METHOD OF AND APPARATUS FOR OPERATING A SUPERCHARGER

Abstract

A method of and apparatus for operating a supercharger for an automotive engine is disclosed. The supercharger has: an input shaft for coupling to an engine crankshaft, and coupled to the rotor of a first electrical machine and a first component of an epicyclic gear train; and an output shaft connected to a compressor and a second component of the epicyclic gear train; wherein the third component of the epicyclic gear train is connected to the rotor of a second electrical machine. The first electrical machine is selectively operable to supply electrical energy to the second electrical machine. The method includes the steps of: (a) calculating a required speed of the second electrical machine that would give rise to a required pressure at an outlet of the compressor; and (b) setting the speed of the second electrical machine to the calculated required speed.

Claims

1. A method of operating a supercharger for an automotive engine, the supercharger having: an input shaft for coupling to an engine crankshaft, and coupled to a rotor of a first electrical machine and a first component of an epicyclic gear train; and an output shaft connected to a compressor and a second component of the epicyclic gear train; wherein a third component of the epicyclic gear train is connected to a rotor of a second electrical machine, wherein the first electrical machine is selectively operable to supply electrical energy to the second electrical machine, and wherein the method includes the steps of: (a) calculating, using a controller, a required rotor speed of the second electrical machine that would give rise to a given target engine inlet pressure using a model-based approach; and (b) setting, using the controller, the rotor speed of the second electrical machine to the calculated required rotor speed.

2. A method according to claim 1, wherein step (a) includes sensing the supercharger input shaft speed, the pressure and temperature at an inlet of a compressor of the supercharger supercharger, or the airflow at that inlet.

3. A method according to claim 2, wherein step (a) further includes calculating the required speed of the electrical machine from at least these sensed values, from a characteristic ratio of the epicyclic gear train, and from the required pressure at the outlet of the compressor.

4. A method of operating a supercharger for an automotive engine, the supercharger having: an input shaft for coupling to an engine crankshaft, and coupled to a rotor of a first electrical machine and a first component of an epicyclic gear train; and an output shaft connected to a compressor and a second component of the epicyclic gear train; wherein a third component of the epicyclic gear train is connected to a rotor of a second electrical machine, wherein the first electrical machine is selectively operable to supply electrical energy to the second electrical machine, wherein the supercharger is provided in series with a turbocharger, and wherein the method includes the steps of: (a) calculating, using a controller, a required rotor speed of the second electrical machine that would give rise to a given target engine inlet pressure using a model-based approach; and (b) setting, using the controller, the rotor speed of the second electrical machine to the calculated required rotor speed.

5. A method according to claim 4, wherein step (a) includes sensing the supercharger input shaft speed, the pressure and temperature at an inlet of a compressor of the supercharger supercharger , or the airflow at that inlet.

6. A method according to claim 5, wherein step (a) further includes calculating the required speed of the electrical machine from at least these sensed values, from a characteristic ratio of the epicyclic gear train, and from the required pressure at the outlet of the compressor.

7. An apparatus for operating a supercharger for an automotive engine, the supercharger having: an input shaft for coupling to an engine crankshaft, and coupled to a rotor of a first electrical machine and a first component of an epicyclic gear train; and an output shaft connected to a compressor and a second component of the epicyclic gear train; wherein a third component of the epicyclic gear train is connected to a rotor of a second electrical machine, wherein the first electrical machine is selectively operable to supply electrical energy to the second electrical machine, and wherein said apparatus comprises a control system configured to: (a) calculate a required rotor speed of the second electrical machine that would give rise to a given target engine inlet pressure using a model-based approach; and (b) set the rotor speed of the second electrical machine to the calculated required rotor speed.

8. An apparatus according to claim 7 and including processing means operable to execute computer-readable instructions such that the apparatus carries out the steps of: sensing the supercharger input shaft speed, the pressure and temperature at the supercharger compressor inlet, and the airflow at that inlet; and calculating the required speed of the electrical machine from at least these sensed values, from a characteristic ratio of the epicyclic gear train, and from the required pressure at the outlet of the compressor.

9. An apparatus for operating a supercharger for an automotive engine, the supercharger having: an input shaft for coupling to an engine crankshaft, and coupled to a rotor of a first electrical machine and a first component of an epicyclic gear train; and an output shaft connected to a compressor and a second component of the epicyclic gear train; wherein a third component of the epicyclic gear train is connected to a rotor of a second electrical machine, wherein the first electrical machine is selectively operable to supply electrical energy to the second electrical machine, wherein the supercharger is provided in series with a turbocharger, and wherein the apparatus comprises a control system configured to: (a) calculate a required rotor speed of the second electrical machine that would give rise to a given target engine inlet pressure using a model-based approach; and (b) set the rotor speed of the second electrical machine to the calculated required rotor speed.

10. An apparatus according to claim 9 and including processing means operable to execute computer-readable instructions such that the apparatus carries out the steps of: sensing the supercharger input shaft speed, the pressure and temperature at the supercharger compressor inlet, and the airflow at that inlet; and calculating the required speed of the electrical machine from at least these sensed values, from a characteristic ratio of the epicyclic gear train, and from the required pressure at the outlet of the compressor.

11. A record carrier having recorded thereon or therein a record of computer-readable instructions executable by the a processing means to cause a control system of an apparatus for operating a supercharger to carry out the steps of: sensing supercharger input shaft speed, pressure and temperature at a supercharger compressor input, and airflow at that input; and calculating a required rotor speed of an electrical machine from at least these sensed values using a model-based approach for controlling a target pressure downstream of a compressor of the turbocharger, from a characteristic ratio of an epicyclic gear train, and from a target engine inlet pressure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0033] FIG. 1 shows a first arrangement of a supercharger and a turbocharger;

[0034] FIG. 2 shows a second arrangement of a supercharger and a turbocharger; and

[0035] FIG. 3 shows an embodiment of a system in which a supercharger is connected in series upstream of a turbocharger, in accordance with an embodiment of the present invention. A controller is used to calculate a required speed of a second electrical machine using a model-based approach for controlling a target pressure downstream of a compressor of the turbocharger that would give rise to a required pressure at an outlet of the compressor downstream of the supercharger and turbocharger. The controller is used to set the speed of the second electrical machine to the calculated required speed.

SPECIFIC DESCRIPTION OF CERTAIN EXEMPLARY EMBODIMENTS

[0036] Specific examples in which the present invention is embodied will now be described in detail. The skilled addressee will understand that information contained hereinabove may be used in combination with that which follows in order to understand embodiments of the invention.

[0037] Embodiments of the present invention may be used to operate a supercharger of the type described hereinabove and in WO-A1-2004/072449. In certain embodiments, the supercharger may be operated without an accompanying turbocharger in series with it.

[0038] In other embodiments, the supercharger may be employed in an arrangement such as that shown in FIG. 1 and FIG. 2.

[0039] The following is a description of operation of the supercharger in an arrangement such as that shown in FIG. 1 and FIG. 2.

[0040] The way the proposed method controls the supercharger can be split into three steps.

[0041] Firstly, the required pressure at point 3 (hereinafter P3) is determined from a number of inputs and a first control algorithm. Existing engine management systems for automotive engines often already have a means of determining this pressure. Look-up tables, for example, are often used. This pressure will be referred to as the target P3 in this specific description.

[0042] Secondly, the target P3 is combined with a number of other inputs and a second control algorithm to produce a target speed for the second electrical machine.

[0043] In the third step, a speed controller (which may be of a known type) is used to achieve the target speed.

[0044] In the case of the configuration illustrated in FIG. 1, the control of the turbocharger(s) can be by known means based on achieving a target pressure P2.

[0045] In the case of the configuration illustrated in FIG. 2, the control of the turbocharger(s) can be based on conventional means to achieve a target pressure difference or ratio (P3P2 or P3/P2).

[0046] Alternatively, the turbocharger(s) in either configuration can be controlled by known means based on achieving a target speed.

[0047] The first control algorithm may include all or some of the following inputs. Some of these inputs may be measured and others may be inferred from the measured inputs as is common practice in engine control systems.

[0048] Inputs for first control algorithm may include one, more or all of: [0049] Pressure at position 1 [0050] Pressure at position 2 [0051] Temperature at position 1 [0052] Temperature at position 2 [0053] Torque demand [0054] Driver demand [0055] Engine speed [0056] Turbocharger speed [0057] EGRdemand [0058] Valve timing (for variable valve timing system)

[0059] In a preferred embodiment, a key output is target pressure at position 3. In an alternative embodiment, a target airflow may be employed in combination with engine mapping data.

[0060] The second algorithm may include all or some of the following inputs. Some of these inputs may be measured and others may be inferred from the measured inputs as is common practice in engine control systems.

[0061] Inputs for second control algorithm may include one, more or all of: [0062] Target pressure at position 3 (preferred) or target airflow [0063] Engine speed [0064] Supercharger input shaft speed [0065] Pressure at supercharger compressor inlet [0066] Temperature at supercharger compressor inlet [0067] Airflow at supercharger compressor inlet [0068] EGRdemand

[0069] For example, from sensing the supercharger input shaft speed, and from the fundamental equation that governs epicyclic gear trains, together with a knowledge of the ratios of the epicyclic gear train, it is possible to arrive at an equation in terms of the speed of the second electrical machine and the compressor shaft speed. Furthermore, normal turbocharger mapping allows the compressor shaft speed to be derived as a function of the pressure and temperature at the supercharger compressor input, the airflow at that input, and the target P3. These two equations can be solved simultaneously to give the target speed of the second electrical machine.

[0070] This algorithm may make use of a measured or inferred value of P3 (preferred) or airflow in order to close the loop and eliminate errors due to inputs, hardware variations or algorithm inaccuracy, thus assuring P3 or airflow stabilises at the required value prescribed by the first algorithm. This correction may be achieved through an integral controller.

[0071] As mentioned above, a known speed controller may then be used to operate the second electrical machine at the target speed.

[0072] By using a model-based approach for controlling P3, rather than direct-control based on sensing P3 and providing closed-loop feedback control, a much more stable form of control of the supercharger, and hence of the engine, results.

[0073] It is noted that a simplified version of algorithms 1 and 2 can be used to control the supercharger on its own (i.e. without a turbocharger). In this case the arrangement is like that of FIG. 1, except the compressor has no effect and positions 1 and 2 are the same.

[0074] Having described the operation of the system, the skilled addressee will be familiar with the components necessary for, and appreciate how, the system can be put into practice. For example, the skilled person will understand how, and by what means, the inputs to the algorithms described above can be sensed and how, and by what means, these can be operated upon.

[0075] It is envisaged that the method be embodied in computer-readable code stored in nonvolatile memory which can be accessed by an engine management system of an automobile in which the supercharger is fitted. For example, the method may be stored as coded instructions in memory of processing means of an electronic control unit (ECU).