JPH0139866Y2 - - Google Patents

Description

[Detailed Description of the Invention] This invention relates to an engine braking device for an internal combustion engine, particularly an internal combustion engine for a large vehicle.

Conventional engine braking devices for trucks, buses, etc. increase the braking effect by closing a butterfly-type normally open valve provided in the exhaust passage to worsen the exhaust action. In addition to such an exhaust brake, an engine braking device, also known as a compression work absorption type, as described in, for example, Japanese Unexamined Patent Publication No. 56-126640, is sometimes used.
This is equipped with a normally closed valve that opens near the top dead center of the engine during the compression process and allows the compressed air in the combustion chamber to flow out through the exhaust passage.When this normally closed valve is open, the fuel is injected. has stopped.
Since this normally closed valve is the third valve provided in the cylinder head separately from the intake valve and the exhaust valve, it will be referred to as the third valve hereinafter.

In such an engine braking system that uses a third valve, as in the case of only an exhaust brake, when the engine brake is activated, the bounce of the exhaust valve, that is, a restart phenomenon occurs near exhaust top dead center, as shown in Figure 1. do. This is because when the exhaust passage is closed, the internal pressure of the exhaust passage becomes higher than the pressure of the valve spring. When this phenomenon of restarting the exhaust valve occurs, noise is generated due to impact when the valve is seated, gas blows through, etc., and problems such as damage to the valve, valve seat, etc. occur.

The purpose of this invention is to provide an engine brake device that is combined with a third valve exhaust brake, which suppresses the bounce of the exhaust valve when the engine brake is activated, thereby preventing noise generation and improving the durability of the valve, etc. It is in.

The above object of this invention is achieved by extending the final opening period of the third valve to near exhaust top dead center, where bounce of the exhaust valve occurs, and returning part of the pressure in the exhaust passage into the combustion chamber.

An embodiment of this invention will be described below with reference to the accompanying drawings. In FIG. 2, each end of an intake passage 3, an exhaust passage 4, and a third valve passage 5 communicating with the exhaust passage 4 are open in the combustion chamber 2 of the engine 1. They are normally closed by an intake valve 6, an exhaust valve 7, and a third valve 8, respectively. Intake valve 6 and exhaust valve 7
are controlled to open and close via a rocker arm, a push rod, a tappet, and a cam on a camshaft (not shown), respectively. The third valve 8 is connected to a cam 11 provided on a camshaft 10 of the fuel injection pump 9 (actually, the camshaft 10 and the cam 11 are provided facing in the left-right direction in the figure). Opening and closing is controlled by a plunger 14 which is driven to force-feed the oil in the oil tank 12 through the pipe 13, a piston 15 which drives the third valve 8 with the pumped oil, and the like.

The third valve 8 is controlled to open and close at the timing shown in Fig. 1 when the engine is rotating at low speed, but when the engine is rotating at high speed, the opening period exceeds exhaust top dead center as shown in Fig. 3. The opening/closing is controlled so that the opening/closing ends after a short distance. For this reason, the third valve 8
The cam 11 that drives the third valve lift curve and the third valve lift curve as shown in FIG.
It consists of two cams with different cam profiles so that the third valve lift curve as shown in the figure can be obtained separately. When the exhaust brake switch 16 is turned on and a high speed signal from the engine speed sensor is input to the control section 17 by a solenoid valve (not shown), the third valve lift curve shown in FIG. 3 is obtained. When such a cam 11 is selected and a low speed rotational speed signal is input, the cam 11 is selected such that the third valve lift curve shown in FIG. 1 is obtained.
1 is selected, and the third valve 8 is operated by the pressure oil sent respectively.

The detailed configuration for controlling the opening and closing of the third valve 8 is as follows:
Various known mechanisms can be employed. For example, the opening/closing control mechanism for the third valve as described in the above-mentioned Japanese Patent Application Laid-Open No. 56-126640, the locking arm mechanism with a valve stop device for the variable cylinder engine of Mitsubishi Motors, or the hydraulic pump and electromagnetic In a hydraulic system equipped with a valve, this may be an on/off control of a solenoid valve or a time control mechanism by changing the diameter or length of a pipe for conveying pressure oil. Further, the signals input to the control unit 17 may be other driving condition signals such as vehicle speed, fuel injection pressure, and cooling water temperature. Furthermore, instead of opening the third valve continuously from near compression top dead center to near exhaust top dead center as shown in Figure 3, the third valve is opened intermittently between near compression top dead center and near exhaust top dead center. They may be opened separately.

As described above, the engine braking device according to this invention includes third valve opening/closing control means for extending the final opening period of the third valve used together with the exhaust brake to near the top dead center of the exhaust stroke of the engine. As a result, part of the internal pressure in the exhaust passage that increases when the engine brake is activated is released into the combustion chamber through the third valve passage, so the pressure in the exhaust passage decreases and the exhaust valve is prevented from reopening. Noise generation and damage to exhaust valves etc. are prevented.

[Brief explanation of the drawing]

FIG. 1 is a graph showing an example of conventional third valve timing, FIG. 2 is a schematic configuration diagram of an engine braking device showing an embodiment of this invention, and FIG.
The figure is a graph showing the third valve valve timing in one embodiment of this invention. 1...Engine, 2...Combustion chamber, 3...Intake passage, 4...Exhaust passage, 5...Third valve passage, 6...
Intake valve, 7...Exhaust valve, 8...Third valve, 9...Fuel injection pump, 10...Camshaft, 11...Cam,
12...Oil tank, 13...Pipe, 14...
...Plunger, 15...Piston, 16...Exhaust brake switch.

Claims (1)

[Scope of utility model registration request] An engine comprising a normally open valve for closing an exhaust passage when engine braking is applied, and a normally closed valve for opening near the top dead center of the engine during the compression process to allow compressed air in the combustion chamber to flow out through the exhaust passage. An engine braking device comprising a normally closed valve opening/closing control means for extending the final opening period of the normally closed valve to near the top dead center of the exhaust stroke of the engine.