Brake System Design and Optimization: Calipers
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Calipers
08.33
| 00:00 | - Now that we've talked about how we generate the required hydraulic brake pressure and distribute it around the car, we're ready to look at how we use it. |
| 00:08 | This is where the brake calipers come in. |
| 00:10 | Essentially converting the pressure back into a useful mechanical force. |
| 00:15 | The brake calipers are responsible for clamping the brake pads against the discs to give us the friction we're after. |
| 00:22 | Looking at a section view of a simple caliper, we can see that it looks a little bit like the reverse of a master cylinder. |
| 00:28 | There's a connection between the brake hose and the caliper that supplies the hydraulic pressure. |
| 00:35 | The pressure inside the body of the caliper acts on any piston in the caliper. |
| 00:39 | There are many different layouts of brake calipers but the fundamentals remain the same regardless of the details. |
| 00:46 | The amount of clamping force applied to the brake pads is a function of the fluid pressure and the total surface area of the pistons and the calliper. |
| 00:55 | Let's have a look at a couple of types now, starting with what you're likely to find in the most basic OE cars, the sliding caliper. |
| 01:03 | In this type, the piston or pistons will only sit on one side of the caliper, the caliper body can slide on its mount, meaning that we get an equal clamping force applied to both pads despite the pistons only being on one side. |
| 01:18 | The main issue we can run into with this style of caliper is it not sliding easily on its pins. |
| 01:26 | This will lead to uneven pad wear between the two brake pads, with the pad being acted on directly by the piston wearing faster. |
| 01:33 | The fix for this isn't major though, it really just comes down to properly maintaining the sliding pins. |
| 01:40 | The other style you'll find in higher performance OE cars and motorsport calipers is where the caliper is fixed rigidly to the upright body and there are opposing pistons on each side. |
| 01:51 | The number of pistons can vary widely, from as few as 2 to as many as 12 in extreme cases. |
| 01:59 | In the majority of motorsport application, 4 and 6 piston calipers are by far the most common. |
| 02:05 | This is where you'll have 2 or 3 pistons per side of the caliper respectively. |
| 02:10 | As we mentioned earlier though, it's the total surface area of the pistons in the caliper that determines the clamping force, not necessarily the number of pistons. |
| 02:19 | A greater piston area will require a greater clamping force for the same hydraulic line pressure but will also require more fluid to be displaced to move the pistons and engage the pads against the disc. |
| 02:32 | Of course the opposite is also true. |
| 02:35 | A smaller piston area means less clamping force but also requires less fluid volume. |
| 02:41 | This means we could achieve the same clamping force with one large piston on a sliding caliper or four smaller pistons on a fixed caliper, the effective surface area of the small pistons would equal the surface area of a single large piston. |
| 02:56 | Exactly the same principle applies as you increase the number of pistons further so if we can achieve the same clamping force with a single piston, why would we bother going to the trouble of making a caliper with many more smaller pistons which is clearly going to be more expensive. |
| 03:14 | One reason is to equalise the surface pressure distribution across the brake pad as much as possible. |
| 03:20 | In the case of a single piston where we apply the high pressures common in motorsport, the pad can actually flex significantly. |
| 03:28 | This results in poorer stopping performance, higher pad wear in the centre of the pad and more heat buildup. |
| 03:36 | Single piston sliding type calipers also suffer from poorer compliance compared to opposing multi piston calipers. |
| 03:43 | This is usually very obvious to see with the wheel off if we watch the caliper while someone else firmly applies the brakes. |
| 03:51 | If we instead add more smaller pistons we can distribute the load more evenly across the pad surface to make more use of the entire pad face. |
| 04:01 | This becomes even more important in motorsport brakes where the pads themselves need to be larger in order to allow them to last longer and give more consistent performance. |
| 04:11 | One detail you'll notice on high end multi piston brake calipers is that they use different piston sizes in different parts of the caliper. |
| 04:19 | This is known as having staggered pistons. |
| 04:22 | In this style of caliper, the smaller pistons are placed where the disc enters the caliper and the larger pistons where the disc exits. |
| 04:31 | This is done in order to reduce the pads wearing with a taper on them. |
| 04:37 | In some cases, where the same size piston is used throughout the caliper, the pads can wear with a taper, with the leading edge of the pad wearing away first. |
| 04:47 | This is something we want to avoid both to maximise pad life but also keep the pad sitting parallel with the disc face. |
| 04:55 | This means that staggered piston calipers are directional. |
| 04:59 | The calipers are sided, meaning the left and right calipers can't be swapped as the smaller pistons must always be at the leading edge where the disc first comes in contact with the pad. |
| 05:11 | You'll often see a small arrow on the caliper body to indicate the required rotation direction of the disc. |
| 05:18 | Again, even in the case of a staggered caliper, it's still the total area of the pistons we care about, meaning we must sum up all the different piston areas individually to get the total effective surface area. |
| 05:32 | Another aspect of higher performance calipers is size and weight. |
| 05:36 | A lighter caliper is always preferred when all other things are equal. |
| 05:41 | This reduces unsprung weight which in turn helps maximise tyre grip and improves suspension operation. |
| 05:49 | Both the materials and design factor into the total weight. |
| 05:52 | Aftermarket calipers are largely made from aluminium and may be either cast or billet parts. |
| 05:58 | An in general terms, caliper design falls into two categories, multi part or mono block. |
| 06:05 | Multi part calipers generally consist of multiple pieces bolted together. |
| 06:11 | This helps to reduce the cost and manufacturing complexity. |
| 06:15 | Monoblock calipers on the other hand are made from a single piece of material which makes them more expensive and challenging to manufacture. |
| 06:24 | An advantage of monoblock calipers is that they tend to have higher stiffness for a given weight. |
| 06:30 | This is simply down to having less bolted joints as part of the main structure. |
| 06:34 | As we touched on earlier in the course, the stiffness of the caliper changes the compliance, with excessive compliance meaning the driver will end up with a longer pedal. |
| 06:45 | Calipers designed for motorsport also use internal components that are capable of withstanding the same conditions. |
| 06:53 | The seals for example are usually thicker and made from material with better heat resistant characteristics. |
| 07:00 | This increases their own thermal capacity and their ability to withstand heat without being damaged and causing leaks. |
| 07:07 | But can also help prevent heat being transferred into the brake fluid. |
| 07:11 | The caliper pistons are usually stainless steel in high end products. |
| 07:15 | However it is possible to get titanium pistons, though as you probably guessed, that drags up the price considerably. |
| 07:23 | The main advantage of titanium is increasing the insulation of the fluid in the caliper from the conductive heat of the pads and secondarily, there is also a small weight saving to be had. |
| 07:35 | Wheel clearance is another factor to consider because larger, wider calipers can have trouble clearing the inner surfaces of wheel spokes. |
| 07:43 | This means your disc and therefore caliper position and width needs to be considered in conjunction with your wheel choice. |
| 07:51 | Calipers are mounted with either lateral or radial style attachments which we can see both examples of here. |
| 07:58 | This means if we're fitting radial mount calipers to an upright that originally had lateral mounting, we'll need to make an adaptor bracket that rotates the mounting bolts by 90°. |
| 08:10 | To summarise this section, brake calipers are responsible for converting the hydraulic pressure in the system into the mechanical force we need to clamp the pads against the brake disc. |
| 08:21 | There's a huge variety of styles of brake calipers available, both in terms of the number and layout of the pistons as well as the construction and mounting options. |
