. Therefore, the present invention should not be construed in a limited manner and can be applied to any other technique belonging within the scope of the idea of the present invention.

1 Variable valve gear 2 Valve 3 Camshaft 4 Rocker shaft 5A 1st cam 5B 2nd cam 6A 1st rocker arm 6B 2nd rocker arm 7 Engagement pin 8 Engagement hole 16 Clearance 23A 1st cam nose part 23B 2nd cam nose part C1 Rocker shaft shaft R Camshaft rotation direction

Claims (3)

The first cam and the second cam provided on the camshaft,
With the rocker shaft
A first rocker arm that is rotatably provided around the axis of the rocker shaft and is in contact with the first cam.
A second rocker arm that is rotatably provided around the axis of the rocker shaft and is in contact with the second cam.
The valve driven by the first rocker arm and
An engaging pin provided on one of the first rocker arm and the second rocker arm so as to appear and disappear,
An engaging hole provided on the other side of the first rocker arm and the second rocker arm and to which the engaging pin can be engaged by insertion.
With
A clearance of a predetermined size is provided between the engaging pin and the engaging hole.
The first cam has a first cam nose portion and has a first cam nose portion.
The second cam has a second cam nose portion and has a second cam nose portion.
The second cam nose portion is formed so as to extend the first cam nose portion rearward in the camshaft rotation direction.
The second cam nose portion, have a larger by cam lift predetermined increment from the first nose portion,
The increase amount is set based on the rocker ratio of the first rocker arm and the decrease amount of the maximum valve lift amount.
The decrease in the maximum valve lift amount is based on the assumption that the maximum cam lift amount of the first cam nose portion and the second cam nose portion are equal and the valve is opened with the engagement pin engaged. , A variable valve operating device for an internal combustion engine, characterized in that the amount of valve lift reduced when the cam driving the valve near the end of the first cam nose portion is switched from the first cam to the second cam. .. The variable valve gear for an internal combustion engine according to claim 1 , wherein the increase amount is set to a value obtained by dividing the decrease amount of the maximum valve lift amount by the rocker ratio of the first rocker arm. The cam profile of the second cam lob portion gradually increases the amount of the second cam lift of the second cam lob portion with respect to the amount of the first cam lift of the first cam lob portion from the phase position before the phase position of the first cam nose portion. The variable valve gear for an internal combustion engine according to claim 1 or 2 , which is set to increase.

Images