KR20060010058A - Method for designing cam profile for variable valve lift apparatus - Google Patents

Abstract

The present invention relates to a cam profile design method for a variable valve lift device installed between a camshaft that is rotated by a driving force of an engine and a valve stem of an intake and exhaust valve to operate the intake and exhaust valves at low lift and high lift. Providing a cam comprising a circular base and a lobe extending from the circular base; Setting the degree of curvature of the end of the lobe such that the lift shift of the valve relative to the rotation angle of the camshaft is constant while the end of the lobe is in contact with the variable valve lift device as the camshaft rotates. It is characterized by. Accordingly, by using the variable valve lift apparatus and the cam profile of only one tappet only, it is possible to reduce noise and vibration generated when opening and closing the valve.

Variable Valve Lifts, Cam Profiles

Description

Method for designing cam profile for variable valve lift apparatus

1 is a structural diagram of a conventional two-stage variable valve lift and cam profile,

2 and 3 is a structural view of the operation of the variable valve lift apparatus by the tappet applied to the present invention,

4 is a graph of valve opening variation and speed variation according to crank angle in the variable valve lift apparatus of FIGS. 2 and 3;

5 is a graph of valve opening variation and valve opening speed according to the crank angle for the camp profile design at high lift in accordance with the present invention;

6 is a graph of valve opening variation and valve opening speed according to crank angle for low profile camp profile design according to the present invention;

7a and 7b are cross-sectional views of the cam profile according to the invention,

<Description of Symbols for Major Parts of Drawings>

 1: Stem 10: Cam Profile

10a: Base 10b: Robe

11: valve rod 12: spring

20: tappet body 21: oil supply path

22: push rod return spring 23: stopper return spring

24: Stopper 25: Push Rod

26: hydraulic chamber

The present invention relates to a variable valve lift device that can increase the performance of the engine by adjusting the lift amount of the valve by one cam at a low speed and a high speed of the engine, and more specifically, noise and vibration generated when opening and closing the valve. A cam profile design method for a variable valve lift apparatus of an engine that reduces engine losses.

In general, an engine generates thermal energy by rotating a crankshaft through a connecting rod connected to the piston to explode force generated by burning fuel in a combustion chamber formed between a cylinder and a cylinder head and a piston reciprocating in the cylinder. To convert.

The cylinder head of such an engine is provided with a combustion chamber for burning fuel to generate power, and the combustion chamber includes an intake valve for providing a mixer containing a fuel to be burned and an exhaust valve for releasing continuous gas. As formed, these intake valves and exhaust valves are configured to open and close the combustion chamber by a valve opening and closing mechanism connected to the crankshaft. The valve opening / closing mechanism converts the rotational motion of the camshaft into the linear motion of the valve. In general, the opening and closing timing or lift of each valve varies according to the change of the curve of the surface of the cam profile, thereby affecting the performance of the engine.

1 is a view illustrating an operation state of a conventional two-stage variable valve lift apparatus during high lift and low lift. As shown in FIG. 1, the conventional two-stage variable valve lift apparatus has two types of profiles, a high cam 101 and a low cam 102 connected to the cam shaft 100, and a special tappet 200. It operates as a two stage variable valve lift. The lock pin and the central axis are integrally formed by the oil pressure during the high lift, so that the entire tappet 200 moves up and down in contact with the high cam 101, and the lock pin is released during the low lift, so only the center axis is the low cam. It moves up and down in contact with 102.

On the other hand, a variable valve lift apparatus (see FIGS. 2 and 3) by tappets operated by one type of cam profile is currently developed, and the variable valve lift apparatus is configured to be variable by hydraulic pressure.

However, in the case of having two types of cam profiles like the variable valve lift of FIG. 1 described above, designing and applying cam profiles for low lift and high lift will cause problems in valve movement characteristics and noise / vibration. none.

However, when the low lift and the high lift are operated at the same time by using the variable valve lift device and the cam profile of only one type by the tappet 20, the following problems arise. In other words, designing for a high lift cam profile causes problems during low lift.

Looking at the graph of the position and speed variation of the lift according to the crank angle shown in FIG. 4, the convex graph is the variation graph of the high lift and the low lift, and the graph indicated by the dotted line is the velocity graph at the high lift and the low lift. . The valve starts to open at the portion indicated by the dotted line in the speed graph. At this time, noise and vibration problems occur at the opening / closing time of the valve because the opening speed of the valve is too fast.

According to a paper published by testing the relationship between cam and engine speed at various ramp speeds in a tappet valve system, the vibration and noise of the cylinder head when the valve is opened are proportional to the speed at which the cam hits the tappet. . That is, since the speed at which the cam hits the tappet and noise are proportional to each other, it is necessary to maintain the constant velocity motion in the ramp section to reduce the amount of impact on the cam hitting the tappet.

Accordingly, the present invention has been made to solve the above problems, using a variable valve lift device by a tappet and a type of camp profile for variable valve lift tappets to reduce the noise and vibration generated when opening and closing the valve. The purpose is to provide a camp profile.

The present invention for achieving the above object, the variable valve lift is installed between the cam shaft and the valve stem of the intake and exhaust valve rotated by receiving the driving force of the engine to operate the intake and exhaust valves low and high lift CLAIMS 1. A method of designing a cam profile for a device, comprising: providing a cam comprising a circular base and a lobe extending from the circular base; Setting the degree of curvature of the end of the lobe such that the lift shift of the valve relative to the rotation angle of the camshaft is constant while the end of the lobe is in contact with the variable valve lift device as the camshaft rotates. Is achieved by.

Here, the section in contact with the end of the lobe and the variable valve lift device is a section in which the valve is opened and closed during the low lift.

The variable valve lift apparatus includes a valve body, a '┕┙'-shaped push rod which is arranged to flow in a central region of the valve body and is connected to the valve stem, and is installed at both sides of the push rod and pressurized by hydraulic pressure. A valve tappet consisting of a stopper for limiting movement of the push rod, a stopper return spring for returning the stopper when the hydraulic pressure is released, and a spring for the push rod return; It is preferable to have a microcomputer to supply hydraulic pressure to the valve body to operate the valve tappet in a high lift, and to release the hydraulic pressure supplied to the valve tappet to operate the valve tappet in a low lift.

Hereinafter, the present invention will be described in detail with reference to the accompanying drawings.

The present invention is based on the premise of implementing a variable valve lift engine using the tappet-only variable valve lift apparatus of FIGS. 2 and 3 and one type of cam profile. The tappet 20 of the variable valve lift apparatus using only the tappet 20 applied to the present invention includes a valve body and a '┕┙' connected to the valve stem 1 so as to be movable in a central region of the valve body. Return the stopper 24, the stopper 24 installed on both sides of the push rod 25 and pressurized by hydraulic pressure to limit the movement of the push rod 25, and the stopper 24 upon release of the hydraulic pressure. The stopper return spring 23 and the push rod return spring 22 are made.

The operation process of the tappet 20 of the variable valve lift apparatus is as follows. When the high lift to supply the oil through the oil supply path 21 to form a high-pressure hydraulic pressure, the stopper 24 springs down while pushing the push rod 25 down to fix both ends of the push rod 25.

On the other hand, during the low lift, when the hydraulic pressure is released and the oil exits the oil supply path 21, the stopper 24 is restored to the original position by the stopper return spring 23. Accordingly, the push rod 25 is moved to the upper part of the tappet body 20 by the push rod return spring 22. Although not shown in the drawings, the inflow and outflow of oil during high lift and low lift is controlled by an ECU (Electronic Control Unit) having a microcomputer that controls the variable valve lift apparatus.

5 is a graph of valve opening variation and valve opening speed variation according to crank angle for cam profile design at high lift according to the present invention. In the graph of FIG. 5, the graph '①' represents the displacement size of the camshaft, and the graph '②' represents the speed differentiating the displacement size of the camshaft with respect to the crank angle, and the graph '③' represents the speed with respect to the crank angle. It is a graph showing differential acceleration.

At high lift, the ECU (not shown) converts the variable lift device into the high lift state by hydraulic pressure, and when the camshaft is rotated, the cam profile 10 rotates, so that the surfaces of the tappet 20 and the cam profile 10 Contact. According to the graph of FIG. 5, the base 10a of the cam profile 10 of FIG. 7A, which will be described later, enters the lobe 10b region, and the tip of the cam profile 10 (hereinafter, referred to as the end of the lobe 10b) is advanced. The section returning back to the base 10a through the lobe 10b area in the section called "part" is a section in which the valve opens and closes. The maximum variation of the valve opening is set as the lift amount of the valve is changed by the cam profile 10 during the passage.

Here, when the camshaft rotates in the high lift state, the section in which the constant speed is almost maintained in the speed graph of FIG. 5 is such that the tip of the cam profile 10 and the adjacent region of the cam profile 10 come into contact with the tappet 20. As a moment, the section maintaining the constant speed ramps during low lift to reduce noise.

Therefore, in the cam profile design, the degree of curvature of the tip of the cam profile is set so that the lift variation of the valve per crank angle becomes constant, that is, at constant velocity.

6 is a graph of valve opening variation and valve opening speed variation according to the crank angle for the cam profile 10 design during low lift according to the present invention. The graph '①' represents the valve opening variation, and the graph '②' represents the velocity differentiating the valve opening variation with the crank angle, and the graph '③' is the graph showing the acceleration differentiating the speed with the crank angle.

Converts the variable lift device to the low lift state and causes the tip portion of the cam profile 10 to contact the tappet 20. According to the graph of FIG. 5, the cam profile 10 rotates as the camshaft rotates, and the tappet 20 and the cam profile 10 contact each other. The section in which the cam profile 10 moves from a predetermined region of the lobe 10b region to the predetermined region of the lobe 10b region through the tip of the cam profile 10 is a section in which the valve opens and closes. It is preferable to set the maximum variation of the valve opening by the cam profile 10 in a section in which the valve is opened and closed so as to be very small as compared with at the time of high lift.

7A and 7B are cross-sectional views of the cam profile 10 based on the graphs of FIGS. 5 and 6. The cam profile 10 is composed of a circular base 10a and a lobe 10b extending inclined from one end of the circular base 10b. When the variable valve lift apparatus is in the high lift state, as the camshaft rotates, the contact state between the lobe 10b of the cam profile 10 and the tappet 20 of the variable valve lift apparatus changes, thereby opening and closing the valve.

That is, the valve opens as the tappet 20 contacts the one end lobe 10b of the cam profile 10 to the tip, and the tappet 20 contacts the tip of the cam profile 10 to the other lobe 10b. As the valve closes.

Similarly, when the variable valve lift apparatus is in the low lift state, as the camshaft rotates, the valve opens while the tappet 20 contacts the predetermined area of the lobe 10b of the cam profile 10 to the tip, and the tappet is at the tip. In close contact with the other region of the lobe 10b the valve is closed.

With this configuration, when opening and closing the valve of the intake and exhaust port, the variable valve lift apparatus and one type of cam profile are used, but the valve is opened / closed when opening and closing the valve with the variable valve lift apparatus in the low lift state. In the ramp section, the cam profile is formed so that the lift shift amount of the valve with respect to the rotation angle of the camshaft is constant, thereby reducing noise and vibration by reducing the shock generated by the cam tapping when the valve is opened / closed. .

As described above, according to the present invention, it is possible to reduce noise and vibration generated when the valve is opened and closed by using the variable valve lift apparatus using a tappet and one kind of camp profile. In addition, the cam profile can reduce the amount of wear of the variable valve lift caused by hitting the tappet.

Claims (3)

In the cam profile design method for a variable valve lift device which is installed between the rotating camshaft and the valve stem of the intake and exhaust valves by receiving the driving force of the engine to operate the intake and exhaust valves in low lift and high lift, Providing a cam comprising a circular base and a lobe extending from the circular base; Setting the degree of curvature of the end of the lobe such that the lift shift of the valve relative to the rotation angle of the camshaft is constant while the end of the lobe is in contact with the variable valve lift device as the camshaft rotates. Cam profile design method for a variable valve lift device, characterized in that. The method of claim 1, And a section in which the end of the lobe is in contact with the variable valve lift apparatus is a section in which the valve is opened and closed during the low lift. The method of claim 1, The variable valve lift device, A valve body, a '┕┙' shaped push rod which is disposed to be movable in a central region of the valve body and connected to the valve stem, and installed on both sides of the push rod and pressurized by hydraulic pressure to move the push rod. A valve tappet comprising a stopper for confining, a stopper return spring for returning the stopper when the hydraulic pressure is released, and a spring for the push rod return; Supplying the hydraulic pressure to the valve body to operate the valve tappet in a high lift, the variable pressure lift device characterized in that it comprises a micom to operate the valve tappet in a low lift by releasing the hydraulic pressure supplied to the valve tappet How to design cam profile.

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