Patent Application
20080173107
1. Field of the Invention
The present invention generally relates to motor vehicle safety systems. More specifically, the invention relates to automotive safety systems having redundant pressure and acceleration sensors to determine the occurrence of an impact event for deployment of automatic safety devices.
2. Description of Related Art
Vehicle safety systems may include automatic safety devices, for example, inflatable restraints such as airbags and seat belt pretensioners. A control unit activates these devices when it detects an impact event. The control unit needs to reliably detect these events since inadvertent deployment of safety systems is highly undesirable. One way this may be accomplished by using redundant pressure sensors and acceleration sensors.
When an impact event occurs, body panels of a motor vehicle may deform causing changes in air pressure within a body cavity of the motor vehicle. The impact event will also impart a sudden acceleration to the motor vehicle at substantially the same time as the change in pressure. Therefore, to confirm the occurrence of the impact event it is desirable to monitor both the pressure change and acceleration at a single location within the vehicle. The control unit then compares a signal from the pressure sensor with a signal from the acceleration sensor. If both sensors register a change exceeding a certain predetermined threshold at substantially the same time, the control unit will positively determine an impact event has occurred and deploy safety devices. Therefore, having two sensors in the same location reduces the chance of a false positive determination of the impact event.
Another benefit of redundant sensors is if one of the sensors fails, the control unit may be configured to determine that a fault condition has occurred. In a fault condition, the control unit will switch to monitoring only the operative sensor for the occurrence of an impact event. In this way, redundant sensors allow the control unit to continue to respond to impacts, even if one of the sensors fail. This also means it is important for the sensors to be located within the motor vehicle in a location where a distinct change in both pressure and acceleration are likely should an impact occur. However, these locations may have a relatively small internal volume.
For the above reasons, it is important for both sensors to measure the properties of the same location as much as possible. Previously this was accomplished by placing more than one sensor assembly in the vehicle, one monitoring pressure and one monitoring acceleration, in each location. This has the disadvantage that, depending on the size of each device, the sensors may be spaced relatively far apart from one another or be limited to sections of the vehicle having larger internal volumes. Spacing the devices apart may result in a small delay between the two signals, or the larger sections of the vehicle may not be well suited for providing an appropriate pressure or acceleration change. In addition, having two separate devices is more costly since they require additional mounting hardware and electrical connectors.
In view of the above, it is apparent that there exists a need for a sensor assembly capable of measuring both pressure and acceleration of a single location of the vehicle having minimal cost and high reliability.
In satisfying the above need, as well as overcoming the enumerated drawbacks and other limitations of the related art, the present invention provides a sensor assembly for impact detection for use in a motor vehicle. The sensor assembly includes a housing, a pressure transducer sensitive to pressure and an accelerometer sensitive to acceleration. The pressure transducer and the accelerometer are each attached to the housing and the housing is attached to a location in the vehicle conducive to measuring pressure and acceleration corresponding to an impact event. The impact events detected may include side impacts, front impacts, rear impacts and other types of impacts.
The sensor assembly provides two independent signals to a control unit. The control unit compares both signals to confirm an occurrence of the impact event. Upon confirmation of the impact event, the control unit sends an activation signal to deploy appropriate automatic safety devices of the motor vehicle to protect vehicle occupants. The safety devices may include any crash deployed system, including examples such as front airbags, side airbags, side curtain airbags, and seat belt pre-tensioning devices.
According to one embodiment, the accelerometer is sensitive to changes in acceleration along a single sensing axis. In other embodiments, the accelerometer may be sensitive to changes along two or three sensing axes.
The location of the control unit in the vehicle is separate from the location of the sensor assembly. The location of the sensor assembly in the vehicle is conducive to detecting a single force component of the impact event acting along a single sensing axis. Advantageously, the location in the vehicle may also be conducive to detecting multiple force components of the impact event acting along multiple axes of orientation.
Further objects, features and advantages of this invention will become readily apparent to persons skilled in the art after a review of the following description, with reference to the drawings and claims that are appended to and form a part of this specification.
A sensor assembly for use in a motor vehicle 8 (see
As best seen in
The control unit 18 is also in communication with safety devices 22 of the motor vehicle 8 by the electrical cables 20. If an impact event is confirmed, the control unit 18 sends an activation signal via the cables 20 to deploy the safety devices 22. The safety devices 22 may be any devices appropriate for protecting an occupant (not shown) of the motor vehicle 8 from injury in the event of an impact. For example, in the embodiment of
The control unit 18 may be configured to deploy all of the safety devices 22 upon confirmation of any impact event. On the other hand, it may distinguish between different types of impacts and only deploy those devices appropriate for each type of impact. For example, if the control unit 18 confirms the occurrence of a pure side impact in a motor vehicle 8 having front and side airbags, the control unit may only activate the side airbags and leave the front airbags inactive if appropriate.
The sensor assembly 10 provides two signals, one from the pressure transducer 14 and one from the accelerometer 16, to the control unit 18. The control unit 18 is preferably a digital control unit, but may be any device capable of monitoring and comparing signals from the pressure transducer 14 and the accelerometer 16. Appropriate software and hardware within the control unit 18 reads a voltage from the pressure transducer 14 and a voltage from the accelerometer 16 both of which are proportional to the respective pressure and acceleration acting on the vehicle. If an impact occurs, the pressure transducer 14 and accelerometer 16 will generate electrical signals proportional to the pressure and acceleration generated by the impact. The control unit 18 then determines if an impact occurred by reading these signals and comparing them to predetermined threshold values stored within the control unit 18.
Referring to
Therefore, it is important that the sensor assembly 10 be located within the motor vehicle 8 in a location where a distinct change in both pressure and acceleration are likely should an impact occur. While only a single sensor assembly 10 is shown in
Each of the above locations 28 and 30 are examples of single axis locations since, for example, a cavity within the front bumper 30 may only experience a significant pressure change from a front impact and not respond appreciably to a side impact. However, a front quarter panel 32 is an example of a multi-axis location. In this example, a cavity formed by the front quarter panel 32 is likely to experience significant pressure changes from both a side impact (i.e. the X-axis) and a front impact (i.e. the Y-axis). This is because portions of the front quarter panel 32 are disposed on both the side and the front of the vehicle 8.
Another benefit of redundant sensors is if one of the two sensors 14 and 16 of the sensor assembly 10 were to fail, the control unit 18 may be configured to determine a fault condition has occurred. In a fault condition, the control unit 18 will only monitor the operative sensor 14 or 16 for the occurrence of an impact event. In this way, redundant sensors allow the control unit 18 to continue to be able to respond appropriately to impacts even if the pressure transducer 14 or the accelerometer 16 fails.
For the above reasons, it is important that both the pressure transducer 14 and accelerometer 16 measure the properties of the same location within the vehicle. Previously this was accomplished by placing more than one sensor device in the vehicle for detection of acceleration and pressure. However, this has the disadvantage that, depending on the size of each device, they may be spaced further apart from one another than is desirable or they may be limited to sections of the vehicle having relatively large internal volumes. This is not desirable because spacing the devices apart may result in a delay between the two signals. In addition, the larger sections of the vehicle may not be sufficiently responsive to pressure changes or acceleration in an impact. Furthermore, two separate devices are more costly, and require additional mounting hardware and electrical connectors.
The present invention solves these problems by incorporating both the pressure transducer 14 and accelerometer 16 into a single housing 12 for mounting to the vehicle. This allows the space occupied by the sensor assembly 10 to be reduced and it also allows the separation between the pressure transducer 14 and the accelerometer 16 to be minimized.
In one embodiment, the pressure transducer 14 and the accelerometer 16 may be separate devices mechanically and electrically combined within the housing 12 of the sensor assembly 10. In another embodiment (not shown), the sensor assembly 10 may be formed as a single solid-state unit. In this embodiment, the housing 12 may include a printed circuit board (PCB) to which the pressure transducer 14 and the accelerometer 16 are electrically and mechanically coupled. As a result, rather than attaching the cables 20 to both the pressure transducer 14 and accelerometer 16 as shown in
It should also be noted that while both the pressure transducer 14 and accelerometer 16 are shown disposed on the same side of the housing 12 in
As a person skilled in the art will readily appreciate, the above description is meant as an illustration of implementation of the principles this invention. This description is not intended to limit the scope or application of this invention in that the invention is susceptible to modification, variation and change, without departing from spirit of this invention, as defined in the following claims.
