At present, the hydraulic transmission cooling system used in forklift mostly builds the hydraulic transmission oil radiator in the water chamber of the engine pipe belt radiator. This heat dissipation method has the following three problems: first, at the initial stage of start-up, the hydraulic transmission oil temperature is low, the oil viscosity is large, and the transmission efficiency is low; Second, the temperature of hydraulic transmission oil is too high under bad working conditions; Third, the hydraulic transmission oil and coolant are easy to cross cavity with each other. In view of the above problems, it is decided to improve the hydraulic transmission cooling system of forklift. The improved hydraulic transmission cooling system includes hydraulic torque converter 1, thermostat 2 and external plate fin radiator 3, as shown in Figure 1. The specific improvement scheme is as follows:
1. Install thermostat
In order to solve the problem of low hydraulic transmission oil temperature at the initial stage of forklift start-up, a thermostat is added in the cooling oil circulation path of hydraulic transmission cooling system. According to the hydraulic transmission oil temperature, the thermostat can automatically change the circulation range of hydraulic transmission oil (large circulation or small circulation), adjust the heat dissipation capacity of the cooling system, and ensure that the hydraulic transmission gearbox works within the appropriate oil temperature range.
When the forklift truck starts working, the hydraulic transmission oil temperature is lower than 70 ℃, and the hydraulic transmission oil has a small circulation. Under the action of the torque converter oil pump, the transmission oil enters the thermostat through the oil outlet of the hydraulic torque converter, the oil outlet C of the thermostat is closed, and the oil returns to the torque converter directly without passing through the oil radiator to form a small circulation, so that the hydraulic transmission oil can quickly rise to the appropriate working temperature.
When the hydraulic transmission oil temperature rises to 70 ~ 80 ℃, the oil outlet a and oil outlet C of the thermostat are half open at the same time. At this time, part of the hydraulic transmission oil flows through the oil outlet C of the thermostat to the radiator for cooling and then enters the hydraulic torque converter, while another part of the hydraulic transmission oil directly returns to the hydraulic torque converter for large circulation and small circulation at the same time.
When the hydraulic transmission oil temperature is higher than 80 ℃, the thermostat oil outlet C is fully opened and the oil outlet B is closed. At this time, the hydraulic transmission oil enters the radiator through the thermostat oil outlet C and then enters the hydraulic torque converter to form a large cycle.
2. Improve radiator structure
In order to solve the problems of high oil temperature and mutual cavity between hydraulic transmission oil and engine coolant under bad working conditions, it is decided to replace the built-in hydraulic transmission oil radiator with an external plate fin radiator. The plate fin radiator is mainly formed by overlapping and welding a group of sandwich structures. Each sandwich structure is composed of two parallel diaphragms 1, wavy fins 2 and seals 3, as shown in Figure 2. After each sandwich structure is welded into a whole, it is equipped with necessary heads, connecting pipes, etc.
Plate fin radiator not only has the characteristics of high heat transfer efficiency, compact structure, high strength and strong adaptability, but also has an expanded secondary surface, which makes its heat dissipation area much larger than that of tube and belt radiator. This type of radiator is not affected by the water chamber space and heat dissipation medium, and its specification can be selected according to the heat dissipation power of the torque converter. In addition, since the hydraulic transmission oil radiator and the engine water radiator are two independent radiators, it is impossible for the hydraulic transmission oil and the engine coolant to cross cavity with each other.
3. Improvement effect
The improved new hydraulic transmission cooling system is trial installed on our 25t forklift. When the forklift works, the hydraulic transmission oil temperature is always in the range of 70 ~ 90 ℃, and the cooling effect is good.
