START-UP METHOD OF AN INTERNAL COMBUSTION ENGINE WITH THE AID OF A BELT-DRIVEN STARTER GENERATOR

Abstract

A method for improving a start-up of an internal combustion engine with the aid of a belt-driven starter generator which includes a stator winding and a rotor winding, the starter generator for generating a start-up torque being operated in such a way that the stator winding and the rotor winding are energized essentially at the same time immediately after a start-up request of the starter generator. Also described is a processing unit to perform the method and a computer readable medium.

Claims

1-10. (canceled)

11. A method for improving a start-up of an internal combustion engine with a belt-driven starter generator, which includes a stator winding and a rotor winding, the method comprising: operating the starter generator for generating a start-up torque so that the stator winding and the rotor winding are energized essentially at the same time immediately after a start-up request of the starter generator.

12. The method of claim 11, wherein a setpoint torque is predefined for a torque buildup by the starter generator, and the stator winding and the rotor winding are energized so that a gradient of a torque increase monotonically increases directly after the start-up request and until a setpoint torque is reached.

13. The method of claim 11, wherein a gradient of a torque increase runs in a band having an upper limit of approximately 2,000 Nm/s and a lower limit of approximately 300 Nm/s.

14. The method of claim 12, wherein the stator winding and the rotor winding are energized so that the gradient resulting from a linear approximation of the torque increase is smaller than the upper limit of the torque increase.

15. The method of claim 11, wherein a current flowing through the stator winding is below a threshold value and a gradual increase of an excitation current through the rotor winding monotonically increases directly after a start-up request and up until reaching the setpoint torque.

16. The method of claim 11, wherein a block-commutated and/or pulse-width modulated supply voltage is applied to the stator winding for the energization.

17. The method of claim 11, wherein the torque necessary for starting up the internal combustion engine is effectuated by the belt-driven starter generator.

18. A processing unit, comprising: a non-transitory computer readable medium having a computer program, which is executable by a processor, including a program code arrangement having program code for improving a start-up of an internal combustion engine with a belt-driven starter generator, which includes a stator winding and a rotor winding, by performing the following: operating the starter generator for generating a start-up torque so that the stator winding and the rotor winding are energized essentially at the same time immediately after a start-up request of the starter generator.

19. A non-transitory computer readable medium having a computer program, which is executable by a processor, comprising: a program code arrangement having program code for improving a start-up of an internal combustion engine with a belt-driven starter generator, which includes a stator winding and a rotor winding, by performing the following: operating the starter generator for generating a start-up torque so that the stator winding and the rotor winding are energized essentially at the same time immediately after a start-up request of the starter generator.

20. The computer readable medium of claim 19, wherein a setpoint torque is predefined for a torque buildup by the starter generator, and the stator winding and the rotor winding are energized so that a gradient of a torque increase monotonically increases directly after the start-up request and until a setpoint torque is reached.

21. The method of claim 11, wherein a gradient of a torque increase runs in a band having an upper limit of approximately 1,000 Nm/s and a lower limit of approximately 330 Nm/s.

22. The method of claim 12, wherein the stator winding and the rotor winding are energized so that the gradient resulting from a linear approximation of the torque increase is smaller than the upper limit of the torque increase, the setpoint torque being reached after approximately 30 ms at the earliest.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 schematically shows a system including an internal combustion engine, a belt-driven starter generator, and a vehicle electrical system, such as the one on which the present invention may be based.

[0019] FIG. 2 shows one specific embodiment of a starter generator including a current converter and controllable switching elements, such as the one on which the present invention may be based.

[0020] FIG. 3 shows a schematic equivalent circuit diagram of a separately excited one-phase synchronous machine.

[0021] FIG. 4 shows an illustration of input and output variables effectuated by a method for switching on an electric machine according to the related art.

[0022] FIG. 5a shows an illustration of input and output variables effectuated by a method according to the present invention for switching on an electric machine according to a first exemplary embodiment.

[0023] FIG. 5b shows an illustration of input and output variables effectuated by a method according to the present invention for switching on an electric machine according to another exemplary embodiment.

[0024] FIG. 6 shows a parameter study of a dynamic behavior, effectuated by a primary excitation, of an elastically coupled system to masses.

DETAILED DESCRIPTION

[0025] The present invention is based on a system illustrated in FIGS. 1 and 2, in which identical elements are provided with identical reference numerals.

[0026] In FIG. 1, a system 200 including an internal combustion engine 300, a belt-driven starter generator 100 as the electric machine, and a vehicle electrical system 30 is illustrated, based on which the specific embodiments (cf. FIG. 5 in particular) of the present invention are elucidated.

[0027] Internal combustion engine 300 is connected to starter generator 100 via a belt 310, a belt tensioner being provided which is configured as a reciprocating belt tensioning system 320 and which is capable of tensioning belt 310 during operation independently of the torque direction. Belt 310 thus represents an elastic coupling between starter generator 100, the crankshaft of internal combustion engine 300, and possible other components, for example an air-conditioning compressor for an air conditioning system (not illustrated).

[0028] In FIG. 2, starter generator 100 is schematically shown in the form of a circuit diagram. The starter generator includes a generator component 10 and a current converter component 20. The current converter component is usually operated as a rectifier during the generator operation of the machine and as an inverter during the motor operation.

[0029] Generator component 10 is illustrated only schematically in the form of stator windings 11 which are interconnected in a star-shaped manner and in the form of an excitation or rotor winding 12 which is connected in parallel to a diode. The rotor winding is switched in a clocked manner with the aid of a power switch 13 which is connected to a terminal 24 of current converter component 20. The activation of power switch 13 takes place via an activation line 14 according to a field controller 15, power switch 13 being generally integrated into an application-specific integrated circuit (ASIC) of the field controller similarly to the diode which is connected in parallel to rotor winding 12. The excitation current may be set via a pulse-width modulated voltage signal.

[0030] Within the scope of the present application, a three-phase generator is illustrated. In principle, the present invention is, however, also applicable in the case of generators having fewer or more phases, e.g., five-phase generators.

[0031] Current converter component 20 is implemented in this case as a B6 circuit and includes switching elements 21 which may be implemented as MOSFETs 21, for example. MOSFETs 21 are, for example, connected via busbars to particular stator windings 11 of the generator. Furthermore, the MOSFETs are connected to terminals 24, 24 and make available a direct current for a vehicle electrical system 30 including the battery of a motor vehicle if accordingly activated. The activation of switching elements 21 takes place with the aid of an activation device 25 via activation channels 26, not all of which being provided with reference numerals for the sake of clarity. Activation device 25 receives the phase voltage of the individual stator windings via phase channels 27 in each case. In order to provide these phase voltages, additional devices may be provided which are, however, not illustrated for the sake of clarity.

[0032] During motor operation, starter generator 100 is used to start up internal combustion engine 300. Here, current converter component 20 is operated according to one embodiment of the present invention, as described in the following by way of example of a separately excited one-phase synchronous machine (cf. FIG. 3). The starter generator is supplied with power by the battery.

[0033] FIG. 3 shows an equivalent circuit diagram of a separately excited one-phase synchronous machine. To generate a torque, excitation current I.sub.Err is generated in the rotor winding (field winding) through voltage U.sub.f taking into consideration resistance R.sub.F. This excitation current I.sub.Err induces synchronous generated voltage U.sub.p in the stator winding 11 when electric machine 100 is rotating. Phase voltage U.sub.s generated by inverter 20 is applied to the terminals of phase winding 11 (cf. FIG. 2). Amplitude and phase position of voltage U.sub.s are set with the aid of pulse-width modulation (PWM). This voltage U.sub.s generates corresponding phase current I.sub.Phase in phase winding 11 taking into consideration resistance R.sub.s and inductance L.sub.s. To generate a torque, excitation current I.sub.Err as well as phase current I.sub.Phase are required, both being switched on immediately after a start-up request S of an internal combustion engine 300 according to the present invention and increased in such a way that the time necessary for starting up internal combustion engine 300 may be kept short.

[0034] In FIG. 4, the chronological progressions of torque, excitation current I.sub.Ex, and phase current are illustrated which result in the case of an application of a method known from the related art for initiating a start-up of an internal combustion engine 300 with the aid of a belt-driven starter generator 100. At point in time t=0.1 s, a start-up request S takes place and a torque D.sub.setpoint of 50 Nm is requested. Thereafter, excitation current I.sub.Ex is initially switched on. At point in time t=0.2 s, the excitation current has reached its setpoint value and the phase currents are switched on with a time delay. Phase currents I.sub.Phase are controlled with the aid of the field-oriented control in such a way that a torque progression D results in the shape of a ramp having slope 1,000 Nm/s. Due to the energization of stator winding 11 and rotor winding 12 falling apart over time, there is a latency in which no torque is transferred from electric machine 100 to internal combustion engine 300. Accordingly, the overall time of a start-up is also slowed down due to a belt-driven starter generator 100 activated in this manner.

[0035] In FIGS. 5a and 5b, the chronological progressions of torque 120a, b, excitation current I.sub.Err, and phase current I.sub.Phase are illustrated which result in the case of an application of a method according to the present invention for improving a start-up of an internal combustion engine 300 with the aid of a belt-driven starter generator 100. According to the first exemplary embodiment (FIG. 5a), a start-up request S takes place at a point in time t=0.1 s and immediately thereafter, excitation current I.sub.Err and phase current I.sub.Phase are switched on at the same time. A setpoint torque D.sub.setpoint of 50 Nm is predefined and excitation current I.sub.Err and phase current I.sub.Phase are controlled in such a way that a torque gradient D (slope) 1,000 Nm/s is predefined.

[0036] Since phase current I.sub.Phase may not exceed a certain maximum value I.sub.Pmax, typically 200 amperes, generated torque 120a is smaller than predefined torque D.sub.setpoint, as long as desired excitation current I.sub.Err has not been reached. In the present case, maximum value I.sub.Pmax is provided by the envelope of phase current progression I.sub.Phase Excitation current I.sub.Err is controlled to a setpoint value, the setpoint value for the excitation current being stored in a look-up table as a function of the setpoint torque and the rotational speed. This setpoint value is set via a PI controller. The torque control takes place via the phase current, the instantaneously measured excitation current being incorporated into the setpoint value computation for the phase currents. The time required to build up the torque necessary for cranking the internal combustion engine is still shortened as compared to the related artin the case of comparable boundary conditionsfrom 250 ms (cf. FIGS. 4) to 190 ms.

[0037] In addition, stator winding 11 and rotor winding 12 may be energized in such a way that the gradient of torque increase 120a in a first time window Z1, which directly chronologically follows start-up request S, is reduced as compared to the gradient of torque increase 120a in a further time window Z2, which chronologically follows first time window Z1. In this way, the gradient of torque increase 120a is adjusted in such a way that it is possible to crank internal combustion engine 300 with the aid of electric machine 100 not jerkily, but smoothly by a correspondingly adjusted torque progression. In a second time window Z2 directly following first time window Z1, the gradient of torque 120a is correspondingly increased to ensure a rapid start-up of internal combustion engine 300. In this case, the chronological progression of the gradient is configured to be linear, in particular in the shape of a ramp, in the further time window. The flattening of the torque progression in first time window Z1 may be in particular established by the coil inductances, in particular field coil 12, since a retardation in the excitation current start-up results due to the self-inductance of the coil.

[0038] The specific embodiment illustrated in FIG. 5b is different from the specific embodiment illustrated in FIG. 5a in that torque gradient D (slope) is only 333 Nm/s. Based on this predefined value, setpoint torque D.sub.setpoint of 50 Nm is reached at the same point in time as in the related art (cf. FIG. 4), this takes place, however, at a considerably reduced torque gradient D as compared to the method known from the related art, which has a positive effect on the stress of the belt drive and in addition reduces dynamic overshoots in the overall system of the driven components.

[0039] In the two cases described above, a ramp-shaped torque increase may be achieved, the slope of the torque ramp being predefined as a function of the type of operation and the ramps also being different for the two cases described above.

[0040] In FIG. 6, a parameter study is illustrated of a dynamic behavior, effectuated by a primary excitation P, of a system of coupled masses, as illustrated in FIG. 1, for example. In the present case, three different forms of an excitation and their effect on an elastically coupled system, as described by way of example in FIG. 1, is discussed. The duration over time of excitation t.sub.a, which is a measure for the gradient of an excitation (similarly to the slope in the torque progression), was normalized using period duration T, to the oscillation resulting from the excitation. Consequently, the amplitude of the excitation or the amplitude of the oscillation resulting from the excitation is illustrated in FIG. 6 in arbitrary units as well as time t.sub.a/T which is normalized using the period duration and which corresponds in angular frequencies to t.sub.a/2.

[0041] In first case F1, normalized excitation duration is t.sub.a/T<=0.2. The gradient of the excitation is therefore great enough for this excitation to be referred to as pulsed. The dynamic of the overall system resulting herefrom is very great, since due to the constant intrinsic damping of the overall system in the present case the amplitude is not attenuated to a minor residual value until after eight oscillation amplitudes. In second case F2, the duration over time of the excitation is in interval 0.2<t.sub.a/T<=5.0. The excitations occurring in this interval are referred to as chronologically controllable. Here, it is clearly apparent that the resulting amplitudes have almost already completely attenuated after a very short period of time.

[0042] A further case F3 describes an excitation in open interval 5.0<t.sub.a/T. In the case of this excitation duration, the constant intrinsic attenuation of the overall system is great enough compared to the excitation, that the system does not even start oscillating. On the basis of this model, an estimation about a maximally admissible torque gradient was deduced which allows for the torque gradient to be selected exactly great enough that, on the one hand, a rapid cranking of internal combustion engine 300 may be ensured and on the other hand, an excessively dynamic application to the overall system is avoided. The limiting value or the limiting range ascertained by way of this model is approximately at 2,000 Nm/s.

[0043] The energization of stator winding 11 may take place during an unclocked (so-called block operation) or a clocked (so-called pulse-width modulated (PWM) operation) pulse-controlled inverter operation. The selected activation pattern may be selected in this case independently of the rotational speed and the desired torque. In the case of the block commutation, the semiconductor switches remain permanently switched on for the time period of a phase activation in contrast to the pulse-width modulated operation. During the pulse-width-modulated operation, the semiconductor switches may be activated at a high frequency (typically between 2 kHz and 20 kHz) using a specific activation pattern, which causes a harmonic progression of the phase current, thus resulting in a reduced torque waviness and an improved efficiency. Both methods are known from the related art.