Patent Abstract:
At least one embodiment relates to magnetic field sensors being operable at different calibration modes, wherein the magnetic sensor is capable of switching between the different calibration modes during normal operation of the sensor. The switching may be possible in response to different motion types detected within the sensor. Such sensors may be used in vehicles such as cars, the sensors for example being part of the engine control system or the ABS. Another embodiment relates to a method of changing calibration modes during operation of sensors.

Full Description:
BACKGROUND 
     The present invention relates to magnetic field sensors being operable at different calibration modes, wherein the magnetic sensor is capable of switching between the different calibration modes during normal operation of the sensor. The switching may be possible in response to different motion types detected within the sensor. In modern automotive products such as for example cars, magnetic sensors are used in various places of such a car. An example of such magnetic field sensor is the use of the magnetic field sensor in combination with a crankshaft of an engine, so that a rotational movement and/or position of the crankshaft may be derivable from an output signal generated by the magnetic field sensor. 
     In modern vehicles there is a tendency to reduce and/or simplify electronic components, such as for example an engine control system. Therefore a magnetic field sensor used to determine a current state of the crankshaft needs to implement more and more sophisticated algorithms in order to provide sufficient accuracy of the determined rotational position of the crankshaft. 
     In order to achieve this, such magnetic field sensors are already powered up, once one or more doors of a vehicle are being opened. This is helpful to achieve an operational state of the sensor even before starting the engine. 
     For similar reasons it is not uncommon in the art to power up magnetic field sensors pertaining to the ABS system and/or tyre pressure management system upon opening of doors of the vehicle. 
     As a trade-off the now operational, i.e. powered-up sensors may become sensitive to movements of the vehicle not caused by the engine, i.e. within the drive train, but for example by loading or offloading goods to/from the vehicle. As an unwanted consequence an engine management warning may be triggered albeit the engine as such did not move whatsoever and is in perfect condition to be started. Such a safety warning may be distressing for the driver and unwanted for the manufacturer of the vehicle, alike. 
     It is therefore an aim of the present invention to provide a magnetic field sensor and a vehicle overcoming the problems of the prior art. The invention further discloses a method of operating such sensor. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The invention shall in the following be explained based on the accompanying drawings, wherein 
         FIG. 1A  shows a first embodiment of a transmitter wheel in combination with a magnetic field sensor. 
         FIG. 1B  shows a second embodiment of a transmitter wheel in combination with a magnetic field sensor. 
         FIG. 2  shows a typical output signal of a magnetic field sensor. 
         FIG. 3  shows a block diagram of a magnetic field sensor according to a first embodiment of the invention. 
         FIG. 4  shows a diagram displaying a method according to the invention. 
     
    
    
     DETAILED DESCRIPTION 
     The following detailed description explains exemplary embodiments of the present invention. The description is not to be taken in a limiting sense, but is made only for the purpose of illustrating the general principles of embodiments of the invention while the scope of protection is only determined by the appended claims. 
     In the exemplary embodiments shown in the drawings and described below, any direct connection or coupling between functional blocks, devices, components or other physical or functional units shown in the drawings or described herein can also be implemented by an indirect connection or coupling. Functional blocks may be implemented in hardware, firmware, software, or a combination thereof. 
     Further, it is to be understood that the features of the various exemplary embodiments described herein may be combined with each other, unless specifically noted otherwise. 
     In the various figures, identical or similar entities, modules, devices etc. may have assigned the same reference number. Example embodiments will now be described more fully with reference to the accompanying drawings. Embodiments, however, may be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these example embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope to those skilled in the art. In the drawings, the thicknesses of layers and regions are exaggerated for clarity. 
     In the described embodiments, various specific views or schematic views of elements, devices, features, etc. are shown and described for a better understanding of embodiments. It is to be understood that such views may not be drawn to scale. Furthermore, such embodiments may not show all features, elements etc. contained in one or more figures with a same scale, i.e. some features, elements etc. may be shown oversized such that in a same figure some features, elements, etc. are shown with an increased or decreased scale compared to other features, elements etc. 
     The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises,” “comprising,” “includes,” and/or “including,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, and/or components. 
       FIG. 1 a    schematically depicts a magnetic field sensor  10  or magnetic sensor  10 . The magnetic sensor  10  is operable with a rotatable transmitter wheel  50 , for example in a rotational direction as indicated by the arrow. The transmitter wheel  50  is shown with four sprockets or teeth carrying little magnets (not shown) in order to convey a pattern of alternating magnetic fields to the magnetic sensor upon rotation of the transmitter wheel  50 . Without limitation the transmitter wheel  50  may comprise more than four teeth. With increasing accuracy requirements for the determination of a rotational position of an axis relative to the sensor  10 , one may increase the number of teeth arranged on the transmitter wheel  50 . The magnetic sensor  10  is in a state operable with the transmitter wheel  50 , as long as it is provided that the magnetic sensor  10  is able to detect the pattern of alternating magnetic fields. Typically in technical applications in the automotive field there is an air gap of a few millimeters between the transmitter wheel  50  and the magnetic sensor  10 . 
       FIG. 1B  depicts a second embodiment of a transmitter wheel  50  mounted on a rotating shaft  60 , such as an axle portion around which a wheel of a car is rotating. Such an embodiment of the transmitter wheel  50  may be used for example in combination with an ABS system and the like. A person skilled in the art will readily appreciate other scenarios in which such a transmitter wheel  50  may be useful in combination with the magnetic sensor  10 . 
       FIG. 2  depicts a sinusoidal input signal received from the transmitter wheel  50 . The amplitude of such the input signal may be irregular in amplitude due to irregularities of the transmitter wheel  50  and/or its arrangement relative to the rotating axis. For ease of explanation each minimum and subsequent maximum within the input signal are labelled with a number of a tooth of the transmitter wheel  50  causing this portion of the input signal. The output signal provided by the magnetic sensor  10  is an output switching signal as indicated below the sinusoidal curve in  FIG. 2 . It is common in the art to use a threshold or offset, when evaluating the input signal of the sensor  10  in order for the output signal to securely reflect the movement of the transmitter wheel  50 . This may lead to a phase error within the output switching. 
     Such methods as explained in  FIG. 2  are of particular interest in situations with the transmitter wheel spinning or evolving around the shaft. This is a state of a crankshaft once the engine is running. Likewise this is the normal condition of an individual wheel of such a vehicle comprising an ABS system. It is also known in the art to derive a direction of motion of the transmitter wheel  50 , i.e. directional information from the sensor input signal. The directional information may be useful in order to overcome the problems of the prior art mentioned before. 
       FIG. 3  schematically depicts a block diagram of a magnetic sensor  10  according to an embodiment of the present invention. The magnetic sensor  10  comprises a direction module  15 . The direction module  15  is adapted to derive the directional information from the input signal of the magnetic sensor  10 . According to an embodiment of the invention the magnetic sensor  10  further comprises a calibration module  20 . The calibration module  20  may be configured to calibrate an offset, as explained above, when the sensor  10  is in operation with the transmitter wheel  50 . According to an embodiment the calibration module may be adapted to select a specific calibration mode  22   a ,  22   b  out of a plurality of calibration modes. 
     According to an embodiment of the invention the calibration module may be selected, i.e. amended during operation of the sensor  10 . Such a possibility has the advantage to provide dedicated calibration modes  22   a , . . . ,  22   b  according to different states of the engine, and/or the vehicle. 
     Such different calibration modes  22   a , . . . ,  22   b  may be of interest should the magnetic sensor  10  be powered-up before the actual start of the engine, as is the case in modern cars. So suppose the vehicle is being loaded/unloaded. The loading activities may cause movement to the car which projects to the crankshaft of the engine. Under normal operational conditions the rotation of the crankshaft may be a rotation in a given direction, clockwise or anticlockwise. 
     Different the rotational movement in a given direction, the movement projecting to the crankshaft while the engine is switched off, mostly resembles a gentle or shallow rocking movement of the crankshaft. The rocking movement is not in a fixed direction but changes direction from clockwise to anticlockwise or vice versa. 
     When calculating an offset for the magnetic sensor  10  for normal operational conditions of the engine, one may average over all teeth of the transmitter wheel  50  as indicated in  FIG. 2 . However such a calibration mode would require one or more full revolutions of the crankshaft in order to correctly represent the movement of the crankshaft in the output switching of the magnetic sensor  10 . With increasing requirements on reaching reliable switching signals from the sensor  10  such a calibration mode may take too long to reach a reliable offset value. Hence one may refer to such a calibration mode as a “slow” calibration mode. In the slow calibration mode  22 , one does typically not make use of the directional information contained within the input signals of the sensor  10 . 
     In order to improve accuracy of the offset values more quickly, there is an interest to devise a calibration mode yielding a reliable offset faster. Therefore one could consider a sensor input signal pertaining to only one or a smaller number of teeth of the transmitter wheel  50  and extract a first offset from this input signal. The tradeoff of such a “fast” calibration mode being that the first offset value may not yet be a perfect match for all teeth of the transmitter wheel  50 . 
     Both “slow” and “fast” calibration modes are still susceptible to false switching output when confronted with the rocking movement projecting to the crank shaft or the axle of the ABS system, while the vehicle is being loaded/unloaded in a parked position. 
     In order to overcome this problem it is suggested to select a calibration mode  22   a ,  22   b  during operation of the magnetic sensor  10 . In particular one may use a detected motion type of the transmitter wheel  50  in order to choose an appropriate calibration mode  22   a ,  22   b  leading to an offset value no longer susceptible to false interpretation of the rocking motion. 
     The motion type detectable at the detection module  15  may comprise a rotational movement of the transmitter wheel  50  in the clockwise or the anticlockwise direction. A further motion type is the above mentioned rocking motion, typically not reaching a full revolution of the crankshaft or the axle monitored by the ABS system and further changing its rotational direction. 
     Using the directional information from the direction module  15  will improve the sensor switching output. A decision which of the calibration modes  22   a ,  22   b  to use, based on the directional information prevents the sensor  10  from not recognizing the rocking motion and in extreme cases causing a system warning to the driver, due to movement even before starting the engine. 
     It is to be noted even though the calibration module  20  in  FIG. 3  is only shown as linked to the input signal via the direction module  15 , there may be a direct link from the calibration module  20  to the input signal without departing from the present invention. 
     So according to an embodiment of the present invention, a first calibration mode  22   a  usable in combination with a rocking motion may be the “fast” calibration mode described above. It is of interest to choose the first calibration mode  22   a  based on a detection of a rocking motion by the direction module  15 . The first calibration mode  22   a  may for example use a signal from a first tooth of the transmitter wheel passing the sensor  10 . 
     Without limitation the first calibration mode  22   a  may use an (input) signal pertaining to a plurality of teeth, for example 2-5 of the transmitter wheel  50 . It is of interest not to use a signal pertaining to a full revolution of the transmitter wheel  50 , as such a (slow) calibration scheme may under some circumstances take too long to reach a reliable value. Such circumstances could be for example during the first few seconds after starting the engine. 
     Further the first calibration mode  22   a  may not correctly represent the rocking movement. It may therefore be of interest to consider a number of teeth lower than half, a quarter or an eighth of the total number of teeth in the transmitter wheel  50 . A person skilled in the art will readily appreciate, that an appropriate portion of all teeth to be considered is directly linked to the total number of teeth in a given transmitter wheel. 
     When there is no rocking movement, it may instead be of interest to use a variant of the “slow” calibration as a form of the second calibration mode  22   b , taking into account a signal pertaining to a larger number of teeth, in particular one or more full revolutions of the transmitter wheel  50  when calibrating the offset. Likewise the second calibration mode  22   b  may be of interest after the engine is started for a few seconds. Again a number of teeth to be considered obviously depends on the total number of teeth within the transmitter wheel  50  used. 
     It will be appreciated that considering the directional information from the direction module  15  will allow switching from the first calibration mode  22   a  to the second calibration mode  22   b  once the rocking movement is no longer present. This will provide greater reliability in achieving appropriate offset factors adapted to different conditions of the vehicle, including a parked vehicle exposed to rocking movement. 
     It will be appreciated that according to an embodiment this disclosure teaches a vehicle comprising the inventive sensors according to one or several of the embodiments explained before. The vehicle may be in particular a car. The transmitter wheel  50  may be for example coupled to an axle portion. Thereby the magnetic sensor  10  could form part of an ABS system of the vehicle, and a movement of the transmitter wheel  50  would reflect rotation of a wheel of the vehicle rotating around the axle portion. 
     For the vehicle according to an embodiment of the invention, the magnetic sensor  10  may be operable before start of the engine. Further the magnetic sensor  10  may alternatively or additionally operable upon opening of at least one door of the vehicle. 
     The present invention according to a further aspect discloses a method of calibrating a magnetic sensor  10 . The method is schematically shown in  FIG. 4 . 
     In a step  100  a motion type is detected. This may happen using the direction module  15  and for a transmitter wheel  50 , as explained above. In a further step  200  a calibration mode is being selected during operation of the magnetic sensor  10 . It is to be understood that the method according to the present invention therefore allows more flexibility in choosing an adapted calibration mode than the prior art. It is of interest to select the calibration mode  22   a ,  22   b  according to the detected motion type of the transmitter wheel  50  as explained before. 
     The method may further comprise a step of calibrating  300  the offset of the magnetic field sensor  10  according to the selected calibration mode. Therefore the achieved offset parameters are more reliable in different conditions of the vehicle, in particular for the parked vehicle being exposed to the rocking movement. 
     It will be appreciated by a person of ordinary skill in the art that the present invention also allows for changing a previously selected calibration mode by returning to step  100  after completion of step  300 . Therefore the present invention provides more flexibility and reliability in calculating the offset for changing conditions for the vehicle as outlined above.

Technology Classification (CPC): 6