JPS6368706A - Valve system for engine - Google Patents

Abstract

PURPOSE:To prevent a bounce during high-speed rotation, by determining the configuration of a cam which sets an in-take and exhaust valve in opening and closing motions in such way that the valve speed may reach the minimal value just before the in-take and exhaust valves are nearly placed on their seats, and that the valve speed may gain the maximal value as a valve lift becomes smaller. CONSTITUTION:The configuration of a cam is specified in a valve system where the rotation of the cam is setting an in-take and exhaust valve to be driven in opening and closing motions. Namely, it is set in such a way that when a valve acceleration alpha4 is constant from the point D on the way of descending intake exhaust valve, and a valve speed mu4 is falling linearly, the valve speed is set so as to reach the minimal value (m) in the position (c) located shortly before the initial position (b) where the valve is to be placed on its seat. Said minimal valve (m) is set almost equal to the minimum speed mu0 at the start and finish of lifting of the valve. In addition, the configuration of the cam is determined so that the valve speed may represent the lift characteristic of gaining the maximal value M, as the valve lift decreases. Thus, the valve is allowed to be placed quietly on its seat for redeuced noises.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to an engine valve train, and more specifically, to an engine valve train.
This invention relates to technology for improving the lift characteristics of exhaust valves.

(Prior Art) A valve train that opens and closes intake and exhaust valves has a lift characteristic such as that shown in FIGS. The settings are as shown in (C).

When the cam rotates and the cam reaches the valve clearance (vertical clearance) S, the valve opens at point (A).
T. Start. Next, between AB, the valve acceleration α is constant,
The valve speed U increases linearly up to the maximum value Um, changes to a negative acceleration α2 at point B, and the speed U2 increases between BC.
falls linearly to O. After the valve pressure reaches its maximum at point 0, the situation between CD and DE is opposite to the above, and when the lift part of the cam comes to valve gap S, the valve seats on the valve seat at point (B). do.

Note that the valve gap S is due to the difference in thermal expansion between each part, etc.
It is provided to prevent the engine from becoming unresponsive (References: Internal Combustion Engine Lecture (Part 1) 1! Kendo).

(Problems to be Solved by the Invention) However, in such conventional examples, as the engine rotation increases, the acceleration of the valve increases.
As the deformation of the structure supporting the intake and exhaust valves increases, the valves are seated in the expected position ((b) in Figure 3(a)).
It ends up being done at a higher position than the valve position. For this reason, when the engine speed is high, the seating speed of the valve increases more than the increase in engine speed, resulting in the problem that the valve is likely to collide with the valve seat and cause bounce.

Note that if the valve seating speed (U4 in Fig. 3(b)) is set small in advance, the seating ramp section will become longer and the seating position will change greatly due to engine temperature changes, for example, so the engine This seriously impairs the performance of the device.

This invention aims to solve these problems.

(Means for solving problem α) The present invention provides a valve train in which the intake and exhaust valves of an engine are opened and closed via a cam that rotates in synchronization with the engine rotation. The cam shape is determined so that the speed of the valve takes a minimum value immediately before seating on the valve seat, and as the lift amount of the valve becomes smaller, the speed of the valve takes a maximum value.

(Function) Therefore, as the engine speed increases, even if the intake and exhaust valves are seated on the valve seats at a lift position higher than the predetermined position,
At this time, the valve speed does not increase, but approaches the minimum value, so it is maintained at an appropriate seating speed.

(Example) Figures 1 (a), (b), and (c) show an example of the present invention in characteristic diagrams of lift, speed, and acceleration of valves (intake and exhaust valves). Against the 7th start (a) to A
, B, C, and D are shown in Figure 3 (a) = (b) - (c
) is the same as

Then, from point D on the way down of the valve, the discrimination speed α4 is constant and the valve speed U decreases linearly, until the valve reaches the expected position (B) where it is seated on the valve seat (intake, exhaust The valve speed is determined to take a minimum value at a position (c) just before the designed position (assuming no deformation of the structure supporting the valve).

This minimum value m is determined to be approximately the same as the minimum speed U at the start and end of the lift of the valve.

Next, from the position (c), the valve speed U is set so as to once increase and take the maximum value M, after which the valve speed U6 is determined to decrease to the minimum speed U0.

This maximum value M is determined to be the position (b) above, and the distances a and lα before and after it are constant.

That is, after the valve has been rotated 97 times to the 0 point, it passes through point D and descends, but the valve speed is set so that it is once at a minimum at the position (c) just before the intended seating position (b). and
The cam shape of the valve train that operates the valve is determined to have such a lift characteristic. Note that S is the valve gap.

Therefore, when the acceleration of the valve increases as the rotation speed increases, the deformation of the structure supporting the valve increases, causing the valve to move from its original position (b) to a high valve lift (
The valve starts to shift toward the (c) side, but at this time the valve speed approaches the minimum value theory, so the valve sits quietly on the valve seat at a small speed.

This prevents the valve from colliding with the valve seat due to the increased seating speed of the valve at high engine speeds (as in conventional models), the occurrence of bounce can be suppressed, engine noise can be reduced, and various parts can be Improves durability.

In addition, when the engine is running at low speed, the valve comes to be seated at almost the intended position (B), and at this time the valve speed is almost at the maximum value M.
This increases the seating speed, but since the valve speed is originally slow at low engine speeds, the actual seating speed does not increase, so the valve seats quietly at an appropriate speed.

FIGS. 2(a), (b), and (e) are characteristic diagrams of another embodiment of the present invention, which is equipped with a lash 7 noja star that automatically adjusts the valve gap S, and a cam (with which the discrimination speed characteristic is a curve). For example, it is applied to a valve train system using a polygain cam.

In this case as well, the position facing the valve's intended seating position (b) (c)
The valve speed is determined so as to take the minimum value m, but this method reliably prevents the occurrence of bounce, and also slows down the change in the discrimination speed and reduces high-order harmonic components. Harmful vibrations caused by this can be sufficiently reduced.

It should be noted that each of the embodiments can be applied regardless of the valve train system such as an OHC system or an OHV system.

(Effects of the Invention) As described above, according to the present invention, since the valve speed is made to take a minimum value immediately before the intake and exhaust valves are seated on the valve seats, bouncing at high engine speeds can be prevented, and noise This makes it possible to reduce the amount of damage and improve the reliability of the device.

[Brief explanation of drawings]

Fig. 1 (aL (b), (c) is each characteristic diagram showing an example of the present invention, Fig. 2 (a), (b), (C) is each characteristic diagram showing other embodiments, fjS3 Figures (a), (b), (e)
are characteristic diagrams of the conventional example. Procedural amendment (method) December 3, 1985 Patent M No. 213491 No. 2 of 1985 Name of the invention Relationship to the case of person who corrects engine valve train 3.11'll Patent applicant address Kanagawa Prefecture Name of No. 2 Takaracho, Kanayō Ward, Yokohama City (3
99) Nissan Motor Co., Ltd. 4, Agent 5, Date of amendment order: November 5, 1985 (Shipping date: November 25, 1986) 6: ``Brief explanation of drawings'' in the specification subject to amendment Columns and drawings. 7. Details of correction (1) Lines 8 to 11 of No. 7 of the specification will be corrected as follows. "Figure 1 is a characteristic diagram showing an embodiment of the present invention, Figure 2 is a characteristic diagram showing another embodiment, and Figure 3 is a characteristic diagram of a conventional example." (2) Figure f51 ~ @ of the drawing Figure 3 is corrected as shown in the attached sheet.

Claims (1)

[Claims] In a valve train that opens and closes the intake and exhaust valves of an engine via cams that rotate in synchronization with the engine rotation, the speed of the intake and exhaust valves reaches a minimum value just before the intake and exhaust valves are seated on the valve seats. A valve operating device for an engine, characterized in that the cam shape is determined so that the speed of the valve takes a maximum value as the lift amount of the valve becomes smaller.