JP2663555B2 - Valve train for 4-cycle multi-cylinder engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a valve train for a four-cycle multi-cylinder engine that drives intake and exhaust valves of a four-cycle engine.

[Conventional technology]

Generally, in a four-cycle engine mounted on a vehicle such as an automobile or a motorcycle, an intake / exhaust valve is disposed above the combustion chamber, and the valve train includes a camshaft for operating the intake / exhaust valve. I have. When the camshaft is rotated by the power of the engine, the intake / exhaust valve is moved up and down at a predetermined timing by a cam having a unique cam profile formed on the camshaft, so that the mixture is sucked and the combustion gas is exhausted.

In the above-described conventional valve train, each of the intake and exhaust valves is always operated by a cam having the same cam profile. Therefore, the opening and closing of each valve set according to the engine speed is performed. The lift amount of the valve moved up and down by the timing and the rotation of the cam is always constant without fluctuation.

On the other hand, in the above-described four-stroke engine mounted on a vehicle such as a motorcycle, it is required to obtain a high output within a wide rotation speed range from a low rotation speed range to a middle and high rotation speed range, that is, to obtain a wide power band. Have been.

However, in the above-described conventional valve train, each of the intake and exhaust valves is always operated by a cam having the same cam profile, so that the opening / closing timing of each valve and the lift amount of the valve are always constant without fluctuation. Therefore, the output characteristic of the engine is generally limited by the cam profile of the cam that operates the valve, and has an output characteristic having a peak value in a specific engine speed range, and therefore, from a low speed range to a middle / high speed range. Higher output could not be obtained in a wide speed range.

In view of the above circumstances, the applicant of the present application switches the cam to be used by rotating the rocker shaft, thereby improving the output in a wide rotation speed range from a low rotation speed range to a middle / high rotation speed range. We proposed a cam switching device for a 4-cycle engine.

FIG. 5 is a conceptual perspective view showing a main part of the cam switching device 1 proposed by the applicant of the present invention. The cam switching device 1
Are provided at two locations, one each for the intake valve side and the exhaust valve side for one cylinder.

The cam switching device 1 includes a camshaft 4 in which two types of cams 2 and 3 having different cam profiles are formed adjacently,
First and second rocker arms 5 and 6 disposed below the camshaft 4 and the respective rocker arms 5 and 6
And a rocker shaft 7 which is fitted into each of the support portions 5a and 6a and rotatably supported by a bearing (not shown).

Of these, the cam 2 formed on the camshaft 4 has a cam profile (hereinafter referred to as low speed) having a cam profile suitable for improving the output of the engine in a so-called low speed rotation range where the cam lift is small and the valve opening / closing period is set short. On the other hand, the cam 3 formed adjacently has a larger cam lift amount and a longer valve open / close period than the cam 2 symmetrically with the cam 2 over the entire circumference. Further, the cam has a cam profile suitable for improving the output of the engine in a so-called middle / high speed rotation range (hereinafter referred to as a high speed rotation cam).

The first rocker arm 5 of the first and second rocker arms 5 and 6 is disposed below the low-speed rotation cam 2 formed on the camshaft 4, and the tips 5b and 5c are bifurcated. The valve stems 8 and 9 of the valve for opening and closing the combustion chamber of the engine (not shown) are arranged so as to directly contact the heads.

The adjacent second rocker arm 6 is disposed below the high-speed rotation cam 3 formed on the camshaft 4, and the tip 6b is engaged with the tip upper surface 5d of the first rocker arm 5. It is arranged.

On the other hand, the above-mentioned first and second rocker arms 5, 6
The rocker shaft 7 that rotatably supports the rocker shaft 7 has an eccentric large-diameter portion 10 whose diameter is larger than that of the other portion of the rocker shaft 7 and whose axis is eccentric from the axis of the other portion. , This eccentric large diameter part
Reference numeral 10 is fitted into the support portion 6a of the second rocker arm 6. The eccentric large-diameter portion 10 is an eccentric bush that is inserted into the rocker shaft 7.
The eccentric bush 11 includes a pin 12 for fixing the eccentric bush 11 to the rocker shaft 7.

The eccentric bush 11 and the rocker shaft 7 are arranged as shown in FIG.
Holes 11a and 7a whose dimensional tolerance is strictly controlled and whose diameter is slightly smaller than the diameter of the pin 12 are formed.
The eccentric bush 11 and the rocker shaft 7 are driven by driving the pin 12 into the holes 11a and 7a.
Are fixed to each other.

In FIG. 5, reference numeral 13 denotes a screw portion for adjusting a valve clearance, and reference numeral 14 denotes a valve spring.

 Next, the operation of the above-described cam switching device 1 will be described.

When the rocker shaft 7 is rotated by a predetermined angle in a low rotation speed range of the four-cycle engine and stopped at the position shown in FIG. Since the surface 11b of the eccentric bush 11, which is farthest from the bottom, is located at the lowermost position, only the support portion 6a of the second rocker arm 6 is relatively downward with respect to the support portion 5a of the first rocker arm 5. Go and stop there.

According to such a stop position of the rocker shaft 7,
Since only the support portion 6a of the second rocker arm 6 moves relatively downward with respect to the support portion 5a of the first rocker arm 5, as shown in FIG. In addition, a gap t is formed between the peripheral surface of the high-speed rotation cam 3 formed on the camshaft 4 and the second rocker arm 6, so that the high-speed rotation cam 3 and the second The contact of the rocker arm 6 with the peripheral surface is released, and the high-speed rotation cam 3 rotates in an idle swing state.

It goes without saying that the outer diameter and the amount of eccentricity of the eccentric bush 11 are set so as to form the above-mentioned gap t.

On the other hand, according to the stop position of the rocker shaft 7 shown in FIG. 5, the first rocker arm 5 is constantly pushed upward about the axis of the rocker shaft 7 by the urging force of the valve spring 14, so that The first rocker arm 5 and the peripheral surface of the low-speed rotation cam 2 are always in contact with each other. Therefore, when the camshaft 4 rotates at the stop position of the rocker shaft 7 shown in FIG. The stems 8 and 9 are the cams 2 for low-speed rotation.
Therefore, the valve opens and closes the combustion chamber at a low speed rotation while securing a suitable valve opening / closing timing and a valve lift amount.

On the other hand, the rocker shaft 7 is rotated by a predetermined angle from the position shown in FIG. 5 in a medium / high-speed range of the four-cycle engine by a rotating means such as a servo motor (not shown) described above, and the same parts as in FIG. When stopped at the position shown in FIG. 8 indicated by the same reference numeral, since the surface 11b of the eccentric bush 11 farthest from the axis of the rocker shaft 7 is located at the uppermost end, only the support portion 6a of the second rocker arm 6 is provided. Rises to a position equivalent to the support portion 5a of the first rocker arm 5 and stops there.

According to such a stop position of the rocker shaft 7,
Since only the supporting portion 6a of the second rocker arm 6 moves relatively upward with respect to the supporting portion 5a of the first rocker arm 5, as shown in FIG. To
The peripheral surface of the high-speed rotation cam 3 formed on the camshaft 4 comes into contact with the second rocker arm 6.

On the other hand, when the peripheral surface of the high-speed rotation cam 3 formed on the camshaft 4 shown in FIG. 8 comes into contact with the second rocker arm 6, the high-speed rotation cam 3 becomes the lower-speed rotation cam. The second rocker arm 6 is formed so that the cam lift is larger than that of the second rocker arm 6.
6b is disposed so as to engage with the upper end surface 5d of the first rocker arm 5, so that when the camshaft 4 rotates at the stop position of the rocker shaft 7 shown in FIG. The cam 2 rotates in an idling state and the first rocker arm 5 is operated by being pushed by the tip 6b of the second rocker arm 6, so that the valve stems 8, 9 of the valves for opening and closing the combustion chamber are rotated at the high speed. The valve moves up and down following the cam profile of the cam 3, so that the valve opens and closes the combustion chamber at a high speed while securing a suitable valve opening / closing timing and valve lift.

According to the cam switching device 1 described above, the cam profile of the cam that operates the valve according to each rotation range of the engine can be selected from two types of cams, one for high-speed rotation and the other for low-speed rotation. Opening and closing timing and valve lift can be changed to optimal values according to the engine speed range.
The output of the four-stroke engine can be improved within a wide rotation speed range up to a high rotation speed range.

[Problems to be solved by the invention]

When the above-described cam switching device 1 is applied to a four-stroke parallel four-cylinder engine, as shown in the conceptual plan view of FIG. 10, one rocker shaft 7 is provided on each of the intake and exhaust sides of the cylinder head. The first and second rocker arms 5 and 6 of the cam switching device 1 that are operated by the high-speed rotation and low-speed rotation cams 2 and 3 are supported by the number corresponding to the number of cylinders. Then, the rocker shafts 7 provided one by one on the suction / exhaust side are independently rotated by independent drive devices (for example, servo motors and wires) (not shown). It is conceivable to perform the operation at once for each of the intake and exhaust sides.

Although not shown in FIG. 10, one cam shaft 4 for driving all the rocker arms on the intake side is provided above the rocker arms 5 and 6 on the intake side, and each rocker arm on the exhaust side. Needless to say, another camshaft 4 for driving all the exhaust-side rocker arms is also provided above the arms 5 and 6, respectively.

Since the valves on the intake and exhaust sides have different opening / closing timings, it is not possible to simultaneously switch all of the plurality of cam switching devices 1 disposed on both the intake and exhaust sides of the cylinder head. Therefore, each of the rocker shafts 7 disposed on the intake / exhaust side independently rotates the pair of rocker shafts 7 located on the intake / exhaust side using independent driving devices having different operation timings. I have to move.

On the other hand, in a parallel four-cylinder engine, the crank rotation angle between the # 1 and # 2 cylinders is usually 180 °, and the # 3 and # 4
The crank rotation angle between the cylinders is also 180 °. Therefore, in order to operate a plurality of rocker arms respectively disposed on the intake / exhaust sides, a camshaft 4 disposed above the rocker arm is provided with a camshaft 4 according to a phase difference of a crank rotation angle between the cylinders. A plurality of cams (eight high-speed and four low-speed cams on a single camshaft, each of which is eight in a parallel four-cylinder system) for driving each rocker arm are formed. For example, taking the high-speed rotation cam 3 as an example,
As shown in FIG. 11 which is an enlarged side view as viewed from A in FIG. 10, the high-speed cam 3 corresponds to the operation timing of the rocker arm of each cylinder.
Are formed on the same camshaft 4 out of phase by 180 °. Note that in FIG.
(# 1) is a high-speed cam 3 for operating the rocker arm of the cam switching device 1 provided in the # 1 cylinder.
(# 2) is a high-speed cam 3 for operating the rocker arm of the cam switching device 1 provided in the # 2 cylinder,
(# 3) is a high-speed cam 3 for operating the rocker arm of the cam switching device 1 provided in the # 3 cylinder.
(# 4) shows the high-speed cams 3 for operating the rocker arm of the cam switching device 1 provided in the # 4 cylinder.

However, as shown in FIG. 11, each of the cams 3 (# 1), 3 (# 2), 3 (#
3) The rocker shaft 7 is rotated at a predetermined medium / high rotation speed range with respect to 3 (# 4), and the eccentric large diameter portion is rotated.
If the plurality of second rocker arms 6 arranged for each cylinder are to be simultaneously moved upward according to 10 (FIG. 8), the second rocker arm 6 corresponding to any one of the cylinders will It is conceivable that the contact with the cam profile at the time of the valve lift of No. 3 may occur.

When the second rocker arm 6 comes into contact with the cam profile during the valve lift of the high-speed cam 3 as described above, the rocker shaft 7 is pressed by the pressing force of the cam at that time.
A large load is applied to the rotation operation of the rocker shaft 7, which makes it impossible not only to ensure smooth rotation of the rocker shaft 7 at the time of cam switching, but also due to the pressing force of the cam at that time, the rocker arm 6 and the rocker shaft 7
To the rocker arm 6 and the rocker shaft 7 in extreme cases.

The present invention has been made in view of the above circumstances, and in a valve train of a four-cycle multi-cylinder engine equipped with a cam switching device that switches a cam to be used by rotation of a rocker shaft, when switching a cam to be used, stress is applied to the rocker shaft. The present invention provides a valve train for a four-cycle multi-cylinder engine in which the rotation thereof is allowed without giving a cam switch and the four-cycle multi-cylinder engine equipped with the cam switching device is made compact.

[Means for solving the problem]

In order to solve the above-mentioned problem, in the present invention, a rocker shaft is divided into two for each intake and exhaust with a center of a cylinder head as a mirror, and a rocker arm supported by each of the rocker shafts by rotating a cam shaft. A four-cycle multi-cylinder engine in which intake and exhaust valves are operated at predetermined timings via a camshaft, and a low-speed rotation cam and a high-speed rotation cam are arranged on at least one of the intake and exhaust side camshafts. And a cam switching device for continuously switching between the low-speed rotation cam and the high-speed rotation cam by rotating each rocker shaft.
In the valve operating device for a cycle multi-cylinder engine, at least a pair of pinions are formed so as to face each central end of each of the divided rocker shafts at the center of the cylinder head, and a rack meshing with the pinions is independently provided for each pinion. The low-speed rotation cam and the high-speed rotation cam by independently rotating the divided rocker shafts at predetermined timings via racks independently provided for the respective pinions. Is switched continuously.

〔Example〕

Hereinafter, an embodiment of a valve train of a four-cycle multi-cylinder engine according to the present invention will be described in detail.

FIG. 1 is a conceptual plan view showing a cylinder head of a four-cycle parallel four-cylinder engine equipped with a valve train according to the present invention, and the same parts as those in FIGS. 5 to 11 are denoted by the same reference numerals.

In the cylinder head of this four-cycle parallel four-cylinder engine, the cams that can switch the type of cam to be used by rotating the rocker shaft on the intake / exhaust sides of the # 1, # 2, # 3, and # 4 cylinders. The switching devices 1 are provided at eight locations (four at the intake side and four at the exhaust side) corresponding to the number of cylinders.

The rocker shafts that operate the respective cam switching devices 1 include a first rocker shaft 21 that operates only the two cam switching devices 1 disposed on the intake side of the # 1 and # 2 cylinders, and # 1 and #. A second rocker shaft 22 that operates only two cam switching devices 1 disposed on the exhaust side of the two cylinders, and two cam switching devices 1 disposed on the intake side of the # 3 and # 4 cylinders. And a fourth rocker shaft 24 that operates only the two cam switching devices 1 disposed on the exhaust side of the # 3 and # 4 cylinders. I have.

Therefore, the first to fourth rocker shafts 21, 22,
The first and fourth rocker shafts 21, 22, 23, 24 can rotate independently of each other,
Is rotated, each of the two cam switching devices 1 disposed on each of the suction and exhaust sides of each cylinder is operated independently.

The first to fourth rocker shafts 2 described above are used.
Needless to say, 1, 22, 23 and 24 have the same function as the rocker shaft 7 shown in FIG.

On the other hand, in the above-described four-cycle parallel four-cylinder engine, #
The # 1 and # 2 cylinders have crank rotation angles 180 ° out of phase, and the # 3 and # 4 cylinders
Since the crank rotation angle is 180 ° out of phase, for example, as shown in FIG. 3 shown in an enlarged side view shown in FIG. 1B, it is arranged on the intake side of cylinders # 1 and # 2. A pair of high-speed rotation cams 3 formed on the provided camshaft 4
In the case of (# 1) and 3 (# 2) as an example, there is no lift between the high-speed rotation cams 3 (# 1) and 3 (# 2) on their cam profiles, that is, both cams 3 (# 1), 3
In both (# 2), there is a section L where the second rocker arm 6 rotates without load.

Therefore, in a predetermined middle / high rotation speed range, the first rocker shaft as shown in FIG. 4 is set within the period in which the high-speed rotation cams 3 (# 1) and 3 (# 2) pass through this section L. Rotate 21 and # 1, # by its eccentric large diameter part 10
When the two second rocker arms 6 (FIG. 1) disposed on the intake side of the two cylinders are simultaneously moved upward, the respective rocker arms 6 become the high-speed rotation cams 3 (# 1), 3 ( #
2) The first rocker shaft 21 rotates without being stressed since it rises without receiving a load from
Therefore, the switching operation of the pair of cam switching devices 1 on the intake side by the rotation of the first rocker shaft 21 is smoothly performed.

The timing at which the section L in which the pair of high-speed rotation cams 3 rotates in a no-load state with respect to the second rocker shaft 6 constituting the above-described cam switching device 1 is formed as follows.
Although the cylinders # 1 and # 2 are different from the cylinders # 3 and # 4, and the intake and exhaust sides are different from each other, the rocker shafts for switching the cam switching device 1 as shown in FIG. Since the exhaust side and the # 1 and # 2 cylinders and the # 3 and # 4 cylinders are separately arranged, the separated first to fourth rocker shafts 21, 22, and 23 are separated. , 24 with a pair of high-speed rotating cams 3 formed on corresponding camshafts at different timings.
If they are rotated at a time forming a section L in which the high-speed cam rotates with no load applied to the second rocker shaft 6, the cam switching device disposed in the cylinder head of the four-stroke parallel four-cylinder engine 1st switching operation 1
In addition, the rotation operations of the fourth to fourth rocker shafts 21, 22, 23, and 24 are all performed smoothly.

In addition, each of the above-described first to fourth rocker shafts 2
In order to rotate 1, 22, 23, and 24, the cylinders of the first to fourth rocker shafts 21, 22, 23, and 24, as shown in FIG. Racks 30, 31, 32, and 33 that integrally form pinions 21a, 22a, 23a, and 24a at the center end of the head, and that are independently driven.
The racks 30, 31, 32, and 33 are engaged with the pinions 21a, 22a, 23a, and 24a respectively. 2
The rocker shaft 6 may be rotated at a time when a section L that rotates with no load is formed.

In each of the above embodiments, the cam switching device 1 according to the present invention is applied to a so-called four-valve engine having two valves on each of the intake and exhaust sides, but the present invention is limited to the above embodiments. Without being sucked
The valve train according to the present invention may be applied to a so-called two-valve four-cycle parallel four-cylinder engine having one valve on each exhaust side.

Further, in the above embodiment, the eccentric large diameter portion 10 is constituted by the eccentric bush 11 and the pin 12, but the present invention is not limited to the above embodiment, and the eccentric large diameter portion 10 is formed integrally with the rocker shaft 7. You may.

〔The invention's effect〕

As described above, according to the valve train of the present invention,
The rocker shaft for operating the cam switching device provided on the cylinder head of the 4-cycle multi-cylinder engine is divided into two for each intake and exhaust with the center of the cylinder head as a boundary, and the divided rocker shaft is located at the center of each cylinder head. A pair of pinions are formed facing each other at the ends, racks meshing with the pinions are independently provided for each pinion, and the divided rocker shafts are independently provided for each pinion. The cam for low-speed rotation and the cam for high-speed rotation are continuously switched by independently rotating at predetermined timings through the racks.
When a pair of high-speed rotation cams arranged for each suction / exhaust side rotates with no load on the rocker arm, the rocker shaft can be rotated to switch the cam of the cam switching device. When operating the cam switching device arranged in the cycle multi-cylinder engine, the rotation of the rocker shaft can be allowed without applying stress to the rocker shaft, and the cam switching operation can be performed smoothly. Since the pinion and the rack for driving the rocker shaft disposed in each of the above are arranged so as to be concentrated in the center of the cylinder head, a four-cycle multi-cylinder engine having a cam switching device can be provided compactly.

[Brief description of the drawings]

1 and 2 are conceptual plan views of a cylinder head of a four-stroke parallel four-cylinder engine equipped with a valve train according to the present invention, and FIGS. 3 and 4 are conceptual enlarged side views of FIG. FIG. 5 is a conceptual perspective view of a cam switching device applied to the valve train of the present invention, FIG. 6 is a fragmentary plan view of FIG. 5, and FIG. FIG. 8, FIG. 8 is a conceptual perspective view showing the operation of the cam switching device, FIG. 9 is a sectional side view of a main part of FIG. 8, FIG. 10 is a conceptual plan view of a cylinder head of a four-cycle parallel four-cylinder engine. FIG. 11 is a conceptual enlarged side view as viewed from A in FIG. DESCRIPTION OF SYMBOLS 1 ... Cam switching device, 2 ... Low-speed rotation cam, 3 ... High-speed rotation cam, 4 ... Cam shaft, 5, 6 ... Rocker arm, 21, 22, 23, 24 ... Rocker shaft, 21
a, 22a, 23a, 24a ... pinion, 30, 31, 32, 33 ... rack,

Claims (1)

(57) [Claims] A rocker shaft is divided into two for each intake and exhaust with the center of the cylinder head as a mirror, and a camshaft is rotated to operate intake and exhaust valves via rocker arms supported by the rocker shafts. A four-cycle multi-cylinder engine operated at a predetermined timing, wherein a low-speed rotation cam and a high-speed rotation cam are juxtaposed on at least one of the intake and exhaust camshafts, and each of the lockers In a valve operating device for a four-cycle multi-cylinder engine having a cam switching device for continuously switching between the low-speed rotation cam and the high-speed rotation cam by rotating a shaft, the divided rocker shaft has a center side of each cylinder head. At least a pair of pinions are formed at the ends so as to face each other, and a rack meshing with the pinions is attached to each pinion. The low-speed rotation cam and the high-speed rotation are performed by independently rotating the divided rocker shafts at predetermined timings via racks independently disposed for the respective pinions. A valve train for a four-stroke multi-cylinder engine, wherein the cams are continuously switched.