has it been entirely eliminated on lorries with electronic controlled brakes. Do all new trucks come with brake by wire, And if full air systems still exist what are the time delays now for the air lag?
Intresting
Don’t quite get the air lag question ,unless iam being really thick I can only pressume that your referring to a non Ebs drum brake lorry where the brakes are out of adjustment and the slack adjusters are travelling a fair bit ?
I wonder if Bluey Circles is thinking of the early ABS equipped trailers, where at lower speeds the wheels could lock up fully then release and not re-apply for several seconds…long enough delay that you could have travelled a considerable distance before the buggers worked again…a few heart stopping moments they caused.
I was very pleased when the systems were fixed to cut out low speed problems, they put me off ABS on lorries for a long time.
As for response times for a functioning ABS/EBS system being triggered by emergency braking on slippery roads, i don’t know but would guess that air pressure can’t be fed and dumped as quickly as hydraulics on a car, but would be interested to read any responses from the lorry mechanics here.
probably a poorly asked question. Prior to EBS brake lag (the time from pressing the pedal to the brakes operating was noticeable ) But even with EBS there is always a slight delay in comparison to the hydraulic system fitted to cars, I believe 10ish years ago it was something like 0.1 - 0.2 seconds (which is fast but still a car length at 56mph)
So my question is what is the lag time now on state of the art trucks (I guess there will always be some delay with air as it has to charge the pipe before the brake)
Bluey Circles:
So my question is what is the lag time now on state of the art trucks (I guess there will always be some delay with air as it has to charge the pipe before the brake)
Brake lag in an air brake system should be less than brake lag in a hydraulic brake system due to the difference in the levels of viscosity meaning that any pressure changes are going to occur faster and at a faster rate in an air powered system than a fluid powered one.
I’m interested to know why the question is being asked. The only reason I could think of it being asked is that someone is trying to find a way out of being personally held liable for an accident and trying to blame it on the braking system instead. The variance in reaction times between different people is going to be far in excess of the variance in brake lag times. If the brake lag time is a factor in you hitting or not hitting something then you were already braking far too late in the first place.
Conor:
Bluey Circles:
So my question is what is the lag time now on state of the art trucks (I guess there will always be some delay with air as it has to charge the pipe before the brake)Brake lag in an air brake system should be less than brake lag in a hydraulic brake system due to the difference in the levels of viscosity meaning that any pressure changes are going to occur faster and at a faster rate in an air powered system than a fluid powered one.
I’m interested to know why the question is being asked. The only reason I could think of it being asked is that someone is trying to find a way out of being personally held liable for an accident and trying to blame it on the braking system instead. The variance in reaction times between different people is going to be far in excess of the variance in brake lag times. If the brake lag time is a factor in you hitting or not hitting something then you were already braking far too late in the first place.
No it shouldn’t. Fluid in a hydraulic brake system can’t be compressed, therefore it’s like a solid connection between the pedal and the brake shoe/pad, so it’s instantaneous. Back in the day when I first started driving artics, jack knifes were caused partly by the trailer brakes coming on after the unit/tractor brakes and pushing the drive axle out of line.
Obviously the brakes are still air actuated ultimately but yes you are correct the ‘signal’ to operate the brakes on a trailer obviously travels much faster as an electrical signal than an air one.
Avoiding a too wide ranging and in depth discussion on how it works an explanation of one significant way a truck air brake system differs to an hydraulic brake system on a car.
In a car, generally, you press the pedal which is directly connected to a cylinder that pushes the oil in the circuit which pushes out the pistons in the calipers.
On a truck air system the brake pedal is just a switch. Yes it operates on air but that same air does not directly operate the brakes. There is a reservoir of air and pushing the brake pedal is like opening and closing the floodgate on that reservoir it’s just coincidence/convenience that the mechanism to open and close the floodgate is also air - with EBS it is obviously electric.
So it’s like using a smaller stream of water to open the floodgates on a much bigger more powerful source of water this puts a lag in the system compared to car hydraulic brakes.
Brake lag depends on the distance the relay valve is from the brake chamber,and the length of the signal line.Full ebs brakes use an electronic signal to open the relays which is virtually instantaneous.Full EBS trailers dont need a yellow signal line as the EBS will operate the relay valves using the 2 signal wires on the EBS suzie.They keep the yellow line as a default system if the EBS goes down,so again its down to the distance between the relay and the chambers.