１．Abstract

In recent years, electrification has proceeded in the truck industry to achieve carbon neutrality. It is necessary to be addressed that the deteriorating of the working conditions due to increased logistics volume and labor shortage. The electric parking brakes with functions to alleviate the burden on drivers, such as full-range Adaptive Cruise Control and Hill Hold Assistance, have been highly demanded.

The recipients have developed the world’s first motor gear units (MGU) which realize both high clamp load and excellent durability as the electric parking brakes (EPB) for twin-piston disc brakes. The products have been supplied to the new EV trucks since 2023.

２．Contents of Technology

The conventional EPBs were based on calipers with a single piston and were practical for vehicles up to 3.5 tons of GVW. The developed MGUs of EPBs are mounted on twin-piston disc brakes and are applicable for tracks of more than 8.5 tons of GVW by generating high clamp load.

Fig. 1 Twin Piston EPB

The distinctive features are: the structure in which 2 pistons are driven by 1 motor contributes to weight reduction and miniaturization. The differential mechanism with LSD distributes the motor torque and generates clamp load at both pistons. The built-in electromagnetic brake maintains the parking brake force once it reaches the specified value (Fig. 2).

Fig. 2 Motor Gear Unit

The differential mechanism (Fig. 3) consists of a compact planetary gear system. Once the clamp load difference between the 2 pistons is generated due to the uneven wear of the brake pads, one of the pistons stops moving forward (shown in the red line in Fig. 4). After another side generates an equal load, both start moving forward again to generate equal force. Because of the LSD mechanism with a compression spring, it enables the secure release of the clamp load.

Fig. 3 Differential Mechanism

Fig. 4 Piston Stroke Diagram (uneven wear)

Because the increased clamp load is required for the EPBs on the trucks, a highly efficient ball-screw mechanism is used in the brake caliper. As a result, the back-driving torque is loaded on the MGU when the clamp load is generated. An electromagnetic brake (Fig. 5) with multiple rotors is installed in the MGU so that the back-driving torque can be maintained. It holds the torque by a compression spring and enables the motor to rotate only when the MGU is energized to generate the clamp load as the negative brake structure is adopted.

Fig. 5 Electromagnetic Brake Mechanism

３．Conclusion

This development has enabled the MGU to be in commercial production. It is the first EPB based on twin-piston disc brakes for small and midsize trucks. This technology is expanding to various domestic and international vehicle models. By promoting its adoption across the automotive industry committed to sustainability, it aims to make a significant contribution to establishing a safe and eco-conscious society.

Shinjiro Masuko(Akebono Brake Industry Co., Ltd.)
Michio Suzuki(Akebono Brake Industry Co., Ltd.)
Yuta Yamaguchi(Akebono Brake Industry Co., Ltd.)
Hiroyasu Ishikawa(Akebono Brake Industry Co., Ltd.)
Hiroyuki Kato(Akebono Brake Industry Co., Ltd.)