Brake System Design and Optimization: Pedals and Pedal Boxes
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Pedals and Pedal Boxes
05.24
| 00:00 | - In this section of the course, we'll be going through each of the major components that make up a motorsport braking system. |
| 00:06 | We'll look at each part roughly in the order they're placed in the system and outline what it is, why we use it, how it works and any relevant details and variations available. |
| 00:17 | The first part of the braking system the driver comes in contact with is the brake pedal. |
| 00:23 | This is the part that transfers the mechanical force from the driver's foot into the brake master cylinder. |
| 00:30 | The brake pedal is generally arranged with the other pedals in an assembly that forms a pedal box. |
| 00:35 | This means all of or some of the pedals share some parts of the total bracket for packaging and stiffness reasons. |
| 00:42 | The brake pedal has by far the most amount of force applied to it compared to the throttle and clutch pedals. |
| 00:50 | As a result, it's usually the bulkiest part of the system. |
| 00:53 | The main purpose of the brake pedal is to multiply the force that the driver can produce with the braking foot by changing the leverage ratio. |
| 01:01 | Without this, the driver would have to push directly on the back of the master cylinder piston and would not be able to produce enough force to build a sufficient amount of hydraulic pressure to operate the brakes. |
| 01:14 | By using leverage, we can multiply the force applied to the master cylinder at the expense of reducing the travel transferred to the master cylinder. |
| 01:22 | Although, in a well designed and maintained system, this isn't a problem. |
| 01:27 | If you're choosing an aftermarket pedal box, this leverage ratio is the important thing to understand as the ratio can vary considerably between brands and types of pedal boxes. |
| 01:39 | In many models, the user often has the ability to adjust the leverage ratio which is usually in the range of 4:1 to 6:1. |
| 01:48 | This leverage or pedal ratio is found by dividing the distance from the centre of the brake pedal pad to the pivot point by the distance from the master cylinder push rod to the pivot point. |
| 02:00 | For a 5:1 pedal ratio, this means the master cylinder will see a force 5 times higher than what the driver applies with their foot and at 1/5th of the travel. |
| 02:11 | The pedal ratio will be discussed in more detail later in the course when we go through the brake system design. |
| 02:17 | In OE applications, the pedal box is most often set up to operate a tandem style brake master cylinder. |
| 02:24 | We'll discuss master cylinders in more detail later but for now, all you need to know is that the brake pedal only has a single force output. |
| 02:32 | In motorsport applications, it's normal to run a double master cylinder setup where the cylinders are split between the front and rear brake circuits. |
| 02:42 | This style of pedal box has dual force outputs, one for each master cylinder and as a result, the structure and layout of an aftermarket pedal box differs significantly from an OE style box. |
| 02:54 | Pedal boxes can be arranged in a number of ways, with one important distinction being whether the pedals pivot at the top or the bottom. |
| 03:02 | In OE applications, the pedals almost always pivot at the top whereas in aftermarket, both styles are available. |
| 03:11 | The choice largely comes down to what package is best for your application and mounting position. |
| 03:17 | The pedal box is subject to high forces so finding or making a place for it to mount with sufficient stiffness is important. |
| 03:24 | Top pivoting pedal boxes mount the master cylinders up high, usually on the firewall which requires the firewall to have sufficient stiffness. |
| 03:33 | Bottom pivoting pedal boxes will have the master cylinders down low close to the floor. |
| 03:39 | This often requires extra structure to be added to the floor pan in order to be able to support the braking loads without excessive compliance. |
| 03:48 | The other main difference in available styles is the orientation of the master cylinders. |
| 03:53 | This can apply to both top and bottom pivoting pedals. |
| 03:57 | The is simply whether the master cylinders sit in front of or behind the brake pedal. |
| 04:02 | There is no significant difference in the way these operate, it's just more a question of packaging. |
| 04:08 | In cars with small cabins or footwells and certainly where tall drivers need to be accommodated, reverse mounted master cylinders can be a good option as it allows the pedal box to sit further forward without the master cylinders coming in contact with the floor or chassis. |
| 04:25 | Some aftermarket high end pedal boxes have the ability to have their position adjusted. |
| 04:30 | This usually means they're mounted on sliding rails. |
| 04:33 | The purpose of this is to accommodate for different sized drivers and is particularly common in endurance racing where the driver changes need to happen multiple times during the race. |
| 04:45 | This can be necessary to allow the seat to be rigidly mounted to the chassis for safety. |
| 04:49 | The downside is that adding a sliding mechanism to the pedal box results in a much higher cost overall which may rule them out as an option for some people. |
| 05:00 | In summary, a pedal box is a mechanism that mounts the brake pedal and allows the force multiplication to happen between the driver's foot and what the master cylinders are subject to. |
| 05:12 | Pedal boxes are available in a range of different configurations, the choice of which depends on the application and space available in the car. |
