Brake System Design and Optimization: Brake Boosters
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Brake Boosters
03.35
| 00:00 | - Brake boosters, also known as brake servos are fitted to almost all OE road cars but are actually uncommon in motorsport applications. |
| 00:09 | They're used to decrease the amount of pedal force required by the driver to slow the car by using pneumatics to add force to the brake pedal once it's depressed by the driver. |
| 00:22 | This is done because manufacturers of road cars understand that in normal day to day driving, consumers don't want to have to exert a lot of force on the brake pedal to slow the car down. |
| 00:33 | The brake booster normally sits between the pedal box and the brake master cylinder. |
| 00:39 | The main body of the booster is a chamber with an internal piston that's sealed to the booster body. |
| 00:46 | On the back of the booster, the pedal box has a rod that connects to a valve. |
| 00:51 | When the driver presses the brake pedal, this moves the valve off its seat. |
| 00:55 | On the front of the booster, there'll be a connection to a pneumatic vacuum source, normally this is connected to the inlet manifold of the engine via a one way valve. |
| 01:06 | The brake master cylinder is also mounted to the front of the booster. |
| 01:11 | When the driver depresses the brake pedal, the valve on the rear is lifted off its seat. |
| 01:16 | This allows ambient air pressure into the rear chamber. |
| 01:20 | Because there's a vacuum on the front of the booster chamber and ambient air pressure on the rear, the piston is subject to a force that acts on the brake master cylinder via an actuating rod. |
| 01:32 | This force adds to the brake pedal force input by the driver, thereby decreasing the required pedal force to slow the car. |
| 01:40 | In road car applications, this is a good thing, however in motorsport applications, some of the downsides of a brake booster mean they're not generally used. |
| 01:50 | The first issue is that boosters tend to make it more difficult to finely modulate brake pressure, particularly on release during the trail braking phase where the driver needs a lot of fine control of the pedal. |
| 02:04 | Another issue is inconsistency in the amount of force assistance. |
| 02:08 | Boosters usually aren't able to provide a consistent force addition throughout every braking event which means the amount of hydraulic brake pressure in the system for a given amount of brake pedal force will vary. |
| 02:20 | Making it impossible to brake consistently. |
| 02:24 | The most common solution to removing brake boosters is to make or buy a brake booster delete. |
| 02:30 | This generally involves removing the master cylinder and brake booster with the booster being replaced with a solid section to keep the master cylinder in a similar location. |
| 02:42 | The downside of removing the brake booster is the driver will need to apply more pedal force for a given hydraulic pressure in the brake system. |
| 02:51 | However the gains in control and consistency will generally far outweigh the downsides. |
| 02:57 | In some cases, the brake pedal ratio or master cylinder size may need to be changed as part of removing the brake booster. |
| 03:05 | This can go some way to reducing the increase in pedal force required due to the loss of the booster. |
| 03:12 | So in summary, brake boosters are used in the OE world to reduce the required pedal effort for the driver during braking. |
| 03:20 | They are not commonly used in motorsport applications as they tend to make it more difficult for the driver to be accurate with their brake inputs which is a critical part of maximising the performance of the car. |
