Patent Application
20090030578
The present invention concerns a method and a device for occupant detection and classification for a vehicle seat, in particular a motor vehicle seat. The method and the device of the invention pertain firstly to detecting the presence of an occupant on a vehicle seat, but also to classifying the occupant of an occupied seat according to his weight, that is, determining whether the occupant is a child or an adult, and into which weight range the adult falls.
According to PCT patent No. WO 98/41424, a device is known for controlling the activation of an airbag system in a motor vehicle. The passenger seat of the vehicle has a frame and a string network attached to the frame to support the weight of an occupant on the seat. The device includes a sensor coupled to a part of the string network in order to measure a tensile stress exerted on the network by the weight of the seat occupant and to send a signal representing this stress. There is also a computer connected to the sensor output that produces an airbag deployment control signal when the tensile stress reaches a predetermined threshold value.
The use of pressure sensing layers integrated into the inner padding of seats to detect the presence of a passenger is also known. Each of the sensors modifies its electrical resistance as a function of the pressure on it. These data then enable a measurement system to calculate a pressure profile, automatically correcting for the effects of the vehicle movement and the changes in position of the person sitting on the seat.
Such systems known to prior art entail considerable integration constraints (comfort, design, etc.) and a cost added to the vehicle. Moreover, these systems do not distinguish between various types of occupation, and thus cannot classify the occupant according to various categories.
A first purpose of the present invention is to devise a method and a device for occupant detection and classification for a vehicle seat that makes it possible to eliminate the current detection layers without adding a weight sensor.
A second purpose of the present invention is to devise a method and a device for occupant detection and classification for a seat that makes it possible to adjust the deployment strategies for the restraining means in an accident, for example, without affecting the passenger comfort settings. Note that other applications involving the weight of the occupant are targeted, particularly occupant recognition applications for the comfort settings, including, for example, occupant recognition for seat adjustment, for the massage or air conditioning function, changing the vehicle attitude and adjusting the lights or shock absorbers according to the weight of the occupants, mechanical diagnosis by kinematic readings (autodiagnosis of the seat based on wear), etc.
Another purpose of the present invention is to make such a device dependable and inexpensive.
In order to achieve these goals, the present invention implements a new method for occupant detection and classification for a vehicle seat, which seat has at least one displacement adjustment controlled by at least one displacement actuator. This new method includes the following steps:
Note that the actuator can be an electric actuator, for example, a rotary or linear motor, or a pneumatic or analog actuator.
It is preferable to achieve said increase with a power control means.
It is also preferable to perform said increase following a linear-type profile.
It is also preferable that said increase follow a profile adjusted for previous measurement(s).
According to a particular embodiment of the invention, the variable characteristic is the cyclical ratio of a chopped voltage, but any other method known per se of varying power supplied to the actuator can be applied.
According to a preferred embodiment of the invention, prior to steps a) to c) of said method, an adequate is performed to take up the mechanical slack in the seat, or as a variant, an action is performed that makes it possible to not include the mechanical slack in the measurement.
Also according to the preferred embodiment of the invention, the method is repeated on a periodic and/or event basis in view of determining the presence of an occupant and his classification at each moment.
The method according to the invention is applied with such modifications as are necessary to the detection and classification by weight of an object in lieu of an occupant on the vehicle seat.
According to a preferred embodiment of the invention, after step c), a reverse action of said actuator is performed in order to cancel the changes in said seat adjustment.
Said displacement adjustment controlled by at least one displacement actuator can be a translational displacement adjustment of the seat or a rotary displacement adjustment of the seat, or a combination of the two.
Preferably, steps a) to c) are carried out when no seat command is activated, so as not to interfere with the measurement and to give priority use to the occupant.
In order to achieve the previously cited goals, and implement the method defined above, the present invention produces a new device for occupant (or object) detection and classification for a vehicle seat, which seat has at least one displacement adjustment controlled by at least one displacement actuator. This new device includes:
Said means for applying a predefined power profile to said displacement actuator of said seat is preferably means for controlling the power supplied to said actuator.
Also, preferably, said means for applying a predefined power profile to said displacement actuator for said seat is a computer on board the vehicle.
According to a preferred embodiment of the invention, said computer is the means for detecting the movement of said seat actuator, and is also the means for comparing said value of the characteristic measured at the moment said actuator starts with a series of predetermined reference values for said characteristic.
Also according to a preferred embodiment of the invention, the actuator is an electric motor, preferably a rotary electric motor.
Other advantages and characteristics of the invention will appear in the following description of a preferred, non-limiting mode of embodiment of the object and scope of the present patent application, accompanied by drawings in which:
At the outset, occupant classes were defined according to weight in a manner known per se. The thresholds of this classification match those in the following table:
A percentile represents the percentage of individuals who weigh less than a given mass. Thus, 95% of individuals weigh less than 86 kg. According to the thresholds given above, the seat is considered empty for a weight between 0 and 5 kg. The seat is considered to be occupied by a child or a child in a CRD (child restraint device) or in a booster seat.
In
The occupant detection and classification operation for the seat 1 includes two different time intervals: a first interval R, during which a compensation is made for the mechanical slack in the seat 1, and a second interval M, during which the actual measurement is taken (see
In order to take the actual measurement, the vertical adjustment actuator(s) for the seat 1 is (are) energized using a power profile PA (
The instruction sent by the computer is a chopped voltage. Note that any other method of varying power supplied to the actuator can be applied. As indicated by its name, the voltage is chopped into a series of periodic rectangles (see
R
CYC
=Th/T=Th/(Th+Tb)
The cyclical ratio is always less than 1, and is expressed as 0.5 if Th=Tb, or as 50%.
The chopped voltage is smoothed by the actuator coil in a manner known per se. An average voltage is obtained whose value depends on the cyclical ratio. Therefore, the variation in the cyclical ratio RCYC will be reflected in the smoothed, average voltage.
As soon as the startup of the actuator is detected (point DM on
The method according to the invention can also be described by the algorithm shown in the drawing in
First, a compensation is made for the mechanical slack R.
In phase 200, the actuator is activated. The actuator is in motion or rotating (phase reference MT1), and is stopped (phase 300) when said compensation is finished. In the phase labeled MS1, the actuator is held pre-tensioned to prevent any motor reversal along with the loss of the pretensioning.
Then the actual measurement, labeled M, is begun.
In phase 400, the seat adjustment actuators are energized using the power profile PA and, as indicated above, the cyclical ratio begins to vary (also known as the PWM measurement, or Pulse Width Modulation). As soon as the actuator begins to move (phase MT2), the actuator is stopped (phase 500), and simultaneously (phase 550), the value of the cyclical ratio at the moment the actuator started is memorized. This value of RCYC is called RCYC (Start), and is sent to the computer (in phase 600) to be compared to the occupant classification thresholds in
To give an example, as can be seen in the drawing in
During the so-called actual measurement phase M, the seat adjustment controls are deactivated so as to not interfere with the results.
In
As previously indicated, in order to achieve a precise and dependable detection and classification result, all of the mechanical slack in the seat must be taken up before taking the actual measurement. As soon as the rotation of the actuator is detected, the actuator is stopped so as to not change the passenger comfort settings. Electrical seat actuators have a nominal speed of approximately 3000 rpm. If the rotation of the actuator is detected in one complete revolution (at most), and if the measurement takes two revolutions, including one to take up slack and one for detection), then the time period during which the actuator is activated is approximately (60/3000)×2=0.04 seconds, which makes the movement of the seat practically imperceptible to the passenger. If it is desired to decrease the measurement time, it is possible to detect the movement of the actuator by analyzing the current. This way, it is not necessary for the actuator to reach a sensor position in order to detect its movement.
Note that the manner in which the above-described measurement is taken is controlled according to detection/classification needs. This measurement can be taken on a periodic or event basis. In this way, a system has been devised that is useful and accommodates any detection strategy, as well as any type of displacement actuator. In each case, it is a matter of changing the detection and classification thresholds in the algorithm.
Note also that in order to steer clear of the potential edge effects of the seat and to avoid taking measurements when the seat is abutting a stop, software stops must be defined before the mechanical stops of the seat. This way, we ensure that all measurements are taken in identical conditions, regardless of the initial position of the seat.
Note also that of the many parameters involved in actuator fault thresholds, the primary ones are battery voltage, temperature, and aging of the actuator and the seat linkages. Consequently, it is helpful to monitor these parameters and to perform autocalibration sequences over the whole life of the device.
The device for implementing the method according to the invention includes:
The means used to apply a predefined power profile to the seat displacement actuator is means for generating a chopped voltage with a variable cyclical ratio.
This power profile is defined by an electronic computer on board the vehicle. This computer is also the means for detecting the startup DM of the seat actuator.
The same electronic computer is the means for comparing RCYC (start) with a series of predetermined reference values for RCYC according to weight.
The above-described method and device provide real advantages for vehicles equipped with electrical seats. The latter need few hardware and software modifications, because the current computers can be used to control the seat actuators and perform occupant detection/classification.
Since the detection and classification thresholds are adjusted at the software level, as previously mentioned, no external intervention is required, even during the production phase.
Adjusting the detection thresholds makes it possible to adapt the various strategies for the airbag to the conditions of use:
This measurement is also provided to every device for which the present occupant's weight data is useful (comfort adjustment, air conditioning, etc.).
