GB2490942A

GB2490942A - Controlling an electrically driven compressor

Info

Publication number: GB2490942A
Application number: GB1108407.6A
Authority: GB
Inventors: Tommaso De Fazio; Cesare Maria Meano; Edmondo Lanzillotta
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2011-05-19
Filing date: 2011-05-19
Publication date: 2012-11-21
Also published as: GB201108407D0

Abstract

A method for controlling an electrically driven compressor 1 installed in the intake line of an internal combustion engine 110, where the method comprises selecting an intake line pressure set point value on the basis of the engine operating point from a map of preset values stored in the ECU, comparing the set point value with a measured intake line pressure value to determine an intake line pressure error value, deriving a rotation speed set point value of the compressor based on the intake line pressure error value and bringing the rotation speed of the compressor to the rotation speed set point value. Preferably the rotation speed set point value can be multiplied by a degrading factor to produce a rotation speed corrected value. The intake pressure may be measured by at least one sensor. A computer program is also claimed.

Description

A method to control an electrically driven compressor installed in the intake line of an internal combustion engine

Technical field

The present invention relates to method for controlling an electrically driven compressor installed in the intake line of an internal combustion engine.

In particular, the invention relates to a method for controlling the rotation speed of the additional electrically driven compressor on the basis of the intake line pressure.

Bac Jçg round Turbocharged engines are subjected to the problem commonly known as "turbo lag", i.e. the time required to bring the turbocharger up to a speed where it can function effectively.

This is noticed, for example, by the driver as a hesitation in the response to a quick action on the acceleration pedal, caused by the time taken for the exhaust system driving the turbine to come to high pressure and for the turbine rotor to overcome its rotational inertia and reach the rotation speed necessary to supply the required boost pressure.

The effects of the turbo lag are particularly evident in the case of small turbocharged engines installed on heavy vehicles: it results in negative effects on drivability, driver feelings, and also limits to the possibility of engine downsizing.

Lag can be reduced by lowering the rotational inertia of the turbine, for example by using lighter parts to allow the spool-up to happen more quickly. Another technique in the turbine design is the use of variable-geometry architectures.

A recent proposed solution to the above reported problems of the turbocharged engines, known as electrical boosting, provides an high speed electrical motor driving an additional compressor installed on the intake line in order to speed and create a step-like boost before the energy of the exhaust gases become big enough to allow the turbine rotor to reach the speed necessary to supply boost pressure.

In view of the above, there is the need to control the electric motor provided to drive the additional compressor, which is commonly known as "E-compressor" and, in particular, to perform an accurate and efficient management of the latter in order to allow the turbine to supply the required boost pressure.

Therefore, it is an object of an embodiment of the present invention to provide a method for controlling the electrically driven compressor in order to allow the reduction of the turbo lag effects which negatively affects the drivability and the customer feelings during the vehicle use, and at the same time providing the electrically driven additional compressor with the best rotation speed instant by instant in order to achieve the desired boost pressure with minimal response time.

Moreover, it as another object of an embodiment of the present invention to provide a method for controlling the electrically driven compressor which guarantees its safety operation, for example protection against over-speed, and by allowing the E-compressor deactivation in case of faults or other engine and vehicle problems.

Summary

These objects are achieved by a method for controlling an electrically driven compressor installed in the intake line of an internal combustion engine according to claim 1.

Further aspects of an embodiment of the present invention are set out in the dependent claims.

The method comprises the steps of; a) selecting an intake line pressure set point value on the basis of the engine operating point from a map of preset values stored in the ECU; b) comparing the intake line pressure set point value provided in step a) with a measured intake line pressure value for deriving an intake line pressure error value; c) deriving a rotation speed set point value of the electrically driven compressor on the basis of the intake line pressure error value; d) bringing the rotation speed of the electrically driven compressor to the rotation speed set point value.

Advantageously the control method acts on the rotation speed of the electrically driven compressor, which is correlated to its boost capability, thus allowing an efficient and fine control of the E-cornpressor in order to reach the required pressure set point value in the intake line.

The control strategy activates the E-compressor by providing a rotation speed set point value which is a function of the pressure error value between the desired intake line pressure value (set point value), on the basis of the engine operating point from a map of preset values stored in the engine control unit (ECU), and the intake line pressure measured value.

Thus, it is possible to reach the best rotation speed value instant by instant for achieving the intake line pressure set point value, which is the desired intake line pressure value for the current operating point of the engine, with minimal response time.

According to an aspect of an embodiment of the present invention the rotation speed set point value of the electrically driven compressor is derived on the basis of said intake line pressure error value by means of a one-dimensional map of values of said pressure error value and the rotation speed of the E-compressor.

More in detail, the claimed control method allows a step-like activation of the E-compressor when the driver requires power through accelerator pedal, and a smooth deactivation of the E-compressor when the measured intake line pressure value is approaching the desired value.

According to an aspect of an embodiment of the present invention, the method further comprises the step of carrying out a correction of the rotation speed set point value of the electrically driven compressor provided in above mentioned step c) by a degrading factor in order to derive a rotation speed corrected value of the electrically driven compressor.

Preferably, the degrading factor is multiplied to the rotation speed set point value of the electrically driven compressor in order to derive the rotation speed corrected value, and the value the degrading factor is comprised in the range 0 -1.

It has to be noted that the control strategy based on the pressure error value allows to perform an efficient control of the additional compressor CE-compressor) with the management of the boost pressure during transient condition of the engine operation without exceeding engine mechanical limits, and in particular boost and torque limits.

Moreover, the degrading factor which is multiplied to the rotation speed set point value of the electrically driven compressor, which is the output variable of thee claimed control method, allows to take into account functional conditions of the E-compressor and/or of the engine and/or of the vehicle, and possible failures or malfunctions.

It has to be noted that the method according to an aspect of the present invention allows the control of the additional compressor without requiring extra sensors to be installed on the vehicle or on the engine.

Other advantages of the claimed method are improved vehicle drivability and the possibility to enable the combustion engine downsizing.

Another aspect of an embodiment of the invention provides a computer program comprising computer executable codes for carrying out the method for controlling the additional compressor, described above. The computer program, stored in a computer readable medium includes: a computer executable code for selecting an intake line pressure set point value, a computer executable code comparing said intake line pressure set point value with a measured intake line pressure value for deriving an intake line pressure error value, a computer executable code deriving a rotation speed set point value of said electrically driven compressor on the basis of said intake line pressure error value, a computer executable code to bring the rotation speed of the electrically driven compressor to the rotation speed set point value.

Brief Description of the Drawings

Further advantages and features of an embodiment of the present invention will be more apparent from the

description below, provided with reference to the

accompanying drawings, purely by way of a non-limiting

example, wherein:

* Figure 1 is a schematic flow chart of method for controlling an electrically driven compressor installed in the intake line of an internal combustion engine; * Figures 2 and 3 show possible embodiments of an automotive system; * Figure 4 is a simplified diagram of an automotive system including an internal combustion engine and an electrically driven compressor wherein is used the

method according to the present disclosure.

Detailed Description

Figure 1 shows a simplified flow chart of the method for controlling an electrically driven compressor 1, commonly known as "E-compressor", installed in the intake line 205 of an internal combustion engine 110 is based on the comparison of an intake line pressure set point value Eintake39, selected on the basis of the engine operating point from a map of preset values stored in the ECU, with a measured intake line pressure value PintakeMEAS in order to derive a error vale, i.e. an intake line pressure error value PintakeERR.

Figures 2 and 3 show some embodiments of an automotive system 100 on which the electrically driven compressor 1 could be installed, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to rotate a crankshaft 145. A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150. A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received a fuel source 190. Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145.

The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200. An air intake duct, or intake line, 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, is provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. The exhaust gases exit the turbine 250 and are directed into an exhaust system 270. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust system 270 may include an exhaust pipe, or exhaust line, 275 having one or more exhaust aftertreatment devices 280. The aftertreatment devices may be any device configured to change the composition of the exhaust gases.

Some examples of aftertreatment devices 280 include, but are not limited to, catalytic converters (two and three way), oxidation catalysts, lean NOx traps, hydrocarbon adsorbers, selective catalytic reduction (SCR) systems, and particulate filters. Other embodiments may include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, exhaust pressure and temperature sensors 430, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system, and send and receive signals to/from the interface bus. The memory system may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

In Figure 4 is shown a simplified scheme of an automotive system provided with an internal combustion engine 110 with a turbocharger 230 and an additional electrically driven compressor 1, commonly known as E-compressor, connected to a suitable power source (not shown in the figure).

Although the E-compressor 1 is installed up-stream with respect to the turbocharger 230 along the air intake line 205, other configurations could be used. According to a possible embodiment, as shown in figure 4, the E-compressor is placed on a by-pass of the intake line 205, thus it is possible to by-pass it for example in case of faults when the E-compressor is switched off, as described above, or when the intake line pressure reaches the desired value and the turbocharger 230 can function effectively. For this purpose a valve 6, or similar means are installed on the intake line 205 for excluding or allowing the intake flow to pass inside the E-compressor 1.

As already mentioned above in connection to figures 2 and 3, it has to be noted that other systems could installed in the intake line 205 and in the exhaust line 275 of the engine 110, such as Diesel Particulate Filter (DPF) Intercooler, etc., and the present method can be applied to control electrically driven compressor installed on the intake line of an internal combustion engine with other configurations different from that shown in the non-limiting example embodiments of figures 2, 3 and 4.

As already mentioned above, according to the claimed method, the control of the electrically driven compressor 1 installed in the intake line 205 of an internal combustion engine 110 is based on the comparison of an intake line pressure set point value Pintake9 with an intake line pressure value PintakeNEAS, measured e.g. by sensor 350, in order to derive an error value, i.e. an intake line pressure error value PintakeERR.

The intake pressure set point value Pintake is the desired pressure amount into the intake line for the current engine operating point.

It has to be noted that the pressure in the intake line is measured, according to a preferred aspect of an embodiment of the present invention, by means of a sensor, or sensors, already installed on the engine. On the basis of the intake line pressure error value PintakeERR the present control method provides a rotation speed value N5 of the electrically driven compressor.

The rotation speed of the electrically driven compressor is brought to the rotation speed set point value N3, derived as disclosed above.

The rotation speed of the E-compressor is correlated to the pressure boost generated, in other words, the boost pressure capability is a function of the E-compressor rotation speed.

Thus, on the basis of the pressure error value PintakeERR, it is possible to reach the best rotation speed value instant by instant for achieving the intake line pressure set point value Pintake, which is the desired intake line pressure value for the current operating point of the engine, with minimal response time.

In other words, the boost capability of the electrically driven compressor is a functidn of its rotation speed, and the present control method by acting on this output variable allows to reach the desired pressure value in the intake line, i.e. said intake line pressure set point value Pintake, with minimal response time.

It is clear that the measured intake line pressure value PintakeMEAS is the feedback variable of the present control method.

According an aspect of an embodiment of the present invention, the rotation speed set point value Np is derived on the basis of the intake line pressure error value PintakeERR by using a one-dimensional map l-D map of values.

In fact, as already mentioned above, for a certain electrically driven compressor the pressure boost that can be exerted is a function of its rotation speed, thus, by means of a map describing said function, it is possible to derive a speed set point value N5 on the -basis of the intake line pressure error value PintakeERR.

Although in the above described embodiment of the present method, a one-dimensional map of values is used in order to derive the rotation speed set point value Nsp on the basis of the intake line pressure error PintakeERR, obviously other predetermined correlation sets of values between the rotation speed and the pressure boost capability of the E-compressor could be used for this purpose.

The present control method allows a step-like activation of the E-compressor when the driver requires power through the accelerator pedal, in this way, the control strategy leads to a maximum effect of the E-compressor after a request of power by the driver trough the accelerator pedal, in fact, in these operating points the desired pressure value Pintake5 and the measured (current) pressure value PintakeMEAS in the intake line are really different and the pressure error value PintakeERR is significant.

On the other hand, when the measured pressure value PintakeMEAS is approaching the desired pressure value Pintake5, the present control methods allows a smooth deactivation of the E-compressor.

The control strategy of the additional compressor (E-compressor) based on the pressure error value allows control of the boost pressure during transient condition of the engine operations without exceeding engine mechanical limits, and in particular boost and torque limits.

According to an aspect of an embodiment of the control method, the rotation speed set point value Nsp, which is the output variable of the method, is corrected by means of a degrading factor F, which is multiplied to the set point rotation speed value Nsp, for deriving a rotation speed corrected value Ncogg of the electrically driven compressor.

It has to be noted that the degrading factor F is used mainly, but not exclusively for safety reasons, and is intended to take into account functional conditions of the engine, of the vehicle and of their systems, and also possible failures or malfunctions.

For these reasons, the value of the degrading factor F could be obtained by a combination of different contributions, for example relating to different protection or diagnosis functions. It is clear that more than one degrading factor F could be used, even independently of each other.

Preferably, the value of the degrading factor F is comprised in the range 0 -1, and the present control method comprises a further step of selecting the value of the degrading factor F in the range 0 -1, on the basis of at least mechanical and/or electric status of the electrically driven compressor and/or of said internal combustion engine.

For example a degrading factor whose value is comprised in the range of 0 and 1, is used for taking into account mechanical and/or electric diagnosis of the electrically drive compressor and/or of the engine, vehicle systems, etc. This means that if some faults happen, the degrading factor is set to zero to switch off the E-compressor, and if no faults are present the value is equal to 1.

Furthermore, in the case of electrical power supply issue, e.g. an insufficient battery state of charge, the degrading factor is set to a value lower than 1, the worst case is 0.

Obviously, other protection functions can be developed which could result in a degrading factor value selected from the range 0 -1.

The method for controlling the electrically driven compressor described above, may be carried out by means of a computer program comprising program codes (computer executable codes) for performing the controlling steps already described above.

The computer program comprises computer executable codes that can be stored on the ECU, or on a computer readable medium, or a storage unit, such as CD, DVD, flash memory, hard-disk, or the like.

The computer program comprises computer executable code for selecting an intake line pressure set point value Pintake9, a computer executable code for comparing the intake line pressure set point value Pintake with a measured intake line pressure value PintakeMEAs for deriving an intake line pressure error value PintakeERR and a computer executable code for deriving a rotation speed set point value N52 of the electrically driven compressor on the basis of the intake line pressure error value PintakeERfl.

Starting from the measured intake line pressure value PintakeHE3, the ECU compares the latter with a set point pressure value Pintake52, and by further comparing said measured and set point (desired) pressure values it derives an intake line pressure error value PintakeERR. The ECU 450 further derives a rotation speed set point value N52 of the electrically driven compressor 1 on the basis of the intake line pressure error value PintakeERR. Preferably, a one-dimensional map l-D map of values is used for deriving the rotation speed set point value N52 of on the basis of the intake line pressure error value PintakeERfl. As already mentioned above, according to an aspect of an embodiment of the present control method, the derived rotation speed set point value N52 is corrected by means of a degrading factor F, which is multiplied to it, in order to derive a rotation speed corrected value NCORR of the electrically driven compressor.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

Claims

CLAIMS1. A method for controlling an electrically driven compressor (1) installed in the intake line (205) of an internal combustion engine (110) comprising the steps of: a) selecting an intake line pressure set point value (Pintake5p) on the basis of the engine operating point from a map of preset values stored in the engine control unit ECU; b) comparing said intake line pressure set point value (Pintake5p) provided in step a) with a measured intake line pressure value (PintakeMEAS) for deriving an intake line pressure error value (PintakeERR); c) deriving a rotation speed set point value (N3) of said electrically driven compressor on the basis of said intake line pressure error value (PintakeERR); d) bringing the rotation speed of said electrically driven compressor (1) to said rotation speed set point value (N52).
2. The method according to claim 1, further comprising the step of correcting said rotation speed set point value (N52) of said electrically driven compressor provided in step c) by a degrading factor (F), which is multiplied to said rotation speed set point value (N52), in order to derive a rotation speed corrected value (NCORR) of said electrically driven compressor and bring the rotation speed of said electrically driven compressor (1) to said rotation speed corrected value (NCORR)
3. The method according to claim 2, wherein the value of said degrading factor (F) is comprised in the range 0 -1.
4. The method according to claim 3, further comprise the step of selecting the value of said degrading factor (F) in said range 0 -1, on the basis of at least the mechanical and/or electric status of said electrically driven compressor and/or of said internal combustion engine.
5. The method according to claim 1, wherein said rotation speed set point value (Nap) of said electrically driven compressor is derived on the basis of said intake line pressure error value (PintakeERR) by using a one-dimensional map (l-D map) of values.
6. The method according to claim 1, wherein said intake line pressure value (PintakeMEAs) is measured by at least one sensor (350)
7. A computer program comprising computer executable codes for controlling an electrically driven compressor (1) installed in the intake line (205) of an internal combustion engine (110), said computer program being stored on computer-readable medium or a suitable storage unit and comprises: A) a computer executable code for selecting an intake line pressure set point value (Pintake52) on the basis of the engine operating point from a map of preset values stored in the engine control unit ECU; B) a computer executable code for comparing said intake line pressure set point value (Pintake5p) provided in step A) with a measured intake line pressure value (PintakeMEAS) for deriving an intake line pressure error value (PintakeERR); C) a computer executable code for deriving a rotation speed set point value (Nsp) of said electrically driven compressor on the basis of said intake line pressure error value (PintakeERR); D) a computer executable code to bring the rotation speed of said electrically driven compressor (I) to said rotation speed set point value (Ns).
8. A computer program according to claim 7, further comprising computer executable code for executing further steps of the method according to claims I to 6.
9. A computer readable medium storing a computer program according to previous claim 7 or 8.
10. An electronic control unit (ECU) for an internal combustion engine (110) provided with an electrically driven compressor (1) installed in the intake line (205) of said internal combustion engine comprising a digital central processing unit (CPU) and a storage memory for storing a computer program according to previous claims 7 or 8 comprising computer executable codes for controlling said electrically driven compressor, said digital central processing unit (CPU) being able to receive and to execute said computer executable codes of said computer program.