JPS6147295B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention makes the opening/closing timing of the exhaust valve and intake valve of an internal combustion engine variable according to the operating condition to appropriately control the amount of residual gas in the cylinder (hereinafter referred to as the internal EGR amount). The present invention relates to a valve driving device for an internal combustion engine.

Exhaust gas recirculation system (EGR) is widely known as a technology for reducing NOx emitted from internal combustion engines, but NOx is normally recirculated through the EGR passage that connects the exhaust passage and intake passage. However, in this case, the EGR gas is cooled while flowing through the relatively long EGR passage, and when introduced into the intake passage, the
The temperature is 200℃, which is not much different from the intake mixture.

Introducing high-temperature EGR gas into the intake system can be expected to have the effect of heating the air-fuel mixture, promoting vaporization of the fuel and making the mixture more uniform, so it is important to keep the EGR gas as cool as possible.

Based on this, we utilized the phenomenon in which exhaust gas blows back into the intake passage via the combustion chamber due to negative intake pressure during valve overlap, when the engine's intake and exhaust valves are both open from the end of the exhaust stroke to the beginning of the intake stroke. inside to
The EGGR system is starting to attract attention.

This internal EGR system blows high-temperature exhaust gas directly back into the intake system, resulting in much higher temperatures than the external EGR system described above.

However, since the flow rate of internal EGR is determined by the differential pressure between the exhaust pressure and suction negative pressure, the reflux amount tends to be large in low load areas where the suction negative pressure is large, and decrease in high load areas. The problem was that not only did it not match the EGR characteristics, but it was also difficult to control the flow rate.

In addition, whenever high-temperature gas blows back, it returns from the combustion chamber to the low-temperature intake passage (intake manifold) via the intake valve, so the temperature decreases significantly due to cooling, making it difficult to effectively utilize the thermal energy of the reflux gas. losses are unavoidable.

In order to solve these problems, the present invention closes the exhaust valve early in the middle of the exhaust stroke to confine the residual gas within the cylinder, and also relatively delays the opening timing of the intake valve so that this residual gas can be absorbed into the intake air. By preventing the gas from returning to the passageway, the purpose is to control high-temperature residual gas to an optimal value depending on operating conditions, effectively reducing NOx and improving operating performance.

Embodiments of the present invention will be described below based on the drawings.

As shown in FIG. 1, the present invention variably controls the valve timing of the intake valve and exhaust valve depending on the operating condition, thereby making it possible to perform maximum EGR in the engine medium load range.

The exhaust valve begins to open near the exhaust bottom dead center like a normal engine, but its closing timing is variably controlled depending on the operating state before reaching the exhaust top dead center.

Therefore, when the exhaust valve closes before top dead center, the remaining gas trapped in the cylinder will be compressed as the piston moves upward.

The amount of residual gas increases as the exhaust valve closes earlier.

On the other hand, the intake valve is preferably opened after the pressure of the residual gas is lower than when the exhaust valve is closed, during the intake stroke when the piston begins to descend after the exhaust (intake) top dead center.

By delaying the opening timing of the intake valve in accordance with the closing timing of the exhaust valve in this manner, residual gas trapped within the cylinder is prevented from being forced out into the intake system when the intake valve is opened.

The closing timing of the intake valve is set at a fixed position near the bottom dead center of the intake, as in a normal engine.

FIG. 2 shows an embodiment for controlling the operation of the intake and exhaust valves in this manner.

Camshaft 2 attached to the top of cylinder head 1
is rotatably and slidably supported between bearings 3, 3, and rotates in synchronization with engine rotation (crankshaft rotation) through a chain wheel 5 that engages with a spline portion 4 formed at the end of the shaft. communicated.

A freely sliding piston 7 is connected to a hydraulic cylinder 6 at the other end of the camshaft 2, and when the piston 7 is displaced in accordance with the hydraulic pressure supplied to the hydraulic chamber 8, the camshaft 2 is moved integrally with the piston 7. Move in the axial direction.

The exhaust valve cam 10 attached to this camshaft 2 is
This is a so-called three-dimensional cam whose profile is variable as the axial displacement occurs, and the closing timing of the exhaust valve 11 changes as the camshaft 2 moves.

Hydraulic pressure that increases in conjunction with the opening degree of the accelerator pedal acts on the piston 7, moving the camshaft 2 proportionally, so that as the load increases, the cam 10 moves along the solid line in FIG. The cam profile is formed so that the exhaust valve closing timing gradually advances from the position to the dotted line position, reaches the dotted line position in the middle load range, and then returns to the solid line position as the load further increases.

In other words, the internal EGR amount is controlled so as to gradually increase from low load to medium load, reach the maximum value at medium load, and then gradually decrease as the load increases.

In addition, the opening timing of the intake valve is variably set during the piston descent process from the intake top dead center, and in principle, the period (crank angle) from the exhaust valve closed position to the exhaust top dead center and the intake An intake valve cam (not shown) is attached to the camshaft 2 so that the period from top dead center to the open position of the intake valve is equal.
cam profile is set.

Therefore, in the present invention, in order to increase internal EGR, the valve timing is such that as the exhaust valve closes earlier, the intake valve starts opening later. This is completely different from increasing internal EGR depending on the size of the valve overlap.

A controller 12 that controls the pressure oil supplied to the hydraulic cylinder 6 increases the oil pressure as the accelerator opening increases in conjunction with an accelerator pedal (not shown).

A lever 13 interlocked with the accelerator pedal drives a piston 16 via a sleeve 14 and a spring 15, and a valve body 17 connected to the piston 16 connects a discharge passage 18 from the oil pump P and a supply passage 19 communicating with the hydraulic chamber 8. The communication port 20 is opened and closed to increase the oil pressure in proportion to the accelerator opening.

In addition, supply oil pressure acts on the oil chamber 21 via a passage 22 to compensate for the movement of the piston 16 in response to differential pressure fluctuations, while excess flow is sent to the oil tank T via a return passage 23 with an orifice. return.

With the above configuration, when the hydraulic pressure supplied by the hydraulic controller 12 increases in proportion to the accelerator opening, the camshaft 2 is pushed by the piston 7 of the hydraulic cylinder 6 and moves, and accordingly, the exhaust valve 11 is moved. The closing timing becomes gradually earlier before the exhaust top dead center, and at the same time, the opening timing of the intake valve gradually becomes later after the intake top dead center.

For this reason, the amount of combustion gas pushed out into the exhaust passage during the exhaust stroke decreases as the exhaust valve closes earlier, and on the other hand, gas equivalent to the cylinder volume when the valve is closed is trapped in the combustion chamber as residual gas.

This residual gas is then slightly compressed as the piston rises, and when it expands to its original state after passing the top dead center of the intake, the intake valve opens and fresh air from the intake passage is sucked into the cylinder. begins to be

The residual gas pressure in the cylinder when the intake valve opens is in a pre-compression state, unlike when the intake valve opens in a compressed state, so it is maintained at approximately atmospheric pressure.
Moreover, since the piston is descending in a direction to expand the cylinder volume, a large amount of this residual gas does not flow into the intake system, and most of the residual gas remains inside the cylinder as it is.

As a result, the residual gas is difficult to cool, and it reliably imparts high thermal energy to the newly drawn air-fuel mixture, significantly promoting vaporization of the fuel or homogenization of the mixture.

Note that even if the residual gas is compressed after the exhaust valve closes, the intake valve does not open until it expands to its original state, so there is almost no energy loss during this time.

As the accelerator opening increases, the exhaust valve closes earlier and the intake valve opens later.The amount of residual gas reaches its maximum in the medium load range (or from medium load to high load), and the This is intended to effectively reduce NOx in this load area, which is frequently used and where NOx generation increases.

Next, in the engine high load range, in order to maximize the amount of intake air (fresh air) and ensure full engine output performance,
It is preferable to reduce residual gas, but
Due to the further movement of the camshaft 2, the closing timing of the exhaust valve is gradually delayed and approaches the normal fixed valve timing, so the amount of residual gas decreases, and moreover, the intake efficiency and exhaust efficiency are increased to high output. The engine produces sufficiently high output because it matches the characteristics required during operation. This example shows an example in which the valve timing of the intake and exhaust valves is controlled by a three-dimensional cam, but the camshafts of the intake and exhaust valves can be configured separately to adjust the rotational phase of the intake valve camshaft in response to an increase in load. The exhaust valve camshaft may be controlled to be relatively delayed and the phase of the exhaust valve camshaft may also be relatively advanced.

Also, the timing of closing the exhaust valve and the opening timing of the intake valve do not necessarily have to be symmetrical about the top dead center position, but even in this case, the intake valve should start opening after the intake top dead center. Make it.

As explained above, according to the present invention, the closing timing of the exhaust valve is variably controlled during the exhaust stroke, and the opening timing of the intake valve is correspondingly delayed. EGR
gas) can be controlled accurately according to the operating conditions, and most of the residual gas can be confined within the cylinder, preventing temperature drops and reducing the air-fuel mixture and EGR.
Combustion is improved by relatively increasing the temperature of the gas after mixing with gas, and therefore NOx can be effectively reduced without impairing engine operating performance.

Furthermore, if the temperature of EGR gas increases relatively, the volume occupied by EGR gas will increase if the EGR rate is the same, and at this time, the amount of intake air will decrease with the same suction negative pressure, so it is necessary to maintain the same engine output. If the throttle opening is increased to keep the amount of intake air (fresh air) the same, the pumping loss of the engine will be reduced by the amount that the intake negative pressure is relatively reduced, and fuel efficiency will be improved.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram showing the opening and closing characteristics of the intake and exhaust valves of the present invention, and FIG. 2 is a sectional view showing an embodiment of the valve mechanism. 2...Camshaft, 6...Hydraulic cylinder, 7...Piston, 10...Cam (three-dimensional cam), 12...Hydraulic controller.

Claims (1)

[Claims] 1. In a reciprocating internal combustion engine equipped with intake and exhaust valves that open and close in synchronization with engine rotation, the opening timing of the intake valve and the closing timing of the exhaust valve are variably controlled according to the operating state. A valve mechanism is installed, and the exhaust valve closing timing is variable to a position earlier than the exhaust top dead center, and the intake valve opening timing is variable to a position later than the intake top dead center. A valve drive device for an internal combustion engine configured to control the amount of residual gas in a cylinder by setting the crank angle to dead center and the crank angle from intake top dead center to the intake valve open position to be approximately the same. . 2. The internal combustion engine according to claim 1, wherein the exhaust valve has an opening timing set at a substantially constant time near the exhaust bottom dead center, and the intake valve has a closing timing set at a substantially constant time near the intake bottom dead center. Engine valve drive.