JPS58217711A - Dynamic valve device for internal-combustion engine - Google Patents

Abstract

PURPOSE:To reduce a friction loss at a cam shaft by a method wherein a spring load of a valve spring is made variable in response to the operating condition of the internal-combustion engine. CONSTITUTION:A spring for use in biasing a valve 3 in its closing direction is composed of an inner spring 7 and an outer spring 8. At least one of the seats 6 for the springs 7 and 8 is formed with a piston 13 and the seat 6 can be moved in an extending or retracting direction under a hydraulic pressure applied in the hydraulic chamber 16. In a low speed range, the spring load is decreased lower than that found in a high speed range, thereby a lubricating condition at the cam shaft can be improved and a friction loss of the engine can be decreased.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a valve train for an internal combustion engine, and particularly to a technique for reducing friction loss in a camshaft by varying the spring load of a valve spring depending on the operating state of the engine.

Generally, in an automobile internal combustion engine, the power to open the intake and exhaust valves is transmitted from the crankshaft to the camshaft via a gear or chain, and the rotational motion of this camshaft is converted into reciprocating motion via a rocker arm, etc. This opens and closes the intake and exhaust valves.

Conventionally, there is a type of valve train as shown in FIG. 1, for example (Page 413, (C) Yokendo, published in 1980).

First, intake and exhaust valves 3 are slidably held in the cylinder head 1 via a valve guide 2.

A valve spring retainer 5 is attached to the vicinity of the valve end of the suction/redo air valve 3 via a collet 4, and the suction/exhaust valve An inner cylinder 7 and an outer spring 8 are interposed to always bias the valve 3 in the valve closing direction.

Further, at the valve end of the intake/exhaust valve 3, one end of a rocker arm 1o, which is freely supported by a rocker shaft 9 at its central portion, is connected to a valve adjust screw 1.
The other end of this rocker arm 10 is in contact with a cam shirt 12.

Therefore, the camshaft 12 is synchronized with the crankshaft (not shown).
When the camshaft 12 rotates, p changes according to the lift amount of the camshaft 12.
The lever arm 10 swings upward and downward in the figure, thereby opening and closing the intake and exhaust valves 3 in synchronization with the rotation of the engine.

By the way, the spring force of the above-mentioned valve spring 7.8 is constantly applied to the camshaft 12 via the rocker arm 10.
Considering the 0-rotation load, as shown in Figure 2, at low speeds (for example, 3000 rpm), the spring force (spring load M) of the valve spring 7°8, which is compressed according to the amount of valve lift, is approximately equal to the spring force (spring load M), and the maximum It is largest during lift.

When the rotational speed of the camshaft 12 becomes high (for example, 5000 rpm), the load applied to the camshaft 12 is the spring force plus the inertia of the valve train, and the spring force increases near the start of the lift. The force becomes the sum of the inertia force and becomes significantly large, but near the maximum lift it becomes the spring force minus the inertia force and becomes small.

Therefore, as a design method for the spring force and spring constant of the valve spring 7.8 in the conventional example, first, when the valve is closed, a clearance is not created in the intake and exhaust valves 3 due to the action of suction negative pressure and the entrainment of soot [9]. The applied load is set. Furthermore, in order to prevent the load 1 applied to the camshaft 12 at the maximum rotation of the engine from becoming zero due to the above-mentioned inertia force (that is, if it becomes zero, the movement of the camshaft 12 will be absorbed and the exhaust valve 3 will no longer follow). Load is set.

In this way, since the spring force near the maximum lift is determined from the inertia force at the maximum rotation, the spring force near the maximum lift at low speeds becomes excessive.

On the other hand, considering the friction at the contact part between the camshaft 12 and the rocker arm 1o, the lubrication state of the contact part is a mixed lubrication state in which the boundary lubrication region and the fluid lubrication region are mixed, depending on the sliding speed, surface pressure, contact surface shape, etc. It is thought that.

tb, the higher the surface pressure and the lower the sliding speed.

Solid contact between sliding surfaces is likely to occur, resulting in a state of boundary lubrication; conversely, areas where the surface pressure is low and the sliding speed is high.

An oil film is formed between the sliding surfaces, creating a state of fluid lubrication.

Therefore, when the rotational speed of the camshaft 120 is low, the sliding speed is low, and as mentioned above, the inertial force is small, so the load is high near the maximum lift and the radius of curvature of the camshaft 120 at this time is also small. Since the surface pressure is also high, the boundary lubrication state becomes dominant. On the other hand, cam shirt) 1
20 When the rotation speed is high, the sliding speed is high, and as mentioned above, the inertial force is large, so the load is low near the maximum lift, and the surface pressure is also low (note that the lift start position at high rotation As mentioned above, the load is high in the vicinity, but since the radius of curvature of the cam shirt 12 at this time is large, the surface pressure does not become that high), so the fluid lubrication state becomes dominant.

Between the boundary lubrication and fluid lubrication, the coefficient of friction is orders of magnitude larger in the boundary lubrication.

In this way, in the conventional valve train, the spring force of the valve spring 7.8 is determined by the above-mentioned mounting load, inertia force at maximum rotation, etc., and this spring force is Since the spring force was always constant up to the high speed range, the spring force became excessive in the low speed range, and the lubrication condition of the camshaft 12 decreased due to a significant increase in surface pressure in addition to the decrease in the sliding speed, resulting in boundary lubrication. Become.

As a result, as shown in FIG. 3, the friction torque is significantly large in the low speed range, which is an important factor in deteriorating fuel efficiency.

This invention was made by focusing on such conventional problems, and it makes the spring load of the above-mentioned valve spring variable according to the operating condition of the engine, so that the spring load is made variable in the low speed range than in the high speed range. The purpose is to improve the lubrication state of the camshaft by reducing the amount of friction, thereby reducing engine friction loss and improving fuel efficiency.

To this end, the present invention provides a valve train for an internal combustion engine in which two valve springs, an inner spring and an outer spring, are used to transmit the movement of the camshaft to the intake and exhaust valves. At least one pedestal of the outer spring is provided so as to be movable in the direction of expansion and contraction of the valve spring, and means is provided for moving the pedestal in accordance with the operating state of the engine.

Embodiments of the present invention will be described below based on the drawings.

As shown in FIG. 4, a pedestal part 6 supports the inner spring/gua and outer spring 8 on the cylinder head 1 side.
is composed of a cylindrical piston body 13 disposed concentrically with the valve guide 2, and a similarly cylindrical stop horn f14 disposed so as to accommodate this piston body 13,
The end of the inner spring 7 is placed on the piston body 13,
Further, the end portions of the outer springs 8 are supported on the strut arms 14, respectively.

The stopper 14 is fixed to the upper surface of the cylinder head 1 with a screw or the like.

On the other hand, the piston body 13 has its small diameter cylindrical portion 13A in sliding contact with the valve guide 2, and its large diameter cylindrical portion 13B in sliding contact with the circular guide groove 15 bored in the upper surface of the cylinder head l.
The large diameter cylindrical portion 13 is provided to be movable in the valve axis direction (valve spring expansion/contraction direction), and is provided between the cylinder head l and the large diameter cylindrical portion 13.
It is located inside B and defines a hydraulic chamber 16.

Further, the amount of movement of the piston body 13 is
The maximum value thereof is set depending on the height of the above-mentioned stopper 14 that engages with the large diameter cylindrical portion 13B in the valve axis direction and the depth of the guide groove 15.

As a means for moving the piston body 13 according to the operating condition of the engine, an oil supply hole 17 is open and connected to the above-mentioned hydraulic chamber 16 as shown in FIG. 'l□ Engine lubricating oil is supplied to the hydraulic chamber 16 from an oil pump (not shown) via a connected oil supply passage 18.
is being supplied to.

An oil relief passage 19 is further branched at the connection portion between the oil supply hole 17 and the oil supply passage 18, and an electromagnetic switching switch is provided at this branch point in response to a rotary switch 20 that turns 0N-OFF at the set rotation speed of the engine. A valve 21 is interposed.

When the engine speed is lower than the set value and the rotation switch 20 is OFF, the electromagnetic switching valve 21
8 communicates only with the oil supply hole 17, and conversely, when the rotation switch 20 is turned on at a value greater than or equal to the set value, the oil supply passage 18 in turn communicates with the oil relief passage 19, while the oil supply hole 17 also communicates with the oil relief passage 19. It is designed to switch so that it communicates with the side.

The rest of the configuration is the same as that in FIG. 1, so a detailed explanation will be omitted here with reference to FIG.

Because of this configuration, the outer spring 8 described above
The spring constant of the spring 8 is made slightly smaller (compared to the conventional example), and the support is set so that only the spring 8 carries the mounting load when the one-way valve is fully closed. The above mounting load is to prevent the valve from opening due to suction negative pressure when the valve is fully closed, and the mounting load is required to be equivalent to that of the conventional example.

On the other hand, the inner spring 7 is connected to the intake and exhaust valves 3 during high-speed rotation.
Therefore, the load of the spring 7 at the maximum lift) ft plus the load of the outer spring 8 described above is the same as that of the conventional example. The spring constant is set as follows.

In this way, in the low speed range of the engine (the range where the set rotation speed is not reached by the rotation switch 20), the engine lubricating oil from the geo-oil pump is transferred to the oil relief passage 19 by the switching operation of the electromagnetic switching valve 21 as described above. Everything seems to flow to the side. Therefore, no hydraulic pressure is applied to the hydraulic chamber 16 and the piston body 13 is in a lowered state, so that the inner spring 7, which is supported by the piston body 13 at one end, is forced into the valve snoring retainer 5 at the other end. are in contact with each other, and the spring load of the spring 7 does not act on the camshaft 12.

As a result, as shown in Fig. 6 in the relevant operating range, the load applied to the camshaft 12, especially near the maximum lift, is significantly reduced due to the reduction in the spring force, and as a result, the surface pressure is also significantly reduced. As a result, fluid and lubrication conditions can be maintained in the camshaft 12, and the engine's 7-stroke impact can be significantly reduced.

On the other hand, in the high speed range of the engine (the range where the rotation speed set by the rotation switch 20 has been reached), this time the electromagnetic force is reversed.

Engine lubricating oil from the oil I pump is introduced into the hydraulic chamber 16 by the switching valve 21 .

As a result, the piston body 13 is raised by the oil pressure until it comes into contact with the stone/4'14. At this time, the position (height) of the piston/4' 14 is set in advance to such a height that the other end of the inner spring/gua comes into contact with the valve spring retainer 5 when the valve is fully closed, and the hydraulic chamber 16
The area of is set in advance to be a sufficient area such that the spring load of the inner spring 7 at maximum lift can be supported by the hydraulic pressure.

As a result, the combined spring force (spring load) of the inner cylinder 7 and the outer spring 8 is applied to the cam shirt (cam shirt) 12 in the operating range, and as mentioned above, this spring force is greater than the conventional example near the maximum lift. Since the spring force is set in advance to obtain a spring force equivalent to that of Reliably follows the movements of 12.

In the above embodiment, the same effect can be obtained by using the outer spring 8 as the valve spring controlled by the piston body 13 and reversing the spring characteristics of the inner spring 7 and the outer spring 8.

In addition, in the above embodiment, the spring characteristic of the inner cylinder 7 is given a two-stage spring constant as shown in FIG. If the valve is set in a tight state when the valve is fully closed (increased by hydraulic pressure), it is possible to maintain a spring load approximately the same as in the above embodiment in the low speed range of the engine, while the other end of the inner spring 7 is always connected to the valve spring. It can be brought into contact with the retainer 5 and generation of noise can be prevented.

As explained above, according to the present invention, the spring load of the valve spring is made variable according to the operating condition of the engine, and the spring load is reduced particularly in the low speed range as well as in the high speed range. The lubrication condition of the camshaft can be improved without sacrificing functionality, reducing engine friction loss and improving fuel efficiency.

[Brief explanation of the drawing]

Fig. 1 is a sectional view of the main part of the conventional example, Fig. 2 is a load characteristic diagram thereof, Fig. 3 is a comparative characteristic diagram of friction torque, and Figs. 4 and 5 are a sectional view of the main part of the embodiment of the present invention. A schematic configuration diagram, FIG. 6 is a load characteristic diagram thereof, and FIG. 7 is a spring characteristic diagram of another embodiment of the present invention. 12...Camshaft, 3...Suction and exhaust valves, 7...
・Inner spring, 8...Outer spring, 6・
... Pedestal part, 13... Piston body, 14... Stone A? , 16... Hydraulic chamber, 17... Oil supply hole, 18...
...Oil supply passage, 21...Solenoid switching valve, 20...Rotary switch. Figure 1 0 1 吋(,y++@ ]幇

Claims (1)

[Claims] L A valve spring that biases the intake and exhaust valves in the valve closing direction,
In a valve train for an internal combustion engine that uses two springs, an inner spring and an outer spring, at least one base of the inner spring and the outer spring is provided to be movable in the direction of expansion and contraction of the valve spring, and
A valve train for an internal combustion engine, comprising means for moving the pedestal according to the operating state of the engine. 2. The valve train for an internal combustion engine according to claim 1, wherein the pedestal moves in the direction of extension of the valve spring in a low speed range of the engine and in the direction of contraction in a high speed range of the engine.