GB2122395A - Safe-slope alarm system - Google Patents

Abstract

A safe-slope meter 10 e.g. for use on a tractor, consists of a pendulum transducer 12 comprising a damped pendulum and coupled to a potentiometer 14. The analogue output of the potentiometer 14, following a brake test with the tractor, is sampled in a peak/trough detector 16. A microprocessor 18 comprising signal processing unit 20 and arithmetic unit 22 controls the sampling and sums, averages and displays the safe-slope limit in degrees on a digital display 24. If desired, a suitable programmed small computer may be used in place of microprocessor 18. With the meter 10 described above, the driver can predict the safe working limit of slope for any tractor/implement combination by doing a simple locked-wheel brake test. Tests may be done continually or based on a predetermined number and the results arranged. An alarm is provided when the actual slope angle equals or exceeds a critical value. <IMAGE>

Description

SPECIFICATION Safe-slope alarm system The present invention relates to a safe-slope alarm system for use, in particular, but not exclusively, with tractors and other agricultural equipment.

Severe tractor accidents often occur when the driver unwittingly attempts to operate the tractor on slopes above the safe working limit.

The tendency for tractors to "toboggan" in such circumstances has long been recognised as an important safety problem and, in a paper published in the Journal of Agricultural Engineering Research (1981), Spencer s Owen describe how a pendulum accelerometer can be used in a brake test to determine the safe working limit of such slopes for a particular tractor or tractor combination and ground surface condition. This paper establishes that there is a relationship between brake-induced decelleration and downhill slope safety assuming the same surface conditions, tractor configuration (including ballast distribution) and the presence or not of a trailed vehicle.

The decellerometers currently used in brake tests e.g. in M.O.T. tests, employ a damped pendulum the displacement of which from its usual (vertical) position will depend on the amount of decelleration taking place. A ratchet mechanism is incorporated in the decellerometer to prevent the pendulum returning to the vertical before a reading can be taken. In brake tests for exclusively road-using vehicles, the presence of the ratchet presents no special problem but in the agricultural context it does. This is because for the decellleration tests to be valid as an indication of the critical safe-slope value, the surface conditions (amongst other things) for the decelleration test must be as near possible (preferably identical) to those obtaining where the tractor is to be used.Because the sites for the decelleration tests must be chosen with this requirement in mind, rather than for their general suitability for such tests, it will often happen that localised surface regions will be present at the test site which will provide better than average grip and this will cause the decellerometer pendulum to "peak". That is to say the above-average decelleration occuring during travel over these localised regions will swing the pendulum further than it would otherwise have gone and the ratchet mechanism will prevent it from returning to what may be considered its "correct" displacement. This of course leads to over-optimistic results which means that the critical slope value at which downhill tobogganing effects will first occur is in fact less and possibly significantly less than that predicted by the decelleration tests.

In the safe-slope alarm system of the present invention, on the other hand, the ratchet mechanism is omitted and the decellerometer is instead linked to a microprocessor which averages out the peaks (and subsequent troughs) occurring when surface regions providing a better than average grip are encountered during the decelleration tests. For the reasons indicated above, this facility is essential if the decelleration tests are to be at all reliable as an indication of safe-slope values.

The output signal from the microprocessor may be used in one of the following three ways: (1) to calculate the critical descent slope from one or more brake tests; (2) to display continuously the angle of ascent or descent with respect to the direction of travel of the vehicle to which the system is attached; and (3) to give audio and/or visual warnings to the driver of the vehicle when the angle of the vehicle reaches some predetermined relationship with the critical descent angle, e.g. when it is equal or greater to the critical descent angle.

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 safe-slope meter in accordance with the present invention.

Thus referring to the drawing, a safe-slope meter 10 e.g. for use on a tractor, consists of a pendulum transducer 1 2 comprising a damped pendulum e.g. limited to + 45 , and coupled to a potentiometer 14. The analogue or digital output of the potentiometer 14, following a brake test with the tractor, is sampled in a peak/trough detector 16. A microprocessor 1 8 comprising signal processing unit 20 and arithmetic unit 22 controls the sampling, and sums, averages and displays the safe-slope limit in degrees on a digital display 24. If desired, a suitably programmed small computer may be used in place of microprocessor 1 8. The meter is fitted in the tractor cab within sight and reach of the driver.

With the meter 10 described above, the driver can predict the safe working limit of slope for any tractor/implement combination by doing a simple locked wheel brake test.

First the meter is switched to 'test'. The driver then makes one to six locked-wheel brake tests on a level or a lightly sloping section of ground and preferably in the same field as he intends to work in. The meter works on the principle that the braking efficiency can be converted direct into the safe-slope limit. After six tests, or more if necessary, the instrument will average the readings and output the safeslope limit in degrees. The slope limit can be outputted for any number of tests between one and ninety-nine by an override switch.

The instrument can also be switched to 'con tinuous mode' when the slope on which the tractor stands will be continuously monitored and displayed. An alarm will sound if required, should this exceed the predicted level of a specific test. The test must be repeated if machine, field or ground conditions are changed.

In more detail, whenever the power supply to the meter 10 is switched on, the controlling microprocessor, (or computer) performs a self-test function. This begins with all the indicators on the front panel being illuminated for approximately four seconds. After this period only the 'present angle' indicator will stay illuminated and the display will show the present angle. 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. To preset the meter so that the alarm will only be activated if the slope exceeds some predetermined 'critical angle', the vehicle is positioned as for a brake test and the START button is pressed. The display will show "00" and the TEST indicator will illuminate.This indicates that no brake tests have been completed.

Next the brake test is performed. Whenever the brake is actuated in this way to produce a deliberate skid, the display 24 will go blank for three seconds and will then start to flash rapidly showing the critical angle calaculated.

If the result is plausible, then pressing the ENTER button on the meter will 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 pressing the START button wil cause the result to be ignored and the display will revert to showing the number of successful test so far completed.

The above procedure is repeated until the required number of test have 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 critical angle.

The display will revert to showing the present angle. Pressing the CALCULATE button when no tests have been successfully completed will cause the critical angle value stored in the microprocessor to remain unchanged.

If desired, up to ninety-nine tests may be performed but as indicated earlier a much lesser member will usually suffice.

Pressing the CRITICAL ANGLE button at any time will cause the dispay 24 to show the critical angle for as long as the button is kept pressed.

Whenever the present angle is equal to or greater than the stored critical angle, then the display will flash at a slow rate and the audible alarm will sound. Pressing the ALARM PAUSE button will silence the alarm for approximately two minutes but the display will continue to flash.

Should the present angle exceed four degrees greater than the critical angle then the alarm will sound irrespective of the state of the ALARM PAUSE button. The only way to silence the alarm in this situation is to reduce the slope angle of the vehicle.

After switching on the power the initial angle is set to forty-five degrees until the first brake test is performed.

To facilitate the correct mounting of the meter, a small red dot will illuminate in the bottom left hand corner of the display whenever the decelerometer pendulum is at exactly nought degrees. This is accurate to one-sixth of a degree whereas the main display is filtered and rounds to the nearest degree. The angle of the pendulum transducer 1 2 in relation to the meter box can readily be adjusted using a screwdriver.

Claims (4)

1. A safe-slope alarm system for use with a vehicle comprising a decellerometer linked to a microprocessor or the like which averages out the peaks and subsequent troughs occurring when vehicle-supporting surface regions of the ground provide the vehicle wheels with a better than average grip during decelleration tests on the vehicle.

2. An alarm system as claimed in Claim 1 in which the output signal from the microprocessor is fed to a display means operative to display the critical descent slope calculated from one or more brake tests and/or the angle of ascent or descent with respect to the direction of travel of the vehicle.

3. An alarm system as claimed in Claim 1 or Claim 2 operative to give audio and/or visual warnings to the driver of the vehicle when the angle of the vehicle reaches some predetermined relationship with the critical descent angle.

4. A safe-slope alarm system substantially as hereinbefore described with reference to and/or as illustrated in the accompanying drawing.