JPH11350923A - Engine valve train system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide the engine valve train system that enables stabilization of valve behavior in still higher-speed range, while improving durability thereof, and downsizing of the engine when adopting the cam profile for the intake cam nose and/or the exhaust cam nose. SOLUTION: An engine valve train system comprises cam shafts which adopt for at least one of the exhaust cam profile or the intake com profile which is so designed that: the absolute value of the valve acceleration coefficient y'' near the maximum valve lift becomes smaller than the absolute value of the valve acceleration coefficient y'' within the valve lift range adjacent to the advance side or the retard side, or the radius of curvature near the maximum valve lift is greater than the radius of curvature in a valve lift range adjacent to the advance side and the retard side; and that the constant valocity range wherein the valve velocity becomes maximum and constant falls within at least one of the valve lift increase range (ascending slope) or the valve lift decrease range (descending slope).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a valve train for opening and closing an exhaust valve and an intake valve of a four-stroke engine, and more particularly to improving the durability and operational stability of the engine and reducing the size of the engine. To improve the cam profile that was able to do.

[0002]

2. Description of the Related Art A valve train of a four-stroke engine is for opening and closing an exhaust valve and an intake valve in synchronism with rotation of a crankshaft through a lifter, a rocker arm and the like by an exhaust cam nose and an intake cam nose.

A conventional cam nose of a camshaft is, for example, shown in FIG.
5, a cam valve rotation angle-one-valve lift (head) curve y, a velocity coefficient curve y 'for each cam shaft rotation angle when the cam shaft rotates at a unit angular velocity, and an acceleration coefficient curve y''
Is generally provided with a cam profile having

The cam nose of the camshaft comprises a base circle portion and a lift portion for actually opening and closing the valve, and the base circle portion is set so as to form a circle having a constant radius Ro centered on the cam shaft center. Have been. On the other hand, the lift section gradually increases the valve lift near the opening of the ramp section and the valve opening until the cam starts pushing the valve directly or via the rocker arm, etc., then increases and decreases in a parabolic manner, and closes the valve. The cam profile is set so as to gradually decrease again near the end and after the camshaft rotation angle at which the valve is seated on the valve seat.

[0005] With such a cam profile, the conventional camshaft velocity coefficient curve y '(differentiating the valve lift curve with the camshaft rotation angle as a variable) is used to determine that the camshaft rotates at a unit angular velocity. The value obtained by calculating the velocity in the direction) shows the maximum value on the positive side in the above-mentioned parabolic increase region of the valve lift, reverses from the positive side to the negative side in the maximum lift region, and becomes the negative side in the above-mentioned parabolic decrease region. Indicates the maximum value.

An acceleration coefficient curve y '' (obtained by further differentiating the speed coefficient curve y 'with the camshaft rotation angle)
Indicates the maximum value on the positive side near the parabolic increase start area and the decrease end area of the valve lift, and shows the maximum value on the negative side in the maximum lift area in the area between them, and changes gradually and continuously. .

In the case of the conventional camshaft, as can be seen from the acceleration coefficient curve y '', the acceleration coefficient shows a negative maximum value in the maximum lift range. Therefore, the load acting between the cam nose and the lifter or the rocker arm near the maximum lift is reduced, and when the engine speed is increased, the followability of the two becomes poor, and the limit speed cannot be increased.

The radius of curvature of the cam is expressed by the sum of the equivalent cam lift, the acceleration coefficient, and the radius of the base circle portion in the case of the direct acting type. In the conventional cam profile, the acceleration coefficient near the maximum lift is negative. As can be seen from the maximum value on the side, the radius of curvature near the maximum lift is set small.

The load acting on the cam surface is the inertial mass (valve,
Part of valve spring, rocker arm with rocker arm,
(A valve lifter or the like) and acceleration, and the resilience of the valve spring. On the other hand, since the stress on the cam surface can be considered as contact between the cylinder and the plane, the stress is proportional to the square root of the load acting on the cam surface and inversely proportional to the square root of the radius of curvature of the cam.

In the case of the conventional cam profile, in a low-speed or middle-speed rotation region where the rotation speed of the camshaft is low and the influence of acceleration is small, the stress at the maximum lift portion of the cam surface where the spring force of the valve spring becomes the largest is increased. It shows the maximum value when viewed in the entire profile. When such a conventional cam profile is employed in a valve train of an automobile engine in which low-speed and medium-speed rotations are commonly used, the above-mentioned high stress in the maximum lift portion lowers the durability of the entire valve train. It will be.

Accordingly, the present applicant sets the radius of curvature in the maximum lift region larger than the radius of curvature in the adjacent lift region, thereby reducing the negative side acceleration coefficient in the maximum lift region, thereby reducing the vicinity of the maximum lift. The load acting between the cam nose and the lifter or rocker arm is increased, the followability of both is improved, the limit rotational speed can be increased, and the cam surface stress near the maximum lift is reduced to reduce the overall valve gear. We are developing cam profiles that can improve durability.

[0012]

By the way, it is considered effective to increase the maximum speed of the valve lift in order to increase the maximum lift. On the other hand, the maximum speed of the valve lift has a positive correlation with the length of the arm that pushes the valve.
Therefore, in order to increase the maximum speed, it is necessary to increase the diameter of the lifter in the case of the direct drive type, and it is necessary to increase the length of the slipper in the case of the rocker arm type. For this reason, there is a concern that the cylinder head becomes large, the lifter or the rocker arm becomes large and these become heavy, and the inertia force of the valve train increases.

According to the present invention, when the cam profile according to the above development is applied to one or both of an intake cam nose and an exhaust cam nose, the behavior of the valve in a high-speed rotation region can be further stabilized and the durability is improved. It is an object of the present invention to provide a valve train for an engine, which can further reduce the size of the engine.

[0014]

According to the first aspect of the present invention, the absolute value of the acceleration coefficient near the maximum valve lift is smaller than the absolute value of the acceleration coefficient in the valve lift regions adjacent to the advance side and the retard side. Or a section in which the radius of curvature in the vicinity of the maximum valve lift is larger than the radius of curvature in the valve lift areas adjacent to the advance side and the retard side, and in which the valve lift increases (up section), A camshaft having at least one of an exhaust cam profile and an intake cam profile is provided in at least one of the decreasing sections (downward sections) so as to have a constant velocity section in which the valve lift speed is maximum and constant. It is characterized by:

According to a second aspect of the present invention, in the first aspect, the ascending section and the descending section have a constant velocity section, and the ascending section,
When the lengths of the constant velocity sections in the down section are φup and φdn, a camshaft having at least one of an exhaust cam profile and an intake cam profile set so that φup> φdn is provided.

According to a third aspect of the present invention, when the maximum acceleration values in the ascending section and the descending section are αup and αdn, the exhaust cam profile and the intake cam profile are set so that αup> αdn. A camshaft having at least one is provided.

According to a fourth aspect of the present invention, in the third aspect, the positive acceleration section length of the ascending section and the descending section is set to θ0up, θ0dn.
In this case, a camshaft having at least one of an exhaust cam profile and an intake cam profile set so that θ0up <θ0dn is provided.

According to a fifth aspect of the present invention, in the third aspect, when the section lengths of the ascending section and the descending section are θ1up and θ1dn, the exhaust cam profile and the intake cam profile are set so that θ1up <θ1dn. A camshaft having at least one is provided.

According to a sixth aspect of the present invention, in the fifth aspect, the positive acceleration section lengths of the ascending section and the descending section are set to θ0up, θ0dn.
In this case, a camshaft having at least one of an exhaust cam profile and an intake cam profile set so that θ0up <θ0dn is provided.

[0020]

According to the first aspect of the present invention, the absolute value of the acceleration coefficient near the maximum valve lift is made smaller than the absolute value of the acceleration coefficient in the valve lift regions adjacent to the advance side and the retard side. Or the radius of curvature near the maximum valve lift is larger than the radius of curvature in the valve lift area adjacent to the advance side and the retard side, so the action between the cam nose and the lifter or rocker arm near the maximum valve lift Therefore, it is possible to prevent the following performance from decreasing when the engine speed is increased.

Further, the radius of curvature near the maximum valve lift is made larger than the radius of curvature in the valve lift areas adjacent to the advance side and the retard side, so that the radius of curvature near the maximum valve lift can be prevented from decreasing. An increase in surface stress can be prevented. That is, since the stress on the cam surface is inversely proportional to the square root of the radius of curvature, even if the load acting between the cam nose and the lifter or the rocker arm does not decrease or rather increases, it is possible to prevent the increase in the stress on the cam surface, and to operate the valve. A decrease in the durability of the device can be prevented.

According to the first aspect of the present invention, the ascending section,
Since a constant speed section in which the valve speed is constant at the maximum speed is provided in at least one of the descending sections, the maximum speed section becomes longer without increasing the lifter diameter, and the maximum lift can be increased, and the lifter diameter can be increased. Therefore, it is not necessary to increase the length of the rocker arm, and it is possible to avoid an increase in the size of the engine and an increase in the inertia force of the valve operating diameter.

Here, based on FIG. 12, by providing a constant speed section where the valve speed becomes constant at the maximum speed, the maximum speed section becomes longer without increasing the lifter diameter, and the maximum lift can be increased. Will be described in more detail.

In FIG. 13, the base radius of the cam nose is Ro, the coordinates of the contact point Q of the cam nose with the lifter are (Xo, Yo), and the substantial radius of the lifter is PQ, y ^*.
Is the valve lift, In ΔORXo, OR = Xo cos θ ΔQSXo, RP = SXo = Yosin θ From this, OP = Xo cos θ + Yosin θ (1) When both sides are differentiated by θ, dy ^* / dθ = −Xo sin θ + Yo cos θ (2) Since the profile of the cam is obtained as the self-entangling line of the straight line PQ, the above equations (1) and (2) are simultaneously used to eliminate θ.
If both sides of equation 2 are squared and added, then (y ^* + Ro) ² + (dy ^* / dθ) ² = (Xocos θ + Yosin θ) ² + (− Xo sin θ + Yocos θ) ² = Xo ² + Yo ^2. (3) From formula (3), (dy ^* / dθ) ² = (Xo ² + Yo ² ) − (y ^* + Ro) ² (4) where (y ^* + Ro) ² = OP ² , and Since Xo ² + Yo ² = OQ ² , from formula (4), (dy ^* / dθ) ² = (Xo ² + Yo ² ) − (y ^* + Ro) ² = OQ ² −OP ² = PQ ^{2, that} is, PQ = dy ^* / dθ = dY / dQ. Note that Y is a valve lift with respect to the crankshaft rotation angle Q, and Y = ∫vdQ. In the present invention, since the exhaust cam profile and the intake cam profile are set so as to have a constant velocity section, the substantial radius PQ of the lifter is set.
, The valve lift Y can be increased, that is, the maximum lift can be increased without increasing the lifter diameter, and the engine performance can be improved while avoiding an increase in the size of the engine.

Further, it is considered effective to accurately change the behavior of the valve in the high-speed rotation range of the engine by reducing the change in the acceleration in the descending section where the valve Litoff decreases. Since the acceleration is proportional to the inertial force, if the acceleration changes suddenly, the inertial force also changes suddenly, causing the camshaft and the valve shaft to vibrate, and the valve spring surging occurs. Behavior becomes unstable.
Also, a sudden change in the acceleration at the time of sitting causes a bounce phenomenon which causes damage to the valve.

Therefore, according to the invention of claim 2, the constant speed section length φdn of the descending section is increased by the constant speed section length φdn of the ascending section.
Because it is smaller than up, the change in acceleration in the down section can be made gentler than the change in acceleration in the up section, stabilizing the behavior of the valve in the high speed rotation range, and reducing the bounce phenomenon when the valve is seated. Can be prevented.

According to the third aspect of the present invention, the maximum value αdn of the positive acceleration in the down section is increased by the maximum value αdn of the positive acceleration in the up section.
Since it is smaller than up, sudden changes in acceleration can be prevented, changes in inertia can be moderated, and valve behavior in high speed rotation range can be improved, and changes in acceleration especially when sitting down can be reduced. The bounce phenomenon at the time of valve seating can be avoided.

According to the fourth aspect of the present invention, the length θ0dn of the downward positive acceleration section is made larger than the length θ0up of the upward positive acceleration section, so that the product of the valve opening area and the opening time is obtained. The angle area obtained based on the maximum acceleration αdn in the descending section can be suppressed from being reduced by reducing the maximum acceleration αdn.

FIGS. 14A, 14B and 14C show a valve lift curve y, a velocity coefficient curve y 'and an acceleration coefficient curve y'', respectively. In the figure, since .alpha.dn is made smaller than .alpha.up and .theta.0dn is made larger than .theta.0up, the area H, which is the integral value of acceleration, can be increased, and the maximum value y'Dmax in the speed curve y 'can be increased. Qualitatively, the larger the value y'Dmax, the larger the maximum value ymax in the valve lift curve y. If ymax can be increased, the area B (angular area) can be increased, and the intake performance can be sufficiently secured to improve the engine performance.

According to the fifth aspect of the invention, the section length θ1dn of the down section is made larger than the section length θ1up of the up section, so that the product of the valve opening area and the opening time is the same as in the fourth aspect of the invention. The angle area determined based on the maximum acceleration αdn in the down section can be suppressed from being reduced by reducing the maximum acceleration αdn,
The engine performance can be improved by securing sufficient intake air volume.

According to the invention of claim 6, the section length θ1dn of the down section is made larger than the section length θ1up of the up section, and the length θ0dn of the positive acceleration section in the down section is set to the length of the positive acceleration section on the up side. Since it is larger than θ0up, it is possible to more reliably prevent the angular area from being reduced by reducing the maximum acceleration αdn in the descending section, and to secure a sufficient intake air amount to improve the engine performance.

[0032]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIGS. 1 to 7 are views for explaining a valve train of an engine according to a first embodiment of the present invention. 1 is a sectional side view of a SOHC type valve train, FIG. 2 is a sectional side view of a DOHC type valve train, FIG. 3 is a schematic view showing a profile of a cam nose, FIG.
Is a diagram showing the profile of the cam nose as a radius of curvature, FIG. 5 shows the relationship between the cam shaft rotation angle and the acceleration coefficient and speed coefficient, FIG. 6 shows the relationship between the cam shaft rotation angle and the load between the cam nose and lifter, and FIG. FIG. 4 is a characteristic diagram for explaining a relationship between a camshaft rotation angle and a stress on a cam surface.

In FIG. 1, reference numeral 1 denotes a water-cooled, four-cycle, multi-cylinder engine provided with an SOHC type valve train, which has a cylinder body 10 and a cylinder head on an aluminum alloy crankcase (not shown). 1
1, a head cover 20 is laminated and connected, and a piston 14 is slidably inserted and arranged in a cylinder bore of a cylinder liner 10c pressed into the cylinder body 10, and the piston 14 is connected to a crankshaft in the crankcase by a connecting rod. FIG. 1 is a cross-sectional side view of a valve operating device for one cylinder.

A combustion recess 11a forming a combustion chamber E is formed in the cylinder head 11 on the cylinder body side facing surface. The combustion recess 11a has three intake valve openings 18 and two exhaust valve openings. 15 are arranged and opened along the outer periphery of the combustion chamber E, and the intake valve opening 18 and the exhaust valve opening 15 are led out to the rear wall and the front wall of the cylinder head 11 by the intake port 31 and the exhaust port 32. ing. 10a is a water-cooled jacket formed on the cylinder body 10, and 30b is an electrode of a spark plug.

Each of the intake valve openings 18 and each of the exhaust valve openings 15
Is opened and closed by valve heads 25a and 26a of an intake valve 25 and an exhaust valve 26 which are driven forward and backward by a valve train 40. The intake valve 25 and the exhaust valve 26 are disposed so that their valve shafts 25b, 26b protrude into a cam chamber 24 formed by the cylinder head 11 and the head cover 20, and are movable in the axial direction. A valve spring 35 interposed between a retainer 34 mounted on the protruding end and a spring seat of the cylinder head 11
Urged in the closing direction.

The valve gear 40 is provided with one camshaft 36 arranged in the crankshaft direction so as to pass over substantially the center of the combustion chamber E, and on both sides of the camshaft 36 and above. An intake rocker shaft 46 and an exhaust rocker shaft 47 are provided, and three intake rocker arms 43 and two exhaust rocker arms 42 per cylinder are supported by the respective rocker shafts 46 and 47 so as to be swingable.

The camshaft 36 has three intake cam nose 36a and two exhaust cam nose 36b for each cylinder.
A substantially central portion and both end portions of the combustion chamber are rotatably supported by a cam bearing formed on the cylinder head 11 and a bearing cap mounted on the cam bearing.

The intake rocker shaft 46 and the exhaust rocker shaft 47 are fixedly supported by bosses 20a, 20a projecting downward from the inner surface of the head cover 20. Sliding surfaces 43a and 42a are formed at inner ends of the intake rocker arm 43 and the exhaust rocker arm 42 so as to slide on the cam nose 36a and 36b, and valve shafts 25b of the intake valve 25 and the exhaust valve 26 are formed at the outer end. , 26b are screwed in such a manner that the adjusting bolts 48, 49 contacting the upper end surfaces thereof can be adjusted in axial position. Reference numerals 48a and 49a denote lock nuts, and reference numeral 50 denotes a valve gap adjusting cap detachably mounted on the head cover 12.

In FIG. 2, reference numeral 1 denotes a water-cooled four-stroke engine provided with a direct-acting DOHC type valve train 60, and the same reference numerals as those in FIG. 1 denote the same or corresponding parts. The valve gear 60 includes an intake valve 25 and an exhaust valve 26 each having an independent intake camshaft 61 and an exhaust camshaft 62.
a and 36b are driven to open and close via lifters 63a and 63b.

Each of the camshafts 36, 61, 6 shown in FIGS.
The intake cam nose 36a and the exhaust cam nose 36b have a cam profile which is a feature of the present embodiment, and the cam profiles will be described in detail. In the following description, the case of the intake cam nose 36a in the direct acting valve train shown in FIG. 2 is mainly described, but the same applies to the exhaust cam nose 36b. Also, the intake cam nose 36a and the exhaust cam nose 36b in the valve train of FIG.
The same applies to.

FIGS. 3 and 4 are views for explaining the cam profiles of the intake cam nose 36a and the exhaust cam nose 36b which rotate counterclockwise, and show states at the same timing. In the figure, TDCin is the top dead center in the exhaust / suction stroke, BDCin is the bottom dead center in the suction / compression stroke, TDCex is the top dead center in the compression / explosion stroke, BDC
ex indicates the bottom dead center in the explosion and exhaust strokes. Θin,
θex is the above TDCin and TD before 1 combustion cycle, respectively.
The camshaft rotation angles γin and γex based on Cin ′ are the camshaft rotation angles from the TDCin and TDCin ′ to the contact points Bin and Bex between the cam nose and the lifter, respectively.
Bexo is the contact point at the time of the maximum lift, Pin is the above contact point Bin
, The center of curvature located on a straight line perpendicular to the sliding contact surface of the lifter 63a, and Rin indicates the radius of curvature of the contact point Bin.

In FIG. 3, the exhaust cam nose is β
The relative position between the exhaust cam nose and the lifter when returned by the angle is shown by moving the lifter while fixing the exhaust cam nose. The lifter at this time is 63b ', and θex' is the l combustion at this time. The camshaft rotation angle based on TDCin 'before the cycle, Bex' is the contact point between the cam nose and the lifter,
γex ′ is the rotation angle of the cam shaft from the contact point Bex ′ between the cam nose and the lifter with reference to TDCin ′ one combustion cycle before, and Pex ′ is the straight line perpendicular to the sliding contact surface of the lifter 63b ′ from the contact point Bex ′. The curvature center located above, Rex ', indicates the radius of curvature of the contact point Bex' portion.

In FIG. 3, a virtual TDCin line fixed to the cam profile is a virtual TDCin line fixed to the cam profile when the piston is located at the top dead center of the exhaust / suction stroke when this line coincides with the axis of the lifter 63a. The TDCex line is a line in which the piston is located at the top dead center of the compression / explosion stroke when this line coincides with the axis of the exhaust lifter 63b. In the illustrated state, the intake cam nose 36a rotates the TDCin line by θin from the top dead center position of the exhaust / intake stroke in the direction of the arrow (the direction of rotation of the camshaft), and the exhaust cam nose 36b detects the TDCin ′ one combustion cycle before. This indicates that the reference has been rotated by θex (= θin + 360 °) as a reference.

The intake cam nose 36a includes a base circular portion 70a that does not perform a valve lift operation, and a lift portion 70b that includes a ramp portion and a portion that actually lifts the valve. The exhaust cam nose 36b similarly has a base circular portion 71b. And a lift 71b. The base circle portions 70a, 7
1a is an arc having a radius Ro centered on the cam shaft center C, and the radii of curvature of the lift portions 70b, 71b are determined according to the cam shaft rotation angles θin, θex (or γin, γex) in FIG.
It is set as shown in

In FIG. 4, the solid and broken lines represent the radii of curvature of the exhaust cam nose 36b and the intake cam nose 36a, respectively, using the camshaft rotation angle θ and the crankshaft rotation angle Q as parameters. As can be seen from the figure, the base circle 7
The portions 0a and 71a have a constant radius Ro, and no lift action of the valve occurs.

On the other hand, regarding the radii of curvature of the lift portions 70b and 71b, the vicinity a near the start of opening of the valve and the vicinity b near the end of closing of the valve b
Is set to the maximum value, so the lift amount increases gradually near the start of valve opening or near the end of valve closing,
Or decrease. Further, in the portion c between the vicinity of the opening start and the vicinity of the closing end, the radius of curvature is equal to the base circular portions 70a, 7
The value is set smaller than the radius Ro of 1a, and the valve lift increases in a parabolic manner.

In the case of the conventional cam profile, the radius of curvature in the portion c between the opening start and the closing end is fixed or set to be convex downward in FIG. Are set to be larger by ΔR than the curvature radii Rexo ′ and Rino ′ of the portions adjacent to the advance side and the retard side thereof. That is, the cam profile of the maximum lift portion of the conventional camshaft is sharp, whereas the cam profile of the maximum lift portion of the present embodiment is closer to the radius of the base circle portion than the conventional one.

Here, there is a certain relationship between θin and γin, which is determined from the shape of the cam, that is, γin = f1 (θin). Rin is also a function of γin and a function of θin. That is, there is a relationship of Rin = f2 (γin) = f2 (f1 (θin)) = g1 (θin). Note that g1 (θin) means data indicating the radius of curvature shown in FIG. Therefore, Rin = g1 shown in FIG.
Given the data of (θin), Rin = f2 (γin),
And γin = f1 (θin), and thus the shape of the cam nose is determined. That is, when the distance between the camshaft center C and the contact point Bin is Zin, and the distance between the camshaft center C and the lifter in the normal to the lifter lowered from the camshaft center C is yin, the radius of curvature Rin ( Once γin) is determined, Zin (γin) that determines the geometric cam profile and yin (θin) that determines the valve lift amount with respect to the camshaft rotation angle when the intake cam is rotated at a constant camshaft rotation angular velocity are determined. . The distance yin between the cam shaft center C and the lifter is a cam lift curve in the intake cam nose referred to in the present application. The same applies to the exhaust cam nose.

FIG. 5 shows a cam lift curve y (mm) and an acceleration coefficient curve y '' with respect to a change in the camshaft rotation angle (θ).
= D ² f (θ) / dθ ² (mm / rad ² ).
The profile of the cam nose of the first embodiment is such that the absolute value α of the acceleration coefficient near the maximum valve lift is the absolute value α ′ of the acceleration coefficient in the valve lift region adjacent to the advance side and the retard side.
A constant velocity section φu in which the valve lift speed is maximum and constant in both the section where the valve lift increases (ascending section) and the section where the valve lift decreases (down section) so as to be smaller by Δα.
It is set to have p, φdn. It is also possible to provide a constant velocity section only in one of the ascending section and the descending section.

FIG. 6 shows the load acting between the cam nose and the lifter using the camshaft rotation angle as a parameter. The load acting between the cam nose and the lifter is
The load generated by the valve spring and the inertial force [a product obtained by multiplying the inertial mass consisting of the valve, lifter, and part of the valve spring by acceleration. Near the maximum lift, the acceleration coefficient is negative, and the inertial force is negative. The acceleration is the acceleration coefficient y ″ (mm / rad ² ) in FIG.
Multiplied by the square of the actual camshaft rotation angular velocity (eg, ωrad / sec), that is, y ″ × ω ² (mm / sec ² )
Becomes ]]. In the case of the cam profile of the present embodiment, as can be seen from FIG. 5, since the negative acceleration coefficient near the maximum lift is small, the load F between the cam nose and the lifter near the maximum lift is smaller than the conventional load. It increases by ΔF as compared with the load F ′. As a result, the followability of the lifter to the cam nose is improved, and the lifter operates stably up to higher speeds, thereby increasing the limit rotational speed.

FIG. 7 shows the stress acting on the cam surface of the cam nose using the camshaft rotation angle as a parameter. As can be seen from the Hertz stress equation, the stress on the cam surface is proportional to the square root of the load acting between the cam nose and the lifter, and is inversely proportional to the square root of the radius of curvature of the cam. In the cam profile of the present embodiment, the radius of curvature near the maximum lift is set large as described above, so that the cam surface stress becomes σ, and the stress is reduced by Δσ from the conventional cam surface stress σ ′.

Since the inertia force is proportional to the square of the camshaft rotation speed, the inertia force is relatively small with respect to the valve spring load in the low-speed and medium-speed rotation ranges. Generally, the stress of the lift portion shows a maximum value. Accordingly, in the case of an automobile engine in which low-speed and medium-speed rotations are commonly used, the high stress in the maximum lift region lowers the durability of the entire valve train. In the present embodiment, as described above, the cam surface stress near the maximum lift is reduced by Δσ from the conventional one, so that the durability of the camshaft and, consequently, the entire valve train can be improved.

FIG. 8 is a characteristic diagram showing a relationship between a camshaft rotation angle and a valve lift, a speed coefficient, and an acceleration coefficient for explaining a second embodiment according to the second aspect of the present invention. In the second embodiment, in addition to the first embodiment, the constant velocity section length φdn of the descending section where the valve lift decreases is smaller than the constant velocity section length φup of the ascending section where the valve lift increases. Has a cam nose cam profile.

In the second embodiment, since the constant speed section length φdn of the descending section is smaller than the constant speed section length φup of the ascending section, the change in acceleration in the descending section is compared with the change in acceleration in the ascending section. The valve can be moderated, the behavior of the valve in a high-speed rotation region can be stabilized, and the bounce phenomenon at the time of seating of the valve can be prevented.

FIG. 9 is a characteristic diagram showing a relationship between a camshaft rotation angle and a valve lift, a speed coefficient, and an acceleration coefficient for explaining a third embodiment according to the third aspect of the present invention. In the third embodiment, in addition to the above-described second embodiment, the maximum value αdn of the acceleration coefficient in the descending period in which the valve lift decreases decreases the maximum value α of the acceleration coefficient in the ascending section in which the valve lift increases.
The cam nose cam profile is set to be smaller than up.

In the third embodiment, since the maximum value αdn of the acceleration in the descending section is smaller than the maximum value αup of the acceleration in the ascending section, the change in the positive acceleration in the descending section can be moderated.
In particular, it is possible to suppress the bounce phenomenon at the time of sitting, which is greatly affected by the positive acceleration in the down section, and to stabilize the behavior at the time of seating the valve.

FIG. 10 is a characteristic diagram showing a relationship between a camshaft rotation angle and a valve lift, a speed coefficient, and an acceleration coefficient for explaining a fourth embodiment according to the fourth aspect of the present invention. Book 4
In the embodiment, in addition to the third embodiment, the positive acceleration section length θ0dn in the descending section where the valve lift decreases is represented by
The cam profile is set so as to be longer than the positive acceleration section length θ0up in the rising section where the valve lift rises.

The length θ0dn of the positive acceleration section in the down section
Is made larger than the length θ0up of the positive acceleration section on the ascending side, so that the angular area obtained based on the product of the valve opening area and the opening time can be suppressed from being reduced by reducing the maximum acceleration αdn in the descending section. .

That is, in FIGS. 14A, 14B and 14C, while αdn is made smaller than αup, θ0dn is made θ0up
Since it is larger, the area H which is the integral value of the acceleration can be increased, and the maximum value y'Dmax in the speed curve y 'can be increased. Qualitatively, the larger the value y'Dmax, the larger the maximum value ymax in the valve lift curve y. y
If max can be made large, the area B (angular area) can be made large, and the intake performance can be sufficiently secured to improve the engine performance. Since the maximum value αdn of the acceleration in the positive acceleration section on the downside can be reduced, the bounce at the time of closing the valve can be prevented, and the behavior at high rotation can be improved.

FIG. 11 is a characteristic diagram showing a relationship between a camshaft rotation angle and a valve lift, a speed coefficient, and an acceleration coefficient for explaining a fifth embodiment according to the fifth aspect of the present invention. In the fifth embodiment, in addition to the above third embodiment, the cam profile is set so that the section length of the down section is θ1dn and the section length of the up section is larger than θ1up.

In the fifth embodiment, the angle area obtained based on the product of the valve opening area and the opening time can be suppressed from being reduced by reducing the maximum acceleration αdn in the descending section, and the intake air amount can be sufficiently reduced. To improve engine performance.

FIG. 12 is a characteristic diagram showing a relationship between a camshaft rotation angle and a valve lift, a speed coefficient, and an acceleration coefficient for explaining a sixth embodiment according to the sixth aspect of the present invention. Book 6
In the present embodiment, in addition to the fourth embodiment, the cam profile of the cam nose is set such that the length θ0dn of the positive acceleration section in the descending section is larger than the length θ0up of the positive acceleration section on the rising side.

In the sixth embodiment, the length θ0dn of the positive acceleration section in the descending section is changed to the length θ0up of the positive acceleration section in the ascending section.
Since the angle area is increased, it is possible to more reliably prevent the angular area from being reduced by reducing the maximum acceleration αdn in the down section, and it is possible to secure a sufficient intake air amount and improve the engine performance.

[Brief description of the drawings]

FIG. 1 shows an SO according to a first embodiment of the present invention;
It is sectional side view of HC type valve gear.

FIG. 2 is a cross-sectional side view of a DOHC type valve train to which the first embodiment is applied.

FIG. 3 is a view schematically showing a cam nose of a cam shaft of the first embodiment device.

FIG. 4 is a characteristic diagram showing a cam profile of a cam nose of the device of the first embodiment by a radius of curvature.

FIG. 5 is a characteristic diagram showing a relationship between a camshaft rotation angle, an acceleration coefficient, a speed coefficient, and a valve lift in the first embodiment.

FIG. 6 is a graph showing a camshaft rotation angle and a cam nose-lifter load characteristic according to the first embodiment.

FIG. 7 is a characteristic diagram of a camshaft rotation angle and a cam surface stress according to the first embodiment.

FIG. 8 is a characteristic diagram of a camshaft rotation angle and an acceleration coefficient according to a second embodiment of the present invention.

FIG. 9 is a characteristic diagram of a camshaft rotation angle and an acceleration coefficient according to a third embodiment of the present invention.

FIG. 10 is a camshaft rotation angle / acceleration coefficient characteristic diagram according to a fourth embodiment of the present invention.

FIG. 11 is a characteristic diagram of a camshaft rotation angle and acceleration coefficient according to a fifth embodiment of the present invention.

FIG. 12 is a characteristic diagram of a camshaft rotation angle and acceleration coefficient according to a sixth embodiment of the present invention.

FIG. 13 is a diagram for explaining the function and effect provided by providing a constant velocity section in the present invention.

FIG. 14 is a diagram for explaining the function and effect provided by providing a constant velocity section in the present invention.

FIG. 15 is a diagram for explaining a relationship between a conventional camshaft rotation angle and acceleration acceleration.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 25 Intake valve 26 Exhaust valve 36 Camshaft 40, 60 Valve train y Valve lift curve y '' Acceleration coefficient αdn Maximum value of downward section acceleration αup Maximum acceleration of ascending section θ0dn Downward section positive acceleration section length θ0up Ascending section Length of positive acceleration section θ1dn Length of downhill section θ1up Length of ascending section φdn Length of constant speed section of descent section φup Length of constant speed section of ascending section

Claims (6)

[Claims] The absolute value of the acceleration coefficient in the vicinity of the maximum valve lift is made smaller than the absolute value of the acceleration coefficient in the valve lift region adjacent to the advance side and the retard side, or in the vicinity of the maximum valve lift. At least one of a section in which the valve lift is increased (ascending section) and a section in which the valve lift is decreased (down section) such that the radius of curvature is larger than the radius of curvature in the valve lift region adjacent to the advance side and the retard side. An engine valve operating device comprising: a camshaft having at least one of an exhaust cam profile and an intake cam profile set so as to have a constant speed section in which a valve lift speed is maximum and constant. 2. The method according to claim 1, wherein when the ascending section and the descending section have a constant velocity section, and the lengths of the constant velocity sections of the ascending section and the descending section are φup and φdn, φup> φdn. An engine valve gear comprising a camshaft having at least one of a set exhaust cam profile and an intake cam profile. 3. A cam having at least one of an exhaust cam profile and an intake cam profile set so that αup> αdn, where αup and αdn are maximum acceleration values in an ascending section and a descending section. A valve train for an engine, comprising a shaft. 4. The method according to claim 3, wherein when the positive acceleration section lengths of the ascending section and the descending section are θ0up and θ0dn, at least one of the exhaust cam profile and the intake cam profile set so that θ0up <θ0dn is satisfied. A valve train for an engine, comprising a camshaft having the same. 5. A cam having at least one of an exhaust cam profile and an intake cam profile set such that θ1up <θ1dn, where θ1up and θ1dn are section lengths of the ascending section and the descending section. A valve train for an engine, comprising a shaft. 6. The exhaust cam profile and the intake cam profile that are set so that θ0up <θ0dn, where the positive acceleration section lengths of the ascending section and the descending section are θ0up and θ0dn. A valve train for an engine, comprising a camshaft having the same.