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Feedback Properties of Vehicle Controls
Published in Guy H. Walker, Neville A. Stanton, Paul M. Salmon, Vehicle Feedback and Driver Situation Awareness, 2018
Guy H. Walker, Neville A. Stanton, Paul M. Salmon
The other instance of the direct zero-order relationship faltering is due to a phenomenon termed brake fade. If the heat generated by the brakes reaches a certain level, and cannot be dissipated quickly enough, then brake pedal effort increases whilst braking performance decreases (the brakes feel ‘wooden’). Brake fade occurs due to the braking components not being able to dissipate the heat generated by the vehicles kinetic energy, and this in turn can cause the hydraulic fluid which supplies the braking force to the callipers to boil and/or the friction materials to catch fire. With the brakes in this condition the direct linear relationship between braking force and brake pedal position fails. Brake fade becomes counterintuitive to the driver who invariably will press the brake pedal even harder. In a situation not dissimilar to sudden unintended acceleration the feedback loop reverses. In this condition the brake needs to cool down, and continuing with a brake application will achieve the reverse of what the driver is demanding. Thus the situation becomes that of unstable ‘positive feedback’, or continuing with the very activity that only serves to make the error worse.
Chassis systems
Published in Tom Denton, Advanced Automotive Fault Diagnosis, 2020
Disc brakes provide for good braking and are less prone to brake fade than drum brakes. This is because they are more exposed and can get rid of heat more easily. Brake fade occurs when the brakes become so hot that they cannot transfer energy any more and stop working. This type of problem can happen, for example, after keeping the car brakes on for a long time when travelling down a long steep hill. This is why a lower gear should be used to employ the engine as a brake. It is clearly important to use good-quality pads and linings because inferior materials can fail if overheated.
Chassis systems
Published in Tom Denton, Automobile Mechanical and Electrical Systems, 2018
Disc brakes are less prone to brake fade than drum brakes (Fig. 4.92). This is because they are more exposed and can get rid of heat more easily. They also throw off water better than drum brakes. Brake fade occurs when the brakes become so hot they cannot transfer any more energy, and they stop working. Disc brakes are self-adjusting. When the pedal is depressed, the rubber seal is preloaded. When the pedal is released, the piston is pulled back owing to the elasticity of the rubber sealing ring.
CFD-aided approach of modelling and dynamic characteristic optimization for a highly nonlinear auxiliary braking system
Published in Engineering Applications of Computational Fluid Mechanics, 2022
Konghua Yang, Xichun Guan, Xiaoli Zhang, Chunbao Liu
Heavy-duty vehicles are an important transport means and are widely used to deliver people and goods over long distances, such as in public transportation (Bravo et al., 2018; Broniszewski & Piechna, 2019; Kumar & Rajagopal, 2020). In China, 31% of the length of highways passes through and over mountains, hills, and plateaus, and therefore, have long downhill sections (Qian et al., 2020). Most of the commercial trucks are heavy-duty vehicles and need high braking power while slowing over a long distance. Traditional frictional braking transforms the kinetic energy into heat energy, which can cause brake fade; this not only is a safety risk but also prevents energy recovery and reuse (Xu & Cai, 2020; Ye et al., 2019; Yevtushenko et al., 2015). The braking system of a heavy-duty vehicle requires a high braking torque and quick response time, and it must be able to handle the frequent starts and stops as the vehicle travels at full speed and along downhill sections. It is difficult for traditionally available braking systems to simultaneously fulfil all of these requirements.
Dynamics performance of long combination vehicles with active control systems
Published in Vehicle System Dynamics, 2023
Wei Huang, Mehdi Ahmadian, Amir Rahimi, Luke Steiginga
The maximum grade that a fully loaded LCV can descend with constant speed while moving on a down-hill route with a certain speed and friction level is known as the downgrade holding capability performance measure. Unlike the stopping distance characteristic that is commonly assessed by the brake system capability, down-grade holding capability is mostly achieved by the engine braking system and compact retarders as well as the transmission system control strategies [31]. The reason for this is that on severe down-grades the energy absorbed by the brake pads to impede the wheels’ motion is converted to heat, leading to remarkable brake fade and possible loss of vehicle control.