JPS6023442Y2 - Internal combustion engine valve train - Google Patents

Description

[Detailed explanation of the idea] This invention relates to improvement of a valve train for an internal combustion engine.

Various valve train systems have been proposed in the past that are configured so that the valve lift of the intake and exhaust valves is variable, and the opening period and lift amount of the intake and exhaust valves can be optimally controlled according to the engine operating state. .

As this valve lift control device, for example, Fig. 1a,
There are some as shown in b (see Japanese Patent Application No. 54-74994 and Japanese Unexamined Patent Publication No. 55-14973).

To explain this, the cam lift of the intake and exhaust cam (drive cam) 1 that rotates in synchronization with the engine rotation is controlled by the variable lid device 2.
A swing cam 5 disposed on the upper part of the oil tappet 3 and a bushing rod 4, which constitute the shaft 6, is caused to swing about the fulcrum of the shaft 6.

The cam lift of the swing cam 5, which increases in proportion to the swing angle, drives the rocker arm 7 provided at the top of the swing cam 5.
The intake and exhaust valves 8 are lifted.

At this time, if the control oil pressure (adjusted oil pressure) supplied to the oil pressure chamber 9 of the oil tappet 3 is sufficiently high, such as during high load (or high speed rotation), the oil in the oil pressure chamber 9 will cause the oil tappet to The plunger (piston) 10 of No. 3 is a coil spring 11 that urges the swing cam 5 in the counterclockwise direction.
It rises against the urging force of the variable lid device 2, thereby expanding the effective length of the variable lid device 2 to the maximum.

Therefore, the body (cylinder) 12 of the oil tappet 3
When the rocker arm 7 is in sliding contact with the base circle of the cam 1, the rocker arm 7 is in a position immediately before the operation where it comes into sliding contact with the lift rising portion 5b.

When the cam 1 starts to lift from this state, the body 12 receives an upward force and tries to flow the oil in the hydraulic chamber 9 back upstream, causing the ball valve 13 to sit on the seat 14. As a result, the body 12 and plunger 10 are pushed up together.

Therefore, at the same time as the cam 1 starts lifting, the swing cam 5 is driven and the valve 8 is lifted.

In this way, since the valve 8 is lifted at the same time as the drive cam 1 is lifted, the opening period and valve lift of the valve 8 take maximum values, as shown by the solid line A in FIG.

However, the cam 1 indirectly controls the valve timing of the valve 8 by regulating the rotation direction and speed of the swing cam 5, and the swing cam 5 works to regulate the lift amount of the valve 8 via the rocker arm 7. Therefore, the characteristics of the valve 8 are a composite of the characteristics of the cam 1, the characteristics of the swinging cam 5, and the characteristics of the rocker arm 7 (rocker ratio).

Further, the swing cam 5 has a base circle 5a concentric with the shaft 6, and has a buffer curved lift portion 5c that smoothly rises from the base circle 5a.

On the other hand, when the control oil pressure supplied to the oil tappet 3 is relatively low depending on the engine load (or engine speed), such as during partial load (or during medium-low speed rotation), the plunger 10 The bushing rod 4 is lowered to a position where the biasing force of and the hydraulic pressure of the hydraulic chamber 9 are balanced, and the bushing rod 4 is relatively lowered.

Therefore, before the body 12 of the oil tappet 3 comes into sliding contact with the lift portion of the cam 1, the swing cam 5 rotates counterclockwise, and the rocker arm 7 moves to the base circle 5a before the rising portion 5b of the swing cam 5. The phase shifts to the point where they make sliding contact.

The lower the engine load (or rotational speed), the lower the control oil pressure becomes, so the phase is relatively expanded and the time taken for the rocker arm 7 to reach the rising portion 5b increases.

Even if the oil tappet 3 is lifted by the cam 1 from this state, the valve 8 will not be lifted until the rocker arm 7 reaches the rising portion 5b.

As a result, as the engine load (or engine speed) decreases, the amount of cam lift absorbed increases relatively, and as shown by solid line B in Figure 2, the valve opening period and valve lift decrease relatively. do.

When using such a valve lift control device to reduce pumping loss in the low and medium speed range of the engine by controlling the intake air amount by controlling the opening period of the intake valve without using the throttle valve, in the low load range It was necessary to control the operating angle of the intake valve to a small value as shown in Figures 3a and 3b.

In this case, the effective length of the variable lifter device 2 decreases, and at the same time, the lift amount of the intake valve also naturally decreases, and even if it is desired to increase it, the cam profile of the drive cam 1 is constrained to always have a positive radius of curvature. For this reason, unless the lift circle range of the cam 1 is increased, a sufficient lift amount cannot be obtained, which has the drawback of increasing throttling loss due to the intake valve.

In addition, Fig. 3a shows the exhaust valve closed at around 400° after top dead center to suck the exhaust gas back into the cylinder to perform internal EGR, and Fig. 3a shows the exhaust valve closed at around 30° before top dead center to exhaust the exhaust gas. This shows a system for performing internal EGR by confining the engine in a cylinder.

Therefore, this idea was developed to expand the lift circle range of the cam and increase the effective lift amount by providing an annular step on the outer circumference of the intake valve that slides against the inner circumference of the valve seat only during a predetermined stroke. The purpose is to provide a valve device.

An embodiment of this invention will be described below with reference to the drawings.

FIG. 4 is an enlarged view of the intake valve portion, and the other configurations are the same as those shown in FIGS. 1a and 1b, so the same reference numerals will be used for the same members and detailed explanation will be omitted.

An annular step 17 concentric with the valve stem 16 is formed on the outer periphery of the cap 15 of the intake valve 8'. Formally imposing.

The lower part of the annular stepped portion 17 forms a conically expanding slope 20, and this slope 20 comes into contact with and separates from the seat surface of the valve seat 19.

21 is a valve guide, and 22 is an intake port.

Therefore, if the intake valve 8' is configured in this way, the intake valve 8'
Even if the lifting action of
H substantially overlaps the intake valve 8'
is held closed.

Therefore, the intake valve cam 1 (Fig. 1a) that drives the intake valve 8'
Set the operating angle of the lift circle (see) to a larger operating angle than the conventional operating angle.

Therefore, in the actual low load range as shown in Fig. 5, the open range of the intake valve 8' is no different from the conventional operating range, but its actual maximum lift h1 is lower than the conventional maximum lift h2. It can be made larger than that.

The rising and falling parts of the lift surface of the cam 1 must always have a positive curvature, at least equal to or less than the tangent to the base circle (to stabilize the valve opening/closing operation). If it is too small, the maximum lift cannot be sufficiently large, but by providing the overlap H in this way, the angle of inclination of the cam lift surface at the point where the intake valve 8' actually starts to open can be increased, and the subsequent opening/closing acceleration can be increased. Therefore, the effective lift amount from the time the opening starts to the maximum lift point is much larger than that of the conventional case including the rising portion even at the same operating angle.

In this way, according to this invention, the effective lift amount can be increased without changing the actual operating angle of the intake valve, so that the throttling loss due to the intake valve in the low and medium speed range of the engine can be reduced. This has the effect that it is possible to reduce the pumping gas and improve the performance, and also to easily achieve internal exhaust gas recirculation.

[Brief Description of the Drawings] Figures 1a and 1b are schematic longitudinal cross-sectional and plan views of the valve lift control device, Figure 2 is its valve lift characteristic diagram, Figure 3a,
FIG. 4 is a cross-sectional view of the intake valve of this invention, and FIG. 5 is an explanatory view showing the relationship between its operating angle and lift. 8'... Intake valve, 2... Variable lifter device, 1... Drive cam, H... Overlap amount, 19... Valve seat, 18...
...Sliding contact part, 17... Annular stepped part.

Claims (1)

[Scope of utility model registration request] In a valve train for an internal combustion engine configured to control the amount of intake air by increasing or decreasing the intake valve operating angle depending on the operating condition via a variable lifter that follows the intake valve cam, the lift circle portion of the intake valve cam is A valve operating device for an internal combustion engine, characterized in that the range is set to be large, and an annular stepped portion is provided on the outer periphery of the intake valve to slide into contact with the inner periphery of the valve seat only during a predetermined stroke.