Brake System Design and Optimization: Pressure Measurement
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Pressure Measurement
05.07
| 00:00 | - With temperature covered, the next type of measurement to discuss is pressure. |
| 00:04 | While temperature measurement is more about understanding the result or output of the system, pressure is more about understanding the input side of the braking system. |
| 00:16 | When we measure brake pressure, we're talking about measuring the internal pressure of the brake fluid. |
| 00:21 | This is an important metric to understand as we know already that the brake pressure is the way we can understand the forces in the system both on the input and output side. |
| 00:32 | Brake fluid pressure measurement is done by adding a pressure sensor into the system. |
| 00:38 | One of the fundamental properties of pressure in an enclosed fluid is that the pressure within the fluid will be equal in all parts of the system. |
| 00:47 | The implication of this is that it doesn't matter where we place the sensor in a given brake circuit, the pressure measurement will be the same. |
| 00:55 | An important distinction here is that we can have different pressures within our brake system as a whole. |
| 01:02 | For example, in a typical arrangement where the master cylinders are in dual or tandem arrangement, it's normal to have different master cylinder sizes. |
| 01:12 | If this is the case, we know from earlier in the course that this will result in different fluid pressures in both the front and rear circuits. |
| 01:21 | This means if we place sensors after the master cylinders in each circuit we'd get different measurements which is to be expected. |
| 01:30 | The same would be true of adding cylinders before and after an active proportioning valve. |
| 01:36 | Above the activation pressure, we'd measure a lower pressure after the valve than before it. |
| 01:42 | What remains true is that if we take the front system in isolation, regardless of where in the system we place the sensor, we'll get the same pressure reading if we put the sensors directly after the master cylinder in one of the brake lines in the middle or directly at the calliper. |
| 02:00 | The same pressure will be measured as there's no loss in the system. |
| 02:04 | The pressure sensors themselves need to be compatible with the brake fluid and be rated to a sufficient pressure. |
| 02:12 | In motorsport brake systems, we can see pressures in excess of 1000 psi which is roughly 70 bar. |
| 02:20 | In the OE world, the brake pressure is often measured internally within the ABS pump both for the input pressure applied by the master cylinder and the output pressure. |
| 02:31 | In modern cars, each corner of the car has a separate output on the pump to allow it to modulate each corner individually, this means having a pressure sensor on each of these outputs as well. |
| 02:44 | In the motorsport world, it's normal to have at least one sensor in the front and rear circuits. |
| 02:50 | Often this means plumbing each sensor into the circuit with a T piece. |
| 02:54 | Some aftermarket master cylinders also have a provision to attach the pressure sensor to the outlet directly which helps to simplify the plumbing and insulation. |
| 03:04 | Being able to measure the master cylinder outlet pressure on the front and rear circuits, not only allows us to know how hard the driver is pressing the brake pedal, it also allows us to calculate the hydraulic brake bias. |
| 03:18 | This is simply achieved by dividing the front brake pressure by the front and the rear brake pressures added together and multiplying the result by 100. |
| 03:28 | On the topic of understanding the brake inputs and modulation, this information can be used for various different aspects of driver development. |
| 03:37 | From the more simple examples of brake application and release timing into corners, to trail braking and easing off the brakes as the speed decreases in high downforce cars, or even assessing how well the driver maintains brake pressure during a heel and toe downshift. |
| 03:55 | On a side note, in our professional motorsport data analysis course, we spend a lot of time analysing and processing brake pressure data, both in terms of the raw logged data and making use of math channels to add more functionality. |
| 04:10 | This is a great course to check out if you're wanting to learn more about exploiting your brake pressure data. |
| 04:17 | If a car already has brake pressure sensors built into it, like when they're within the ABS pump, we can often access this data and make use of it without having to fit our own external pressure sensors. |
| 04:29 | This information is often available on the vehicle's CAN bus. |
| 04:33 | If you're interested in learning more about how to access this information from your car's CAN bus for yourself, I encourage you to also check out our dedicated CAN Bus Communications Decoded course. |
| 04:47 | In summary, the brake pressure is a critical aspect of brake operation and measuring it allows us to understand and help tune our brake system. |
| 04:56 | Brake pressure measurement can take various forms, either by tapping into existing sensors built into our system or by adding our own. |
