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1. WO2016139174 - METHOD AND SYSTEM FOR RESTORING CORRECT OPERATION OF A PREFEED PUMP OF A PUMP UNIT USED TO FEED FUEL TO AN INTERNAL-COMBUSTION ENGINE

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[ EN ]

CLAIMS

1. Method for restoring the correct operation of a prefeed pump of a pump unit (1) used to feed fuel, preferably diesel, to an internal-combustion engine (3), the pump unit (1) having a high-pressure pump (6) used to feed the fuel to the internal-combustion engine (3) and said prefeed pump (7) being able to draw the fuel from a tank (2) before feeding same to the high-pressure pump (6) and comprising an electrical gear pump, which has a pair of meshed gears (28, 29), a permanent-magnet brushless three-phase electric motor (24) used to drive the two gears (28, 29) and an electronic pump control unit (36) that can control said electric motor (24) and to communicate with an engine control unit (38) of the internal-combustion engine (3), the method comprising:

- measuring the phase current (IS) of the electric motor (24) using current measurement means (41, 43) related to the electronic pump control unit (36), and

- using the engine control unit (38) to temporarily invert the direction of rotation of the electric motor (24) if the measured phase current (IS) exceeds a

predetermined threshold current value (1ST), in order to purge the prefeed pump (7) of any dust and/or waste in the fuel and/or of any particles caused by abrasive wear that have been deposited in the pair of gears (28, 29) or in the axial space between said gears (28, 29).

2. Method according to Claim 1, characterized in that the direction of rotation of said electric motor (24) is inverted for a predetermined number of revolutions (REV) to prevent commencement of a fuel flow from said high-pressure pump (6) to said tank (2).

3. Method according to Claim 1 or 2, characterized in that the temporary inversion of the direction of rotation of the electric motor (24) entails, in the following order:

- when the measured phase current (IS) exceeds said threshold current value, stopping the rotation of the electric motor (24),

- inverting the direction of rotation of the electric motor (24) for a certain number of revolutions (REV), and

- gradually returning the electric motor (24) to the previous direction of rotation.

4. Method according to one of Claims 1 to 3, characterized in that said engine control unit (38) provides said pump control unit (36) with a reference speed (VR) for the electric motor (24), the temporary inversion of the direction of rotation of the electric motor (24) being controlled by adjusting said reference speed (VR) if the measured phase current (IS) exceeds said threshold current value (1ST).

5. Method according to Claim 3, characterized in that said engine control unit (38) provides said pump control unit (36) with a reference speed (VR) for the electric motor (24), said reference speed (VR) usually being equal to a first speed value (VR1), rotation of the electric motor (24) is stopped by adjusting the reference speed (VR) to zero, and the direction of rotation of the electric motor (24) is inverted by adjusting the reference speed (VR) to a second speed value (VR2) having the opposite sign to the first speed value (VR1).

6. Method according to Claim 5, characterized in that said electric motor (24) is returned to the previous direction of rotation by adjusting the reference value (VR) according to a linear time slope running from said second speed value

(VR2) to the first speed value (VR1).

7. Method according to one of Claims 1 to 6, characterized in that said electronic pump control unit (36) has a three-phase inverter (39) with three half-H bridges to control the electric motor (24), said current measurement means including a shunt resistor (41) connected between the low common terminal (39a) of the half-H bridges and the reference terminal (39b) of the power supply voltage (VDC) of the inverter (39) to produce a signal (IS") indicating said phase current (IS).

8. Method according to one of Claims 1 to 6, characterized in that said electronic pump control unit (36) includes a three-phase inverter (39) to control the electric motor (24), said current measurement means having a plurality of shunt resistors (43), each of which is connected between a respective output phase (39c) of the inverter (39) and a respective stator input (24a) of said electric motor (24) to produce a signal (IS") indicating said phase current (IS).

9. System for restoring the correct operation of a prefeed pump of a pump unit (1) used to feed fuel, preferably diesel, to an internal-combustion engine (3), the pump unit (1) having a high-pressure pump (6) used to feed the fuel to the internal-combustion engine (3) and said prefeed pump (7) being able to draw the fuel from a tank (2) before feeding same to the high-pressure pump (6) and comprising an electrical gear pump, having a pair of meshed gears (28, 29), a permanent-magnet brushless three-phase electric motor (24) used to drive the two gears (28, 29), the system comprising an electronic pump control unit (36) that can control said electric motor (24) and includes current measurement means (41, 43) to measure the phase current (IS) of said electric motor (24), and an electronic engine control unit (38) that is able to control the internal-combustion engine (3) and is connected to the pump control unit (36) by a communication bus (37), the engine control unit (38) being configured to implement the method according to one of Claims 1 to 8.

10. System according to Claim 9, characterized in that said electronic pump control unit (36) has a three-phase inverter (39) with three half-H bridges to control the electric motor (24) and a microcontroller (40) to control the inverter

(39), said current measurement means including a shunt resistor (41) connected between the low common terminal (39a) of the half-H bridges and the reference terminal (39b) of the power supply voltage (VDC) of the inverter (39) to produce a signal (IS') indicating the phase current (IS), and is coupled directly to an input (40a) of an analogue-to-digital converter of the microcontroller (40) to enable this latter to acquire values for said signal (IS').

11. System according to Claim 9, characterized in that said electronic pump control unit (36) includes a three-phase inverter (39) to control the electric motor (24) and a microcontroller (40) to control the inverter (39), said current measurement means having a plurality of shunt resistors (43), each of which is connected to a respective output phase (39c) of the inverter (39) and a respective stator input (24a) of said electric motor (24) to produce a signal (IS") indicating said phase current (IS), and coupled directly to a respective input (40b) of an analogue-to-digital converter of the microcontroller (40) to enable this latter to acquire values for said signal (IS").