# Design Optimization of Underground Mining Vehicles Based on Regenerative Braking Energy Recovery
## 2 Design of Regenerative Braking System for Underground Mining Vehicles
### Selection of a Regenerative Braking System  
Currently, regenerative braking systems are classified into two types based on the decoupling of the brake pedal force and hydraulic braking force: additive regenerative braking system (RBS) and cooperative regenerative braking system (CRBS). To determine the most efficient and concise system for energy recovery, a comparison between these two regenerative braking systems is conducted [16].  
In the additive regenerative braking system (RBS), the brake pedal force and the hydraulic pressure in the brake wheel cylinder are not decoupled. As shown in Figure 2, when the brake pedal is pressed during the braking process, the brake wheel cylinder generates hydraulic braking force, with the motor braking being simply added to supplement this force. Consequently, there is still some energy loss, resulting in a lower energy recovery rate [17; 18; 19].  
Figure 1: Mining locomotive and mining vehicles.  
Figure 2: Non-decoupling of brake pedal force and hydraulic brake force.  
In the cooperative regenerative braking system (CRBS), the brake pedal force and the hydraulic pressure in the brake wheel cylinder are decoupled. As illustrated in Figure 3, when the brake pedal is depressed, the controller gathers information on the current brake pedal position and the rate at which it is changing to identify the driver's braking demand. It then calculates the necessary braking force. In this system, the motor braking force serves as the primary source of braking, while the hydraulic braking force acts as a supplementary component. Both forces are dynamically coordinated and controlled to maximize the proportion of motor braking and optimize energy recovery.  
The main distinction between the two systems is whether the brake pedal is decoupled from the brake actuator. In the braking scenario of an electric vehicle, the braking torque is derived from two sources: hydraulic braking generated by the brake wheel cylinder, and regenerative braking provided by the motor through the drive shaft [20; 21]. In Figure 4, when the brake pedal and brake actuator are not decoupled, regenerative braking is applied in addition to hydraulic braking during light braking. However, due to limitations, regenerative braking results in some energy loss and incomplete energy recovery. Conversely, when the brake pedal and brake actuator are decoupled, regenerative braking is initially employed during the braking process. If the required braking force exceeds the regenerative braking force (F1) of the motor, hydraulic braking is then utilized as auxiliary braking. This enables regenerative braking to be present throughout the entire braking process, maximizing the recovery of braking energy.  
Based on the comparison presented in Table 1, the decision is made to install the cooperative regenerative braking system on underground mining vehicles. This choice is driven by the goal of fully recovering wasted energy during the braking process, maximizing the endurance of these vehicles, and improving the efficiency of underground operations. By implementing the cooperative regenerative braking system, the desired objectives can be achieved.  
Figure 4: _Cont._  
Figure 3: Decoupling of brake pedal force and hydraulic brake force.