Trailer Stability Monitor

This invention relates generally to tractor-trailer vehicles and more particularly to a trailer stability monitor to alert the operator to the existence of conditions which, if unabated, may lead to a trailer rollover, hopefully in sufficient time to permit the operator to respond and avoid such incident.

One type of accident involving tractor-trailer vehicles is caused when the manner of vehicle operation and/or road conditions result in changes in the dynamics of the vehicle causing the trailer to tip up on one side. The trailer will generally roll over starting at the rear and continuing to the front until the whole rig, including the tractor, is on its side. While it is possible that the operator may sense the lateral force acting on the trailer, the operator may not be aware of an incipient rollover condition; and, if the forces which caused this condition continue unabated, the operator may not be able to avoid the rollover.

In many instances, the tilting action normally preceding an actual rollover is greatest at the rear of the trailer. The rear set of wheels on the trailer may even leave the road for a short time without the operator being cognizant thereof. If the operator were made aware of excessive lateral forces occurring at the rear of the trailer, there might still remain sufficient time within which the tilting action can be countermanded by the operator reducing speed, applying brakes, increasing the turning radius of the vehicle, or other actions appropriate to reducing the lateral forces and prevent the tractor-trailer from rolling over. Of course, the lateral force conditions may arise so quickly, due to the manner of operation of the vehicle or external factors, that the operator may be unable to react even if immediately alerted to such conditions.

Prior art approaches to alleviation of the problem of sensing an impending rollover condition generally provide sensor means coupled to means for effecting remedial actions. In See et al U.S. Pat. No. 3,804,435, means were provided for protecting an operator and reducing possible injury in the event of a rollover particularly of a bulldozer which is frequently operated on steep hillsides where lateral tipping and rollover may be a considerable danger. Operator restraint means were combined with means responsive to the tilt angle of the vehicle beyond a predetermined angle for actuating the operation of the air bag restraint means. The tiltsensor taught was a conventional single pole, single throw mercury switch which completes a circuit from a power source to the valve means when the vehicle attains a predetermined angle with respect to the vertical. The angle is set at a point whereat the vehicle center of gravity just exceeds the pivot point which varies with different vehicles.

The system suggested by See et al is not intended for use in sensing the impending rollover conditions, but rather is directed to protecting the operator upon the occurrence of rollover. The combination suggested by See et al is not adapted for installation on a tractor-trailer rig and does not contemplate the dynamic lateral forces arising from the highway operation of trucks. Additionally, a warning to the operator in advance of rollover was not contemplated by See et al.

The approach offered by Eagle U.S. Pat. No. 4,592,565 provides relatively complex apparatus for detecting an incipient overturning moment in a vehicle which comprises position-controlling servomechanism means, centrifugal force measuring means which includes a pressure-to-electrical signal transducer for generating a pressure indicating signal depending on a centrifugal force acting on the vehicle in a generally lateral direction, pressure indicating signal to error signal conversion means coupled to an output of said transducer means and providing an error signal at its output, the servomechanism means accepting and amplifying the error signal for transmitting a position-controlling force related to the error signal to means for avoiding the incipient overturning moment to prevent turning over of the vehicle. Further, the Eagle disclosure also contemplates providing road-curvature indicating means for measuring the curvature of the road travelled on by the vehicle, speed-indicating means for measuring the speed of the vehicle and means to combine the two measurements to provide a signal indicative of an incipient overturning moment. This signal is transmitted to control servomechanism means operating upon the brake pedal, the acceleration pedal, and/or the steering wheel to reduce the incipient overturning moment prevent such overturning.

The trailer stability monitor provides an early warning of conditions conducive to a trailer rollover comprising lateral force sensor means mounted, preferably detachably, on the trailer, radio-frequency transmitter means coupled to said sensor means and sensitive thereto for transmitting a signal upon the occurrence of an event, radio-frequency receiver means spaced from said trailer for receiving said signal and alarm means coupled to said receiver means and capable of being activated by said signal, preferably the alarm means being auditory by nature. One embodiment employs through-the-air transmission of the signal produced when the motion detector switch is closed. A modified embodiment of the invention uses one pair of the electrical lines of the tractor-trailer rig as a r.f. line carrier for carrying the r.f. signal by superimposing the signal thereon. A time delay can be provided to avoid a warning set off by jostling of the lateral force sensor.

The invention further includes a unique lateral force or tilt sensor including a pair of parallel normally open mercury switches disposed at opposite acute angles to the horizontal to respectively sense the tilt angle of the trailer and/or the lateral forces acting on the trailer in either direction and a vertical normally closed mercury switch in series with the parallel switches wherein the vertical switch disables the warning circuit momentarily to prevent false signals if the trailer experiences sudden vertical movement as by the rig hitting a bump in the road which rapidly raises the trailer vertically momentarily, in contrast to the excessive lateral force or tilting motion of the trailer which indicates impending rollover.

FIG. 1 represents a tractor-trailer vehicle having the trailer stability monitor of the invention operably installed thereon;

FIG. 2 is a block diagram of the stability monitor according to the invention; and

FIG. 3 is an electrical circuit representation of a modified embodiment of the stability monitoring system according to the invention.

The trailer stability monitor described herein is intended to provide an early warning consisting of an audible alarm capable of alerting the operator of a tractor-trailer vehicle of the existence of conditions conducive to trailer rollover, the alarm being set off by a signal received from a sensor mounted on the trailer and capable of sensing angular tilt and/or lateral force sufficient to induce rollover of the trailer. It will be appreciated that if the tractor-trailer vehicle is parked on a soft shoulder or berm of a road that the trailer will have to tilt to set off the alarm. However, when the tractor and trailer are being operated on the highway, it is desirable for the alarm to be set off by lateral forces alone, without any necessity for the trailer to actually tilt.

Referring first to FIG. 1, the trailer stability monitor of the invention is represented as installed on a tractor-trailer vehicle 20. The trailer stability monitor generally designated comprises a sensor/transmitter unit 12 mounted on the trailer 14 at the rear thereof and a receiver/alarm unit 16 mounted in the cab 18 of the tractor-trailer vehicle 20. The sensor/transmitter is preferably detachably mounted as by magnets to the trailer frame on a transverse horizontal frame member above the suspension.

As represented in FIG. 2, the sensor/transmitter unit 12 comprises a motion sensor formed of a pair of normally open, mercury switches 22 and 24 each mounted at an acute angle, here 15.degree., relative the horizontal but in opposed directions. Switch 22 functions to sense tilt and/or lateral forces to the left while switch 24 functions to sense tilt and/or lateral forces to the right. The two switches 22 and 24 are connected in parallel and then connected in series with a third mercury switch 26 which is mounted vertically relative to switches 22 and 24 and is normally closed. Switch 26 functions to permit the sensor/transmitter unit 12 to be disabled by inversion of the unit. Switch 26 further functions as an inertia switch to momentarily break the circuit should one or the other of the switches 22, 24 be closed by sudden vertical movement as may be encountered by the trailer 14 hitting a large bump or hole in the road. The switches 22, 24 and 26 are connected to a lithium-battery 28 and then directly to a small, UHF digital oscillator module 30 which transmits a digitally coded low power signal by direct radiation off of the oscillator coil any time the circuit is completed by closing of one or the other of the switches 22 and 24 as a result of the tilt or the lateral forces acting on the trailer 14 reaching a level conducive to a rollover.

The receiver/alarm unit 16 is mounted on the cab 18 of the tractor-trailer 20 and contains a super regenerative digital receiver 32. The digital receiver 32 is powered from the vehicle electrical system (not shown) and is always energized. The signal from the sensor/transmitter unit 12 is received via a six-inch receiving antenna 34 mounted on the outside of the receiver/alarm unit 16. The receiver 32 processes and decodes the incoming signal and, after a one-tenth second delay via time delay means 36, activates a loud tone alarm 40. The alarm 40 continues to sound as long as the receiver 32 detects a sustained signal from the transmitter/sensor unit 12. When the operator hears the warning sound, he can perform the manual acts which he considers necessary to abate the rollover conducive conditions such as releasing the accelerator pedal, manipulating the steering wheel, and/or applying the brake until the warning alarm becomes silent, thus taking action to prevent the tractor-trailer vehicle 20 from overturning. It should be appreciated that the conditions causing rollover are dependent in many cases on the manner in which the tractor-trailer vehicle is operated and that in some cases these conditions may arise so quickly that the operator may not have sufficient time to react after he is alerted by the trailer stability monitor to avoid a rollover. Nevertheless, it is believed that the trailer stability monitor will provide a sufficiently early warning in most cases for the operator to prevent a rollover from occurring.

Referring to FIG. 3, a modified trailer stability monitor 10' is illustrated diagrammatically. A motion sensor 12', in the form of a lateral force sensor, is connected across line carrier circuit 42, the lateral force sensor 12' being mounted on the trailer 14' at the rear thereof. Conventionally, presently available tractor-trailer truck rigs employ an SAE standard 7-pin connector to carry electrical signals from the tractor to the trailer. Signalling from the trailer to the tractor generally has been thought not possible using such connector simply because there are no unused circuits. However, any one pair of these lines can comprise circuit 42. The circuit 42 includes the vehicle battery 44 as its power source. Mounted on the trailer 14' is a 100 to 150 KHZ r.f. oscillator/transmitter 48 connected across the circuit 42 and coupled in series with blocking capacitor 44 to define an r.f. coupling to said lines 42' and 42", line 42" being coupled to ground. The motion sensor, in the form of lateral force sensor 12' substantially of the same construction as lateral force sensor 12, is coupled to the transmitter 48. Thus, when the lateral force sensor 12' is activated because lateral forces on the trailer become sufficiently extreme to be conducive to a rollover, the sensing circuit is closed and a low power signal is coupled onto the D.C. line 42'. A signal receiving mean, preferably a phase locked loop detector 52 is mounted in the cab 18 and is coupled through a capacitor 54 to the D.C. line 42'. When the detector 52 detects the signal emanating from the oscillator/transmitter 48, the output of said detector 52 is fed to an alarm 40' which may be either a visual alarm and/or an audible alarm so as to alert the operator of impending danger. The alarm tone and/or visual alarm display continues so long as there is a signal from the sensor/transmitter 12'

It is to be understood that the foregoing description is merely illustrative of preferred embodiments of the invention and that the scope of the invention is not to be limited thereto but is to be determined by the scope of the claims appended hereto.