Evaluation circuit and method for monitoring and reading out a passive rotational speed sensor
Patent Information
- Application Number
- EP2023702300
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- Priority Date
- 2022-02-02
- Filing Date
- 2023-01-26
- Publication Date
- 2024-12-11
AI Technical Summary
Conventional evaluation circuits for passive speed sensors in vehicles lack reliability due to complexity and interference issues, leading to short circuits, incorrect installations, and high production costs, which hinder long-term operational effectiveness.
An evaluation circuit with a comparator, operational amplifier, and voltage limiter, along with redundant signal outputs and a control unit, is designed to detect faults and ensure reliable monitoring by comparing sensor signals with a reference voltage and filtering out interference, using discrete components for cost-effectiveness and adaptability.
The solution provides reliable and cost-effective monitoring and fault detection for passive speed sensors, ensuring long-term operational reliability and reducing interference, enabling accurate wheel speed measurement even in harsh environments.
Smart Images
Figure 1.1
Abstract
Description
[0001] DESCRIPTION
[0002] Evaluation circuit and method for monitoring and reading a passive speed sensor
[0003] The present invention relates to an evaluation circuit for a passive speed sensor (speed sensor), a method for monitoring and reading the passive speed sensor and in particular to an input circuit for passive speed sensors.
[0004] Passive speed sensors are used in vehicles, for example, to monitor the speed of wheels for an anti-lock braking system (ABS) or other vehicle control and regulation systems. This enables targeted intervention if the wheel speed does not correspond to a target value. The wheel can be any wheel, such as a magnetic wheel coupled to a braked wheel or a gear (e.g. in the transmission). Such speed sensors are exposed to considerable environmental influences and must be highly reliable in continuous operation. Malfunctions include, for example, short circuits to the supply voltage (e.g. battery voltage) or to ground, a missing connection, or incorrect installation. However, the desired high level of operational reliability can only be ensured if damage to the speed sensor is detected in a timely manner.
[0005] For this purpose, specific input circuits are used which, on the one hand, reliably record the sensor signal of the speed sensor and, on the other hand, allow tests for the speed sensor to detect errors.
[0006] However, conventional input circuits do not yet offer the desired level of reliability, as the sometimes complex integrated circuits contain many sources of interference. Therefore, they are often not trouble-free for extended periods (e.g., more than 15 years). Furthermore, due to their complexity, they are often not cost-effective to produce. Therefore, there is a need for input circuits or, more generally, evaluation circuits for passive speed sensors that ensure reliable monitoring and operation during long-term operation.
[0007] At least some of the above-mentioned problems are solved by the evaluation circuit according to claim 1 and a method for operating the evaluation circuit according to claim 11. The dependent claims relate to further advantageous developments of the subject matter of the independent claim.
[0008] The present invention relates to an evaluation circuit for a passive speed sensor of a vehicle (e.g., commercial vehicle), wherein the passive speed sensor is designed to detect a speed of a wheel and, based thereon, to generate a sensor signal. The evaluation circuit comprises a first terminal and a second terminal for electrically connecting the speed sensor, a comparator, an operational amplifier, a first signal output, and a second signal output. The comparator is designed to compare the sensor signal with a reference voltage and, based on the comparison, to generate a pulsating output signal. The operational amplifier is configured as a buffer circuit and maintains the reference voltage at a predetermined level.The first signal output and the second signal output are each connected to an output of the comparator to provide a redundant pulsating output signal for determining the wheel's rotational speed. The comparator is also connected to the first and second terminals.
[0009] Optionally, the comparator comprises a further operational amplifier with an inverting and a non-inverting input, wherein the first terminal and second terminal are each coupled to one of the inputs, so that the further operational amplifier effectively analyzes a differential signal from an input / output of the passive speed sensor. At the same time, the reference voltage is applied to one of the inputs of the further operational amplifier, so that a predetermined voltage level is present there. Optionally, the evaluation circuit further comprises a voltage limiter configured to limit the input voltages of the operational amplifier.
[0010] Optionally, the operational amplifier is designed as a voltage follower. In particular, the operational amplifier is designed to provide a low-impedance voltage to the comparator. For example, the voltage can be provided in a low-impedance manner from a non-inverted input of the operational amplifier to an inverted input of the comparator (an optional resistor can be inserted between them). This voltage also serves as a reference voltage for positive feedback of an output signal from the comparator.
[0011] Optionally, the operational amplifier includes a sensor signal input, a reference signal input, and an output. The sensor signal input is connected to the output. The voltage limiter can comprise two oppositely connected diodes, and a current node between the oppositely connected diodes can be connected to the output of the operational amplifier to safely limit the comparator's input voltage to its input voltage range (or functional voltage range).
[0012] Optionally, the evaluation circuit includes at least one of the following inputs and outputs:
[0013] - a test signal input for feeding in a test signal, wherein the test signal input is connected to the first terminal and / or to the second terminal,
[0014] - a first status signal output connected to the first terminal,
[0015] - a second status signal output connected to the second terminal.
[0016] Optionally, the evaluation circuit comprises a control unit which is designed to receive signals from one or more of the following connections: the first signal output, - the second signal output,
[0017] - the first status signal output,
[0018] - the second status signal output,
[0019] - the test signal input.
[0020] Optionally, the control unit is configured to monitor the passive speed sensor based on the received signals. The control unit can also optionally determine the wheel speed based on the pulsating output signal at the first signal output and / or the second signal output. However, the speed can also be detected by another unit (e.g., a control unit in the vehicle).
[0021] Optionally, the control unit is further configured to detect at least one of the following errors:
[0022] - a short circuit of the first terminal to ground,
[0023] - a short circuit of the second terminal to ground,
[0024] - a short circuit of the first terminal to a supply voltage,
[0025] - a short circuit of the second terminal to a supply voltage,
[0026] - a short circuit between the first terminal and the second terminal,
[0027] - crosstalk between the first terminal and the second terminal or crosstalk between an external signal line to the first terminal or to the second terminal,
[0028] - an open electrical connection at the first terminal or at the second terminal (e.g. a missing or incorrectly connected speed sensor).
[0029] The detection of the error can be based on signals at at least one of the following outputs: at the first status signal output, - at the second status signal output,
[0030] - at the first signal output,
[0031] - at the second signal output.
[0032] In particular, differential signals can also be recorded.
[0033] Optionally, the first terminal or the second terminal is connected to a supply terminal (e.g. indirectly via at least one resistor) so that in a fault-free state, even when the wheel is stationary, a voltage is present at the first terminal and / or the second terminal or drops between the two terminals.
[0034] Optionally, the control unit is designed to detect the error by measuring the voltage at the first connection or at the second connection using the first status signal output or the second status signal output. For this purpose, the control unit can input a test signal at the test signal input or not input a test signal or set the test signal input to a predetermined potential level (e.g. ground). This makes it possible to detect one of the above-mentioned errors before the start of a journey, i.e. when the vehicle is at a standstill or in a low frequency range. In particular, the control unit can also detect the difference signal between the first connection and the second connection (i.e. the voltage drop) in order to detect one of the above-mentioned errors.
[0035] Optionally, the evaluation circuit includes a low-pass filter on at least one of the following outputs or connections:
[0036] - at the first signal output,
[0037] - at the second signal output,
[0038] - at the first status signal output,
[0039] - at the second status signal output, between the first and second terminals. This makes it possible to detect a DC voltage component at the status signal outputs with high sensitivity. These DC voltage components allow the detection of short circuits, reverse polarity, or a faulty connection of the speed sensor. Furthermore, the low-pass filters filter out potential interference signals (e.g., from solenoid valves of a brake), which could otherwise lead to errors in speed detection.
[0040] Embodiments also relate to an anti-lock braking system (ABS) for a (commercial) vehicle with at least one passive speed sensor and at least one previously described evaluation circuit. Generally, at least one speed sensor is provided for each (braked) vehicle wheel (but there may also be several). The evaluation circuit can be integrated, for example, into an ABS control unit, but it can also be configured separately.
[0041] The vehicle does not have to be a commercial vehicle. The examples are applicable to any vehicle or other application areas for speed sensors and are intended to include these.
[0042] Embodiments also relate to a method for monitoring and reading a passive speed sensor, wherein the method carries out an evaluation of signals of the passive speed sensor of a vehicle using a previously described evaluation circuit.
[0043] Optionally, the method includes detecting a short circuit and / or a faulty contact and / or crosstalk. To this end, at least one of the following steps can be performed:
[0044] - Input of a test signal on the test signal input,
[0045] - Analysis of a signal status on the first status signal output,
[0046] - Analysis of a signal status on the second status signal output,
[0047] - Analysis of a signal at the first signal output and / or the second signal output, or of a differential signal between the first signal output and the second signal output. A faulty contact should include, in particular, an open contact and thus also the absence of the speed sensor.
[0048] It is understood that all of the previously described functions of the evaluation circuit can be implemented as additional optional process steps. Furthermore, it is understood that the order in which the steps are listed does not restrict the order in which the process steps are executed. The steps can also be performed in a different order, or only some of the process steps are executed.
[0049] Embodiments overcome problems of conventional evaluation circuits. Conventional evaluation circuits for passive speed sensors use discrete and integrated input circuits, which have various problems with signal conditioning. Furthermore, conventional evaluation circuits do not offer the possibility of providing output signals based on targeted test signals. Embodiments overcome these problems and provide a cost-effective, testable input circuit for a passive speed sensor.
[0050] In particular, the evaluation circuit is used as an input circuit, and (only) discrete components are used, which operate very reliably and can be adapted to requirements over a very wide range. Further advantages of exemplary embodiments are that there are few problems with attaching the speed sensors in the vehicle, namely through a reduction in high-frequency signal components that can arise from poor speed sensor mountings. Exemplary embodiments also enable (analog) filtering of analog feedback down to very low frequency ranges, which leads to savings in computing resources during digital filtering of the signals. Otherwise, these signals would have to be digitally filtered at a high cost, which would consume computing resources. Exemplary embodiments also allow feedback of the sensor amplitude.No special components are required, and a wide variety of tests can be performed without great effort. The embodiments of the present invention will be better understood with the following detailed description and the accompanying drawings of the various embodiments, which, however, should not be construed as limiting the disclosure to the specific embodiments, but are for explanation and understanding only.
[0051] Fig. 1 shows an evaluation circuit for a passive speed sensor according to an embodiment of the present invention.
[0052] Fig. 2 shows an exemplary embodiment of the evaluation circuit with further details. Fig. 3 shows an exemplary embodiment of a possible wiring of the evaluation circuit.
[0053] When an element is described below as being "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be other intervening elements. Conversely, when an element is described as being "directly connected" or "directly coupled" to another element, no intervening elements are present. Other words used to describe the relationship between elements should be interpreted in the same way (e.g., "between" as opposed to "directly between," "adjacent" as opposed to "directly adjacent," etc.).
[0054] The terminology used herein is for the purpose of describing illustrative embodiments only and is not intended to be limiting. The singular forms used herein include the plural forms, unless the context clearly indicates otherwise. It is further understood that the terms "comprising" and "having," respectively, when used herein, refer to the presence of certain features, steps, acts, elements, and / or components, but do not preclude the presence or addition of one or more other features, steps, acts, elements, components, and / or groups thereof. Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which the examples belong. It is further understood that terms, e.g.those defined in commonly used dictionaries should be interpreted to have a meaning consistent with their meaning in the context of the relevant field and should not be interpreted in an idealized or overly formal sense unless expressly so defined herein.
[0055] Finally, the phrase "elements connected in series / parallel between two components" should be understood in the context of an electrical circuit, in the sense that the relative position of the components to each other along a current direction is defined, resulting in a series or parallel connection. The word "between" therefore does not necessarily refer to the physical position or arrangement on a circuit substrate (e.g., printed circuit board).
[0056] Fig. 1 shows an evaluation circuit 100 for a passive speed sensor 10 according to an embodiment. The evaluation circuit 100 can also be referred to as an input circuit. The passive speed sensor 10 is designed to detect a speed of a wheel and to generate a sensor signal based thereon. The evaluation circuit 100 comprises a first terminal 101 and a second terminal 102, which are provided for the electrical connection of the speed sensor 10. The evaluation circuit 100 also comprises a comparator 110, which is designed to compare the sensor signal with a reference voltage and to generate a pulsating output signal based on the comparison. The evaluation circuit 100 further comprises an operational amplifier 120, which is configured as a buffer circuit and which maintains the reference voltage at a predetermined level. The reference voltage can, for example, be a center voltage (e.g.of the operational amplifier 120 or an amplifier in the comparator 110). In the circuit of Fig. 1, the buffer circuit 120 is not controlled by a signal at the second terminal 102, but rather provides a low-impedance reference voltage.
[0057] The evaluation circuit 100 also includes a first signal output 141 and a second signal output 142, each connected to an output of the comparator 110 to provide the pulsating output signal redundantly. This offers the advantage that errors in the signal transmission to downstream circuit components (dirty contacts, leakage currents, interference with neighboring signal transmissions, etc.) can be reliably detected or eliminated.
[0058] In the simplest case, the passive speed sensor 10 is a coil in which a periodic electric current is induced by the rotation of a magnetic wheel / gearwheel. The amplitude of this current or of a voltage (e.g., across a resistor) is generally not constant, but depends on the rotational speed. Therefore, at higher speeds, for example, larger amplitude values occur, which makes evaluation more difficult, particularly if the same sensitivity is to be achieved for low speeds as for high speeds. Therefore, the evaluation circuit 100 from Fig. 1 optionally comprises a voltage limiter 130 which is designed to reliably limit the input voltage of the comparator 110 to its input voltage range (e.g., 0V to the comparator's supply voltage). In this way, large fluctuations in the amplitude values can be avoided.The dashed line indicates that this is an optional component.
[0059] Fig. 2 shows an embodiment of the evaluation circuit 100, which has further details. This evaluation circuit 100 can have the following connections (as input, output or for monitoring): a first connection 101, a second connection 102, a supply connection 104, a first signal output 141, a second signal output 142, a first status signal output 151, a second status signal output 152, a test signal input 160, a first ground connection 106a and a second ground connection 106b. The first ground connection 106a can be a common ground with a downstream microcontroller (control unit). The second ground connection can be a vehicle ground, for example. They can also be connected to one another. The supply connection 104 can, for example, be used for a connection to a vehicle battery or another power supply.
[0060] In addition, the evaluation circuit 100 again comprises the comparator 110, the operational amplifier 120 and the voltage limiter 130 from Fig. 1.
[0061] Comparator 110 includes a reference signal input (-) and a signal input (+). The reference signal input can be an inverted input (-) and the signal input can be a non-inverted input (+) of another operational amplifier (but it can also be the other way around).
[0062] The operational amplifier 120 may also have a reference signal input (+) and a signal input (-). The signal input (-), for example, is the inverted input and is connected to the output of the operational amplifier 120. Therefore, the operational amplifier 120 practically does not amplify (G=1), but serves as a buffer circuit to provide a stable reference voltage. In this circuit, the output impedance of the operational amplifier 120 is very low (e.g., less than 10 ohms).
[0063] The voltage limiter 130 comprises, for example, a diode arrangement with at least two diodes arranged with opposite polarity, which connect the first terminal 101 to the second terminal 102. A current node between the two diodes can be connected to the output of the operational amplifier 120. Due to its wiring, the voltage limiter 130 can reliably limit an input voltage of the comparator 110 to its input voltage range. This is intended to ensure that reliable detection of a sensor signal is always possible. If an input voltage at the comparator 110 were too high, the comparator 110 would not be able to output a sensor signal, since the fluctuations would occur below the operating range.This limitation of the input voltage is particularly advantageous for the passive speed sensors used, since these generate sensor signals with speed-dependent amplitudes and therefore there is a risk that high sensor signals can no longer be reliably detected.
[0064] The first terminal 101 can, for example, be a so-called high-side terminal, since it can be connected to the supply terminal 104, for example, in a series connection of a resistor R10 and a resistor R18. The second terminal 102 can, for example, be a so-called low-side terminal and is connected to the test signal terminal 160, for example, in a series connection of a resistor R11 and a resistor R17.
[0065] The first terminal 101 and the second terminal 102 can also be connected to each other via a resistor R1. A DC voltage component can be dropped across the resistor R1, which can be generated by connecting the first terminal 101 to the supply terminal 104 and which can be used for testing purposes (see below). The first terminal 101 can be connected to the signal input (+) of the comparator 110 via a series connection of a capacitor C4 and a resistor R4. The second terminal 102 can be connected to the reference signal input (-) of the comparator 110 via a series connection of a capacitor C5 and a resistor R5. The inverted input can be used as the reference signal input (-) and the non-inverted input can be used as the signal input (+). High-pass filtering can thus be achieved for both terminals, with the DC voltage component being filtered out.
[0066] The output of comparator 110 may be connected to the output of operational amplifier 120 via two series-connected resistors, a resistor R12 and a resistor R13. A current node between resistor R12 and resistor R13 may be connected to the non-inverted input (+) of comparator 110 via a resistor R16. The output of operational amplifier 120 may also be connected to the inverted input (-) of comparator 120 via a resistor R3. The inverted input (-) of comparator 110 may also be connected to the output of operational amplifier 120 via a capacitor C10 connected in series. Furthermore, the non-inverted input (+) of comparator 110 may be connected to the output of operational amplifier 120 via a capacitor C11.
[0067] The non-inverting input (+) of operational amplifier 120 can be connected to a current node between a resistor R14 and a resistor R15, wherein resistor R14 and resistor R15 are both connected in series between supply terminal 104 and second ground terminal 106b to form a voltage divider. As already mentioned, operational amplifier 120 is configured as a voltage follower to provide a voltage, which can be adjusted using resistor R14 and resistor R15, to comparison operational amplifier 110 via resistor R3 in a low-impedance manner. This voltage also serves as a reference voltage for positively coupling the output signal of comparator 110, which is also configured as an operational amplifier, by means of resistor R12 and resistor R13 via resistor R16 to the non-inverting input (+) of comparator 110.
[0068] According to embodiments, the evaluation circuit may comprise various further filter units:
[0069] A first low-pass filter can be formed between the output of comparator 110 and first signal output 141, with a resistor R6 and a subsequent capacitor C6 connected in series to connect the output of comparator 110 to first ground terminal 106a and to couple first signal output 141 to a current node between resistor R6 and capacitor C6. This first filter unit thus represents a low-pass filter for the signal at first signal output 141.
[0070] A second low-pass filter can be formed between the output of comparator 110 and second signal output 142, wherein a series connection of a resistor R7 and a subsequent capacitor C7 is formed from the output of comparator 110 to first ground terminal 106a, and the second signal output 142 is coupled to a node between resistor R7 and capacitor C7. This second filter unit thus represents a low-pass filter for the output signal at second signal output 142.
[0071] A third low-pass filter can be connected between the first terminal 101 and the first status signal output 151 and comprises a resistor R2 and a capacitor C2, wherein the capacitor C2 connects the first status signal output 151 to the first ground terminal 106a and the resistor R2 connects the capacitor C2 in series with the first terminal 101. This filter unit thus represents a low-pass filter for a signal on the first terminal 101 and / or on the first status signal output 151, wherein the resistor R2 effects a current limitation between the first terminal 101 and the first status signal output 151 (e.g., during a status test).
[0072] A fourth low-pass filter may be connected between the second terminal 102 and the second status signal output 152 and comprises a resistor R8 and a capacitor C3, wherein the capacitor C3 connects the second status signal output 152 to the first ground terminal 106a and the resistor R8 connects the capacitor C3 in series with the second terminal 102. This filter unit thus represents a low-pass filter for a signal on the second terminal 102 and / or on the second status signal output 152, wherein the resistor R8 effects a current limit between the second terminal 102 and the second status signal output 152 (e.g., during a status test).
[0073] The third and fourth low-pass filters can be used to determine the potentially present DC voltage component on the first and second terminals 101, 102 via the first status signal output 151 and the second status signal output 152, respectively. If the DC voltage component does not have an expected value, a potential error such as a short circuit to ground or a short circuit to the supply voltage exists. On the other hand, this DC voltage component can be filtered out by the aforementioned high-pass filters C4, R4 or C5, R5 upstream of the inputs of the comparator 110 and thus does not interfere with the speed signal. A fifth filter unit can be connected between the first terminal 101 and the second terminal 102 and comprises, in series, the resistor R10, a capacitor C9, and the resistor R11, wherein the capacitor C9 can be arranged in the center. The fifth filter unit represents a low-pass filter for a speed signal.This achieves damping so that the signal voltage increases only slightly across the entire usable frequency range. Passive speed sensors are, in the simplest case, a coil, so that faster changes in the magnetic field at higher speeds induce a stronger sensor signal. As a result, the signal amplitude changes with the rotational speed. Strongly fluctuating signal amplitudes are detrimental to subsequent signal analysis. The fifth filter unit therefore dampens the high amplitude components (which primarily contain the high-frequency components) using capacitor C9. As a result, the amplitudes of the sensor signal do not fluctuate as much with the speed.
[0074] It is understood that only the circuit components shown are sufficient for the desired functions. Therefore, further embodiments relate to an evaluation circuit where only the components shown, or a portion thereof, are configured to achieve the desired functions. A significant advantage of embodiments is precisely that the functions are enabled by a simple circuit, without the need for complex integrated circuits such as those used in conventional input circuits. In contrast, embodiments use only discrete components and not multifunctional integrated circuits.
[0075] It is also understood that the described passive components (e.g. resistors and capacitors) have predetermined, specifically selected characteristics (e.g. resistance values, capacitances) in order to achieve a desired effect. This includes, for example, limiting the current and filtering out high / low frequency components. The selected resistance values and the capacitances of the capacitors naturally depend on the specific speed sensors and the vehicle. They should generally be selected so that the sensor signal can be reliably detected (e.g. from a signal strength of 100 mV) and interference signals can be reliably filtered out. Such interference signals include, for example, the switching of solenoid valves (e.g. in the braking system), which can trigger voltage or current pulses.
[0076] Fig. 3 shows a system configuration with the passive speed sensor 10, which can be connected to the first terminal 101 and the second terminal 102 of the evaluation circuit 100. Furthermore, the evaluation circuit 100 is connected to a control unit 200, wherein the first ground terminal 106a forms a common ground for the evaluation circuit 100 and the control unit 200. The first signal output 141 and the second signal output 142 redundantly provide the output variable from the comparator 110 to the control unit 200. The control unit 200 is connected, for example, to the evaluation circuit 100 via the test signal input 160. Furthermore, the control unit 200 can be connected to the evaluation circuit 100 via the first status signal output 151 and the second status signal output 152.
[0077] According to further embodiments, the control unit 200 can be an optional component of the evaluation circuit 100. However, it can also be designed as a separate component, as shown in Fig. 3.
[0078] Embodiments allow the following functions to be controlled by the control unit 200:
[0079] The first terminal 101 can be used to measure a speed sensor voltage (e.g., the DC voltage component) in the low frequency range, for example, to check whether the speed sensor 10 has been correctly installed. For this purpose, the first status signal output 151 can be used, which can measure a voltage level at the first terminal 101.
[0080] The first and second sensor signal outputs 141, 142 ensure redundant acquisition of the sensor signal, so that even if a cable fault occurs on one of the signal lines, reliable speed detection can still be achieved. The control unit 200 can receive both sensor signals and can indicate an error if deviations exceed a tolerance threshold.
[0081] According to embodiments, the control unit 200 uses the test signal input 160 to input targeted test signals and to determine an error based on the response. The test signal acts on the first terminal 101 and the second terminal 102 via the capacitor C9. A response to the test signal can be obtained via the signal outputs 141, 142. In addition, a response can also be tapped at the first status signal output 151 and / or the second status signal output 152. This allows the following errors to be reliably detected and differentiated from one another: a short circuit of the first terminal 101 to ground, a short circuit of the second terminal 102 to ground, a short circuit of the first terminal 101 to the supply voltage, a short circuit of the second terminal to the supply voltage, or a short circuit between the first terminal 101 and the second terminal 102.
[0082] For example, if there is no response to the input of a test signal via test input 160 at the status signal outputs 151, 152 (e.g., if the voltage level there remains constant), it can be assumed that, depending on the applied potential level, there is a short circuit to ground or a short circuit to the supply voltage (battery voltage). From the differences between the two status signals present at the first status signal output 151 and the second status signal output 152, conclusions can be drawn as to whether one of the above-mentioned errors is present.
[0083] Embodiments can be used in particular for anti-lock braking systems for (commercial) vehicles, where (at least) a separate evaluation circuit 100 is provided for each wheel in order to determine the rotational speed of the wheel.
[0084] Further embodiments also relate to a method for monitoring and reading a passive speed sensor, wherein signals from a passive speed sensor 10 of a vehicle are evaluated using the evaluation circuit 100. The method may, in particular, include detecting a short circuit and / or crosstalk. This may be achieved by at least one of the following steps:
[0085] - Input of a test signal on the test signal input 160,
[0086] - Analysis of a signal status on the first status signal output 151 ,
[0087] - Analysis of a signal status on the second status signal output 152,
[0088] - Analysis of a signal of a signal status on the first signal output 141 and / or the second signal output 142.
[0089] It is understood that a test signal does not necessarily have to be input. According to exemplary embodiments, the status at the first terminal 101 and the second terminal 102 can also be analyzed without inputting a signal (via the status signal outputs 151, 152). Since the first terminal 101 is connected to the supply terminal 104, a certain voltage should be present there in a fault-free state. If this is not the case, an error is present, for example.
[0090] All previously described functions of the evaluation unit and / or the control unit 200 can form further optional process steps (filtering of signals, voltage tracking for the reference voltage, etc.).
[0091] The features of the invention disclosed in the description, the claims and the figures may be essential for the realization of the invention, both individually and in any combination.
[0092] LIST OF REFERENCE SYMBOLS
[0093] 10 Speed sensor
[0094] 100 evaluation circuit
[0095] 101 , 102 Connections for the speed sensor
[0096] 104 Supply connection (for power supply)
[0097] 106a first ground connection (e.g. ground of the control unit)
[0098] 106b second ground connection
[0099] 110 comparators (e.g. another operational amplifier)
[0100] 120 operational amplifiers
[0101] 130 voltage limiters
[0102] 141 , 142 signal outputs (redundant)
[0103] 151 , 152 Status signal outputs
[0104] 160 test signal input
[0105] 200 control unit
[0106] R1 , R2, ... various resistors
[0107] C1, C2, ... various capacitors
Claims
PATENT CLAIMS 1. Evaluation circuit (100) for a passive speed sensor (10) of a vehicle, wherein the passive speed sensor (10) is configured to detect the rotational speed of a wheel and to generate a sensor signal based thereon, characterized by a first terminal (101) and a second terminal (102) for the electrical connection of the speed sensor (10); a comparator (110) connected to the first terminal (101) and the second terminal (102) and configured to compare the sensor signal with a reference voltage and to generate a pulsating output signal based on the comparison; an operational amplifier (120) configured as a buffer circuit to maintain the reference voltage at a predetermined level;a first signal output (141 ) and a second signal output (142), wherein the first signal output (141 ) and the second signal output (142) are each connected to an output of the comparator (110) in order to redundantly provide the pulsating output signal for determining the rotational speed of the wheel.; 2. Evaluation circuit (100) according to claim 1 , characterized by a voltage limiter (130) which is designed to limit an input voltage at the comparator (110) to its input voltage range.
3. Evaluation circuit (100) according to claim 2, characterized in that the operational amplifier (120) is designed as a voltage follower, so that the reference voltage for the comparator (110) is available at low impedance.
4. Evaluation circuit (100) according to claim 3, wherein the operational amplifier (120) has a sensor signal input (-), a reference signal input (+) and an output, and the sensor signal input (-) is connected to the output, characterized in that the voltage limiter (130) has two diodes connected in opposite polarity and a current node between the diodes connected in opposite polarity is connected to the output of the operational amplifier (120) in order to reliably limit an input voltage of the comparator (110) to its input voltage range.
5. Evaluation circuit (100) according to one of the preceding claims, characterized in that the circuit has at least one of the following inputs or outputs: - a test signal input (160) for injecting a test signal, wherein the test signal input is connected to the first terminal (101) and / or to the second terminal (102), - a first status signal output (151) which is connected to the first terminal (101), - a second status signal output (152) which is connected to the second terminal (102).
6. Evaluation circuit (100) according to claim 5, characterized by a control unit (200) configured to receive signals from one or more of the following connections: - the first signal output (141 ), - the second signal output (142), - the first status signal output (151 ), - the second status signal output (152), - the test signal input (160), wherein the control unit is further developed to monitor the passive speed sensor (10) based on the received signals.
7. Evaluation circuit (100) according to claim 6, characterized in that the control unit (200) is further developed to detect at least one of the following faults: - a short circuit of the first terminal (101) to ground, - a short circuit of the second terminal (102) to ground, - a short circuit of the first terminal (101) to a supply voltage, - a short circuit of the second terminal (102) to a supply voltage, - a short circuit between the first terminal (101) and the second terminal (102), - crosstalk between the first terminal (101) and the second terminal (102) or crosstalk between an external signal line and the first terminal (101) or the second terminal (102), - an open electrical connection at the first terminal (101) or at the second terminal (102), wherein detection is based on signals at at least one of the following outputs: - at the first status signal output (151 ), - at the second status signal output (152), - at the first signal output (141 ), - at the second signal output (142).
8. Evaluation circuit (100) according to claim 7, characterized in that the first terminal (101) or the second terminal (102) is connected to a supply terminal (104) so that, in a fault-free state, a voltage drops across the first terminal (101) and the second terminal (102) even when the wheel is stationary, and in that the control unit is designed to detect the fault by measuring the voltage at the first terminal (101) or at the second terminal (102) using the first status signal output (151) or the second status signal output (152), wherein the control unit is further designed to feed a test signal or not feed a test signal into the test signal input (160).
9. Evaluation circuit (100) according to one of the preceding claims, characterized in that a low-pass filter is provided at at least one of the following outputs and connections: - at the first signal output (141 ), - at the second signal output (142), - at the first status signal output (151 ), - at the second status signal output (152), - between the first port (101) and the second port (102).
10. Anti-lock braking system, ABS, for a commercial vehicle with at least one passive speed sensor (10), characterized by at least one evaluation circuit (100) according to one of claims 1 to 9.
11. Method for monitoring and reading a passive speed sensor (10), characterized by Evaluation of signals from a passive speed sensor (10) of a vehicle using an evaluation circuit (100) according to one of claims 1 to 9.
12. The method of claim 11, which further comprises at least one of the following steps for detecting a short circuit and / or a faulty contact and / or crosstalk: - Input of a test signal on the test signal input (160), - Analysis of a signal status on the first status signal output (151 ), - Analysis of a signal status on the second status signal output (152), - Analysis of a signal on the first signal output (141) and / or on the second signal output (142) or of a difference signal between the first signal output (141) and on the second signal output (142).