Exhaust pressure modulation valve

An exhaust gas pressure modulation valve for a diesel engine vehicle combines the functions of an exhaust brake and a warm-up valve and has a single butterfly valve (12) to close the exhaust passage. The butterfly is reactive and opens automatically at a predetermined back pressure to prevent engine damage. The butterfly includes a small bypass passage or aperture (29) to permit a low throughput of exhaust gas when closed.

This invention relates to an exhaust pressure modulation valve, and in 
particular to a valve for the exhaust system of a diesel engined vehicle. 
Devices known as `exhaust brakes` can be fitted into the vehicle exhaust 
system and which, by generating a back pressure, can assist the vehicle in 
braking. Similar devices, termed `warm-up` valves, can also assist in cab 
heating and in reducing the emission of unburnt hydrocarbons by reducing 
the time for the engine to reach normal operating temperature. 
In general the greater the back pressure generated by an exhaust brake, the 
more effective the braking effect becomes. But the level of back pressure 
generated (typically 2-8 bar) must not exceed the maximum design back 
pressure of the engine, which is limited, for example, by the load of the 
engine exhaust valve springs. 
To limit the back pressure, the exhaust brake, normally a butterfly valve 
or a sliding gate, must either be locked into a position which is almost 
but not quite closed, allowing some exhaust gas to escape around the edge, 
or have one or more bleed passages formed in or around the butterfly or 
sliding gate. It is usual in practice to drill a hole or holes, and allow 
the butterfly or gate to sit in a fully closed position. The leakage rate 
is determined by the size and number of bleed passages and is dictated by 
the maximum allowable back pressure when the engine is running at the 
highest speed, and the flow of exhaust gas through the exhaust brake is 
thus at its maximum. Typically the bleed passages may total 200 mm.sup.2 
for a butterfly diameter of 100 mm, about 2.5% of total butterfly area. 
It follows that at lower engine speeds, especially in the normal driving 
range, the bleed holes apertures are larger than is necessary to reach the 
maximum back pressure at these lower speeds. Accordingly such exhaust 
brakes are rather ineffective at moderate gas flow rates because the back 
pressure generated is much less than the maximum permissible. 
Warm-up valves are desirable because the time for the engine to reach 
operating temperature is substantially reduced, typically from 80 to 40 
minutes--this leads to a substantial reduction in the emission of unburnt 
hydrocarbons and a considerable improvement in fuel economy. 
The design requirements of a warm-up valve, when used to reduce the time 
for the engine to reach normal temperature, are not however the same as 
those applicable to exhaust brakes. In general only a very small bleed 
passage is required, typically not more than 5 mm in diameter for a 
butterfly diameter of 100 mm, because the engine is running at tickover 
speed, and the vehicle is stationary; back pressure generated is about in 
the range 0.5-2.0 bar, depending on the engine application. In a typical 
application, the back pressure generated by a warm-up valve will be only 
about 25% of the maximum back pressure generated during operation of an 
exhaust brake. A conventional exhaust brake would thus be useless as an 
aid to reducing engine warm-up time because the bleed apertures are too 
large to generate significant back pressure at these low engine speeds and 
gas flow rates. 
Warm-up valves may be driver operated, to minimise the time for the cab 
heater to begin to work, or may be operated automatically in response to 
emission control apparatus, to reduce the quantity of unburnt hydrocarbons 
exhausted whilst the engine is warming up. 
A particular danger with warm-up valves is that the driver may drive off 
with the warm-up valve closed; because the bleed passage is very small, 
the back pressure generated may quickly exceed the design limit of the 
engine, and engine damage may follow. 
The present invention seeks to provide an exhaust pressure modulation 
valve, which combines the functions of an exhaust brake and warm-up valve 
and has a single butterfly to close the exhaust tract. 
According to the present invention, there is provided an exhaust pressure 
modulation valve comprising a body having an inlet, an outlet, and a 
passageway between said inlet and outlet, a butterfly pivotable in the 
body to close communication between said inlet and outlet, said butterfly 
having a spindle and said spindle pivot axis being offset from an axis of 
symmetry of said passageway such that a resultant torque generated in 
response to increasing pressure at said inlet tends to open the butterfly, 
said valve further comprising operating means for closing said butterfly 
and adapted to apply to said spindle axis a closing torque of the same 
magnitude as said resultant torque generated at a pre-determined pressure 
at said inlet, and bleed means from one side of said butterfly to the 
other, said bleed means being sized to ensure a significant back pressure 
when said butterfly is in use closed and the flow of gas through said 
valve is significantly less than the maximum flow of gas through said 
valve, said bleed means having an area not greater than 0.25% of the 
cross-sectional area of said passageway. 
Such a valve has a butterfly which reacts to inlet pressure so that the 
butterfly opens when the predetermined inlet pressure is exceeded. The 
predetermined inlet pressure is set at or just less than the safe maximum 
design back pressure of the engine thus ensuring that the butterfly will 
open if excessive back pressures are generated. 
Typically said pre-determined pressure would be in the range 2-8 bar, 
depending on the application, and the bleed means would be sized to impose 
a back pressure of about 25% of maximum or about 0.5-2.0 bar at flow rates 
commensurate with an engine running at tickover speed. 
Preferably said bleed means has a total area of less than 0.25% of the area 
of said butterfly. Thus the bleed means is in size an order of magnitude 
less than the bypass aperture in a conventional exhaust brake. 
In a preferred embodiment having a butterfly area of 7850 mm.sup.2, a 
single bleed aperture having an area of 12.5 mm.sup.2 was found adequate 
to impose a back pressure of approximately 0.5 bar at engine tickover; the 
maximum permissible back pressure at maximum engine speed being about 4 
bar. 
The valve is safe when used in `warm-up` mode because the butterfly will 
react to excessive back pressures. The area of said bleed means is too 
small to significantly affect reactive operation of the butterfly and in 
any event the pre-determined inlet pressure can be set at a level which 
compensates for the effect of a small throughput of exhaust gas. Such an 
exhaust pressure modulation valve provides three functions with a single 
butterfly and additionally significantly improves the effectiveness of the 
exhaust brake at moderate engine speeds. 
Preferably said bleed means comprises a single bleed aperture; in a 
preferred embodiment, a hole in the butterfly is provided. In a preferred 
embodiment the hole is on the opposite side of said offset axis to said 
axis of symmetry. 
In this arrangement, the bleed aperture is on the side of the butterfly 
with smallest area exposed to inlet pressure; accordingly the turning 
movement tending to open the butterfly is not reduced. 
The offset of the butterfly pivot axis is typically in the range 2 to 4 mm, 
for a valve having a circular exhaust tract and a diameter of 100-150 mm. 
In one embodiment, the butterfly spindle is loaded by a return spring and 
operably connected to actuator means via a control spring whereby the 
resultant torque tending to close the butterfly can be set by for example, 
appropriate selection of one or both of the springs so as to balance the 
opening torque generated at a predetermined level of back pressure. 
This arrangement of balanced torques acting on the valve is particularly 
valuable because the butterfly is sensitive to very small changes in back 
pressure at the predetermined level at which the butterfly is set to open. 
Accordingly hysteresis in valve opening and closing loads is also minimal. 
It is preferred that the said valve closing torque be adjustable. In the 
case of an actuator arranged to push or pull a torque arm pivotal with the 
valve, adjustment of the applied torque can be achieved by varying the 
length of the torque arm. This arrangement is suitable whether the 
actuator is mechanically electrically, pneumatically or hydraulically 
operated. 
Pneumatic actuators are usually connected to a compressed air supply line 
providing line pressure to act against an internal return spring. In a 
preferred embodiment of the present invention such a pneumatic or indeed a 
hydraulic actuator is connected to the fluid supply via a pressure control 
valve which is preferably adjustable to control the pressure of fluid 
admitted to the cylinder of the actuator, whereby the resultant force 
(tending to close the valve) can be varied as appropriate to balance the 
maximum permitted back pressure. 
Actuation of the butterfly may be in response to driver action, for example 
in exhaust brake or cab heat mode, or may be under automatic control, for 
example to control exhaust emissions. 
The predetermined pressure at which the butterfly opens reactively may be 
varied by control means in accordance with engine management or other 
systems to suit particular operating requirements.

The dotted line illustrates the effect of conventional exhaust brake on 
back pressure (P) with increasing engine gas flow (F); gas flow of course 
increases with increasing engine speed. 
A conventional exhaust brake includes one or more relatively large holes in 
the butterfly so that at maximum gas flow (maximum engine speed) the back 
pressure developed by the exhaust brake does not exceed the maximum design 
back pressure of the engine--this is illustrated by point C1. 
Accordingly at low gas flow rates, the butterfly holes are too large to 
generate an effective back pressure, and in the normal operating range of 
the engine, the back pressure generated may be only 20-50% of the maximum 
permissible illustrated--by points C2 and C3. 
In contrast, the solid line of FIG. 1 illustrates the operating curve of a 
reactive exhaust brake according to the invention. The butterfly contains 
only a relatively small aperture (typically less than one-tenth of the 
total area of the holes in a conventional exhaust brake butterfly) and 
thus on application the exhaust brake generates almost maximum back 
pressure throughout the normal operating range of the engine. 
The exhaust brake of FIGS. 2-4 includes a cylindrical valve body 10 for 
connection by end flanges 11 to an exhaust tract and within which is a 
butterfly-type valve 12 mounted upon a spindle 14 to pivot about an axis 
displaced by a predetermined distance d (typically 3 mm for a valve of up 
to 5" diameter) from a diameter of the valve body 10. The direction of gas 
flow is indicated by arrow D. Rigidly mounted on the butterfly valve 
spindle 14 externally of the valve body 10 is a double ended lever 16, one 
end 18 of which is connected to a return spring 20 anchored at a fixed 
abutment 21 of a mounting plate 19. The other end 22 of lever 16 is 
connected via an override spring 24 to a control cable 26 leading to the 
vehicle cab (not shown) for operation by the driver. The mounting plate 
includes an abutment 27 for the cable sheath 28a. 
In the illustrated position the lever 16 is held in abutment with a stop 28 
by the return spring 20, the valve 12 being in the fully open position and 
the control cable 26 being relaxed. 
In operation the valve 12 is closed by pulling the cable 26 in the 
direction of abutment 27, the cable spring 24 extends, generating a torque 
which opposes the torque of the return spring 20 and the torque generated 
on the spindle 14 by exhaust gas back pressure. This latter torque is a 
result of the spindle axis being offset from the centerline of the valve 
body 10. 
As exhaust gas back pressure reaches the maximum permissible level, the 
spindle torque due to exhaust pressure increases to a point at which it 
balances the excess torque of cable spring 24 over return spring 20. At 
this point the valve is balanced with zero net torque and any further 
increase in exhaust pressure will tend to open the valve 12. 
The valve 12 is thus reactive and opens at a pre-set back pressure to 
prevent engine damage while ensuring that the valve is fully effective as 
an exhaust brake throughout the normal operating range of the engine. 
The return spring 20 is capable of re-opening the valve 12 when the closing 
force is removed, in this case when the cable 26 is relaxed. The offset of 
the valve spindle 14 allows the gas pressure to generate an opening torque 
proportional to the back pressure. 
The valve 12 also includes a hole 29, as illustrated in FIG. 4, or a bypass 
through the wall of the body 10, which allows the valve to be used as a 
warm-up valve to bring the engine up to working temperature. In this mode 
the valve 12 is closed when the engine has just been started from cold. 
The valve imposes a relatively low back pressure on the engine (typically 
1 bar) because the engine is running at slow speed (around 800 rpm) and 
the bleed hole 29 permits a small throughput of exhaust gas. This small 
back pressure dramatically reduces the time for the engine to reach normal 
operating temperature, typically from around 80 to 40 minutes. In the 
event that the engine speed increases, for example if the vehicle driver 
moves off without releasing the cable 26, the valve will operate as a 
reactive exhaust brake as described above. Engine damage when used as a 
warm-up valve is thus prevented. 
The valve is designed to prevent back pressure being generated above 
prescribed levels if the butterfly is closed when the engine RPM, and thus 
the gas flow, is large enough to generate excessive back pressure, or if 
the valve is held closed while engine RPM increases above that which would 
generate an excessive back pressure. 
A similar arrangement could be used when the valve is closed by pneumatic, 
electric vacuum, hydraulic or any other means. 
In the case of a pneumatically operated butterfly valve it is possible to 
make use of the return spring within the pneumatic actuator itself. One 
such embodiment is shown in FIGS. 5 to 7. The butterfly valve 32 and 
cylindrical valve body 30 with flanges 31, are arranged in substantially 
the same manner as shown in FIGS. 2 to 4. In this embodiment one end 
flange 31a is adapted for mounting directly to a turbocharger outlet. One 
end 34 of the lever 36 is connected to an adjustable piston rod 38 of a 
pneumatic actuator 40 held by the actuator return spring against the stop 
42 with the butterfly 32 in the fully open position. Spindle offset is 
indicated by `d`, and gas flow by arrow D. 
The butterfly 32 is closed by compressed air supplied to the actuator 40 by 
a pressure control valve 44 connected to a source S of compressed air, the 
air supplied acting against the actuator return spring to generate a 
closing torque on the butterfly valve 32 and urge the valve closed. 
The pressure of air supplied to the actuator is controlled by the valve 44 
which is set to hold the valve closed against the actuator return spring 
and the torque generated by the exhaust gas at the prescribed maximum back 
pressure level. 
If the back pressure starts to rise under the action of increased exhaust 
gas flow an imbalance is created, and the resulting torque combined with 
the actuator return spring torque overcomes the pneumatic actuator torque 
so that the valve opens returning the back pressure to the prescribed 
level. 
The level of back pressure required can be achieved by a combination of 
butterfly offset, lever length, actuator return spring and the pressure of 
air supplied to the actuator. 
Another method of giving a suitable actuator load is to dispense with the 
pressure control valve and vary the actuator return spring or springs. The 
spring or springs may be adjustable at the actuator or selected to apply a 
predetermined load to suit a particular application.