MASS ADDITION DETECTOR

Abstract: The mass addition detector is particularly suitable for use with vehicles. The detector senses change in mass using a combination of one or more load sensors (21) adapted to detect small changes in the mass of a stationary vehicle, discrimination means adapted to discriminate between long term and short term changes and alarm means adapted to provide an indication of any long term mass changes. Preferably, the or each load sensor (21) is attached within the body of the vehicle, for instance by association with the suspension system (23). In one form at least one load sensor (21) is associated with a spring suspension system (23) and senses relative movement between the vehicle body (24) and the spring (23). In an alternative form the load sensor is located on a surface of a resilient mounting bush (22) mechanically joining the spring and the vehicle body. The load sensor may be provided with sensor control means to engage and disengage the sensor from the suspension system. The preferred load sensor is a strain gauge. The discrimination means is a microprocessor programmed to analyse the signals and programmed to analyse the signals so that when a mass change exceeds a predetermined magnitude and lasts for a predetermined time period an alarm signal is produced.

Description: MASS ADDITION DETECTOR This invention relates to mass addition detectors partic- -ularly suitable for use with vehicles. The security of vehicles, particularly when unattended, is of prime importance. Many types of violation result in small changes in mass. Explosive charges placed to kill or injure drivers are likely to add at least 4kg to a vehicle. The concealment of contraband goods may cause a similar change in mass. Theft will often cause a loss of at least 2 kg from the mass of a loaded vehicle. However changes in the mass of a parked vehicle can occur of a non-detrimental nature as transient events. Animals may alight on the vehicle and solid precipitation, such as snow or hail, may build up on a vehicle. Other transient changes in mass may also be caused by wind pressure due to metrological conditions or by the close passage of moving vehicles. - - The present invention provides a method of detecting small permanent mass changes in a stationary vehicle, rejecting transient mass changes and providing indication directly or remotely to any permanent mass change. According to the present invention there . is provided a mass change detector for a vehicle characterised by a combinat¬ ion of one or more load sensors adapted to detect small changes in the mass of a stationary vehicle, discrimination means adapted to discriminate between long term and short term changes and alarm means adapted to provide an indication of any long term mass changes. Preferably the load sensors are associated with the vehicle suspension system. The mass change detector preferably comprises a load sensor attached within the body of the vehicle. Signals corresponding to changes of the vehicle mass detected by the sensor are fed to discrimination means. The discrimination means is preferably a microprocessor programmed to analyse the signals. When a mass change exceeds a predetermined magnitude and lasts for a predetermined time period an alarm signal is produced. The alarm signal may be used directly to operate a warning device within the vehicle or remote from it. Alternat¬ ively the alarm signal may be stored for subsequent retrieval by interrogation means. In a most preferred embodiment the load sensor is associated with the vehicle suspension system. In a typical coil suspension the load sensor is mechanically positioned when the vehicle is stationary so that it senses force changes between the top of the spring and the vehicle chassis. Such changes will represent changes in the vehicle mass. Sensor control means may provided to engage and disengage the sensor from the suspension system. During normal vehicle motion the sensor may be disengaged but when the vehicle is parked or otherwise stationary for long periods it is engaged with the suspension and senses mass changes occurring in the vehicle. In coil and similar suspension systems the upper spring housing is connected to the vehicle body by a reslient bush, usually fabricated from rubber. A load sensor, preferably in the form of a strain gauge, may be attached to the surface of the bush. Force changes between top of the spring and the vehicle body modulate or distort the surface of the bush and the resultant signals from the strain gauge represent changes in vehicle mass. In such an embodiment the sensor is permanently engaged with the vehicle suspension system but the associated discrimination means and/or alarm means are rendered inoperative during vehicle use. In order that the invention may be clearly understood it will now be described with reference to the accompanying drawings in which: Figure 1 is an enlarged view of a load sensor which may be used in a mass change detector according to the invention, Figure 2 is an enlarged view of the sensor element, Figure 3 is a schematic diagram of a vehicle suspension system including the load sensor shown in Figure 1 , Figure 4 is a schematic diagram of a vehicle suspension system showing sensor control means, and Figure 5 is a schematic diagram of a vehicle suspension system showing an alternative arrangement of the mass change detector according to the invention. A load sensor 1 , see Figure 1 , comprises a balanced strain gauge bridge of known type. One end of the sensor 1 is contained in a locking device 2 which ensures that it is mechanically coupled to a push rod 3. Pressure between the top of the sensor 1 and the push rod 3 will cause a bridge unbalance providing signals related to the ampli¬ tude and direction of any pressure change. When the sensor 1 is installed so that the sensor is directly or indirectly in contact with the ground and the push rod is in contact with a load the sensor will respond to changes in the mass of the load. The sensor element, see Figure 2, comprises a rod 4 carrying a set of strain gauges 5 adhesively fixed to its surface. The changes in the resistance of the gauges 5 are measured through leads 6. The load sensor, see Figure 3, is fitted across a suspens¬ ion/bush spring 8 on a vehicle. One end 9 of the suspens¬ ion/bush spring 8 is be coupled to the main vehicle body while the other end 11 will be coupled to the spring/damper 12 and hence the ground on which the vehicle stands. Any changes in the mass of the vehicle or its load will alter the pressure on the bush/spring 8 and the sensor 1 which will provide a resistance change according to the amplitude and direction of the load change. Computer means, not shown, receive the signals from the sensor 1 and store them. The stored signals are processed. Mass changes exceeding a preset value for amplitude and duration result in an alarm signal which is also stored. The alarm signal may be used to trigger warning devices, such as sirens or flashing lights, in the vehicle. Alt- ernatively the alarm signal may be transmitted, e.g. by electromagnetic radiation, to a remote position where appropriate action can be initiated. In a preferred form of the invention the alarm signal is revealed by external interrogation. A driver, guard or other operator may direct a radio or infra-red source at a suitable receiver installed in the vehicle. On receipt of the interrogation signal the computer means may reveal the presence of any mass change exceeding the preset limits. It is also possible, using suitable display means, for the computer means to show either the amplitude of the mass change or the time of occurence of the mass change or both and also to indicate its location. In an alternative embodiment, see Figure 4, a load sensor 13 is shown attached to the upper portion of a suspension spring 8. A pushrod 14 is moveable in a vertical direction by means of an electric motor 15. The motor 15 and hence the rod 14 is rigidly attached by means of a bracket 16 to a spring shield 17 forming part of the vehicle body. The upper portion of the spring is connect- ed to the vehicle body through a resilient bush 18. When the vehicle is in motion the pushrod 14 is disengaged from the load sensor 13. When the vehicle is stationary the motor 15 is activated and the pushrod 14 is driven into locking engagement with a locking device 18 attached to the load sensor 13. When the pushrod 14 and the sensor 13 are engaged any change in mass of the associated vehicle will cause a change in the pressure on the spring 8 which will be revealed by the sensor 13. The motor 15 may be activated manually by the vehicle operator or automatically by control means whenever the vehicle motor is switched off or the parking brake operated. The vehicle may be fitted with a plurality of load sensors feeding a single microprocessor which analyses the signals form them. Such an arrangement can provide indication of the location of any mass change. In an alternative embodiment, see Figure 5, a load sensor 21 is attached to the surface of a rubber bush 22, shown in cross section, which mechanically . connects a suspension spring system 23 to a vehicle body structure 24. The lower portion of the spring system 23 is attached to a damper 25 in conventional manner. A housing 26 covers the top of the spring 23. The base of the bush 22 rests on the upper surface of the housing 26. The weight of the vehicle, transmitted from the body structure 24, is carried by the bush 22 so that the rubber deforms to an extent dependent on the vehicle weight. The load sensor 21 is a strain gauge, for instance of the type described with reference to Figure 2, and is adhesiv¬ ely attached to the surface of the bush 22 so that deform¬ ation of the surface is detected. The output of the sensor 21 is supplied to computer means for storage and processing as hereinbefore described. In an similar manner, see Figure 4, a strain gauge type load sensor can be attached to the exposed lower surface of the bush 18. Such a sensor would replace or supplement the system based on the load sensor 13. The invention has been described in detail with particular reference to preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention.

Claims: C LA I MS 1. A mass change detector for a vehicle character¬ ised by a combination of one or more load sensors adapted to detect small changes in the mass of a stationary vehicle, discrimination means adapted to discriminate between long term and short term changes and alarm means adapted to provide an indication of any long term mass changes . 2. A mass change detector according to claim 1 characterised in that the or each load sensor is attached within the body of the vehicle. 3. A mass change detector according to claims 1 or 2, characterised in ' that at least one load sensor is associated wi-th the suspension system. 4. A mass change detector according to claim 3, characterised in that at least one load sensor is associated with a spring suspension system. 5. A mass change detector according to claim 4, characterised in that the load sensor is located in a manner that senses relative movement between the vehicle body and the spring. 6. A mass change detector according to claim 5, characterised in that the load sensor is provided with sensor control means to engage and disengage the sensor from the suspension system. 7. A mass change detector according to claim 4, characterised in that the load sensor is located on the surface of a resilient mounting bush mechanically joining the spring and the vehicle body. 8. A mass change detector according to claim 7, characterised in that the load sensor is a strain gauge. 9. A mass change detector according to any of the preceding claims, characterised in that the discrimination means is a microprocessor programmed to analyse the signals. 10. A mass change detector according to claim 9, characterised in that the discrimination means is programmed to analyse the signals and when a mass change exceeds a predetermined magnitude and lasts for a predetermined time period an alarm signal is produced.

Inventors: EDWARDS DAVID GEOFFREY, EDWARDS, DAVID, GEOFFREY
Applicants: GD ENG ASS, G.D. ENGINEERING ASSOCIATES LIMITED
Application year: 1991
Main classification: B60R25
IPC codes: B60R25, G01G19