Next test block of Expert mode: Fuel system.
Live data example of this menu:
Legend:
At first, I thought this test block had one drawback: no PWM data of HPFP pressure regulation valve are available.
Good news: this value can be found in ISTA call up functions:
Why is it so essential to see precisely the PWM? Setpoint and the actual value of pressure indicate if HPFP can maintain the required force. Instead, PWM means how much “effort” the pump has to make to perform this task. But, when I checked the PWM value of the HPFP valve in actual driving conditions, I was surprised:
Here is a video in which I drive in speeds 1, 2, and 3 with a partially open/completely open throttle. As you see, the PVM value is not changing! Why so? How is that possible – PWM is not switching, but the pump is still managed?
This time BMW engineers are managing the pump in a slightly different way than assumed for, for example, N53/N43 series engines. To change the pump’s flow rate, the moment of the valve management (with a fixed Q/length of the impulse) against the eccentric shaft is changed, not the PWM supplied to the valve. This is called the phase control method.
Conclusion – the valve activation signal (PWM) does not give any helpful information. If only – confirms that the valve has been manageable (or – is not managed in the emergency mode of the valve).
Let’s go back to the Expert mode graph.
In the Expert mode, for HPFP management, we see two essential parameters:
a. expected and confirmed phase of the valve management;
b. required and real Rail pressure.
HPFP management works in closed-loop mode. DME compares required Rail pressure with value, reported by the Rail sensor, and calculates the difference between both parameters (difference from the ideal); the speed of changes of this difference, and “polarity”.
Using the parameter maps of the HPFP pump, DME “predicts” how the HPFP valve should be managed for the pump to ensure the required flow rate and pressure. This “prediction” is necessary to minimize the reaction time of the system and ensure the correct transition process (for example, to avoid “waving”, vibration” of the pressure).
Based on the discrepancies and data regarding pump parameters, DME manages the HPFP valve so that the Rail pressure reaches the necessary value as soon as possible. For the management parameters (phases) of HPFP, the “good old” long term (and the adaptation parameter, allowed to it) and short-term management system is used. Similar to the one, which is used, for example, management of LPFP.
Here, in the image – the required and real Rail pressure curves are accented. From 26th to 38th second: the car’s acceleration in speeds 1, 2, and 3 with partially open/open throttle.
Required Rail pressure: green; bold (3rd value scale)
Actual Rail pressure: blue; bold (3rd value scale)
And in this image: intended and confirmed values of HPFP management phase:
Intended valve management phase: red; bold (2nd value scale)
Confirmed valve management phase: yellow; bold (2nd value scale)
As we see, for correctly performing HPFP, the intended and confirmed values of both parameter groups are practically equivalent. Only for a brief moment (parts of the second), very slight inadequacies can be seen.
For B58 series engines, the Rail pressure (in full functionality mode) is maintained in the range of 10 .. 20 MPa (100 .. 200 bar). The pressure rises when the RPM and/or required torque increase. For example, 100bar is typical for the idle. Without load, increasing RPM to 4000+, Rail pressure linearly increases till 150 bar. The same (linear) increase of Rail pressure is observed when the required torque increases.
In this image, the PWM values of LPFP management are marked.
PWM of LPFP valve: grey; bold (2nd value scale)
Nothing new in the LPFP management – already familiar “picture”. More about LPFP management read here and here.
