Low tire warning system

• US 5,721,528 A
• Filed: 12/23/1996
• Issued: 02/24/1998
• Est. Priority Date: 12/23/1996
• Status: Expired due to Term

• Current Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Original Assignee: Ford Global Technologies, LLC (Ford Motor Company)
• Inventors: Boesch, Mathew Alan, Rhode, Douglas Scott
• Primary Examiner(s): Hofsass, Jeffrey
• Assistant Examiner(s): TONG, NINA C
• Application Number:
  US08/772,642
• Time in Patent Office: 428 Days
• Field of Search: 340/442, 340/444, 340/445, 340/446, 340/447, 340/448, 73/146.2, 73/146.3, 73/146.4, 73/146.5, 116/34 R, 200/61.22, 364/565, 364/424.034
• US Class Current: 340/442
• CPC Class Codes: B60C 23/061 by monitoring wheel speed measuring distance traversed on the ground by vehicles G01C22/00

Abstract

A system and method that monitors four wheel sensors of an automotive vehicle to determined changes in the effective rolling radii of any wheel and a low pressure tire condition. Certain vehicle operating conditions, such as excessive or very low speeds, braking, and turns, are determined from the sensor outputs and are used to prevent erroneous detection of changes in effective rolling radii. Data from the sensors that is determined to be acceptable is accumulated over time as displacement values for each wheel. When the displacement values exceed a predetermined value, a metric function is used to compare differences detected in accumulated displacement values for the front pair of wheels and for the rear pair of wheels. If the difference between compared pairs of wheels is excessive, as compared with a predetermined baseline metric value, a low tire condition is detected. Further accumulation of instances where the metric indicates a detected condition, provides confidence that the condition actually exists and a warning is provided to the vehicle operator. Resetting of the system and the baseline metric is performed when the low tire condition is corrected or when the tires are checked and properly inflated.

Claims

1. A low tire inflation warning system for an automotive vehicle comprising:

a wheel containing a pneumatic tire on both sides of the front of the vehicle;

a wheel containing a pneumatic tire on both sides of the rear of the vehicle;

angular displacement sensors associated with each wheel, to provide output signals corresponding to the rotation of each wheel;

processor means for sampling said output signals of said angular displacement sensors over predetermined time periods to determine the occurrence of a low tire; and

warning means that is activated when said processor means indicates the occurrence of a low tire greater than a predetermined threshold number of occurrences;

said processor means is programmed to;

determine a velocity value for said each wheel, a longitudinal acceleration value for said each wheel, a lateral acceleration value for the front pair of wheels, a lateral acceleration value for the rear pair of wheels, a displacement value for said each wheel, and a metric value based upon a predetermined relationship of an accumulation of displacement values for said each wheel during several sampling periods;

prevent the determining of the displacement of said each wheel when any velocity value is outside upper and lower predetermined limits;

prevent the determining of the displacement of said each wheel when any longitudinal acceleration value is above a predetermined maximum limit;

prevent the determining of the displacement of said each wheel when the smaller of the two said lateral acceleration values is above a predetermined maximum limit; and

prevent the determining of the metric value until the accumulation of the displacement values for any wheel exceeds a predetermined threshold displacement value.

2. A low tire inflation warning system as in claim 1, wherein said processor means is further programmed to compare each determined metric value with a predetermined base-line metric value and to accumulate each occurrence that comparison results in said each determined metric value differs from said predetermined base-line metric value by a predetermined amount;

and to provide an activation signal to said warning means when said accumulated occurrences exceed a second predetermined value.

3. A method of detecting a partially deflated pneumatic tire on a vehicle having a wheel at both sides of the front of the vehicle and a wheel at both sides of the rear of the vehicle, comprising the steps of:

sensing the angular rotation of each wheel;

calculating a velocity value of said each wheel according to the sensed angular rotation over several predetermined sampling periods;

calculating and accumulating displacement values θ

for said each wheel over said several predetermined sampling periods;

calculating a metric value

U=((θ

fl-θ

fr)/θ

flθ

fr)-((θ

rl-θ

rr)/θ

rlθ

rr) when said displacement values θ

for any wheel exceeds a predetermined displacement value, wherein

θ

fl is the front left wheel accumulated displacement value,

θ

fr is the front right wheel accumulated displacement value,

θ

flθ

fr is the mean value of the front left wheel accumulated displacement value θ

fl and the front right wheel accumulated displacement value θ

fr,

θ

rl is the rear left wheel accumulated displacement value,

θ

rr is the rear right wheel accumulated displacement value,

θ

rlθ

rr is the mean value of the rear left wheel accumulated displacement value θ

rl and the rear right wheel accumulated displacement value θ

rr;

comparing said calculated metric value with a predetermined metric value;

accumulating each occurrence that said comparing step results in said calculated metric value differing from said predetermined metric value by at least a predetermined amount; and

providing an activation signal to a warning means when said accumulated occurrences exceed a predetermined threshold number of occurrences.

4. A method as in claim 3, wherein said accumulating step includes positively accumulating each occurrence that said comparing step results in said calculated metric value differing from said predetermined metric value by at least said predetermined amount and negatively accumulating each occurrence that said comparing step results in said calculated metric value not differing from said predetermined metric value by said at least the predetermined amount;

and providing an activation signal to said warning means when the sum of said positively and negatively accumulated occurrences exceeds said predetermined threshold number of occurrences.

5. A method as in claim 3, which further includes the step of providing for inputting a resetting command to deactivate said activation signal after a sensed low tire has been serviced.

6. A method of detecting a partially deflated pneumatic tire on a vehicle having a wheel at both sides of the front of the vehicle and a wheel at both sides of the rear of the vehicle, comprising the steps of:

sensing the angular rotation of each wheel;

calculating a velocity value of said each wheel according to the sensed angular rotation over a predetermined sampling period;

deriving a longitudinal acceleration value of said each wheel over said predetermined sampling period;

comparing each velocity value with a predetermined minimum acceptable velocity value and a predetermined maximum acceptable velocity value to determine if any velocity value is below the predetermined minimum acceptable velocity value or above the predetermined maximum acceptable velocity value;

comparing each longitudinal acceleration value with a corresponding predetermined maximum acceptable longitudinal acceleration value to determine if any longitudinal acceleration value is above the corresponding predetermined maximum acceptable longitudinal acceleration value;

calculating and accumulating displacement values θ

for said each wheel over several of said predetermined sampling periods in which said comparing steps indicate velocity values and acceleration values are within acceptable limits;

calculating a metric value

U=((θ

fl-θ

fr)/θ

flθ

fr)-((θ

rl-θ

rr)/θ

rlθ

rr) when said displacement values θ

for any wheel exceeds a predetermined displacement value, wherein

θ

fl is the front left wheel accumulated displacement value,

θ

fr is the front right wheel accumulated displacement value,

θ

flθ

fr is the mean value of the front left wheel accumulated displacement value θ

fl and the front right wheel accumulated displacement value θ

fr,

θ

rl is the rear left wheel accumulated displacement value,

θ

rr is the rear right wheel accumulated displacement value,

θ

rlθ

rr is the mean value of the rear left wheel accumulated displacement value θ

rl and the rear right wheel accumulated displacement value θ

rr;

comparing said calculated metric value with a first predetermined metric value;

accumulating each occurrence that said calculating metric comparing step results in said calculated metric value exceeding said first predetermined metric value by at least a predetermined amount; and

providing an activation signal to a warning device when said accumulated occurrences exceed a predetermined occurrence value.

7. A method as in claim 6, wherein said accumulating step includes positively accumulating each occurrence that said comparing step results in said calculated metric value differing from said first predetermined metric value and negatively accumulating each occurrence that said comparing step results in said calculated metric value not differing said first predetermined metric value;

and providing the activation signal to said warning means when the sum of said positively and negatively accumulated occurrences exceeds said predetermined occurrence value.

8. A method as in claim 6, wherein said step of calculating the velocity value V of said each wheel is performed by using a filter technique according to the relationship:

space="preserve" listing-type="equation">Vk=α

(Vk-1)+(1α

)(μ

k),

wherein

Vk becomes the filtered velocity value for the most recent of k samples;

α

is a constant, less than 1;

Vk-1 is the filtered velocity value for the sampling immediately preceding the most recent sampling; and

μ

k is the sensed angular rotation rate for the most recent sampling.

9. A method as in claim 8, further including the steps of:

deriving a lateral acceleration value of the front pair of wheels over said predetermined sampling period; and

deriving a lateral acceleration value of the rear pair of wheels over said predetermined sampling period; and

wherein said steps of deriving the lateral acceleration values A_lat of each said pair of wheels is performed by using the filter technique according to the relationship;

space="preserve" listing-type="equation">A.sub.latf =κ

(V.sub.wfl -V.sub.wfr) (V.sub.wfl +V.sub.wfr) and A.sub.latr =κ

(V.sub.wrl -V.sub.wrr) (V.sub.wrl +V.sub.wrr),

wherein

κ

is a constant;

V_wfr is the velocity value calculated for the front left wheel;

V_wfl is the velocity value calculated for the front right wheel;

V_wrl is the velocity value calculated for the rear left wheel; and

V_wrr is the velocity value calculated for the rear right wheel.

10. A method as in claim 6, further including the steps of:

deriving a lateral acceleration value of the front pair of wheels over said predetermined sampling period; and

deriving a lateral acceleration value of the rear pair of wheels over said predetermined sampling period; and

wherein said steps of deriving the lateral acceleration values A_lat of each said pair of wheels is performed by using the a filter technique according to the relationship;

space="preserve" listing-type="equation">A.sub.latf =κ

(V.sub.wfl -V.sub.wfr) (V.sub.wfl +V.sub.wfr)and A.sub.latr =κ

(V.sub.wrl -V.sub.wrr) (V.sub.wrl +V.sub.wrr),

wherein

κ

is a constant;

V_wfl is the velocity value calculated for the front left wheel;

V_wfr is the velocity value calculated for the front right wheel;

V_wrl is the velocity value calculated for the rear left wheel; and

V_wrr is the velocity value calculated for the rear right wheel.

11. A method as in claim 6, wherein said step of deriving the longitudinal acceleration value A_lng of said each wheel is performed by using a filter technique according to the relationship:

space="preserve" listing-type="equation">A.sub.lng k=α

(A.sub.lng k-1)+β

Vk-Vk-1!,

wherein

α

is a constant, less than 1;

β

is a constant;

Vk is the most recently calculated velocity for the most recent of k samplings of sensed angular rotation rate of several samplings that occur during the predetermined sampling period;

Vk-1 is the calculated velocity for the sampling of sensed angular rotation rate immediately preceding the most recent sampling; and

A_lng k-1 is the longitudinal acceleration derived from the calculated velocity immediately preceding the most recently calculated velocity.

12. A method as in claim 6, further including the step of comparing the smaller value of the derived lateral acceleration values of the front pair and rear pair of wheels with a predetermined maximum acceptable lateral acceleration value prior to said step of calculating and accumulating displacement values.

13. A method of detecting a partially deflated pneumatic tire on a vehicle having a wheel at both sides of the front of the vehicle and a wheel at both sides of the rear of the vehicle, comprising the steps of:

sensing the rotation of each wheel;

sampling said sensed rotation of said each wheel over predetermined time periods to determine the occurrence of a low tire; and

warning the vehicle operator when said step of sampling indicates the occurrence of a low tire over a predetermined threshold number of occurrences; and

said sampling step includes the steps of;

determining a velocity value for said each wheel, a longitudinal acceleration value for said each wheel, a lateral acceleration value for the front pair of wheels, a lateral acceleration value for the rear pair of wheels, a displacement value for said each wheel, and a metric value based upon a predetermined relationship of an accumulation of displacement values for said each wheel during several sampling periods;

preventing the determining of the displacement value of said each wheel when any velocity value is outside upper and lower predetermined limits;

preventing the determining of the displacement value of said each wheel when any longitudinal acceleration value is above a predetermined maximum limit;

preventing the determining of the displacement value of said each wheel when the smaller of lateral acceleration values is above a predetermined maximum limit; and

preventing the determining of the metric value until the accumulation of the displacement values for any wheel exceeds a predetermined threshold displacement value.

14. A method as in claim 13, wherein said sampling step further includes the steps of comparing each determined metric value witha predetermined base-line metric value and accumulating each occurrence that comparing results in said metric value differing from said predetermined base-line metric value by at least a predetermined amount;

and to provide a warning when said accumulated occurrences exceed apredetermined threshold number of occrrences.