WO1989011025A1

WO1989011025A1 - Cleaning exhaust gas

Info

Publication number: WO1989011025A1
Application number: PCT/GB1989/000466
Authority: WO
Inventors: Cedric Paul Davies
Original assignee: Ford Motor Company Limited; Ford Werke A.G.; Ford France S.A.; Ford Motor Company
Priority date: 1988-05-06
Filing date: 1989-05-03
Publication date: 1989-11-16
Also published as: GB2218008A; 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 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. In European patent specification 0 194 131, a method and apparatus is described for filtering solid particulate matter from a diesel engine exhaust. This specification describes the use of a filter through which the particulate bearing gasses are passed and where the particulate material is trapped.

Periodically, the filter is back-flushed by passing a gas stream through the filter in the opposite direction to the normal, filtering direction. This back- flushing therefore dislodges the particles and cleans the filter.

The back-flushing air flow is drawn from outside the engine. Engine suction is used at a specific point in the cycle to draw clean air in from outside the engine to back-flush the filter. In order to produce a pressure pulse to create a shock wave through the filter which dislodges the particulates, a frangible diaphragm is used.

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. In a preferred embodiment the valves are internconnected by a fixed linkage, and an operating mechanism works on the linkage to simultaneously operate both valves. The operating mechanism can comprise a rapid-acting piston/cylinder unit connected to the fixed linkage through a pivoted plate which grips the linkage when it is moved in one direction, but slides over the linkage when it moves in the opposite direction.

The linkage prefeably includes an inclined straight rod or bar, with a weight freely slideable on the rod or bar, the inertia of the weight being such that when the operating mechanism moves suddenly, the weight travels up the bar to contact the plate and to knock the plate from the position where it grips the linkage to a position where it releases the linkage, so that the linkage can return to its start position under the influence of a separate spring.

In this way, it is possible to move the valves from one end position to the other end position very rapidly, and for a very short space of time. Typically this time can be about 0.25 seconds.

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;

Figure 2 is a detailed view of a small part of the installation of Figure 1.

Figure 3 is a schematic view of an alternative form of exhaust gas cleaning installation in accordance with the invention; and

Figure 4 is a pneumatic circuit diagram relating to the embodiment of Figure 3.

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

5 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

10 valve 34 which opens communication between a vacuum reservoir (eg 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

15 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

20 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

25 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,

^•30 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 35 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. In the alternative embodiment shown in Figure 4, parts which correspond to parts already described in Figure 1 bear the same reference numerals. The valves 24 and 28 are shown in their normal positions where they do not obstruct the flow cross sections of the respective passages 60 and 18. The passage 60 represents the normal exhaust gas flow into the filter housing 20, whereas the passage 18 is the exit to the exhaust outlet. In the position shown in Figure 3 however the valve 24 closes the end of the passage 44, in the same manner as illustrated in Figure 2.

Both valves 24 and 28 take the form of butterfly flaps which are mounted for rotation on shafts 62, 64 and radial arms 66, 68 are secured on the shafts. The radially outer ends of both arms are connected to one another by a fixed length link 70. Although the link is of fixed length, it may be provided with an adjustment arrangement to facilitate initial setting up. The link has a central rod portion 72 of constant cross-section, and a weight 74 which can slide freely on this cross- section. The link is inclined as shown so that one end is lower than the other and the weight 74 naturally rests at the bottom end of the link.

The mechanism is operated by a rapid-acting piston/cylinder unit 76 mounted at one end to a fixed point and having a plate 78 hinged to the end of its piston rod 80. The plate 78 has a hole through which the rod 72 passes. The diameter of this hole in the plate is larger than the diameter of the rod 72 so that when the plane of the hole is at right angles to the axis of the rod, the plate can move freely relative to the rod. However when the plate capsizes, it will grip the rod.

A spring 82 normally keeps the plate 78 in its "capsized" position, and an abutment 84 limits pivoting movement of the plate. A tension spring 86 normally keeps the valves 24 and 28 and link 70 in the positions shown in Figure 3.

Figure 4 shows the circuit for operating the cylinder 76. An air supply 88 is connected to a solenoid valve 90 which connects the cylinder either to the air supply 88 or to atmospheric pressure at 96. The solenoid valve is operated by a signal from the pressure transducer 30 which senses a rise in back pressure on the upstream side of the filter. The air supply 88 is also connected to the other side of the piston in the cylinder 76 through an orifice 94, and to the atmosphere through a further orifice 92. The orifice 92 is slightly larger than the orifice 94. For example orifice 92 may have a diameter of 0.5mm whereas orifice 94 will have a diameter of 0.4mm.

In use, the mechanism will remain in the position shown in Figure 3 during normal running. However when the engine back pressure builds up as a result of the filter 22 becoming clogged, a signal will be produced by the transducer 30 causing the solenoid valve 90 to open rapidly and to freely admit compressed air from the supply 88 to the right hand side of the cylinder 76 which will cause the piston rod 80 to be rapidly retracted. Because the spring 82 maintains the plate 78 in a position where it grips the rod 72, this will also cause the linkage between the two valves to be operated to turn both valves through an angle of 90. As a result, the exhaust gas flowing from the engine

(indicated by arrow 96) will be prevented from passing down the passage 60 and will instead flow through the auxiliary passage 44 to the inside of the filter 22 and particulate material collected on the outside of the filter will be dislodged and carried through the passage 46 back to the inlet side of the engine as shown in Figure 1.

However this situation (when 100% of the exhaust gas is passed back to the engine intake) should only last for a very short time (about 0.25 sec). To return the engine to its normal operating condition it is necessary to disengage the plate 78 from the rod 72, and this is done by the weight 74. When the cylinder 76 moves rapidly to move the linkage, the weight 74 is given momentum. When the link reaches the end of its travel, the momentum possessed by the weight 74 is sufficient to propel the weight up the rod 72 until it hits the plate 78 and knocks it from its capsized position to its upright position (against the force of spring 82) and once this happens the main spring 86 can rapidly return the valves 24 and 28 to their normal positions. The piston rod 80 will return more slowly to its extended postion as the compressed air from the source 88 bleeds through the orifice 92 to the other end of the pistons 98.

The pressure at the transducer 30 which triggers the operation of this mechanism may for example be 12 kPa. With the arrangements described here, the exhaust gas itself is used to back-flush the filter. Whilst back-flushing is taking place, the exhaust passage 18 is closed by the valve 28 so no unfiltered exhaust gas reaches atmosphere.

It is important that the changeover from normal to back-flushing mode take place rapidly so that a short sharp pulse of back-flushing gas is passed through the filter to provide a shock wave which will help to dislodge the collected particulate matter.

The filter 22 must be capable of withstanding the 0 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. A 5 suitable filter is a metal membrane filter soild under the trade mark PMM by Pall Process Filtration Limited. Such a filter has a stainless steel wire mesh with a thin sintered matrix of stainless steel powder within the pore structure of the mesh. A filter of this type 0 can remove particles down to 0.5 from exhaust gases. Because of the stainless steel construction, the filter is capable of withstanding high gas temperatures and repeated back- flushing.

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30.

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Claims

1. An exhaust cleaning installation for use in the exhaust gas path of a diesel engine, the installation comprising a filter (22) and means for mounting the filter in the exhaust gas path (14) so that the exhaust gas passes through the filter (22) before being exhausted to atmosphere, characterised in that an auxiliary exhaust gas path (44,46) across the filter (22) such that when the exhaust gas travels along the auxiliary path (44,46) it traverses the filter (22) in the opposite direction to the normal flow direction and dislodges particles accumulated on the filter (22) .

2. An installation as claimed in Claim 1, including valves (24,28) on either side of the filter (22), the valves (24,28) being adapted to operate simultaneously to close or substantially close the main exhaust flow path through the filter (22) and to open the auxiliary path (44,46) .

3. An installation as claimed in Claim 2, including means (30) for sensing the pressure in the main flow path upstream of the filter (22) and for operating the valves (24,28) in response to a signal indicating a rise in the pressure above a predetermined value.

4. An installation as claimed in Claim 2 or Claim 3, wherein the valves (24,28) are interconnected by a fixed linkage (42,70), and an operating mechanism works on the linkage to simultaneously operate both valves (24,28)

5. An installation as claimed in Claim 4, wherein the operating mechanism comprises a rapid-acting piston / cylinder unit (76) connected to the fixed linkage (70) through a pivoted plate (78) which grips the linkage (70) when it is moved in one direction, but slides over the linkage (70) when it moves in the opposite direction. -»o-

6. An installation as claimed in Claim 5, wherein the linkage (70) includes an inclined straight rod or bar (72) , with a weight (74) freely slidable on the rod or bar, the inertia of the weight (74) being such that when the operating mechanism moves suddenly, the weight (74) travels up the bar (72) to contact the plate (78) and to knock the plate from the position where it grips the linkage to a position where it releases the linkage, so that the linkage can return to its start position under the influence of a separate spring (86) .

7. An installation as claimed in any preceding claim, wherein the auxiliary flow path is connected, downstream of the filter (22) , into an EGR system (48) so that the particulate matter is recycled to the engine.

8. An installation as claimed in any preceding claim, wherein vacuum is used as the power source to operate the valves (24,28) .