Measuring and testing – Brake testing
Reexamination Certificate
1999-03-26
2001-12-25
McCall, Eric S. (Department: 2855)
Measuring and testing
Brake testing
C073S129000, C701S070000
Reexamination Certificate
active
06332354
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method and apparatus for determining vehicle brake effectiveness and changes in vehicle mass.
BACKGROUND OF THE INVENTION
In order for a driver to operate a vehicle safely he must know and have confidence in the stopping distance, and thereby the deceleration rate, of the vehicle in all environments. Drivers learn to judge this distance based on vehicle speed, road slope, road surface and load conditions.
Two conditions that can alter the driver's perception of a safe stopping distance are a non-functioning or partially functioning brake system or an unknown overload condition. As brakes do not wear linearly and can be affected by temperature, brake lining condition, moisture, adjustment, and mechanical problems, stopping distance can change over a short period. In addition, a vehicle may take on an unexpectedly heavy load, thus affecting stopping distance or vehicle deceleration rate.
Various systems for checking the effectiveness of vehicle braking systems are known. Common methods include visual inspection, mechanical devices (roller testers, plate testers), brake pressure gauges, and weigh scales to assure proper vehicle mass.
U.S. Pat. No. 5,299,452 (Caron et al.) determines vehicle braking effectiveness by first measuring engine torque to automatically calculate vehicle mass and then employing a complex averaging method to attempt to mitigate the effects of road slope, head winds, tail winds and the like. The accuracy of vehicle mass calculated by this method, using engine torque, is dependant on constant engine horsepower, transfer of horsepower to the wheels, fuel consumption, altitude, road surface and a level acceleration area. Changing vehicle conditions and variations in normal driving conditions such as uneven terrain, can significantly distort the calculation of vehicle mass using this method. In addition, estimating brake effectiveness based on level road conditions does not account for travelling up or down a slope. A brake effectiveness test that does not take into consideration road slope does not offer the real time feedback necessary to provide a true safety application.
It would therefore be desirable to provide a method and apparatus for providing feedback on vehicle brake effectiveness for vehicles that do not decelerate in the expected rate over a large spectrum of environments.
It would further be desirable to provide a method and apparatus of assessing vehicle brake effectiveness which takes into consideration travelling up or down a slope, differences in drag forces such as air friction and engine friction and engine brake engagement.
It would also be desirable to provide a method and apparatus of assessing vehicle brake effectiveness which includes a means of manually or automatically inputting the actual mass of the vehicle for use in calculating vehicle brake effectiveness.
It would further be desirable to provide a method and apparatus of assessing vehicle brake effectiveness based on a comparison with known vehicle deceleration rates for a known vehicle mass at 100% braking effectiveness.
It would also be desirable to provide a method and apparatus of assessing vehicle brake effectiveness based on a comparison with the minimum acceptable deceleration rate for the vehicle.
It would also be desirable to provide a method and apparatus of assessing vehicle brake effectiveness based on driver expected deceleration rates or on vehicle braking effectiveness history. Data collected on historical braking effectiveness can provide trends which may be critical in assessing real time vehicle safety and monitoring vehicle maintenance requirements.
A further desirable object is to provide an apparatus and method for alerting an operator to a deterioration in braking effectiveness or to a mass overload situation so that corrective action could be taken before the problem becomes critical.
It is also desirable that a method and apparatus be provided which will permit easy access to stored vehicle brake effectiveness data by certain authorized government regulatory agencies for the purpose of accessing vehicle safety.
While other methods of assuring effective braking for the main purpose of driver feedback and safety have a certain degree of efficiency in certain environments or braking areas, they do not provide the advantages of the improved methods and apparatus of the present invention as hereafter more fully described.
SUMMARY OF THE INVENTION
Determination of vehicle brake effectiveness is accomplished by comparing predicted vehicle deceleration rates and driver expected deceleration rates, with actual measured vehicle deceleration. Predicted and expected deceleration rates are adjusted for variations in driving conditions such as slope and drag.
If vehicle brake effectiveness is considered to be 100%, relative gross vehicle weight (GVW) can also be estimated by a comparison of predicted vehicle deceleration rates with the actual measured vehicle deceleration rate.
An input device, which may be an interactive display/input device, allows the operator to input load information manually, or automatically through a radio frequency (RF) input interface or other standard communication means connected to an automated weigh scale. In this way, mass stored in memory provides an accurate figure, which can always be assured. As mass has a great impact on deceleration it is important that this figure be accurate and consistent. A minimum acceptable deceleration rate is also input and fixed in memory for comparison to actual vehicle deceleration rates.
For economic considerations it is desirable that the device obtain data from various existing sensors which gather and use the data for other purposes. This eliminates the need for the installation of additional sensors and control devices. Most modern tractor semi-trailers are equipped with an electronic control unit (ECU) which generates a signal representative of vehicle wheel speed, distance, RPM, gear ratio and brake system pressure. In some older vehicles which do not have the necessary sensors or ECU, it may be necessary to install sensors and ECUs to gather and process the required data.
Pressure transducers located throughout the vehicle measure pressure applied to the brake air chambers when the vehicle is being decelerated during an application of its brakes. This data is sent to the vehicle ECU via the automatic braking system (ABS) and a signal representative of the brake system pressure is generated. At the same time, or in the alternative, a brake treadle pressure sensor may be used to determine brake system pressure.
Road slope is calculated by comparing measurements from a low-G accelerometer with wheel based deceleration rates taken from the ABS. Slope angle is used to adjust deceleration rates for a more accurate comparison with actual and expected values.
In addition, the main ECU provides data on vehicle speed, engine torque, engine RPM and engine brake engagement (exhaust brake) which is used to adjust deceleration for drag forces. Engine brake engagement is monitored to assess the validity of any results. If the engine brake is engaged, results are invalidated and discarded.
Actual deceleration is compared to predicted deceleration which has been adjusted for slope and drag. Actual deceleration is also compared to driver expected deceleration rates and a minimum acceptable deceleration rate. Historic deceleration data stored by the computer can-be used to assess vehicle brake effectiveness over time and determine maintenance schedules or provide data for government safety inspections. Comparisons are highly accurate due to the various adjustments for slope and drag and the accurate value for vehicle mass which has been manually or automatically input. The computer collects and stores data on vehicle brake effectiveness over time for the purposes of historical comparison, maintenance assessment and brake inspection.
The invention provides feedback on vehicle deceleration rate and signals a trend of degrading brake effectiveness during vehicle
Lalor Tom
Loam John
Luker Craig
Hoffman Wasson & Gitler
Lalor Tom
McCall Eric S.
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