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doubt regarding yaw rate circuit in abs/esp

Discussion in 'General Electronics Discussion' started by bobdxcool, Apr 15, 2012.

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  1. bobdxcool

    bobdxcool

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    Mar 9, 2012
    guys the diagarm i have attached is the interfacing circuit for yaw rate and lateral acceleration sensor combined in Electronic stability control /ESC/ESPused in vehicles.


    could someone expain how the circuit works?

    (yaw rate sensor (and lateral acceleration sensor) measures the rotational acceleration of a vehicle along the vertical axis.)
     

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  2. bobdxcool

    bobdxcool

    98
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    Mar 9, 2012
    doubt regarding wheel speed sensor circuit in abs/esp

    guys the diagarm i have attached is the interfacing circuit for wheel speed sensor in Electronic stability control /ESC/ESP and ABS used in vehicles.


    could someone expain how the circuit works..

    actually there are 2 comparators in the circuit for comparing the wheel speeds between different tyres ...but i cant understand why 2nd level hystersis compaartor 74hc14 is used..

    could someone expain the circuit operation?
     

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  3. bobdxcool

    bobdxcool

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    Mar 9, 2012
    DOUBT regarding steering angle circuit in esp

    guys the diagarm i have attached is the interfacing circuit for steering angle sensor in Electronic stability control /ESC/ESPused in vehicles.


    could someone expain how the waveforms are generated (which i have attached) from the microcontroller pins which is connected to optical encoder of steering wheel to measure steering wheel angle. atleast the basic concept of waves generation will help me.
     

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  4. jackorocko

    jackorocko

    1,284
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    Apr 4, 2010
    did you really need to start 3 threads all over basically the same issue, the electronic stability control /esc/esp used in vehicles?
     
  5. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I think you'll find that the wheel speed sensor pulls the input low for a brief (and constant) duration with the period between the pulses dependant on speed.

    The output is thus low at speeds exceeding some value, and high otherwise.

    I would imagine that this is designed some function at a certain crossover speed.

    The hysteresis of the Schmitt trigger inverter is used so that a definite mode is selected. It will not rapidly switch between both modes when you are driving at (or very near) the corossover speed.

    Some examples that I'm aware of are

    1) air-bags being disabled at low speeds
    2) active steering operating in a different mode for high speed steering as opposed to low speed manoeuvring.
    3) ABS systems also need to know if the wheels have stopped due to the vehicle stopping, or due to a single wheel locking up. At low seeds the ABS is disabled so you can use the brake to hold the vehicle stationary!
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    I wouldn't have thought so. I've spent time answering one.
     
  7. TedA

    TedA

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    16
    Sep 26, 2011
    > could someone expain how the circuit works?

    > (yaw rate sensor (and lateral acceleration sensor) measures the rotational acceleration of a
    > vehicle along the vertical axis.)

    The diagram shows an input network followed by a Sallen-Key low pass filter. Presumably some sort of transducer signal enters at "XAIN".

    The DC component of the input signal will be amplified a bit, while the higher frequency signal components are attenuated. The output has a low impedance.

    The input network, R1, R2, C1, and D1, may provide a specified load to the signal source. It provides a DC path to ground for the non-inverting input of U5. If the signal source has a finite impedance, C1 will provide some low pass filter function. This network, along with the signal source, forms part of the following Sallen-Key filter stage. The diodes prevent excessive signals from reaching U5, and may improve transient response to overloads.

    Once you know what to Google, info on Sallen-Key filters is not hard to find.

    An LMX324 is no doubt a riff on the National LM124 family of quad op-amps. Since we have no component values, the parameters of the filter are unknown, but we can guess that there might be a little DC gain and that the expected output will not extend beyond a few kilohertz. The signal had better be positive-only, relative to the op amp's negative power pin.


    For now, I think I will pass on your second circuit, since someone else is helping with that. We really don't have enough information about the rest of the story to get too far with this one.


    > could someone expain how the waveforms are generated (which i have attached) from the microcontroller pins > which is connected to optical encoder of steering wheel to measure steering wheel angle. atleast the basic
    > concept of waves generation will help me.
    Here's my best shot at what's going on here:

    U1 is a controller IC. Only a few of its pins are shown in this diagram. The three pins connected to U4 are all digital inputs to the controller. The pin connected to pin 4 of U2 is an output, conveying serial data. The pin connected to pin 4 of U2 is an input for serial data.

    U4 is a rotary encoder. The encoder has three digital outputs. It has two quadrature outputs, PP1 and PP2, plus an index output, INT. As the mechanical input to the encoder rotates, these outputs convey information about the rotation. There is plenty of info online, once you know the key words describing the device. Look here, for instance:
    http://zone.ni.com/devzone/cda/tut/p/id/4763

    Note that you see the nice pair of squarewaves on the quadrature outputs when the rotation is at a constant speed. When you stop the rotation, the signals become constant DC levels.

    U2 is a CAN bus interface IC. The CAN bus ties together a vehicular network. Same sort of thing as an Ethernet. Digital signals on both sides of the interface IC.

    The waveforms illustrate how the signals from the rotary encoder are interpreted by the processor.

    The three encoder output signals are shown at the top. These are digital signals, but you could probe them with an analog 'scope and see what is shown here.

    The lower, staircase, waveform represents how the processor interprets the encoder signals. This waveform might represent the value of a variable in the processor's memory. There is no voltage in the circuit that would look like this when probed by your analog 'scope.

    In the drawing, we first see the INT signal go high. With most encoders, this signal happens only once over the range of rotation we are encoding. Perhaps it goes low only at one extreme of the steering gear's rotation. The lower graph would then indicate one endpoint for the possible values reflecting the rotation.

    We next see a series of quadrature pulses on PP1 and PP2 that indicate fairly constant rotation on one direction. The lower graph steps up each time an edge occurs at either quadrature signal.

    About one third of the way across our graph, the encoder signals indicate that the rotation stops, then reverses direction. There is a brief interval of back and forth motion too small to cause a pulse at PP2. For a short time, our graph isn't going anywhere. ( We are at the top of the stairs.)

    Next the encoder outputs indicate a fairly constant rotation in the other direction. The graph steps down to a low value.

    Another reversal of direction is seen about two thirds of the way across the graph. Once again, after a bit of dither, the graph steps upward.

    It is not clear why no additional change is seen in the INT signal. One would expect to see INT go low again about two thirds of the way across, while our graph actually falls below the initial value. I suspect that this is a drafting error. ( Perhaps it's an old car and there is a lot of play in the steering. Better run one front tire a little soft. Never mind…)

    There is no way to tell what the processor is doing with this information. It could be sending a number representing the position reported by the encoder out onto the can bus. It could be combining the position information with other parameters, perhaps from additional sensors, and sending commands to a motor that applies torque to the steering gear.

    I hope this is of help to you.

    Ted
     
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