AGR Delete Pipe: Find Special Part Now

Hello, especially to the electronics experts.

Since an increasing number of new vehicles (including mine) are displaying error messages related to the EGR valve, I'm considering designing a simple circuit that would "lower" the mass airflow sensor (MAF) signal in proportion to the EGR control signals.

A semiconductor component that can pass a signal current of, say, 1 mA with virtually no voltage drop (or less than 5 mV), depending on the control signal, or can gradually reduce this current would be very helpful.

"I don't think this can be solved with standard bipolar transistors, but I have an idea about "self-biasing" FETs - although I'm not very familiar with that area."
However, FETs likely have the advantage of not loading the LMM output with control currents.

Does anyone here know of an affordable component that can be used to solve the problem mentioned above?

Hi!

Semiconductors always have threshold voltages, including FETs.

But the problem is still solvable.

Assuming the LMM (Linear Motion Module) provides a positive analog signal to the control unit, you simply feed this signal into a two-stage transistor amplifier (2 x emitter circuit = non-inverting), where the gain is precisely adjusted to 1 using strong negative feedback and an input voltage divider. This ensures that the signal is passed through without any loss. Due to the strong negative feedback, deviations caused by non-linearities are negligible.

The emitter resistor of the second transistor now effectively provides a non-inverting second input, which allows the output signal to be 'pulled down' by injecting a signal, without affecting the LMM (likely referring to a specific circuit element).

'If you provide me with the environmental conditions (voltage range and output impedance of the mass flow meter signal, input impedance of the control unit), I can design a circuit for you.'

Regards,

Best regards,

Hello,

It should be possible to achieve this with a rail-to-rail op-amp, a small FET, and a small shunt resistor. If you can provide more specific details about the voltage and current levels, I can help you design the circuit.

What you're referring to are depletion-mode FETs. They are very rare in MOSFETs. For example, with JFETs like the BF245, the threshold voltage and current exhibit very large variations between individual devices.

Best regards,
Christian.

SeatArosa1.7SDI wrote:

If you provide me with the environmental conditions (voltage range and internal resistance of the LMM signal output, input impedance of the control unit), I will design a circuit.

Hi,

Okay: Signal voltage range approximately 1 - 5 volts, load resistance (input of the engine control unit) = 10 kOhms, output impedance of the mass airflow sensor is unknown.

I would ideally like to implement the whole thing "passively," meaning without having to provide a power supply for the circuit that would introduce a "back current" – a supply that would likely need to provide more voltage than the maximum 5V of the signal. Because if the supply voltage were to pass through a defect in the fake circuit and into the input of the engine control unit, the latter could potentially be damaged .

In my opinion, a self-biasing FET would be ideal for this application. With a load of 10 kOhms, it should have an on-resistance of approximately 20 Ohms without any gate biasing (at an Ids of around 0.5 mA), which would increase to about 5 kOhms when the gate is biased negatively.

@chris11: Thanks for the reply. I'll see if I can manage with a BF 245... if I can find one at Conrad.

Hello Ulf,

Does the LMM (likely referring to a mass airflow sensor) not also output a 5V voltage in addition to the LMM signal (0-4.5V)?
"Then, I would build a differential amplifier circuit using a low-power rail-to-rail op-amp and power it with these 5V. The LMM output would be connected to the positive input (and will then appear at the output of the op-amp with a gain of exactly 1), and the AGR drive signal would be connected to the negative input of the differential amplifier, after being appropriately low-pass filtered and attenuated. An op-amp like the LT1782 only requires about 50uA of current, so it shouldn't have a significant impact."

Best regards,
Christian.

Because if the power supply voltage, due to a defect in the fake circuit, leaks into the input of the engine control unit, the latter could potentially malfunction .

Don't worry, a 5V Zener diode and an RC circuit connected in parallel with the fake circuit's output will reliably protect against overvoltage and interference spikes.

The voltage range of 1-5V is ideal for a simple discrete circuit. In my opinion, specialized FETs or amplifiers are not necessary.

I have just designed a circuit with 3 transistors (BC-type small-signal devices) and 6 resistors. Unfortunately, I don't have an image server to put the gif here. I'm calling this circuit the '99cent circuit'.

To ensure a constant amplification factor (=1), the circuit should be powered by a small longitudinal regulator with a stabilized voltage.[/img]

@ulf

In my opinion, a self-biasing FET would be ideal for this, which, considering the 10 kOhm load, would have a maximum on-resistance of approximately 20 Ohms (at Ids ~ 0.5 mA) without any gate drive, and which would increase to about 5 kOhm when the gate is biased negatively.

Hi ulf, I think you can forget about a FET with an absolute drain-source voltage drop of 5mV (see your 1st post). Because the specified 20 Ohm on-resistance refers to the dynamic drain-source resistance. This applies under the condition that the drain-source threshold voltage has already been exceeded: Rds(dyn.) = Delta U / Delta I.

Despite everything, good luck with your search. Maybe you'll find him after all.

Hi,

How about the following specialized component(s)?
- AGR pipe with branch, hose, and T-connector for connecting to the EGR cooler.
- 2mm steel sheet with 2 mounting holes?

Definitely provides the least stress .

Best regards, Rainer.

SeatArosa1.7SDI wrote:

I have just designed a circuit with 3 transistors (BC-type small-signal types) and 6 resistors. Unfortunately, I don't have an image server to put the GIF here. I'm calling this circuit the "99cent circuit".

Hi,

Can you please email me the schematic? -> [email protected]
If you like, I can put them in as an attachment here.

Rainer K. wrote:

How about the following special component(s): - AGR pipe with branch, hose, and T-connector for connecting to the EGR cooler. - 2mm steel sheet with 2 mounting holes?

Hi Rainer,

What exactly would you create with it?

I suspect it has something to do with using KGE gases instead of exhaust gases, but I'm still not entirely clear on how it works.

SeatArosa1.7SDI wrote:

Hi ulf, I think you can forget about a FET with an absolute DS voltage drop of 5mV (see your 1st post).

It seems like... I just measured the D-S resistance of a BF 245 transistor a while ago: it's over 200 ohms.

In a test setup with 5V -> FET -> 10 kOhm resistor -> ground, a voltage drop of over 100 mV was also observed across the FET, even though the gate voltage (Ugate) was equal to the source voltage (Usource).

Then I will definitely need to include a (Reed-)relay to bypass the transistor, which will be opened by a threshold switch when the EGR is active (or should be active ).

Hi Ulf,

The fake AGR could use the connection for the KGE (Katalytische Gasreinigung) at the intake manifold to draw in fresh air .

Best regards, Rainer.

Rainer K. wrote:

The fake AGR could use the connection for the KGE at the intake manifold to draw in fresh air

.
Hi Rainer,

However, the KGE inlet is located behind the LMM – at least in the engines I am familiar with.
That means the air drawn from there also passed through the mass airflow sensor (MAF), and would therefore not reduce its measured value not , but that's exactly what we're trying to do (reduce the MAF value).

Furthermore, the flow would likely run in the wrong direction: the "AGR mixing valve" is located behind the turbocharger, while the KGE (Knock Gas Exhaust) connection is located in front of it. This means that the turbocharger would partially pump air uselessly in a loop: out of the AGR valve, into the KGE connection, through the turbocharger, and back to the beginning...

Or have I completely misunderstood something ?

Damn... You're right, I didn't think it through completely .
It's a shame, but where can you find clean, fresh air these days? And that extra little "mushroom filter" on the modified EGR pipe isn't exactly ideal either...

Therefore, a solution that modifies the airflow sensor's output voltage based on the throttle valve opening would likely be more effective.

How about connecting the HFM output signal to the positive input of an op-amp, connecting the EGR valve control voltage to the negative input via a potentiometer/RC circuit, and powering the whole thing with +5V from the HFM?

Best regards, Rainer.

Hi Ulf, the reed relay gave me an idea. If you connect a two-terminal component with a constant voltage drop in parallel with the relay's normally open contact, you can achieve a switchable reduction of the entire mass flow rate (LMM) signal level by a constant amount.

To reduce the LMM value by 300 mV, a germanium or Schottky diode is suitable. For a reduction of 500 to 600 mV, a silicon diode is more appropriate.

To determine if these values correspond to the actual EGR system behavior, you should measure them with the engine running. Do this by measuring the mass airflow sensor (MAF) signal, opening and closing the EGR valve, and observing the signal voltage.

The relative fluctuations in the LMM signal do not affect the diode itself, but rather it simulates a constant volume flow of exhaust gas. Whether the control unit can be so easily fooled remains to be seen, because the exhaust gas volume flow is not constant, unlike the voltage drop of the diode.

Okay, I'm now emailing you the 99-cent circuit diagram, which I will of course expand further. You can feel free to draw it neatly using a circuit diagram program (I only have paint ) and post it if you think it's worth sharing.

Best regards and happy Easter to you.

Rainer K. wrote:

How about an op-amp, with the HFM output signal connected to the positive input, the AGR solenoid valve control voltage connected to the negative input via a potentiometer/RC circuit, and the whole thing powered by +5V from the HFM?

Hi Rainer,

I had already designed something similar, based on an LMM correction circuit.
It seems that no one has tried this before (or posted the results).

Right now, I'm working on developing a simpler/cheaper solution...

Hi,

Quote:

The relative fluctuations in the LMM signal do not affect the diode itself, but rather it simulates a constant volume flow of exhaust gas. Whether the control unit can be so easily fooled remains to be seen, because the exhaust gas volume flow is not constant, unlike the voltage drop of the diode.

I think that's precisely why it won't be that simple. The engine control unit initiates an action (e.g., opening or closing the EGR valve) and checks the effect based on the mass airflow sensor (MAF) values. These MAF values should then change, but that's not what happens with this setup.

In my opinion, it's impossible to build something like that without reintroducing the AGR control signal.

Best regards,

Jan.