Wheel excavator has the characteristics of fast walking speed and convenient transfer, and is suitable for farmland water conservancy and municipal construction. There are two kinds of brake system for wheel excavator, one is gas-liquid braking, which is mature in technology and low price. It is widely used in some low-speed wheel excavators. However, due to the existence of two kinds of media, the structure is complex, the braking is lagging behind and the reliability is poor. The other is full hydraulic braking. Through hydraulic oil and hydraulic control elements, the oil is directly sent to the caliper disc or wet brake, which produces braking torque to implement braking. It has the advantages of low maintenance cost and good reliability, and is applied in wheel excavator above medium gear.
Single way system and wet brake of rear axle are adopted. The whole brake system can be divided into two parts: service braking, parking / emergency braking. The components include hydraulic pump, filling brake valve, accumulator, foot brake valve and brake. The working principle is described as follows.
1. filling process: start the engine to transmit power to the hydraulic pump, and the pressure oil output by the hydraulic pump enters the charging valve. At this time, the main valve is closed, and the hydraulic oil enters the accumulator through the one-way valve, and the pressure of the accumulator gradually increases. When the storage pressure rises to the upper limit, the control valve opens, and the pilot oil of the main valve flows through the oil tank. The pressure difference occurs on both sides of the main valve core, forcing the main valve core to move to the left position to the right, and the hydraulic oil passes through the steering system. When the accumulator pressure drops to the lower limit, the control valve closes, and the pilot oil of the main valve is closed under the action of spring force. At this time, the accumulator is refilled.
2. service braking process: press the foot brake valve, and the high-pressure oil of the accumulator enters the service brake through the foot brake valve to implement the brake. The operating force between the foot brake valve and the pedal, that is, the travel of the foot pedal, controls the brake pressure in proportion. After stepping down the foot pedal, the vehicle decelerates through wheel braking, the greater the pedal travel, the greater the braking force. Release the pedal after braking, and the oil returns to the tank through the brake valve. The parking brake is installed on the transmission output shaft, which is normally closed. During driving, the solenoid valve is usually powered up, and the pressure oil enters the brake to open it. When the solenoid valve is off power during parking or emergency braking, the oil returns to the tank, and the parking brake is applied under the action of spring. When the vehicle needs to be towed out in case of a fault, the parking brake must be released, and the pressure in the accumulator is not enough to release the parking brake. At this time, the parking brake needs to be released by manual pump.
The two-way control is adopted, and the two brake circuits independently control the front and rear axle braking. When one circuit fails and the other can still be normally braking, the reliability of excavator service braking is ensured. The double circuit charging valve is filled with two accumulator. Series type double circuit foot brake valve controls the brake pressure of front and rear axle respectively. The solenoid valve controls the parking brake and uses the pilot oil circuit of the joystick.