JPS6032912A - Variable valve timing machanism of internal-combustion engine - Google Patents

Abstract

PURPOSE:To enable variation of valve timing without great modification of the design of a variable valve timing mechanism by rotatably mounting a bracket which retains an idler on a hub formed on the timing pulley of a cam shaft. CONSTITUTION:Rotation of a crankshaft is received by a timing pulley 12 via a timing belt and then transmitted to a cam shaft 14. An externally extending cylindrical projection 34 is formed on the hub 12A of the pulley 12 and a bracket 36 is rotatably mounted via a bush 38 on the cylindrical projection 34. The bracket 36 is provided with an idler 18 which comes into contact with the timing belt in the front and at the rear of the pulley 12. By turning the bracket 36 through the center of the cam shaft 24, valve timing may be varied according to operating conditions of an engine. Trifle modifications only on the design of the pulley 12, as such, may achieve variation of valve timing.

Description

TECHNICAL FIELD OF THE INVENTION The present invention relates to variable valve timing mechanisms for internal combustion engines.

BACKGROUND ART Various mechanisms for varying the pulp timing of internal combustion engines have been proposed up to now, but among them, Ganto Honda moved a pair of idlers close to the timing nozzle on the camshaft to a position on the axis of the camshaft. The timing belt is mounted on a bracket that can be freely rotated around the crankshaft, and by rotating the bracket, the tension of the timing belt is changed.This turns the camshaft relative to the crankshaft, thereby making the pulp timing variable. The proposed C patent application No. 57-36174).

OBJECT OF THE INVENTION The purpose of the present invention is to improve the variable valve timing mechanism proposed by the applicant, and more specifically, to make it possible to install such a mechanism into an existing internal combustion engine with almost no modification. I'm excited about what's possible.

Structure of the Invention According to the variable valve timing mechanism of the present invention, a cylindrical projection is formed in the opposite direction to the camshaft from the hub portion of the timing groove on the camshaft, and is located on both sides of the timing groove on the camshaft. A bracket holding a pair of tension rollers (idlers) is rotatably fitted to the cylindrical projection of the timing groove on the camshaft. With the configuration of the present invention, the timing pulley can be attached to an existing timing pulley with only a slight design change.

EXAMPLE To explain the following with the drawings, in FIG. 1 schematically showing the front part of an internal combustion engine, 10 is a timing pulley on the crankshaft, 12 is a timing pulley for the intake camshaft, and 14 is a timing pulley for the intake camshaft.
16 is a timing pulley for the exhaust cam, and 16 is a timing pulley frequently used for auxiliary equipment such as an oil pump, which is wrapped around by a timing belt 17. 18,20.2
2 is a tension roller (or idler).

The timing pulley 12 for the intake camshaft is provided with a variable pulp timing mechanism according to the present invention.

That is, as shown in FIG. 2, the above-mentioned pulley 12 is provided on the intake camshaft 24, and is fastened by a bolt 28 via a washer 26. 30 is a turning pin. A cylindrical protrusion 34 integrally extends from the hub portion 12A of the timing pulley 12 in the opposite direction to the camshaft 24 in the same direction as the axis of the camshaft 24. A bracket 36 is rotatably fitted into this cylindrical projection 34. In the embodiment, a bearing 38 is provided to ensure smooth rotation of the bracket 36 relative to the cylindrical protrusion 34.
is included, but this is optional.

Idlers 18 and 20, which sandwich the timing pulley 12 for the intake camshaft, are held at both ends of the bracket 36.

As shown in FIG. 2, the idler 18 is mounted via a bearing 40 on a bush 38 which is fitted into a bracket 36. The structure of the idler 20 is also similar.

Reference numeral 41 shows a drive mechanism for switching the pulp timing as an example, and the bracket 36 is connected to a pin 42 . Connecting rod 44. It is connected to a crank wheel 48 via a pin 46. The crank wheel 48 meshes with a drive wheel 50, and the drive wheel 50 is connected to a rotary drive motor (not shown).

The rotation of the motor causes the drive wheel 50 to rotate the crankshaft 48, and the connecting rod 44 swings between the left and right dead centers of the crank mechanism. At the dead center position on the right side shown in the figure, the bracket 36 assumes the position indicated by the solid line, which is the most counterclockwise opened position in the figure. At this time, the idlers 18 and 20 also assume the solid line position, and the timing belt 17 assumes the solid line tension state, so that the timing pulley 12 on the camshaft 24 is relatively rotated counterclockwise. The cam (not shown) on the camshaft 24 by this amount of rotation opens the pulp at a later time if the camshaft 24 were to turn in the direction of the arrow (ie, clockwise).

Immediate timing is delayed.

When the crank wheel 48 is turned to the left dead center position, the bracket 36 assumes the most clockwise rotated position in the figure (dotted chain line 9), and the idler 18, 20 similarly assumes the position shown in the double dot chain line. Therefore, the belt 17 is tensioned as shown by the two-dot chain line, and the timing pulley 12 on the camshaft is rotated relatively clockwise compared to when the belt is tensioned as shown by the solid line. Therefore, the pulp timing proceeds in the opposite direction.

In the structure according to the present invention, the bracket 36 includes a cylindrical protrusion 34 extending from the hub portion 12A of the timing pulley 12.
It can be installed by fitting it from the front, simplifying assembly work, and can be installed with almost no changes to existing parts.

By the way, the applicant's earlier application (1987-
No. 36174), the bracket 36 was not provided on the timing groove as in the present application, but was attached to the cylinder head side so as to be rotatable around the axis of the camshaft. Therefore, it was necessary to process or modify the cylinder head and camshaft, and it was not possible to install it on an existing engine. The present invention improves this point.

The illustrated embodiment is an example of application to a so-called DOHCm internal combustion engine having two camshafts, and a variable pulp timing mechanism is provided for the intake camshaft.

However, it can also be applied to 5OHC type internal combustion engines.

Moreover, it can also be provided on the exhaust camshaft even if it is a DOHCW. Further, although a crank mechanism is used to drive the bracket 36, the same operation can be achieved by using a linear reciprocating drive such as a linear solenoid instead.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of the belt transmission mechanism of the front side of the internal combustion engine according to the present invention, and FIG. 2 is an enlarged sectional view taken along the line ■-■ in FIG. 12... Timing pulley on camshaft, 12A... Hub part, 17... Timing belt, 18.20...
Idler, 34...Cylindrical projection, 36...Bracket. Patent Applicant Toyota Motor Corporation Patent Application Agent Akira Aoki Patent Attorney Kazuyuki Nishidate Patent Attorney Takao Mitsui Patent Attorney Akira Yamaguchi Patent Attorney Masaya Nishiyama

Claims (1)

[Claims] In a power transmission system in which a timing belt connects the timing pulley on the crankshaft of an internal combustion engine and a timing pulley on the camshaft, and a pair of idlers is provided to sandwich the timing pulley on the camshaft, the timing pulley on the camshaft is A cylindrical projection is formed in the hub portion of the timing pulley in the opposite direction to the cam shaft, and the bracket for holding the pair of idlers is rotatably fitted to the cylindrical projection of the timing pulley on the cam shaft. Variable valve timing mechanism.