There is nothing attached on the hydraulic line in-between the front brakes master cylinder and the front brake calipers.
ERS brake pressure reduction valve is on the main line (hydraulic line) between rear master cylinder and rear brake calipers.
The brake pedal controls the braking of the front and rear axles via two separate brake master cylinders. With the driver able to adjust the brake bias between the front and rear ends.
When the driver ‘stub’s the brakes 'to' hard the MGU-K will harvest more. When the driver ‘stubs’ the brakes softer the MGU-K will harvest less.
...Since so many members seem to have inside information I thought someone might have an answer....
Strad, if anyone here has inside information on current tech (particularly on the creative interpretation of the rules surrounding current tech) they're so locked down by an NDA that they will never reveal details on anything, even basic questions. In short, you are never going to get a straight answer...
What I love about this site is it's mostly just educated guessing, and even though those guesses are sometimes fanciful, they can still make for quite interesting thought exercises.
My take on anything F1 (or any competitive sporting code for that matter) - if there's an opportunity to bend the rules take it because your competitors certainly will. If any of us here identify an opportunity for a less-than-kosher competitive advantage you can be sure an F1 team has reams of data on the subject. It's only cheating after the TD says you can't do it anymore
I am just asking for expert input on the use and purpose of the ERS Brake Pressure Reduction Valve.
The diagram I saw that valve was on the main brake line. Not the front or rear and wired into the ECU.
Since it is pretty much out in the open and not hidden I can only assume it's legal so my question remains,,, What is it's purpose?
IF when a driver stabs the brakes too hard does it automatically lessen the line pressure? I would think that amounts to an anti-lock device and as such would be illegal. Since it is apparently on all or almost all cars I can't/don't believe that's it. So my question. Since so many members seem to have inside information I thought someone might have an answer.
If a mod wants to delete this thread that's fine. I was in the dark before and can remain in the dark if the question is going to stir up conspiracy theory's.
The braking system can be thought of as conventional with the driver pedal action providing pressure to the front and rear brake callipers. In addition to this conventional system is the KERS system. This supplies additional braking effort to the rear axle. To preserve the balance of the conventional system the pressure on the rear brakes has to be reduced. This is what the Brake Pressure Reduction Valve does. Both it and the KERS are under ECU control.
Contrary to what @Savior Stivala says except at low speed the MGU-K runs at its maximum 120kW and the brake pressure is reduced to allow for its input. Below about 120kph the rear brake pressure is zero and the MGU-K power is reduced to provide the braking force on the rear wheels the driver is demanding and would obtain in a conventional braking set up.
The system is fail safe in that if the electrical system fails the BPRV is locked out and the braking system performs conventionally, albeit with limited capacity.
Fortune favours the prepared; she has no favourites and takes no sides.
Truth is confirmed by inspection and delay; falsehood by haste and uncertainty : Tacitus
With the change in the energy recovery system (ERS) the use of brake-by-wire was allowed for rear brakes, as the MGU-K recovers energy under braking, the drug of the MGU-K acts as a brake, also slowing the car, however, this effect isn’t constant, the braking effort from the MGU-K will vary depending on its regenerative setting and how charged the battery is. With this change in ERS braking effort, the driver will suffer imbalanced braking, sometimes getting rear braking from ERS, sometimes not always with warning, so the rules allow a system termed ‘BBW’ to control the rear brakes. There is still a rear master cylinder at the pedal, but the brake line terminates at the ‘BBW’ unit. This unit recognizes the braking demand by the driver, and based on the pressure in the rear brake line, it will then deduct one from the other and via a hydraulically operated active master cylinder it will apply only the pressure at the rear brakes needed to off the ERS effect. Giving the driver a balanced braking event. That is the simple explanation. The actual software to give a constant braking effort to the driver is far more complex. Moreover, the driver will get a different feel at the pedal, as the rear master cylinder is effectively capped off. So some compliance is put into the system to replace the pedal conventional feeling. Being safety critical, the BBW unit has a failsafe. Should the sensors or active master cylinder including MGU-K fail, the brakes return to being operated by the pressure in the rear brake line. Also to prevent ant pseudo anti-lock brake software being used, wheel speed cannot be a factor in the system.
“Except at low speed the MGU-K runs at its maximum 120kw, and the brake pressure is reduced to allow for its input”.
ERS parts that makes-up the BBW system installed in/on/connected to the rear brakes system, in-between the rear master cylinder pressure outlet and the rear calipers. In that order:- Compliance chamber “gives driver more feel”, Electronic control unit/MGU-K “that slows the MGU-K and through an actuator – Actuator “creates pressure in the rear brake calipers”.
Two notes here;-. Actuator “creates pressure in the rear brake calipers” this is an auxiliary master cylinder. Fail safe normal pressure line that bypasses the BBW system, take-off point is between rear master cylinder and compliance chamber and bypasses the BBW system ending at the rear calipers.
The braking effort at the rear is through a combination of pressure on the brakes and deceleration effort of the MGU-K being charged by heat energy being recovered. The ‘extant’ of the later is dictated by ‘how much’ energy is being ‘recovered’. At any given time. With regulations stipulating a maximum yield of 2mj per lap.
So it reduces pressure to the rears to prevent lock up?
No. It reduces the pressure so that the combined braking force at the rear from the friction brakes and the MGU-K matches the drivers demand.
Fortune favours the prepared; she has no favourites and takes no sides.
Truth is confirmed by inspection and delay; falsehood by haste and uncertainty : Tacitus
So it reduces pressure to the rears to prevent lock up?
"Also to prevent any pseudo 'anti-lock' software being used, 'wheel speed' cannot be a factor in the system".
I believe the above will answer your original concern and/or doubt at start of thread about the use of 'anti-lock'.
The pressure generated by the driver in the rear brake circuit may be reduced by use of an ERS Brake Pressure Reducing Valve. The valve must be manufactured by an FIA designated supplier and installed in accordance with the fitting instructions which may be found in the appendix to the technical regulations.
Now when I looked in the technical regulations they just bounced me between 11.9 and 8.2.
But the above quote from the FIA answers the question except for their usual convoluted double talk.
11.1.2 The brake system must be designed in order that the force exerted on the brake pads within each circuit are the same at all times.
11.7.1 No braking system may be designed to prevent wheels from locking when the driver applies pressure to the brake pedal.
11.9 Rear brake control system : The pressure in the rear braking circuit may be provided by a powered control system provided that : a) The driver brake pedal is connected to a hydraulic master cylinder that generates a pressure source that can be applied to the rear braking circuit if the powered system is disabled. b) The powered system is controlled by the control electronics described in Article 8.2.
8.2 Control electronics : 8.2.1 All components of the power unit, gearbox, clutch and differential, in addition to all associated actuators, must be controlled by an Electronic Control Unit (ECU) which has been manufactured by an FIA designated supplier to a specification determined by the FIA. The ECU may only be used with FIA approved software and may only be connected to the control system wiring loom, sensors and actuators in a manner specified by the FIA. Additional information regarding the ECU software versions and setup may be found in the Appendix to the Technical Regulations.
To achieve anything, you must be prepared to dabble on the boundary of disaster.”
Sir Stirling Moss
11.1.2 disallows brake steering. It assumes the MGU-K torque cannot be distributed unequally across the axle.
Fortune favours the prepared; she has no favourites and takes no sides.
Truth is confirmed by inspection and delay; falsehood by haste and uncertainty : Tacitus
11.1.2 disallows brake steering. It assumes the MGU-K torque cannot be distributed unequally across the axle.
Nope. That's not possible already by fact, that the MGU-K is located basically at the engine side of the powertrain. You can argue that with a limited slip differential it's a bit like brake steering to a certain degree, but certainly not like they would have active torque vectoring.
11.1.2 disallows brake steering. It assumes the MGU-K torque cannot be distributed unequally across the axle.
Nope. That's not possible already by fact, that the MGU-K is located basically at the engine side of the powertrain. You can argue that with a limited slip differential it's a bit like brake steering to a certain degree, but certainly not like they would have active torque vectoring.
Agreed. That’s why they only mention the friction brakes.
However. The rules that cover torque variation across the axle are:
9.9 Torque transfer systems :
9.9.1 Any system or device the design of which is capable of transferring or diverting torque from a
slower to a faster rotating wheel is not permitted.
9.9.2 Any device which is capable of transferring torque between the principal axes of rotation of the two front wheels is prohibited.
If I created a system that used a cyclic variation in the direction of MGU-K torque to one side of the diff I don’t think it would infringe either rule.
Which is why I said there was an implicit assumption in the rules.
Fortune favours the prepared; she has no favourites and takes no sides.
Truth is confirmed by inspection and delay; falsehood by haste and uncertainty : Tacitus
But how can one create a system that uses a cyclic variation in the direction of MGU-K torque to one side of the diff when anything that the MGU-K can output is outputted to the ICE crankshaft with the result that output will be a combination/mix of crankshaft MGU-K output. Unless they drive the car by MGU-K output alone.
But how can one create a system that uses a cyclic variation in the direction of MGU-K torque to one side of the diff when anything that the MGU-K can output is outputted to the ICE crankshaft with the result that output will be a combination/mix of crankshaft MGU-K output. Unless they drive the car by MGU-K output alone.
During braking the crankshaft power would be engine braking, which isn’t really regulated. Below 120kph rear braking can be achieved by MGU-K alone.
This is purely a hypothesis. I am simply suggesting a mechanism to increase yaw rate under braking. I can’t find regulations that would make it illegal.
Fortune favours the prepared; she has no favourites and takes no sides.
Truth is confirmed by inspection and delay; falsehood by haste and uncertainty : Tacitus
But how can one create a system that uses a cyclic variation in the direction of MGU-K torque to one side of the diff when anything that the MGU-K can output is outputted to the ICE crankshaft with the result that output will be a combination/mix of crankshaft MGU-K output. Unless they drive the car by MGU-K output alone.
During braking the crankshaft power would be engine braking, which isn’t really regulated. Below 120kph rear braking can be achieved by MGU-K alone.
This is purely a hypothesis. I am simply suggesting a mechanism to increase yaw rate under braking. I can’t find regulations that would make it illegal.
