Anti-lock braking system containing look-up table for determining wheel velocity and acceleration
First Claim
1. An anti-lock braking system comprising;
- a mechanism for releasing a brake on a wheel; and
an electronic System Coupled to the mechanism, wherein the electronic system senses velocity of the wheel and controls when the mechanism to releases the brake to prevent locking, the electronic system comprising;
a motion sensor adapted to measure a time required for the wheel to move a fixed distance and generate a first signal indicating a fixed point representation of the time;
a shift circuit coupled to receive the first signal, wherein the shift circuit shifts the first signal to generate a second signal which indicates a factor;
a look-up table memory coupled to receive the second signal from the shift circuit and generate a data signal indicating a value which is stored in the look-up table memory, at an address indicated by the second signal, the value indicating a multiplicative inverse of the factor indicated by the second signal; and
a decompressor coupled to receive the data signal from the look-up table memory, wherein the decompressor converts the data signal to a signal indicating the velocity of the wheel.
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Abstract
An anti-lock braking system includes a mechanism for releasing a brake and a digital circuit for determining a wheel velocity and controlling the mechanism to prevent the brake from locking. The digital circuit uses a look-up table which, in response to an address signal, provides a signal indicating a multiplicative inverse of a number between 1 and 2. The circuit receives a measured time for a wheel to move a fixed distance and factors the time as product a power of two and a factor between 1 and 2. An address signal indicating the factor is applied to the look-up table, and the look-up table provides a signal which indicates the inverse of the factor. The signal from the look-up table is then converted to the proper scale for the time. Factoring and conversion may be accomplished with logical shifts so that no multiplier is required. The look-up table may be compressed by not storing bits of inverses, which are constant or only change once within the range of the look-up table and by only storing look-up values for every other number within the range of the look-up table. A code bit in each look-up table value permits generation of correct inverses for values not stored.
16 Citations
8 Claims
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1. An anti-lock braking system comprising;
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a mechanism for releasing a brake on a wheel; and an electronic System Coupled to the mechanism, wherein the electronic system senses velocity of the wheel and controls when the mechanism to releases the brake to prevent locking, the electronic system comprising; a motion sensor adapted to measure a time required for the wheel to move a fixed distance and generate a first signal indicating a fixed point representation of the time; a shift circuit coupled to receive the first signal, wherein the shift circuit shifts the first signal to generate a second signal which indicates a factor; a look-up table memory coupled to receive the second signal from the shift circuit and generate a data signal indicating a value which is stored in the look-up table memory, at an address indicated by the second signal, the value indicating a multiplicative inverse of the factor indicated by the second signal; and a decompressor coupled to receive the data signal from the look-up table memory, wherein the decompressor converts the data signal to a signal indicating the velocity of the wheel. - View Dependent Claims (2, 3, 4, 5, 6)
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7. A velocity sensor for an anti-lock braking system, comprising:
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a motion sensor which, in response to a wheel moving a fixed distance, asserts a first signal which represents a time for the wheel to move the fixed distance; a shift circuit coupled to receive the first signal, wherein the shift circuit shifts bits in the first signal to generate a second signal which indicates a factor of the time; a look-up table memory having an address bus coupled to receive the second signal from the shift circuit; and a decompressor circuit coupled to the look-up table, wherein the decompressor circuit converts a data signal from the look-up table to a third signal representing a velocity of the wheel. - View Dependent Claims (8)
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Specification