The Secrets of Braking: An Introduction and Analysis of Automotive Braking Systems

　　Years ago, automobiles were solely focused on driving performance. Today, however, the focus has shifted to convenience, comfort, and simplified driving, leading to a rapid increase in electronic devices. This is also true for braking systems, which demand high reliability. Electronic braking systems are emerging in hybrid and electric vehicles, and electronic parking brakes offer additional driver-friendly features. However, traditional braking systems will not disappear. Let's explore these systems and discuss usage precautions.

　　What are the components of a vehicle braking system?

　　A machine that cannot stop is not a good machine. The vehicle braking system ensures that a vehicle can decelerate or stop at any time according to the driver's wishes. Braking is achieved by the caliper piston pushing the friction pads against the brake disc, using friction to slow the vehicle. While this process seems simple, the entire system requires an actuating device (brake pedal), a power supply (brake master cylinder), an actuator (brake caliper), and a transmission device (hydraulic lines).

　　Disc brakes and drum brakes are likely familiar to everyone, and I don't want to dwell on them. Most current vehicles use disc brakes; only some commercial vehicles (minivans) or small cars use drum brakes on the rear. Disc brakes are widely used due to their heat dissipation, drainage, and ease of maintenance and repair. Even the electronically controlled braking systems in electric and hybrid vehicles are developed based on disc brakes.

　　Can't stop the car manually?

　　Try pressing the brake pedal with the engine off. The first two times will be similar to normal driving; by the third time, you'll likely find it difficult to press further. This is because the vehicle's braking system uses engine vacuum to assist the driver in braking. The vacuum remaining from the last engine start is only enough for 2-3 operations.

　　Behind the pedal is the vacuum booster. Most vehicles obtain vacuum from the engine intake manifold to achieve assistance; some vehicles use a separate vacuum pump. Regardless of the structure, vacuum cannot be provided after the engine is turned off. Therefore, if the engine unexpectedly stops while driving, the correct method is to keep the brake pedal pressed, not to repeatedly operate it.

　　The issue of brake failure reminds us of the accelerator pedal incident involving a certain brand a few years ago. The reason for the inability to provide braking force was that when the accelerator pedal was pressed deeply, the large amount of air intake by the engine disrupted the vacuum environment, making it impossible to provide assistance after operating the brakes 2-3 times under driver stress.

　　What is brake priority?

　　The solution is to ensure that the accelerator pedal is not stuck. While this is the principle, who can guarantee it? Driver error is unavoidable. Therefore, a special logic is needed to compensate for unexpected events. Manufacturers have designed a brake priority logic. Even if the throttle is open and the brake pedal is pressed, the system will automatically determine the driver's intention and close the throttle. This only applies to electronic throttles. For cable-controlled throttles, the system will reduce fuel injection and lower the ignition frequency.

　　Do electric/hybrid vehicles also use this system?

　　As a forefront of technological advancement, electric vehicles differ significantly from traditional automobiles. The most obvious difference is that electric vehicles do not have an engine. So, what if a vacuum-assisted braking system is used? Let's investigate.

　　First, it should be stated that electric vehicles are not incapable of using hydraulic systems; they simply cannot obtain vacuum from the engine intake manifold for assistance like traditional powertrains. An electric vacuum pump solves this problem. It's worth noting that electric vacuum pumps can be used in electric vehicles, hybrid vehicles, and traditional powertrain vehicles.

　　Some electric vehicles also use electronically controlled braking systems. This system does not involve hydraulics. The brake pedal only transmits the driver's intention as a signal to the ESP control unit, which causes the caliper to actuate. The caliper structure is also completely different from traditional calipers. The caliper integrates an electronic control system, a motor, a gear mechanism, a piston, and a parking brake. When the driver presses the pedal, the ESP electronic control unit transmits the received signal to the caliper's electronic control system. This system initially uses a motor to drive the gear mechanism to extend the piston for braking. This system does not require hydraulic transmission, resulting in faster response speed. However, because the braking force is slightly smaller than that of a traditional hydraulic system, it is often used for rear-wheel braking.

　　Is the brake energy recovery system related to the braking system?

　　I've heard 4S shop staff tell me about a certain car equipped with a brake energy recovery system. This is indeed an energy-saving technology, but it doesn't involve modifications to the braking system itself; rather, it involves adjustments to the engine and motor.

　　For traditional powertrain vehicles, vehicles with brake energy recovery systems add a clutch between the generator and the engine. During normal driving, the two are not connected, reducing the engine load. When coasting or braking, the clutch engages, and the generator charges the battery. For hybrid and electric vehicles, during braking, the motor directly converts into a generator to charge the power battery, increasing the driving range.

　　Traditional Mechanical Parking Brake

　　The traditional mechanical parking brake is a cable structure. The driver operates the parking brake handle located in the center console. The handle drives the cable to lock the caliper or brake shoe on the brake disc or drum. Inside the parking brake handle is a ratchet; when the handle is pulled, the pawl engages the ratchet, keeping the handle fixed in place.

　　Electronic Parking Brake

　　Whether it's technology making people lazy or laziness driving invention, technology always reduces human labor. The most obvious example is the advent of automatic transmissions. Similarly, next to the gear lever near the center console, the parking brake lever will no longer exist, replaced by a button.

　　A typical parking system uses a lever to pull the rear brake cables. Some electronic parking brakes use a motor to control the movement of the cables; the motor is controlled by this button. This structure basically does not change the original structure and does not matter whether the parking system is disc or drum type. It is a simple way to achieve electronic control. Another structure integrates the motor with the rear-wheel active system. The motor uses a reduction mechanism to control the brake piston to press the friction pad for braking. Some supercars also add a separate caliper specifically for parking brake.

　　So what are the advantages of an electronic parking brake? First, it doesn't require you to engage the parking brake every time you start. When the system receives a torque signal of a certain magnitude, the system automatically releases the parking brake, and the driver only needs to step on the accelerator. This completely solves the problem of my colleague who, while driving from home to work, was still wondering where the smell of burnt food came from.

　　Secondly, in an emergency (when the driver pulls up the handbrake), if it is a mechanical handbrake, it can only brake the rear wheels. The braking force depends entirely on the force applied, which can cause tail-spinning, very dangerous; if it is an electronic handbrake system, the ESP system will react and brake all four wheels with slightly less than full force, ensuring driving stability, but also making drifting impossible with an electronic handbrake system.