JPS5920856B2 - Exhaust purification device for engine with cylinder number control - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides an EGR device that recirculates a portion of engine exhaust gas to the intake side to remove NOx from the exhaust gas,
Regarding a cylinder number control engine that is equipped with a catalyst that removes HC, etc. and stops fuel supply to some groups of cylinders during light loads, the catalyst temperature may drop due to air flowing in from the idle cylinders whose fuel supply has been stopped. It is designed to prevent this.

Conventionally, fuel efficiency tends to improve when an engine is operated under a high load, and for this reason, in multi-cylinder engines, when the engine load is low, fuel supply to some groups of cylinders is cut to stop operation. A cylinder number control engine is known in which the load on the remaining operating cylinders is relatively increased by this amount, thereby improving overall fuel efficiency in the low load range.

In this case, if a catalyst is installed in the exhaust system for the purpose of oxidizing inorganic harmful components, the exhaust (fresh air) from the idle cylinder group will mix with the exhaust from other operating cylinder groups while some cylinders are operating. and flows into the catalyst.

If exhaust gas whose temperature has been lowered by mixing with fresh air flows into a catalyst that exhibits high exhaust gas purification efficiency only in a predetermined active temperature range, the catalyst temperature may gradually drop and the purification efficiency may also decrease.

This tendency is particularly seen when partial cylinder operation is performed continuously for a long period of time.

To prevent exhaust air from idle cylinders from flowing into the catalyst,
For example, by installing an air cutoff valve in the intake manifold of the idle cylinder and closing this cutoff valve when some cylinders are in operation,
A method can be considered that prevents air from being sucked into the idle cylinders, thereby preventing fresh air from being discharged into the exhaust passage, but in this case, there is a problem in that the blocked air causes energy loss during the intake stroke.

There is also a method that forcibly closes the intake and exhaust valves of idle cylinders, but in this case, in addition to the energy loss during the intake stroke due to the blocked air, there is also the energy loss during the exhaust stroke due to the blocked air. There is a problem that arises.

All of these methods do not discharge any air into the exhaust system, but for example, a passage is provided that communicates with the exhaust passage of the idle cylinder to bypass the catalyst, and a switching valve is installed at the entrance of this bypass passage to ensure that all cylinders There is also a system that allows all exhaust gas to flow into the catalyst during operation, but during two-cylinder operation, allows exhaust air from the idle cylinder to flow through a switching valve to a bypass passage to prevent a drop in catalyst temperature.

However, in this case, unless the operating timing of the switching valve is controlled very accurately, there is a possibility that the exhaust gas will directly flow out from the bypass passage when switching to partial cylinder operation, which is not desirable in terms of exhaust emissions. When a fuel injection valve is installed in the intake port, there is also the problem that a portion of the injected fuel goes around to the intake port of the idle cylinder, is taken into the idle cylinder as it is, and then flows to the bypass passage.

By the way, when the exhaust system is equipped with a catalyst device for the purpose of oxidizing HC and Co, a part of the exhaust gas is returned to the intake air through an exhaust gas recirculation device (EGR device) to maximize combustion. Many of them suppress the temperature and reduce the generation of NOx.

Focusing on this EGR device, it has the effect of circulating some of the exhaust gas into the intake system, so if the exhaust air from the idle cylinders is circulated through the EGR device, the drop in catalyst temperature can be reduced. It can be prevented even in minutes.

The present invention has been made in view of this point, and in order to prevent a temperature drop in the catalyst of an engine with cylinder number control, independent EG
By installing an R device and setting the EGR device of the idle cylinder to the maximum recirculation amount when some cylinders are in operation, the exhaust air is recirculated almost unchanged to the intake system, thereby reducing the temperature of the mixed exhaust gas with the operating cylinder side. The purpose of the present invention is to provide an engine with a controlled number of cylinders that prevents this from occurring and thereby maintains the purification efficiency of the catalyst at a good level at all times.

The present invention will be described in detail below based on the drawings.

1 is a 6-cylinder engine, and cylinders #1 to ## are deactivated at low load.
3 and cylinders #4 to #6, which are always in operation.

2a to 2f are fuel injection valves, 3 is an intake pipe, 4 is a throttle valve, 5 is an intake air amount sensor, and 6a and 6b are exhaust pipes, which correspond to cylinder groups #1 to #3 and #4 to #6. It is divided into sections.

Reference numerals 7a and 7b refer to recirculation control valves 8a which are normally operated by receiving control negative pressure for the purpose of EGR control.

Reference numeral 8b denotes an exhaust gas introduction pipe divided corresponding to cylinder groups #1 to #3 and #4 to #6, and each branch of the intake pipe 3 communicates through a through hole 9.

The reflux control valve is located in the middle of the reflux pipe 10atlOb connecting the inlet pipes 8a, 8b and the exhaust pipes 6a, 6b. a.

7b is provided.

Control negative pressure from a negative pressure supply device 12 for EGR control and intake air are supplied to the operating negative pressure chamber of one of the recirculation control valves 7a by switching a three-way solenoid valve 11 that is activated by a signal from a cylinder number control circuit, which will be described later. The intake negative pressure of the pipe 3 is selectively introduced.

That is, when cylinder groups #1 to #3 are in a rest state, the high negative pressure in the vacuum tank 14 is recirculated through the check pulp 13 and the vacuum tank 14 arranged between the three-way solenoid valve 11 and the intake pipe 3. It is supplied to the negative pressure operating chamber of the control valve 7a and maintained at the maximum opening state.

Note that EGR control negative pressure is always introduced to the other recirculation control valve 7b.

Reference numeral 15 is an oxidation catalyst that oxidizes CO and HC and exhibits good conversion efficiency above a predetermined temperature.

As shown in FIG. 3, the cylinder number control circuit transmits pulse signals from a fuel injection control circuit (hereinafter referred to as EGI circuit) 30 to fuel injection valves 2a to 2a of cylinder groups #1 to #3 and #4 to #6.
2f, which selectively supplies the pulse width comparator 16,
17. Reference voltage setter '18, 19 that outputs the pulse width setting value (WH) (WL) as a comparison value, respectively, Engine speed comparator 20, Engine speed that outputs the rotation speed setting value (NO) as a comparison value It is composed of a reference voltage setter 21, an OR circuit 22, AND circuits 23 and 24, inverters 25 and 26, and a flip-flop 27.

Here, the EGI circuit 30 outputs a pulse signal determined based on the outputs of the intake air amount sensor 5 and the rotation speed sensor 28, and sends this signal to the fuel injection valves 2d to 2f of cylinders #4 to #6. It is directly applied to put cylinder groups #4 to #6 into operation.

No pulse signal is applied to the other cylinder groups #1 to #3 until the gate of the AND circuit 24 is opened.

This AND circuit 24 opens when the output level of the flip-flop 27 is 1'' to put cylinder groups #1 to #3 into operation, but closes the gate when the output level is 0'' and outputs the pulse from the EGI circuit 30. Block the signal.

The output level of the flip-flop 27 is determined when the pulse width (W) of the pulse signal is equal to or greater than the reference value (WH) or when the rotation speed (
When N) is less than the reference value (No) (cylinder area in Figure 4), it becomes 21", and the pulse width (W) is less than the reference value (WL
) or less and the rotational speed (N) is greater than or equal to the reference value (No) (3-cylinder region in FIG. 4), it becomes "0".

The flip-flop 270 set input terminal is connected to the OR circuit 22
In addition, since the reset input terminals are respectively connected to the AND circuit 23, a region in which the number of cylinders is maintained as shown in FIG. 4 is formed.

In this way, when the pulse width of the fuel injection pulse signal from the EGI circuit 30 (proportional to the engine load) and the engine speed are within the 6 cylinder region shown in FIG. ~ #6 is all in operation, exhaust pipe 6a
The exhaust gas that has passed through t6b is purified by the oxidation catalyst 15.

At this time, the catalyst inflow temperature becomes characteristic A in FIG. 5, allowing the oxidation catalyst 15 to function efficiently without causing a temperature drop.

At this time, the three-way solenoid valve 11 is switched to the EGR negative pressure supply device 12 side by the output "■" of the flip-flop 27, and the two-way recirculation leg valve 7a is switched to the EGR negative pressure supply device 12 side.

The opening degree of the valve 7b is controlled based on this supplied negative pressure and functions as a normal EGR control valve, and each exhaust pipe 6a.

A part of the exhaust gas from 6b is transferred to reflux pipe 7a, depending on the operating condition.
7b and introduction pipes 8a and 8b, it is recirculated to the intake side of each cylinder #1 to #6.

This EGR suppresses the generation of NOx.

On the other hand, when the pulse width (W) and engine speed (N), which are proportional to the load, pass through the region where the number of cylinders is maintained and reach the 3-cylinder region, the output of the flip-flop 2γ changes to the level "0" as described above.
", and cylinders #1 to #3 are put into a rest state.

At the same time, the three-way solenoid valve 11 is switched, and the high negative pressure in the vacuum tank 14 is guided to one of the recirculation control valves 7a, making it fully open.

Therefore, most of the exhaust gas (fresh air) from the exhaust pipe 6a is circulated as it is to the idle cylinders #1 to #3, and by repeating this circulation, the downstream catalyst of the exhaust gas (fresh air) from the idle cylinders #1 to #3 is 15, and increase the temperature of fresh air.
This allows the catalyst inflow temperature to be kept high as shown by the opening in FIG.

In this temperature range, the characteristics are almost the same as those in 6-cylinder operation, and the oxidation function of the oxidation catalyst 15 is fully demonstrated.

On the other hand, in the case of temperature characteristic C when normal EGR is performed as is during three-cylinder operation, the conversion efficiency gradually decreases.

In this embodiment, cylinders #1 to #3 are grouped as cylinders that are inactive during light loads, but cylinders #4 to #6 may also be used.

As described above, according to the present invention, the recirculation control valve, which normally operates as an EGR control valve, operates as a recirculation valve that returns almost unchanged fresh air discharged from the idle cylinder to the intake system of the idle cylinder during partial cylinder operation. Therefore, while using the conventional EGR mechanism, it is possible to prevent a drop in the catalyst inlet temperature that occurs during partial cylinder operation, and the extremely simple structure has the effect of always maximizing the ability of the catalyst.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention; FIG. 1 is a schematic configuration diagram, FIG. 2 is a sectional view of an intake pipe, FIG. 3 is a block diagram of a cylinder number control circuit, and FIG. 4 is a cylinder number control pattern. An explanatory diagram of
FIG. 5 is a graph showing characteristics of catalyst inflow temperature. #1 to #6... Cylinder, 2a to 2f... Fuel injection valve, 3... Intake pipe, 6 a, 6 b.
·····Exhaust pipe,? a. 7b...reflux control valve, 8a, 8b...reflux pipe.

Claims (1)

[Claims] 1. In a multi-cylinder engine equipped with a fuel supply device that controls the amount of fuel supplied, and a cylinder number control circuit that cuts off a fuel supply signal from the fuel supply device to a predetermined group of idle cylinders according to the engine load. , an exhaust pipe provided for each of the inactive cylinder group and the active cylinder group that operates when fuel supply to this group is cut off, and a catalyst provided in a passage where exhaust gas from each group of the exhaust pipes joins; Exhaust gas recirculation devices are provided independently to correspond to the inactive cylinder group and operating cylinder group, and the exhaust gas recirculation device corresponding to the inactive cylinder group is provided when the cylinder number control circuit cuts off the fuel supply signal to the inactive cylinder group. An exhaust gas purification device for an engine with a controlled number of cylinders, comprising a recirculation control means for fully opening a recirculation device.