JPH0619766Y2 - Intake and exhaust system for internal combustion engine - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial field of application) The present invention relates to an intake / exhaust device for variably controlling the operation timing of intake / exhaust valves of an internal combustion engine.

(Prior Art) An exhaust gas recirculation system is already known in which, in order to reduce NO _x emitted by an internal combustion engine, a part of exhaust gas is recirculated into intake air to suppress combustion and lower the combustion temperature. In this case, the combustion gas remains in the cylinder for the external exhaust gas recirculation method in which the exhaust gas that has once exited from the cylinder to the exhaust passage is introduced into the intake passage via the recirculation passage, and is then sucked in the next intake stroke. The method of mixing with fresh air
It is called internal exhaust gas recirculation.

(Problems to be solved by the invention) The required exhaust gas recirculation amount changes depending on the operating conditions, and is large in the low and medium load regions where the operating frequency is high and small in the high load region where the engine high output is required.

In order to increase or decrease the exhaust gas recirculation amount according to the operating conditions in the internal exhaust gas recirculation system, the valve timing of the intake and exhaust valves is variably controlled to change the valve overlap amount,
Adjust the percentage of residual gas contained in the cylinder.

However, variably controlling the valve timing of the intake / exhaust valve causes the structure of the intake / exhaust valve drive system to become complicated and the operation to be performed as disclosed in Japanese Patent Laid-Open No. 62-20625, for example. It had the drawback of lacking reliability.

It is an object of the present invention to provide an intake / exhaust device for an internal combustion engine capable of variably controlling the valve timing of the intake / exhaust valve with a relatively simple structure.

(Means for Solving Problems) Therefore, according to the present invention, a camshaft is composed of a hollow outer shaft and an inner shaft that relatively rotates therein, and an intake cam and an exhaust cam that drive an intake valve and an exhaust valve. One of the two is fixed to the outer shaft and the other is fixed to the inner shaft, and a cam fixed to the inner shaft is rotatably fitted to the outer shaft, and a rotational phase difference is provided between the outer shaft and the inner shaft. A differential mechanism provided and a transmission means for rotating the camshaft in synchronization with engine rotation are provided.

In addition, the outer shaft is configured to be axially separable according to the number of engine cylinders through a joint, and the differential mechanism engages a common cylindrical member with a helical gear whose lead angles are opposite to each other. The rotational phase difference is generated by moving the cylindrical member in either direction via a lever that swings around a rotating shaft in accordance with the operating state of the engine.

(Operation) The intake cam and the exhaust cam open and close the intake valve and the exhaust valve by the rotation of the camshaft. When the rotational phase of the outer shaft and the inner shaft is changed by the differential mechanism, the operating positions of the intake cam and the exhaust cam change, and the valve overlap amount of the intake valve and the exhaust valve changes. When the valve overlap amount is small, the internal exhaust gas recirculation amount becomes large and N
O _x reduction of Hakare, is large valve overlap amount is increased intake and exhaust efficiency, thereby improving and smoke reduction in the output.

(Example) The Example of this invention is described based on drawing.

As shown in FIG. 1, the camshaft 2 rotatably supported by the cylinder block 1 via the bearing portion 9 is
It is composed of a hollow outer shaft 3 and an inner shaft 4 inserted into the hollow outer shaft 3 so as to be rotatable relative to each other. An exhaust cam 5 for driving an exhaust valve is integrally formed on the outer shaft 3, while an intake cam 6 for driving an intake valve is rotatably fitted to the outer shaft 3 and attached to the inner shaft 4. It is fixed via the pin 7.

As shown in FIG. 2, the pin 7 penetrates the window portion 3a formed in the outer shaft 3 to connect the inner shaft 4 and the intake cam 6, and the window portion 3a connects the inner shaft 4 and the outer shaft 3 to each other. As will be described later, the window width in the circumferential direction is set so as to allow relative rotation at a predetermined rotation angle.

It should be noted that the camshaft 2 is divided according to the number of cylinders in the middle so as to correspond to a multi-cylinder internal combustion engine, and is connected by a joint 8 so that the intake cam 6 can be inserted into the outer shaft 3.

At the projecting end of the camshaft 2 from the bearing 9, a helical gear 10 is coupled to the outer shaft 3, and a helical gear 11 is coupled to the inner shaft 4 projecting from the outer shaft 3 via keys 10a and 11a, respectively. The helical gears 10 and 11 are set to have opposite leads, and the helical gears 10 and 1
1 is provided with a cylindrical member 12 that meshes with each other via internal gears 12a and 12b, and a lever 14 that axially displaces the cylindrical member 12 is provided, and the displacement of the cylindrical member 12 causes a gap between the helical gears 10 and 11. It constitutes a differential mechanism that generates the rotational phase.

The tip end of the lever 14 is held by the cylindrical member 12 via a thrust bearing 16, and by rotating the lever 14 around a rotating shaft 15, the cylindrical member 12 is displaced in the axial direction.

External teeth 12c are formed on the outer periphery of the cylindrical member 12, and a drive gear 13 that transmits engine rotation meshes with the external teeth 12c. The drive gear 13 is formed with a wide tooth width so that the meshing with the outer teeth 12c does not come off even if the cylindrical member 12 is displaced in the axial direction.

The lever 14 is driven via an actuator that responds to a signal from a control circuit (not shown) according to the operating state.

Reference numeral 17 is a thrust bearing that prevents the cam shaft 2 from moving in the thrust direction, and reference numerals 18 and 19 are keys for engaging the helical gears 10 and 11 with the outer shaft 3 and the inner shaft 4.

It is configured as described above, and the operation will be described below.

The drive gear 13 rotates the cylindrical member 12, and the rotation is transmitted to the helical gears 10 and 11 on the inner periphery thereof. As a result, the outer shaft 3 and the inner shaft 4 that form the camshaft 2 rotate together, and the exhaust cam 5 that is integral with these rotates.
And the intake cam 6 rotates. In this way, the intake / exhaust valve (not shown) is opened / closed in synchronization with the engine rotation.

When the lever 14 is rotated about the rotating shaft 15, the cylindrical member 12 is displaced in the corresponding direction, whereby each internal gear 1
Since the lead angles of the helical gears 10 and 11 meshing with the gears 2a and 12b are set in opposite directions, the helical gears 10 and 11 relatively rotate in opposite directions in proportion to the lead angle.

As a result, the outer shaft 3 and the inner shaft 4 rotate relative to each other, and at this time, the intake cam 6 is moved by the pin 7 through the window 3a of the outer shaft 3 by the pin 7.
Rotates integrally with.

Then, the relative positions of the intake valve and the exhaust valve with respect to the camshaft 2 are displaced, and the opening / closing timing of the intake / exhaust valve, that is, the valve timing is changed.

As shown in FIG. 3 (A), the intake valve opens before the exhaust valve completely closes near the end of the exhaust stroke, and when both are open, the valve overlap period θ is positive. Since the combustion gas is reliably discharged, the amount of residual gas trapped inside is smaller than that in the negative valve overlap state as shown in FIG. 3 (B).

As shown in FIG. 3 (B), when the exhaust valve is closed before the exhaust top dead center and the intake valve is opened after the top dead center, the combustion gas is not completely exhausted in the exhaust stroke and remains in the cylinder. A portion remains, and this residual gas amount increases in proportion to the negative valve overlap period.

Therefore, by operating the lever 14 as described above, the exhaust valve is closed earlier before the exhaust top dead center in the low and medium load range of the engine to eliminate the overlap with the intake valve (negative valve overlap). The internal exhaust gas recirculation amount can be increased to reduce the NO _x in the exhaust gas and the pumping loss in the compression stroke can be reduced. When required, the intake and exhaust efficiency can be improved by appropriately increasing the overlap period (positive valve overlap) in which both the intake valve and the exhaust valve are open (see FIG. 4). .

Next, in the embodiment shown in FIG. 5, the operation timing of the exhaust valve is fixed,
It shows the one in which only the operation timing of the intake valve is variably controlled.

The drive gear 13 is the outer shaft 3 to which the exhaust cam 5 is attached.
The cylindrical member 12 has only the internal gears 12a and 12b, and is fixed directly to the helical gears 10 and 11.
Meshes with.

Therefore, in this case, due to the displacement of the cylindrical member 12 via the lever 14, the outer shaft 3 is in a fixed relationship with the drive gear 13 synchronized with the engine rotation, so that only the inner shaft 4 relatively rotates and the intake valve The operation timing of changes.

By delaying the opening timing of the intake valve from top dead center,
The valve overlap with the exhaust valve decreases or becomes a negative value, which makes it possible to reduce NO _x and pumping loss. Conversely, by increasing the valve overlap, the intake amount is increased to improve output and smoke. It can be reduced.

As described above, according to the present invention, one of the intake cam and the exhaust cam that drives the intake valve and the exhaust valve is fixed to the outer shaft and the other inner shaft, and is also fixed to the inner shaft. It is a valve that is optimal for the operating condition, though it has a simple structure in which the cam is rotatably fitted to the outer shaft and a differential mechanism that provides a rotational phase difference between the outer shaft and the inner shaft is provided. The overlap can be set, and the internal exhaust gas recirculation can be increased in the low and medium load range to reduce NO _x , and the intake and exhaust efficiency can be increased in the high load range to improve the engine output.

Further, in the present invention, since the outer shaft is configured to be axially separable according to the number of engine cylinders through the joint, the cam can be easily inserted into the outer shaft during the manufacturing process, Cost can be reduced by using a common outer shaft part regardless of the number of parts.

Further, in the differential mechanism, a cylindrical member common to a helical gear having lead angles opposite to each other is meshed with one of the cylindrical members via a lever that swings around a rotary shaft according to an engine operating state. Since the rotational phase difference is generated by moving in the direction of, there is also an advantage that an appropriate valve opening / closing timing corresponding to the engine operating state can be set according to the swing angle of the lever.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of the present invention, FIG. 2 is a sectional view taken along line XX of FIG. 1, and FIGS. 3 (A) and (B) are explanatory views showing valve timings of intake and exhaust valves, respectively. FIG. 4 is an explanatory view showing the relationship between the valve lift and the crank angle, and FIG. 5 is a sectional view of another embodiment. 2 ... Cam shaft, 3 ... Outer shaft, 4 ... Inner shaft, 5 ... Exhaust cam, 6 ... Intake cam, 7 ... Pin, 1
0, 11 ... Helical gear, 12 ... Cylindrical member, 13 ... Drive gear, 14 ... Lever.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor, Kitamura, 1-chome, Daio, Saitama City, Nissan Daisel Industry Co., Ltd. (72) Keiichi Niimura 1-1, 1-o, Ageo, Saitama Prefecture Incorporated (72) Inventor Shuichi Nakamura 1-1, Oji, Ageo-shi, Saitama Nissan Diesel Industry Co., Ltd. (56) References: 58-120809 (JP, U)

Claims (1)

[Scope of utility model registration request] 1. A camshaft having a hollow outer shaft,
It consists of an inner shaft that rotates relative to the inside,
One of an intake cam and an exhaust cam that drives the intake valve and the exhaust valve is fixed to the outer shaft and the other is fixed to the inner shaft, and the cam fixed to the inner shaft is rotatably fitted to the outer shaft. However, a differential mechanism for imparting a rotational phase difference to the outer shaft and the inner shaft, and a transmission means for rotating the cam shaft in synchronization with engine rotation are provided, and the outer shaft is connected to the number of engine cylinders through a joint. Correspondingly, the differential mechanism is configured to be dividable in the axial direction, and the differential mechanism engages with a cylindrical member common to a helical gear whose lead angles are opposite to each other, and oscillates around a rotating shaft according to the engine operating state. And an exhaust device for an internal combustion engine, characterized in that a rotational phase difference is generated by moving the cylindrical member in either direction via a lever. .