Patent Description:
Accurate and reliable information on the speed of a combustion engine is an important measure in terms of controlling and monitoring operation of the combustion engine. In a practical implementation the engine speed measurement typically relies on a speed sensor arranged to detect rotation speed of the crankshaft and/or the flywheel of the combustion engine and to generate an electrical speed signal that comprises a pulse train whose pulse frequency is descriptive of the speed of the crankshaft/flywheel of the combustion engine, thereby serving as an indication of a rotation speed of the combustion engine. Engine speed measurement using such a basic mechanism is well known in the art it is therefore not discussed herein in more detail.

Any anomalies in engine control or engine performance due to errors or inaccuracies in the engine speed measurement may result in increased fuel consumption and/or increased emissions or may lead to compromised or even interrupted power supply. While such compromised performance of a combustion engine in any usage scenario should be avoided to extent possible, such compromised performance may be especially disadvantageous in usage scenarios where one or more combustion engines are applied as the supply of mechanical energy in demanding industrial environments such as power plants, marine vessels, offshore platforms such as oil rigs, etc. where the combustion engine(s) are continuously operated for prolonged periods of time and where efficient and uninterrupted power supply from the combustion engine is typically a critical characteristic.

In this regard, reliability of the engine speed measurement does not only concern numerical accuracy of the measured engine speed but also involves recognition of various error conditions that may disturb or completely disable the engine speed measurement to facilitate efficient and swift maintenance in case such condition arises.

In related art, <CIT> discloses a symmetric voltage divider is connected between the terminals of an inductive sensor. The tap of said voltage divider is fed to a reference voltage via a resistor. A diagnostic voltage is present on the tap. The diagnostic voltage is first compared with two threshold values at rest and then sampled in an operating state. The difference is calculated from the largest and smallest sample value, said difference being compared with a third threshold value. Short circuits or line interruptions are recognized/displayed from the comparison result.

Further in related art, <CIT> discloses a diagnostic method for a sensor in a motor vehicle equipped with an internal combustion engine. According to said method, during the operation of the motor vehicle, an output signal of the sensor is analysed to determine whether a maximum value of the output signal falls below a first threshold value and/or whether a minimum value of the output signal exceeds a second threshold value. In the latter case, a signal is sent to a control unit, said signal indicating to the latter that the sensor may deliver incorrect data when the motor vehicle is started again.

In view of the foregoing, it is an object of the present invention to provide a technique for measuring speed of a rotating component, such as the rotation speed of a combustion engine in an accurate manner while enabling recognition of one or more predefined error conditions that may be involved in the speed measurement.

The object(s) of the invention are reached by a circuit, by an apparatus and by a method defined in the respective independent claims.

According to an example embodiment, a circuit for measuring a rotation speed of a combustion engine is provided, the circuit comprising a state detector coupled between an operating voltage and a ground potential and coupled to receive, from a speed sensor, an electrical signal that has a time-varying signal voltage that exhibits local maxima at a frequency that has a predefined relationship to the rotation speed, wherein the state detector is arranged to derive, based on the electrical signal, a state indication that indicates whether the electrical signal represents one of a high state or a low state, and a diagnostic signal that is descriptive of the operational state of the speed measurement circuit, wherein the diagnostic signal conveys a diagnostic value that is descriptive of current operational state of the speed measurement circuit, wherein current operational state is one of a normal operational state or an abnormal operational state and wherein the state detector is arranged to derive the diagnostic value based on the signal voltage of the electrical signal; and a controller coupled to receive the state indications and the diagnostic signal and arranged to compute the rotation speed based on a time series of the state indications in dependence of the diagnostic signal in view of said predefined relationship, wherein the state detector has defined therefor: two or more predefined signal voltage sub-ranges, each associated with a respective abnormal operational state of the speed measurement circuit two or more predefined intermediate diagnostic voltage sub-ranges, each representing a respective abnormal operational state of the speed measurement circuit.

According to another example embodiment, a method for measuring a rotation speed of a combustion engine is provided, the method comprising receiving, from a speed sensor coupled to measure the rotation speed, an electrical signal that has a time-varying signal voltage that exhibits local maxima at a frequency that has a predefined relationship to the rotation speed; deriving, based on the electrical signal, a state indication that indicates whether the electrical signal represents one of a high state or a low state; deriving, based on the electrical signal, a diagnostic signal that is descriptive of the operational state of the speed measurement circuit, wherein the diagnostic signal conveys a diagnostic value that is descriptive of current operational state of the speed measurement circuit, wherein current operational state is one of a normal operational state or an abnormal operational state and wherein the diagnostic value is derived based on the signal voltage of the electrical signal; and deriving the rotation speed based on a time series of the state indications in dependence of the diagnostic signal in view of said predefined relationship, wherein the diagnostic value is derived via application of the following: two or more predefined signal voltage sub-ranges, each associated with a respective abnormal operational state of the speed measurement circuit two or more predefined intermediate diagnostic voltage sub-ranges, each representing a respective abnormal operational state of the speed measurement circuit.

The exemplifying embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" and its derivatives are used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features described in the following are mutually freely combinable unless explicitly stated otherwise.

Some features of the invention are set forth in the appended claims. Aspects of the invention, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of some example embodiments when read in connection with the accompanying drawings.

<FIG> schematically illustrates a speed measurement circuit <NUM> according to an example, (conceptually) divided into an analog subsystem 100a and a digital subsystem 100b. The speed measurement circuit <NUM> comprises a speed sensor <NUM> is coupled to a state detector <NUM> by a signal line <NUM>. The speed sensor <NUM> is arranged to provide an analog electrical signal via the signal line <NUM> to the state detector <NUM>, which is arranged to determine whether the electrical signal currently received thereat represents one of a high state or a low state and to issue a respective state indication <NUM> to a controller <NUM> to enable rotation speed calculation therein based on a time series of state indications <NUM>. The speed sensor <NUM> may comprise, for example, a hall sensor. The speed sensor <NUM> and the state detector <NUM> may be coupled to operating voltage Vs and to a ground potential VGND. The speed sensor <NUM> is arranged to derive the electrical signal as one that is descriptive of rotation speed of a rotary component, e.g. the rotation speed of a crankshaft or a flywheel of a combustion engine. In this regard, in the following the present disclosure simply refers rotation speed of a combustion engine. However, the rotation speed of a component of the combustion engine serves as a non-limiting example and the speed measurements circuits described in the present disclosure are applicable for measuring rotation speeds also in frameworks different from combustion engines.

The electrical signal conveyed via the signal line <NUM> as an analog signal that has a time-varying voltage and that exhibits local maxima at a frequency that has a predefined relationship to the rotation speed of the combustion engine. This relationship is also known by the controller <NUM> and it depends on the number of measurement points included in the rotary component of the combustion engine speed of which is being measured by the speed measurement circuit <NUM>. As non-limiting examples, in case of a single measurement point there is one local maxima per revolution and the frequency of local maxima directly corresponds to the rotation speed, whereas in case of N evenly distributed measurement points there are N local maxima per revolution and the frequency of local maxima corresponds to the N times the rotation speed.

A voltage of the electrical signal received via the signal line <NUM> may be referred to as a signal voltage V<NUM>. The state detector <NUM> may be arranged to compare the signal voltage V<NUM> to a high reference voltage Vref,high and to a low reference voltage Vref,low and to issue a state indication <NUM> to the controller <NUM> in consideration of the signal voltage V<NUM> in view of the high and low reference voltages Vref,high, Vref,low, where the high reference voltage Vref,high is larger than (or equal to) the low reference voltage Vref,low and the state indication <NUM> indicates one of a high state or a low state.

As an example, the state indication <NUM> may comprise a high state indication in response to the signal voltage V<NUM> exceeding the high reference voltage Vref,high and it may comprise a low state indication in response to the signal voltage V<NUM> being smaller than the low reference voltage Vref,low. In case the signal voltage V<NUM> is between the high and low reference voltages Vref,high, Vref,low, the output of state detector <NUM> is undecided and it may, for example, issue the state indication <NUM> as one comprising a dedicated 'undecided state' indication instead of issuing one of the high or low state indications or refrain from issuing the state indication <NUM>.

The operating voltage Vs may be provided by a suitable DC voltage source, whereas characteristics of the first resistor R<NUM> as well as the high and low reference voltages Vref,high, Vref,low may be selected in view of the characteristics of the applied speed sensor <NUM> and/or the applied operating voltage Vs.

The controller <NUM> may be arranged to compute the rotation speed of the combustion engine based on the time series of state indications <NUM> obtained from the state detector <NUM> in view of the knowledge of the predefined relationship between the frequency of local maxima in the signal voltage V<NUM> and the rotation speed and provide a speed indication <NUM> that indicates the derived rotation speed. As an example in this regard, the controller <NUM> may be arranged to derive the rotation speed directly based on respective timings of the state indications <NUM> obtained from the state detector <NUM>, whereas in another example the controller may be arranged to construct a digital speed signal based on the state indications <NUM> obtained from the state detector <NUM> and to derive the rotation speed based on the digital speed signal. In this regard, the controller <NUM> receives, from the state detector <NUM>, a time series of state indications <NUM> that are useable, in view of the knowledge of the relationship between the frequency of local maxima in the signal voltage V<NUM> and the rotation speed, for deriving the digital speed signal in a form of a pulse train whose pulse frequency follows the frequency of local maxima in the signal voltage and V<NUM> is descriptive of the rotation speed in view of the knowledge of the predefined relationship between the frequency of local maxima in the signal voltage V<NUM> and the rotation speed.

As an example, computation of the rotation speed directly from the time series of state indications may comprise computing rotation speed based on respective frequencies of changes from the low state to the high state (a rising edge) and/or changes from the high state to the low state (a falling edge) in the time series of state indications <NUM> in view of the predefined relationship between the frequency of local maxima in the signal voltage V<NUM> and the rotation speed. In another example, computation of the rotation speed may comprise derivation of the digital speed signal based on the time series of state indications <NUM> in the controller <NUM> and computing the rotation speed based on the digital speed signal in view of the predefined relationship between the frequency of local maxima in the signal voltage V<NUM> and the rotation speed. Therein, reception of the first high state indication that follows reception of a low state indication indicates a rising edge of the digital speed signal while a time period starting from the rising edge and continuing until reception of the next low state indication may represent a binary high state of the digital speed signal, whereas reception of the first low state indication that follows reception of a high state indication indicates a falling edge of the digital speed signal while a time period starting from the falling edge and continuing until reception of the next high state indication may represent a binary low state of the digital speed signal. Consequently, the resulting digital speed signal typically consists of alternating periods of binary high states and binary low states (e.g. binary ones and binary zeros), i.e. a pulse train, wherein the pulse frequency substantially matches the frequency of local maxima in the signal voltage V<NUM>.

<FIG> schematically illustrates an implementation of the speed measurement circuit <NUM> according to an example, where the state detector <NUM> comprises a first resistor R<NUM> coupled between the signal line <NUM> and the ground potential VGND and where the signal line <NUM> is coupled to a first input terminal of a first comparator <NUM> and to a second input terminal of a second comparator <NUM>. A second input terminal of the first comparator <NUM> is coupled to the high reference voltage Vref,high and a first input terminal of the second comparator <NUM> is coupled to the low reference voltage Vref,low. The first comparator <NUM> may be arranged to provide a first predefined voltage (e.g. a zero voltage) when the signal voltage V<NUM> fails to exceed the high reference voltage Vref,high and to provide a second predefined voltage (e.g. a non-zero voltage) that serves as the high state indication in response to the signal voltage V<NUM> exceeding the high reference voltage Vref,high. The second comparator <NUM> may be arranged to provide the first predefined voltage when the signal voltage V<NUM> exceeds the low reference voltage Vref,low and to provide the second predefined voltage that serves as the low state indication in response to the signal voltage V<NUM> being smaller than the low reference voltage Vref,low. Hence, the respective voltages provided from the respective outputs of the first and second comparators <NUM>, <NUM> serve as the state indication <NUM>.

<FIG> schematically illustrates the relationship between the signal voltage V<NUM> received at the state detector <NUM> and the pulse train derived in the controller <NUM> according to an example. In this regard, the illustration (a) depicts the signal voltage V<NUM> as a function of time, whereas the illustration (b) depicts the pulse train derivable based on the time series of state indications <NUM> derived from the signal voltage V<NUM> of the illustration (a). Hence the first and second comparators <NUM>, <NUM>, at least conceptually, serve to provide an edge detection functionality via providing the time series of state indications <NUM>, which in turn enables computation of the rotation speed either directly based on respective frequencies of the raising edges and/or falling edges derivable based on the time series of state indications <NUM> or via derivation of the digital speed signal in the form of the pulse train, as described in the foregoing with references to the controller <NUM>.

In the speed measurement circuit <NUM> a failure e.g. in electrical connection (for example due to a wire break) between the speed sensor <NUM> and the state detector <NUM> or within the state detector <NUM> typically results in the state indicator <NUM> indicating the low state or an undecided state. in the former scenario the controller <NUM> has no way of telling such error condition apart from the low state, whereas in the latter scenario the controller <NUM> may be able to deduce that a malfunction has occurred due to prolonged time period of the state controller <NUM> not indicating either the high state or the low state. Nevertheless, even if being able to detect an occurrence of such a malfunction, the controller <NUM> does not have any indication regarding possible type of the malfunction occurring in the state detector <NUM> and/or in electrical connections thereto.

<FIG> schematically illustrates an improved speed measurement circuit <NUM> according to an example, (conceptually) divided into an analog subsystem 200a and a digital subsystem 200b. The speed measurement circuit <NUM> comprises the speed sensor <NUM>, a state detector <NUM> and a controller <NUM>. The speed sensor <NUM> is arranged to provide an analog electrical signal via the signal line <NUM> to the state detector <NUM>, which is arranged to determine whether the electrical signal currently received thereat represents the high state or the low state and to issue a respective state indication <NUM> to the controller <NUM> to enable rotation speed calculation therein based on a time series of state indications <NUM>. Moreover, the state detector <NUM> may be arranged to derive based on the electrical signal, a diagnostic signal <NUM> that is descriptive of at least one aspect of an operational state of the speed measurement circuit <NUM> (e.g. that of the analog subsystem 200a) for provision to the controller <NUM>. The speed sensor <NUM> and the state detector <NUM> may be coupled to an operating voltage Vs and to a ground potential VGND.

Characteristics of the electric signal conveyed via the signal line <NUM> are similar to those described in the foregoing in context of the speed measurement circuit <NUM>, e.g. the electrical signal comprises an analog signal that is descriptive of rotation speed of a rotary component, e.g. rotation speed of a rotary component of a combustion engine, e.g. a crankshaft or a flywheel of the combustion engine, and it has a time-varying signal voltage V<NUM> that exhibits local maxima at a frequency that has a predefined relationship to the rotation speed of the combustion engine. This relationship is also known by the controller <NUM> and it depends on the number of measurement points included in the rotary component of the combustion engine speed of which is being measured by the speed measurement circuit <NUM>, as described in the foregoing in context of the speed measurement circuit <NUM>. The state detector <NUM> may be arranged to compare the signal voltage V<NUM> to the high reference voltage Vref,high and to the low reference voltage Vref,low and to issue the state indication <NUM> to the controller <NUM> in consideration of the signal voltage V<NUM> in view of the high and low reference voltages Vref,high, Vref,low, where the state indication indicates one of the high state or the low state.

As in case of the state detector <NUM>, also the state indication <NUM> obtained from the state detector <NUM> may comprise the high state indication in response to the signal voltage V<NUM> exceeding the high reference voltage Vref,high and it may comprise the low state indication in response to the signal voltage V<NUM> being smaller than the low reference voltage Vref,low, whereas in case the signal voltage V<NUM> is between the high and low reference voltages Vref,high, Vref,low, the output of state detector <NUM> is undecided and it may be handled, for example, as described in the foregoing in context of the state detector <NUM>.

The diagnostic signal <NUM> may convey a diagnostic value that is descriptive of the current operational state of the speed measurement circuit <NUM>, which diagnostic value indicates one of a normal operational state of the speed measurement circuit <NUM> or an abnormal operational state of the speed measurement circuit <NUM>. The state detector <NUM> may set or adjust the diagnostic value into a respective predefined value or into a value in a respective predefined value range in dependence of the signal voltage V<NUM>. As an example in this regard, the diagnostic value may comprise a diagnostic voltage Vd that is set or adjusted to a predefined voltage or to a voltage within in a predefined voltage range in dependence of the signal voltage V<NUM>. Consequently, the controller <NUM> is able to observe the operational state of the speed measurement circuit <NUM> based on a time-varying diagnostic value (e.g. a time-varying diagnostic voltage Vd) received as the diagnostic signal <NUM> from the state detector <NUM> and the controller <NUM> may compute the rotation speed in dependence of the diagnostic signal <NUM>.

A non-limiting example in this regard is illustrated in <FIG>, where the diagnostic value is provided as the diagnostic voltage Vd and where the voltage range is divided into five diagnostic voltage sub-ranges by a high voltage threshold Vthr,high, a low voltage threshold Vthr,low, a first intermediate voltage threshold Vthr,<NUM> and a second intermediate voltage threshold Vthr,<NUM>. In this example, the diagnostic voltage Vd in a high diagnostic voltage sub-range above the high voltage threshold Vthr,high or in a low diagnostic voltage sub-range below the high voltage threshold Vthr,high indicates a normal operational state of the speed measurement circuit <NUM>, whereas the diagnostic voltage Vd in a first intermediate diagnostic voltage sub-range between the high voltage threshold Vthr,high and the first intermediate voltage threshold Vthr,<NUM> indicates a first predefined abnormal operational state of the speed measurement circuit <NUM>, the diagnostic voltage Vd in a second intermediate diagnostic voltage sub-range between the first and second intermediate voltage thresholds Vthr,<NUM>, Vthr,<NUM> indicates a second predefined abnormal operational state of the speed measurement circuit <NUM> and the diagnostic voltage Vd in a third intermediate diagnostic voltage sub-range between the second intermediate voltage threshold Vthr,<NUM> and the low voltage threshold Vthr,low indicates a third predefined abnormal operational state of the speed measurement circuit <NUM>.

While the example of <FIG> applies two intermediate voltage thresholds Vthr,<NUM>, Vthr,<NUM> and, consequently, three intermediate diagnostic voltage sub-ranges that each represent a respective one of the three (different) predefined abnormal operational states of the speed measurement circuit <NUM>, in general the range of voltages between the high and low threshold voltages Vthr,high, Vthr,low may be divided by one or more intermediate voltage thresholds Vthr,k into respective two or more intermediate diagnostic voltage sub-ranges that each represent a respective one of two or more predefined abnormal operational states of the speed measurement circuit <NUM>. Moreover, in a variation of the example which is not part of the invention described via references to <FIG>, there may be only a single intermediate diagnostic voltage sub-range that is associated with a predefined abnormal operational state of the speed measurement circuit <NUM>. In such a scenario the intermediate voltage sub-range may be defined via two intermediate voltage thresholds Vthr,<NUM>, Vthr,<NUM> (with Vthr,<NUM> > Vthr,<NUM>) that define a limited sub-range of the range from Vthr,low to Vthr,high. Consequently, with the knowledge of the voltage thresholds Vthr,high, Vthr,low, Vthr,k the controller <NUM> is able to detect the operational state of the speed measurement circuit <NUM> based on the diagnostic voltage Vd received as the diagnostic signal <NUM> from the state detector <NUM>.

According to an example, the diagnostic voltage Vd that serves to indicate a given (normal or abnormal) operational state of the speed measurement circuit <NUM> may be set or adjusted to any voltage within the diagnostic voltage sub-range that represents the given operational state, whereas in another example the diagnostic voltage Vd may be set or adjusted to a predefined voltage within the diagnostic voltage sub-range that represents the given operational state.

In the state detector <NUM>, the signal voltage V<NUM> falling within a high signal voltage sub-range above the high reference voltage Vref,high or within a low signal voltage sub-range below the low reference voltage Vref,low serves as an indication of a normal operational state of the speed measurement circuit <NUM> and, consequently, the state detector <NUM> may be arranged to convert such signal voltages V<NUM>, respectively, into a diagnostic voltage Vd that is within the high or low diagnostic voltage sub-range to indicate the normal operational state to the controller <NUM>. On the other hand, instead of indicating one of the high state or the low state (and hence a normal operational state of the speed measurement circuit <NUM>), the signal voltage V<NUM> may fall into a signal voltage sub-range that serves as an indication of a predefined abnormal operational state of the speed measurement circuit <NUM>. In this regard, there may be one or more predefined signal voltage sub-ranges that are each associated with a respective abnormal operational state of the speed measurement circuit <NUM> and that are, consequently, each associated with the respective diagnostic voltage sub-range that represents the respective abnormal operational state of the speed measurement circuit <NUM>. Consequently, the state detector <NUM> may be arranged to convert the signal voltage V<NUM> that falls within a predefined signal voltage sub-range that is associated with a respective abnormal operational state into a diagnostic voltage Vd that is within a diagnostic voltage sub-range that represents the respective abnormal operational state.

While the example described in the foregoing with references to the illustration of <FIG> applies the diagnostic voltage Vd as an example of the diagnostic value, the example readily generalizes into diagnostic values of different type, mutatis mutandis.

<FIG> schematically illustrates an implementation of the speed measurement circuit <NUM> according to an example. Therein, the state detector <NUM> comprises the first resistor R<NUM>, a second resistor R<NUM> and a diode D<NUM>, where the signal line <NUM> is coupled to the ground potential VGND via the first resistor R<NUM> (as in the state detector <NUM>) and where the operating voltage Vs is coupled to the signal line <NUM> via the second resists R<NUM> and, optionally, through the diode D<NUM>. The coupling of the signal line <NUM> and the high and low reference voltages Vref,high, Vref,low to the first and second comparators <NUM>, <NUM> is the same as described in the foregoing for the state detector <NUM>. Moreover, the operation of the state detector <NUM> with respect to respective operation of the first and second comparators <NUM>, <NUM> is the same as described in the foregoing for the state detector <NUM>, the respective voltages provided from the respective outputs of the first and second comparators <NUM>, <NUM> thereby serving as the state indication <NUM>.

The state detector <NUM> further comprises a diagnostic voltage generator <NUM> that is arranged to generate, based on the signal voltage V<NUM>, the diagnostic voltage Vd and to provide the diagnostic voltage Vd as the diagnostic signal <NUM> output from the state detector <NUM>. Along the lines described in the foregoing, the diagnostic voltage generator <NUM> may be arranged to convert the signal voltage V<NUM> that falls within a predefined signal voltage sub-range that is associated with a respective abnormal operational state into a diagnostic voltage Vd that is within a diagnostic voltage sub-range that represents the respective abnormal operational state. Non-limiting examples of such signal voltage sub-ranges include the following:.

The signal voltage V<NUM> may be considered to be close to a respective one of the error voltages Verr,k if it is within a predefined margin Merr from the respective error voltage Verr,k, i.e. Verr,k - Merr < Verr,k < Verr,k + Merr.

Assuming the exemplifying error voltages Verr,<NUM>, Verr,<NUM>, Verr,<NUM> and corresponding diagnostic voltage sub-ranges (or respective predefined voltages within the corresponding diagnostic voltage sub-ranges) defined for the diagnostic voltage Vd in the example of <FIG>, the diagnostic voltage generator <NUM> may be arranged to convert the signal voltage V<NUM> that is within the margin ±Merr from the first error voltage Verr,<NUM> into the diagnostic voltage Vd within the first intermediate diagnostic voltage sub-range, to convert the signal voltage V<NUM> that is within the margin ±Merr from the second error voltage Verr,<NUM> into the diagnostic voltage Vd within the second intermediate diagnostic voltage sub-range, and to convert the signal voltage V<NUM> that is within the margin ±Merr from the third error voltage Verr,<NUM> into the diagnostic voltage Vd within the third intermediate diagnostic voltage sub-range. Moreover, the diagnostic voltage generator <NUM> may be further arranged to convert the signal voltage V<NUM> that exceeds the high reference voltage Vref,high into the diagnostic voltage Vd within the high diagnostic voltage sub-range and to convert the signal voltage V<NUM> that is below the low reference voltage Vref,low into the diagnostic voltage Vd within the low diagnostic voltage sub-range.

In a non-limiting example, the speed sensor <NUM> may comprise a hall speed sensor, the operating voltage Vd may be <NUM> V (with the ground potential VGND representing <NUM> V) and each of the first and second resistors R<NUM>, R<NUM> may have resistance <NUM> kΩ. Consequently, the first error voltage Verr,<NUM> may be approximately <NUM> V, the second error voltage Verr,<NUM> may be approximately <NUM> V, the third error voltage Verr,<NUM> may be approximately <NUM> V and the margin Merr may be approximately <NUM> V, whereas the high reference voltage Vref,high may be set to <NUM> V and the low reference voltage Vref,low may be set to <NUM> V.

In an example, the diagnostic voltage generator <NUM> may be arranged to apply a linear conversion from the signal voltage V<NUM> to the diagnostic voltage Vd. Such linear conversion may involve scaling of the signal voltage V<NUM> by a predefined scaling factor to derive the corresponding diagnostic voltage Vd. In an example, the scaling factor is smaller than unity, the diagnostic voltage generator <NUM> hence serving to attenuate the signal voltage V<NUM> in order to derive the diagnostic voltage Vd, whereas in another example the scaling factor is larger than unity, the diagnostic voltage generator <NUM> hence serving to amplify the signal voltage V<NUM> in order to derive the diagnostic voltage Vd, Such scaling of the signal voltage V<NUM> in order to derive the diagnostic voltage Vd, may be provided to convert the signal voltage V<NUM> into a voltage range that is suitable for the controller <NUM>. In a further example, the scaling factor is (substantially) unity, the diagnostic voltage generator <NUM> hence serving to pass the signal voltage V<NUM> as the diagnostic voltage Vd,.

<FIG> schematically illustrates some components of the diagnostic voltage generator <NUM> according to an example, comprising an amplifier <NUM> having the signal line <NUM> coupled to its first input terminal and the output of the amplifier <NUM> coupled to its second input terminal with the amplifier <NUM>. The amplifier <NUM> may comprise a differential amplifier that is arranged to provide an output voltage V<NUM> that is derived as the difference between the respective voltages received at its first and second input terminals multiplied by the predefined scaling factor gd, e.g. as V<NUM> = gd(V<NUM> - V<NUM>), which serves as a buffer with setting gd = <NUM>. <FIG> schematically illustrates some components of the diagnostic voltage generator <NUM> according to another example, comprising the amplifier <NUM> having the signal line <NUM> coupled to its first input terminal and a diagnostic reference voltage Vref,d coupled to its second input terminal. Along the lines of the example above, the amplifier <NUM> may comprise a differential amplifier that is arranged to provide an output voltage V<NUM> that is derived as the difference between the respective voltages received at its first and second input terminals multiplied by a predefined scaling factor gd, e.g. as V<NUM> = gd(V<NUM> - Vref,d). In an example, the scaling factor gd is larger than one and it may be referred to as a gain factor, whereas in another example the scaling factor gd is smaller than one and it may be referred to as an attenuation factor.

The diagnostic voltage generator <NUM> may provide the output voltage V<NUM> as the diagnostic voltage Vd or, optionally (as shown in the respective illustrations of <FIG>), the diagnostic voltage generator <NUM> may be arranged to apply a low pass filter <NUM> to the output voltage V<NUM> and provide the low-pass filtered output voltage as the diagnostic voltage Vd.

The parameters in the examples <FIG>, i.e. the scaling factor gd and the diagnostic reference voltage Vref,d (if applicable) are selected, in view of respective characteristics of the first and second resistors R<NUM>, R<NUM>, the high and low reference voltages Vref,high, Vref,low, the applied speed sensor <NUM> and/or the applied operating voltage Vs such that a desired conversion from the signal voltage V<NUM> to the diagnostic voltage Vd is provided to ensure suitable handling of the diagnostic signal <NUM> in the controller <NUM>.

Referring back to the speed measurement circuit <NUM>, the controller <NUM> may be arranged to compute the rotation speed and possibly also construct the digital speed signal based on the state indications <NUM> obtained from the state detector <NUM> in dependence of the diagnostic signal <NUM>. In this regard, the controller <NUM> may be arranged to determine, based on the diagnostic signal <NUM>, whether the operational state of the speed measurement circuit <NUM> is normal or abnormal: in case the diagnostic signal <NUM> indicates the normal operational state, the controller <NUM> may proceed into computing the rotation speed and providing the speed indication <NUM> to indicate the computed rotation speed as described in the foregoing in context of the controller <NUM>, whereas in case the diagnostic signal indicates an abnormal operational state, the controller <NUM> may issue an operational status indication <NUM> pertaining to an abnormal operational state of speed measurement circuit <NUM> identified based on the diagnostic signal <NUM>. In case of an abnormal operational state, the controller <NUM> may, optionally, refrain from computing the rotation speed and/or providing the speed indication <NUM> due to possible malfunction appearing in the speed measurement circuit <NUM>. Moreover, in case of the normal operational state, the controller <NUM> may optionally issue the operational status indication <NUM> as one pertaining to the normal operational state of the speed measurement circuit <NUM>.

Along the lines described in the foregoing, the diagnostic signal <NUM> may be arranged to indicate one of one or more predefined abnormal operational states of the speed measurement circuit <NUM>, such that the diagnostic value conveyed by the diagnostic signal <NUM>, e.g. the diagnostic voltage Vd, identifies the abnormal operational state. The abnormal operational states may involve two types thereof: in a first type of abnormal operational states the state indications <NUM> obtained from the state detector <NUM> (and/or the digital speed signal derived therefrom) indicate presence of one or more pulses or a pulse train but the diagnostic value conveyed by the diagnostic signal <NUM> reveals a failure in operation of the state detector <NUM> (e.g. a failed electrical connection therein or thereto), whereas in a second type of abnormal operational states the state indications <NUM> obtained from the state detector <NUM> (and/or the digital speed signal derived therefrom) do not indicate presence of a pulse train (which already serves as an indication of malfunction in the state detector <NUM>) while the diagnostic value conveyed by the diagnostic signal <NUM> further confirms the failure in (e.g. electrical connections to or within) the state detector <NUM>.

As described in the foregoing, the diagnostic signal <NUM> may provide the controller <NUM> with a time series of diagnostic values (e.g. one derived based on the time-varying diagnostic voltage Vd) that is descriptive of the operational state of speed measurement circuit <NUM> as a function of time and, consequently, the controller <NUM> may derive the operational status indication <NUM> based on one or more diagnostic values received in the diagnostic signal <NUM> (e.g. based on the diagnostic voltage Vd at a given time instant or during a given time segment). The controller <NUM> may be arranged to derive the operational status indication <NUM> based on a time segment of the diagnostic signal <NUM> (e.g. based on the diagnostic voltage Vd or changes therein during the time segment) having at least a predefined duration. This may facilitate avoiding unintentionally considering time periods during which the signal voltage V<NUM> increases from the low reference voltage Vref,low to the high reference voltage Vref,high or time periods during which the signal voltage V<NUM> decreases from the high reference voltage Vref,high to the low reference voltage Vref,low that periodically occur during normal operational state of the speed measurement circuit <NUM> as an indication of an abnormal operational state.

Depending on characteristics of the diagnostic signal <NUM> received at the controller <NUM>, the operational status indication <NUM> may comprise one of an indication of normal operational state of the speed measurement circuit <NUM> or an indication of abnormal operational state of the speed measurement circuit <NUM>. Moreover, in case the operational status indication <NUM> reports abnormal operational state, the operational status indication <NUM> may further comprise an indication concerning characteristics of the abnormal operational state of the speed measurement circuit <NUM> derivable at the controller <NUM> based on the diagnostic signal <NUM>, e.g. based on known predefined mapping between diagnostic values (e.g. diagnostic voltages Vd) and value ranges (e.g. the diagnostic voltage sub-ranges) corresponding to the abnormal operational states of the speed measurement circuit <NUM>.

The operational status indication <NUM> issued by the controller <NUM> may be provided, for example, to a system controller to enable continuous monitoring of operation of the combustion engine, rotation speed of which the speed measurement circuit <NUM> serves to measure. The system controller, in turn, may respond to an abnormal operational state of the speed measurement circuit <NUM> indicated via the operational status indication <NUM> by showing an alert or warning in this regard via a user interface (UI) and/or by storing an indication in this regard in a memory. The alert/warning shown via the UI and/or the indication stored in the memory may indicate presence of an abnormal operational state of the speed measurement circuit <NUM> and it may further comprise the indication concerning characteristics of the abnormal operational state of the speed measurement circuit <NUM>.

<FIG> schematically illustrates the relationship between the signal voltage V<NUM> received at the state detector <NUM>, the pulse train derived in the controller <NUM>, the output voltage V<NUM> of the amplifier <NUM>, and the diagnostic voltage Vd at the output of the (optional) low pass filter <NUM> according to an example. Herein, the illustrations (a) and (b) are the same ones already described with references to <FIG>. The illustration (c) depicts the output voltage V<NUM> of the amplifier <NUM> as a function of time, whereas the illustration (d) depicts the diagnostic voltage Vd as a function of time, where the diagnostic voltage Vd is obtained by low pass filtering the output voltage V<NUM>. Hence, the output voltage V<NUM> (and the diagnostic voltage Vd) follows the envelope of the signal voltage V<NUM>, while the amplitude may be different due to scaling that may take place in the diagnostic voltage generator <NUM>.

<FIG> schematically illustrates the relationship between the signal voltage V<NUM> received at the state detector <NUM> (the illustration (a)), the pulse train derived in the controller <NUM> (the illustration (b)), the output voltage V<NUM> of the amplifier <NUM> (the illustration (c)), and the diagnostic voltage Vd at the output of the (optional) low pass filter <NUM> (the illustration (d)) according to another example. Therein, the first two pulses are similar to those of the corresponding illustrations of <FIG>, whereas after the second pulse (at time instant t<NUM>) a failure occurs in the speed measurement circuit <NUM>, leading to a situation where the signal voltage V<NUM> is set to the voltage Verr,<NUM> and, consequently, resulting in the output voltage V<NUM> substantially immediately following the change in the signal voltage V<NUM> (possibly at different amplitude) and the diagnostic voltage Vd following the change in the signal voltage V<NUM> (possibly at different amplitude) with a delay arising from operation of the low pass filter <NUM>. Referring to the example described in the foregoing, this may serve as an indication of a failed electrical connection in the signal line <NUM> between the state detector <NUM> and the speed sensor <NUM> occurring at the time instant t<NUM>. Furthermore, at time instant t<NUM> there is a momentary increase in the signal voltage V<NUM>, which may be caused for example by structural vibrations etc. momentarily restoring the electrical connection in the signal line <NUM> between the state detector <NUM> and the speed sensor <NUM>. This may result in a short pulse in the pulse train derived in the controller <NUM> and result in the output voltage V<NUM> substantially immediately following the change in the signal voltage V<NUM> (possibly at different amplitude). On the other hand, due to delay arising from operation of the low pass filter <NUM>, the diagnostic voltage Vd exhibits only a small change following the change in the signal voltage V<NUM> (possibly at different amplitude) but failing to reach voltage level that corresponds to the high state of the signal voltage V<NUM>. Hence, the controller <NUM> is able to observe the following aspects from the output voltage V<NUM> (if provided as the diagnostic voltage Vd) and/or the from the diagnostic voltage Vd:.

The controller <NUM> may be provided as an electrical circuit arranged to carry out the functionality described in the foregoing for the controller <NUM>, by a processor provided with program instructions that cause the processor to carry out the functionality described in the foregoing for the controller <NUM>, or by a combination of the two. Herein, the reference(s) to a processor should not be understood to encompass only programmable processors, but also dedicated circuits such as field-programmable gate arrays (FPGA), application specific circuits (ASIC), etc..

In the foregoing, various aspects related to operation of the speed measurement circuit <NUM> are described with references to the state detector <NUM> and/or to the controller <NUM>. These aspects of operation may be, alternatively, provided and/or described as steps of a respective method. As non-limiting examples in this regard, <FIG> depicts a flowchart that illustrates steps of a method <NUM> that may be implemented by one or more circuits or apparatuses in order to provide the functionality described in the foregoing with references to the state detector <NUM> and/or to the controller <NUM>. The method <NUM> may be varied in a number of ways, for example in accordance with the examples described in the foregoing and/or in the following.

The method <NUM> serves to measure a rotation speed of a combustion engine and it proceeds from receiving, from the speed sensor <NUM> coupled to measure the rotation speed of the combustion engine, an electrical signal that has a time-varying signal voltage V<NUM> that exhibits local maxima at a frequency that has a predefined relationship to the rotation speed, as indicated in block <NUM>. The method <NUM> further comprises deriving, based on the electrical signal, the state indication <NUM> that indicates whether the electrical signal represents one of a high state or a low state, as indicated in block <NUM>, and deriving, based on the electrical signal, the diagnostic signal <NUM> that is descriptive of the operational state of the speed measurement circuit <NUM>, as indicated in block <NUM>. The method <NUM> further comprises deriving the rotation speed based on a time series of the state indications <NUM> in dependence of the diagnostic signal <NUM> in view of said predefined relationship, as indicated in block <NUM>.

Claim 1:
A speed measurement circuit (<NUM>) for measuring a rotation speed of a combustion engine, the speed measurement circuit (<NUM>) comprising:
a state detector (<NUM>) coupled between an operating voltage (Vs) and a ground potential (VGND) and coupled to receive, from a speed sensor (<NUM>), an electrical signal that has a time-varying signal voltage (V<NUM>) that exhibits local maxima at a frequency that has a predefined relationship to the rotation speed, wherein the state detector (<NUM>) is arranged to derive, based on the electrical signal,
a state indication (<NUM>) that indicates whether the electrical signal represents one of a high state or a low state, and
a diagnostic signal (<NUM>) that is descriptive of the operational state of the speed measurement circuit (<NUM>), wherein the diagnostic signal (<NUM>) conveys a diagnostic value that is descriptive of current operational state of the speed measurement circuit (<NUM>), wherein current operational state is one of a normal operational state or an abnormal operational state and wherein the state detector (<NUM>) is arranged to derive the diagnostic value based on the signal voltage (V<NUM>) of the electrical signal; and
characterized in that the speed measurement circuit (<NUM>) comprises a controller (<NUM>) coupled to receive the state indications (<NUM>) and the diagnostic signal (<NUM>) and arranged to compute the rotation speed based on a time series of the state indications (<NUM>) in dependence of the diagnostic signal (<NUM>) in view of said predefined relationship,
wherein the state detector (<NUM>) has defined therefor:
two or more predefined signal voltage sub-ranges, each associated with a respective abnormal operational state of the speed measurement circuit (<NUM>), and
two or more predefined intermediate diagnostic voltage sub-ranges, each representing a respective abnormal operational state of the speed measurement circuit (<NUM>).