LPFP. Management

In this entry – about some nuances in the management of LPFP.

LPFP is managed via EKP. EKP manages the power of the pump, using PWM. PWM (not linear regulation) is chosen to reduce the heat losses in the power switch (MOSFET/IPS).

The pressure sensor of the LPFP contour is connected directly to DME. The meaning of its PINs:
1. GND;
2. analog signal (depends on the pressure, according to the curve);
3. 5.0V power supply voltage

Connection of the EKP module:
1. +12V 30th bus (power connection)
13. +12V 15th bus (power supply of the management)
2. GND;
4. (+) output of the pump;
9.; 16. CAN connection for the data exchange.

EKP measures the following parameters:
1. power supply voltage (buses No.30 and No.15);
2. output voltage (supplied to the pump);
3. current thru the pump;
4. internal temperature of the module.

EKP measures the supply voltage not only to detect Overvoltage and Undervoltage situations but also to correctly calculate PWM to reach the required output voltage.
EKP measures the output voltage both for self-diagnostics (damage of the output transistor – short-circuit or disruption of the connection) and for correction of the intended output voltage.

EKP measures the current through the pump both for self-diagnostics (damage of the connection, short-circuit, current consumption too high; current consumption too low) and for determination of the electrical power, used by the motor: calculation of flowrate and RPM of the pump.

Via CAN, EKP receives information regarding consumable flowrate of HPFP, indications of LPFP sensor and also directions, in which mode to work (via PWM management; emergency mode with PWM 100%; the pump turned off with PWM 0%, etc.), instead, to the DME the information regarding all measured analog parameters is sent, also the calculated parameters and status info (data of self-diagnostics).

LPFP pump is a collector type DC electric motor. The management of the electric motor is executed, managing it with a voltage (not, for example, current or power) according to the management map. The current via electric motor is used to calculate its load and flowrate.

The management map is created by the initial reference value map + adaptation map. The adaptation map is updated relatively slowly (within tens of seconds), which means: in case of swift change of parameters or load of the pump the inadequacy of the LPFP pressure to the ideal one is possible.

Important nuance: the largest part of the power (electric and mechanical energy) of the pump is used to pump the fuel between both sides of the fuel tank. As EKP live data indicate, by fuel consumption of 0 l/h, around 140 l/h of fuel is pumped via pump to ensure the fuel pumping to the ”correct” fuel tanks side.
Fuel consumption in idle is around 1 l/h, which means: more than 99% of all flowrate of the pump is used to pump the fuel, but less than 1% – for needs of the HPFP.
In the high power conditions (high requested torque) + high RPM, the fuel consumption is significantly higher (even till 40 .. 50 l/h), but even then the needs of HPFP increase the total flowrate only for 20 .. 25%.


How the LPFP EKP live data look. Conditions: idle, warmed-up engine:

0:00 till 0:30 you see:
1. theoretically calculated dynamics of dS/dt of the pump (these are not data of the RPM of the pump, so they don’t correspond the required RPM);
2. theoretically calculated RPM of the pump;
3. theoretically calculated necessary (required) flowrate of the pump;
4. value of the PWM register.

0:30 till 0:57 we can see:
1. temperature of the management power stage;
2. voltage supplied to the pump;
3. power supply voltage of the bus No.30 (power connection);
4. current via a pump;
5. power supply voltage of the bus No.15 (management connection).

In this video, you can see the parameter values and jittering of a correctly working LPFP pump.
As you see, the pump is managed with a voltage (in this case management voltage: 7,5V), the current via the pump fluctuates in the range of 8.5 .. 9.1A or +/-3.3%.

Displayed data steps value of the calculated parameters and jittering (steps):
1. required flowrate: 1.0; +/-1
2. calculated RPM: 15; +/-1
3. PWM register: 1; 50*
PWM depends (is inversely proportional) to the supply voltage in bus No.30.

Looking at live data, the following nuances have to be taken into account:

  • as the HPFP flowrate consumption is a very small part of all flowrate of LPFP, the performance (consumed current) of LPFP and its stability can be evaluated also for running engine, in idle: it has to be stable (jittering can be evaluated in the video above):
  • reasons for increased jittering can be:
    • LPFP system has some mechanical defects (“shivering” of some valve, damage of the pipe connection),
    • complete crash of HPFP of strong leaking of injectors.
  •  To exclude the previously mentioned cause of jittering – problems of HPFP, leaking injectors:
    • turn off the engine, status: Ignition ON;
    • turn on (using test block of ISTA/INPA) LPFP;
    • evaluate LPFP pressure using a manometer (or, if it is not possible, – current, consumed by LPFP and pressure sensor data) values and their stability/jittering. In this situation, the fuel consumption of HPFP is 0 l/h and it does not affect the measurements;
  • to exclude the possible impact of the defect of the LPFP pressure sensor (jittering of its values), you can use the test module of LPFP itself. With the assistance of the test module: set up the exact PWM in the output of the EKP (for example, 60%) and then observe the stability/jittering of the current, consumed by the pump. It is recommended to perform this test with a turned-off engine, so the changes in the onboard voltage do not affect the voltage, supplied to the pump (in case of fixed PWM, it will affect the power, supplied to the pump, and consumed current – it can cause incorrect conclusions).