Method for controlling a bi-fuel engine and associated engine

Abstract

The present invention relates to a method for controlling a bi-fuel internal combustion engine (10), the engine comprising: - a first injection device (14) for injecting a fuel of a first type into the engine (10) in a first operating mode (M1); - a second injection device (16) for injecting a fuel of a second type, distinct from the first type, into the engine (10) in a second operating mode (M2); - at least one high-pressure pump (18) configured to supply at least one injection rail (20) with fuel of the first type at high pressure, the method comprising the following steps: a) determining the resistive torque (Cr) applied by the high-pressure pump (18) to the engine when the engine (10) is operating in the second operating mode (M2); b) adjusting the power setpoint used by an engine control unit (22) as a function of the resistive torque (Cr) determined in step a).

Description

[0001] Method for controlling a dual-fuel engine and associated engine

[0002] DESCRIPTION

[0003] Technical field of the invention

[0004] The present invention relates to a method of controlling a dual-fuel engine, that is to say, a combustion engine capable of operating with two different fuels.

[0005] The invention relates more particularly to a method of controlling a dual-fuel engine equipped with a high-pressure fuel pump and an associated internal combustion engine.

[0006] Technical background

[0007] It is known to design a dual-fuel internal combustion engine. This type of engine generally includes a dual injection system, at least one of which is equipped with a high-pressure fuel injection pump.

[0008] For example, the engine includes a first injection device using a first type of fuel, for example gasoline, and a second injection device using a second type of fuel, for example liquefied petroleum gas (LPG).

[0009] The engine is controlled according to a command given by the vehicle driver, which takes into account the engine power and other parameters that influence the movement of the vehicle that the engine equips.

[0010] One drawback of existing solutions is that the power delivered by the motor is not always suited to the driver's input. This can be due, for example, to certain accessories fitted to the motor that draw some of the energy supplied in order to operate. The present invention aims to provide a solution to improve motor operation and enhance the response to control commands.

[0011] Summary of the invention

[0012] The invention proposes a method for controlling a dual-fuel internal combustion engine comprising:

[0013] - a first injection device designed to inject a fuel of a first type into the engine according to a first operating mode, - a second injection device designed to inject a fuel of a second type, distinct from the first type, into the engine according to a second operating mode,

[0014] - at least one high-pressure pump configured to supply at least one fuel injection rail with high-pressure fuel of the first type,

[0015] - a motor control unit which controls the motor at a predetermined operating speed according to a power setpoint, the process comprising the following steps:

[0016] a) determination of the resistive torque applied by the high-pressure pump to the motor when the motor is operating in the second operating mode,

[0017] b) adjusting the power setpoint used by the motor control unit to control the motor, according to the resistive torque determined in step a), and in such a way as to compensate for the loss of torque related to the resistive torque.

[0018] According to other features of the invention:

[0019] - during step a), the resistive torque is calculated at least as a function of the volume of fuel compressed by the high-pressure pump;

[0020] - the high-pressure pump being controlled by a camshaft driven in rotation by the engine, the cam cooperating with a piston capable of compressing the fuel of the first type in a compression chamber, the piston being equipped with a return spring which forces the piston towards the cam, during step a), the resistive torque is calculated as a function of the force produced by the return spring and as a function of the angular position of the cam; - the high-pressure pump having an inlet valve which controls the flow of fuel towards the compression chamber, during step a), the resistive torque is calculated as a function of the position of the piston and as a function of the angular position of the engine at the time of the closing of the inlet valve;

[0021] - the closing time of the intake valve is determined according to the cam profile;

[0022] - the process includes a synchronization step between the activation of the high-pressure pump and the compensation of the torque loss during which the triggering time of step b) is determined with an angular offset, relative to the time expected for the closure of the inlet valve, so as to transmit the torque loss compensation command before the closure of the inlet valve;

[0023] - the process also includes the following steps:

[0024] -- measurement of instantaneous pressure in the injection rail,

[0025] -- comparison of the instantaneous pressure in the injection rail with a pressure setpoint,

[0026] -- determination of an engine angle setpoint for triggering the closure of the intake valve, when the pressure in the injection rail deviates from the pressure setpoint, the engine angle setpoint being intended to restore the pressure in the injection rail to a value corresponding to the pressure setpoint.

[0027] The invention also proposes a dual-fuel internal combustion engine comprising:

[0028] - a first injection device designed to inject a fuel of a first type into the engine according to a first operating mode, - a second injection device designed to inject a fuel of a second type into the engine according to a second operating mode,

[0029] - at least one high-pressure pump configured to supply at least one fuel injection rail with high-pressure fuel of the first type,

[0030] - a motor control unit which is configured to control the motor at a determined operating speed according to a power setpoint, to determine the resistive torque applied by the high-pressure pump on the motor when the motor is operating in the second operating mode, and to adjust the power setpoint according to the resistive torque determined previously.

[0031] According to other engine characteristics:

[0032] - the high-pressure pump is controlled by a camshaft driven in rotation by the engine, the cam cooperating with a piston capable of compressing the fuel of the first type in a compression chamber, the piston being equipped with a return spring which forces the piston towards the cam;

[0033] - the high-pressure pump includes an intake valve which controls the flow of fuel to the compression chamber, the opening of said intake valve being dependent on the angular position of the cam.

[0034] Brief description of the figures

[0035] Other features and advantages of the invention will become apparent upon reading the detailed description that follows, for an understanding of which reference should be made to the attached drawings in which:

[0036] [Fig.1] is a diagram that represents a dual-fuel internal combustion engine equipped with a high-pressure injection pump;

[0037] [Fig.2] is a schematic cross-sectional view that represents the high-pressure injection pump of Figure 1 in a first phase where the piston descends following a cam, which draws fuel into a compression chamber through an open intake valve;

[0038] [Fig.3] is a view similar to that of figure 2 which represents the high pressure injection pump of figure 1 in a second phase where the piston rises and the intake valve is in the open state;

[0039] [Fig. 4] is a view similar to that of Figure 2, which represents the high-pressure injection pump of Figure 1 in a third compression phase where the piston rises and compresses the fuel, transferring it to an injection rail, with the intake valve in the closed position. Detailed description of the invention

[0040] In the description that follows, identical, similar or analogous elements will be designated by the same reference numbers.

[0041] Figure 1 represents a dual-fuel internal combustion engine 10 comprising at least one cylinder 12 and comprising a first injection device 14 for injecting a fuel of a first type, for example gasoline, into the cylinder 12, according to a first operating mode M1. The engine 10 also comprises a second injection device 16 for injecting a fuel of a second type, for example liquefied petroleum gas (LPG), into the cylinder 12, according to a second operating mode M2.

[0042] The first operating mode M1 of the engine 10 corresponds to the first type of fuel injection using the first injection device 14. The second operating mode M2 ​​of the engine 10 corresponds to the second type of fuel injection using the second injection device 16.

[0043] The first and second operating modes M1, M2 of the engine 10 are mutually exclusive, so that in the second operating mode M2, the first injection device 14, which is used only in the first operating mode M1, is not used.

[0044] The engine 10 is also equipped with a high-pressure pump 18 configured to supply at least one injection rail 20 with high-pressure fuel of the first type.

[0045] Here, a high-pressure pump 18 is defined as a pump that can be used to inject fuel such as gasoline and is capable of delivering fuel pressure at a specific setpoint. Depending on the type of pump and the requirements, such a high-pressure pump can be designed to deliver a pressure of a few tens of bars, for example 50 bar, or a few hundred bars, for example 200 or 300 bar.

[0046] The motor 10 is equipped with an electronic motor control unit 22 which is configured to control the motor 10 at a predetermined operating speed according to a power setpoint. The power setpoint can be provided by an engine map or by the pressure of a user on an accelerator pedal.

[0047] The electronic motor control unit 22 includes, for example, a printed circuit board equipped with at least one microprocessor, or computer, and auxiliary components such as memory elements for data storage.

[0048] According to the embodiment shown here in figures 2 to 4, the high-pressure pump 18 is controlled by a camshaft 24 driven in rotation by the motor 10. The high-pressure pump 18 is equipped with a piston 26 which is mounted to slide in a bore 28 so as to be able to draw fuel of the first type into a compression chamber 30 and to be able to compress this fuel of the first type to send it to the injection rail 20 through an outlet valve 32.

[0049] The camshaft 24 carries a cam 34 whose profile is adapted to control the axial displacement of the piston 26 according to a specific kinematic, depending on the angle of rotation of the engine 10.

[0050] The piston 26 is here equipped with a return spring 36 which forces the piston 26 towards the cam 34.

[0051] The intake of the first type of fuel into the compression chamber 30 is controlled by an intake valve 38. The opening of the intake valve 38 is determined by the engine control unit 22 as a function of the angular position of the cam 34, which is a function of the angular position of the engine 10, i.e. the angular position of the transmission shaft (not shown) of the engine 10.

[0052] The method for controlling the motor 10 according to the invention is now described. The method according to the invention is advantageously implemented directly by the motor control unit 22. Alternatively, it is implemented by an auxiliary computer configured to provide a power command to the motor control unit 22.

[0053] During a determination step called step a), the engine control unit 22 determines the resistive torque Cr applied by the high-pressure pump 18 on the engine 10 when the engine 10 is operating in the second operating mode M2, i.e. when the engine 10 is supplied with fuel of the second type by the second injection device 16.

[0054] Indeed, when the engine 10 operates in the second operating mode M2, the piston 26 of the high-pressure pump 18 continues to slide in the bore 28 and must overcome the return force of the return spring 36, while displacing the fuel contained in the compression chamber 30, the intake valve 38 being in the open state, as illustrated by figures 2 and 3.

[0055] During step a), the resistive torque Cr is calculated as a function of: - the volume of fuel compressed by the high-pressure pump 18 in the compression chamber 30, and

[0056] - the force produced by the return spring 36, which is a function of the angular position of the cam 34.

[0057] Note that the calculation of the resistive torque Cr also takes into account the position of the piston 26 and the angular position of the engine 10 at the time of the closing of the intake valve 38.

[0058] Advantageously, the engine control unit 22 of the engine 10 determines the closing time of the intake valve 38 as a function of the profile of the cam 34 and its angular position.

[0059] The control process may include a step of measuring the instantaneous pressure Pri in the injection rail 20, followed by a step of comparing the instantaneous pressure Pri in the injection rail 20 with a pressure setpoint Pre.

[0060] When the instantaneous pressure Pri in the injection rail 20 falls below a threshold value Prs, below the pressure setpoint Pre, the engine control unit 22 determines the appropriate engine angle to trigger the closure of the intake valve 38. This allows the pressure to rise in the compression chamber 30 by means of the piston 26, and then transfers the pressurized fuel to the injection rail 20, as illustrated by Figure 4.

[0061] During an adjustment step called step b), the motor control unit 22 adjusts the value of the power setpoint transmitted to the motor according to the resistive torque Cr determined in step a). For example, the motor control unit 22 increases the power setpoint by a certain percentage in order to compensate for the resistive torque Cr proportionally.

[0062] Thus, the present invention proposes to transmit the information of torque loss induced by the resistive force applied by the piston 26 and the fuel on the camshaft 24.

[0063] As explained previously, this loss of torque is a function of the angular position of the cam 34 at the time of the closing of the intake valve 38.

[0064] The resistive force associated with fuel compression in the compression chamber 30 is directly dependent on the volume of fuel compressed by the piston 26 during its sliding motion. This volume depends on the angular position of the cam 34 at the moment the intake valve 38 closes.

[0065] It is noted that the engine control unit 22 can determine the axial position of the piston 26 as a function of the angular position of the cam 34 which is a function of the angular position of the camshaft 24.

[0066] The control method according to the invention may provide for delaying the closing of the intake valve 38 so as to ensure that the corresponding torque loss has been calculated, and then synchronizing the application of closing the intake valve 38 with the compensation of the torque loss by an appropriate adjustment of the engine control by the engine control unit 22.

[0067] In the case of the delay mentioned above, the engine control unit 22 can also correct the intake valve closing command 38 according to the expected time of application of the closing command and an expected evolution of the pressure in the injection rail 20.

[0068] It is also possible to provide a maximum threshold for the intake valve closing setpoint 38 to limit the compensation applied by the engine control unit 22.

[0069] The invention therefore allows, when the instantaneous pressure Pri in the rail 20 is below the threshold Prs, the following operations to be triggered: - calculation of a closing setpoint for the intake valve 38 as a function of the angular position of the camshaft 24,

[0070] - calculation of the torque loss or resistive torque Cr linked to the activation of the high pressure pump 18 by closing the intake valve 38, - sending the torque loss data to the engine control unit 22, - synchronization between the activation of the high pressure pump 18 and the compensation of the torque loss.

[0071] LEGEND

[0072] 10: engine

[0073] 12: cylinder

[0074] 14: First injection device

[0075] 16: Second injection device

[0076] 18: High-pressure pump

[0077] 20: injection rail

[0078] 22: Motor control unit

[0079] 24: camshaft

[0080] 26: piston

[0081] 28: bore

[0082] 30: Compression chamber

[0083] 32: outlet valve

[0084] 34: came

[0085] 36: return spring

[0086] 38: intake valve

[0087] Cr: resistive couple

[0088] M1: First operating mode

[0089] M2: Second operating mode

[0090] Pre: pressure setpoint in the injection rail

[0091] Pri: instantaneous pressure in the injection rail

[0092] Prs: pressure threshold in the injection rail

Claims

DEMANDS 1. Method for controlling a dual-fuel internal combustion engine (10) comprising: - a first injection device (14) intended to inject a fuel of a first type into the engine (10) according to a first operating mode (M1), - a second injection device (16) intended to inject a second type of fuel, distinct from the first type, into the engine (10) according to a second operating mode (M2), - at least one high-pressure pump (18) configured to supply at least one injection rail (20) with high-pressure fuel of the first type, - a motor control unit (22) which controls the motor (10) at a predetermined operating speed according to a power setpoint, The process involves the following steps: a) determination of the resistive torque (Cr) applied by the high-pressure pump (18) on the motor when the motor (10) operates in the second operating mode (M2), b) when the engine 10 is supplied with fuel of the second type by the second injection device 16, adjustment of the power setpoint used by the engine control unit (22) to control the engine (10), according to the resistive torque (Cr) determined in step a), and in such a way as to compensate for the loss of torque related to the resistive torque (Cr).

2. Control method according to the preceding claim, characterized in that, during step a), the resistive torque (Cr) is calculated at least as a function of the volume of fuel compressed by the high-pressure pump (18).

3. A control method according to any one of the preceding claims, the high-pressure pump (18) being controlled by a camshaft (24) driven in rotation by the motor (10), the cam (34) cooperating with a piston (26) suitable for compressing the fuel of the first type in a compression chamber (30), the piston (26) being equipped with a return spring (36) which forces the piston (26) towards the cam (34), characterized in that, during step a), the resistive torque (Cr) is calculated as a function of the force produced by the return spring (36) and as a function of the angular position of the cam (34).

4. Control method according to the preceding claim, in which the high-pressure pump (18) includes an inlet valve (38) which controls the flow of fuel to the compression chamber (30), characterized in that, during step a), the resistive torque (Cr) is calculated as a function of the position of the piston (26) and as a function of the angular position of the engine (10) at the time of the closure of the inlet valve (38).

5. Control method according to the preceding claim, characterized in that the closing moment of the intake valve (38) is determined as a function of the profile of the cam (34).

6. Control method according to the preceding claim, characterized in that it comprises a synchronization step between the activation of the high-pressure pump (18) and the compensation of the torque loss during which the triggering time of step b) is determined with an angular offset, relative to the time expected for the closure of the inlet valve (38), so as to transmit the torque loss compensation command before the closure of the inlet valve (38).

7. A control method according to any one of claims 4 to 6, the method further comprising the following steps: - measurement of the instantaneous pressure (Pri) in the injection rail (20), - comparison of the instantaneous pressure (Pri) in the injection rail (20) with a pressure setpoint (Pre), - determination of an engine angle setpoint for triggering the closure of the intake valve (38), when the pressure (Pri) in the injection rail (20) moves away from the pressure setpoint (Pre), the engine angle setpoint being intended to restore the pressure (Pri) in the injection rail (20) to a value corresponding to the pressure setpoint (Pre).

8. Dual-fuel internal combustion engine (10) comprising: - a first injection device (14) intended to inject a fuel of a first type into the engine (10) according to a first operating mode (M1), - a second injection device (16) designed to inject a second type of fuel into the engine (10) according to a second operating mode (M2), - at least one high-pressure pump (18) configured to supply at least one injection rail (20) with high-pressure fuel of the first type, - a motor control unit (22) which is configured to control the motor (10) at a determined operating speed according to a power setpoint, to determine the resistive torque (Cr) applied by the high-pressure pump (18) on the motor (10) when the motor (10) is operating in the second operating mode (M2), and to adjust the power setpoint according to the resistive torque (Cr) determined previously.

9. Engine (10) according to the preceding claim, characterized in that the high-pressure pump (18) is controlled by a camshaft (24) driven in rotation by the engine (10), the cam (34) cooperating with a piston (26) capable of compressing the fuel of the first type in a compression chamber (30), the piston (26) being equipped with a return spring (36) which forces the piston (26) towards the cam (34).

10. Engine (10) according to the preceding claim, characterized in that the high-pressure pump (18) comprises an intake valve (38) which controls the flow of fuel to the compression chamber (30), the opening of said intake valve (38) being dependent on the angular position of the cam (34).

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