Piston pump and relative control method

1. A piston pump ( 1 ) for feeding a liquid in a vehicle; the piston pump ( 1 ) comprises:

at least one piston ( 2 ), which is configured to cyclically slide inside a housing ( 3 ) between a top dead centre (PMS) and a bottom dead centre (PMI);

a suction duct ( 5 ), which is configured to be connected, in use, to a tank;

a delivery duct ( 6 ), which is configured to be connected, in use, to a delivery line and along which the liquid is fed, in use, along a main feeding direction (D P ) of the piston pump ( 1 ), which is oriented from the suction duct ( 5 ) to the delivery duct ( 6 );

a first solenoid valve ( 7 ), which is arranged in the suction duct ( 5 );

a second solenoid valve ( 8 ), which is arranged in the delivery duct ( 6 ); and

an electronic control unit (ECU) configured to operate the two solenoid valves ( 7 , 8 ) so as to reverse the liquid feeding direction from the main feeding direction (D P ) to a secondary feeding direction (D S ) opposite the main feeding direction (D P );

the piston ( 2 ) is operated by a electromechanical actuator comprising an electromagnet; and

wherein the solenoid valves ( 7 , 8 ) are configured to be operated by the electronic control unit (ECU) as a function of movement (S) of the piston ( 2 ) determined through a current (CE) absorbed by the electromagnet.

2. The piston pump ( 1 ) according to claim 1 , wherein the electronic control unit (ECU) operates the two solenoid valves ( 7 , 8 ) so as to adjust a cylinder capacity (V) of the piston pump ( 1 ) and wherein the solenoid valves ( 7 , 8 ) are configured to be operated by the electronic control unit (ECU) as a function of movement (S) of the piston ( 2 ) determined through the current absorbed by the piston pump ( 1 ).

3. The piston pump ( 1 ) according to claim 1 , wherein:

the solenoid valves ( 7 , 8 ) are configured to be operated independently of one another;

in the main feeding direction (D P ), the liquid is sucked in through the first solenoid valve ( 7 ) and delivered through the second solenoid valve ( 8 ); and

in the secondary feeding direction (D s ), the liquid is delivered through the first solenoid valve ( 7 ) and sucked in through the second solenoid valve ( 8 ).

4. The piston pump ( 1 ) according to claim 1 , wherein each solenoid valve ( 7 , 8 ) comprises an electromagnet ( 13 ), a rod ( 10 ), which is controlled by the electromagnet ( 13 ), a spring ( 9 ), which acts through the rod ( 10 ) upon a closing element ( 11 ), which at least partially engages or disengages a passage port ( 12 ) of the solenoid valve ( 7 , 8 ), so as to allow the liquid to flow through the passage port ( 12 ) of the solenoid valve ( 7 , 8 ) or prevent it from doing so.

5. The piston pump ( 1 ) according to claim 4 , wherein the two springs ( 9 *, 9 **) of the two solenoid valves ( 7 , 8 ) have different pre-loads.

6. A control method to control a piston pump ( 1 ) for feeding a liquid in a vehicle; the control method comprises the steps of:

providing a piston pump ( 1 ) comprising: at least one piston ( 2 ), which is configured to cyclically slide inside a housing ( 3 ) between a top dead centre (PMS) and a bottom dead centre (PMI), a suction duct ( 5 ), which is provided with a first solenoid valve ( 7 ), and a delivery duct ( 6 ), which is provided with a second solenoid valve ( 8 ); wherein, along a main feeding direction (D P ), the liquid is fed from the suction duct ( 5 ) to the delivery duct ( 6 );

detecting the position of the piston ( 2 ) inside the housing ( 3 ), so as to know whether the piston ( 2 ) is in a suction phase or in a delivery phase; and

operating the two solenoid valves ( 7 , 8 ) independently of one another so as to reverse the liquid feeding direction from the main feeding direction (D P ) to a secondary feeding direction (D S ) opposite the main feeding direction (D P ); operating the piston with an electromechanical actuator comprising an electromagnet; and

determining movement (S) of the piston by detecting development of a current (CE) absorbed by the electromagnet.

7. The control method according to claim 6 and comprising the further step of operating the two solenoid valves ( 7 , 8 ) independently of one another so as to adjust a cylinder capacity (V) of the piston pump ( 1 ) and determining the movement (S) of the piston ( 2 ) by detecting development of the current absorbed by the piston pump ( 1 ).

8. The control method according to claim 6 and comprising the further step of operating the opening or the closing of the solenoid valves ( 7 , 8 ) with at least one time offset (Δ 1 , Δ 2 , Δ 3 , Δ 4 ) relative to a corresponding theoretical instant (A, B, C, D).

9. The control method according to claim 8 and comprising the further step of adjusting the at least one time offset (Δ 1 , Δ 2 , Δ 3 and Δ 4 ) “off-line” and subsequently optimizing them “on-line” based on a signal obtained from a pressure sensor arranged in a liquid delivery circuit.

10. The control method according to claim 6 , wherein, in order to reverse the liquid feeding direction, the second solenoid valve ( 8 ) is commanded to be flowed through by the liquid sucked in and the first solenoid valve ( 7 ) is caused to be flowed through by the delivered liquid.

11. The control method according to claim 6 and comprising, in order to vary a cylinder capacity (V) of the piston pump ( 1 ), the further step of varying an actuation frequency (f) of the piston ( 2 ).

12. The control method according to claim 6 and comprising, in order to vary the cylinder capacity (V) of the pump, the further step of operating the two solenoid valves ( 7 , 8 ) advancing or delaying closing of the first solenoid valve ( 7 ), which is flowed through by the liquid sucked in.

13. The control method according to claim 6 and comprising, in order to vary a cylinder capacity (V) of the pump, the further step of controlling the first solenoid valve ( 7 ), which is flowed through by the liquid sucked in, with a pulse width modulation having a variable duty cycle.

14. The control method according to claim 6 and comprising, in order to vary the cylinder capacity (V) of the pump, the further step of advancing closing of the second solenoid valve ( 8 ), which is flowed through by the delivered liquid.