Regenerative Braking: Beyond Electric Cars and Hybrid Vehicles

Regenerative braking is a technology that has been utilized in various forms for decades, not just in electric and hybrid cars. This article explores how regenerative braking works, not only in electric vehicles but also in heavy vehicles and even in electric rail systems. We will also introduce alternative methods such as electric and hydraulic retarders.

Introduction to Regenerative Braking

The concept of regenerative braking is not new; it dates back half a century when it was first used on heavy vehicles. Initially, this technology involved attaching a device to the tail shaft, where the current generated was fed into a bank of onboard resistors. While this method did help reduce speed, it was predominantly used in mountainous regions of Europe due to the terrain's unique challenges. Over time, advancements in technology have led to more efficient and versatile forms of regenerative braking.

Regenerative Braking in Electric railways

Although regenerative braking is now more commonly associated with electric and hybrid cars, it also plays a significant role in electric railways. Streetcars and trams descending hills can generate and return energy to the overhead wire system. However, the energy is distributed among the entire network. As a tram descends, it generates extra energy that is fed back into the wire system. This energy helps power trams that are ascending the same hill. While the majority of the energy used by the streetcars on the line is produced by the main power plant, the regenerative braking system significantly reduces the overall energy consumption during these climbs and descents.

Electric Retarders: A Modern Twist on Regenerative Braking

Electric retarders are a more recent adaptation of regenerative braking technology. These units use electromagnetic induction to provide a retardation force. An electric retardation unit can be placed on an axle, transmission, or driveline, consisting of a rotor attached to the axle, transmission, or driveshaft, and a stator securely attached to the chassis. This system operates without any contact surfaces between the rotor and stator, nor any working fluid. When retardation is required, electrical windings in the stator receive power from the vehicle battery, producing a magnetic field through which the rotor moves. The induced eddy currents in the rotor create an opposing magnetic field, thereby slowing the rotor and the connected components to which it is attached. An inherent advantage of electric retarders is that the rotor incorporates internal vanes for air cooling, thus not placing a load on the vehicle’s engine cooling system. Moreover, the operation of these systems is extremely quiet.

Hydraulic Retarders: An Alternative Solution

Hydraulic retarders provide another method to decelerate a vehicle using the viscous drag forces between dynamic and static vanes in a fluid-filled chamber. There are several types of hydraulic retarders, including those that use standard transmission fluid, gear oil, separate oil supplies, water, or a mixture of oil and magnetic retardation. A simple retarder consists of vanes attached to the transmission driveshaft, positioned between the clutch and roadwheels. These vanes are enclosed in a static chamber with small clearances to the chamber walls, which are also vaned like an automatic transmission.

Conclusion

While regenerative braking is primarily associated with electric and hybrid vehicles, its applications extend much further. In addition to electric railways, technologies like electric and hydraulic retarders offer efficient solutions for deceleration in heavy vehicles and other applications. These systems not only contribute to energy conservation but also provide a quieter and more reliable method of slowing down the vehicle.