JPH0338415Y2 - - Google Patents

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to a compression work absorption type engine braking device used in a supercharged engine.

<Prior art> Freight vehicles equipped with relatively high-output diesel engines are known to incorporate exhaust braking devices and compression work absorption type engine braking devices to assist in braking force during loading. ing.

The compression work absorption type engine braking device is
When the driver takes his foot off the accelerator pedal while the vehicle is running, the fuel supply to the combustion chamber is stopped and the rotation of the drive wheels is actively suppressed by the resistance during the compression stroke of the piston. It is. For this reason, it is desirable to connect the high-pressure combustion chamber to the exhaust manifold side just before the end of the compression stroke to exhaust the air supply.Generally, only during engine braking, the combustion chamber is opened from near the end of the piston's compression stroke to the middle of the expansion stroke. An auxiliary exhaust valve (third valve) is attached to each cylinder to communicate the exhaust gas to the exhaust manifold side.

In this way, the compression work absorption type engine braking device actively suppresses the rotation of the drive wheels by the resistance during the compression stroke of the piston, so it uses engine exhaust gas to overflow the intake air into the combustion chamber of the engine. If used in combination with a supercharger that supplies (increases boost pressure), it is possible to generate an even stronger suppressing force (braking force).

<Problems to be solved by the invention> Generally, a supercharger cannot achieve a sufficient supercharging effect when the engine is in a low speed rotation range or under a low load state. For this reason, there is a problem in that the effect of increasing the braking force described above cannot be sufficiently achieved by simply combining a compressive work absorption type engine braking device with a conventionally common engine equipped with a single supercharger. Ta.

The present invention has been made in view of the above-mentioned conventional circumstances, and an object of the present invention is to provide an engine braking device that can sufficiently increase the braking force of a compression work absorption type engine braking device even when the engine is in a low speed rotation range or under low load. With the goal.

<Means for Solving the Problems> The engine braking device for a supercharged engine according to the present invention has a plurality of intake passages communicating in parallel with each other to the intake ports of the engine, and supercharged air is supplied to each of the intake passages. a plurality of exhaust passages that communicate with exhaust ports of the engine in parallel with each other and guide exhaust gas for operating the turbochargers to each of the turbochargers; In a supercharged engine equipped with a switching valve that distributes to the exhaust passage and a control circuit that operates the switching valve according to the driving state of the vehicle, engine braking is performed by determining the operation of the engine brake based on the driving state of the vehicle. an engine brake control means for operating the switching valve so that only one of the superchargers for low speed and low load operates at the time of engine braking, and stopping the supply of fuel to the combustion chamber of the engine; The present invention is characterized by comprising a valve mechanism that communicates the combustion chamber of the engine with the exhaust passage to the low-speed, low-load supercharger from near the end of the compression stroke of the piston to the expansion stroke.

<Operation> According to the present invention, when the supercharging efficiency of the supercharger decreases, such as when the engine rotates at low speed or under low load, the switching valve is operated so that only the low speed and low load supercharger is activated. This allows the engine to operate, concentrates a small amount of exhaust gas, and prevents a drop in supercharging efficiency to the combustion chamber. Therefore, sufficient boost pressure can be obtained and the braking increase of the compression work absorption type engine braking device can be sufficiently maintained.

<Example> Hereinafter, an example of the present invention will be described based on the drawings.

First, a supercharged engine to which the present invention is applied will be explained based on FIG. 1, which schematically shows its configuration. In the figure, 1 is the cylinder head of the engine.
As shown in FIG. 2, this cylinder head 1 includes:
Two divided intake ports 2 and 3 are formed, and these intake ports 2 and 3 merge together at an opening in the cylinder to open and close a combustion chamber in the cylinder 5 by opening and closing one intake valve 4. 5a, or, as shown in FIG.
Intake air is supplied into the combustion chamber 5a within the combustion chamber 5a.

Further, an intake pipe 7 is installed in the cylinder head 1, and this intake pipe 7 has intake ports 2 and 3.
Intake passages 8 and 9 corresponding to the cylinder head 1 are connected to each other, and an exhaust pipe 10 is connected to the cylinder head 1 from which exhaust gas is discharged from the exhaust port.
is installed.

Two superchargers 13 and 14 consisting of a compressor 11 and an exhaust turbine 12 installed coaxially are installed in the intake system and exhaust system of the engine. Exhaust turbines 12 of each of the superchargers 13 and 14 are communicated with exhaust passages 15 and 16 through which exhaust gas passing through the exhaust pipe 10 is supplied, and the compressor 11 of each of the superchargers 13 and 14 is connected to the exhaust turbine 12 of each of the superchargers 13 and 14. The intake passages 8 and 9 of the intake pipe 7 are communicated with each other, so that supercharged intake air supplied from the compressor 11 is introduced into the combustion chamber 5a through the intake passages 8 and 9. ing.

On the other hand, a switching valve 17 such as a gate valve is installed at the branching part between the exhaust pipe 10 and the exhaust passages 15 and 16.
It is selectively driven by a solenoid valve 19 that opens and closes in response to a signal from a control circuit 18 that is controlled by a load, etc., and an actuator 20 that is activated by opening and closing this solenoid valve 19. The flow of exhaust gas is now controlled. Note that 21 in the figure is an intercooler, which reduces the temperature of the intake air in the intake passages 8 and 9 and increases the density of the compressed air introduced into the cylinder 1.

In such a configuration, a switching valve 17 installed at a branch point between the exhaust pipe 10 and the exhaust passages 15 and 16
is operated depending on engine rotation, load, etc., and one exhaust passage 16 is blocked in the low engine speed range or under low load, so only one supercharger 13 for low speed and low load is driven. Since supercharged intake air with a small pressure drop is introduced into the combustion chamber 5a, high supercharging efficiency (boost pressure) can be obtained. Also,
In the high-speed rotation range of the engine, the switching valve 17 operates to open both exhaust passages 15 and 16, and the two superchargers 13 and 14 are driven, allowing highly efficient supercharging.

Next, a compression work absorption type engine braking device combined with the above-mentioned supercharged engine will be described with reference to FIG. 4, which schematically shows its configuration. In FIG. 4, which shows the part related to the low-speed, low-load supercharger 13, the combustion chamber 5a has an intake pipe 7 partitioned off via intake valves 4, 6a, and 6b, and an exhaust pipe 7 partitioned off via an exhaust valve 22. In addition to the pipe 10, an auxiliary exhaust passage 23 that communicates with the exhaust pipe 10 is connected via an auxiliary exhaust valve 24, and this auxiliary exhaust valve 24 is opened only when the engine brake is activated by an engine brake control device (not shown). The operation is controlled via a valve driving means (not shown) so that the following occurs. That is, when the engine brake is activated, the engine brake control device stops the operation of the fuel injection device (not shown) to cut off the supply of fuel to the combustion chamber 5a, while the valve driving means is activated, as shown in FIG. The opening timing is set so that the auxiliary exhaust valve 24 opens from near the end of the compression stroke of the piston 25 to the middle of the expansion stroke as shown in FIG.

The engine brake control device determines when the engine is braking based on signals from a clutch switch that detects whether the clutch is on or off, a vehicle speed sensor, and an accelerator switch that detects the accelerator opening.

Therefore, when a clutch (not shown) interposed between the engine and a transmission (not shown) is in a connected state and the driver releases the accelerator pedal (not shown) while the vehicle is running, the engine brake is activated. The control device determines that the engine is in a braking state, operates the valve drive means, and stops the operation of the fuel injection device. As a result, the compressor 11 of the low-speed, low-load supercharger 13 rotates at high speed together with the turbine 12, and high-pressure intake air is sent into the combustion chamber 5a during the intake stroke of the piston 25. It acts as a resistance, making it possible to use highly efficient engine braking even when the engine is rotating at low speeds or under low load.

Note that when the engine is not rotating at low speed or under low load, the switching valve 17 is operated to the position shown by the solid line in FIG.
Sufficient engine braking is achieved with high boost pressure from both superchargers 13,14.

Although the above-mentioned embodiment shows an example equipped with two superchargers, a larger number of superchargers may be provided to set more detailed conditions. Alternatively, the auxiliary exhaust valve 24 may not be provided, and the existing exhaust valve 22 may also serve as the auxiliary exhaust valve.

<Effects of the Invention> According to the present invention, compared to a system provided with only one supercharger, sufficient engine braking can be applied even when the engine is rotating at low speed or under low load. Further, since the intake air supercharged by each supercharger is introduced into the combustion chamber of the engine through the respective intake passages, the supercharging performance of the engine is also improved.

[Brief explanation of the drawing]

Fig. 1 is a schematic configuration diagram of a supercharged engine to which an embodiment of the present invention is applied, Figs. 2 and 3 are explanatory diagrams showing the A-A cross section in Fig. 1, and Fig. 4 is FIG. 5 is a schematic configuration diagram showing the main parts of the engine braking device according to the present invention, and FIG. 5 is a valve opening stroke diagram showing the timing of opening and closing the valves of the engine. In the drawing, 4, 6a, 6b are intake valves, 5a is a combustion chamber, 8, 9 are intake passages, 13, 14 are superchargers, 1
5 and 16 are exhaust passages, 17 is a switching valve, 18 is a control circuit, 22 is an exhaust valve, 24 is an auxiliary exhaust valve, and 25 is a piston.

Claims (1)

[Scope of utility model registration request] A plurality of intake passages that communicate in parallel with each other to the intake ports of the engine, a plurality of superchargers that respectively introduce supercharging air into each of the intake passages, and a plurality of intake passages that communicate with each other in parallel to the exhaust ports of the engine and operate the superchargers. a plurality of exhaust passages that guide the exhaust gas to each of the superchargers, a switching valve that distributes exhaust gas from the exhaust port to each of the exhaust passages, and a control circuit that operates the switching valve according to the operating state of the vehicle. In a supercharged engine equipped with a supercharger, the operation of the engine brake is determined based on the driving state of the vehicle, and the switching valve is operated so that only one of the superchargers for low speed and low load operates during engine braking. and engine brake control means for stopping the supply of fuel to the combustion chamber of the engine, and supercharging the combustion chamber of the engine for low speed and low load from near the end of the compression stroke of the engine piston to the expansion stroke during the engine braking. An engine braking device for a supercharged engine, characterized by comprising a valve mechanism communicating with an exhaust passage to an engine.