GB2218008A

GB2218008A - Cleaning exhaust gas

Info

Publication number: GB2218008A
Application number: GB8810678A
Authority: GB
Inventors: Cedric Paul Davies
Original assignee: Ford Motor Co
Current assignee: Ford Motor Co
Priority date: 1988-05-06
Filing date: 1988-05-06
Publication date: 1989-11-08
Also published as: WO1989011025A1; GB8810678D0

Abstract

In order to clean particulates from the exhaust gasses from a diesel engine, a filter (22) is fitted in the exhaust gas path (14, 18) leading from the engine (10). In addition to the main exhaust gas path there is an auxiliary exhaust gas path (46) and the exhaust gasses are periodically led along the auxiliary path to reverse the flow through the filter and to clear the filter of accumulated solids.

Description

CLEANING EXHAUST GAS This invention relates to an exhaust gas cleaning installation for use in cleaning the exhaust gas from a diesel engine.

One emission component which has to be strictly controlled under current regulations is the particulate emission, ie the quantity of solid particles present in the exhaust emitted to the atmosphere. Various techniques have been proposed for catching these particles, but none of the known techniques are adequate to reduce the particulate emissions to the extremely low levels which are likely to become legal requirements in the near future.

According to the present invention there is provided an exhaust cleaning installation for use in the exhaust gas path of a diesel engine, the installation comprising a filter and means for mounting the filter in the exhaust gas path so that the exhaust gas passes through the filter before being exhausted to atmosphere, the installation also comprising an auxiliary exhaust gas path across the filter such that when the exhaust gas travels along the auxiliary path it traverses the filter in the opposite direction to the normal flow direction and dislodges particles accumulated on the filter.

The installation preferably includes valves on either side of the filter, the valves being adapted to operate simultaneously to close or substantially close the main exhaust flow path through the filter and to open the auxiliary path.

The valves are preferably operated in response to a signal indicating a rise in back pressure (as a result of a clogged filter) in the main flow path upstream of the filter.

The auxiliary flow path is preferably connected, downstream of the filter, into an EGR system so that the particulate matter is recycled to the engine.

Vacuum is preferably used as the power source to operate the valves.

The invention will now be further described, by way of example, with reference to the accompanying drawing, in which: Figure 1 is a schematic view of an exhaust gas cleaning installation in accordance with the invention: and Figure 2 is a detailed view of a small part of the installation of Figure 1.

In Figure 1, an engine block 10 is shown with an inlet manifold 12 and an exhaust manifold 14. The engine is a diesel engine and air enters the manifold 12 through an inlet tract 16. Exhaust gas leaves the engine through the exhaust manifold 14 and via an exhaust gas cleaning installation through to an exhaust pipe 18.

The cleaning installation comprises a main filter housing 20 containing a tubular filter element 22.

Dirty exhaust gas enters the outside of the chamber 20 from the manifold 14 and to get there it has to flow past a butterfly valve 24 which is shown in Figure 1 in the wide open position. The gas passes through the wall of the filter 22 into a clean gas space 26 and from there into the exhaust pipe 18 where the gas passes a second butterfly valve 28 which is also shown in the wide open position.

As the dirty exhaust gas passes through the filter 22, it deposits the particulate matter carried by the gas on the outside of the filter. As the deposit on the outside of the filter builds up, so the back pressure in the exhaust manifold 14 will increase. The filter must be cleaned periodically to prevent this back pressure reaching unacceptable proportions. To do this a pressure transducer 30 communicates with the upstream side of the filter and is set so as to produce a signal when the back pressure reaches a certain, predetermined level. When this level is reached the transducer sends a signal along a line 32 to a vacuum valve 34 which opens communication between a vacuum reservoir (e.g. the brake reservoir) 36 and a roll-sock vacuum actuator 38.

The actuator 38 has an actuator rod 40 connected to a valve linkage 42.

The linkage 42 which connects the butterfly valves 24 and 28 has only two positions. In one position both valves 24 and 28 move to close the passages in which they are situated and in the other end position both passages are fully open, as shown in Figure 1.

When the valves 24 and 28 are closed, an auxiliary flow passage comes into operation. A branch pipe 44 leads out of the exhaust passage upstream of the valve 24.

When the main exhaust passage is closed by the valve 24, then the exhaust gas can still pass through the auxiliary passage 44 and thereby is fed directly into the clean gas space 26 inside the filter. Because the valve 28 is now closed the only exit route for the gas is out through the filter 22, in the opposite direction to which the gas passes during normal filtering operation. As a result of this reverse flow, the particulate deposit which has built up on the outside walls of the filter 22 is dislodged and is carried by the exhaust gas along a pipe 46 leading to an exhaust gas recirculation system indicated schematically at 48.

The EGR unit 48 allows exhaust gas to recirculate to the engine through a duct 50.

In practice, to avoid undue pressures arising in the passage 46 (particularly if the EGR system 48 dictates that no EGR should enter the intake system at the time when there is flow in the passage 46), the valve 28 may be constructed with a hole in it or may otherwise be arranged to leak to a certain degree.

The system will normally be arranged so that flow through the passages 44 and 46 only occurs for an instant, but at sufficiently regular intervals to ensure that the build up of particulates is cleared from the outside of the filter. For example the actuator 38, 40 may be arranged so that as soon as it has completed one stroke, it is returned to its starting position and in the embodiment shown the actuator is provided with a spring 52 to ensure that this happens.

In a further feature the upstream opening of the passage 44 is closed during normal operation of the engine by the butterfly valve 24, and Figure 2 shows the end of the passage 44 and the butterfly valve on a larger scale. It will be seen that the passage 44 has an end which is cut at right angles to the passage axis and is positioned so that it is covered by the butterfly plate when the plate is in its "open" end position.

In order to enable the reverse flushing of the filter to take place whatever the state of the EGR unit 48, a buffer volume 54 may be built into the passage 46 as indicated.

The filter 22 must be capable of withstanding the temperatures which exist in the exhaust pipe of a diesel engine. The mesh size must be sufficient to ensure that the desired proportion of particulate materials are captured and to ensure that the filter body can be regularly back flushed to clear accumulated solids.

Claims

CLAINS

1. An exhaust cleaning installation for use in the exhaust gas path of a diesel engine, the installation comprising a filter and means for mounting the filter in the exhaust gas path so that the exhaust gas passes through the filter before being exhausted to atmosphere, the installation also comprising an auxiliary exhaust gas path across the filter such that when the exhaust gas travels along the auxiliary path it traverses the filter in the opposite direction to the normal flow direction and dislodges particles accumulated on the filter.

2. An installation as claimed in Claim 1, including valves on either side of the filter, the valves being adapted to operate simultaneously to close or substantially close the main exhaust flow path through the filter and to open the auxiliary path.

3. An installation as claimed in Claim 2, including means for sensing the pressure in the main flow path upstream of the filter and for operating the valves in response to a signal indicating a rise in the pressure above a predetermined value.

4. An installation as claimed in any preceding claim, wherein the auxiliary flow path is connected, downstream of the filter, into an EGR system so that the particulate matter is recycled to the engine.

5. An installation as claimed in any preceding claim, wherein vacuum is used as the power source to operate the valves.

6. An exhaust gas cleaning installation substantially as herein described with reference to the accompanying drawing.