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How does brake assist and collision avoidance systems work on the IS F?
Hi,
So I was reading up some more about the IS F and I found that the car uses a conventional brake booster system, not brake by wire. Now I know how ABS and EBD work, and I know how brake assist and PCS detect things, but I was wondering how PCS changes brake pressure, without the actual pedal being depressed. Does it just move the brake pedal, or does it just compress the fluid? If it just compresses the fluid, how does it do that without use of depressing the brake pedal?
Didn't even know it had this ... but I have an 08 so that may be the issue.
Well from reading the Product Information PDF's, it seems as if all models ABOVE 2010 had it, but maybe 2008/2009 had it because those PDF's were destroyed, so I can't find the info about those.
Well from reading the Product Information PDF's, it seems as if all models ABOVE 2010 had it, but maybe 2008/2009 had it because those PDF's were destroyed, so I can't find the info about those.
I think that the system just applies brake pressure (by use of the piston) without the pedal being depressed. I found this here: The mechanics of the brakes themselves are the same as on cars without automatic braking systems. Whether the driver or a computer decides the car needs to slow down or stop, the same basic parts and principles are used to actually stop your car.
Brake pedal is pushed (or computer calculates and activates pressure to the piston – step 2).
Piston pushes fluid to master cylinder.
Master cylinder pushes fluid to slave cylinders.
Slave cylinders fill and push pistons out.
Pistons push calipers with brake pads.
Brake pads grip rotors (discs) attached to wheels.
Friction between brake pads and rotors slows wheels.
Good question I have wondered about this.my 2cents , I THINK it's the abs being controlled via front radar then the computer takes over, I should have Google first , cheers from OZ The county on fire.
Good question I have wondered about this.my 2cents , I THINK it's the abs being controlled via front radar then the computer takes over, I should have Google first , cheers from OZ The county on fire.
well m8, you are probably wrong, bc the ABS/EBD only controls the fluid pressure in the lines by valving. PCS is actually the piston inside the master cylinder being compressed by an electric motor or something of the sort. Here is a diagram: (it doesn't show the PCS module or anything)
well m8, you are probably wrong, bc the ABS/EBD only controls the fluid pressure in the lines by valving. PCS is actually the piston inside the master cylinder being compressed by an electric motor or something of the sort. Here is a diagram: (it doesn't show the PCS module or anything)
What? The ABS pump does everything. The master cylinder is only actuated by the pedal. Nothing else. All other functions applying the brakes use the ABS control to make braking happen. Not sure where that diagram came from, but it's not Toyota.
What? The ABS pump does everything. The master cylinder is only actuated by the pedal. Nothing else. All other functions applying the brakes use the ABS control to make braking happen. Not sure where that diagram came from, but it's not Toyota.
How would the ABS pump apply pressure without the master cylinder being actuated? I understand that ABS/EBD use valving to quickly pulse the wheels and change the brake pressure to the wheels, but they don't control the brake pressure coming from the master cylinder. PCS somehow applies the brakes even when the brake pedal is not pushed. Like it says in the article that I read about automatic braking systems,
Brake pedal is pushed (or computer calculates and activates pressure to the piston – step 2).
Piston pushes fluid to master cylinder.
Master cylinder pushes fluid to slave cylinders.
Slave cylinders fill and push pistons out.
Pistons push calipers with brake pads.
Brake pads grip rotors (discs) attached to wheels.
Friction between brake pads and rotors slows wheels.
That's not at all how ABS or other systems work on the IS F or other Lexus vehicles. It's not just valving, there are active pumps involved. VDIM wouldn't be able to control wheel speed as it does without active pumps working the brakes. Note the pumps in the schematic diagram below. This is an extract from the 48 pages in the 2008 IS F New Car Features explaining how all these systems work. Computers in the car have ACTIVE control over the braking system without the master cylinder doing anything. I know this well because VDIM intervened on my behalf on my very first track day and caused me to cook my brakes (Carbotech XP-12 full race pads) in the fourth session of the day because VDIM was applying the brakes through a couple of turns and it wasn't possible to hear any warnings with windows down and helmets on. I later discovered those same turns couldn't possibly be negotiated at full throttle the way VDIM permitted me when it was turned on. I no longer drive with VDIM on at the track for this reason. You learn very little with it injecting itself into the equation.
That's not at all how ABS or other systems work on the IS F or other Lexus vehicles. It's not just valving, there are active pumps involved. VDIM wouldn't be able to control wheel speed as it does without active pumps working the brakes. Note the pumps in the schematic diagram below. This is an extract from the 48 pages in the 2008 IS F New Car Features explaining how all these systems work. Computers in the car have ACTIVE control over the braking system without the master cylinder doing anything. I know this well because VDIM intervened on my behalf on my very first track day and caused me to cook my brakes (Carbotech XP-12 full race pads) in the fourth session of the day because VDIM was applying the brakes through a couple of turns and it wasn't possible to hear any warnings with windows down and helmets on. I later discovered those same turns couldn't possibly be negotiated at full throttle the way VDIM permitted me when it was turned on. I no longer drive with VDIM on at the track for this reason. You learn very little with it injecting itself into the equation.
So, basically, the ABS module on the IS F can add brake pressure to the brakes WITHOUT the master cylinder being actuated? So in a sense, ESC and EBD both work in the same space as the ABS? Looks sort of advanced if you ask me.
So, basically, the ABS module on the IS F can add brake pressure to the brakes WITHOUT the master cylinder being actuated? So in a sense, ESC and EBD both work in the same space as the ABS? Looks sort of advanced if you ask me.
Exactly correct. In the later models (like the wife's GS F) the pre-collision system will actuate the brakes with ZERO operator input. This makes a needle thread pass a heart stopping event. I turned it off permanently because I don't need a computer programmed by the legal department making braking decisions for me. I don't text and drive.
Exactly correct. In the later models (like the wife's GS F) the pre-collision system will actuate the brakes with ZERO operator input. This makes a needle thread pass a heart stopping event. I turned it off permanently because I don't need a computer programmed by the legal department making braking decisions for me. I don't text and drive.
Yeah lol, texting and driving is for losers
Also, does the ABS function like normal ABS, (basically, does it quickly pulse the brake pressure coming from the master cylinder)?
It does, but it's a lot more quiet than some of the earlier versions. The first car I owned with ABS was a '93 Celica GTS. When ABS engaged it sounded like an iron works. Hammering sound very loudly engaged, and was a bit intimidating until you realized what was happening. The IS and GS F platforms do make some noise when ABS engages but its a lot less intrusive unless you're running full race pads (they are too aggressive for ABS to work as designed and will allow significant wheel lock before they release).
When VDIM engages to manage stability, there is a whole lot less noise in comparison. None of it is audible on track with the windows down (as most HPDEs require) and a helmet on. Besides, eyes are up on track, not on gauges, so the VDIM light flashing isn't catching your attention at all.
It does, but it's a lot more quiet than some of the earlier versions. The first car I owned with ABS was a '93 Celica GTS. When ABS engaged it sounded like an iron works. Hammering sound very loudly engaged, and was a bit intimidating until you realized what was happening. The IS and GS F platforms do make some noise when ABS engages but its a lot less intrusive unless you're running full race pads (they are too aggressive for ABS to work as designed and will allow significant wheel lock before they release).
When VDIM engages to manage stability, there is a whole lot less noise in comparison. None of it is audible on track with the windows down (as most HPDEs require) and a helmet on. Besides, eyes are up on track, not on gauges, so the VDIM light flashing isn't catching your attention at all.
Alright, thanks for clearing everything up. So if I have this correctly, the ABS/EBD/VDIM module can apply brake pressure when needed, and the ABS part of it just pulses the brake pressure coming from the master cylinder (like a normal ABS module)?
Alright, thanks for clearing everything up. So if I have this correctly, the ABS/EBD/VDIM module can apply brake pressure when needed, and the ABS part of it just pulses the brake pressure coming from the master cylinder (like a normal ABS module)?
The ABS control system can add or subtract pressure going to the calipers under a wide range of circumstances including ABS.
02-02-20, 11:36 AM
How does brake assist and collision avoidance systems work on the IS F?
