The utility model provides the following technical scheme: a direct connected oil-free air compressor comprises a crankcase, a crankshaft is rotationally connected in the crankcase, one end of the crankshaft is connected with the motor, the other end of the crankshaft is fixed with a fan, a mounting block is integrated on the top of the crankcase, a cylinder is fixed on the mounting block, a piston for compressed air is arranged in the cylinder, and the piston is driven and connected with the crankshaft, The crankcase is cylindrical, the fan is located in the crankcase and is coaxial with the crankcase, the mounting block is provided with an air guide hole for cooling the outer wall of the cylinder, the air guide hole is connected with the inner cavity of the crankcase and the top surface of the mounting block, the side wall of the cylinder is provided with a heat sink, a heat dissipation channel is formed between the heat sink and the outer wall of the cylinder, and the air guide hole is facing the heat dissipation channel.

The preferred of the utility model: the cylinder is circular, the mounting block is rectangular, the center of the mounting block is provided with a cylinder connecting hole, the air guide hole is located on both sides of the connecting hole, and the air guide hole is provided with stiffeners.

The utility model preferably has the following advantages: the wall thickness on both sides of the air guide hole is equal.

The preferred of the utility model is that the crankcase and the cylinder are made of aluminum.

Compared with the prior art, the beneficial effect of the utility model is that the crankcase is cylindrical, the fan is located in the crankcase and coaxial with the crankcase, and a fan is fixed at one end of the crankshaft. When the crankshaft rotates, the driving piston moves up and down in the cylinder to compress air. At the same time, the fan fixed on the crankshaft also rotates together to produce air flow, The air flow cools the outer wall of the cylinder through the air guide hole. The crankcase is cylindrical. Compared with the crankcase of rectangular, trapezoidal and other shapes, the resistance generated by the air flow is smaller. The fan is located in the crankcase and coaxial with the crankcase. The distance from the outer edge of the fan to the inner wall of the crankcase is uniform and easy to control in a small range, which can improve the flow rate of the air flow, The outer wall of the cylinder is cooled better, and the air guide hole is directly connected to the heat dissipation of the cylinder

The air flow generated by the fan can be more fully used to cool the outer wall of the cylinder.