PDE Control: Questions and Answers

Hello,

The yellow Bosch PD manual describes the electrical control of positive displacement elements.

After the initial activation phase of the solenoid valve, the valve flow is regulated to the holding value using pulse-width modulation.
And for shutting it off = precise timing of the fuel injection cutoff (attention, here it comes).

Boschbuch wrote:

occurs when a high clamping voltage is applied to quickly discharge the energy stored in the solenoid valve.

What exactly is meant by that ?

Where does the motor computer intend to obtain a high voltage to counteract the induced voltage of the magnetic coil?
"14 volts from the vehicle's electrical system are likely to be quite low in this case, in my opinion."

What exactly is meant by "clamping voltage" here? (not: clampings voltage!)


Could some PD-Boxes be experiencing problems with these mysterious processes, which is why they deliver so little performance gain?

Hi Ulf,

The energy stored in an inductor causes high voltages to be induced when the current is switched off. According to the law of induction, the voltage reverses polarity in order to maintain the current flow. This is why 'reverse-biased' protective diodes are used, for example, in relay coils, which allow the stored energy to be 'discharged.' The energy is consumed or converted into heat in the forward resistance of the diode and the copper resistance of the coil. Because the internal resistance of the diode and the coil resistance are relatively low, this results in a slightly longer current flow, which leads to a (slight) delay in the relay deactivation or, in this case, a delayed closing of the nozzle.
The discharge of the coil can be accelerated by applying an additional reverse voltage. This increases the discharge current and must be disconnected at the correct time (when the magnetic field of the coil is zero). Therefore, what is needed is not a quenching pulse with a higher voltage, but a temporally defined quenching pulse with a negative or reverse voltage.
And that is something the control unit should be able to generate.

Did I shed some light on the matter?

Greetings.

Eike.

eike wrote:

Therefore, it is not a erase pulse with a higher voltage that is needed, but rather a time-defined erase pulse with a negative or reversed voltage. And that is something the control unit should be able to generate. Did I shed some light on the matter?

Hi Eike,

probably yes... in my own words:

To switch off, the valve opening voltage is reversed, meaning the coil effectively receives -14 volts.
As soon as the current in the coil drops to zero (presumably detected via a low-resistance series resistor?), the voltage is completely switched off.
Is that correct?

Then the question arises: how (or with what polarity) do power boxes intend to extend the opening time, especially when the engine control unit initially counteracts them with a voltage reversal?

ulf wrote:

Then the question arises: how (or with what polarity) do power boxes intend to extend the opening time, when the engine computer initially counters them with a voltage reversal...?

Modern power boxes for PDs should definitely incorporate a microcontroller. This microcontroller can easily detect the desired shutdown point of the MSG (voltage reversal). The microcontroller then keeps its output driver polarized in the "correct" direction for a short period before reversing the voltage itself (quenching voltage) to shut down the PDs, and switches off at the moment of zero current.

As a Powerbox developer, this is how I would implement it. Hopefully, the actual Powerbox developers will do something similar, and they won't be undermined by some finance/controlling person who throws a wrench in the works...

Regards,
Guste.

guste100 wrote:

The microcontroller then keeps its output driver polarized in the "correct" direction for a slightly longer period.

. . . and this shorts the "delete output voltage" of the engine computer -> causing a sputter .
Okay, you can prevent that with a diode, but I'm still not entirely clear about the possible voltage sequences.
When the 0-volt wire of the PDE is raised to +14V by the engine computer to trigger its deactivation, the positive wire, in my opinion, should receive at least approximately 20 volts from the power box to ensure it remains open.


But with the anti-spark diode, at least in principle, we would have a rather crude tuning method.
Connect a high-current diode in series with the common lead of the power devices (PDEs), and connect a matching flyback diode in parallel with each PDE.
This bypasses the quick shut-off, meaning the pressure drop valves (PDVs) remain open for "a little longer" - and unfortunately, they also close more slowly, which results in a "less clean" end to the injection process.

But the injection duration extension would always be the same thanks to the regulated holding current. At low engine speeds, the excess amount would be small due to the fixed injection rate (mg / °KW), while it increases with the engine speed and is more than four times higher at 4000 rpm compared to idle.

The only question would be how much extra would actually end up being added.

Hi Ulf,

It seems we were completely talking past each other. I would like the output of the MSG to terminate in the P-box. This would eliminate any direct connection between the MSG and the PDE. The P-box would then use the MSG signal solely as an input signal. The P-box would have its own control electronics for the PDEs. The P-box would drive its output stage directly with battery voltage, not with the connection from the MSG.

EDIT: To be more explicit: The P-box has a power H-bridge at its output, which, as a center-tapped connection, is only connected to the PDEs (Power Distribution Elements) and not to the MSG (Main System Generator). The top and bottom of the H-bridge are connected to the battery voltage (with a possible current shunt in series at the bottom). It is driven by the microcontroller of the P-box.

That's how I, as a P-box developer, would implement it. I can't tell you if it actually looks like that in reality; these are just my thoughts on the matter.

Regards,
Guste.

guste100 wrote:

I would have the output of the MSG end in the P-box. This would avoid a direct connection between the MSG and the PDE. The P-box only uses the MSG signal as a pure input signal.

Okay, I understand.

The box I tried is wired differently:
The 4 individual wires from the MSG (Measurement Signal Generator) to the PDEs (Partial Discharge Evaluators) are only tapped into, but not interrupted.
The collector electrode is being short-circuited by the box, because inside (according to the measurements) there is a Schottky diode in the "PDE opening direction."

Advantage: Without the operating voltage applied to the unit, the motor remains operational under normal conditions, and the unit can be switched on and off smoothly without any jolts or interruptions.

Hi,

hat nicht irgendjemand ein Speicheroszi und kann mal den Spannungsverlauf am PDE mitloggen? Und evtl auch den Stromverlauf über einen 2. Channel.
Then we will have certainty...

Greetings.

Eike.