Abstract:
A device for detecting a change in a generator output signal of a vehicle generator includes a window comparator for comparing a signal amplitude of the generator output signal to at least one threshold value which limits a signal amplitude range, a detector for detecting a change in the generator output signal based on an output signal of the window comparator, a detection unit for detecting a signal amplitude difference between a maximum signal amplitude and a minimum signal amplitude of the generator output signal, and an adaptation unit for adapting the signal amplitude range of the window comparator, based on the signal amplitude difference, when there is the change in the generator output signal.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to vehicle generators which are used for supplying electrical power to a vehicle for example. 
     2. Description of Related Art 
     Generators which are driven by a drive source, for example, an internal combustion engine, are often used to supply power in vehicles. Such generators are often three-phase or multiphase, a phase signal, for example, a U, V or W signal in the form of a generator output signal, being assigned to each phase and output. Most generator output signals form a total multiphase generator signal, which may be fed into a vehicle electrical system after rectification, for example. 
     Based on a coupling between the drive source, for example, an internal combustion engine, and the generator, each of the generator output signals may be used for detection of the running drive source and thus also an instantaneous generator speed. For example, a generator regulator, which uses one or more generator output signals to analyze a phase frequency, i.e., a frequency of a generator output signal and/or a phase amplitude, i.e., an amplitude of a generator output signal, may be used for this purpose. 
     For frequency analysis, for example, a change in a generator output signal may be detected, a number of changes in the generator output signal within a predetermined period of time allowing an inference regarding its frequency, so-called phase frequency. The frequency analysis is usually performed by an analysis circuit, for example, a frequency or phase analysis circuit. For detecting a change in a generator output signal, for example, one fixed threshold or two fixed thresholds and a hysteresis may be used, whose difference defines a signal amplitude range. In the case of generator output signals of variable amplitude, variable thresholds may also be provided, as described in published German patent application document DE 19732961 A1, for example. In addition, the frequency analysis may be performed on the basis of a differentiation between generator output signals assigned to two different phases. 
     Known methods for detecting a frequency of a generator output signal are based on its sinusoidal or square-wave curve.  FIGS. 1 and 2  show examples of curves 101 and 201 of such generator output signals. However, based on the development of modern generators having three or more phases, based on mechanical changes or the use of compensation magnets or permanent magnets, a generator output signal to be analyzed may change greatly in the flank area in particular, which may result in an analysis of a phase amplitude or a phase frequency no longer being performable in all frequency and load ranges.  FIGS. 3 ,  4  and  5  show a few curves 301, 401 and 501 of such generator output signals as examples. The flank transitions, which are no longer vibration-free and which sometimes may have high-frequency components, are problematical for the analysis methods known so far. 
     In addition, one must also take into account the fact that a speed range of a generator may be in a speed band between 0 and 20,000 rpm. This yields a phase frequency of 0 to 2000 Hz for a six-claw pole pair generator or 0 to 2700 Hz for an eight-claw pole pair generator, so that the frequency analysis must often be performed in a wide frequency band. Furthermore, interference signals whose interference frequency may be at low speeds and therefore low-phase frequencies in the case of a useful signal frequency of a generator output signal may be superimposed on the generator output signals at high generator speeds or generator phase frequencies. 
       FIG. 6  shows as an example a curve  601  of a generator output signal having a voltage amplitude U Phase  at low speeds, an interference signal of duration t stör  being superimposed on this generator output signal within a time interval  603 . A curve  605  of a generator output signal at higher frequencies is shown for comparison; its period  607 , which corresponds to a useful duration t Nutz , may correspond to interference period  603 . 
     The interference signals also distort the amplitudes of the generator output signals. If the amplitudes of the generator output signals are low at a peak-to-peak voltage of less than 1 V SS , then interference levels whose interference amplitude is greater than 1 V SS  have a negative effect on the analysis accuracy of threshold-based frequency analysis concepts. 
     To analyze the frequency of a generator output signal, for example, a configuration shown in  FIG. 7   a  may be used. A generator output signal, for example, a U, V or W phase component of a generator total output signal, is conveyed to a first comparator  703  and to a second comparator  705  via an input terminal  701 . The outputs of comparators  703  and  705  are connected to a detection element  707 , which detects whether thresholds predetermined by comparator  703  and  705  have been undershot or exceeded. A first output  709  of detection element  707  indicates that an upper threshold has been exceeded; a second output  711  indicates that the generator output signal has dropped below a lower threshold. A third output  713  indicates that the generator output signal is within the window range predetermined by comparators  703  and  705 . An incrementer and decrementer  715  is connected downstream from detection element  707 , whose output is connected to a d.c. voltage offset element  717 . One output of d.c. voltage offset element  717  is connected to a second input of comparator  705  and to an element  718 , whose additional output is connected to another input of comparator  703 . The upper and lower thresholds for comparators  703  and  705  may be set via element  718  in advance. Furthermore, an element  719 , which transmits a regulator status of a generator regulator to element  718 , is also provided. One output of detection element  707  is also connected to a frequency detection element  721 , over whose output the phase frequency may be output. Therefore, a change in the generator output signal from which the phase frequency may be derived, for example, may be implemented on the basis of a window comparator having a detector and counter downstream from the latter. 
       FIG. 7   b  shows a block diagram of a device for detecting a change in an output signal, which is completely digital. For this purpose, this device, in contrast with the device from  FIG. 7   a , includes an upstream analog-to-digital converter  719 . Furthermore, an element  720 , which transmits a regulator status of a generator regulator to element  718 , is also provided. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention is based on the finding that an efficient concept for detecting a change in a generator output signal, for example, a phase signal of a total multiphase generator signal, may be accomplished for a plurality of generator implementation variants by an adaptive design of the signal window range defined by an upper threshold and a lower threshold of a window comparator. A single generator output signal, for example, the U, V or W signal of a total multiphase generator signal, may be processed. 
     According to one aspect of the present invention, a device is provided for detecting a change in a generator output signal of a vehicle generator having a window comparator for comparing a signal amplitude of the generator output signal with at least one threshold value, which limits a signal amplitude range, and a detector for detecting a change in the generator output signal based on an output signal of the window comparator. The device also includes a detection unit for detecting a signal amplitude difference between a maximum signal amplitude and a minimum signal amplitude of the generator output signal, so that an amplitude swing of the generator output signal is detected in the form of a peak-to-peak voltage and/or a peak-to-peak current. The device also includes an adaptation unit for adapting the signal amplitude range of the window comparator on the basis of the signal amplitude difference when there is a change in the generator output signal. By adapting the signal amplitude range by which a signal amplitude window of the window comparator is established, the efficiency range of the window comparator may be adaptively matched with each type of generator output signal. 
     According to one specific embodiment, the window comparator includes a first comparator for comparing the signal amplitude with an upper threshold value of the signal amplitude range and a second comparator for comparing the signal amplitude with a lower threshold value of the signal amplitude range. The signal amplitudes may be, for example, current or voltage amplitudes, the implementation of the window comparator using the two separate comparators being an efficient and advantageous implementation option. 
     According to another exemplary embodiment, the detection unit is designed to detect the signal amplitude difference within a predetermined or preselectable time interval. A detection time interval may thereby be adapted advantageously to an expected period of the generator output signal. 
     According to one specific embodiment, the detection unit includes a processor unit for determining a control parameter as a function of the signal amplitude difference according to a computation rule. The processor unit may advantageously be provided to determine the control parameter by reducing the signal amplitude difference by one half or by one third or on the basis of a lookup table in which various control parameters are assigned to various signal amplitude differences and to send the control parameter to the adaptation unit, which then increases or decreases the signal amplitude range in response thereto. Therefore, a simple rule is provided on the basis of which the signal range of the window comparator may be adapted advantageously as a function of a range of the generator output signal. The processor unit may be implemented in software or hardware using a processor having a microcontroller, for example, or as a discrete digital circuit. 
     According to one specific embodiment, the detection unit is designed to determine the signal amplitude difference on the basis of the generator output signal itself or on the basis of an output signal of the detector, so that advantageous circuit flexibility is achieved. 
     According to one specific embodiment, the detector includes a detection element for detecting a change in the signal amplitude difference and a counter downstream from the detection element to increment or decrement a numerical value as a function of the change in the signal amplitude difference. The concept according to the present invention may thus also be used to advantage in existing systems. 
     According to one specific embodiment, the detector is connected downstream from the window comparator, so that a direct signal analysis is possible. 
     According to one specific embodiment, a d.c. voltage offset element is provided for transmitting a d.c. voltage offset to the adaptation unit, which applies the signal amplitude range as a function of the d.c. voltage offset, so that the range is easily shiftable along a signal amplitude axis. 
     According to one specific embodiment, a frequency detection element is provided for detecting a frequency of the generator output signal on the basis of a change in the signal amplitude frequency. The frequency detection element is preferably downstream from the detection unit of the detector and is provided for determining the frequency of the generator output signal on the basis of a detected change with respect to one or more threshold values within a predetermined time interval, for example. A speed of a drive source driving the generator as well as a drive start are detectable in a particularly advantageous manner in this way. 
     According to one specific embodiment, the device includes an upstream filter unit for filtering the generator output signal to obtain a filtered generator output signal. The filter unit preferably has a predetermined filter characteristic having a cutoff frequency which may be variable. The device also includes a detection unit for detecting a frequency of the filtered generator output signal to thereby obtain the frequency of the generator output signal. Furthermore, an adaptation unit is provided for adapting the cutoff frequency of the filter unit as a function of the detected frequency. The passband of the filter unit is therefore enlarged or decreased, for example, so that a useful frequency adaptation may always be performed. 
     According to one specific embodiment, the filter characteristic of the filter unit is a low-pass characteristic or a band-pass characteristic or a high-pass characteristic, so that the cutoff frequency may be an upper or a lower cutoff frequency. The filter unit may advantageously be designed as a digital or analog unit in the form of an input filter having an adjustable cutoff frequency. 
     According to one specific embodiment, the filter unit has a filter characteristic of the first or second filter order or at most the third filter order. This advantageously ensures that even useful frequency components may be detected outside of the cutoff frequency filters on the basis of the lower damping associated with these filter orders. 
     According to one specific embodiment, the filter unit has a filter characteristic, which correlates with damping in a predetermined frequency range outside of the cutoff frequency, preferably not exceeding a predetermined damping value. The increase in damping may amount to 6 dB per octave, 12 dB per octave or 18 dB per octave, for example. Therefore, in an analysis of an energy or power of the generator output signal in a frequency band outside of the cutoff frequency, the known damping characteristic may be taken into account in an advantageous manner. 
     According to one specific embodiment, the adaptation unit is preferably designed to increase the cutoff frequency if the detected cutoff frequency is outside of the cutoff frequency and a signal value exceeds a predetermined threshold value at the detected frequency. The signal value may be a signal amplitude or a signal power or a signal energy of the generator output signal, for example. The predetermined threshold value may be expressed in percent, for example, and may be 1%, 2% or 10% of a signal value at the cutoff frequency. This permits a more accurate detection of the useful frequency range. 
     According to one specific embodiment, the adaptation unit is designed to reduce the cutoff frequency if the detected cutoff frequency is lower than the cutoff frequency and a generator signal value falls below a predetermined threshold value at the detected frequency. This threshold value may also be expressed in percent and amounts to, for example, less than 1% of a signal value at the cutoff frequency. Therefore in an advantageous manner an optimal adaptation of the passband at the useful frequency band is achieved with a reduction in interference at the same time. 
     According to another aspect of the present invention, a method is provided for detecting a change in a generator output signal of a vehicle generator by comparing a signal amplitude of the generator output signal with at least one threshold value, which limits a signal amplitude range, detecting a change in the generator output signal on the basis of an output signal of the window comparator, detecting a signal amplitude difference between a maximum signal amplitude and a minimum signal amplitude of the generator output signal and adapting the signal amplitude range of the window comparator on the basis of the signal amplitude difference when there is a change in the generator output signal. Additional method steps are derived directly from the functionality of the device according to the present invention for detecting a change in a generator output signal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a generator output signal. 
         FIG. 2  shows a generator output signal. 
         FIG. 3  shows a generator output signal. 
         FIG. 4  shows a generator output signal. 
         FIG. 5  shows a generator output signal. 
         FIG. 6  shows a generator output signal. 
         FIGS. 7   a  and  7   b  show block diagrams of a device for detecting a change in a generator output signal. 
         FIG. 8  shows a block diagram of a device for detecting a change in a generator output signal. 
         FIG. 9  shows a block diagram of a device for detecting a change in a generator output signal. 
         FIGS. 10   a - 10   c  show signal curves as a function of time. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 8  shows a block diagram of a device for detecting a change in a generator output signal, for example, a change in phase or frequency. The device includes an input terminal  801 , to which a generator output signal, for example, a U or V or W signal, may be applied. A window comparator is connected downstream from input terminal  801  which has a first comparator  803  and a second comparator  805 , for example. A detector  806  is connected downstream from the window comparator and has, for example, a detection element  807  and a counter  809 , which is connected downstream from detection element  807  and whose output forms an output of detector  806 . Furthermore, a detection unit  811  is connected downstream from detector  806 . 
     Detection unit  811  preferably includes a determination unit  813  for determining a signal amplitude difference and a processor unit  815 , which is connected downstream from determination unit  813 , which determines a control parameter as a function of the signal amplitude difference conveyed to it. One output of processor unit  815  is connected to an input of adaptation unit  817 . Adaptation unit  817  is connected to the window comparator and for this purpose includes, for example, outputs, each of which is connected to first comparator  803  and second comparator  805 . 
     The output of detector  806  is also connected to a d.c. voltage offset element  819 , which is situated between ground and adaptation unit  817 , for example. One output of d.c. voltage offset element  819  is also connected to the window comparator, for example, to an input of second comparator  805 . 
     The device optionally includes a timer  821 , which is coupled to determination unit  813  and is provided for specifying a time window in which the signal amplitude difference is to be determined. The device also includes a frequency analysis unit  823 , which is connected downstream from detection element  807 . 
     The device shown in  FIG. 8  may have both digital and analog elements. For example, the window comparator and adaptation unit  817  and d.c. voltage offset element  819  may be designed as analog elements, for example. The other circuit elements are preferably digital. 
     During operation, a generator output signal having a signal amplitude, for example, a signal amplitude U V , is conveyed to the device shown in  FIG. 8  via a phase terminal of a generator, for example, and is supplied to first comparator  803  and to second comparator  805  of the window comparator via input terminal  801 . First comparator  803  is provided, for example, to compare the generator output signal to an upper threshold value, while second comparator  805  compares the generator output signal to a lower threshold value. A difference between the upper threshold value and the lower threshold value yields a threshold value range, which corresponds to a comparator window. First comparator  803  generates an output signal, for example, if the signal amplitude of the generator output signal exceeds the upper threshold value. Similarly, second comparator  805  generates an output signal if the signal amplitude of the generator output signal falls below the lower threshold value. Detection element  807  downstream from the window comparator detects a change in the corresponding output of corresponding comparator  803  and  805  and generates on this basis an output signal, which prompts downstream counter  809  to increment, to decrement or to remain in the present state. For this purpose, detection element  807  may have a single output, which is supplied to the counter. Alternatively, detection element  807  may have three outputs, so that exceeding the upper threshold is indicated via a first output  825 , dropping below the lower threshold is indicated via a second output  827 , and the generator output signal remaining within the signal amplitude range predetermined by the window comparator is optionally indicated via a third output  829 . In addition, it is also possible to recognize, on the basis of dropping below or exceeding the upper or lower threshold, whether the generator output signal is within the window comparator range or above or below that. 
     A phase cycle and thus a phase frequency could be inferred from the change in one of the output signals of corresponding comparator  803  and  805 . For this purpose, a signal indicating a change in the corresponding comparator output is conveyed to frequency detection unit  823  via detection element  807 . Frequency detection unit  823  ascertains a present frequency of the generator output signal on the basis of a number of changes in the comparator output signals within a predetermined time interval, for example. 
     Counter  809 , which is connected downstream from detection element  807 , increments or decrements a numerical value as a function of whether the signal amplitude exceeds the upper threshold value and/or drops below the lower threshold value. Determination unit  813  connected downstream from counter  809  detects a signal amplitude difference, i.e., a difference between a maximum signal amplitude and a minimum signal amplitude within a predetermined time interval, which may be predefined by time window element  821 , for example. Information about the signal amplitude difference, for example, a difference between the peak voltage values, is conveyed to the processor unit, which ascertains a control parameter for adaptation unit  817  on this basis. For this purpose, the processor unit may reduce the signal amplitude difference by one half or one third, for example, to obtain the control parameter. The control parameter is conveyed to adaptation unit  817 , which increases or reduces the signal amplitude range of the window comparator on this basis, so that a detection window is increased or reduced. The signal amplitude range of the window comparator is thus determined exclusively on the basis of a range of the generator output signal and/or a variable depending on this range. 
       FIG. 9  shows as an example a completely digital structure of a device for detecting a change in a generator output signal, which includes an upstream analog-to-digital converter  901  in contrast with the structure shown in  FIG. 8 . According to one specific embodiment, determination unit  813  may still detect the signal amplitude difference on the basis of the output signal of counter  809 , just as before. According to another specific embodiment, it is possible on the basis of upstream analog-to-digital converter  801  for determination unit  813  to be able to determine the signal amplitude difference, for example, a difference between a maximum amplitude and a minimum amplitude of the generator output signal, directly on the basis of a digital output signal, which represents the generator output signal and is output by the analog-to-digital converter. 
     In this case, determination unit  813  is able to determine the signal amplitude difference from a difference between a maximum digital value and a minimum digital value of the output signal of the analog-to-digital converter, for example. Control parameter U AC  determined by processor unit  815  may be determined, for example, in the form of a voltage amplitude, which defines a window width of the window comparator. This voltage amplitude is no less than 0.6 V, for example, and no greater than 6 V. To determine the voltage amplitude, processor unit  815  may divide the ascertained peak-to-peak voltage, i.e., a difference between a minimum voltage and a maximum voltage, by a factor which may be equal to 2 or 3, for example. In general, control parameter U AC  may be determined in the form of a voltage value, for example. 
     Alternatively, processor unit  815  may be designed to determine the control parameters in the form of the voltage value as a function of a peak-to-peak voltage of generator output signal U Phase,ss  as follows, for example:
     U Phase     —     SS =0 . . . &lt;2 V . . . 2 V . . . &lt;3 V 3 V . . . &lt;6 V 6 V . . . &lt;12 V   U AC =0.6 V 1.0 V 2.5 V 4.5 V   

     According to the present invention, the window comparator threshold, for example, an a.c. (a.c.: alternating current) window comparator threshold is determined as a function of the measured signal amplitude of the generator output signal. The generator output signal may be, for example, one of the phase signals representing the respective phase of a total multiphase generator signal. Therefore, the window comparator threshold or the window comparator range of the signal amplitude fit adaptively to the signal amplitude and thus allow an optimal signal-to-noise ratio between a useful signal and an interference amplitude, which is optimal for each operating range and each generator. This achieves the result in an advantageous manner that no application-dependent adjustment of the phase analysis is necessary in the future. 
     As illustrated in  FIGS. 8 and 9 , the frequency analysis is implemented by a downstream d.c. voltage offset (d.c. offset) and a connected window comparator threshold with the aid of the window comparator. The window comparator generates a control signal for incrementer/decrementer  809 , which holds its count or increments or decrements the count. The window comparator threshold, which forms a hysteresis between an upper and a lower switching threshold, i.e., between the upper threshold value and the lower threshold value, however, is not implemented as a fixed threshold having predefined voltage values, as is the case in the exemplary embodiments illustrated in  FIGS. 7   a  and  7   b , for example. Depending on a regulator status for the starting operation or for an emergency start, a sensitive threshold may be selected, for example, by element  719 . During normal operation, however, a much higher threshold having a larger signal-to-noise ratio is selected to mask out interference ripples. According to the present invention, however, the window comparator threshold is not predefined but instead depends on an amplitude of the generator output signal, i.e., on a phase amplitude, and is tracked adaptively. Therefore, an optimal signal-to-noise ratio is always made possible at each operating point. 
     Adaptation unit  817  adapts the window comparator threshold, i.e., the signal amplitude range defined by the window comparator, for example, via a variable adjustable voltage value, which may be supplied digitally or in the form of an analog value. The adaptation may be performed on the basis of a time interval, which is established by timer  821 , so that a time window is predefined for detection of the generator output signal amplitude. This is detected by analysis of the numerical values of counter  809  or an output signal of converter  901 . For example, minimum values and maximum values of the amplitude of the generator output signal, for example, the voltage amplitude, measured and detected in the predefined time interval, belong to the detection of the signal amplitude difference. For example, on the basis of a computation rule or characteristics map, processor unit  815  calculates or ascertains from the measured amplitude a control value in the form of the control parameter for the height of the window comparator threshold and conveys it to adaptation element  718 . 
       FIGS. 10   a ,  10   b  and  10   c  show the process sequences over time again in greater detail.  FIG. 10   a  shows the curve of a generator output signal voltage U V , which represents the generator output signal. The signal amplitude difference may be represented, for example, in the form of a voltage value  1001 , which may correspond to a value U Phase     —     SS , for example, and is designated by the arrows shown in  FIG. 10   a .  FIG. 10   b  illustrates the definitive time intervals for tracking of the window comparator threshold.  FIG. 10   c  illustrates the corresponding curve of the peak-to-peak voltage as a function of time.