CONTROL CIRCUIT FOR AN ACTIVE SPEED SENSOR

Description

[0001] The present invention relates to a control circuit for an active speed sensor and in particular to a circuit for controlling, signal conditioning and monitoring an active speed sensor, which in particular includes: activating and deactivating and adjusting a supply voltage, detecting an overcurrent including an automatic emergency shutdown of the speed sensor.

[0002] Active wheel speed sensors are used in vehicles to monitor wheel speeds, for example, for anti-lock braking systems (ABS) or other driver assistance systems. This allows for targeted intervention if a wheel speed deviates from a target value. These sensors are exposed to significant environmental influences and must exhibit high reliability in continuous operation. Faults include, for example, short circuits to the supply voltage (e.g., battery voltage) or to ground. It is also crucial for these sensors not only to monitor the current flowing into and out of the sensor but also to shut it down promptly if limit values ​​are exceeded. However, the desired high reliability can only be guaranteed if damage to the active wheel speed sensor caused by such critical conditions (overcurrent, overvoltage, etc.) is reliably prevented.

[0003] Specific control circuits are used for this purpose, which on the one hand supply the speed sensor with the necessary supply voltage and on the other hand provide protection for the speed sensor and the subsequent electronics.

[0004] Conventional control circuits do not yet offer the desired level of reliability, as the sometimes complex integrated circuits present many sources of interference. They are often not reliable over extended periods (for example, more than 15 years). Furthermore, their complexity often makes them cost-effective to manufacture.

[0005] Document US2007 / 274013A1 discloses a state-of-the-art control circuit.

[0006] Therefore, there is a need for control circuits for active speed sensors that allow reliable monitoring and ensure high reliability during long-term operation.

[0007] At least some of the aforementioned problems are solved by the control circuit according to claim 1 and a method for operating the control circuit according to claim 13. The dependent claims relate to further advantageous embodiments of the subject matter of the independent claim.

[0008] The present invention relates to a control circuit for an active speed sensor of a vehicle. The active speed sensor is designed to detect the rotational speed of a wheel and, based on this, output a sensor signal. The control circuit comprises a monitoring circuit which includes the following: a first terminal and a second terminal for the electrical connection of the speed sensor and for receiving the sensor signal; a supply terminal for connection to a supply voltage and a ground terminal for connection to a ground; a sensor signal output for providing the sensor signal from the active speed sensor; a first switch configured to switch the first terminal with the supply terminal; a second switch configured to switch the second terminal with the ground terminal; an overcurrent detector configured to detect an overcurrent through the supply terminal or through the ground terminal and, upon detection, to open the first switch or the second switch; and a voltage controller configured to adjust an electrical voltage between the first terminal and the ground terminal to a setpoint.

[0009] The supply voltage can be the vehicle's battery voltage or another predetermined voltage. It is understood that switching can be either opening or closing, or establishing or breaking an electrical connection between the relevant terminals. For example, the overcurrent detector can open the first switch in the event of an overcurrent at the supply terminal. Alternatively or additionally, the overcurrent detector can open the second switch in the event of an overcurrent to ground. Once the critical overcurrent situation has passed, the switch can be closed again by a precisely timed control signal (e.g., from a microcontroller). It is understood that no separate control unit or similar logic is required to actuate the switches or readjust the voltage in critical situations. This is done automatically by the example overcurrent detector or voltage controller.

[0010] Optionally, the sensor signal comprises a speed signal with (at least) one pulse and an information signal with a multitude of pulses, where the pulses of the information signal encode information about the speed sensor and have a smaller amplitude than the (at least) single pulse of the speed signal. The information about the speed sensor can include an identification of the speed sensor or indicate a current status (e.g., readiness). A Manchester code, pulse width coding, or another encoding method can be used for this purpose.

[0011] Optionally, the control circuit includes a readout circuit with a sensor signal input connected to the sensor signal output, a speed signal output, and an information signal output. The readout circuit can also include a first signal detector connected to the sensor signal input to detect the speed signal and provide a speed signal at the speed signal output. The readout circuit can further include a second signal detector connected to the sensor signal input to detect the information signal and provide the encoded information about the speed sensor at the information signal output.

[0012] The readout circuit can also include a feedback switch configured to change the sensitivity of the second signal detector upon detection of the speed signal by the first signal detector (for the purpose of detecting the information signal). The feedback switch can be coupled to the first signal detector to receive the trigger information for changing the sensitivity. The sensitivity can be changed or set via a reference voltage or a threshold value. The evaluation of the information and speed signals can be performed by a separate microcontroller or control unit.

[0013] Since the information signal is transmitted periodically with each pulse of the speed signal, it is optionally possible to determine the rotational speed redundantly via the information signal. Depending on the flywheel, approximately 100 (or more or fewer) pulses of the speed signal, each followed by the information signal, can be sent per revolution.

[0014] Optionally, the control circuit includes an evaluation circuit designed to determine the wheel speed based on the speed signal at the speed signal output. The evaluation circuit can be further configured to determine at least one piece of information or a state of the active speed sensor based on the coded information at the information signal output.

[0015] Optionally, the monitoring circuit for independent monitoring of the first terminal and / or the second terminal includes the following: a first status signal terminal connected to the first terminal (directly or indirectly), and / or a second status signal terminal connected to the second terminal (directly or indirectly).

[0016] Optionally, the evaluation circuit is further developed to receive signals from the first status signal terminal and / or the second status signal terminal in order to detect a short circuit of the first terminal and / or the second terminal and / or crosstalk (e.g., between the first and second terminals). The short circuit can be at least one of the following: short circuit to ground (e.g., from the first and / or the second terminal), short circuit to the supply voltage (e.g., from the first and / or the second terminal), short circuit of the first terminal with the second terminal.

[0017] Optionally, the voltage controller includes a current mirror to reflect current changes resulting from changes in the supply voltage and to inject a mirrored current between the first switch and the first terminal to achieve voltage adjustment. Voltage adjustment can, in particular, involve maintaining a predetermined voltage. According to exemplary embodiments, this is also achieved without logic or a separate control unit. The circuit itself automatically regulates the voltage to the desired level.

[0018] Optionally, the overcurrent detector includes a first overcurrent detector for detecting a first current between the supply terminal and the first terminal and / or a second overcurrent detector for detecting a second current between the second terminal and the ground terminal.

[0019] Optionally, the first overcurrent detector includes a first filter to filter out overcurrent events below a fixed minimum duration and to open the first switch if this minimum duration is exceeded. The second overcurrent detector can optionally include a second filter to filter out overcurrent events below a fixed second minimum duration and to open the second switch if this second minimum duration is exceeded. The first minimum duration can be the same as the second minimum duration or different. According to the exemplary embodiments, this also occurs without logic or a separate control unit. The minimum durations can be fixed in the hardware (e.g., via appropriately selected capacitors).The filters can be designed as RC circuits and act as damping elements, achieving damping in the detection of the overcurrent in order to implement a desired inertia.

[0020] Optionally, the first and / or second signal detector each include a comparator with a reference voltage input and a sensor signal input. The reference voltage input of the second signal detector is connected to the feedback switch to change a reference voltage value at the comparator of the second signal detector in response to the detection of the velocity signal by the first signal detector. The reference voltage input can be, for example, a non-inverting or an inverting input of a comparator. The sensor signal input can correspondingly be the inverting or non-inverting input of the comparator. When no sensor signal is present, the reference voltage values ​​at the reference voltage inputs can have predetermined values, which in turn can be encoded in the hardware (e.g., via voltage dividers). No active components or logic are required for this.

[0021] The monitoring circuit can be a primary monitoring circuit for a first speed sensor. Optionally, a second monitoring circuit, identical in design to the first, can be configured for a second speed sensor. Similarly, the readout circuit can be a primary readout circuit, and optionally, a second readout circuit can be identical in design to the first. The respective primary signal detectors can then be configured as a primary 4-channel comparator. Likewise, the respective secondary signal detectors can be configured as a secondary 4-channel comparator.

[0022] Optionally, the feedback switch includes a transistor circuit designed to set the reference voltage value of the comparator of the second signal detector to a midpoint amplitude value of the pulse of the velocity signal.

[0023] Further embodiments relate to an anti-lock braking system for a commercial vehicle with at least one active wheel speed sensor, wherein the system includes a control unit with at least one of the previously described control circuits. It is understood that a separate wheel speed measurement is typically performed for each individual wheel, so that generally several of the aforementioned control circuits can be implemented. As already explained, the wheel speed measurements can be combined in a single circuit (e.g., on a circuit board) by using multi-channel comparators.

[0024] Further embodiments relate to a method which performs the control and / or monitoring of an active speed sensor in a vehicle using a control circuit mentioned above.

[0025] Optionally, the method may include the detection of a short circuit and / or crosstalk, where the short circuit may be to ground or to the supply terminal, from the first and / or the second terminal. For this purpose, the method may optionally perform at least one of the following steps: Input of a first signal on the first status signal port, input of a second signal on the second status signal port, analysis of a signal status on the first status signal port, analysis of a signal status on the second status signal port, comparison of a first signal status on the first status signal port with a second signal status on the second status signal port.

[0026] Examples of this implementation offer the following advantages: The control circuit is cost-effective to manufacture and offers a high degree of reliability over extended periods. No special components are used; instead, standard components are employed that have been proven to ensure reliable operation for periods exceeding 10 or 20 years. For example, discrete components or standard operational amplifiers are used, which can be flexibly adapted over a wide range of applications and meet the required specifications throughout their entire lifespan.

[0027] The supply voltage and current can be continuously monitored to ensure optimal conditions for the speed sensor. Separate power supply cutoff is provided on both the ground and power supply sides. Inputs are provided for targeted testing of specific functions. Furthermore, exemplary embodiments allow the supply voltage to be adapted to specific speed sensors.

[0028] The embodiments of the present invention are better understood from the following detailed description and the accompanying drawings of the different embodiments, which, however, should not be understood as limiting the disclosure to the specific embodiments, but merely serve for explanation and understanding. Fig. 1 shows a control circuit according to an embodiment of the present invention. Figs. 2A and 2B show further optional circuits that can be used with the control circuit from the Fig. 1 They can be combined. Fig. 3 shows an example sensor signal of a possible active speed sensor. Fig. 4 shows an embodiment of the monitoring circuit with further details. Fig. 5 shows an embodiment of the readout circuit with further details.

[0029] In the following, when an element is described as "connected" or "coupled" to another element, it may be directly connected or coupled to the other element, or there may be intermediate elements. Conversely, when an element is described as "directly connected" or "directly coupled" to another element, there are no intermediate elements. Other words used to describe the relationship between elements should be interpreted similarly (e.g., "between" as opposed to "directly between," "adjacent" as opposed to "directly adjacent," etc.).

[0030] The terminology used here serves only to describe illustrative examples and is not to be understood as restrictive. The singular forms used here also include the plural forms, unless the context clearly indicates otherwise. Furthermore, it is understood that the terms "comprise" and "exhibit," when used here, denote the presence of certain features, steps, processes, elements, and / or components, but do not exclude the presence or addition of one or more other features, steps, processes, elements, components, and / or groups thereof.

[0031] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as they are commonly understood by a person skilled in the art in the field to which the examples belong. It is further understood that terms, e.g., those defined in commonly used dictionaries, should be interpreted in a manner consistent with their meaning in the context of the relevant field and not in an idealized or overly formal sense, unless expressly defined as such herein.

[0032] Finally, the statement that elements are connected in series / parallel between two components should be understood in the context of an electrical circuit, specifically in the sense that the relative position of the components to each other is defined along a current direction, 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., a printed circuit board).

[0033] Fig. 1 Figure 1 shows a control circuit according to an exemplary embodiment. The control circuit comprises a monitoring circuit 100, which has a first terminal 101, a second terminal 102, a supply terminal 104, and a ground terminal 106. The monitoring circuit also includes a sensor signal output 108, a first switch 110, a second switch 120, a first and a second overcurrent detector 131, 132, and a voltage controller 140. The active speed sensor 10 can be connected between the first terminal 101 and the second terminal 102. However, exemplary embodiments are not limited to the case where two independent current detectors are provided, but also include the case where only the first current detector 131 or only the second current detector 132 is provided.

[0034] The first overcurrent detector 131 and the first switch 110 are connected in series between the supply terminal 104 and the first terminal 101. The second overcurrent detector 132 and the second switch 120 are connected in series between the ground terminal 106 and the second terminal 102. The order of the first and second switches 110, 120 and of the first and second overcurrent detectors 131, 132 can also be different.

[0035] An electrical connection to the voltage controller 140 is provided at a current node between the first switch 110 and the first overcurrent detector 131. The voltage controller is configured to regulate a predetermined voltage at the first terminal 101. The sensor signal is tapped between the second switch 120 and the second overcurrent detector 132 and output via the sensor signal output 108.

[0036] In the present embodiment, the speed sensor 10 outputs the sensor signal via the second terminal 102 (on the ground side) and can therefore be accessed via the sensor signal output 108 at the second switch 120. However, this is only an example and not mandatory. According to further embodiments, the speed sensor 10 can also output the sensor signal at the first terminal 101 (on the supply voltage side), in which case the sensor signal output 108 can be located before or after the first switch 110 (e.g., at an input or output of the first overcurrent detector 131).

[0037] The first overcurrent detector 131 is configured to detect a current to / from the supply terminal 104 and, upon exceeding a threshold value, to open the first switch 110. The second overcurrent detector 132 is configured to detect a current to / from the ground terminal 106 and, upon exceeding a further limit value, to open the second switch 120.

[0038] The first overcurrent detector 131 and / or the second overcurrent detector 132 optionally include damping circuits to activate the first switch 110 or the second switch 120, respectively, only if the threshold is exceeded for a predetermined minimum time. This predetermined minimum time is set by the selection of passive components such as capacitors and resistors, but not by logic.

[0039] Fig. 2A und Fig. 2B further optional circuits are shown, which, according to exemplary embodiments, are connected to the control circuit from the Fig. 1 can be combined.

[0040] In the Fig. 2A A readout circuit 200 according to a further embodiment is shown. The readout circuit 200 comprises a sensor signal input 202, a speed signal output 206, and an information signal output 208. A first signal detector 210 is formed between the sensor signal input 202 and the speed signal output 206. A second signal detector 220 is formed between the sensor signal input 202 and the information signal output 208. The readout circuit 200 also includes a feedback switch 230, which is configured to change the sensitivity of the second signal detector 220 in response to an output signal of the first signal detector 210.

[0041] The speed signal output 206 and the information signal output 208 can be connected to an evaluation circuit 300, such as a microcontroller. The sensor signal input 202 can be connected to the sensor signal output 108 of the monitoring circuit 100 from the Fig. 1 be connected.

[0042] During operation, a sensor signal is input via the sensor signal input 202. The sensor signal comprises a speed pulse 12 and a multitude of information pulses 14, which can repeat periodically depending on the rotational speed of the wheel. The first signal detector 210 is configured to detect the speed signal 12, for which, for example, a threshold comparison can be performed. The threshold can be selected such that the amplitude value of the speed signal 12 is reliably detected, but not necessarily the pulses of the information signal 14.

[0043] A detection signal is provided as a speed signal at speed signal output 206. It simultaneously serves as a trigger signal for the feedback switch 230, which in response changes the sensitivity of the second signal detector 220. This is achieved by raising the threshold of the second signal detector 220 via the feedback switch 230, so that the second signal detector 220 can detect as many pulses as possible, including the pulse from speed signal 12, with the same pulse width and output them as a (binary) pulse sequence to the information signal output 208. The first pulse (from speed signal 12) can then serve as a trigger pulse to decode the subsequent information signal 14.If the threshold of the second signal detector 220 were not raised, there would be a risk that the pulse of the velocity signal 12 would be significantly wider than all other pulses due to its larger amplitude. This artificial broadening would otherwise have to be corrected by signal processing in a subsequent microcontroller. Raising the threshold solves this problem automatically.

[0044] In this way, the subsequent evaluation circuit 300 receives information about the presence of a speed pulse via the speed signal output 206 and can determine the speed of rotation of the wheel, whose rotation is measured by the active speed sensor, from the time course or the number of pulses per minute. Furthermore, the evaluation circuit 300 can receive additional information via the information signal output 208.

[0045] Fig. 2B shows an exemplary embodiment of a possible wiring configuration of the monitoring circuit 100 (see Fig. 1 ), the readout circuit 200 and the evaluation circuit 300. A speed sensor can be connected to the first terminal 101 and the second terminal 102. This sensor is supplied with a supply voltage and current by the monitoring circuit 100 and outputs the received sensor signals via the sensor signal output 108. The readout circuit 200 then separates the speed signal 12 from the information signal 14 (see Fig. 2A ) and forwards both signals separately to an evaluation circuit 300.

[0046] The monitoring circuit 100 in the embodiment of the Fig. 2B It also includes a first status signal input 301 and a second status signal input 302. The first status signal input 301 is electrically coupled to the first input 101. The second status signal input 302 is electrically coupled to the second input 102. These inputs 301 and 302 are intended for status signals, so that the evaluation circuit 300 can specifically monitor the first input 101 and the second input 102, or, by selectively controlling the inputs, determine whether there is a short circuit to the supply voltage or to ground. For example, the evaluation circuit 300 can selectively send voltage pulses to the inputs and analyze their effect on the speed signal output 206, the information signal output 208, the status signal input 301, and the status signal input 302. The evaluation circuit 300 is therefore able to determine whether an expected result arrives at the outputs 206 and 208.If this is not the case, the evaluation circuit 300 can detect a fault (e.g. a short circuit).

[0047] Fig. 3 Figure 16 shows an example of a sensor signal 16 as it can be output by an active speed sensor 10, with the left side showing the state of standstill or movement at very low speeds. The right side shows the driving state or the state at higher speeds. A predetermined limit (e.g., 1 km / h) can be defined to differentiate between high and low speeds.

[0048] The active speed sensor 10 is designed to output a signal 16 even when the vehicle is stationary. The first pulse can be the speed signal 12, followed by a multitude of pulses that form the information signal 14. The signal 16 is, for example, a current signal with variable current, while the information signal 14 can be a binary signal with two predetermined amplitude values, for example, 7 mA as a low state (logic 0) and 14 mA as a high state (logic 1). The speed signal 12 can, for example, have an amplitude of 28 mA when the vehicle is in motion and assume a high state when stationary. However, these values ​​are only examples. It is also possible that, according to further embodiments, a different encoding is used, or that the encoding depends on the specific active speed sensor 10.

[0049] This signal sequence 16 repeats periodically, with the period being the rotational speed of the wheel, which also limits the maximum amount of information in the information signal 14. The information signal 14 can encode the state or identification of the speed sensor 10 as a binary signal. A Manchester code, for example, can be used for encoding. Here, the total signal length of the information signal 14 is divided into predetermined time windows (10 time windows for 10-bit encoding), where a rising edge within a time window represents a logic 1 and a falling edge within the time window represents a logic 0.

[0050] The active speed sensor 10 can be, for example, a Hall sensor or another active speed sensor that can actively generate the speed signal 12 and the information signal 14 and provide them to the control circuit. An advantage of these active sensors 10 is the transmission of the additional information encoded in the information signal 14. In particular, the information signal 14 can also be transmitted when the vehicle is stationary, so that the identification of the installed speed sensor 10 as well as the status of the active speed sensor 10 can be determined even before the journey begins. Using the information signal 14, various parameters of the active speed sensor 10 can be output, such as: whether a (correct) voltage is present, whether a predetermined electrical current is available, or other electrical parameters from which the correct operation of the active speed sensor can be determined.

[0051] Fig. 4 Figure 1 shows the monitoring circuit 100 with further details according to another embodiment. The monitoring circuit 100 comprises the following connections: the first connection 101, the second connection 102, the power supply connection 104, the ground connection 106, a sensor signal output 108, a first status signal connection 301, a second status signal connection 302, an input for a first activation signal 303, an input for a second activation signal 307, and a further ground connection 306 (e.g., ground of the evaluation circuit 300).

[0052] The following components are connected in series between the supply terminal 104 and the first terminal 101: a first transistor T1, a resistor R2, a resistor R3, a transistor T3, and a first rectifier D1. Component C21 indicates that transistor T1 can be a dual-collector power transistor, with both collectors connected together. One emitter of transistor T1 is connected to the supply terminal 104. Resistors R2 and R3 are connected in series between the collector of transistor T1 and one emitter of transistor T3. One collector of transistor T3 is connected to the first rectifier D1, which is located between the first terminal 101 and transistor T3. A current node M1 between resistors R2 and R3 is connected to ground via a capacitor C5.

[0053] A resistor R1 and a capacitor C1 are connected in parallel between the supply terminal 104 and the control terminal of transistor T1. A current node M2, located between the collector of transistor T1 and resistor R2, is connected to the collector of transistor T3 via a series connection of capacitor C2 and resistor R4. Furthermore, current node M2 ​​is connected to ground 106 via a series connection of transistor T4 and resistor R5, with the emitter of transistor T4 coupled to current node M2. The control terminal of transistor T4 is connected to a current node M3 located between capacitor C2 and resistor R4. The collector of transistor T4 is also connected to the control terminal of transistor T3.

[0054] The control terminal of transistor T1 is connected to ground 106 via a series connection of transistor T6 and resistor R8, with one emitter of transistor T6 connected to resistor R8 and one collector of transistor T6 connected to the control terminal of transistor T1. Additionally, current node M1 is connected to ground 106 in a series connection of transistor T5 and resistor R8, with one emitter of transistor T5 connected to resistor R8. Current node M1 is also connected to ground 106 via a connection of resistors R6 and R7. A current node between resistors R6 and R7 is connected to a control terminal of transistor T5. A control terminal of transistor T6 is connected to the input of the first activation signal 303 via resistor R9.

[0055] A resistor R10 and a resistor R12 are connected in series between the first terminal 101 and the first status signal terminal 301. A current node M4 between resistors R10 and R12 is connected to ground 106 via a resistor R11. The first status signal terminal 301 is connected to the second ground terminal 306 via a capacitor C3. A second rectifier D2 and a resistor R13 are connected in series between the second terminal 102 and the second status signal terminal 302. The second status signal terminal 302 is connected to the second ground terminal 306 via a capacitor C4. The second ground terminal 306 can be connected to ground terminal 106 (forming a common ground).

[0056] Between the second terminal 102 and the ground terminal 106, the second rectifier D2, a transistor T2, and a resistor R14 are connected in series. Resistor R14 is formed between transistor T2 and ground terminal 106, and an emitter of transistor T2 is electrically connected to resistor R14. Additionally, an emitter of transistor T2 is connected to the sensor signal output 108. A collector of transistor T2 is connected to ground terminal 106 via resistor R16, and in a parallel circuit, the collector of transistor T2 is also connected in series to ground terminal 106 via resistor R15 and capacitor C5.One control terminal of transistor T2 is connected to ground terminal 106 via transistor T7, with one emitter of transistor T7 also connected to ground terminal 106 and one control terminal of transistor T7 coupled to a current node between resistor R15 and capacitor C5. Additionally, the control terminal of transistor T2 is connected to input 307 for the second activation signal via resistor R17.

[0057] The one with the Fig. 1 The described functions – first and second switches 110, 120, voltage controller 140, overcurrent detectors 131, 132 – are fulfilled by the circuit shown as follows: Transistor T1 or transistor T3 can be used as the first switch 110, which is controlled (switched) via input 303 for the first activation signal. The first activation signal initially switches transistor T6, which then switches (e.g., closes) transistor T1.

[0058] Transistor T5, together with transistor T6, forms a current mirror that reflects the current from supply terminal 104 to ground terminal 106 via transistor T6. The voltage controller 140 is reached via this current mirror, as the reflected current couples at current node M1 between resistors R2 and R3, thus increasing or decreasing the voltage level there, resulting in dynamic adjustment of the voltage level (depending on the current through transistor T6). The desired voltage level is set via the voltage divider with resistors R6 and R7. For example, if the resistance value of R7 is increased, the reflected current through transistor T5 also increases, and consequently, so does the voltage value at current node M1.

[0059] Transistor T4 (and similarly transistor T7) represents the first overcurrent detector 131 (second overcurrent detector 132), which detects a current flow between the first terminal 101 and the supply terminal 104 and, when a threshold value is exceeded, which is given by the resistance values ​​or the threshold voltage of the transistors, leads to a shutdown of transistor T3 (or transistor T2).

[0060] Resistor R4 and capacitor C2 (or resistor R15 and capacitor C5) form a damping element, preventing transistor T4 (or T7) from switching off immediately in response to minor fluctuations, which would cause transistor T3 (or T2) to switch on. Instead, it only switches off after prolonged overcurrent events. The time constant for this is set by the capacitance of capacitor C2 (or C5). Only when the defined (time) threshold is exceeded does the current flow to or from supply terminal 104 (or ground terminal 106) stop.

[0061] On the ground side (so-called "low side"), transistor T2 functions as the second switch 120, which is switched via input 307 for the second activation signal. As already mentioned, transistor T7 functions as the second overcurrent detector 132, which causes a shutdown on the ground side if the current flow, and thus the voltage drop across resistor R14, becomes too high, causing the potential at the control terminal of transistor T7 to rise above a threshold value.

[0062] The first rectifier D1 and the second rectifier D2 can be formed by diodes connected in parallel (e.g. to allow a high current at low resistance) and ensure that a directed current flow to / from the active speed sensor is achieved.

[0063] Resistor R12 and capacitor C3 form a low-pass filter to divert high-frequency components to the additional ground terminal 306. Similarly, resistor R13 and capacitor C4 form a low-pass filter to divert high-frequency components from the second terminal 102 to the additional ground terminal 306.

[0064] Fig. 5 Figure 200 shows the readout circuit 200 with further details according to another embodiment. The readout circuit 200 comprises a first readout circuit 200a and a second readout circuit 200b, which are arranged symmetrically to enable the simultaneous reading of speed signals from two wheels.

[0065] The one in Fig. 5 The first readout circuit 200a shown above comprises: the sensor signal input 202, a first power supply 304, the speed signal output 206, a second power supply 305, the information signal output 208, and the ground connection 106. The first power supply 304 and the second power supply 305 can, for example, be at the same potential (electrically connected), but can also be configured with different connections in the circuit to apply different potentials. The first signal detector 210 is connected between the sensor signal input 202 and the speed signal output 206, and a resistor R20 is also connected between the first signal detector 210 and the sensor signal input 202.The first signal detector 210 is exemplified by a first comparator with an inverted input (-) and a non-inverted input (+), wherein the inverted input (-) is connected to the sensor signal input 202 via resistor R20 and the output of the comparator 210 is connected to the speed signal output 206. The inverted input (-) of the first comparator 210 is also connected to ground terminal 106 via capacitor C20.

[0066] The non-inverting input (+) of the first comparator 210 is electrically connected to the first power supply 304 via resistor R21 and to ground terminal 106 via resistor R22. The output of the first comparator 210 is also electrically connected to the non-inverting input (+) via resistor R23.

[0067] The sensor signal input 206 is also electrically connected in series to the information signal output 208 via resistor R20 and the second signal detector 220. The second signal detector 220 can also be configured as a second comparator with an inverted input (-) and a non-inverted input (+). The non-inverted input (+) of the second comparator 220 is electrically connected to the output of the second comparator 220 via resistor R27. Furthermore, the non-inverted input (+) of the second comparator 220 is connected to the first power supply 304 via resistor R25 and to ground 106 via resistor R26. The output of the second signal detector 220 is connected to the first power supply 304 via resistor R29.

[0068] The feedback circuit 230 is implemented as a transistor circuit and includes, for example, a transistor T20, wherein an emitter of transistor T20 is connected to the second power supply 305 via a resistor R30, and the collector of transistor T20 is connected to the non-inverting input (+) of the second comparator 220 via a resistor R28. The control terminal of transistor T20 is connected to the output of the first comparator 210 via a resistor R32. The control terminal of transistor T20 is also electrically connected to the emitter of transistor T20 via a resistor R31.

[0069] The one in Fig. 5 The second readout circuit 200b shown below is constructed in the same way as the first readout circuit 200a. Since the second readout circuit 220b is intended for detecting the rotational speed of a different wheel, the following connections are provided separately: the sensor signal input 202b, the speed signal output 206b, and the information signal output 208b. The other connections are connected to each other according to the illustrated embodiment; that is, both readout circuits share the first power supply 304, the second power supply 305, and the ground connection 106.

[0070] According to further embodiments, the respective first signal detectors 210 are configured as a first 4-channel comparator 210. Likewise, the respective second signal detectors can be configured as a second 4-channel comparator 220. In this way, the circuits can be implemented compactly. According to further embodiments, the first comparator 210 together with the second comparator 220 is configured as a 4-channel comparator, e.g., as a 2-channel evaluation circuit.

[0071] According to further embodiments, a power supply unit 350 is provided for supplying power to the comparators, which has two terminals, one of which is connected to the first voltage supply 304 and the second to the ground terminal 106. Both terminals are also connected to each other via a capacitor C30, for example to filter high-frequency components.

[0072] The one with the Fig. 2AThe described functions are implemented in this embodiment as follows. The function of the readout circuit 200 consists of separating the speed signal 12 from the information signal 14, which is implemented by adjusting the detection thresholds and can be described as follows.

[0073] The first comparator 210 and the second comparator 220 each compare the sensor signal at sensor signal input 202 with respective reference values ​​(threshold values) at the non-inverting inputs (+) of comparators 210 and 220. The reference value at the first comparator 210 can be selected so that it reliably detects the speed signal 12, but not the information signal 14. Therefore, only the pulses of the speed signal 12 can be output at sensor signal output 206, from whose frequency the rotational speed of the wheel can be determined (e.g., one pulse or 100 pulses occur per revolution). When this pulse is present, transistor T20 switches the connection of the non-inverting input (+) of the second comparator 220 to the second power supply 305. This changes the reference voltage at the second comparator 220 when the speed pulse 12 is present.

[0074] The reference voltage at the second comparator 220 can be selected before modification such that the second comparator 220 can reliably detect all pulses of the information signal 14 and output the information signal 14 accordingly. However, the pulse of the speed signal 12 is higher, and the capacitor C20 can cause the speed pulse 12 to be broadened at the level of the pulses of the information signal 14, only above which it has the same pulse width as the pulses of the information signal 14. To achieve the same pulse width for all pulses, the feedback switch 230 causes the reference voltage at the second comparator 220 to be raised during the pulse of the speed signal 12, so that detection occurs at a value where the speed pulse 12 ideally has the same width as the pulses of the information signal 14. This "level shift" is controlled by the selection of resistors R28 and R30.

[0075] As a result, all pulses with the same pulse width are detected. The evaluation then takes place in the evaluation circuit 300. REFERENCE MARK LIST

[0076] 10 (active) speed sensor 12 speed signal 14 information signal 100 monitoring circuit 101, 102 first connection, second connection 104 power supply connection 106, 306 ground connections 108 sensor signal output 110 first switch 120 second switch 130, 131, 132 overcurrent detector(s) 140 voltage controller 200 readout circuit 202 sensor signal input 206 speed signal output 208 information signal output 210 first signal detector 220 second signal detector 230 feedback switch 300 evaluation circuit 301, 302 status signal connections 303, 307 inputs for activation signals 304 first power supply 305 second power supply 350 adjustment unit for the supply voltage R1, R2, ... various resistors C1, C2, ...various capacitors D1, D2, ...rectifiers T1, T2,...various transistors

Claims

1. Control circuit for an active rotational speed sensor (10) of a vehicle, wherein the active rotational speed sensor (10) is configured to detect a rotational speed of a wheel and to output a sensor signal based thereon, comprising a monitoring circuit (100) which has the following: - a first terminal (101) and a second terminal (102) for the electrical connection of the rotational speed sensor (10) and for receiving the sensor signal; - a supply terminal (104) for connection to a supply voltage of the vehicle and a ground terminal (106) for connection to a ground; - a sensor signal output (108) for providing the sensor signal from the active rotational speed sensor (10); - a first switch (110), which is configured to switch the first terminal (101) with the supply terminal (104); - a second switch (120), which is configured to switch the second terminal (102) with the ground terminal (106); - an overcurrent detector (130), which is configured to detect an overcurrent through the supply terminal (104) or through the ground terminal (106) and, upon detection, to open the first switch (110) or the second switch (120); and - a voltage controller (140), which is configured to affect an adjustment of an electrical voltage between the first terminal (101) and the ground terminal (106) to a setpoint value.

2. Control circuit according to claim 1, wherein the sensor signal has a speed signal (12) with one pulse and an information signal (14) with a plurality of pulses, wherein the pulses of the information signal (14) encode a piece of information about the rotational speed sensor (10) and have a smaller amplitude than the speed signal (12), characterized by a read-out circuit (200) having the following: - a sensor signal input (202) which is connected to the sensor signal output (108); - a speed signal output (206) and an information signal output (208); - a first signal detector (210), which is connected to the sensor signal input (202) and is configured to detect the speed signal (12) and provide a speed signal at the speed signal output (206) based thereon; - a second signal detector (220), which is connected to the sensor signal input (202) and is configured to detect the information signal (14) and provide the encoded information about the rotational speed sensor (10) at the information signal output (208); and - a feedback switch (230), which is configured to change a sensitivity of the second signal detector (220) in response to a detection of the speed signal (12) by the first signal detector (210) for detecting the information signal (14).

3. Control circuit according to claim 2, characterized by an evaluation circuit (300) which Is configured - to determine the rotational speed of the wheel based on the speed signal at the speed signal output (206), and - to determine at least one piece of information or a state of the active rotational speed sensor (10) based on the encoded information at the information signal output (208).

4. Control circuit according to any one of the preceding claims, characterized in that the monitoring circuit (100) for independently monitoring the first terminal (101) and the second terminal (102) has the following: - a first status signal terminal (301) connected to the first terminal (101), and / or - a second status signal terminal (302) connected to the second terminal (102).

5. Control circuit according to claim 4, provided that it refers back to claim 3, characterized in that the evaluation circuit (300) is further configured to receive signals from the first status signal terminal (301) and the second status signal terminal (302), to determine a short circuit of the first terminal (101) and / or the second terminal (102) or a crosstalk, wherein the short circuit is at least one of the following: a short circuit to ground, a short circuit to the supply voltage, a short circuit of the first terminal (101) with the second terminal (102).

6. Control circuit according to any of the preceding claims, characterized in that the voltage controller (140) has a current mirror for mirroring current changes resulting from changes in the supply voltage and for feeding a mirrored current between the first switch (110) and the first terminal (101) in order to affect the voltage adjustment.

7. Control circuit according to any one of the preceding claims, characterized in that the overcurrent detector (130) has the following: - a first overcurrent detector (131) for detecting a first current between the supply terminal (104) and the first terminal (101) and / or - a second overcurrent detector (132) for detecting a second current between the second terminal (102) and the ground terminal (106).

8. Control circuit according to claim 7, characterized in that - the first overcurrent detector (131) has a first filter for filtering out overcurrent events below a fixed first minimum time period, and for opening the first switch (110) when the fixed first minimum time period is exceeded, and / or - the second overcurrent detector (132) has a second filter for filtering out overcurrent events below a fixed second minimum time period, and for opening the second switch (120) when the fixed second minimum time period is exceeded.

9. Control circuit according to any one of claims 2 or 3 to 8, provided that they refer back to claim 2, characterized in that the first signal detector (210) and the second signal detector (220) each have a comparator with a reference voltage input (+) and a sensor signal input (-), wherein the reference voltage input (+) of the second signal detector (220) is connected to the feedback switch (230), in order to change a reference voltage value at the comparator of the second signal detector (220) in response to a detection of the speed signal (12) by the first signal detector (210).

10. Control circuit according to claim 9, wherein the monitoring circuit (100) is a first monitoring circuit (100a) for a first rotational speed sensor, and a second monitoring circuit (100b) is configured to be structurally identical to the first monitoring circuit (100a) for a second rotational speed sensor, and wherein the read-out circuit (200) is a first read-out circuit (200a), and a second read-out circuit (200b) is configured to be structurally identical to the first read-out circuit (200a), characterized in that the respective first signal detectors are configured as a first 4-channel comparator (210), and / or the respective second signal detectors are configured as a second 4-channel comparator (220), and / or the first signal detector (210) and the second signal detector (220) of a respective read-out circuit (200a, 200b) are configured as a 4-channel comparator.

11. Control circuit according to claim 9 or claim 10, characterized in that the feedback switch (230) comprises a transistor circuit which is configured to apply the reference voltage value of the comparator of the second signal detector (220) to an amplitude value of the speed signal, so that the second signal detector (220) detects all pulses as far as possible with the same pulse width.

12. Anti-lock braking system for a commercial vehicle with at least one active rotational speed sensor (10), characterized by a control device with at least one control circuit according to any one of claims 1 to 11.

13. Method characterized by controlling and monitoring an active rotational speed sensor (10) of a vehicle using a control circuit according to any one of claims 1 to 11.

14. Method according to claim 13, which further has at least one of the following steps for detecting a short circuit and / or a crosstalk: - inputting a first signal at the first status signal terminal (301), - inputting a second signal at the second status signal terminal (302), - analyzing a signal status at the first status signal terminal (301), - analyzing a signal status at the second status signal terminal (302), - comparing a signal status at the first status signal terminal (301) and the second status signal terminal (302).