Brake System Design and Optimization: Tuning Brake Temperature
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Tuning Brake Temperature
10.02
| 00:00 | - In the components section of this course, we covered cooling in some detail. |
| 00:04 | We've also discussed methods of measuring brake temperature and took a deep dive into choosing the best pad compounds for our application and how the temperature can have a significant impact on the friction force produced by the pad. |
| 00:19 | Putting all that together in this module we'll cover how to tune and control this temperature to maximise our braking performance as well as ensure our brakes continue to work safely and reliably. |
| 00:31 | As we're well aware by now, brakes convert kinetic energy into heat energy and this is mostly transferred into the brake disc so these are going to be the key focus of our cooling efforts, especially for tuning purposes. |
| 00:45 | Though with that said, many more parts should be considered which we'll discuss in a moment. |
| 00:50 | The common misconception with braking systems for motorsport applications is that more cooling is always better. |
| 00:57 | But we know that this is far from the truth as we need to make sure our pads are in their specific temperature range so over cooling can be just as bad for performance as overheating. |
| 01:08 | Clearly, this is not a set and forget process and conditions change constantly between different sessions on track, letalone different days. |
| 01:17 | The systems needs to be designed to allow for adequate cooling in the hottest conditions and then for other conditions we can tune and reduce the cooling from there to get the optimum temperature. |
| 01:29 | There's a lot more to brake temperature than the performance aspect of keeping the pads in their operating range. |
| 01:35 | Specifically around reliability, keeping all the components whether they're in the braking system or just close enough to be affected by it, within their safe temperature limits to avoid any damage. |
| 01:47 | To start with we need a way to understand the temperature of our braking system, this is vital to make informed decisions when changing the setup or tuning and making adjustments. |
| 01:57 | If we don't have access to brake temperature data, there are some telltale signs that the brakes are too hot or too cold. |
| 02:04 | This does require some experience and will never let us know the actual operating temperatures but it's still valuable information that's worth discussing. |
| 02:12 | If our brakes are too cold, this can just be as simple as not achieving the expected braking force. |
| 02:19 | This is often the case with the rear brakes on front wheel drive cars so naturally this will present itself in bias issues. |
| 02:27 | Since the rear brakes won't be producing enough force, we'd expect to see signs of an overly forward brake bias like early locking of the front brakes. |
| 02:36 | At the other end of the spectrum, brakes that are too hot can show up in a wider range of ways. |
| 02:42 | Probably the most common being brake fade which is where the temperature of the pad is above the ideal operating range. |
| 02:49 | Brake fade can be recognised by the pedal remaining firm but much more pedal effort is required to slow the car at the same rate. |
| 02:58 | Or an inability to slow the car irrespective of how much braking force is applied. |
| 03:03 | Another common issue is the brake fluid boiling. |
| 03:06 | As we've covered in the components section of this course, this causes small air bubbles to form inside the fluid which are compressible and results in compliance. |
| 03:16 | Therefore the pedal will feel soft and spongy and the hydraulic brake pressure transferred from the pedal to the calliper will be reduced. |
| 03:24 | If we're still experiencing fade and fluid boiling even with high quality motorsport pads and fluid then we need to look at improving our brake's thermal capacity, efficiency and cooling system. |
| 03:37 | These are both factors that you can recognise from brake feel when driving the car but there are some other signs of the brakes being too hot which can be identified from inspecting components after use. |
| 03:49 | Although brake pads are a wear item and we should expect to replace them relatively regularly, if the brake pads or the discs are wearing at an alarming rate, for example burning through a set of pads in just a few 30 minute track sessions, then there's a good chance the components are getting too hot. |
| 04:06 | Similarly if the calliper seals are leaking, despite being relatively new and within their maintenance life, then this can be a result of them getting too hot and loosing their elasticity. |
| 04:17 | Suspension ball joints can also wear out prematurely from too much radiant heat. |
| 04:22 | Although this can just be a result of not having shielding protecting the ball joints, it does show that there's been significant heat produced by the brakes. |
| 04:31 | The final sign would be the anodising on the disc hats and callipers discolouring. |
| 04:36 | If painted callipers are discolouring, this shouldn't be an issue as the paint usually can't withstand the temperatures seen on a regular track day. |
| 04:44 | Anodising on the other hand, can withstand much higher temperatures so if it's discolouring then the heat is likely too high. |
| 04:53 | The best method is of course using data including disc temperature paint and calliper strips. |
| 04:58 | This allows us to measure brake temperature and get accurate figures on where we're operating and the maximum values. |
| 05:05 | These methods were all discussed in detail in the brake measurement section of the course so check back if you need a refresher. |
| 05:12 | Given that we're able to determine the operating temperature of the brake system and understand if this is too hot or cold, let's look at methods of tuning and controlling the brake temperature. |
| 05:23 | Firstly, we can look at reducing temperatures by increasing your thermal mass of components in the system, meaning more heat energy can be absorbed and the increase in temperature of the components will be reduced. |
| 05:36 | This is most commonly done by using larger diameter or thicker discs and also thicker brake pads or pads with more surface area. |
| 05:46 | Cooling efficiency can also be gained by using brake discs with better designed vanes, curved rather than straight for example. |
| 05:54 | The distance between the inner and outer diameter of the disc which directly correlates to the pad size, is referred to as the annulus. |
| 06:03 | The width of this has a significant effect on the temperature of the disc, with a wider annulus allowing for more cooling effect from longer vanes and a larger pad with more thermal mass. |
| 06:16 | However, this can lead to increased temperature variation across the disc and pad taper in the radial direction due to the large difference in the angular velocity of the disc across the annulus. |
| 06:28 | Additionally the callipers must allow for appropriate sized pads to be used and better ventilated callipers and seals designed for high temperatures will also increase the heat capacity of the system. |
| 06:42 | These methods are those that can't be tuned but if the key issue is too high brake temperatures, and the aim is just to reduce this, these methods should be considered first before ducting. |
| 06:52 | This is because the extra complication ducting brings around packaging, installation and maintenance, along with the associated cost and weight penalty. |
| 07:02 | However if we want the best performance across a range of conditions, we're going to need to tune the temperatures of the braking system and this is where ducting comes in. |
| 07:12 | As we've already discussed, this involves heat transfer via convection as the fresh air flows through the vanes of the brake disc. |
| 07:21 | This is the area with the most cooling ability so it's the most effective method of tuning. |
| 07:26 | Of course this needs to be done correctly and that means ducting air from a high pressure source to the inlet of the disc vanes, ideally using a backing plate to cover the rest of the internal diameter of the disc but not the entire disc as that could trap and reflect heat making the situation worse. |
| 07:45 | We can only improve the cooling using ducting if it's allowing the vanes to pump more fresh ambient air. |
| 07:52 | If they're only being fed air that's already been heated by the brakes, they're not going to be particularly effective. |
| 07:58 | All this means that if the ducts aren't fed from a good high pressure source, it can actually hinder the process. |
| 08:05 | All of which can be difficult to know without testing. |
| 08:08 | Assuming we've got it right and can supply enough high pressure air to cool the brakes, in the most demanding conditions, we can then blank off sections of the ducting inlets to reduce the cooling effect under less demanding conditions and can keep our brakes in their optimum temperature range. |
| 08:26 | The final thing to mention here is that the heat transfer via conduction through attached equipment like the hub, upright and other suspension components. |
| 08:35 | This is by far the least amount of heat transfer in the braking system and there's not a lot that can be done to change it so it's not something we focus on but it's still worth understanding and keeping in mind if you're stuck and wondering where all the extra heat is coming from. |
| 08:52 | Before we wrap up, let's summarise the key points of this module. |
| 08:56 | There's a lot more to brake temperatures than keeping everything as cold as possible. |
| 09:01 | The aim is to keep the brakes in an ideal temperature range to achieve maximum performance and avoid damaging components. |
| 09:08 | While there are some clear signs of the temperatures being outside the idea ranges, that can be felt by the driver and from inspecting components, the most accurate way is using data from sensors, disc temperature paint and calliper strips which gives us a better understanding of the actual temperatures our brake system experiences and can make informed decisions in tuning the system and changing the components. |
| 09:33 | The key methods of doing this are changing the thermal mass of the components, their cooling and the braking efficiency. |
| 09:41 | And using ducting to cool the brake discs. |
| 09:44 | Brake ducting is our most powerful tuning tool but the system must be designed correctly to allow for effective cooling of the brakes for the most demanding conditions, then blanking of the ducting can be used to achieve the desired brake temperature in less demanding conditions. |
