The use of hydraulic wet-braking valve systems in loaders

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The use of hydraulic wet braking valve systems in loaders: Loaders operate under relatively harsh conditions, as they move forward and backward frequently and change gears during operation. As a result, their braking systems suffer significant wear and generate a large amount of heat. Since gas-boosted oil braking systems produce a lot of heat, an additional water cooling system is required in high-altitude areas. In contrast, the fully hydraulic wet braking system has friction pads immersed in gear oil, which provides better heat dissipation, greater resistance to contamination, a longer service life, and more reliable braking. It is widely used internationally and is gradually replacing gas-boosted oil braking systems. Senior consultant Engineer Li believes that modern fully hydraulic wet braking systems are generally composed of the following components: Power pump: Most braking systems have a separate pump to meet the braking requirements of the entire system; its displacement is usually small, and it is mostly a gear pump. Filling valve: It provides a stable pressure for the braking system, controls the filling pressure and flow rate, directs any excess hydraulic oil to other systems, thereby ensuring the reliability of the braking system. Service brake valve: The main control component of the system; it is a pressure-reducing valve that allows the high-pressure oil in the system to enter the wheel brakes after pressure reduction. To facilitate operation, the rotation angle of the brake valve is approximately proportional to the output pressure. Double-circuit brake valves are used in loaders. Park brake valve: It can be an electronically controlled or manually operated valve that supplies pressure oil to release the park brake. Accumulator: An energy storage device that allows the entire system to continue braking for a short period of time after the engine is turned off, and reduces the time required to fill the system with fluid. Different companies make various improvements to their respective complete systems to make them more efficient, but the basic principles remain the same. Here is a brief introduction: Engineer Li believes that in addition to the conventional wet braking system, Caterpillar has introduced a composite braking system in its models equipped with electric motors and fully automatic transmissions. This system integrates the control logic for downshifting and braking into the left brake pedal, so that the rotation angle of the foot brake valve and the braking pressure generated are linked to the main controller of the vehicle, as shown in the diagram. When the pedal is in position A, the vehicle only uses normal service braking; when it is in position B, the main controller issues a command to reduce engine output. In position C, the transmission automatically shifts to neutral, cutting off power delivery and thereby reducing the oil temperature in the axles, which extends the lifespan of the brakes and lowers operating costs. Another approach is to install an electronically controlled power cut-off valve switch on the foot brake valve; during operation, the operator turns on this switch, and while applying the brake, the cut-off valve interrupts the power output to the gearbox, thereby reducing the braking torque and minimizing power loss in the system. During normal driving, the switch is turned off, but power output is not cut off when braking. However, when working on site, the operator may forget to turn the switch on, rendering it ineffective. A new braking system: This is a fully hydraulic wet braking system. It features only one foot brake valve, but it can handle three functions – service braking, emergency braking, and parking braking. The basic working principle is as follows: The pressurized oil output by the hydraulic pump flows through ports A and B of the filling valves to fill the two accumulators, while port N supplies the oil to other systems in the vehicle. The foot brake valve has a limit device between A and B, and a contact switch at point B. When the service brake is applied, the brake valve pedal is pressed, and the high-pressure oil in the accumulator flows into the wet brakes of the front and rear axles to achieve braking; the angle of the brake valve, the pressure output, and the operating force all lie within the 0–a range ； When an emergency brake is required, the operator applies more force by stepping on the pedal, causing it to flip; this compresses the limit spring and overcomes the controlling force at point A. The brake valve then moves to point B, where the contact switch closes and sends a signal E to the overall controller, resulting in the pressure in the transmission system being reduced to zero and power output being interrupted. When the foot from the brake valve is removed, the contact switch opens, and the pressure in the transmission system returns to normal, thereby enhancing the braking effect. And when the parking brake is engaged, power output is also cut off. When the vehicle is moving or operating on a slope, since there are step changes in the control force that are fed back to the operator, it is advisable to avoid disengaging the power brake so as to prevent unstable phenomena such as the vehicle sliding down the slope when starting.