Application Of Hydraulic Valve In Hydraulic System Of Walking Machinery
Application of hydraulic valve in hydraulic system of walking machinery
In general walking machinery, the full hydraulic steering system is often used with the working device hydraulic system to share a pump source, consisting of a single pump (or dual-pump) dual-loop system. Because of the advantages of simple system and reliable work, it is widely used in small and medium tonnage forklift trucks.
All hydraulic braking system consists of hydraulic brake valve, the wheel side brakes and accumulator are composed of the hydraulic brake valve and accumulator, which are connected with each other in the common single pump (or double pump) dual-loop hydraulic system's steering system loop, which composes the whole hydraulic power steering and braking system. hydraulic valve The single steady shunt valve in the steering pump oil output through multi-way directional valve (for working hydraulic system) stably outputs a constant flow, which leads to the brake valve and accumulator. When the hydraulic brake valve does not move, the constant oil flows into the full hydraulic steering gear or for the steering, or no load back to the tank. When stepping down the brake pedal, the brake valve can provide oil to the brake wheel cylinder to implement the brake (while charging the accumulator).
The system can also perform braking at the same time as the steering, and has the function of emergency braking.
Structure and working principle of brake valve
The brake valve is the core component of the hydraulic braking system, as shown in Fig. 2. The valve has a total of 5 control oil ports (P, N, Br, T, PA), respectively, the steering pump, steering gear, brake cylinder, fuel tank and accumulator, mainly by putt 13, putter piston 10, spring 8, Slide valve 7, Spring 6, feedback piston 5, closed stem 3 and one-way ball valve 12 and other components, has the following four working states.
(1) State of the brake (Free State)
At this point the position of the parts, p and N mouth connected with the e cavity, the steering pump output constant oil flow through p, N day to the full hydraulic steering gear (or for steering, or no four-tank), hydraulic valve brake wheel cylinder oil through the BR mouth, F-cavity, e-cavity, sliding valve 7 and push rod piston 10 inside the small hole out of the T-mouth back to the tank, brake off. At this time PA mouth due to the one-way effect of ball valve 12 with the F-cavity disconnect.
(2) Braking state
When stepping down the brake pedal, push 13, push the piston 10 left, while the spring 8 pushes the slide valve 7 and the feedback piston 5 left SHIFT, the channel between the e-cavity and the T-Port is closed first, then the channel between the e-cavity and the P-port is opened, while the P-port is connected with the BR mouth through the e-cavity, and the F-cavity is communicated with the N-Port, and the P-Port is basically free
When the slide valve 7 moves further left, gradually closes the channel between PN, p-Port pressure increases, the BR port and the brake wheel cylinder pressure also increases, brake start; This pressure simultaneously acts on the left side of the feedback piston to produce a right thrust, and the compression force of the Spring 8 is balanced, so that the BR daily braking pressure (two times pressure) is raised with the push rod 13 of the trip is linearly proportional, while the brake pressure through the valve of the relevant parts and rods to the operator's foot, so that the operator can feel the size of the braking force. hydraulic valve The push rod piston is fitted with a limit nut 11, during the braking process, when its top to the valve body baffle, the push rod stops moving, the BR pressure reaches the highest, that is, by adjusting the nut position, it can limit the maximum value of the braking pressure.
When the pedal is released, the slide valve 7 is returned to the initial position under the action of the feedback piston pressure and the four-bit spring force.
(3) Emergency braking status
When the hydraulic pump is damaged or the engine flameout, because the P-port without pressure, and therefore can not implement normal braking, the system has an emergency braking function, the principle is as follows:
The emergency braking power source is provided by the accumulator. The accumulator is a spring type with a safety valve and a low-pressure alarm pressure switch, a hydraulic pump connected with two external oil ports, and a Shimin port. When the system to implement the steering or normal braking, the hydraulic pump through the one-way valve accumulator filling pressure, the role of the safety valve is to limit the maximum energy storage pressure, the role of low-voltage alarm switch is not stored in the accumulator pressure, the alarm buzzer or LED, to the operator alarm.
At this time, step on the brake pedal, hydraulic valve brake valve internal sliding valve 7, feedback piston 5 and closed stem 3 will be connected to move to the left, closed stem will be open one-way ball valve 12, the accumulator oil port p. With the BR port, the pressure oil in the accumulator will directly effect the emergency braking in the brake wheel cylinder. Release the pedal, slide valve 7, feedback piston 5 and closed stem 3 at the same time move to the right, ball valve 12 seat seat, disconnect PA port and BR Day channel. After closing the stem 3 to the original position, the feedback piston 5 with the slide valve 7 further right, open the channel between the E-T, the brake wheel cylinder internal oil through the brake between the br mouth, f cavity, E cavity, t-mouth back to the tank.
(4) The simultaneous implementation of the braking state
When turning the steering wheel (steering) and not stepping on the pedal to implement the brake, P-Port oil Pressure Although the rise (this is dependent on the steering load), but due to P-E channel closure, and E-T channel, the BR port without pressure, in a non braking state.
If you step on the brake pedal at this time, because the sliding valve 7 left, so that the E-t channel closed and P-E access, the pump part of the pressure oil into the brake wheel cylinder, that is, while the steering can still be implemented brake.
Characteristics of full hydraulic braking system
From the above analysis, it can be seen that the system has the following main characteristics:
(1) The steering and braking system share a hydraulic oil source, which can be operated separately, if necessary, hydraulic valve and can be combined and interfered.
(2) compared with the conventional full hydraulic braking system, besides its main advantages, the components are less (no pressure-filled valve), and the system is simpler.
(3) The Pedal connection mode is compatible with the brake master pump, it is easier to install and decorate.
To sum up, this system is especially suitable for the technical renewal demand of small and medium sized walking machinery, such as forklift, hydraulic valve grader steering and braking system.