JP2663556B2 - 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]

In general, in a four-stroke engine mounted on a vehicle such as an automobile or a motorcycle, an intake / exhaust valve is disposed above a combustion chamber, and a valve train includes a camshaft for operating the intake / exhaust valve. When the camshaft is rotated by the engine power, 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. The output characteristic of the engine is generally limited by the cam profile of the cam that operates the valve, and becomes an output characteristic having a peak value in a specific engine speed range.
Higher output could not be obtained in a wide rotation speed range from a low rotation speed range to a middle and high rotation speed range.

Then, in view of the above-mentioned circumstances, the applicant of the present application switches the cam to be used by rotating the rocker shaft, thereby improving the output within a wide rotation speed range from a low rotation speed range to a middle / high rotation speed range. Proposed a cam switching device for a four-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 is provided at a total of two locations, one cylinder at each of the intake valve side and the exhaust valve side with respect to 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 adjacent to each other.
And first and second rocker arms 5, 6 disposed below the camshaft 4, and bearings (not shown) which are inserted into the support portions 5a, 6a of the rocker arms 5, 6, respectively. And a rocker shaft 7 which is rotatably supported by a portion.

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, it is a cam having a cam profile suitable for improving the output of the engine at a so-called medium / high speed rotation (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 composed of an eccentric bush 11 inserted into the rocker shaft 7 and a pin 12 for fixing the eccentric bush 11 to the rocker shaft 7.
In addition, as shown in FIG.
The eccentric bush 11 and the rocker shaft 7 have strictly controlled dimensional tolerances, and are formed with holes 11a and 7a having a diameter slightly smaller than the diameter of the pin 12.
The eccentric bush 11 and the rocker shaft 7 are fixed to each other by driving the pin 12 into a and 7a.

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 by a rocker shaft rotating device (not shown) such as a servomotor and a wire, and stopped at the position shown in FIG. The surface of the eccentric bush 11 farthest from the axis
Since 11b is located at the lowermost end, 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, and stops 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.
The valve moves up and down following the cam profile, so that the valve opens and closes the combustion chamber while rotating at a low speed and securing a suitable valve timing and 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 rotation range of a four-cycle engine by a rocker shaft rotating device such as a servo motor (not shown) as shown in FIG. When the same part is stopped at the position shown in FIG.
Eccentric bush 11 farthest from the axis
Since the surface 11b of the second rocker arm 6 is located at the uppermost end, only the support portion 6a of the second rocker arm 6 rises to a position equivalent to the support portion 5a of the first rocker arm 5 and stops there.

Note that the rotation direction of the rocker shaft 7 when switching the cam may be either clockwise or counterclockwise.

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. Accordingly, 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.

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, the rocker shafts 7 are arranged one by one on 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 driving means (for example, a servo motor and a wire) (not shown). It is conceivable to perform the operation at one time for each of the intake and exhaust sides.

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
Since the crank rotation angle between the cylinders is also 180 °, in order to operate the plurality of rocker arms 5, 6 disposed on the intake and exhaust sides, respectively, the rocker arms 5,
A plurality of camshafts 4 that drive each rocker arm in accordance with the phase difference of the crank rotation angle between the cylinders (a single camshaft and a low-speed (8 cams for each 4 cams). For example, taking the high-speed rotation cam 3 as an example, FIG.
As shown in FIG. 11, a total of four high-speed cams 3 are formed on the same camshaft 4 with a phase shift of 180 ° each corresponding to the operation timing of the rocker arm of each cylinder. In addition,
In FIG. 11, reference numeral 3 (# 1) denotes a high-speed cam 3 for operating the rocker arm of the cam switching device 1 provided in the # 1 cylinder, and 3 (# 2) denotes a # 2 cylinder. The high-speed cam 3 for operating the rocker arm of the cam switching device 1 is a high-speed cam 3 for operating the rocker arm of the cam switching device 1 provided in the # 3 cylinder. Reference numeral 3 (# 4) denotes the high-speed cam 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 at the time of valve lift of the high-speed cam 3 in this manner, a large load is applied to the rotation of the rocker shaft 7 by the pressing force of the cam at that time. Not only cannot smooth rotation of the rocker shaft 7 be ensured at the time of switching, but also a large stress is applied to the rocker arm 6 and the rocker shaft 7 by the pressing force of the cam at that time. In this case, the rocker shaft 7 may be damaged.

In view of the above-mentioned circumstances, the applicant of the present application has further considered that in the valve train of a four-stroke parallel four-cylinder engine equipped with a cam switching device, when switching the cam to be used, the rotation of the rocker shaft is performed without applying stress to the rocker shaft. A valve train was proposed to allow for

FIG. 12 is a conceptual plan view showing a cylinder head of a 4-cycle parallel 4-cylinder engine equipped with the above-described valve train,
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. Eight switching devices 1 are provided corresponding to the number of cylinders. A rocker shaft for operating the cam switching device 1 includes a first rocker shaft 21 for operating only two cam switching devices 1 disposed on the intake side of the # 1 and # 2 cylinders, and # 1 and # 2. Only the second rocker shaft 22 that operates only the two cam switching devices 1 disposed on the exhaust side of the cylinder, and only the 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. Has been established.

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, the switching of the cams of the two cam switching devices 1 provided on each of the intake and exhaust sides of each cylinder is independently operated.

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 angles are 180 ° out of phase, they are arranged on the intake sides of cylinders # 1 and # 2, for example, as shown in FIG. 13 shown in an enlarged side view shown in FIG. A pair of high-speed rotation cams 3 formed on a camshaft 4 provided
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, during a period in which the high-speed rotation cams 3 (# 1) and 3 (# 2) pass through this section L in a predetermined middle / high rotation speed range, as shown in FIG. Rotate 21 and # 1, # by its eccentric large diameter part 10
When the two second rocker arms 6 (FIG. 12) 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.
The cylinders # 1 and # 2 are different from the cylinders # 3 and # 4, and the intake and exhaust sides are also different.
As shown in FIG. 12, the rocker shafts for switching the cam switching device 1 are separately disposed on the intake / exhaust side and further on the # 1, # 2 cylinders and # 3, # 4 cylinders. The separated first to fourth rocker shafts 21, 22, 23, and 24 are separated from each other by a pair of high-speed rotation cams 3 formed on corresponding camshafts at different timings with respect to the second rocker shaft 6. If the cam is rotated at the time of forming a section L in which the high-speed cam rotates under load, the first to fourth switching operations of the cam switching device 1 provided in the cylinder head of the 4-cycle parallel 4-cylinder engine are performed. The rotation operation of each of the rocker shafts 21, 22, 23, 24 is smoothly performed.

[Problems to be solved by the invention]

By the way, as specific rocker shaft rotation devices for driving the first to fourth rocker shafts 21, 22, 23, 24 of the above-described valve train, the first to fourth rocker shafts 21, 22, Pulleys are fixed to the outer ends of the cylinder heads 23 and 24, and the wires wound around the pulleys are operated at predetermined timing by four independent servo motors, whereby each rocker shaft 21, 22, It is conceivable that the cams are switched by rotating the 23 and 24 independently, but according to the rocker shaft rotating device using such a servo motor, four servo motors are used and each of the servo motors is used. Since an electronic control unit is also required, the structure becomes extremely complicated and the manufacturing cost increases significantly. Since the space for unexpected needs to be secured in the cylinder head the cylinder head is large, there is a drawback that it is impossible to produce a 4-cycle multi-cylinder engine having a cam switching device 1 compact.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a valve train of a four-cycle multi-cylinder engine which has a simple structure and is compact in size.

[Means for solving the problem]

In order to solve the above-mentioned problem, according to the present invention, a cam chain chamber is provided in the center of a cylinder head, and a rocker shaft is divided into two parts by the cam chain chamber to be independent for each intake and exhaust, and the cam shaft is rotated. A four-cycle multi-cylinder engine that operates intake / exhaust valves at a predetermined timing through rocker arms supported by the respective rocker shafts, wherein the camshaft on at least one of the intake / exhaust sides rotates at a low speed. Of 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 the respective rocker shafts by arranging a rotation cam and a high-speed rotation cam in parallel. In the valve device, at least one pair of pinions is opposed to the cam chain chamber side end of each of the divided rocker shafts. A rocker shaft rotating device, in which a hydraulic plunger formed with a rack meshing with the pinion is independently provided for each pinion, is provided in the cam chain chamber, and the rocker shaft rotating device Each of the divided rocker shafts is independently rotated by the hydraulic pressure supplied to each of the hydraulic plungers via the, and the low-speed rotation cam and the high-speed rotation cam are continuously switched.

〔Example〕

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

FIG. 2 is a conceptual plan view of a cylinder head 30 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 14 are indicated by the same reference numerals.

The type of cam used in the cylinder head 30 of this four-cycle parallel four-cylinder engine is switched to the intake and exhaust sides of the # 1, # 2, # 3, and # 4 cylinders by rotating the rocker shaft. A total of eight cam switching devices 1 (4 on the intake side, 4 on the exhaust side) corresponding to the number of cylinders
Locations).

A cam chain chamber 31 is formed at an intermediate portion of the cylinder head 30, and a cam chain (not shown) is wound around a pair of cam sprockets 32 and 33 provided facing the cam chain chamber 31. Turning. The cam sprockets 32 and 33 are fixed to the central portions of the camshafts 4 and 4 disposed on the intake and exhaust sides, respectively.

Therefore, when the engine is started, a pair of camshafts 4 and 4 rotate via cam sprockets 32 and 33 by a cam chain (not shown).

On the other hand, as shown in FIG. 1 showing the state where the camshafts 4 and 4 have been removed from FIG. 2, the cylinder head 30 of this four-cycle parallel four-cylinder engine has # 1 and #
A first rocker shaft 21 that operates only the cam switching devices 1 disposed at two locations on the intake and exhaust sides of the # 2, # 3, and # 4 cylinders and on the intake side of the # 1, # 2 cylinders; Only the second rocker shaft 22 that operates only the two cam switching devices 1 disposed on the exhaust side of the # 2 cylinder, and only the cam switching devices 1 disposed on two intake sides of the # 3 and # 4 cylinders And a fourth rocker shaft 24 that operates only the cam switching device 1 disposed at two locations on the exhaust side of the # 3 and # 4 cylinders, respectively, and is independent of each other. It is configured to be able to rotate.

Therefore, the first to fourth rocker shafts 21, 22,
Each of the cam switching devices 1 provided at two locations on each of the suction and exhaust sides of each cylinder by independent rotation of 23 and 24.
Will operate independently.

On the other hand, the above-described first to fourth rocker shafts 2
A rocker shaft rotating device (hereinafter, simply referred to as a rotating device) 40 for independently rotating 1, 22, 23, and 24 is provided at the center of the cam chain chamber 31 of the cylinder head 30 conventionally treated as a dead space. As shown in FIG. 3 which is an enlarged cross-sectional view of a main part of FIG. 1, the rotating device 40 includes first to fourth rocker shafts 21, 22, 2
Pinions 21a, 22a, 23a, 24a integrally formed opposite to each other at the cam chain chamber side ends of 3, 24, and racks 41a, 4 meshing with the corresponding pinions 21a, 22a, 23a, 24a.
2a, 43a and 44a are constituted by four hydraulic plungers 41, 42, 43 and 44 integrally formed at the tip.

These hydraulic plungers 41, 42, 43, 44 are housed and arranged in a casing 50 integrally formed.

On the other hand, a pressure chamber for applying pressure to each of the pistons 41b, 42b, 43b, 44b constituting each of the hydraulic plungers 41, 42, 43, 44
One inlet port 46 (FIGS. 1 and 3)
Hydraulic oil is supplied through the hydraulic pressure plungers 41, 42, 43, and 44, respectively.
b, 42b, 43b, 44b with each hydraulic plunger 41, 42, 43, 44
Are pressed with the same pressure against the resilience of the return spring 47 disposed in the front end of the spring.

Further, in the embodiment, the working oil uses a lubricating oil supplied from an oil pump (not shown) which pressurizes the lubricating oil to each sliding portion of the engine, and the lubricating oil is supplied using pipe means (not shown). Supply into inlet port 46. The supply structure of the hydraulic oil is, for example, the cylinder head shown in FIG.
An oil pipe (not shown) for supplying lubricating oil, which is provided on a cylinder head cover (not shown) that covers the 30, is branched, and the downstream end of the branched oil pipe is communicated with the inlet port 46. The oil pump is usually driven by the power of the engine, and its discharge pressure increases as the engine speed increases.

Next, the operation of the rocker shaft rotation device 40 will be described, and the configuration will be described in more detail.

While the four-cycle parallel four-cylinder engine is stopped, the oil pump (not shown) does not operate, so that no hydraulic oil is supplied into the pressure chamber 45 of the rotating device 40.
The pistons 41b, 42b, 43b, 44b of 1, 42, 43, 44 are stopped at the initial positions shown in FIG.

Each hydraulic plunger 41, 42, 43, 44 shown in FIG.
In the initial position, the first to fourth rocker shafts 21, 22, 23, 24 shown in FIG. 1 are connected to the second rocker arm 6 of the cam switching device 1 as shown in FIG. It stops at a position moved downward relative to the rocker arm 5.

When the engine is started and the oil pump is driven, the pressure of the hydraulic oil supplied into the pressure chamber 45 of the rotating device 40 shown in FIG. 3 increases according to the engine speed. -Up to the high rotation speed range, the biasing force of the return spring 47 is superior, and therefore each hydraulic plunger 41, 42,
Since each rack 41a, 42a, 43a, 44a of 43, 44 does not move, and therefore each rocker shaft 21, 22, 23, 24 does not rotate, the second rocker arm 6 of the cam switching device 1 as shown in FIG. Is moved upward by the eccentric large-diameter portion 10 and the used cam is not switched to the high-speed rotation cam 3, but is maintained in the state shown in FIG. 5, that is, the state in which the low-speed rotation cam 2 operates the valve.

The spring constant of the above-described return spring 47 is
Urging force on the piston by the return spring 47,
The setting is made so that the hydraulic oil discharged from the oil pump at a predetermined engine speed (a predetermined rotation speed in a middle / high rotation speed range) set to switch the cam to be used is substantially equal to the pressure applied to the piston.

On the other hand, when the engine reaches a predetermined medium / high rotation speed or more, the hydraulic pump of the oil pump applied to the pistons 41b, 42b, 43b, 44b of the hydraulic plungers 41, 42, 43, 44 shown in FIG. The pressure is larger than the urging force of the return spring 47 on each of the pistons 41b, 42b, 43b, and 44b.

Therefore, the rack 41 of each hydraulic plunger 41, 42, 43, 44
a, 42a and 43a move in the directions shown by the arrows in FIG. 3 to switch the cam to be used from the low-speed rotation cam 2 to the high-speed rotation cam 3, and move through the respective pinions 21a, 22a, 23a and 24a. First to fourth rocker shafts 21, 22, 23, 24
Try to rotate each. However, when the rotation is performed at the time of the cam lift of the high-speed rotation cam 3 shown in FIG. 11, the rotation of the high-speed rotation cam 3 is regulated by the load applied to the second rocker arm 6. Therefore, the low-speed rotation cam 2
Cannot be switched from the cam to the high-speed rotation cam 3.

However, the camshaft 4 rotates further from that position,
As shown in FIG. 13, when a pair of high-speed rotation cams 3 formed on the camshaft 4 reach a section L where the second rocker shaft 6 rotates with no load, a pair of high-speed rotation cams is formed. 3, the load on the second rocker arm 6 is eliminated, so that the rotation regulation of the rocker shaft is released,
Therefore, as shown in FIG. 4, a hydraulic plunger (in FIG. 4, the rocker shaft 21 is rotated) in order to rotate the corresponding rocker shafts in the order in which the pair of high-speed rotation cams 3 reaches the section L. Hydraulic plunger 41
Only the rack 41) moves in the direction of the arrow against the urging force of the return spring 47, and rotates the rocker shaft to smoothly switch the cam to be used to the high-speed rotation cam.

Although the operation timing is different due to the same operation, the rack of the hydraulic plunger rotates the corresponding rocker shaft one after another in the order in which the pair of high-speed rotation cams 3 reaches the section L, and the used cam is changed from the low-speed rotation cam 2. The high-speed rotation cams 3 are switched independently and smoothly.

On the other hand, when the engine speed falls from the predetermined middle / high rotation speed or higher to the predetermined middle / high rotation speed or lower, each piston 41 of the hydraulic oil discharged from the oil pump is turned off.
The pressing force applied to b, 42b, 43b, 44b is smaller than the urging force of the return spring 47 on each of the pistons 41b, 42b, 43b, 44b.
The racks 41a, 42a, 43a of 1, 42, 43, 44 are retracted by the urging force of the return spring 47 and return to the initial position shown in FIG. When returning, each rack 41a, 42a, 43
a is a first to a fourth through each pinion 21a, 22a, 23a, 24a
Each of the rocker shafts 21, 22, 23, and 24 is rotated, and the second rocker arm 6 is moved to the first position as shown in FIG.
Is moved relatively downward with respect to the rocker arm 5, so that the cam to be used is switched from the high-speed rotation cam 3 to the low-speed rotation cam 2. When the cam to be used is switched from the high-speed rotation cam 3 to the low-speed rotation cam 2, no load is applied to the racks 41a, 42a, and 43a by the high-speed rotation cam 3 in the retreating direction. It will be done smoothly.

〔The invention's effect〕

As described above, according to the valve train of the present invention,
A rocker shaft for operating a cam switching device provided on a cylinder head of a four-cycle multi-cylinder engine cylinder,
A cam chain chamber formed in the center of the cylinder head is divided into two parts, and a pair of pinions are formed so as to face a cam chain chamber side end of each divided rocker shaft, and a rack meshing with the pinions is formed. A rocker shaft rotating device, in which a hydraulic plunger is provided independently for each pinion, is provided in the cam chain chamber, and each of the hydraulic plungers is divided by the hydraulic pressure supplied to each hydraulic plunger via the rocker shaft rotating device. Since the rocker shaft is independently rotated to continuously switch between the low-speed rotation cam and the high-speed rotation cam, the structure of the rocker shaft rotation device is simplified, and it was conventionally treated as a dead space. Since the rocker shaft rotating device is arranged in the cam chain chamber, the rocker shaft rotating device is installed in the cylinder head. By ensuring a special space for disposing, also it is not necessary to perform special processing, Thus it is out to provide a compact four-cycle multi-cylinder engine having a cam switching device.

Also, since the hydraulic plunger of the rocker shaft rotating device that operates independently is configured to apply hydraulic pressure from one place, the routing structure of the pipe that applies hydraulic pressure is extremely simple,
It can be implemented without making significant changes to the conventional lubricating oil supply structure.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1 and 2 are conceptual plan views showing a cylinder head of a four-cycle parallel four-cylinder engine equipped with a valve train of the present invention, and FIGS. 3 and 4 show the present invention. 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 a main part of FIG. 5, and FIG. 5 is a conceptual perspective view showing the operation of the cam switching device, FIG. 9 is a side sectional view of the essential parts in FIG. 8, and FIG. 10 is a four-cycle parallel four-cylinder engine. Fig. 11 is a conceptual plan view of the cylinder head.
FIG. 12 is a conceptual enlarged side view of FIG. A, FIG. 12 is a conceptual plan view of a cylinder head of a four-cycle parallel four-cylinder engine equipped with four rocker shafts, and FIGS.
It is a conceptual enlarged side view by B view of the figure. 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 ... cylinder head, 31 ... cam chain chamber, 40 ... rocker shaft rotating device, 41, 42, 43, 44 ... hydraulic plunger.

Claims (2)

(57) [Claims] A cam chain chamber is provided at the center of a cylinder head, and a rocker shaft is divided into two parts by the cam chain chamber so as to be independent for each intake and exhaust, and the respective rocker shafts are rotated by rotating a cam shaft. A four-cycle multi-cylinder engine in which intake and exhaust bubbles are actuated at a predetermined timing via a rocker arm pivotally supported by a low-speed rotation cam and a high-speed rotation cam on at least one of the intake and exhaust side camshafts. And a cam switching device that continuously switches between the low-speed rotation cam and the high-speed rotation cam by rotating the rocker shafts.
In the valve train for a cycle multi-cylinder engine, at least a pair of pinions are formed so as to face the cam chain chamber side end of each of the divided rocker shafts, and a hydraulic pressure is formed in which a rack meshing with the pinions is formed. A rocker shaft rotating device in which a plunger is independently arranged for each pinion is provided in the cam chain chamber, and each of the divided by the hydraulic pressure supplied to each of the hydraulic plungers via the rocker shaft rotating device. A valve train for a four-stroke multi-cylinder engine, wherein a rocker shaft is independently rotated to continuously switch between the low-speed rotation cam and the high-speed rotation cam. 2. The valve train of a four-cycle multi-cylinder engine according to claim 1, wherein said rocker shaft rotating device operates each of said hydraulic plungers by hydraulic oil supplied from one place.