Hydraulic Transmission System Introduction

Hydraulic transmission consists of hydraulic components (hydraulic oil pump), hydraulic control components (various hydraulic valves), hydraulic actuators (hydraulic cylinders and hydraulic motors, etc.), hydraulic accessories (pipes and accumulators, etc.) and hydraulic oil system.

Introduction

The hydraulic pump converts mechanical energy into liquid pressure energy. The hydraulic control valve and hydraulic accessories control the pressure, flow and flow direction of the hydraulic medium, and transmit the pressure energy output by the hydraulic pump to the actuator, which converts the liquid pressure energy into mechanical energy. , to complete the required action.

Components

1. The power element, namely the hydraulic pump, its function is to convert the mechanical energy of the prime mover into the pressure kinetic energy of the liquid, and its function is to provide pressure oil for the hydraulic system, which is the power source of the system.

2. Actuating element refers to hydraulic cylinder or hydraulic motor, whose function is to convert hydraulic energy into mechanical energy and perform external work. The hydraulic cylinder can drive the working mechanism to realize reciprocating linear motion, and the hydraulic motor can complete the rotary motion.

3. Control elements, which means that various valves can use these elements to control and adjust the pressure, flow and direction of the liquid in the hydraulic system, so as to ensure that the executive elements can work according to people's expected requirements.

4. Auxiliary components, including fuel tanks, oil filters, pipelines and joints, coolers, pressure gauges, etc. Their role is to provide the necessary conditions for the normal operation of the system and facilitate monitoring and control.

5. The working medium, that is, the transmission fluid, is usually called hydraulic oil. The hydraulic system realizes the movement and power transmission through the working medium, and the hydraulic oil can also lubricate the moving parts in the hydraulic components.

Working Principle

The following figure shows the composition and working principle of the hydraulic transmission system of a simple grinder. The electric motor drives the hydraulic pump to suck oil from the oil tank, and the hydraulic pump converts the mechanical energy of the electric motor into the pressure energy of the liquid. The hydraulic medium enters the left chamber of the hydraulic cylinder through the throttle valve and the reversing valve through the pipeline, and pushes the piston to drive the worktable to move to the right. The hydraulic medium discharged from the right chamber of the hydraulic cylinder flows back to the oil tank through the reversing valve. After the reversing valve is reversed, the hydraulic medium enters the right chamber of the hydraulic cylinder, which makes the piston move to the left and pushes the worktable to move in the opposite direction. The movement speed of the hydraulic cylinder can be adjusted by changing the opening of the throttle valve. The pressure of the hydraulic system can be adjusted by a relief valve. When drawing the hydraulic system diagram, for the sake of simplicity, the prescribed symbols are used to represent the hydraulic components, which are called functional symbols.

Basic Circuit

1.  Overview

A typical oil circuit composed of related hydraulic components used to complete a specific function. Any hydraulic transmission system is composed of several basic circuits, and each basic circuit has a certain control function. Several basic loops are combined together to control the movement direction, working pressure and movement speed of the actuator according to certain requirements. According to different control functions, the basic loop is divided into pressure control loop, speed control loop and direction control loop.

2.  Pressure control loop

A circuit that uses a pressure control valve (see Hydraulic Control Valve) to control the entire system or a local range of pressure. According to different functions, the pressure control loop can be divided into 4 loops: pressure regulation, pressure transformation, pressure relief and voltage regulation.

● Pressure regulating circuit: This circuit uses a relief valve to adjust the highest constant pressure of the hydraulic source. The relief valve in Figure 1 plays this role. When the pressure is greater than the set pressure of the relief valve, the opening of the relief valve is enlarged to reduce the output pressure of the hydraulic pump and maintain the system pressure basically constant.

● Transformer circuit: It is used to change the pressure in the local area of the system. If a pressure reducing valve is connected to the circuit, the pressure after the pressure reducing valve can be reduced; when a booster is connected, the pressure after the booster can be increased. at the hydraulic source pressure.

● Pressure relief circuit: When the system does not need pressure or only needs low pressure, the pressure of the system is reduced to zero pressure or low pressure through the pressure relief circuit.

● Voltage stabilization circuit: It is used to reduce or absorb the pressure fluctuations generated in the local area of  the system and keep the system pressure stable, such as using an accumulator in the circuit.

3. Speed control loop

A loop that controls the movement speed of the actuator by controlling the flow of the medium. According to different functions, it is divided into speed control loop and synchronous loop.

●Speed control loop: It is used to control the movement speed of a single actuator, and a throttle valve or a speed control valve can be used to control the flow. The throttle valve in Figure 1 plays this role. The throttle valve controls the flow of the hydraulic pump into the hydraulic cylinder, thereby controlling the movement speed of the hydraulic cylinder. This form is called throttle speed regulation. It can also be used to adjust the speed by changing the output flow of the hydraulic pump, which is called volume speed regulation.

●Synchronous circuit: a circuit that controls the synchronous operation of two or more actuators. For example, the method of rigidly connecting the two actuators is used to ensure synchronization; the throttle valve or speed control valve is used to adjust the flow of the two actuators respectively. Make them equal to ensure synchronization; connect the pipelines of the hydraulic cylinders in series to ensure that the flow into the two hydraulic cylinders is the same, so that the two hydraulic cylinders are synchronized.

4. Direction control loop

In the hydraulic system, the circuit that controls the starting, stopping and reversing of the actuator is called the direction control circuit. The direction control loop has a reversing loop and a locking loop. The control method and reversing accuracy of the motor-hydraulic reversing circuit are described in the hydraulic system of the grinder.