DE19855358A1 - Path-measuring device, especially for brake pedal movement in vehicle has at least one analog sensor and at least one incremental sensor to output analog and pulse train signals of path, respectively - Google Patents

Abstract

The device has at least one analog sensor (2,4) to produce an analog signal and at least one incremental sensor (7,8) outputs a pulse train signal as a function of the path to be measured. The analog and the pulse train signals can be set in relation to each other. Preferably there are two of each kind of sensor. The analog sensors may be Hall elements that co-operate with rod magnets (3,5). The incremental sensors may be Hall-circuits that co-operate with a row of alternating magnet poles (10). An Independent claim is included for a method for using the device.

Description

The present invention relates to a device and a Method for determining a distance, in particular a brake pedal travel in a motor vehicle.

Displacement sensors are used for example in electrohydraulic Brakes required for the detection of a brake pedal travel. A path signal is usually under Taking into account a master cylinder pressure signal and one Brake light switch signal calculates a driver brake request, and either as a target brake pressure or as a target Vehicle deceleration to the actuators of the brake passed on and settled there. This Brake request detection is very safety-relevant, and therefore requires high reliability of the used Displacement sensor.

Displacement sensors usually record displacement positions via Sliding contacts using or also contact and non-contact measuring methods. Common types of displacement sensors  are, for example, inductive plunger anchor systems, especially differential transformers. Also potentiometric sensors or Hall sensors in connection with permanent magnets are widely used. As incremental sensors, which as a signal a pulse train output, in particular sensors with optical Scanning or magnetic scanning, in particular Hall or AMR elements can be used. Also digital displacement sensors with absolutely coded standards (optical or magnetic) are widely used. A disadvantage of conventional ones Path sensors is that these are not on the concerns of Path measurements in safety-relevant systems are tailored. For example, for sensors Detection of the brake pedal travel in electrohydraulic Braking is required reliability and accuracy only with very complex sensor arrangements or Signal processing circuits possible.

From DE-OS 196 25 058 a device for Determination of a rotation rate with a first sensor system, which emits a signal dependent on the rotation rate and after a first measuring principle works with signal evaluation means, determine the yaw rate from the supplied signal, known, in addition a second sensor system it is provided that a signal dependent on the rotation rate emits and works on a second measuring principle, wherein the signals of the second sensor system Signal evaluation means are supplied and at the Determination of the rotation rate should also be taken into account. As the first sensor system is an electronic compass, which provides an output signal from the earth's magnetic field is dependent, and as a second sensor system an oscillating  Structure provided by a Coriolis force dependent signal delivers.

The object of the present invention is to provide a measuring device with which a distance, in particular a brake pedal travel in a motor vehicle, in simple and can be specified reliably.

This object is achieved by a device for Determination of a route with the characteristics of Claim 1 and by a method for determination a route with the features of claim 10.

The device according to the invention has the advantage that performed particularly reliable and accurate measurements can be. It is particularly advantageous that the the device according to the invention is inexpensive to produce, as well as the fact that plausibility studies without great effort is possible and a quasi-redundant System is available because if a signal fails Another signal is always available. Achieved are these advantages in that a combination of two independent sensor units for measuring Routes to a single system is performed the combination is such that the disadvantages of Individual systems minimized and the respective advantages of Individual systems become effective. The output signals of both Sensor systems are linked to each other mathematically, being the link in corresponding Signal evaluation means is carried out, for example, as Microprocessor are trained. The invention Device is sufficient both from a manufacturing point of view  from a functional point of view, too a pedal travel sensor.

Advantageous embodiments of the invention Apparatus and the method according to the invention Subject of the subclaims.

According to a preferred embodiment of the invention The device has two analog sensors and / or two incrementally operating sensors. Herewith redundancy is provided, which also applies to Failure of an analog working or incremental working sensor a mathematical link of a Analog signal and a pulse train signal allows. Furthermore, the two pulse train signals, for example to obtain a signal with a higher resolution can be combined with each other.

According to a preferred embodiment of the present Invention is the at least one analog working sensor as a Hall interacting with a bar magnet Element trained. Such sensors are very inexpensive available and deliver reliable and accurate Measurement results. Furthermore, Hall elements build very small. It would also be possible, for example, AMR sensors (Anistotropic Magnetoresistance) to use.

It is further preferred that the at least one incremental sensor as one with a row magnetic pole change interacting Hall switch is trained. Sensors designed in this way  also build small and prove themselves in practice very reliable.

According to a further preferred embodiment, the at least one incrementally working sensor as optical incremental sensor system. With a Such a sensor system can have particularly high resolutions can be achieved.

The incremental sensor is expedient with means for the detection and / or detection of a Index mark with respect to which the pulse train signal is definable, trained. By means of such a Index mark is a particularly reliable and accurate Measuring a path based on the Pulse train signal can be specified. Furthermore, that is also Analog signal in relation to such an index mark definable.

Appropriately, the means to determine and Detection of an index mark as one with a magnetic Pole changing Hall switch or as optically incremental sensor system.

According to a preferred embodiment of the invention Device are the bar magnets and the pole change on a piston rod, in particular a push rod Master brake cylinder of the motor vehicle, and the Hall Elements and Hall switches on a the piston rod surrounding housing attached. This is a special one compact design embodiment of the invention Device achievable.  

It is preferred that the incremental ones Sensors are arranged so that they are 90 ° to each other deliver phase-shifted waveforms. Such Waveforms are calculated in a simple manner Achieving an exact path resolution processable.

According to a preferred embodiment of the invention The method uses at least one analog signal calibrated the at least one pulse train signal, wherein the values of the analog signal are values of the Pulse train signal can be assigned.

A deviation between the Values of the analog signal and the pulse train signal Correction value for the analog signal determined.

It is expedient to relate Analog signal and pulse train signal taking into account an index mark of the incremental signal.

According to an advantageous embodiment of the inventive method two are at 90 ° to each other phase-shifted incremental signals determined, wherein based on these signals a quadrature signal is determined. A quadrature signal has a higher one Resolution than the individual incremental signals, so that on the basis of very precise path determinations possible are.

Appropriately after switching on the device according to the invention until the detection of  Index mark the path to be measured based on the Analog signals determined. This measure will for example, takes into account that after switching on the Ignition of a motor vehicle the brake pedal already can be operated, making it a safety measure represents the incremental signal until the first time Detection of the index mark not to be used or as to look invalid.

A preferred embodiment of the invention The device and the method according to the invention will now explained in detail with reference to the accompanying drawing.

In this shows

Fig. 1 is a side sectional view of a preferred embodiment of the inventive apparatus for measuring a path,

Fig. 2 is a sectional view of the device of FIG. 1 along the line II,

Fig. 3 occurring in a preferred embodiment of the method signals or waveforms.

In Figs. 1 and 2, the housing of a piston rod 6, in particular a push rod of a master cylinder of a motor vehicle shown having 1. The piston rod 6 is displaceable within the housing 1 in accordance with an actuation of a brake pedal (not shown).

Various sensor systems are provided for detecting the position of the piston 6 within the housing 1 in accordance with the embodiment shown in FIGS. 1 and 2. In the exemplary embodiment shown, a first sensor system consists of two analog Hall elements 2 , 4 which, by interacting with two rod-shaped magnets 3 and 5, deliver two analog output signals. The Hall elements 2 , 4 are in this case integrated in the housing 1 , and the rod-shaped magnets 3 , 5 in the piston rod 6 . In principle, the sensitivity and linearity of such an arrangement after adapting the magnet dimensions and Hall parameters to the path to be measured are suitable for the requirements, for example in the case of an electro-hydraulic brake. The magnets 3 , 5 are installed in the piston rod 6 in such a way that their poles of the same name, for example the south poles S in the exemplary embodiment shown, touch on the end face. Due to the corresponding arrangement of the analog Hall elements 2 , 4 , when the piston rod 6 is displaced, two opposing signal voltage profiles U2, U4 arise, as are shown in principle in FIG. 3, below. The Hall elements expediently have an internal amplifier which is designed such that the signal voltages in connection with inexpensive Alnico magnets are in the range between 1 volt and 4 volts, so that a further amplification of the output signals of the Hall sensors is not necessary. The individual length of the rod-shaped magnets 3 , 5 is expediently chosen such that it is greater than the maximum travel of the piston rod 6 (brake pedal travel).

In contrast to the first sensor system, another sensor system is designed as an incremental system. In the exemplary embodiment shown, the second sensor system consists of Hall switches 7 , 8 , which interact with a series of magnetic pole changes 10 . Analogous to the two rod-shaped magnets 3 , 5 of the housing 1 , the pole changes 10 are an integral part of the piston rod 6 . They are preferably made of magnetizable plastics and used as strips in the piston rod 6 . The Hall switches 7 and 8 are arranged in such a way that, in conjunction with the series of magnetic pole changes 10 , they deliver two rectangular signal profiles A, B which are phase-shifted with respect to one another by 90 °, as shown in FIG. 3, above. This is achieved, for example, in that the geometric spacing of the magnetic centers of the Hall switches 7 , 8 is an n. (0.5.a) times the spacing of the magnetic pole centers (n is an integer and a is the width of one) Pole change or the distance between the pole centers). For example, it is possible to produce pole changes with center distances of 1 mm, so that in such a case the distance between the centers of the two Hall switches 7, 8 can be 4.5 mm. By means of such a square-wave signal that is phase-shifted by 90 ° or π / 2, a microcontroller 13 can be used to detect the direction of movement of the piston rod 6 (using known evaluation techniques). If you also evaluate the rising and falling edges of the two rectangular pulse sequences, you get four pulses (quadrature) per pole change. With a pole spacing of 1 mm, for example, a path resolution of 0.25 mm can be achieved. The quadrature signal Q, as generated and evaluated by the microcontroller 13 , is shown in FIG. 4, line 3 .

Another Hall switch 9 is used to scan a separate pole change 11 , which forms an index mark (see FIG. 3, line 4 , signal I). The incremental signal is defined based on this index mark. The incremental displacement sensor therefore delivers a total of three signal profiles, namely the signals A, B, I shown in FIG. 3, which are applied to the input of an evaluation circuit or of the microcontroller 13 .

In the embodiment shown, the rod-shaped magnets 3 , 5 are an integral part of the piston rod 6 , the respectively associated Hall sensors 2 , 4 being located in the housing 1 of the piston rod 6 , which surrounds the piston rod 6 in the region of the magnets 3 , 4 . The housing 1 can be designed so that it either has a through hole in which the piston rod 6 moves, or a U-shaped recess with which the sensor block can be placed on the piston rod 6 . To ensure that the Hall elements 2 , 4 and the Hall switches 7 , 8 , 9 are positioned in the correct position to the magnets 3 , 5 , 10 , 11 or remain in the correct position, an anti-rotation device is realized in that the The outer contour of the magnets 3 , 5 protrudes beyond the outer diameter of the piston rod 6 and engages in a corresponding extension 20 a of the through hole 20 (see FIG. 2). This configuration of the magnets 3 , 5 and the through hole 20 ensures that the piston rod 6 can be moved within the housing 1 without restriction, for which no additional components are required.

The housing 1 is also formed with a recess in which a wiring carrier 14 and the microcomputer 13 including the components required for its operation, such as voltage regulators, quartz, etc., are accommodated. The microcontroller is connected, for example, via lines 12 to a control device of the brake system.

To achieve higher resolutions, the incremental sensor system can also be designed as an optical incremental system. In such a case, the pole changes 10 are replaced by a row of holes which is located in a strip-shaped carrier which protrudes laterally from the piston rod. This row of holes is scanned, for example, with an encoder module such as that implemented by Hewlett Packard (HEDS 97 02). With such elements, resolutions of 0.05 mm can be achieved.

It is also possible by means of optically incremental Systems also evaluate index marks. They are too Combinations of magneto-incremental and optical incremental systems conceivable. Here it is for example possible using the pulse train signal optical encoder and the index mark through a magnetic pole change and corresponding Hall Realize switches.  

The incremental displacement sensor system delivers after detection the index mark a very precise path signal. This way signal does not have to be calibrated, since in principle no offset and no non-linearities occur. Due to the there is also no incremental mode of operation Temperature dependence of the path signal. As a disadvantage at a purely incremental mode of operation proves itself sometimes that none if the index mark is not recognized absolute path position can be derived. By combining the incremental sensor system with that described above Analog system, however, is possible, as below is explained to eliminate this disadvantage.

The incremental path signal can be used to calibrate the two analog measuring systems or sensors 2 , 4 . For this purpose, in a start-up procedure, the microcontroller 13 , which evaluates the sensor signals, is switched into a calibration mode using appropriate software. To carry out the calibration procedure, it is necessary to actuate the piston rod 6 once over the entire path to be measured. The index mark 11 or the signal I of the incremental system must be recognized. Beginning with the detection of the index mark, the two voltage values of the analog Hall sensors 2 , 4 are read into the microcomputer via (not shown in detail) analog-digital converters. Here a measurement value of the incremental system is assigned to their respective voltage value. A correction value for the strongly nonlinear analog path signals of the Hall sensors 2 and 4 is calculated from a deviation between the analog values and the incrementally determined values, and is stored, for example, in a table in the microcomputer 13 (EEPROM). It is also possible to measure the ambient temperature of the device via a temperature sensor (not shown). With this variable, the typical temperature response of the two Hall sensors 2 , 4 working analogously can be corrected if this is necessary for reasons of minimizing the measurement error. In this case, the signal is corrected, for example, on the software side by the microcomputer. The calibration procedure shown is only required once, for example when installing the system in the vehicle. A prerequisite for this type of sensor calibration is a bidirectional interface at the sensor output, in which case a CAN interface (Controller Area Network) is preferably used.

As a result of the calibration procedure, three independent signals are available for the generation of the path signal to be output, namely the corrected or linearized output signal of the analogue Hall sensor 2 , the corrected or linearized output signal of the analogue Hall sensor 4 and that by quadrature and counting the increments signal obtained from the three Hall switches 7 , 8 and 9 .

A typical possible use of the device according to the invention for motor vehicle operation will now be explained in detail. After switching on the ignition of the motor vehicle, it must be assumed that the brake signal can be actuated. In such a case, the output signal of the incrementally operating sensor system 8 , 9 , 11 is initially regarded as invalid because the index mark, which is the prerequisite for the initialization of the incremental system, has not yet been recognized. For this reason, one of the two output signals of the analog system 2 , 4 is used to generate the output signal of the displacement sensor. In the exemplary embodiment shown, the analog Hall sensor 2 is selected, for example. Its output voltage (linearized by means of the calibration explained above) is output via the CAN interface, for example, after various plausibility tests to be explained in more detail.

In the further course after switching on the ignition there will be a point in time at which the brake pedal is released. A corresponding constructive design of the arrangement of the Hall switch 9 or the index mark 11 ensures, in the case of the brake pedal not actuated, that the index mark 11 is reliably recognized by the Hall switch 9 . The detection of the index mark 11 triggers, in particular software-controlled, a switchover from the analog to the incremental measuring system, so that in the further course a measured value which is obtained digitally and has no offset or sensitivity error is output via the CAN interface of the computer can be.

A limitation on the accuracy of the digital signal is given by the achievable resolution of the path signal, which is determined by the distance of the magnetic pole changes is determined. However, it can usually be assumed that a path resolution of 0.25 mm for one to be detected Path length of 22 mm is sufficient. Such Resolution is with pole center distances of 1 mm and generation  of a quadrature signal can be reached. Should that Requirements for path resolution are higher for example the possibility of the incremental signal with the help of one of the two obtained analog Interpolate Hall signals.

In addition to the possibility of a very precise path detection shown, the sensor principle according to the invention also offers the possibility of using path signals that are independent of one another to achieve intrinsic safety of the system. In a first stage, for example, the two analog output voltages of the Hall elements 2 , 4 can be monitored in a differential image. If the difference is plausible, the count of the incremental encoder can be compared with one of the two analog output voltages of the Hall elements 2 , 4 and the output signal of the sensor can be made valid in this way. The defect can also be detected if one of the three measuring systems fails. In this case, information can be sent via the CAN output of the sensor without affecting the overall availability of the sensor.

Another possibility of evaluating the sensor signals obtained is to evaluate only the analog path signals of the Hall elements 2 , 4 and to use the digital signal to support these analog values. This procedure can also be carried out via the software of the microcomputer 13 without additional hardware expenditure.

By means of the device according to the invention, a self-calibrating displacement sensor provided, whose output signal is largely linear and  is independent of temperature. This is guaranteed by that an incremental system has two analog sensors calibrated for sensitivity and offset, the The sensor can be calibrated at the installation site. The respective output signals of the various sensor systems the device according to the invention are in one Microprocessor linked together, whereby the principle-related restrictions of the individual sensors cancel so that the device as a whole Safety requirements for a braking system are taken into account. It is possible to add further sensor signals, for example a Brake light switch signal or a pressure sensor signal in the Microcomputer feed and together with the signals of the Further processing of individual sensors.

Claims (14)

1. Device for measuring a path, in particular a brake pedal path in a motor vehicle, characterized by at least one analog sensor ( 2 , 4 ) which outputs an analog signal depending on the path to be measured, and at least one incrementally working sensor ( 7 , 8 ) , which outputs a pulse sequence signal as a function of the path to be measured, the analog signal and the pulse sequence signal being able to be related to one another in order to determine the path to be measured. 2. Device according to claim 1, characterized in that it has two analog sensors ( 2 , 4 ) and / or two incrementally working sensors ( 7 , 8 ). 3. Device according to one of claims 1 or 2, characterized in that the at least one analog sensor working as a with a bar magnet ( 3 , 5 ) cooperating Hall element ( 2 , 4 ) is formed. 4. Device according to one of the preceding claims, characterized in that the at least one incrementally working sensor ( 7 , 8 ) is designed as a Hall switch interacting with a series of magnetic pole changes ( 10 ). 5. Device according to one of claims 1 to 3, characterized characterized in that the at least one is incremental working sensor as an optical incremental sensor system is trained. 6. Device according to one of the preceding claims, characterized in that the incrementally operating sensor ( 7 , 8 ) with means ( 9 , 11 ) for determining and detecting an index mark, with respect to which the pulse train signal is definable, is formed. 7. The device according to claim 6, characterized in that the means for determining and recognizing an index mark as a with a magnetic pole change ( 11 ) cooperating Hall switch ( 9 ) or as an optically incremental sensor system. 8. Device according to one of the preceding claims 3 to 7, characterized in that the bar magnets ( 3 , 5 ) and the pole change ( 10 , 11 ) on a piston rod ( 6 ), in particular a push rod of a master cylinder of the motor vehicle, and the Hall Elements ( 2 , 4 ) and the Hall switches ( 7 , 8 , 9 ) are attached to a housing ( 1 ) surrounding the piston rod ( 6 ). 9. Device according to one of the preceding claims 2 to 8, characterized in that the incrementally working sensors ( 7 , 8 ) are arranged such that they deliver phase-shifted signal profiles to each other. 10. A method for measuring a path, in particular a brake pedal path in a motor vehicle, using a device according to one of the preceding claims, comprising the following steps:

• 1. Determination of at least one analog signal depending on the path to be measured,
• 2. Determination of at least one incremental signal as a function of the path to be measured, and
• 3. Relation of the analog signal and the incremental signal to obtain a signal which takes into account both the analog signal and the incremental signal and represents the path to be measured.

11. The method according to claim 10, characterized in that the at least one analog signal by means of the at least one an incremental signal is calibrated, wherein Starting from an index mark, the values of the analog signal each assigned a value of the incremental signal become. 12. The method according to claim 11, characterized in that from a deviation between the values of the analog signal and the incremental signal a correction value for the Analog signal is determined. 13. The method according to any one of the preceding claims 10 to 12, characterized in that two are at 90 ° to each other phase-shifted incremental signals can be determined and a quadrature signal based on these signals is calculated.   14. The method according to any one of claims 10 to 13, characterized characterized in that after switching on the device the path to be measured until the index mark is recognized is determined on the basis of the analog signals.