Editor’s note: David Swanson proposes a pretty neat concept for the modern door lock in automobiles. Enjoy and get those creative juices flowing.
It is amazing to me. Not so long ago there was no such thing as a BCM (Body Control Module). Lights and other loads were switched on by, of all things, mechanical switches. Higher current loads were sometimes driven by relays that were driven by switches. Protection came in the form of a fuse. A faulted load would blow a fuse. Those niggly momentary shorts would completely disable a system and were virtually impossible to find. As a mechanic, back in the 70’s a momentary fault in the harness was detectable only by the repeated replacement of fuses over time. The fix often resulted in running a new wire from, you guessed it, the switch to the load.
(Packard was the first to successfully introduce electric door locks in 1956)
Relays were distributed according to their need. The high beam relay/switch was located on the steering column (even earlier they were on the floor left of the pedals), the High blower relay was on the firewall near the HVAC blower motor, and the horn relay was under the hood. Even the alternator voltage regulator was a relay on the fender well. The advent of smart switches brought on the ability to centralize the load driving in one box, the BCM. In order to protect the silicon from the hazards of an automotive electrical system, intelligence was needed. Intelligence in the form of overcurrent protection, thermal protection, and inductive energy clamping. Not to mention things like reverse battery and the standard automotive transients. Most of which a relay either generated itself or didn’t care that much about.
In the process of adding all these protections things got quite a bit more sophisticated. Now momentary faults do not kill a system or systems. A shorted load did not take out several other, sometimes seemingly unrelated, things tied to the same fuse.
Now shorts, even momentary faults, are intelligently detected and dealt with by providing fault codes and higher level diagnostics. It is not just nice to have today. It is required... for most loads that is.
In this age, sophisticated electronics safety is less of a feature and more of a requirement.
When it comes to door locks safety and security are becoming more central… European standards require secondary, or Thatcham, locks that provide a double lock of sorts. Thatcham locks prevent interior door handles from opening doors to thwart thieves. Also, European standards require that doors must unlock during an accident to allow first responders faster access. I would think a fairly important safety feature that should focus on reliability and action at all costs.
Electronic child lock features allow the option for the rear seat interior door handles to be disabled while driving. Thus, keeping little ones from accidentally opening doors while on the road.
The introduction of passive entry systems puts pressure on unlock timing. So much so that one car manufacturer has implemented a third lock motor in their door latch mechanism just to speed up the unlock response time when accessing a door handle. They don’t want the customer to have to wait even 100ms to unlock a door. Those few milliseconds of speed are a feature that they are paying for.
Other security issues might include in the future individual door unlock capability so that passive entry can be done one door at a time… one pull of the handle only unlocks that door… keeping all other doors locked. A second pull on that same handle might then unlock the remaining doors or just the doors on that side of the vehicle. Unlocking the fuel door can keep the doors on the opposite side of the car locked for security. Any number of combinations could be considered. All with safety and security in mind.
Thief stealing a pocketbook while the victim is pumping gas
Watch the video here
Door locking can get quite sophisticated and secure. Alas, the cost of a relay is so low these days that such features could be possible except for the fact that relays are loud, heavy, unreliable, and take up a lot of precious circuit board space in the BCM. When you count up all the relays needed to drive the doors individually, the secondary locks front to rear separately, the fuel door, trunk/liftgate etc. the relay solution can get quite onerous.
No, wait! This is the 21st century. Cars have sophisticated body control modules that regulate the RMS voltage in the exterior lamps to extend the life of the bulbs. There is a lot of sophistication to detect the presence of a bulb or an LED array or a shorted or open load. Yet still door locks are driven by pre-1950’s technology. With pre-1950’s reliability… and pre-1950’s performance for what I would consider a safety and security related function. Mmm… what to do?
If there could be a solution. If there was a central door lock driver IC that can do all of this and more in a footprint of a single relay. This device could answer all of the above needs and then some. It could drive the door locks individually, drive the secondary locks individually or by group (front/rear), drive the trunk/rear hatch lock, and drive the fuel door lock. How can a single IC do all this and not be the size of gas cap? Simple, two words, current regulation.
Today door lock drivers (relays) focus their requirements on the maximum amount of current the door lock motors can demand. How demanding are they you ask? Very. Some door lock systems need multiple fuses and can drive as much as 60 Amps. So, the relays, wires, circuit board traces, and connectors that are required to drive these lock motors must be able to handle this monstrous current.
To make a solid-state switch handle this much current takes a bit of silicon. Facts of life, fire is hot, water is wet, and silicon cost money. There is not much money in body electronics. Car makers are reluctantly willing to pay for a feature that adds wow factor to a car or for something the consumer would appreciate enough to pay for… with margin. i.e. there has to be money in it for the car company. Adding cost and sophistication to a feature that is imperceptible to a consumer has two chances of being implemented, slim and none.
So, we can reduce the cost of the silicon by taking advantage of motor theory and at the same time we can provide features that improve reliability and increase safety, security and convenience for the consumer.