JPH0341656B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an engine braking performance improving device for an internal combustion engine that includes a mechanism that varies valve timing by changing the phase of a camshaft with respect to a crankshaft.

It is desirable that the engine brake performance be as effective as possible to avoid frequent use of the foot brake. 4
Cycle engines have an advantage over two-stroke engines in that they have better engine braking effectiveness.
However, it is necessary to improve engine braking performance even in four-stroke engines.

Japanese Utility Model Application Publication No. 56-117005 discloses a system in which an oil tappet and a swinging cam are provided between the rocker arm of the exhaust valve and the cam, and by expanding and contracting the oil tappet, the effective lift of the cam is changed and the valve timing is changed. is suggesting. Under normal conditions, the oil tappet extends, the effective lift of the cam increases, and the swing angle of the rocker arm increases.At this time, the exhaust valve starts opening at the normal timing and completes closing at the normal timing. When the engine decelerates, the oil tappet contracts, the effective lift of the cam becomes smaller, the swing angle of the rocker arm becomes smaller, the opening of the exhaust valve is delayed, and the valve closes more quickly.

In this conventional technology, by delaying the opening of the exhaust valve, the compression work increases and engine braking becomes effective.

However, with this conventional technology, the exhaust valve closes earlier, which shortens the valve overlap period, and because the intake air flow cannot be utilized, the efficiency of exhaust gas discharge from the combustion chamber deteriorates. This has the disadvantage that there is a greater possibility that gas will flow back into the intake pipe.

The present invention solves this drawback of the prior art, and aims to prevent the amount of overlap from decreasing even if the opening of the exhaust valve is delayed during deceleration.

According to the present invention, in an internal combustion engine equipped with a mechanism for varying valve timing by changing the phase of the camshaft relative to the crankshaft, a means for detecting when the engine is decelerating is provided, and a deceleration detection signal from the detecting means is provided. The crank angle position at which the exhaust valve starts to open is located on the lag side in the direction of crankshaft rotation from bottom dead center relative to the crank angle position at which the exhaust valve starts to open under normal conditions, and the exhaust valve completes closing. The variable valve timing mechanism is characterized in that the variable valve timing mechanism is driven so that the angular position is on the lag side in the direction of rotation of the crankshaft with respect to the crank angular position at which the exhaust valve normally completes closing.

During deceleration, the opening of the exhaust valve is delayed, which increases compression work and improves engine braking performance.

On the other hand, the end of closing of the exhaust valve is delayed during deceleration, so the overlap does not decrease.

Explaining the following with reference to the drawings, in FIG. 1, 10 is a cylinder block, 12 is a piston,
14 is a connecting rod, 16 is a crankshaft,
18 is a cylinder head, 20 is an intake valve, 22 is an exhaust valve, 24 and 26 are rocker arms, 28 is a camshaft, 30 is an intake manifold, 32 is a throttle valve, and 34 is an exhaust manifold. These are well-known components in internal combustion engines and are not related to the features of the present invention, so a detailed explanation of the connection relationship will be omitted.

The valve timing switching mechanism is shown in its entirety at 50. As shown in FIG. 2, this mechanism consists of a camshaft 28 and a timing pulley 52 on the camshaft 28.
(It is connected to a timing pulley on the crankshaft 16 by a timing belt (not shown).). That is, an inner sleeve 54 is fixed to a bolt 56 at the shaft end of the camshaft 28 . An outer sleeve 58 extends integrally from the hub of the timing pulley 52 so as to be coaxial with the inner sleeve 54. Slits 60 and 62 are formed between the inner sleeve 54 and the outer sleeve 58, one of which is straight and the other is inclined. Bearings 66, 68 carried on the radial shaft 65 of the support 64 are provided in the slot. A rotary motor 70 is attached to a timing belt cover 72, and an output shaft 74 is threaded into a nut 76 longitudinally guided in the motor housing. The support 6 is mounted on the nut 76 by means of a bearing 78.
4 is provided. The rotation of the motor 70 is controlled by the nut 76.
The bearings 66, 68 move to the left or right in the figure depending on the direction of rotation of the motor 70. Because the bearings 66 and 68 are located within the intersecting slits 60 and 62, side-to-side movement of the bearings causes the inner sleeve 54 to
Relative rotation occurs between the outer sleeve 58 and the outer sleeve 58 . This relative rotation controls the crank angle position when the cam ridge 28' on the camshaft 28 engages with the rocker arm 24 or 26, that is, the valve timing.

Reference numeral 80 denotes a control circuit that detects whether or not the engine is decelerating and performs valve timing control in the present invention. The control circuit 80 receives a signal from a deceleration detecting means consisting of a throttle switch 81 and an intake pipe negative pressure switch 82. Control circuit 80
outputs a switching signal to the valve timing control device 50 depending on whether or not deceleration is to be performed. The control circuit 82 has a detailed structure shown in FIG. 4, and is composed of an AND gate 83 and a motor drive circuit 84. The motor drive circuit 84 includes two pairs of PNP and NPN transistors 841, 842 and 843, 844 connected in series, the bases of the transistors 841, 842 are directly connected to the input terminal 845, and the bases of the transistors 84
The base of 3,844 is connected to an input terminal 845 via an inverter 846. transistor 84
Junction point of 1 and 842 and transistors 843 and 8
A motor 64 is connected between the junction point with 44.
If the input terminal 845 is at a high level, transistors 841 and 844 are OFF, and transistor 8 is turned off.
42 and 843 are turned on, and the motor 64 rotates in the forward direction. When the input terminal 845 is at a low level, transistors 842 and 843 are turned off, transistors 841 and 844 are turned on, and the motor 64 is rotated in reverse. The control circuit 84 controls the motor 6 depending on the operating conditions.
Rotate 4 forward or reverse.

To describe the operation of the present invention, during operation other than during deceleration, the throttle valve 32 is in a position other than the idle position, and at this time the output of the throttle switch 81 is Low. Therefore, regardless of the output from the negative pressure switch 82, the AND gate 83 outputs a Low output. Therefore, the motor 64 rotates in reverse, and the valve timing assumes its normal value. That is, the exhaust valve 22
As shown in Fig. 5a _, the normal timing is to start opening at an angle α ₁ before the bottom dead center BDC in the rotational direction take.

During deceleration, the throttle switch 81
It becomes High, and the negative pressure switch 82 also becomes High.
Therefore, AND gate 83 outputs a High output.
As a result, the motor rotates in the normal direction, and the valve timing takes a different timing than usual, as shown in FIG. 5b. That is, the exhaust valve 22 is rotated in the crankshaft rotation direction
, it began to open at an angle of α ₂ , well ahead of bottom dead center, and was well past top dead center TDC, but T dead center
It begins to close at an angle of β ₂ , which does not reach BDC.
In this way, since the exhaust valve 22 begins to open at a position well in front of the bottom dead center BDC in the direction of rotation of the crankshaft, there is no place for the gas compressed by the piston 12 to escape even after the bottom dead center, and this causes compression work. This appears as strong engine braking. In this embodiment, since the camshaft 28 is rotated to control valve timing in the SOHC engine, the timing of operation of the intake valve changes according to the timing of operation of the exhaust valve. That is, if the broken line 1 is the opening timing of the intake valve during normal operation, the opening timing of the intake valve during deceleration is as shown by the broken line m. The amount of overlap n during normal operation does not change from the amount of overlap o during deceleration. Therefore, the amount of overlap is the same both during normal operation and during deceleration.

As described above, according to the present invention, engine braking performance can be improved by detecting the time of deceleration and opening the exhaust valve during the exhaust stroke after the bottom dead center has passed considerably. In this invention, not only the opening timing of the exhaust valve is delayed during deceleration, but also the closing of the exhaust valve is delayed. Therefore, the necessary amount of overlap can be obtained even during deceleration, and the flow of intake air during overlap scavenges the exhaust gas in the combustion chamber, increasing the exhaust efficiency of the exhaust gas in the combustion chamber, and This reduces the risk of backflow and maintains engine performance over a long period of time.
The illustrated embodiment shows an application to a so-called SOHC type engine in which an intake valve and an exhaust valve share a single camshaft, but the present invention can equally be applied to a DOHC type engine.

[Brief explanation of the drawing]

Fig. 1 is an overall configuration diagram of an internal combustion engine according to the present invention;
The figure is a vertical cross-sectional view of the valve timing device, FIG. 3 is a view taken in the direction of the arrow in FIG. 2, FIG. 4 is a diagram showing a control circuit, and FIG. 5 is a valve timing diagram. ...Exhaust valve, 28...
...Camshaft, 32...Throttle valve, 50...Variable valve timing device, 81...Throttle switch, 82...Negative pressure switch.

Claims (1)

[Claims] 1. In an internal combustion engine equipped with a mechanism that varies valve timing by changing the phase of the camshaft relative to the crankshaft, a means for detecting when the engine is decelerating is provided, and a deceleration detection signal from the detecting means is used to detect exhaust gas. The crank angle position where the valve starts to open is on the lag side in the direction of crankshaft rotation from bottom dead center relative to the normal crank angle position where the exhaust valve starts to open, and the crank angle position where the exhaust valve completes closing. An engine braking performance improvement device for an internal combustion engine, characterized in that the variable valve timing mechanism is driven to be positioned on the lag side in the rotational direction of the crankshaft with respect to the crank angle position at which the exhaust valve normally completes closing.