Seatbelt Pre-Tensioners

[Nice Nige NZ]

Hi everyone,

I wanted to share an amazing experience I had the other day in my Lexus

Driving along at about 50mph, coming down a dip and then up a hill, another driver was on the left hand side in a driveway and looked like he was going to pull out as he hadn't seen me. I braked hard to slow down, and suddenly the brakes seemed to work harder than I had actually pushed the pedal and then a whirring noise started and the seat belts tightened and pulled me into my seat and I stopped well before the car in the driveway. As soon as I stopped the seat belts loosened.

I was stunned!

In 5 years of LS ownership this had never happened to me before, and although the car is nearing 9 years old, it all worked like clockwork!

I didn't know it had this capability. I am constantly discovering new things about my beautiful Lexus.

It's the most amazing car In the world, we'll ahead of its time, and I'll never part with her.

My car looks after me and I look after her. In all my life (and that's a long time now!) I have never had such an attachment to a car. People who don't own one just don't get it, but those who do, do!

I was wondering if anyone else here has had the same experience?

Nige

[messi]

All cars do this, it's nothing new

[steve2006]

It has a G sensor fitted, this senses rapid deacceleration and activates amongst other things the seat belt pretensioners.

[PEPE]

I must drive like a little old lady. A seat belt pretensioner has never been activated on me!

[steve2006]

Should have said arms the pretensioners not activate them but the inertia belts do lock up.

[Bluesbreaker]

Lexus technology at it's best-dontcha just love these cars.

[scythe]

Hi Nige,

what you're describing is the front pre-crash system (PCS) fitted to some cars. In the LS460, for instance, there is a pair of near-infrared cameras behind the centre driver's mirror, which, along with two infrared illuminators that help it at night, creates a 3D image of what's in front of the car. This, along with radar data, is constantly monitored by a computer, which, if it thinks that in the near future you are going to attempt to occupy the same region of space as another object or vehicle will respond in a number of ways.

It's gentlest response is, when in adaptive cruise control, it realises that to avoid a slowing car in front a greater brake force than about 20% of the maximum is needed. The car beeps at you, flashing yellow, basically asking you to assist with the braking.

Next level of response involves the car flashing red at you, when it thinks things are getting serious. This doesn't require the cruise control to be activated. The car flashes red at you, beeps continously, and gives you a nudge by doing a bit of semi-serious braking.

Third layer of response is when it thinks that collision is a real possibility. First, the doors unlock. Second, the electric pretensioners wind in the seatbelts. Third, the response of the brakes is increased - only a small brake pressure will result in maximum braking force. Fourth, the steering ratio is changed to give maximum steering response. Fifth, the suspension is hardened to its stiffest setting.

The doors unlock to make it easier to rescue you after an accident. In the LS460 they are normally set to lock automatically when you first set off.

The pretensioners are not like the explosive ones found on other cars. Explosive pretensioners are designed to tighten the belt in that tiny fraction of a second after collision has begun. They will hurt you, and they only have a very short time to reel in your seatbelt. Electric pretensioners have a longer timeframe to operate over, in the region of 1 second. They have time to wind in a lot of belt. They don't damage you, but for the five seconds or so until they release you, breathing will become a thing of the past! And being an electric device, once they have released you, they are ready to be used again and again - they don't need replacing like explosive ones do.

The brake force is increased to the point of stability control being needed. This is because, just before an accident, people often don't brake as hard as they could, and when they do, the braking force and/or the noise feel of the ABS makes them stop braking.

The LS460 has a variable steering ratio. How much the wheels turn when you turn the steering wheel (and how much force you need to turn it) varies with a preset program. However, in an accident, people often don't do enough to steer around an obstacle, so in the pre-crash situation a smaller turn of the steering wheel gives the largest possible steering effect.

Hardening the suspension has two effects. First, it improves braking. Second, it makes it less likely that the car's nose will 'dive', causing it to underrun another vehicle, increasing risk to you and your passengers.

Incidentally, there is also a rear crash protention system. Under the rear bumper there is a second radar unit, measuring speed and distance of the car behind you. If it thinks a collision is possible, it responds by rapidly moving front seat headrests til they make contact with the driver and passenger's heads, locking into position for about three seconds, then returning if not needed. If you weren't aware of this system, you might not realise that it had activated itself.

Both my rear and front pre-crash systems have each activated twice. The rear one activated each time in a traffic queue, when the car behind approached too rapidly for comfort. The front system activated once at a roundabout, where, at the last moment, I decided not to go onto the roundabout because a car was coming more quickly than I'd initially though from the right. The other time it activated was, a lot like your situation, Nige, where a car pulled out and I had to stop very quickly.

This is all great technology, I think, that Lexus should be encouraged to continue to develop.

[Cotswold Pete]

All this sounds like I should test drive a 460, as it sounds as safe as houses.

It also sounds like the Lexus team think about the driver first then the technology second, making sure the driver is not harmed (physically or in the wallet area) as a result of an crash or potential crash.