WO2018114627A1

WO2018114627A1 - Method for controlling the shutdown of a pre-feed pump of a pumping assembly for feeding fuel to an internal combustion engine

Info

Publication number: WO2018114627A1
Application number: PCT/EP2017/082911
Authority: WO
Inventors: Pietro De Carlo; Ciro MEDOLLA
Original assignee: Robert Bosch Gmbh
Priority date: 2016-12-23
Filing date: 2017-12-14
Publication date: 2018-06-28
Also published as: IT201600130740A1

Abstract

Method for controlling the shutdown of an electric pre-feed pump of a pumping assembly that can feed fuel to an internal combustion engine provided with a fuel distribution manifold, the pumping assembly (1) having a high-pressure pump (6), a high-pressure hydraulic circuit (19) for connecting the high-pressure pump (6) to the distribution manifold (4), and a low-pressure hydraulic circuit (17, 23, 25, 26) for connecting the pre-feed pump (7) to the high-pressure pump (6), in which the rotational speed (VP) of the pre-feed pump (7) is varied from a steady-state value (VP1), corresponding to the normal operation of the pre-feed pump (7), to an inversion value (VP2) of a sign opposite to the steady-state value (VP1), and is maintained (VP) at the inversion value (VP2) for a first preset time period (T2).

Description

Title

METHOD FOR CONTROLLING THE SHUTDOWN OF A PRE-FEED PUMP OF A PUMPING ASSEMBLY FOR FEEDING FU EL TO AN INTERNAL COMBUSTION ENGINE

The present invention relates to a method for controlling the shutdown of a pre-feed pump of a pumping assembly for feeding fuel, preferably diesel, to an internal combustion engine.

In particular, the present invention relates to a pumping assembly of the type comprising a high-pressure pump, in this case a piston pump, for feeding the fuel to the internal combustion engine; and a pre-feed pump, for example a gear pump, for feeding the fuel from a storage tank to the piston pump.

The aforementioned pumping assembly comprises a low-pressure hydraulic circuit, which connects the pre-feed pump to the high-pressure pump, and a high-pressure hydraulic circuit, which connects the high-pressure pump to the internal combustion engine. The low-pressure circuit comprises an electric metering valve for controlling the instantaneous flow of fuel fed to the pre-feed pump depending on operating parameters of the engine, and an over-flow valve for discharging, into the tank, at least some of the flow of fuel which exceeds that fed through the electric metering valve.

The pre-feed pump is constituted, for example, by an electric pump provided with an electric motor and with a suitable electronic control unit which turns the electric motor on and off for starting and shutting down the pre-feed pump on the basis of a certain control algorithm, which is typically influenced by the control logic of the electronic control unit of the internal combustion engine. The shutdown of the pre-feed pump causes a drop in the back pressure in the low- pressure circuit from a high pressure value, which is typically imposed by the overflow valve, to the atmospheric pressure value, with a drop time which depends on the layout and dimensions of the low-pressure circuit.

The control algorithm implemented in the pump control unit is normally of a sensorless type, i.e. it does not obtain sensor measurements on the angle of the rotor of the electric motor. This means that the sensorless control system has to estimate the angle of the electric motor, and that it is able to control the speed of the electric motor only for values which are greater than or equal to a minimum speed. Between a speed of zero and the minimum speed, the sensorless control system does not operate reliably: in this range, the error in the estimation of the angle is large and does not ensure a correct correlation between current in the windings of the motor and angular position of the rotor, and therefore in the start-up phase the control system simply accelerates the motor from a speed of zero to the minimum speed. As a result, the sensorlessly controlled electric motor, during start up, is not able to supply a sufficiently high torque so as to overcome the back pressure in the low-pressure circuit when said pressure is close to the pressure value imposed by the over-flow valve.

It is an object of the present invention to provide a pumping assembly for feeding diesel to an internal combustion engine, said pumping assembly being free of the above-described disadvantages and, at the same time, being easy and economical to produce.

The present invention provides a method for controlling the shutdown of a pre-feed pump of a pumping assembly that can feed fuel to an internal combustion engine, and a pumping assembly, as defined in the accompanying claims.

The present invention will now be described with reference to the accompanying drawings, which show a non-limiting exemplary embodiment thereof and in which: - Figure 1 shows a hydraulic diagram of a pumping assembly for feeding fuel to an internal combustion engine, said pumping assembly having a pre-feed pump controlled in accordance with the method of the present invention;

- Figures 2 and 3 are two graphs showing a known method for controlling the shutdown of the pre-feed pump and, respectively, a corresponding drop in back pressure in a low-pressure hydraulic circuit of the pumping assembly shown in Figure 1;

- Figures 4 and 5 are two graphs similar to those shown in Figures 2 and 3, but relating to the control method of the present invention; and

- Figure 6 is a graph showing a comparison between the drops in back pressure in Figures 3 and 5.

With reference to Figure 1, 1 denotes in its entirety a pumping assembly for feeding a fuel, preferably diesel, from a storage tank 2 to an internal combustion engine 3, in the case in question a diesel combustion engine.

The engine 3 comprises a fuel distribution manifold 4, commonly referred to by the term "common rail", and a plurality of injectors 5 connected to the manifold 4 and designed to atomize the fuel inside associated combustion chambers (not shown) of said engine 3.

The pumping assembly 1 comprises a high-pressure pump 6 for feeding the fuel to the engine 3, and a low-pressure or pre-feed pump 7, in the case in question an electric pump, for feeding the fuel from the tank 2 to the pump 6.

The pump 6 is a piston pump provided with a pump body 8 comprising a containing casing (not shown) which houses various mechanical elements, including a drive shaft 9 rotating in accordance with a longitudinal axis 10, and a head (not shown), which comprises at least one cylinder 11 having a longitudinal axis 12 thereof transverse to the axis 10 and communicating with the inside of the casing. The cylinder 11 is engaged slidingly by a piston 13, which is movable, under the thrust of an actuating device 14 coupled to the shaft 9, with an alternate rectilinear movement, comprising an intake stroke of the fuel into the cylinder 11 and a compression stroke of the fuel present inside said cylinder 11.

The pumping assembly 1 further comprises a hydraulic circuit 15 comprising, in turn, a first branch 16 for connecting together the tank 2 and the pump 7; a second branch 17, which connects together the pumps 6 and 7, extends through the pump body 8 to lubricate the actuating device 14, and is connected to the cylinder 11 by means of an intake valve 18; and a third branch 19, which extends between the pump 6 and the manifold 4 and is connected to the cylinder 11 by means of a delivery valve 20.

The branch 17 is provided with an electric metering valve 21, which is mounted upstream of the valve 18 in a direction 22 of feeding of the fuel along the branches 16, 17 and 19, is movable between a closed position and an open position of the branch 17, and is designed to control the instantaneous flow rate of fuel fed to the pump 6 depending on the values of a plurality of operating parameters of the engine 3.

The circuit 15 further comprises a fourth branch 23, which connects the branch 17 upstream of the electric valve 21 in the direction 22 to the tank 2, extends through an over-flow valve 24, and allows at least some of the amount of fuel exceeding that fed through said electric valve 21 to be discharged into the tank 2.

The circuit 15 further has a fifth branch 25, which extends between the manifold 4 and the branch 23 and allows the amount of fuel exceeding that necessary for the injectors 5 to be discharged into the tank 2.

The circuit 15 further comprises a sixth branch 26 for discharging into the branch 23, and therefore into the tank 2, the fuel fed through the pump body 8 by the branch 17 and seeping through the support bearings (not shown) of the shaft 9.

The branches 17, 23, 25 and 26 define a low-pressure circuit of the circuit 15, whereas the branch 19 defines a high-pressure circuit of the circuit 15. The pumping assembly 1 further comprises an electronic pump control unit 27 that can control the electric motor of the pump 7 and can communicate, via a communication bus, with an electronic engine control unit 28, the latter being able to control the operation of the engine 3, for example being able to control the electric metering valve 21 depending on the values of a plurality of operating parameters of the engine 3.

With reference to Figures 2 and 3, which show a known method for controlling the shutdown of the pump 7 and, respectively, the corresponding drop in back pressure BPS in the low-pressure circuit of the circuit 15 following the shutdown of the pump 7, the pump control unit 27 is configured, by means of a specific software, to impose on the pump 7 a rotational speed VP equal to a steady-state value VP1 (Figure 2) during normal operation of the pump 7, and to impose on the pump 7, and to make the pump 7 maintain, a rotational speed VP of a zero value when it is necessary to shut down the pump 7. A rotational speed VP which is equal to the steady-state value VP1 corresponds to a back pressure BPS in the low-pressure circuit of the circuit 15 having an average value BPS1 (Figure 3), which is typically imposed by the over-flow valve 24. The shutdown of the pump 7 in accordance with the control strategy of Figure 2 corresponds to the drop in back pressure BPS in the low- pressure circuit of the circuit 15 from the average value BPS1 to the atmospheric pressure value, as shown by Figure 3.

In the example shown in Figures 2 and 3, the steady-state value VP1 is equal to 3000 rpm, the average value BPS1 is approximately equal to 8 bar, and the time it takes for the back pressure BPS to drop to the atmospheric pressure value is greater than 3 seconds.

Figure 4 shows the method for controlling the shutdown of the pump 7 according to the invention, and Figure 5 shows the corresponding drop in back pressure BPS in the low-pressure circuit of the circuit 15. According to the invention, the pump control unit 7 is configured to command a variation in the value of rotational speed VP of the pump 7 from the steady-state value VP1 to an inversion value VP2 of a sign opposite to the steady-state value VP1, and to maintain the rotational speed VP at the inversion value VP2 for a preset time period T2. The inversion value VP2 of the rotational speed VP depends on the type of pre-feed pump used. The time period T2 depends on the minimum amount of time required to reach the atmospheric pressure. In particular, the time period T2 is set depending on the inversion value VP2. At the end of the time period T2, the rotational speed VP is set at the zero value until the pump 7 has to stay at a standstill.

Advantageously, the rotational speed VP is not instantaneously brought from the steady-state value VPl to the inversion value VP2, but rather is set for a short time at the zero value. In other words, the pump control unit 27 is configured to command a variation in the value of rotational speed VP of the pump 7 from the steady- state value VPl to a zero value, analogously to the control method shown in Figure 2, and subsequently to command an inversion of the rotational speed VP of the pump 7 from the zero value to the inversion value VP2.

In particular, the pump control unit 27 is configured to maintain the rotational speed VP at the zero value for a preset time period TO, in the transition from the steady-state value VPl to the inversion speed value VP2. The time period TO is necessary for ensuring that the pump 7 is shut down. The time period TO is shorter than the time period T2. In particular, the sum total of time periods TO and T2 has to be less than the minimum amount of time required for the pump 7 to restart.

In absolute value, the inversion value VP2 is lower than the steady-state value VPl. In the example shown in Figure 4, the inversion value VP2 is equal to -1500 rpm.

The method for controlling the shutdown of the pump 7 in accordance with the invention makes it possible to reduce the duration of the drop in the back pressure BPS from the value BPS1 to the atmospheric pressure value. Figure 5, indeed, shows that the time it takes for the back pressure BPS to drop to the atmospheric pressure value is less than 1 second. The reduction in the drop time of the back pressure BPS which is produced by the method of the invention can be seen in Figure 6, which shows the overlap of the profile shown in Figure 3 (shutdown of the pump 7 without the rotation inversion), shown by a dashed line denoted by CI, with the profile shown in Figure 5 (shutdown of the pump 7 with the rotation inversion), shown by a continuous line denoted by C2.

The rapid reduction in the back pressure BPS in the low-pressure circuit of the circuit 15 which is produced by the control method of the present invention makes it possible to simplify the restarting of the pump 7.

Claims

1. Method for controlling the shutdown of a pre-feed pump, preferably an electric pump, of a pumping assembly that can feed fuel, preferably diesel, to an internal combustion engine provided with a fuel distribution manifold, said pre-feed pump (7) being able to take the fuel from a tank (2), and said pumping assembly (1) comprising a high-pressure pump (6), a high-pressure hydraulic circuit (19) for connecting the high-pressure pump (6) to the distribution manifold (4), and a low- pressure hydraulic circuit (17, 23, 25, 26) for connecting the pre-feed pump (7) to the high-pressure pump (6), the method comprising:

- commanding a variation in the rotational speed (VP) of the pre-feed pump (7) from a steady-state value (VPl), corresponding to the normal operation of the pre-feed pump (7), to an inversion value (VP2) of a sign opposite to the steady- state value (VPl); and

- maintaining the rotational speed (VP) at the inversion value (VP2) for a first preset time period (T2).

2. Method according to Claim 1, and comprising:

- bringing said rotational speed (VP) to the zero value at the end of said first time period (T2).

3. Method according to Claim 1 or 2, in which commanding a variation in the rotational speed (VP) of the pre-feed pump (7) from a steady-state value (VPl) to an inversion value (VP2) of a sign opposite to the steady-state value (VPl) comprises:

- commanding a variation in the rotational speed (VP) of the pre-feed pump (7) from said steady-state value (VPl) to the zero value; and

- subsequently, commanding an inversion of the rotational speed (VP) of the pre- feed pump (7) from the zero value to said inversion value (VP2).

4. Method according to Claim 3, and comprising:

- in the transition from said steady-state value (VP1) to said inversion value (VP2), maintaining the rotational speed (VP) at the zero value for a second preset time period (TO).

5. Method according to Claim 4, in which said second time period (TO) is shorter than said first time period (T2).

6. Method according to any one of Claims 1 to 5, in which said inversion value (VP2) is, in absolute value, lower than said steady-state value (VP1).

7. Pumping assembly for feeding fuel, preferably diesel, to an internal combustion engine provided with a fuel distribution manifold, the pumping assembly (1) comprising a pre-feed pump (7), preferably an electric pump, for taking the fuel from a tank (2), a high-pressure pump (6), a high-pressure hydraulic circuit (19) for connecting the high-pressure pump (6) to the distribution manifold (4), a low- pressure hydraulic circuit (17, 23, 25, 26) for connecting the pre-feed pump (7) to the high-pressure pump (6), and an electronic pump control unit (27) that can control the pre-feed pump (7) and is configured to carry out the method according to any one of the preceding claims.