GB2124383A

GB2124383A - Vehicle break efficiency meter

Info

Publication number: GB2124383A
Application number: GB08221585A
Authority: GB
Inventors: Henry Brian Spencer; Gwilym Morris Owen
Original assignee: National Research Development Corp UK
Current assignee: National Research Development Corp UK
Priority date: 1982-07-26
Filing date: 1982-07-26
Publication date: 1984-02-15

Abstract

A vehicle brake efficiency meter 10 e.g. consists of a damped- pendulum transducer 12 coupled to a potentiometer 14. The analogue output of the potentiometer 14, following a braking test with the vehicle concerned, is sampled in a peak/trough detector 16. A micro- processor 18 comprising signal processing unit 20 and arithmetic unit 22 controls the sampling and sums, averages and displays the deceleration on a digital display 24. A suitably programmed small computer may be used in place of micro- processor 18. <IMAGE>

Description

SPECIFICATION Vehicle brake efficiency meter The present invention relates to a vehicle brake efficiency meter, i.e. to a meter that measures the braking efficiency of a vehicle.

The braking efficiency of a vehicle is usually measured with meters incorporating an accelerometer. The meters of this kind currently in use make use of a mechanical rachet to lock the accelerometer scale at the position reached during the braking test thereby to enable a reading of deceleration to be recorded. Other known accelerometer-based meters use a proper chart record of the deceleration occurring during the braking test.

Both these meters suffer from disadvantages.

Thus the mechanical rachet type will record only the maximum deceleration value and this will not be representative of the average deceleration value if surface conditions vary significantly at the test site. The chart record type, on the other hand, suffers from the disadvantage that it requires further processing to obtain the average deceleration occurring over the test.

In the meter of the present invention, rachet mechanisms and chart records are omitted and the above drawbacks are therefore avoided.

According to the present invention, a vehicle brake efficiency meter comprises a decelerometer linked to a microprocessor or small computer operative to average out any deceleration peaks and subsequent troughs occurring when vehiclesupporting regions at a braking test site provide the wheels of the vehicle with a better than average grip.

Conveniently, the output signal after processing by the microprocessor or computer to determine the average deceleration occurring over the test can be displaced and/or stored for subsequent averaging from repeated brakings tests.

In the latter case, the microprocessor or small computer might, for example, be so programmed that up to 99 tests, say, could be performed, the results stored, and subsequently the mean value obtained and displayed by the meter.

The microprocessor or computer is preferably so programmed that the displayed deceleration can be in selectable units, e.g. "%g" (percentage of acceleration due to gravity); "m s-2" (meters per second squared); or "ft s-2" (ft per second squared). When other units are to be displayed, these can be easily obtained by selecting an appropriate portion of the microprocessor or computer program, e.g. from either a hard wire connection or a selectable switch.

An embodiment of the invention will now be described, by way of example only, with reference to the accompanying drawing which illustrates, in block-diagram form, the essential integers of a particular vehicle brake efficiency meter in accordance with the present invention.

Thus, referring to the drawing, a vehicle brake efficiency meter 10 consists of a pendulum transducer 12 coupled to a potentiometer 14.

Conveniently the transducer 12, which might be an inertial accelerometer, comprises a damped pendulum, e.g. one limited to a +450 displacement.

The analogue or digital output of the potentiometer 14, following a braking test with the vehicle (not shown), is sampled in a peak/trough detector 1 6. A microprocessor 1 8 comprising signal-processing unit 20 and arithmetic unit 22 controls the sampling, and sums, averages and displays the deceleration on a digital display 24. If desired, a suitably programmed small computer may be used in place of microprocessor 1 8. The meter is carried in the vehicle within sight and reach of the driver.

With the meter 10 described above, the driver can measure the deceleration of the vehicle during a locked wheel brake test as follows. First, the meter is switched to 'test'. The driver then makes one to six locked-wheel brake tests, preferably on the level although slight slopes can be tolerated. After six tests, or more if necessary, the meter will average the individual readings and output the vehicle brake efficiency in the chosen units.

In more detail, the power supply to the meter 10 is switched on and the initial decleration is set to 100% g (or equivalent) until the first brake test is performed. Switching the power on in this way causes the controlling microprocessor, (or computer) to perform a self-test function. This begins with all the indicators on the front panel of the meter being illuminated for approximately four seconds. During this initial four second period, any lamp failures may be detected. If the microprocessor finds an internal error, then all the indicators will extinguish and the display 24 will show "99". If this occurs, the meter must be returned for service. In the absence of any internal errors, however, the display 24 will show "00" and the TEST indicator will illuminate. This indicates that no brake tests have been completed.

Next the braking test is performed. Whenever the brake is actuated during the test to produce a deliberate skid, the display 24 will go blank for three seconds and will then start to flash rapidly showing the deceleration calculated. If the result seems plausible to the driver ofthe vehicle, then he will press the ENTER button on the meter to cause the result to be added to a running average.

The display 24 will revert to "01" to indicate that one brake test has been successfully completed.

If, however, the brake was pressed inadvertently or the test was unsuccessful for some other reason, then the vehicle driver will press the START button to cause the result to be ignored and the display will revert to showing the number of successful tests so far completed.

The above procedure is repeated until the required number of tests has been completed.

Whenever the display 24 is showing the number of successful tests, the CALCULATE button may be pressed. This will cause the average result from all the completed tests to be calculated and stored as the average deceleration.

If desired, up to ninety-nine tests may be performed with the meter illustrated in the drawing but, as indicated earlier, a much lesser number, e.g. six, will usually suffice.

To facilitate the correct mounting of the meter on the vehicle, a small red dot will illuminate in the bottom left hand corner of the display whenever the decelerometer pendulm is at exactly nought degrees. This is accurate to onesixth of a degree whereas the main display is filtered and rounds to the nearest degree. The angle of the pendulum transducer 12 in relation to the meter box can readily be adjusted using a screwdriver.

Claims

1. A vehicle brake efficiency meter comprising a decelerometer linked to a microprocessor or the like operative to average out any deceleration peaks and subsequent troughs occurring when vehicle-supporting regions at a braking test site provide the wheels of the vehicle with a better than average grip.

2. A meter as claimed in Claim 1 in which the microprocessor or the like is operative to average the results of a number of braking tests.

3. A meter as claimed in Claim 1 or Claim 2 operative to display the average, or currentlymeasured, deceleration, as the case may be, in units of the operator's choice.

4. A vehicle brake efficiency meter substantially as hereinbefore described with reference to, and/or as illustrated in, the accompanying drawings.