ABSTRACT:
There is a requirement for the 3rd row seats in vans to have belt minder signal so the driver can be warned if seat belts are not buckled, especially with kids in the 3rd row seats.
However, the 3rd row seats are also designed to be removable – either automatically sliding into the floor
well or removed from the van to create additional cargo space.
A wired connection to the seat belt minder creates reliability and potential warranty concerns if the connector is not engaged or damaged during seat removal process.
So a system needs to be designed for the noise factor mentioned above.
Removable Rear Seat Beltminder Functional Requirements
To meet the requirement for 3rd row removable single or two seat assembly 4 technology options 
were reviewed. Basic requirements as below:
- Electrical: 100mA inrush, 1mA min current at 5v
- Circuits: 2 per seat – data communication
- Connector: Sealed
- Operating Temperature: -40C to +85C
- The connector would need to be easy to mate by the customer if the seat was
- Design for 500 removals over 10
- Package designed for easy attachment or
- System interface connector at the end of wire running down seat belt buckle
- Requirement is three connections per
- Operating Temperature -40C to 85C.
Hall Affect Sensor to detect seat belt actuation
Removable Rear Seat Beltminder Technology Investigate
Design Investigate Overview:
Four potential technology options were reviewed as below:
Power by Proxi Qi Magnetic Resonance Data Transfer:
Technology not AR for Ford and will not meet Ford cost targets. Wireless energy and data transfer technology is expensive and the standards are constantly changing.
Energy Harvesting Technology
Opportunity for Ford to explore this but may not meet program cost targets. In addition, signal will only be sent during seat belt usage and has the potential of error based on passenger attaching buckle before ignition on.
This technology is new to automotive but EnOcean already has a large consortium and would be value add to Ford to explore this as a solution for future applications. However, under best design circumstances earliest potential application would not be before 2021 MY.
Removable Rear Seat Beltminder Technology Investigates
Standard Connector Solution:
Any design with standard connector system will have at minimum five components; Connector, Christmas Tree, Clamps, Dressing, Wiring cut leads and Tape.
Reliability will always be a concern during seat removal and attachment by the driver and will be prone to breakage, especially during loading as seats are heavy and get dropped. Recessed attachments will collect debris, liquids.
Also unprotected, conductive surfaces will likely get contaminated and sugary drinks, oil, paint would need to be completed removed. Conductive surfaces can be scratched/damaged
Removable Rear Seat Beltminder Design
Coin Cell Wireless RF Data Transfer:
This is the recommended solution to meet program reliability, cost and timing targets.
Permission will be needed to use the 315.15MHZ wireless data transfer frequency normally used for Keyfob applications but that is fairly standard.
Signal reciver could be the security module or others as to be decided by Ford. Battery life is estimated at 7 – 10 years.
Battery for critical applications are already in use in TPMS so the concept to use coin cell battery as a power source for critical function is not new.
- Cost for coin cell integrated module per seat belt buckle is estimated at $3.50 and as no external wiring is needed that would be full cost
- Packaging can be in the buckle or just outside the buckle for ease of If packaged outside the buckle a small jumper pigtail will be needed but impact on cost would be minimal.
- Timing for fully validated assembly could be < 35 weeks from
- Process could be to use technology design firm like Hirain to take the lead and then have FSS manufacture to design or use directed design strategy with
Removable Rear Seat Beltminder Design
Calculation from Varta battery for Coin Cell
- 0.2 sec=1 min/60sec=1 hr. / 60 min = .0000555 hrs.
- Capacity = 5 mA x .0000555 hrs. = .0002777 mAh
- Ten times a day = .002777 mAh
- 365 days a year = 1.0138 mAh per year
- Self-discharge of approximately 1% per year = 2.3 mAh
- Total per year is 1.0138 + 2.3 = 3.3138 mAh capacity drain per year.
- With a 230 mAh capacity, there should be no issue lasting 10 years with the CR2032.
- With 560 mAh capacity, the CR2450 is even more capable.
CYMBET Energy Management Solution to Improve Battery Life
Standard Wireless Circuit as configured. MCU is always on and drawing some amount of current.
The power and energy calculations in your proposal account for 10 Tx per day. With regular pinging, the battery life will be degraded substantially. In the battery life calculations for 10/day Tx, note that most of the battery energy is consumed not by the Tx, but by the 6uA background current. With the Cymbet energy management approach, that 6uA figure can go to something <0.1uA.
Note also that leakage from the capacitor(s) tied to Vdd (listed in BoM but not shown in schematic) will also present a perhaps non-negligible load on the battery.
You can ignore the sensor part of the circuit labeled “optional.” It’s not really relevant to your circuit.
Cymbet energy management approach, from page 4 of Cymbet AN-1059: Extend Battery Life by Reducing System Power Using the EnerChip RTC
Wireless Data Transfer – Magnetic resonance
ENOCEAN Energy Harvesting Technology
- License free 868 and 315 MHz band with 1% duty cycle.
- Radio design for immunity against interference
- Multiple telegram with checksum
- Short telegrams generate low collision probability with high sensor density
- Frequency 315 MHz
- The energy module ECO 200 is an energy converter for linear motion. It can be used to power the PTM 330C radio module or derivate. The energy output at every actuation of the spring is sufficient to transmit 3 sub-telegrams with a PTM 330C module. Possible applications are miniaturized switches and sensors in building technology and industrial automation.
