KR19980078819A - Variable valve timing mechanism for engines with two-stage characteristic curve - Google Patents

Abstract

The present invention relates to a variable valve timing control mechanism capable of eliminating backlash noise at a mating surface on which a spiral spline of a piston is engaged and quickly responding to supply hydraulic pressure. The variable valve timing control mechanism allows the helical spline piston to be operated laterally of the camshaft by the hydraulic pressure supplied through the camshaft so as to optimize the valve opening / closing timing of the engine for a specific speed range. And a return spring for returning the piston. In such a variable valve timing control mechanism, the return spring has three parts having different pitches from each other.

Description

Variable valve timing mechanism for engines with two-stage characteristic curve

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine of an automobile, and more particularly, by inequalizing a pitch of a return spring for performing a stroke return of a spiral spline (helical gear) piston in an on-off two-stage variable valve timing mechanism. The return spring has a two-stage characteristic curve, which relates to a variable valve timing mechanism of an engine having a quick response time and a noise reduction structure due to backlash.

Typically, when the engine of a vehicle is rotated at high speed, the output increases with longer opening time of the intake valve, but at low speeds, such as in idle zones, if the valve overlaps, the unburned hydrocarbon emissions increase while at the same time residual gas The engine relief phenomenon by appears. Therefore, it is ideal to change the valve opening / closing time or overlap period in accordance with the rotational speed and load of the engine.

However, although the valve opening / closing timing is easy to optimize for a specific speed range by the conventional camshaft and camshaft drive system, it is almost impossible to optimize over the full speed range of the engine. Recently, a cam with a large lift lift when the engine is rotating at high speed, and a cam with a small lift at low speed, or an engine with a mechanism for controlling the opening and closing time of a valve (mainly an intake valve) are added. This has been put to practical use.

1 is a diagram illustrating a valve timing control pulley used in an engine having a variable valve timing mechanism. As is well known, the valve timing control system comprises an inlet camshaft pulley 2 whose phase angle relative to the camshaft can be varied by hydraulic pressure acting on the spiral spline (helical gear) piston 1 with the control valve, It consists of the solenoid 9 (refer FIG. 2) which controls the oil pressure supplied to the camshaft pulley 2, and the inlet camshaft pulley 2 is driven by a timing belt. The engine control unit transmits a common signal to the solenoid 9 in response to the operating state.

The oil controlling this system is fed from the main gallery in the cylinder block via the passage 3 to the front camshaft journal. The oil then flows through the hollow camshaft 4 and the hollow bolt 5 to the piston cylinder 6 cut from the camshaft pulley 2. The hydraulic pressure in the camshaft passage 3 is adjusted by the flow rate through the control valve fitted to the rear of the camshaft 4.

The axial cylinder 6 inside the camshaft pulley 2 houses an annular piston 1 with helical splines on both sides on the inner and outer surfaces of the piston 1. Application of hydraulic pressure moves the piston 1 along the axis of the cylinder 6. This movement changes the angle of the internal camshaft 4 relative to the external camshaft pulley 2 driven by the timing belt, thereby changing the intake valve phase. The permissible upper limit of the valve phase shift is determined kinematically by the spiral angle and pitch diameter of the spline along with the piston travel. This system displaces the piston up to 10 ° for crankshaft angular displacement of up to 20 °. This value is imposed by the actual need on the overall length and acceptable reaction time.

When the solenoid 9 is released, the control valve 7 fitted to the rear of the crankshaft is pushed backward by the action of the return spring 10, as shown in FIG. 2, so that the oil in the camshaft 4 is discharged from the valve ( It flows into the cylinder head through the spill hole in 7). When the solenoid 9 is actuated, the control valve plunger 12 is pushed forward by the armature 11 of the solenoid 9 so that the spill hole 8 is blocked and the oil stops flowing. .

The solenoid 9 is fitted to the rear of the rocker cover and the armature acts to position the control valve under the command of the engine control unit. The solenoid 9 is of an on-off type.

Such a valve timing control system must be short in length so that it can be mounted on a vehicle, while the valve phase shift angle must be large enough to be effective.

However, since the return spring 10 of the conventional on-off type variable valve timing mechanism as described above is formed of a spring having an equal pitch interval as shown in FIG. 3, the load acting on the return spring 10. Since the characteristic graph of the over displacement is linear as shown in FIG. 6, there is a problem that noise occurs due to backlash in the mating surface where the helical spline of the piston is engaged and a delay in response time to the supply hydraulic pressure. there was.

It is therefore an object of the present invention to provide a variable valve timing control mechanism capable of eliminating backlash noise due to the backlash at the engagement surface at which a spiral spline of a piston engages, and capable of quickly responding to supply hydraulic pressure.

1 shows a valve timing control pulley used in an engine having a variable valve timing mechanism.

FIG. 2 is a sectional view showing a control valve and a solenoid of the valve timing control mechanism shown in FIG. 1; FIG.

3 shows a return spring of the variable valve timing control mechanism shown in FIG.

4 illustrates a return spring of a variable valve timing control mechanism having inequality in accordance with the present invention.

5 is a graph showing characteristic curves according to responsiveness, supply oil pressure, and engine speed of a variable valve timing control mechanism having an uneven pitch according to the present invention;

6 is a graph showing a comparison of the load and the spring displacement of the conventional variable valve timing control mechanism and the variable valve timing control mechanism according to the present invention.

Explanation of symbols for the main parts of the drawings

1: piston 2: camshaft pulley

3: camshaft passage 4: camshaft

5: hollow bolt 6: piston cylinder

7: control valve 8: spill hole

9: solenoid 10: return spring

The object as described above is that the spiral spline piston is operated laterally of the camshaft by the hydraulic pressure supplied through the camshaft so as to optimize the valve opening and closing timing of the engine for a specific speed range, the spiral when the voltage of the solenoid is released. A variable valve timing control mechanism having a return spring for returning a spline piston, wherein the return spring has three parts having different pitches from each other.

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

4 is a view showing a return spring of the variable valve timing control mechanism having an inequality pitch according to the present invention.

As shown in FIG. 5, the return spring 10 used in the variable valve timing control mechanism according to the present invention has three portions l ₁ , l ₂ , l ₃ in which the pitches of the springs have different pitches from each other. .

5 is a graph showing characteristic curves according to responsiveness, supply oil pressure, and engine speed of a variable valve timing control mechanism having an inequality pitch according to the present invention;

The variable valve timing control mechanism takes a long time to complete the conversion because the initial response time is low in the rotation of the engine and thus the supply hydraulic pressure is insufficient, but the three uneven pitch portions l ₁ , according to the present invention. By reducing the load in the initial displacement state of the return spring 10 having l ₂ , l ₃ ), as shown in FIG. 5, the initial operation even in a state where the engine speed is low and the pressure of the supply hydraulic pressure is low The time can be made faster by Δt than a conventional variable valve timing control mechanism.

Since it is possible to equalize the load value when the variable valve timing control mechanism is on, as shown in FIG. 6, the load characteristic diagram is provided by having three uneven pitch portions l ₁ , l ₂ , l ₃ . Set the inflection point (Q) at to set the strength and weakness of the load characteristics.

In addition, since it is possible to make the load value at the ON of the variable valve timing control mechanism the same, it is possible to suppress the influence of the noise due to the gear backlash and the return time.

As described above, according to the variable valve timing control mechanism according to the present invention, it is possible to eliminate the noise due to the backlash in the engagement surface where the spiral spline of the piston is engaged and to respond quickly to the supply hydraulic pressure.

On the other hand, the present invention is not limited to the above-described specific preferred embodiments, and various changes can be made by those skilled in the art without departing from the gist of the invention claimed in the claims. will be.

Claims (1)

To optimize the valve opening and closing timing of the engine for a specific speed range, a spiral spline piston is operated laterally of the camshaft by hydraulic pressure supplied through the camshaft, and a return spring that returns the spiral spline piston upon release of the solenoid voltage. In the variable valve timing control mechanism having: And the return spring has three portions having different pitches from each other.