Brake System Design and Optimization: ABS Systems
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ABS Systems
07.27
| 00:00 | - Moving away from the core components of the braking system, let's now discuss ABS which stands for anti lock braking system. |
| 00:09 | The primary purpose of ABS is to modulate the amount of brake pressure applied to the callipers to prevent wheels locking during heavy braking. |
| 00:19 | The genesis of ABS was in trying to make up for poor braking technique during emergency situations in road cars, particularly in situations where reduced tyre grip is concerned like in the wet for example. |
| 00:32 | This is a useful safety feature in normal street cars that are intended to be driven by everyday people without a high level of car control skill which is most of us. |
| 00:43 | Thinking back to the longitudinal tyre forces module from earlier in the course we know that there is a peak slip ratio that needs to be achieved to get the maximum braking forces from the tyres. |
| 00:55 | It then goes without saying that a locked wheel which would correlate to 100% slip ratio isn't great for maximising our braking, letalone the damage it would cause to the tyres with flat spots. |
| 01:08 | The only surface where a slip ratio of 100% can give us maximum braking forces is on gravel but this also is partially down to the effect of the gravel in front of the tyre building up like a wave to help to slow the car. |
| 01:23 | The main components in an ABS are the pump, wheel speed sensors, brake pressure sensors, steering angle sensors, G sensors, gyros and the ABS control unit. |
| 01:35 | The ABS pump is plumbed inline with the main braking system with the master cylinder outlets being connected to the pump. |
| 01:44 | The pump is responsible for modulating the brake pressure to each corner of the car when the ABS is active. |
| 01:51 | When the system is inactive, the pump will allow brake fluid to run through it into the callipers without any interference. |
| 01:59 | However when the ABS activates, it'll modulate the brake pressure demanded by the driver to each wheel individually. |
| 02:06 | The ABS control unit makes decisions about which corners of the car must have their pressure modulated, based on the inputs from the other components in the system. |
| 02:16 | Without getting too deep into the control philosophies behind the ABS, the wheel speed sensors allow the control unit to know which corners of the car are experiencing high slip ratio or are completely locked by comparing their speeds. |
| 02:31 | The brake pressure sensors, steering angle sensors, G sensors and gyros help the control unit understand the situation by knowing the braking demand from the driver and which state the car is in. |
| 02:44 | The level of sophistication and control strategies of ABS have evolved a lot since the technology became commonly fitted to street cars and in most common cars, the ABS is also completely integrated with the stability control system. |
| 03:00 | This means that the ABS isn't only responsible for preventing locked wheels, but also tries to prevent the car from sliding and becoming out of control by braking specific wheels when it predicts the driver is losing control. |
| 03:14 | Depending on the level of sophistication and calibration of the ABS unit, ABS can be a positive or negative in street cars that are converted to use for motorsport. |
| 03:25 | In some cases, disabling or removing the ABS unit completely is the best course of action. |
| 03:31 | This is true in cases where there's too much ABS intervention. |
| 03:36 | In these cases, the ABS is calibrated in a way that it tends to make the system engage in circumstances where the tyres aren't close to their peak sip ratio when running on track. |
| 03:47 | This is particularly true on some older cars fitted with ABS when high grip motorsport tyres are used. |
| 03:54 | The unnecessary intervention in this case will be annoying at best and most likely slow our lap time considerably by preventing us from braking as aggressively as we need to. |
| 04:04 | There are other cars however where the ABS remains useful when driven aggressively on track. |
| 04:10 | A good example of this is our own Toyota 86 development cars. |
| 04:14 | The ABS in these cars allows the cars to be driven extremely hard on track and provides useful assistance to the driver without unnecessary intervention in most cases. |
| 04:26 | Whether or not a car will perform better with or without ABS is a case by case basis. |
| 04:32 | Both in terms of the car and the type of competition we're taking part in. |
| 04:37 | If you decide to disable or remove the ABS from your car, you should do so with caution, a good reason and in compliance with any rules or laws that apply to you. |
| 04:47 | Let's now look at dedicated motorsport ABS which have become quite widespread in the recent years. |
| 04:53 | These systems are most often used in factory built racecars, though aftermarket ABS units can be retrofitted to any car. |
| 05:02 | A well tuned motorsport ABS system is almost always an advantage, even for a professional driver. |
| 05:09 | Not only is the programming of the ABS behaviour on the systems able to be modified and tuned, but there's also generally some control given to the driver to tune the level of ABS intervention to suit their preferences and conditions. |
| 05:23 | The calibration of a motorsport ABS unit is very different to a factory ABS unit too. |
| 05:29 | Factory ABS focuses primarily on allowing the driver to maintain steering input so they can steer around an obstacle. |
| 05:37 | Smoothness of operation and noise are also considered so that an unskilled driver who's never experienced ABS operation before doesn't get startled when the ABS is operating. |
| 05:49 | Maximum retardation is not usually the number one priority. |
| 05:53 | On the other hand, motorsport ABS is calibrated with the sole aim of achieving maximum braking performance. |
| 06:01 | Driver comfort and noise during operation are considered irrelevant. |
| 06:05 | It's also assumed that a driver using a motorsport ABS unit will be able to maintain control of the car when it's on the limit of adhesion or there's a grip differential. |
| 06:14 | Consider a situation where there's a large difference in the available grip on one side of the car compared to the other. |
| 06:23 | Maybe the car has two wheels off the track in the grass for example. |
| 06:27 | Obviously the two wheels on the grass can't offer as much retardation as those on the track and if the ABS allows each wheel to generate the maximum possible retardation, this will cause the car to rotate which a skilled driver will be able to counter. |
| 06:42 | In road car ABS it's generally assumed that the average driver skill is low and hence under the same conditions, the braking performance may be somewhat compromised with that aim at maintaining control. |
| 06:56 | In summary, ABS is originally designed to help unskilled drivers control their road cars in emergency situations. |
| 07:04 | Making use of the factory ABS in a street car used for motorsport may or may not provide a benefit, it all depends on the exact car and type of competition. |
| 07:14 | A dedicated well tuned motorsport ABS will almost always provide a benefit in both performance and drivability in most racing applications. |
