RHR Doseur / Throttle operation

[EDC5]

Is anyone familiar with the operation of the Butterfly in the intake of the DW10BTED4 engine?

Out of curiosity I bought a spare doeseur and connected the vacuum line to it, it didn't seem to do anything with the engine running or even with a few revs but when I turned the engine off it closed as if to choke the engine to make sure it stopped.

I suspect that it may be linked to the EGR system, maybe it partially closes to increase vacuum in the manifold to increase EGR utilisation? however it didn't move during the test I just did.

For the avoidance of doubt, here is the part



Does anyone have any information as to the actual use of these 'Air Doser' units as to me they look like an unnecessary restriction in the air stream?

[MikeT]

You are quite correct. The EGR throttle is used to best control the air intake mix (fresh vs exhaust) and will close when engine is off.

[EDC5]

Would it cause any issue if the vacuum pipe was blocked off? I'm not fond of the idea of a throttle being in the air intake of a diesel... sounds like nonsense to me.

[MikeT]

Would it cause any issue if the vacuum pipe was blocked off? I'm not fond of the idea of a throttle being in the air intake of a diesel... sounds like nonsense to me.

I don't know if it would upset the ECU or running of the engine but what do you consider to be nonsense?

I could guess and say any restriction would be negligible considering you've got positive manifold pressure when needed.

And if, as I suspect, the default position is closed, I'm sure you wouldn't that anyway would you?

[EDC5]

If you look directly down the doser, even in its most open position there is a good part of the bore restricted. It just seems odd to be honest. Do you know how fine degree of control can be achieved by pulsing the vacuum solenoid?

The EGR has a feedback sensor to tell the ECU the true position of the EGR valve that is under vacuum control, the Doser has no feedback at all.

I ask this becuase when I'm driving normally and I apply a bit of power I first hear a sort of 'farting' noise (no better description to be honest), it is only after this sound has stopped does the car accelerate fast. I was wondering if the Doseur takes time to open (if it has been in a semi closed position) thus ruining throttle response.

[MikeT]

I had similar doubts about restrictions when I became familiar with my engine and found it's got two of these throttles!
But she goes well all the same. As such, I've haven't given them much more thought other than to check they weren't at risk of desposit blockage and monitoring the live data (as mine are battery powered).

Is there an actuator test you can utilise? Or perhaps some manual vacuum test you can rig up?

[EDC5]

Ah, does yours have the 'double doser' for bypassing the intercooler? I noticed the 2.0 HDi engines had this when used in Fords and Volvo's .... why I have no idea.

Yeah, I was just wondering about the source of this 'farting sound' and trying to locate parts that could be causing it. I assume it's down to the EGR or this Air Doser as I know for a fact when you floor it the EGR is meant to close to give maximum exhaust pressure to the turbo.

Maybe I could try taking it for a spin with the doser vacuum hose clamped just to see if it makes any difference to pickup?

[MikeT]

Yes, the 2nd butterfly is called on to aid regenerations of the DPF.

I'm intrigued what this noise is you're hearing. It must be incredibly loud to be heard when driving in anger.

[tmead]

Not sure you need to fret too much EDC, there's no feedback on the unit, so it cant run partially open, its either fully open or closed. Admittedly the butterfly does provide some restriction in the airflow when open, but how significant that is I'm not sure. I'd suspect its there to be able to close off the air intake if there is a runaway after oil seal failure and you turn the key off ? That sounds like a damn good plan to me.

[wheeler]

Thats not quite right, the solenoid is OCR controlled by the injection ECU so the opening & closing can be varied anywhere between fully open or fully closed.
You are correct there is no feedback sensor in it.
I plugged the vac pipe on my last RHZ engine to leave it fully open as i dont like the idea of an unnecessary restriction in the air intake. Its there to aid EGR operation but as that got blanked off too there wasn’t really any point in having it operational anyway.

[EDC5]

Thats not quite right, the solenoid is OCR controlled by the injection ECU so the opening & closing can be varied anywhere between fully open or fully closed.
You are correct there is no feedback sensor in it.
I plugged the vac pipe on my last RHZ engine to leave it fully open as i dont like the idea of an unnecessary restriction in the air intake. Its there to aid EGR operation but as that got blanked off too there wasn’t really any point in having it operational anyway.

Interesting, I see your point.

Did the car run any better without this doseur throttle interfering with the air intake?

[tmead]

Yes, in theory the ecu could control the valve to hold it partially open against the return spring, but only if there was a feedback mechanism of some kind to provide a servo loop. Without this the system is not capable of securely and confidently adjusting to any particular position other than fully open or closed as EDC observed. The vnt turbo uses a similar or identical valve and has a feedback device which allows the ecu to adjust the vanes to any required position, which is a different control.

In systems with an intercooler bypass (and two flaps in the doseur like the 307sw install) I can understand how these could be operated to bypass the intercooler to help increase gas temperatures during fap regen, however, with only one unit this is not practical. All the evidence points to the single unit choking airflow when the key is turned off, and nothing else.

[BX]

I don't know for definite why the butterfly is used on PSA engines. However on VW tdi engines its original function was to prevent the engine "jumping" when it is turned off. With an unrestricted intake the engine takes in a full charge of air on the induction stroke. As the engine is now turned off there is no fuel injected to keep the engine turning. On the last rotation before stopping air is inducted into the cylinder. The flywheel does not have enough stored energy to fully compress the charge. Rotation stops. The compressed charge now rotates the engine in the opposite direction. The sudden reversal of direction causes the engine to jump . It also applies reverse pressures to the timing mechanism. Closing the butterfly when the ignition is turned off allows the engine to come to a smooth stop as very little air is inducted and so compression pressure is low. The vacuum pressure is relatively low and so has little effect.
As I say I do not know specifically why Citroen use this device but engine management systems are pretty generic across all makes with only a little customisation for each vehicle manufacturer.

[wheeler]

Yes, in theory the ecu could control the valve to hold it partially open against the return spring, but only if there was a feedback mechanism of some kind to provide a servo loop. Without this the system is not capable of securely and confidently adjusting to any particular position other than fully open or closed as EDC observed. The vnt turbo uses a similar or identical valve and has a feedback device which allows the ecu to adjust the vanes to any required position, which is a different control.

Everything I'm writing here is based on the RHZ & RHY engines.
The air doseur's official name in the technical documentation is the EGR throttle butterfly. It's there to assist the EGR operation. It can be opened to any position between fully open & fully closed, it does this with calculated values from the ECU & doesn't need any feedback sensor. On these engines the EGR valve & turbo wastegate (RHZ only) Also work exactly the same, they are vaccum operated against a spring return, they can be opened to any position & neither have a direct feedback sensor either.

All the evidence points to the single unit choking airflow when the key is turned off, and nothing else.

You can actually watch the valve operating when the engine is idling if you take the air pipe off.

[wheeler]

Did the car run any better without this doseur throttle interfering with the air intake?

I bought the car with the head gasket gone so I didn't really drive it before hand, I blanked the EGR & the EGR throttle butterfly when doing the head as preventative maintenance. It always ran sweet & had plenty of guts. My theory is it cant run any worse without a restriction in the air intake