Hydraulic excavators play a very important role in various types of production

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Caterpillar hydraulic excavators achieve steering by controlling the oil pump to supply oil to the travel motor through control valves, whereas wheel-type hydraulic excavators have their own dedicated steering mechanism. Basic requirements for the steering mechanism: The basic requirements for the steering mechanism of tire-type hydraulic excavators are as follows: 1) Due to the harsh working conditions in which excavators operate, often on uneven terrain, high demands are placed on the strength and service life of the components of the steering mechanism, in order to ensure its safe and reliable operation. 2) Due to the frequent steering operations of the excavator, the control should be easy to operate in order to reduce the driver’s workload and thus improve the excavator’s production efficiency. 3) To overcome the driving resistance of the excavator, ensure the accuracy of its direction of travel and motion path, and reduce tire wear, the wheels should roll purely during steering, with no swaying in the horizontal plane. 4) The inverse efficiency of the steering mechanism should be low to reduce the reaction of the wheels impacting the steering wheel. 5) The steering mechanism should be easy to maintain, with few and simple adjustment points. 6) It ensures that the upper turntable of the excavator can rotate 360 degrees relative to the chassis. The steering methods for tire-type hydraulic excavators include: 1) In terms of the overall steering mechanism, there are methods such as wheel deflection steering and bent-axis steering. 2) Based on the transmission mechanism of the steering system, there are mechanical steering, hydraulic power-assisted steering, hydraulic steering, and pneumatic power-assisted steering, etc. 3) Based on the position of the steering wheels, there are front-wheel steering, rear-wheel steering, and all-wheel steering, etc. Turning principle: At present, tire-type hydraulic excavators widely use hydraulic steering that deflects the front wheels, and rely on feedback mechanisms to address the interlocking issue between the steering wheel and the steering wheels. The hydraulic steering of the front wheels in a tire-type hydraulic excavator is achieved through the operation of the steering gear; the pressure oil generated by the oil pump enters the steering cylinder via the central swivel joint, thereby pushing the left steering knuckle arm and causing it to rotate around the steering knuckle pin. Steering is achieved by the steering tie rod driving the right steering knuckle arm, causing the steering wheels on both sides to deflect simultaneously. The steering gear is controlled by the driver operating the steering wheel. The aforementioned steering knuckle arms can be driven by hydraulic force, hydraulic assist, pneumatic assist, and hydrostatic force, among others; however, hydraulic drive is the most common method. Hydraulic excavators play a very important role in various types of production, which is why it is particularly important to be able to operate them correctly. The following is a detailed introduction to the control system of hydraulic excavators. The hydraulic excavator control system is used to operate the various actions involved in digging tasks, and it constitutes the main control system of the excavator. During the digging operation of a hydraulic excavator, there are mainly four movements: bucket rotation, boom extension and retraction, arm lifting and lowering, and swivel rotation. In work operation systems, the pushing and pulling action of the working cylinders as well as the forward and reverse rotation of hydraulic motors are mostly controlled by three-position axial sliding valves to regulate the direction of fluid flow. The operating speed, on the other hand, is controlled by the operator or through auxiliary devices, depending on the type of hydraulic system (fixed-displacement or variable-displacement system) and the degree of opening of the valves. The basic requirements for the control system of a hydraulic excavator include: (1) The operation control system should be located centrally within the cab, and it must meet the requirements of ergonomics. For example, the control devices and cab are designed and arranged based on a height of 160–180 cm for men and 150–170 cm for women. (2) The start and stop during operation should be smooth, with the speed and force being controlled. Composite actions can be controlled simultaneously. (3) Simple to operate, lightweight, and intuitive. Generally, the operating force on the handle should not exceed 40–60 N; the distance for operating the handle from one side should not be more than 17 cm, and the angle of rotation of the handle should not exceed 35–40 degrees. The rotation angle of the pedal should not exceed 60-70 degrees. The pedal travel range is 6–20 cm, and the pedaling force does not exceed 80–100 N. (4) The lever deformation of the control mechanism should be small, and the gaps and dead strokes within the mechanism structure should also be small. (5) The number of control levers and pedals should be limited; it is preferable to have a combination of hand and foot controls to facilitate complex operations by the operator. (6) It should be ensured that operational performance remains normal within the range of -40 to 50 degrees. These six points are the foundation of the operation control system for hydraulic excavators. I. Based on the power source that drives the main distribution valve, the basic types of operation control systems for hydraulic excavators can be divided into mechanical lever type, hydraulic type, pneumatic type, and electrical type, etc. Due to the high flow rates and pressures in the hydraulic circuits used in hydraulic excavators, the driving force on the stem of the main distribution valve is significant; therefore, the use of hydraulic, pneumatic, and electrical control methods can reduce the workload on operators and facilitate the proper layout of the control system. II. Mechanical control system: Many hydraulic excavators still use a mechanical control system today, and its advantages lie in its simple structure and reliable performance. In a mechanically controlled system, the excavator’s bucket, arm, stick, and swing are each connected to their respective control levers via a main distribution valve. The section from \"fuel supply starting at the front\" to \"fuel supply starting at the back\" is the handle’s idle stroke. The magnitude of the free travel generally depends on the assembly clearance of the pin and the stiffness of the lever; that is, a smaller clearance and greater stiffness result in less free travel, while the opposite is true. The idle stroke should not be too large, so as to ensure timely movement of the excavator’s working equipment; generally, the idle stroke does not exceed 60 mm. The section from \"fuel supply starting at the front and back\" to the \"rated speed\" is the acceleration phase, generally ranging between 20-40 mm. The total movement of the control lever between the front and rear endpoints should not exceed 340 mm. To reduce the time required for the driver to switch control and increase the opportunities for performing combined actions, modern hydraulic excavators have upgraded from the traditional four-handle control system to a two-handle control system, meaning that the four operating functions of the excavator are controlled using just two handles. The mechanical control system is particularly important in the control system of hydraulic excavators. III. Hydraulic control system: The hydraulic control of a hydraulic excavator relies on oil pressure to drive the stem of the main distribution valve; this oil circuit can be an independent one, or it can be derived from the main oil circuit system. More and more hydraulic excavators now use hydraulic control, with types including mechanically feedback-driven systems, integrated control valves and main distribution valves, and pilot valve-controlled systems. The latter is more commonly used. It is further divided into pressure-generating type and pressure-reducing valve type. (1) Operation via a pressure-generated pilot valve. This is a remotely operated valve, in which the driver uses the pressure oil from the pilot valve to control the main distribution valve. (2) Operation via a pressure-reducing valve pilot valve. Similar to the pressure-driven pilot valve control mentioned above, the movement of the main distribution valve spool in this control device is also indirectly controlled through hydraulic guidance. The difference is that a reduced-pressure pilot valve is used. A systematic understanding of the control system of hydraulic excavators plays a very important role in the operation of these excavators; second-hand excavators