Method for cold-start pre-warming of a pressure-charged internal combustion engine and/or of an exhaust gas aftertreatment device

Abstract

A method for cold start pre-warming of a pressure-charged internal combustion engine and/or of an exhaust gas aftertreatment device of a internal combustion engine, includes arranging a cold-starting aid in the intake duct for warming the charge air while the engine is stationary. The internal combustion engine has at least one working cylinder with at least one inlet valve and at least one outlet valve and further includes a device for setting a valve position. The internal combustion engine can be pressure-charged by a pressure-charging device operable by an electric motor. In the method, after detection of a cold start of the internal combustion engine: the cold-starting aid is activated while the engine is stationary; electric-motor operation of the pressure-charging device is activated; and a valve overlap between at least one inlet valve and at least one outlet valve is set.

Claims

1. A method for cold-start pre-warming at least one of a pressure-charged internal combustion engine and an exhaust gas aftertreatment device of the internal combustion engine, wherein a cold-starting aid is arranged in an intake duct and warms charge air while the internal combustion engine is stationary, and wherein the internal combustion engine comprises at least one working cylinder, which in each case has at least one inlet valve, which is connected to the intake duct, and at least one outlet valve, which is connected to an exhaust system, and further comprises a setting device for setting a valve position, and a pressure-charging device operable by an electric motor; the method, comprising the steps of detecting a cold start of the internal combustion engine; and after the detecting of the cold start, activating the cold-starting aid while the engine is stationary; activating operation of the pressure-charging device using the electric motor; and setting, by the setting device, a valve overlap between at least one inlet valve and at least one outlet valve of a working cylinder to deliver at least some of the charge air delivered by the pressure-charging device and pre-warmed by the cold-starting aid directly into the exhaust system.

2. The method according to claim 1, wherein the pressure-charging device operable by the electric motor is one of an exhaust turbocharger with electric motor assistance and an electric compressor.

3. The method according to claim 1, wherein the cold-starting aid is one of a flame-starting device, a glow plug, and a glow grid.

4. The method according to claim 1, wherein the setting device for setting the valve position sets at least one predetermined angular position of the crankshaft, which produces the valve overlap and which, for this purpose, activates a starter motor of the internal combustion engine or a crankshaft starter generator.

5. The method according to claim 1, wherein the internal combustion engine includes an electromagnetic valve gear, which is activated by the setting device to set the valve overlap.

6. The method according to claim 1, wherein the internal combustion engine is equipped with at least two camshafts and at least one camshaft phase adjuster, at least one of the camshaft phase adjusters is activated in such a way as to increase the valve overlap in the step of setting.

7. The method according to claim 1, wherein in the step of setting the valve overlap, the valve overlap is in each case set in succession for the next working cylinder or cylinders to be ignited during the starting process.

8. The method according to claim 1, wherein the internal combustion engine is embodied as an in-line six-cylinder engine and, in the step of setting the valve overlap, the crankshaft is turned three times in succession, in each case by 120°, in each case to set one of two synchronized working cylinders that are the next to be ignited during the starting process to the charge-exchange top dead center position (CETDC).

9. The method according to claim 1, wherein in the step of setting the valve overlap, a slow continuous crankshaft rotation takes place while the engine is stationary.

10. The method according to claim 1, wherein the internal combustion engine operates with self-ignition.

11. The method according to claim 10, wherein the internal combustion engine is a diesel engine.

12. A motor vehicle, comprising an internal combustion engine having an intake duct, at least one working cylinder, which in each case has at least one inlet valve, which is connected to the intake duct, and at least one outlet valve, which is connected to an exhaust system; a pressure-charging device, which can be operated by electric motor, for pressure-charging the internal combustion engine; a setting device for setting an internal combustion engine having an intake take valve position of the working cylinders of the internal combustion engine; an exhaust gas aftertreatment device; a cold-starting aid, arranged in the intake duct, for warming the charge air while the engine is stationary; and a control device for cold-start pre-warming of at least one of the internal combustion engine and of the exhaust gas aftertreatment device while the engine is stationary, using the method according to claim 1.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above-described preferred embodiments and features of the invention can be combined with one another in any desired manner. Further details and advantages of the invention are described below with reference to the attached drawings, in which:

(2) FIG. 1 is a schematic block diagram of an internal combustion engine having an exhaust turbocharger with electric motor assistance;

(3) FIG. 2 is a flow diagram of the method for cold-start pre-warming according to one embodiment of the invention; and

(4) FIGS. 3A, 3B and 3C are schematic diagrams showing, by way of example, the activation of the crankshaft for the purpose of setting the valve overlap for an in-line six-cylinder engine according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) A pressure-charged diesel internal combustion engine 3 for a commercial vehicle and an associated exhaust turbocharger (ET) 10 with electric motor assistance are shown in FIG. 1 in the form of a block diagram. Here, only the components that are necessary for understanding the invention are illustrated. In particular, illustration of the exhaust gas aftertreatment device, the ignition system, the fuel circuit and the cooling circuit, which are in each case embodied in a manner known per se, have been dispensed with.

(6) The exhaust turbocharger 10 with electric motor assistance comprises a turbine 12, which is driven by the exhaust gas from the internal combustion engine 3, which is fed to the turbine via the exhaust line 19. The turbine 12 is generally connected to a compressor 11 by a shaft 13, wherein the compressor 11 compresses charge air to be fed to the internal combustion engine 3 and thus increases the power of the internal combustion engine 3.

(7) The ET 10 is embodied as an exhaust turbocharger with electric motor assistance. The special characteristic of this embodiment consists inter alia in that the electric motor drive of the nonpositive displacement compressor 11 is implemented by a small electric motor 14, which has been integrated into the compressor housing of the compressor 11. The electric motor 14 can be operated both as a motor and as a generator and, for this purpose, is controlled by a control device 15, which is furthermore connected to an electric energy storage device 16. By means of the power electronics of the control device 15, energy from the energy storage device 16 can be made available to the electric motor 14, illustrated by the solid lines 17a, or recovered energy from the operation of the ET can be fed to the energy storage device 16, illustrated by the dashed lines 17b. The exhaust turbocharger 10 is known per se from the prior art and is described on pages 50-55 of edition 3/2014 of the magazine “MTZ—Motortechnische Zeitschrift”, for example. It is emphasized that other design embodiments of an exhaust turbocharger with electric motor assistance can also be used within the scope of the invention.

(8) Via an intake duct 18a, the internal combustion engine 10 obtains the fresh air required for combustion. The fresh air is compressed beforehand in the compressor 11 and, in the illustrative embodiment under consideration, is fed via charge air line 18b to a charge air cooler 4 and then via charge air line 5 to the internal combustion engine 3. Arranged in charge air line 5 or the intake duct 18a there is furthermore a flame-starting device 6, by means of which the charge air can be heated in the case of a cold start. The fact that it is also possible to use a glow plug instead of the flame-starting device 6 has already been mentioned above.

(9) To start the internal combustion engine, a conventional starter can be provided, which, to start the internal combustion engine, engages its starter pinion in a starter gearwheel coupled for conjoint rotation to the crankshaft and drives said gearwheel. As an alternative, as illustrated in a highly schematized way in FIG. 1, an electric machine which can be operated both as a motor and as a generator, in the form of an electric crankshaft starter generator (CSG) 8, which is generally arranged coaxially with the crankshaft 7 and between the internal combustion engine 3 and the transmission (not shown), can be provided to start the internal combustion engine. In this case, the CSG 8 is in operative connection with the crankshaft 7, e.g., by the rotor of the CSG 8 being connected for conjoint rotation in the assembled state to a flywheel arranged on the crankshaft 7. The CSG 8 is furthermore used to set the valve position in the context of cold-start pre-warming, this being explained below.

(10) Also illustrated is a further control device 1, which can be embodied as part of the engine controller, for example. The control device is designed to activate the ET 10, the flame-starting device 6 and the CSG 8 (or the conventional starter) via appropriate control lines 2 as part of the method for cold-start pre-warming.

(11) FIG. 2 shows a flow diagram of the method for cold-start pre-warming according to one embodiment of the invention.

(12) Before cold-start pre-warming is carried out, the system determines whether cold starting of the vehicle is imminent. The presence of a cold-starting process can be determined by the approaches known from the prior art. Typically, a cold-starting process can be distinguished from a warm-starting process by means of the coolant temperature. If the coolant temperature falls below a predetermined threshold value when starting the internal combustion engine, for example, there is a cold start. The threshold value is determined experimentally and is stored in the storage device 1.

(13) If cold starting of the internal combustion engine 3 is detected (step S1), the following steps are carried out. In step S2, the flame-starting device 6 is activated by the control device 1. The control device 1 furthermore controls the controller 15 of the ET 10 in step S3 in order to activate electric-motor operation of the ET 10. The compressor 11 is thus driven electrically and delivers charge air to the flame-starting device 6, whereby the latter is warmed.

(14) In step S4, the inlet and outlet valves (not shown) of one or more cylinders of the internal combustion engine 3 are set to valve overlap. For this purpose, the programming of the control device 1 is designed in such a way that, in response to detection of cold starting in step S1, the rotor of the CSG 8 is energized in such a way that it moves automatically into a predetermined rotational position relative to the stator of the CSG. Here, the predetermined rotational position of the rotor corresponds to a predetermined rotational position, i.e., the angular position of the crankshaft 7 and hence of the camshaft or, in general, of the valve gear, in which at least one inlet valve and at least one outlet valve of at least one cylinder of the internal combustion engine 3 are set to valve overlap. The predetermined rotational position of the rotor is stored in a memory of the control device 1 and has been predetermined, e.g., experimentally.

(15) By means of a position encoder (not shown) which operates inductively or capacitively and is known per se, the current rotational position of the rotor relative to the stator of the CSG and hence of the crankshaft 7 have been predetermined. From practical experience, it is known, for example, that detection of the rotational position of the rotor relative to the stator can be enabled by an additional cup-shaped or pot-shaped component (not shown) which is secured for conjoint rotation on the flywheel. Applied to the component is a special geometry or marking (encoder track), which is sensed by an inductively or capacitively operating sensor of the position encoder to determine the rotational position of the encoder track and hence of the rotor. By forming the difference between the predetermined rotational position and the actual rotational position, the control device 1 calculates the required rotation of the rotor to assume the predetermined rotational position for the valve overlap.

(16) After the setting of the valve overlap, at least some of the charge air delivered by the compressor 11 driven by electric motor 14 is delivered directly into the exhaust system via an open inlet valve and an open outlet valve while the engine is stationary. Electric-motor operation of the ET 10 thus enables charge air to be delivered to the internal combustion engine and to be heated by the activated cold-starting aid 6, despite the engine being stationary and without turbine energy from the combustion air of the internal combustion engine. The setting of the valve overlap and/or of a charge-exchange position between at least one inlet valve and at least one outlet valve of a working cylinder has the effect that the heated charge air flows into the corresponding working cylinder with a valve overlap and is scavenged to the exhaust side via the outlet valve. As a result, the working cylinder, on the one hand, and the exhaust gas aftertreatment system, in particular the exhaust gas aftertreatment catalyst, on the other hand, are pre-warmed.

(17) The internal combustion engine 3 is then started in step S5.

(18) FIGS. 3A, 3B and 3C illustrate by way of example the activation of the crankshaft 7 for the purpose of setting the valve overlap for an in-line six-cylinder engine according to one embodiment of the invention. The individual cylinders 30 are denoted by the reference signs 30_1 to 30_6.

(19) According to this variant embodiment, the crankshaft (CS) 7 is turned successively three times, in each case by 120°, while the engine is stationary in step S4 for the setting of the valve overlap in order in each case to set one of two synchronized working cylinders 30 that are the next to be ignited during the starting process to the charge-exchange top dead centre position (CETDC, TDC=top dead centre).

(20) FIG. 3A shows a first rotational position 0° of the crankshaft 8, in which the pistons of cylinders 30_1 and 30_6 are in the top dead centre position (TDC), wherein the first cylinder 30_1 is in the position of ignition TDC (ITDC, between the compression stroke and the power stroke) and the sixth cylinder 30_6 is in the position of charge-exchange TDC (CETDC, between the exhaust stroke and the intake stroke).

(21) FIG. 3B shows a subsequent crankshaft position, the result of turning further by 120° by the control device through activation of the CSG 8 in step S4. Consequently, the second cylinder 30_2 is now at CETDC and the fifth cylinder is at ITDC. FIG. 3C shows a third crankshaft position, wherein the crankshaft 7 has been turned by a further 120° by the control device 1 in step S4 through activation of the CSG 8. Consequently, the third cylinder 30_3 is at ITDC and the fourth cylinder is at CETDC.

(22) In the CETDC position, the inlet valve and the outlet valve of the corresponding cylinder are in valve overlap. Consequently, cylinders 30_6, 30_2 and then 30_4 are preheated in succession. During the subsequent starting process, these are also the next cylinders 30 to be ignited, which have already been preheated, improving their ignition behaviour.

(23) The invention is not restricted to the above-described preferred illustrative embodiments. On the contrary, a multiplicity of variants and modifications is possible, which likewise make use of the inventive concept and therefore fall within the scope of protection. In particular, the invention also claims protection for the subject matter and the features of the dependent claims independently of the claims to which they refer.

LIST OF REFERENCE SIGNS

(24) 1 control device 2 control line 3 internal combustion engine 4 charge air cooler 5 charge air line 6 flame-starting device 7 crankshaft 8 crankshaft starter generator 10 exhaust turbocharger that can be operated by electric motor 11 compressor 12 turbine 13 shaft 14 electric motor 15 control of the exhaust turbocharger 15 electric energy storage device 17a, 17b lines for energy transfer 18a charge air duct 18b charge air line 19 exhaust line 30, 30_1 to 30_6 working cylinder CETDC charge-exchange TDC, TDC=top dead centre ITDC ignition TDC, TDC=top dead centre