Vehicle speed estimation for antilock braking using a chassis accelerometer

• US 5,579,230 A
• Filed: 06/10/1991
• Issued: 11/26/1996
• Est. Priority Date: 06/10/1991
• Status: Expired due to Fees

• Current Assignee: General Motors Corporation (General Motors Company)
• Original Assignee: General Motors Corporation (General Motors Company)
• Inventors: Sidlosky, David M., Lin, William C.
• Primary Examiner(s): Teska, Kevin J.
• Assistant Examiner(s): LOUIS JACQUES, JACQUES H
• Application Number:
  US07/712,287
• Time in Patent Office: 1,996 Days
• Field of Search: 364/424.05, 364/426.02, 364/424.1, 364/426.05, 364/426.01, 364/426.04, 364/426.03, 303/21 A, 303/21 B, 303/100, 303/156, 303/182, 303/192, 303/158, 303/196, 303/183, 180/197, 73/117, 73/105, 73/862, 280/707
• US Class Current: 701/70
• CPC Class Codes: B60T 2250/04 Vehicle reference speed; Vehicle body speed
• CPC Class Codes: B60T 8/172 Determining control parameters used in the regulation, e.g. by calculations involving measured or detected parameters B60T8/17551 takes precedence

Abstract

Before braking occurs the speed of non-driven wheels is monitored and averaged to determine vehicle speed and an integrator is initialized with that speed. Acceleration is periodically calculated from the vehicle speed, stored in a ring buffer and averaged. The output of a chassis accelerometer is also sampled during the same periods and stored in a similar ring buffer and averaged. Accelerometer bias due to slope or drift is determined as the difference of the two averaged accelerations. The noise level of the accelerometer bias is determined by filtering and rectification. After braking occurs, the accelerometer output is corrected by subtracting the bias and the noise and is then used to continuously update the integrator output to provide an estimate of vehicle speed during braking.

Claims

1. In a vehicle having wheels with wheel speed sensors providing a measure of wheel speed, wheel brakes for braking said wheels, a brake application sensor providing an indication of operation of said wheel brakes for braking said vehicle, and a chassis accelerometer providing a measure of vehicle acceleration that is offset from actual vehicle acceleration due to vehicle inclination, a method of estimating vehicle speed during operation of said brakes for braking said vehicle, the method comprising the steps of:

prior to said brake application sensor providing said indication of operation of said wheel brakes, (A) determining actual vehicle speed as represented by said measure of wheel speed provided by said wheel speed sensors, (B) determining actual vehicle acceleration from said determined actual vehicle speed, and (C) determining a difference between said determined actual vehicle acceleration and said measure of vehicle acceleration provided by said chassis accelerometer, said difference comprising an accelerometer bias, and

while said brake application sensor provides said indication of operation of said wheel brakes, (A) subtracting said accelerometer bias from said measure of vehicle acceleration provided by said chassis accelerometer to obtain a corrected measured vehicle acceleration and (B) estimating vehicle speed by integrating said corrected measured vehicle acceleration from an initial vehicle speed value equal to a last determined actual vehicle speed prior to said indication of operation of said wheel brakes.

2. In a vehicle having wheels with speed sensors providing a measure of wheel speed, wheel brakes for braking said wheels, a brake application sensor providing an indication of operation of said wheel brakes for braking said vehicle, and a chassis accelerometer providing a measure of vehicle acceleration that is offset from actual vehicle acceleration due to vehicle inclination, a method of estimating vehicle speed during operation of said brakes for braking said vehicle, the method comprising the steps of:

prior to said brake application sensor providing said indication of operation of said wheel brakes, (A) determining actual vehicle speed as represented by said measure of wheel speed provided by said wheel speed sensors, (B) determining actual vehicle acceleration from said determined actual vehicle speed, (C) filtering each of said determined actual vehicle acceleration and said measure of vehicle acceleration so that time delays associated with said step of filtering are the same for each of said filtered actual vehicle acceleration and said filtered measure of vehicle acceleration at all frequency components of said determined actual vehicle acceleration and said measure of vehicle acceleration, and (D) determining a difference between said filtered actual vehicle acceleration and said filtered measure of vehicle acceleration, said difference comprising an accelerometer bias, and

while said brake application sensor provides said indication of operation of said wheel brakes, (A) subtracting said accelerometer bias from said measure of vehicle acceleration provided by said chassis accelerometer to obtain a corrected measured vehicle acceleration and (B) estimating vehicle speed by integrating said corrected measured vehicle acceleration from an initial vehicle speed value equal to a last determined actual vehicle speed prior to said indication of operation of said wheel brakes.

3. An apparatus for estimating vehicle speed during vehicle braking, comprising:

means for sensing wheel speed of at least one vehicle wheel;

a chassis accelerometer for measuring vehicle acceleration, said measured vehicle acceleration being offset from an actual vehicle acceleration due to vehicle inclination;

a brake sensor for detecting vehicle braking; and

a computer coupled to said means for sensing speed, said chassis accelerometer and said brake sensor and being programmed to;

before detection of vehicle braking, (A) determine actual vehicle speed as represented by said sensed wheel speed, (B) compute an actual vehicle acceleration value from said actual vehicle speed for each of consecutive sampling periods and store a last predetermined number of computed actual vehicle acceleration values in memory, (C) sample a value of said measured vehicle acceleration in each of said consecutive sampling periods and store said last predetermined number of sampled values of measured vehicle acceleration in memory, (D) average said stored actual vehicle acceleration values, (E) average said stored values of measured vehicle acceleration, and (F) determine a difference between said averages, said difference comprising an accelerometer bias, and

during detection of vehicle braking, (A) subtracting said accelerometer bias from said measured vehicle acceleration to obtain a corrected measured vehicle acceleration and (B) estimating vehicle speed by integrating said corrected measured vehicle acceleration from an initial vehicle speed value equal to a last determined actual vehicle speed prior to detection of vehicle braking.