Capacitive vehicle seat occupancy detection system with detection of vehicle seat heater member interruption

Abstract

A capacitive detection system for detecting occupancy of a vehicle seat includes a signal generating unit and a signal evaluation unit. The vehicle seat has a seat heater member configured for receiving time-varying output signals of the signal generating unit. The signal evaluation unit is configured to generate an output signal that is indicative of the seat heater member to be defective, if the sensed capacitance of the seat heater member is less than a second predetermined threshold value for the sensed capacitance.

Claims

1. A combined seat heater and capacitive seat occupancy detection system for detecting an occupancy of a vehicle seat, wherein the seat heater comprises at least one seat heater member, and the capacitive detection system includes a signal generating unit provided for generating a time-varying output signal at an output port, wherein the time-varying output port is configured to be electrically connectable to the at least one seat heater member for providing the time-varying output signal, and a signal evaluation unit that is provided for sensing an electrical quantity that is indicative of a capacitance of the at least one seat heater member, and that is provided for generating an output signal that is representative of the sensed capacitance and that is usable as a basis for at least one out of detecting and classifying a seat occupancy by comparison to at least a first predetermined value (C.sub.thresh) for a sensed capacitance, wherein the signal evaluation unit is configured to generate an output signal that is indicative of the at least one seat heater member being defective, when the sensed capacitance of the at least one seat heater member is less than a second predetermined threshold value (C.sub.min) for the sensed capacitance.

2. The capacitive vehicle seat occupancy detection system as claimed in claim 1, wherein the second predetermined threshold value (C.sub.min) is less than a capacitance of the at least one seat heater member for a condition of an unoccupied vehicle seat.

3. A vehicle seat with a capacitive vehicle seat occupancy detection system as claimed in claim 1, wherein the capacitive vehicle seat occupancy detection system is at least partially installed in the vehicle seat, the vehicle seat comprising a seat base configured for taking up a seat base cushion, the seat base and the seat base cushion being provided for supporting a bottom of a seat occupant, a backrest configured for taking up a backrest cushion provided for supporting a lumbar and back region of the seat occupant, and at least one seat heater member, wherein the least one seat heater member is at least partially disposed at at least one out of the seat base cushion and the backrest cushion and is electrically connected to the signal generating unit of the capacitive vehicle seat occupancy detection system.

4. A method for detecting a defective seat heater member of a vehicle seat having a capacitive vehicle seat occupancy detection system that is configured for detecting an occupancy of the vehicle seat, the vehicle seat comprising at least one seat heater member, wherein the capacitive vehicle seat occupancy detection system includes a signal generating unit provided for generating a time-varying output signal and a signal evaluation unit that is provided for sensing an electrical quantity that is indicative of a capacitance, the method comprising steps of applying a time-varying electrical signal at least to the at least one seat heater member by the signal generating unit, sensing an electrical quantity that is indicative of a capacitance of the at least one seat heater member by the signal evaluation unit, checking a first condition representing that the sensed capacitance of the at least one seat heater member is less than a second predetermined threshold value (C.sub.min), and generating an output signal that is indicative of the at least one seat heater member when at least the first condition is fulfilled.

5. The method as claimed in claim 4, comprising the step of using a capacitance value of the at least one seat heater member for a condition of the vehicle seat being unoccupied as the second predetermined threshold value (C.sub.min).

6. The method as claimed in claim 4, comprising a preceding step of determining the capacitance value of the at least one seat heater member for the condition of the unoccupied vehicle seat for calibration purposes.

7. The method as claimed in claim 4, wherein the vehicle includes a seat buckle state indicator, and the method comprises a step of checking a second condition of the seat buckle state indicator indicating an unbuckled state, and the step of generating an output signal that is indicative of the at least one seat heater member being defective is carried out when the second condition is fulfilled.

8. The method as claimed in claim 4, wherein the vehicle includes a vehicle speed indicator, and the method comprises a step of checking a third condition of the vehicle speed indicator indicating a vehicle speed of zero, and the step of generating an output signal that is indicative of the at least one seat heater member being defective is carried out when at least one out of the second condition and the third condition is fulfilled.

9. The method as claimed in claim 4, wherein the vehicle includes an ignition state indicator, and the method comprises a step (52) of checking a fourth condition of the ignition state indicator indicating an ignition state being off, and the step of generating an output signal that is indicative of the at least one seat heater member being defective is carried out when at least one out of the second condition, the third condition and the fourth condition is fulfilled.

10. The method as claimed in claim 4, wherein the vehicle includes a keyless entry state indicator, and the method comprises a step of checking a fifth condition of the keyless entry state indicator indicating a keyless entry state being an absent key, and the step of generating an output signal that is indicative of the at least one seat heater member being defective is carried out when at least one out of the second condition, the third condition, the fourth condition and the fifth condition is fulfilled.

11. The method as claimed in claim 4, wherein the vehicle includes a central locking state indicator, and the method comprises a step of checking a sixth condition of the central locking state indicator indicating a central locking state being a locked state, and the step of generating an output signal that is indicative of the at least one seat heater member being defective is carried out when at least one out of the second condition, the third condition, the fourth condition, the fifth condition and the sixth condition is fulfilled.

12. The method as claimed in claim 4, wherein the method comprises a step of starting a predetermined time period if one out of the first condition, the second condition, the third condition, the fourth condition, the fifth condition and the sixth condition are fulfilled, and a step of checking a seventh condition of the predetermined time period having elapsed, and the step of generating an output signal that is indicative of the at least one seat heater member being defective is carried out when the seventh condition and at least one out of the second condition, the third condition, the fourth condition, the fifth condition and the sixth condition are fulfilled.

13. A non-transitory digital memory unit comprising a software module having program code that is stored in the digital data memory unit and that is executable by a processor unit of the capacitive vehicle seat occupancy detection system or a separate control unit to carry out the method of claim 4.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Preferred embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings, in which:

(2) FIG. 1 schematically illustrates a configuration of an embodiment of a capacitive vehicle seat occupancy detection system in accordance with the invention as being partially installed in a vehicle seat of a passenger car;

(3) FIG. 2 shows a flow chart of an embodiment of the method in accordance with the invention; and

(4) FIG. 3 illustrates the logical configuration of the method pursuant to FIG. 2.

DESCRIPTION OF PREFERRED EMBODIMENTS

(5) FIG. 1 schematically illustrates a configuration of an embodiment of a combined seat heater and capacitive vehicle seat occupancy detection system 10 in accordance with the invention to be installed in a vehicle seat e.g. of a passenger car.

(6) The vehicle seat includes a seat base 22, i.e. a seat frame or seat pan, configured for taking up a seat base cushion, the seat base and the seat base cushion being provided for supporting a bottom of a seat occupant. The vehicle seat further comprises a backrest configured for taking up a backrest cushion provided for supporting a lumbar and back region of the seat occupant. Seats of this kind are well known in the art and shall therefore neither shown in a figure nor be described in further detail herein.

(7) The vehicle seat may comprise a plurality of seat heater members, each of which comprises e.g. a piece of electric wire made from a copper-nickel alloy with low temperature coefficient, such as Constantan?, and having an outer electrical insulation layer. The seat heater members are arranged in a meandering manner at various locations of the vehicle seat, as is known in the art. One seat heater member 32 is attached to a seat base cushion front member, and two more seat heater members are attached to a two-part seat base cushion center member, close to the A surface of the seat base cushion. The meandering patterns formed by the seat heater members cover a major portion of the surface of the seat base cushion center member.

(8) The vehicle further comprises a seat heater control unit 24 that is connected to a battery 40 of the vehicle. The seat heater control unit 24 is configured to provide pulse-width modulated electric power of variable duty cycle to the seat heater members 32. To this end, electrical connection ends 34, 36 of each one of the plurality of seat heater members are electrically connected to the seat heater control unit 24 by shielded cables 26 and via common mode chokes 28 for decoupling purposes (exemplarily shown for seat heater member 32 in FIG. 1). The seat heater control unit 24 includes a temperature sensor 38 that is disposed at an appropriate position in the vehicle seat 22 and that is configured for providing signals indicative of a temperature of the vehicle seat 22 to the seat heater control unit 24 for control purposes.

(9) Moreover, the capacitive vehicle seat occupancy detection system 10 includes a signal generating unit 12 and a signal evaluation unit 14, which are installed remotely from the vehicle seat.

(10) The signal generating unit 12 is provided for generating a square-wave or sine-wave output signal and for applying the output signal to seat heat member 32. In this specific embodiment, the time-varying output signal is designed as a square-wave signal with a fundamental frequency of 30 kHz, but other signal forms and/or frequencies are also contemplated that appear to be suitable to the person skilled in the art. The electrical connection ends 34, 36 of the seat heater member 32 that is attached to the seat base cushion front member are also connected to the signal generating unit 12 to enable applying the time-varying output signal.

(11) The electrical connection ends 34, 36 of the seat heater member 32 that is attached to the seat base cushion front member are connected to the signal generating unit 12 which, in turn, is connected to the signal evaluation unit 14. The signal evaluation unit 14 comprises a micro-controller 16 and is provided for sensing an electrical quantity that is indicative of a capacitance of the seat heater member 32 that is connected to the signal generating unit 12.

(12) The signal evaluation unit 14 is further provided for generating an output signal that is representative of the sensed capacitance and that is usable as a basis for detecting and classifying a seat occupancy by comparison to predetermined values for a sensed capacitance. In this specific embodiment, the signal evaluation unit 14 is configured to generate output signals representing seat occupancy classes child/unoccupied seat (class 1) and adult (class 2). In other embodiments, different seat occupancy classes may be chosen that appear to be suitable to the person skilled in the art.

(13) The signal evaluation unit 14 is furthermore configured to generate an output signal that is indicative of the seat heater member 32 that is connected to the signal generating unit 12 to be defective, if the sensed capacitance of the seat heater member 32 that is connected to the signal generating unit 12 is less than a second predetermined threshold value for the sensed capacitance.

(14) The signal evaluation unit 14 is equipped with a communication interface 18 that is connected to an airbag control unit 42 of the vehicle, and is configured for transferring output signals to the airbag control unit 42 for the purpose of air bag activation control. For instance, if the transferred output signal represents the occupancy class adult, an airbag of the vehicle seat will be deployed.

(15) In the following, an embodiment of the method for detecting a defective seat heater member 32 of the vehicle seat 22 is described. A flow chart of the method is given in FIG. 2. In preparation of operating the capacitive vehicle seat occupancy detection system 10, it shall be understood that all involved units, devices and systems are in an operational state and configured as illustrated in FIG. 1.

(16) In order to be able to carry out the method, the signal evaluation unit 14 comprises a software module. The method steps to be conducted are converted into a program code of the software module. The program code is implemented in a digital data memory unit of the signal evaluation unit 14 and is executable by a processor unit of the signal evaluation unit 14. The digital data memory unit and the processor unit are components of the micro-controller 16. Alternatively, the software module may as well reside in and may be executable by a control unit of the vehicle, for instance by the airbag control unit 42, and established data communication means 18 between the signal evaluation unit 14 and the airbag control unit 42 of the vehicle would be used for enabling mutual transfer of data.

(17) In a preparatory and preceding step of the method, a capacitance value of the seat heater member 32 is determined in the condition of the unoccupied vehicle seat 22 for calibration purposes, followed by a step of using the determined capacitance value of the seat heater member 32 for a condition of the vehicle seat 22 being unoccupied as a second predetermined threshold value.

(18) In a first step 44 of the method (FIG. 2), a time-varying electrical signal is applied to the seat heater member 32 by the signal generating unit 12. In a next step 46, the signal evaluation unit 14 senses an electrical quantity that is indicative of a capacitance of the seat heater member 32. Next, a condition representing that the sensed capacitance of the seat heater member 32 is larger than a first predetermined threshold value C.sub.thresh is checked in a step 48. If so, the seat occupancy is classified. If not, a condition representing that the sensed capacitance of the seat heater member 32 is less than the second predetermined threshold value C.sub.min is checked in another step 50. In case of a negative result of the step 50 of checking, the preceding steps (except for the preliminary steps) are automatically repeated.

(19) In case of a positive result of the step 50 of checking, a step 54 of starting a predetermined time period is conducted, and steps 56 of checking a condition CON #7 of the predetermined time period having elapsed are periodically being carried out until the result of the step 56 of checking is positive.

(20) In case of a positive result of the step 56 of checking, a step 52 of checking an additional condition CON #4 of an ignition state indicator of the vehicle indicating an ignition state being OFF is carried out. The condition CON #4 of the vehicle ignition state indicator is transferred to the signal evaluation unit 14 via the communication interface 18, which in this specific embodiment is formed by a Local Interconnect Network (LIN) connection. Alternatively, a CAN (Controller Area Network) bus link could be employed.

(21) In another step 58 then, the signal evaluation unit 14 will generate an output signal that is indicative of the seat heater member 32 to be defective on the basis of the fulfillment of the condition representing that the sensed capacitance of the seat heater member 32 is less than the second predetermined threshold value C.sub.min, and the fulfillment of the condition CON #4 that the ignition state is OFF, which confirms the condition of the vehicle seat 22 being unoccupied.

(22) If one of the two conditions is not fulfilled, the method steps are automatically repeated.

(23) In this way, the condition that the sensed capacitance of the seat heater member 32 is less than the second predetermined threshold value C.sub.min, the condition CON #4 that the ignition state indicator of the vehicle indicating an ignition state is OFF and the condition CON #7 of an elapsed predetermined time period are combined in a logical conjunction. As will be appreciated by those skilled in the art, other conditions may optionally be combined in the same logical AND operation to further increase the reliability of the condition of the vehicle seat 22 being unoccupied.

(24) Examples for these conditions are given in FIG. 3, which illustrates the logical configuration of the method. Therein, the following denotation holds:

(25) CON #2 buckle state indicator indicates UNBUCKLED

(26) CON #3 vehicle speed indicator indicates zero

(27) CON #4 ignition state indicator indicates OFF

(28) CON #5 keyless entry state indicator indicates KEY ABSENT

(29) CON #6 central locking state indicator indicates LOCKED

(30) CON #7 predetermined time period elapsed

(31) While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

(32) Other variations to be disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word comprising does not exclude other elements or steps, and the indefinite article a or an does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting scope.