ELECTRONIC LEVEL MEASURING SYSTEM FOR A TRUCK TRAILER

Abstract: A truck comprising a tractor unit (10) and a trailer (12) is provided with an electronic level measuring system in which a remote level sensing device (32) is mounted on the rear frame (18) of the trailer (12), and a meter (30) for indicating continuously the amount the trailer is tilted laterally is provided in the cab of the tractor unit (10). The meter (30) also indicates the direction of tilt and changes scale when the tilt exceeds a predeter­ mined amount. The system, which is powered by the vehicle battery (44), will work with reverse polarity and provides a continuous reading to the driver of the truck.

Description: This invention relates to a trailer level measuring system for trucks comprising a tractor unit and a trailer. In most cases when a trailer dump truck is to be unloaded, it is at an off-highway location where the terrain is irregular. Because of the length of the truck, even though the tractor may be on substantially level ground, the rear wheels of the trailer may not be. If the driver is not aware of this condition and raises the bed of the trailer, the load may shift to the lower side, and the trailer and the tractor can be turned over by the resulting off-centre load. When this occurs, it not only disrupts the delivery of the material in the trailer but causes extensive damage to the tractor and trailer. In addition, substantial costs are incurred in righting the tractor and trailer and also insurance costs are higher because of the damage encountered. Many attempts have been made to provide devices on the tractor trailers to indicate when the vehicle or the load is off-centre by a predetermined amount. One of these is shown in U.S. Patent No. 3,921,128 to Snead, entitled "Truck Roll Warning System" which has a sensing device mounted on the dump bed which is responsive to a predetermined amount of tilt to cause the dump bed to be lowered and a warning signal to be provided. U.S. Patent No. 4,145,682 to Cook, entitled "Semi-Dump Truck level Indicator" is directed to a level sensing device mounted on a dump bed having mercury switches which are responsive to a tilt either to the left or right and give an indication of the direction of tilt once a predetermined amount of tilt has occurred. Another tilt indicating device is shown in U.S. Patent No. 4,278,854 to Krause, entitled "Tilt Indicating Device" wherein a float in a body of liquid will tilt in response to the tilt of the vehicle and complete a circuit to indicate when a predetermined amount of tilt has occurred. U.S..Patent No. 3,464,755 to Brown, entitled "Dump Trailer Safety Device" provides a dump valve override which senses when the tilt is beyond a predetermined angle and overrides the dump valve. U.S. Patent No. 3,657,695 to Birmingham, entitled "Leveling Indicator" discloses a level indicating device for mounting on a trailer which can be viewed from the vehicle while backing up the trailer and will give an indication as to both lateral and longitudinal tilt when it exceeds a predetermined amount. U.S. Patent No. 4,349,809 to Tomes, entitled "Offroad Vehicle Inclinometer and Alarm" will provide an instantaneous and continuous indication of tilt of an offroad vehicle as that vehicle is being driven across the terrain. However, it is not intended for use on a tractor trailer. Thus, the deficiency of all of the devices which are intended for tractor trailers is that there is no continuous reading of the degree of tilt of the bed and by the time the predetermined angle is reached, the bed may have been raised so high that it is too late to prevent it from tilting over. The following patents are directed to devices for automatically leveling the loads: U.S. Patent No.3,041,111 to Wyrick, Jr., entitled "Automatic Load Leveling System"; U.S. Patent No.3,512,836 to Polich, Jr., entitled "Lateral Stabilizing Means for a Semi-Trailer Dump Body"; and U.S. Patent No.3,640,578 to Finney, entitled "Leveling System for Semi End Dump Trucks". While these devices are satis­ factory to their intended purpose, they are very costly and therefore not normally incorporated in the conventional tractor trailer. In accordance with the present invention, there is provided an electronic level monitoring system for a truck having a tractor unit and a trailer, the system comprising a remote level sensor for attachment to the rear frame of the trailer and arranged to provide an output signal which is proportional to the angle at which the trailer is tilted laterally from the horizontal and which is of one polarity when the trailer is tilted to the left and is of opposite polarity when the trailer is tilted to the right, a source of electrical power connected to the sensor, and a meter for mounting in the cab of the tractor unit and arranged to provide a continuous reading of the amount of the angle of tilt and the direction of tilt of the trailer frame in response to the output signal, and means for transmitting said output signal from the sensor to the meter. Preferably, the level sensor includes means for leveling it on the trailer frame prior to use. The signal may be transmitted by means of a first cable running from the sensor to a junction box, and a second cable running from the junction box to the meter. The meter gives a continuous reading and may include a first light that indicates when the trailer is sufficiently level for dumping and a second override light which indicates when the trailer is tilted beyond a predetermined amount, say 4°. The meter may also include a scale multi­ plier so that when the bed tilts beyond a predetermined amount, such as 4°, the scale on the meter is extended, for example to 10 times the original scale. The electrical power source is preferably the vehicle battery which is connected through the ignition. A polar­ ity converter may be provided so that the polarity of the battery terminals is unimportant. As can be seen, with the system in accordance with the invention, a continuous reading is given so that the driver knows at all times how level the rear frame of the trailer is when he backs up into a dumping position, and he can monitor it during the entire dumping cycle. Thus, the chances of tipping the tractor and trailer over are greatly minimized. One example of a level measuring system in accordance with the invention will now be described with reference to the accompanying drawings, in which: Figure 1 is a side elevation of a trailer truck equipped with the level measuring system, parts being broken away for clarity of illustration; Figure 2A is a rear elevation of the trailer of Fig.1, shown in a level position; Figure 2B is a front elevation of the meter of the system showing the position of the needle when the trailer bed is level as in Fig. 2A; Figure 3A is a rear elevation of the trailer of Fig.1 showing the trailer tilted to the left; Figure 3B is a view of the meter showing the position of the needle when the trailer is tilted as in Fig.3A; Figure 4A is a rear elevation of the trailer of Fig.1 showing the trailer tilted to the right; Figure 4B is a view of the meter showing the position of the needle when the trailer is tilted as in Fig.4A; Figure 5A shows a portion of a circuit diagram of the level measuring system; and Figure 5B shows the remainder of the circuit diagram of the level measuring system. A dump truck is illustrated in Figure 1 which has a tractor unit 10 and a trailer 12 carrying a load 14. A level sensor box 16 is mounted on the rear frame 18 of trailer 12 and is connected by means of a conduit 20, which runs along the underside of trailer 12, to a junction box 22. A second conduit 24 is connected to junction box 22 by means of a connector 26 and extends between junction box 22 and the cab of tractor 10, being carried by support 28. The other end of conduit 24 is connected to a meter 30 mounted in the cab, such as on or under the dashboard. As will be explained more fully below, when the trailer is in the level position shown in Figure 2A, the needle 31 of meter 30 will be in the center position indicating that there is no tilt of the trailer. On the other hand, when the trailer is tilted to the left as shown in Figure 3A, the needle 31 will also move to the left as shown in Figure 3B and indicate the angle of tilt. Similarly, when the trailer is tilted to the right as shown in Figure 4A, the needle 31 will move to the right as shown in Figure 4B to show the degree of tilt to the right. Conveniently, the level sensor box 16 is attached securely to the truck frame 18, as by bolts (not shown), as best seen in Figure 5B, within level sensor box 16 an inclinometer or level sensor 32 is mounted as by a pair of screws 36. Conveniently, the bottom of the sensor has a slot 38 for receiving screw 36 and adjusting the level sensor to be sure that it is perfectly level when the frame 18 of the truck is level. A suitable inclinometer is manufactured by Sperry Sensing Systems, a division of Sperry Corporation, P. O. Box 21111, Phoenix, Arizona 85036 as Model No. 02338-30, which has an analog output signal. The inclinometer has five leads as shown connected to a junction block 40 as shown, which is mounted within level sensor box 16. Conduit 20 includes a four-wire connector whose wires are connected to the junction block 40, as shown. The conduit 20 is in the form of a shielded cable. As previously described, the other end of the cable connects to junction box 22, at the front of the trailer, which in turn is connected to conduit 24 through any suitable four-prong trailer disconnect 26. The meter box 30 includes meter panel 34 having a needle 31, as previously described. A suitable meter panel is manufactured by Crompton Instruments, 1562A Parkway Loop, Tustin, California 92680, under Model No. 223-01. Conveniently, meter panel 34 is mounted in a front panel 42 of meter box 30. Power for the level sensor and meter are provided by the vehicle battery 44. The battery can be either 12 or 24 volts and is connected to a polarity converter 46 in the form of a full wave bridge that insures correct voltage polarity to all electronic components regardless of the vehicle battery polarity. A suitable full wave bridge is Archer Part No. 276-1151, distributed by Radio Shack of Fort Worth, Texas. To activate the system, normally open power-on button 48 is momentarily depressed after the vehicle ignition has been turned on to activate silicon controlled rectifier 50 to provide continuous power to the system. A suitable rectifier is Archer Part No. 276-1067, also manufactured by Radio Shack. The gate voltage to switch 48 is reduced through resistor 51. As shown in Figure 5A, the silicon controlled rectifier is connected to power-on LED 52 through resistor 54, the opposite side of the lamp being connected to rectifier 46. Connected in the same circuit is a panel light 56 which can be activated by switch 58. The panel light is for backlighting the meter panel when the ambient light is not sufficient to see it. Finally, a dump LED 60 and an override LED 62 are provided on the panel. Dump LED 60 may be green in color and indicate that the angle of tilt is within acceptable limits for dumping whereas override LED 62 may be red to indicate that the trailer bed is tipped beyond the acceptable limits and that the dumping operation should be interrupted until this condition can be corrected. Conveniently, a voltage regulator 64 is connected between bridge 46 and SCR 50 and will accept a wide range of voltage inputs between 12 and 35 volts DC. A suitable voltage regulator is Archer Part No. 276-1771, distributed by Radio Shack. It provides a regulated output voltage of 12 volts DC to the rest of the system. A dual output power supply 66, shown in Figure 5B, provides a +15 volts DC and -15 volts DC relative to common ground from a single power source. A suitable power supply is Pico Part No. 12A15D, manufactured by Pico Electronics of Mount Vernon, New York. This is used to supply power to level sensor 32 and to the operational amplifier 68, shown in Figure 5A. A suitable operational amplifier is Archer Part No. 276-007, distributed by Radio Shack. The operational amplifier looks directly at the output signal from level sensor 32. This input signal is then amplified to a more useful voltage that will switch a network of relays that determines a low or high scale reading, as more fully discussed below. The two capacitors 70 associated with dual output power supply 66 work in conjunction therewith to provide a filtered 15 volt DC power source of either polarity. A second polarity converter 72, which is in the form of a full wave bridge rectifier, receives a signal from operational amplifier 68 which is either positive or negative in polarity, depending on whether level sensor 32 is tipped to the left or the right. This may be identical to full wave bridge rectifier 46. The signal is polarized and provides an input to solid state switch 74. A suitable solid state switch is Gray Hill Part No. GRA 7052-01-A-03V, distributed by CSID, Inc. of Denver, Colorado. This solid state switch, which is normally open, is used to switch control relay 76 from a smaller signal to a higher signal from operational amplifier 68 and polarity converter 72 at a predetermined and preset voltage when the tilt of the trailer exceeds 4° in either direction. A suitable control relay is Archer Part No. 275-247, distributed by Radio Shack. Multiple resistors 78 and 80 are used in conjunction with operational amplifier 68 to provide for proper amplification. Resistor 80 is adjusted to turn solid state switch 74 on when the input signal to operational amplifier 68 is at maximum to correspond with more than a 4° tilt indicated by the meter. The meter is scaled to read at either an actual scale or at 10 times the actual scale and when solid state switch 74 is turned on, the meter will be on the high scale. As can be seen from Figure 5A, control relay 76 is a one pole, double throw switch which is activated by current from solid state switch 74. The normally closed position will provide the low scale position but when activated will provide the high scale position by closing the normally open side of the switch. A second control relay 82 is activated from control relay 76 when it is in the normally closed position. This allows a signal from level sensor 32 to pass directly to the meter 34 for a low scale reading. A third control relay 84, which is identical to control relay 82, is activated from control relay 76 when the normally open contact is closed. This allows a signal from the level sensor 32 to pass to the scale multiplier resistor 86 which provides the high scale operation. The output from the normally closed side of control relay 76 passes through a resistor 88 and from the normally open side through resistor 90 to reduce the voltage to the dump mode LED 60 and the override LED 62. Suitable control relays 82 and 84 are Gordos Part No. 5-16710, distributed by Newark Electronics of Denver, Colorado. From the foregoing, the advantages of this invention are readily apparent. A remote level sensor located on the back frame of a truck trailer can be read out remotely on a meter located in the cab of the tractor. The device is made of solid state parts, most of which are contained in the meter box so as not to be exposed to the elements. The device is durable and shock proof and monitors the position of the trailer as it is backed into position and as the box is raised. Thus, the driver has a continuous indication of the level of the trailer bed during both the backing and dumping operation so that should the level of the trailer shift out of a predetermined acceptable limit, such as in excess of 2° left or right, the dumping operation can be terminated. Of course, if the trailer is tilted more than this amount to begin with, the dumping operation will not even be begun. The device will work with reverse polarity and a scale is provided which changes if the tilt is over 4° so that even higher amounts of tilt can be read on a very sensitive scale. This invention has been described in detail with reference to a particular embodiment thereof, but it will be understood that various other modifications can be effected within the spirit and scope of this invention.

Claims: 1. An electronic level measuring system for a truck having a tractor unit (10) and a trailer (12), said system comprising: a remote level sensor (32) for attachment to the rear frame (18) of the trailer (12) and arranged to provide an output signal which is proportional to the angle at which the trailer is tilted laterally from the horizontal and which is of one polarity when the trailer is tilted to the left and is of opposite polarity when the trailer is tilted to the right; a source (44) of electrical power connected to said sensor (32); a meter (30) for mounting in the cab of the tractor unit (10) and arranged to provide a continuous reading of the amount of the angle of tilt and the direction of tilt of the trailer frame (18) in response to said output signal; and means (20,22,24) for transmitting said output signal from said sensor (32) to said meter (30). 2. A system as claimed in claim l, comprising means (36,38) for adjusting said level sensor (32) relative to the trailer frame (18) so that when the frame is level, the level sensor is also level. 3. A system as claimed in claim 1 or claim 2, wherein said transmitting means comprises a first conduit (20) having a first end connected to said level sensor (32) and a second end connected to a junction box (22) for mounting at the front of the trailer frame (18), and a second conduit (24) having a first end connected to said meter (30) and a second end connected to a quick disconnect (26) which is connectable to the junction box (22) in order to connect said first and second conduits together at said junction box. 4. A system as claimed in any one of claims 1 to 3, wherein said meter (30) comprises a meter box containing a circuit board including: a dual output power supply (66) connectable to the electrical power source (44) for providing power to the level sensor (32); an operational amplifier (68) which is powered from said dual output power supply (66) and receives and amplifies said output signal from said level sensor (32); means (74,76) for changing the scale of said meter (30) in response to the value of said amplified output signal; a first LED (60) which is activated when the signal to said meter (30) indicates that the angle of tilt to the level sensor (32) is within acceptable limits; and a second LED (62) which is activated when the signal to said meter (30) indicates that the angle of tilt of the level sensor (32) is beyond acceptable limits. 5. A system as claimed in claim 4, wherein said scale changing means comprises a polarity converter (72) connec­ ted to said operational amplifier (68) to receive said amplified output signal to convert it to a signal of con­ stant polarity; a solid state, normally open, switch (74) which is connected to the output of said polarity converter (72) and which is activated at a preset voltage from said amplified output signal; a first control relay (76) having a normally closed position in which it provides an output to operate said meter (30) at a low scale; a second control relay (82) which is normally open and is closed by the output from said first control relay (76) when said first relay is closed to allow said output signal from said level sensor (32) to pass directly to said meter (30); and a third control relay (84) which is normally open but is closed by the output from said first control relay (76) to provide a high scale signal to said meter (30) when the signal to said solid state switch (74) exceeds a predetermined level and activates said switch (74) to cause said first control relay (76) to move to its open position. 6. A system as claimed in claim 5, comprising adjustable resistors (80,86) in said circuit board for adjusting the high scale of the meter (30). 7. A system as claimed in claim 5 or claim 6, wherein said electrical power source is a battery (44) and said circuit board includes a second polarity converter (46) to ensure correct voltage regardless of the polarity con­ nection to the battery, and a voltage regulator (64) con­ nected to the output of said second polarity converter (46) to provide a constant output voltage to the other components of the circuit. 8. A truck comprising a tractor unit (10) and a trailer (12), and having an electronic level measuring system according to any one of the preceding claims, wherein the level sensor (32) is attached to the rear frame (18) of the trailer so that the sensor is level when the trailer frame is level, and the meter (30) is mounted in the cab of the tractor unit (10). 9. A truck according to claim 8, wherein the electrical power source of the level measuring system is the vehicle battery.

Inventors: OBERG, NEIL G.
Applicants: CARDEL, INC.
Application year: 1987
Main classification: G01C9
IPC codes: G01C9