## 1 Introduction  
Sealing performance is one of the most important indicators used to measure the performance of hydraulic cylinders. The main seals used for hydraulic cylinders can be divided into two groups: extrusion seals and gap seals [1]. A squeeze seal means that in the gap of the sealed area, two surfaces are pressed together to prevent the leakage of a fluid medium. The seal will be elastically deformed when it is subjected to pressure so as to close the cover to prevent leakage and achieve a sealing effect [2]. Gap sealing is achieved through a micron-level matching gap between a piston surface and a cylinder wall; the idea is to use the throttling effect of the gap to control leakage [3]. The combined seal ring is a kind of extrusion seal. Combined seals are widely used in hydraulic cylinder piston seals due to their good sealing performance, high pressure resistance, low friction, and high-speed of operation [4, 5]. During installation, the O-ring acts on the wear ring through a pre-tightening force produced by radial interference compression deformation, which moves the wear ring close to the cylinder wall, thus achieving the purpose of reducing or preventing fluid leakage [6, 7]. [PERSON] et al. [8] structured a simulation model of a complex hydraulic cylinder. He, [PERSON] et al. [9], studied the influence of the contact state of the seal ring and the static pressure mechanical end face sealing performance. [PERSON] et al. [10] used numerical analysis methods to explore the influence of piston groove structure parameters on lubrication conditions and friction. [PERSON] et al. [11] studied the impact of the piston ring surface micro-topography on friction and wear through a hydraulic cylinder in motion tests. [PERSON] et al. [12] and [PERSON] et al. [13] used the Taguchi method and comparative experiment method to explore the friction and the wear relationship between a piston ring and the cylinder wall of a hydraulic cylinder. [PERSON] et al. [14] established a hydraulic cylinder dynamic model based on the results of previous research and studied its friction characteristics. [PERSON] et al. [15]; [PERSON] et al. [16]; [PERSON] et al. [17]; [PERSON] et al. [18]; and [PERSON] et al. [19] studied the effect of the pattern and depth of the surface texture of a piston or cylinder on its friction. Studies have shown that the use of reasonable texture patterns and depth helps to reduce the wear between the seal ring and the hydraulic cylinder. By numerical simulations, [PERSON] et al. [20] investigated the influence of oil temperature on the sealing performance of lip seals. [PERSON] et al. [21] carried out parameterized modeling of the Glyy ring based on the finite element software Abaqus and explored the factors influencing its sealing performance. [PERSON] et al. [22] explored the effect of working pressure, O-ring pre-compression rate, and friction coefficient on a high-pressure star. [PERSON] et al. [23] investigated the influence of parameters such as the ring gap. Due to extreme pressure conditions, the greatest gas loss in the crankcase occurs during the compression and combustion stages. [PERSON] et al. [24] studied wear simulation for the radial shaft sealing ring and uncovered a method to calculate the wear rate. In summary, many researchers have studied the sealing, friction, and wear of reciprocating seals and analyzed the influence of material parameters, working condition parameters, and compressibility on the sealing performance. However, few researchers have designed the structural parameters of a combined seal. Additionally, few researchers have analyzed the key factors affecting the sealing performance of the combined seal ring. In this study, ANSYS was used to analyze the mechanical characteristics of a combined seal ring under a load, the key factors affecting the sealing performance of the combined seal ring were studied, and the influence of the working pressure and the pre-compression rate of the rubber O-ring on the contact stress of the combined seal ring was analyzed.