- 1 Four-valve Cylinder Head Of Diesel Engines Technical field The present invention relates to the field of engines, in particular to a four-valve 5 cylinder head of a diesel engine. Description of the Related Art As is well known, the cylinder head is an important part of the diesel engine, and the installation and use of many parts in the valve mechanism must depend 10 on the cylinder head. In the prior art, the rocker shaft seat is independently processed. During processing, some rocker shafts are manufactured on the rocker shaft seats, some rocker shaft seats are reserved with rocker shaft mounting holes, and some are bolted at the cylinder heads. The inlet valve rocker arm assembly and the exhaust valve rocker arm assembly in the valve 15 mechanism are assembled onto the rocker shaft seat of the cylinder head through the rocker shaft. The rocker shaft seat supplies lubrication and cooling function to the rotary parts of the inlet valve rocker arm assembly and the exhaust valve rocker arm assembly through corresponding lubricating oil channels. At present, the cylinder heads used with the diesel engines usually have no 20 rocker shaft seat, and the rocker shaft seats need processing independently and are assembled onto the cylinder head through bolts. The disadvantages of this structure are that many parts for auxiliary installation and positioning are needed, and has loose structure and low positioning accuracy, which results in poor maintenance and limited freedom of installation space. 25 Summary of the Present Invention The object of the present invention is to overcome the defects in the prior art by -2 providing a four-valve cylinder head of a diesel engine which integrates the rocker shaft seat, has a simple and compact structure, high location accuracy, which is convenient to dissemble and assemble and facilitates maintenance. To this end, the present invention provides a four-valve cylinder head of a diesel 5 engine which comprises: a cylinder head main body which is a four-valve cylinder head structure; a rocker shaft mounting hole for installing a rocker shaft, and the rocker shaft being used to install an outlet-valve rocker arm and an inlet valve rocker arm thereon; and a mounting hole of a valve bridge guide rod for installing a valve bridge guide rod, in which a valve bridge is inserted on the 10 upper end of the valve bridge guide rod. According to a preferred embodiment of the present invention, the top of the cylinder head main body is a polygonal reinforcement frame structure having a reinforcing rib plate. According to a preferred embodiment of the present invention, there are two 15 mounting holes of the valve bridge guide rod, and two valve bridge guide rods are mounted on respective mounting hole of the valve bridge guide rod. According to a preferred embodiment of the present invention, the valve bridge guide rod and the mounting hole of the valve bridge guide rod are assembled in an interference fit manner. 20 According to a preferred embodiment of the present invention, the valve bridge and the valve bridge guide rod are assembled in a clearance fit manner. Compared with the conventional cylinder head, the four-valve cylinder head according to the present invention has the following beneficial effects: the rocker arm mounting holes for installing the rocker shafts and the mounting 25 holes of the valve bridge guide rod for installing the valve bridge guide rods are integrated on the cylinder head main body of a four-valve cylinder head of the diesel engine. On one hand, the integral structural design ensures convenient and quick installation of the rocker shafts, which leads to compact structure, accurate positioning and more reliable operation of the inlet valve rocker arm -3 assembly and exhaust valve rocker arm assembly. The parts for auxiliary installation and positioning and parts for sealing are greatly reduced, thus lowering the cost. On the other hand, since the cylinder head main body is integrated with mounting holes of the valve bridge guide rod and the cylinder 5 head is provided with the valve bridge guide rods, the valve bridges move up and down more accurately during operation and are not easy to rotate and fly off, and the valves are more smoothly and accurately opened and closed. The present invention will be further described through the following embodiments and the accompanying drawings. 10 Description of The Accompanying Drawings The invention will now be described in a non-limiting way with reference to the drawing in which like parts have like reference symbols, and in which: Figure 1 is a plan view of a four-valve cylinder head of the diesel engine of the 15 present invention. Figure 2 is a sectional view of Figure 1 in the A-A direction. Figure 3 is a sectional view of Figure 1 in the B-B direction. Figure 4 is a sectional view of Figure 1 in the C-C direction. 20 Description of the numbers in the drawings: 1-cylinder head main body 11-rocker shaft mounting hole 12- mounting hole of valve bridge guide rod 121-valve bridge guide rod, 25 122-valve bridge, -4 123-inlet valve bearing face 124-exhaust valve bearing face 13-reinforcing rib plate 14-rocker shaft 5 141- outlet valve rocker arm 142- inlet valve rocker arm 143-valve bridge pressing block Detailed Description of the Present Invention 10 The preferred embodiment of the present invention is described in detail with reference to the attached drawings. However, it should be understood that the protective scope of the present invention is not limited by the embodiment. In the present invention, the rocker arm mounting holes for installing the rocker shafts and the mounting holes of the valve bridge guide rod for installing the 15 valve bridge guide rods are integrated on the cylinder head main body of a four-valve cylinder head of the diesel engine. On one hand, the integral structural design ensures convenient and quick installation of the rocker shafts, which leads to compact structure, accurate positioning and more reliable operation of the inlet valve rocker arm assembly and exhaust valve rocker arm 20 assembly. The parts for auxiliary installation and positioning and parts for sealing are greatly reduced, thus lowering the cost. On the other hand, since the cylinder head main body is integrated with mounting holes of the valve bridge guide rod and the cylinder head is provided with the valve bridge guide rods, the valve bridges move up and down more accurately during operation and 25 are not easy to rotate and fly off, and the valves are more smoothly and accurately opened and closed. As shown in Figures 1-4, the four-valve diesel engine according to a preferred -5 embodiment of the present invention comprises a cylinder head main body 1, rocker shaft mounting holes 11 and mounting holes of a valve bridge guide rod 12 formed on the cylinder head main body 1. The rocker shaft mounting hole 11 is used to install a rocker shaft. An inlet valve rocker arm and an exhaust 5 valve rocker arm are installed on the rocker shaft, so the rocker shaft is quick and convenient to install, thus has compact structure and accurate positioning. Meanwhile, the inlet valve rocker arm assembly and the exhaust valve rocker arm assembly work more reliably. The parts for auxiliary installation and positioning and parts for sealing are greatly reduced, thus lowering the cost. 10 The mounting holes 12 of a valve bridge guide rod are used to install the valve bridge guide rods. Therefore, during operation, the valve bridges move up and down more accurately during operation and are not easy to rotate and fly off, and the valves are more smoothly and accurately opened and closed. Preferably, the cylinder head main body 1 is a four-valve cylinder head 15 structure, namely including two inlet valves and two exhaust valves. The top part of the cylinder head main body 1 is a polygonal reinforcement frame structure that has a reinforcing rib plate 13. The polygonal reinforcement frame is used to improve the overall rigidity of the cylinder head. Moreover, after the cylinder head bolts are fastened, the mounting face between the 20 cylinder head and the cylinder block is uniformly pressed and more reliably sealed. As shown in Figures 1 and 3, each rocker shaft mounting hole 11 is equipped with a rocker shaft 14; each rocker shaft 14 is also equipped with an exhaust valve rocker arm 141 and an inlet valve rocker arm 142. Both the exhaust 25 valve rocker arms 141 and the inlet valve rocker arms 142 are provided with the valve bridge pressing blocks 143 therein. During installation, an inlet valve rocker bearing is transversely inserted into an inlet valve bearing hole first, and an inlet valve rocker shaft is inserted into an exhaust valve bearing hole; then, sealing grooves at the inner rocker shaft end and the outer rocker shaft end of 30 the rocker shaft 14 are respectively equipped with O-shaped sealing rings; the -6 inner rocker shaft end penetrates through the rocker shaft 11 penetrating through the rocker shaft mounting hole 11, following by a washer, the inlet valve rocker bearing on the inlet valve rocker arm, a washer, the exhaust valve rocker shaft bearing on the exhaust valve rocker arm and a washer in turn; and finally, the 5 outer rocker shaft end is penetrated into the rocker shaft mounting hole 3. The O-shaped sealing rings on the inner rocker shaft end and the outer rocker shaft end conduct sealing functions; and the washers can prevent wearing between the contact surfaces and effectively ensure the safety of assembling. As shown in Figure 1 and Figure 4, there are two mounting holes 12 of valve 10 bridge guide rod and a valve bridge guide rod 121 is mounted on the respective mounting hole 12 in an interference fit. A valve bridge 122 is inserted on the upper part of each valve bridge guide rod 121 in a clearance fit. During operation of the engine, the valve bridge 122 can move vertically along the axis direction of the valve bridge guide rod 121. In addition, the valve bridge 122 15 includes an inlet valve bearing face 123 for pushing the inlet valve and an exhaust valve bearing face 124 for pushing the exhaust valve. The inlet valve bearing face 123 is used to pull the inlet valve to open when the engine is working, and the exhaust valve bearing face 124 is used to pull the exhaust valve to open when the engine is working. The valve bridge having processed 20 holes is installed with the valve bridge guide rods. The valve bridges can move along the axis direction of the valve bridge guide rods when driven by the inlet valve rocker arm and the exhaust valve rocker arm, thus improving the structural stability of the valve bridges, and avoiding that when the engine runs at a high speed, the valve rocker arms fly off from the valve bridges and do not move 25 synchronously due to the inertia effect. Otherwise, after the valve rocker arms' acting force on the valve bridges deviate, the valve bridges will turn over or bounce to fall off or get stuck, thus affecting the normal working of the engine. In conclusion, in the four-valve cylinder head according to the present invention, the rocker arm mounting holes for installing the rocker shafts and the mounting 30 holes of the valve bridge guide rod for installing the valve bridge guide rods are -7 integrated on the cylinder head main body of a four-valve cylinder head of the diesel engine. On one hand, the integral structural design ensures convenient and quick installation of the rocker shafts, which leads to compact structure, accurate positioning and more reliable operation of the inlet valve rocker arm 5 assembly and exhaust valve rocker arm assembly. The parts for auxiliary installation and positioning and parts for sealing are greatly reduced, thus lowering the cost. On the other hand, since the cylinder head main body is integrated with mounting holes of the valve bridge guide rod and the cylinder head is provided with the valve bridge guide rods, the valve bridges move up 10 and down more accurately during operation and are not easy to rotate and fly off, and the valves are more smoothly and accurately opened and closed. The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms 15 disclosed, and obviously many modifications and variations are possible in light of the above teachings. The exemplary embodiments were chosen and described in order to explain certain principles of the invention. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents. 20