JPS5932651B2 - Exhaust purification device for engine with cylinder number control - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention mainly relates to a cylinder number control engine that stops fuel supply to some groups of cylinders when the engine is lightly loaded. The present invention relates to a device that prevents the temperature of a catalyst device from decreasing.

In general, fuel efficiency tends to improve when an engine is operated under a high load.For this reason, in a multi-cylinder engine, fuel supply to some groups of cylinders is cut to stop operation when the engine load is low. An engine with a controlled number of cylinders was devised that relatively increases the load on the remaining operating cylinders 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 unburned 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 in operation. and flows into the catalyst.

When 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 gradually decreases and the purification efficiency also decreases.

There is a risk. Particularly when partial cylinder operation is performed continuously for a long period of time, the following tendency is observed.

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 while some cylinders are in operation,
A possible method is to prevent 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 method in which all exhaust gas is allowed to flow into the catalyst during operation, but when some cylinders are in operation, exhaust air from the idle cylinders is allowed 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 an intake port, there is also a problem in that part 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 a catalyst device is installed in the exhaust system for the purpose of oxidizing HC and CO, an exhaust gas recirculation device (EGR device) is also installed as a measure against NOx to suppress the maximum fuel temperature and reduce the generation of NOx. There are many things that do this.

If you pay attention to this EGR device, it has the effect of circulating a part of the exhaust gas into the intake system, so if the exhaust air from the idle cylinders is circulated through the EGR device, the catalyst temperature as mentioned above will change. The decline can be prevented to some extent.

On the other hand, in a cylinder number controlled engine, the engine speed is a constant low rotational speed (for example, 1300r, p, m
, ), engine vibration increases, so it is normal to force the engine to return to full cylinder operation.

However, it has been confirmed that when the load is extremely light, such as during engine deceleration operation, the influence of vibration poses almost no problem even if the set value of the rotation speed for returning to all-cylinder operation is further lowered.

Nevertheless, as in the past, the return point (
However, as mentioned above, from the perspective of reducing exhaust emissions, the lower limit of rotation speed for some cylinders is further lowered during light loads. This was considered to be completely undesirable because it may cause a further decrease in the catalyst temperature.

In view of this, the present invention shifts the set value of the rotation speed for forced return to all-cylinder operation to a lower rotation side than normal during extremely light load operation where the influence of engine vibration is hardly a problem. The exhaust recirculation system recirculates a portion of the exhaust gas into the intake air of all cylinders. Under extremely light load conditions, the control valve is set to maximize the amount of recirculation, and the exhaust air from the idle cylinders is recirculated almost as is. To provide a cylinder number control engine which reduces the amount of cold air flowing into a catalyst by circulating it through an intake system, thereby further improving fuel efficiency characteristics, and maintaining good catalyst purification efficiency when controlling the number of cylinders. It is something.

The embodiments shown in the drawings will be described in detail below.

1 is the 6-cylinder engine body, 41 = 1~≠3 and +4~4
I=6 is a cylinder group to which fuel supply is selectively stopped due to light load conditions.

2a to 2f are fuel injection valves, 3 is an intake pipe, 4 is a throttle valve, and 6a.

6b is a cylinder group, exhaust pipes are divided corresponding to 41=1 to +3 and +4 to +6, T is an oxygen sensor installed in the combined exhaust pipe 6 and detects the oxygen concentration in the exhaust, and 8 is this oxygen sensor 7. The output of is compared with a reference value corresponding to the stoichiometric air-fuel ratio to detect it as a deviation signal from the reference value, which is shaped into a waveform and sent to the fuel injection control circuit (hereinafter referred to as EGI circuit) 9 as an air-fuel ratio correction signal. The output air-fuel ratio control circuit performs feedback control so that the air-fuel ratio becomes approximately the stoichiometric air-fuel ratio, thereby maintaining the conversion efficiency of the three-way catalyst 19 as a catalyst device at the optimum point.

As a general rule, the EGI circuit 9 generates pulses 14 . . . corresponding to the intake air amount based on the outputs of the intake air amount sensor 5 and the rotation speed sensor 10 . A fuel injection pulse signal having a rotation speed and synchronized with the rotation speed is supplied to the fuel injection valves 2a to 2f via a cylinder number control circuit (hereinafter referred to as 708 circuit) 20, which will be described later.

Reference numeral 11 designates a recirculation control valve that controls the recirculation amount of exhaust gas flowing through the exhaust pipes 6b of cylinder groups 4F4 to +6, which are always on the operating side except under extremely light load conditions, to the intake side. The electromagnetic valve 12 is selectively supplied with the negative pressure of the intake pipe 3 via the EGR control negative pressure generator 13 or the vacuum tank 14.

NOx is removed by EGR control, and a well-known negative pressure for EGR control is supplied so as to control the opening of the recirculation control valve 11 according to the operating state, except when the load is extremely light.

On the other hand, when the negative pressure working chamber 11a of the reflux control valve 11 is connected to the intake pipe 3 communicating with the vacuum tank 14 via the check valve 15 by switching the three-way solenoid valve 12, it receives this strong negative pressure. The valve reaches its maximum opening degree, and as will be described later as a mere fresh air recirculation valve, most of the exhaust air from the cylinders ≠4 to ≠6, which are inactive at this time, is circulated to the intake system.

16 is an exhaust gas recirculation passage for recirculating exhaust gas to the intake side, and 17 is an exhaust gas introduction port communicating with a branch portion of the intake pipe 3 via a through hole 18.

As a general rule, the vC8 circuit 20 operates under extremely light loads where the throttle valve 4 is fully closed (θ-〇) and when the throttle valve 4 is not fully closed (θN0).
When the load is simply light, cylinder 1 is
Cut fuel to 1 to ≠ 3, and conversely reduce fuel to cylinders - during extremely light loads.
This is to cut the fuel from 1P4 to ≠6 to put the cylinders in a deactivated state.

This vC8 circuit 20 will be explained based on FIG. 2. 21 is an input terminal to which the opening state signal of the throttle valve 4 (a signal with a level of 111" at the throttle opening) is applied, 22 is an inverter, and 23 is a cylinder cylinder. -!/AND circuit that opens and closes the normally closed relay 24 on the P1~≠3 side, 25 is the cylinder +4~+
AND circuit that opens and closes the normally closed relay 26 on the 6 side, 27.2
8 is a pulse width comparator, 29.30 is a pulse width setter that outputs the reference value ■normal 2wL corresponding to low load and high load, respectively, 31 is an engine rotation speed comparator, and 32 is a rotation position reference value No. a rotation speed setting device that selectively outputs N depending on the light load state; 33 is an OR circuit; 34 is an AND circuit;
35 is a flip-flop circuit connected to the OR circuit 33 as a set input and the AND circuit 34 as a reset input.

The output level of this flip-flop circuit 35 is 110"
In the 06 cylinder operating region (see Figure 4), the output level of both AND circuits 23 and 25 is always IT □ //, so both normally closed relays 24 and 26 are not energized, and the solid cylinder group +-1 ~+3 and =#=4~≠6 are kept in operation.

Here, the cylinder number control patterns can be divided into a very light load state of θ=0, which is a light load state, and a simple light load state of θN0, as shown in FIGS. 4a and 4b.

When the throttle opening is θ, which is not fully closed, the engine speed N is the set value N.

Since the vibration worsens as the engine becomes smaller (greater than 1), the rotation range below this set value N1 is set to the 6-cylinder range, but when the throttle is fully closed and θ = 00, vibration increases due to the extremely light load. Since it does not become, N is smaller than N.

The three-cylinder range has been expanded to low rotations.

Therefore, considering the light load state of θ key 00, the rotation speed setting device 32 selects the reference value to N1 with a signal of level 110'' applied to the input terminal 21 other than the throttle fully closed, and the control shown in FIG. Adopt a pattern.

AND circuit 23 which simultaneously receives output via inverter 22
Only the normally closed relay 24 can be energized under the condition of the cylinder number control signal It1''.

In this state (other than fully closed throttle), the AND circuit 25 always closes the gate, so cylinder groups +4 to +6
remains operational.

The output level of the flip-flop 35 becomes II O" when the pulse signal width W is greater than or equal to the reference value, or when the rotational speed N is less than or equal to the reference value N1 (in the 6-cylinder region in Figure 4), and the pulse When the width W is less than the reference value W1 and the rotation speed N is more than the reference value N1 (in the 3-cylinder region shown in Figure 4), 111"
become.

Note that the set input of the flip-flop 35 is connected to the OR circuit 3.
3, since the reset input is connected to the AND circuit 34, a cylinder number maintenance region is formed.

Therefore, if the pulse width W and the rotational speed N are in the 6 cylinder region, the AND circuit 23 also closes the gate and all cylinder groups +
1 to 41 = 6 is maintained in the operating state, but when the cylinder enters the 3 cylinder region, the normally closed relay 24 is energized and opens the contact, and the EGI
Since the fuel injection pulse signal from the circuit 9 is cut off, the cylinders≠1 to =ll=3 are in a rest state.

In this case, the oxygen sensor 7 detects a state different from the actual air-fuel ratio of the combustion cylinders +4 to +6 due to oxygen in the exhaust gas from the deactivated cylinders≠1 to 41=3. Therefore, in order to stop the feedback control via the air-fuel ratio control circuit 8, the proportional constant between the intake air amount per rotation and the injection pulse width is changed, and the feedback value is clamped with the fuel injection amount increased). Three-way solenoid valve 1
2 in the state shown in FIG.
Negative pressure for control is supplied, and exhaust gas recirculation is performed depending on the amount of intake air, for example, to reduce NOx.

Note that in this state, the amount of exhaust heat is relatively large and no extreme drop in exhaust temperature is observed, so the temperature of the three-way catalyst 19 is maintained in a reaction state, which prevents oxidation of HC and CO in the exhaust. can.

(It will be difficult to reduce NOx, but it will be reduced by EGR, so there is no problem.

) Next, at the very light load of θ=0 when the throttle is fully closed,
A level II 1 // is applied to the input terminal 21, and the rotation speed setting device 32 is set to the reference value N.

Then, the cylinder number control pattern is transferred to FIG. 4a.

At the same time, the AND circuit 25 outputs a cylinder number control signal 1!1"
Under the condition that the normally closed relay 26 can be excited,
The other normally closed relay 24 always maintains its contacts closed regardless of this control signal, and keeps cylinder groups ≠1 to #=3 in operation.

When the operating state enters the 3-cylinder region shown in Figure 4a, AN
D circuit 25 opens, energizes normally closed relay 26, and cylinder 41
=4-41=6 is put into hibernation state.

This stops the feedback control of the air-fuel ratio control circuit 8, switches the three-way solenoid valve 12 to the vacuum tank 14 side, and introduces high negative pressure into the working chamber 11a of the recirculation control valve 11, making it fully open.

As a result, most of the exhaust gas (fresh air) passing through the exhaust pipes 6b of 41=4 to +6, which are inactive cylinders, is recirculated to the intake pipe 3 side.

Therefore, the cold air (≠4 to +-6 exhaust air) is transferred to the three-way catalyst 1.
The catalyst is circulated to the intake system without almost flowing into the exhaust gas 9, and is gradually warmed up while being circulated. Therefore, it is possible to prevent the temperature of the exhaust gas flowing into the catalyst from decreasing, which was conventionally remarkable at the time of such a light load.

Note that, at the time of such a very light load, there is no problem even if air is recirculated instead of the combustion exhaust gas because NOx generation is originally small.

On the other hand, considering the effectiveness of the engine brake, the cylinder
= [~= #= When 6 is at rest, the negative pressure value of the vacuum tank 14 may be controlled to adjust the amount of air recirculation, and the recirculated cylinder group +-4 to +, 6 exhaust gas In order to prevent (fresh air) from flowing into the active cylinders ≠ 1 to +3 and disrupting (thinning) the air-fuel ratio control, in this case, either increase the amount of fuel injected or move the air to the active cylinders +1 to +3. A separate oxygen sensor may be provided to provide feedback control of the air/fuel ratio.

Note that an oxidation catalyst may be installed instead of the three-way catalyst 190, and in this case, the air-fuel ratio feedback control device may not be provided.

As described above, according to the present invention, light load states are distinguished into extremely light loads and other light loads, and exhaust gas from cylinder groups that are constantly in operation except for extremely light loads is recirculated to the intake system. At very light loads, the control valve is fully opened, and at the same time, the cylinder group is put into a rest state, and most of the exhaust air is returned to the intake system via the recirculation control valve, so conventional EGR
With a simple configuration that utilizes the entire control device, it is possible to effectively prevent a drop in catalyst inflow exhaust gas temperature, which is the most problematic during extremely light loads, and to make the catalyst work effectively.

In addition, because the cylinder number control pattern is divided into light loads (very light loads) and other light loads, the three-cylinder range during extremely light loads can be extended to even lower speeds, further increasing the effectiveness of cylinder number control. , it is possible to improve fuel efficiency.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention; FIG. 1 is a schematic configuration, FIG. 2 is a block diagram of a cylinder number control circuit, FIG. 3 is a sectional view of an intake pipe, and FIGS. 4 a and b show the number of cylinders. FIG. 3 is an explanatory diagram of a control pattern. +1~4! P6...Cylinder, 2a-2f...Fuel injection valve, 8...Air-fuel ratio control circuit, 9...Fuel injection control, 11...Recirculation control valve, 12...Three-way solenoid valve, 20 ...Cylinder number control circuit.

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 inactive cylinder group and each 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;
a recirculation control valve that is provided in a passage connecting the exhaust pipe and intake pipe of an operating cylinder group and controls to recirculate a part of the exhaust gas of the group; and a recirculation control valve that controls the number of cylinders when an engine deceleration state is detected. Exhaust purification for an engine with cylinder number control, characterized by comprising means for causing a circuit to supply fuel to a group of dormant cylinders, cutting off fuel supply to a group of active cylinders, and at the same time fully opening the recirculation control valve. Device.