Steering system and method of bridge type heavy-load AGV

Abstract

The invention provides a steering system and method of a bridge type heavy-load AGV, and belongs to the field of mobile robots and automatic control. The method can adapt to the use condition of the heavy-load AGV, and regulation and control of related hydraulic pressure and temperature can be accurately operated on the premise that quick response is met. The steering system of the bridge type heavy-load AGV comprises a complete machine controller, a hydraulic pump station module and an action execution module, wherein the hydraulic pump station module and the action execution module are communicated through a pipeline to achieve hydraulic oil circulation operation. And the complete machine controller is used for receiving the data detection signal and sending a control instruction. The steering method of the bridge type heavy-load AGV comprises the steps of (1) starting initialization, (2) steering control, (3) pressure compensation, (4) oil temperature adjustment and (5) pressure relief.

Description

Technical Field

[0001] This application relates to the field of mobile robots and automated control, and specifically proposes a steering system and steering control method for bridge-type heavy-duty AGVs. Background Technology

[0002] With the development and progress of industrial automation technology, various mobile robots, such as AGVs (Automated Guided Vehicles) and unmanned delivery vehicles, are now widely used in logistics warehousing and automated production sites.

[0003] Currently, heavy-duty AGVs generally use axle chassis with a hydraulic steering system. Unlike existing fuel or electric vehicles, this type of steering system cannot meet the omnidirectional driving control requirements of AGVs in terms of response speed and efficiency. Specifically, it can cause problems such as jerking during steering, steering failure due to thick hydraulic oil in winter, and severe tire wear. In high-temperature environments, excessively high oil temperature can lead to aging, deformation, or loss of elasticity of seals, and even oil leaks, causing the hydraulic system to malfunction.

[0004] Therefore, there is an urgent need for a hydraulic control method that can respond quickly and adaptively adjust oil pressure and temperature according to operating conditions. In view of this, this patent application is hereby filed. Summary of the Invention

[0005] The steering system and method for heavy-duty AGVs proposed in this application can adapt to the operating conditions of heavy-duty AGVs and accurately operate the relevant hydraulic and temperature control while meeting the requirements of rapid response.

[0006] To achieve the above-mentioned objectives, the steering system of the bridge-type heavy-duty AGV includes a whole-machine controller, a hydraulic pump station module connected by pipelines to achieve hydraulic oil circulation, and an action execution module; the whole-machine controller is used to receive data detection signals and send control commands; the hydraulic pump station module is composed of the following components connected together:

[0007] Hydraulic oil tank, used to store hydraulic oil running in the overall circulation pipeline;

[0008] A temperature sensor is installed at the bottom of the hydraulic oil tank to detect the temperature of the hydraulic oil.

[0009] The return oil filter is used to filter impurities in the hydraulic oil in the return oil pipeline. Its inlet is connected to the outlet of the cooler, and its outlet is connected to the return oil port of the hydraulic oil tank.

[0010] The cooler is used to cool the hydraulic oil. Its outlet is connected to the inlet of the return oil filter. Its inlet is connected to the outlet of the first solenoid ball valve, the outlet of the first relief valve, and the return oil port of the pump station.

[0011] The motor is used to provide power for the hydraulic oil circulating within the overall hydraulic pump station module, and its output end drives the mechanical bushing connected to the hydraulic pump.

[0012] A hydraulic pump is used to draw hydraulic oil from a hydraulic oil tank and provide pressure for the hydraulic oil circulation. Its inlet is connected to the outlet of the hydraulic oil tank, and its outlet is connected to the inlet of the oil filter.

[0013] The oil outlet filter is used to filter impurities in the hydraulic oil of the oil outlet pipeline. Its oil inlet is connected to the oil outlet of the hydraulic pump, and its oil inlet is connected to the oil inlet of the first solenoid ball valve, the oil inlet of the first relief valve, and the oil outlet of the pump station.

[0014] The first solenoid ball valve is controlled by the whole machine controller through the on and off of its electromagnet DT1 to adjust the working state of the valve; the oil inlet of the first solenoid ball valve is connected to the oil inlet of the first overflow valve, the oil outlet of the oil filter and the oil outlet of the pump station respectively, and its oil outlet is connected to the oil outlet of the first overflow valve, the oil inlet of the return oil filter and the return oil outlet of the pump station respectively.

[0015] The first relief valve is used to monitor the oil pressure of the overall hydraulic pump station module. The oil inlet of the first relief valve is connected to the oil inlet of the first solenoid ball valve, the oil outlet of the oil filter, and the oil outlet of the pump station, respectively. Its oil outlet is connected to the oil outlet of the first solenoid ball valve, the oil inlet of the return oil filter, and the return oil outlet of the pump station, respectively.

[0016] The pump station's oil outlet is connected to the module's oil inlet to supply hydraulic oil to the overall actuator module;

[0017] The pump station return port is connected to the module return port to deliver hydraulic oil back to the hydraulic oil tank 1.

[0018] Furthermore, the action execution module is composed of the following connected components:

[0019] The first check valve has its inlet connected to the module inlet, and its outlet connected to the high-pressure ball valve, the inlet of the first pressure compensator, the inlet of the second pressure compensator, and the inlet of the second solenoid ball valve, respectively.

[0020] The high-pressure ball valve has two interfaces that determine the direction of hydraulic oil flow based on the pressure at both ends. Each interface can be used as an oil inlet or an oil outlet. One end interface is connected to the oil inlet of the first pressure compensator, the oil inlet of the second pressure compensator, the oil inlet of the second solenoid ball valve, and the oil outlet of the first check valve, respectively. The other end interface is connected to the oil outlet of the accumulator.

[0021] The accumulator is used to store hydraulic oil and replenish hydraulic oil according to the actual oil pressure of the hydraulic pipeline. Its oil outlet is connected to the high-pressure ball valve 15.

[0022] The second solenoid ball valve is controlled by the whole machine controller through the on / off state of its solenoid DT16 to regulate the working state of the valve; its oil inlet is connected to the oil inlet of the high pressure ball valve, the oil inlet of the first pressure compensator, the oil inlet of the second pressure compensator, and the oil outlet of the first check valve, respectively; its oil outlet is connected to the oil outlet of the second check valve and the module return oil port, respectively.

[0023] A pressure sensor, used to detect the hydraulic circuit pressure of the overall actuator module and feed it back to the whole machine controller, is installed between the oil inlet of the second solenoid ball valve and the oil outlet of the first check valve.

[0024] A pressure gauge is used to detect the hydraulic circuit pressure of the overall actuator module. It is installed between the oil inlet of the second solenoid ball valve and the oil outlet of the first check valve.

[0025] The first pressure compensator is used to collect the hydraulic oil returning from the first shuttle valve and supply it to the first proportional directional valve to quickly respond to the steering action; its oil inlet is connected to the oil inlet of the high-pressure ball valve, the oil inlet of the second pressure compensator, the oil inlet of the second solenoid ball valve, and the oil outlet of the first check valve, respectively; its oil outlet is connected to the P port of the first proportional directional valve; and its pressure compensation port is connected to the oil outlet of the first shuttle valve.

[0026] The second pressure compensator is used to collect the hydraulic oil returning from the second shuttle valve and supply it to the second proportional directional valve to quickly respond to the steering action; its oil inlet is connected to the high-pressure ball valve, the oil inlet of the first pressure compensator, the oil inlet of the second solenoid ball valve, and the oil outlet of the first check valve, respectively; its oil outlet is connected to the P port of the second proportional directional valve; and its pressure compensation port is connected to the oil outlet of the second shuttle valve.

[0027] The first shuttle valve is used to collect hydraulic oil from the return ports of the left steering cylinder of the first axle and the right steering cylinder of the first axle and supply it to the first pressure compensator. It has two oil inlets and one oil outlet. When oil enters one oil inlet, the other oil inlet is blocked. Its oil outlet is connected to the pressure compensation port of the first pressure compensator, and its two oil inlets are connected to the A port and B port of the first proportional directional valve, respectively.

[0028] The second shuttle valve collects hydraulic oil from the return ports of the left and right steering cylinders of the second axle and supplies it to the second pressure compensator for use in the next steering action. It has two inlets and one outlet. When oil enters one inlet, the other inlet is blocked. Its outlet is connected to the pressure compensation port of the second pressure compensator, and its two inlets are connected to the A and B ports of the second proportional directional valve, respectively.

[0029] The first proportional directional valve is energized and its opening degree is adjusted by the overall controller through the on / off switching of its electromagnets DT5 and DT6. It has four oil circuit interfaces: P, T, A, and B. It has two reversing modes: the first mode is that the P port is connected to the A port, and the connection between the B port and the T port is controlled by the electromagnet DT6; the second mode is that the P port is connected to the B port, and the connection between the A port and the T port is controlled by the electromagnet DT5. Its P port is connected to the oil outlet of the first pressure compensator, its T port is connected to the T port of the second proportional directional valve and the oil inlet of the second check valve, its A port is connected to one of the oil inlets of the first shuttle valve, the rod chamber of the left steering cylinder of the first bridge and the rodless chamber of the right steering cylinder of the first bridge, and its B port is connected to the other oil inlet of the first shuttle valve, the rodless chamber of the left steering cylinder of the first bridge and the rod chamber of the right steering cylinder of the first bridge.

[0030] The second proportional directional valve is energized and its opening degree is adjusted by the overall controller through the on / off switching of its electromagnets DT7 and DT8. It has four oil circuit interfaces: P, T, A, and B. It has two reversing modes: the first mode is that the P port is connected to the A port, and the connection between the B port and the T port is controlled by the electromagnet DT8; the second mode is that the P port is connected to the B port, and the connection between the A port and the T port is controlled by the electromagnet DT7. Its P port is connected to the oil outlet of the second pressure compensator, its T port is connected to the T port of the first proportional directional valve and the oil inlet of the second check valve, its A port is connected to one of the oil inlets of the second shuttle valve, the rod chamber of the left steering cylinder of the second bridge and the rodless chamber of the right steering cylinder of the second bridge, and its B port is connected to the other oil inlet of the second shuttle valve, the rodless chamber of the left steering cylinder of the second bridge and the rod chamber of the right steering cylinder of the second bridge.

[0031] The left steering cylinder of the first axle is installed on the left side of the first axle and is used to achieve left and right turns by controlling the oil inlet and outlet of its two oil chambers. Its rod chamber is connected to port A of the first proportional directional valve, the rodless chamber of the right steering cylinder of the first axle, and one of the oil inlets of the first shuttle valve. Its rodless chamber is connected to port B of the first proportional directional valve, the rod chamber of the right steering cylinder of the first axle, and the other oil inlet of the first shuttle valve.

[0032] The right steering cylinder of the first axle is installed on the right side of the first axle and is used to achieve left and right turns by controlling the oil inlet and outlet of its two oil chambers. Its rod chamber is connected to port B of the first proportional directional valve, the rodless chamber of the left steering cylinder of the first axle, and one of the oil inlets of the first shuttle valve. Its rodless chamber is connected to port A of the first proportional directional valve, the rod chamber of the left steering cylinder of the first axle, and the other oil inlet of the first shuttle valve.

[0033] The left steering cylinder of the second axle is installed on the left side of the second axle and is used to achieve left and right turns by controlling the oil inlet and outlet of its two oil chambers. Its rod chamber is connected to port A of the second proportional directional valve, the rodless chamber of the right steering cylinder of the second axle, and one of the oil inlets of the second shuttle valve. Its rodless chamber is connected to port B of the second proportional directional valve, the rod chamber of the right steering cylinder of the second axle, and the other oil inlet of the second shuttle valve.

[0034] The right steering cylinder of the second axle is installed on the right side of the second axle and is used to achieve left and right turns by controlling the oil inlet and outlet of its two oil chambers. Its rod chamber is connected to port B of the second proportional directional valve, the rodless chamber of the left steering cylinder of the second axle, and one of the oil inlets of the second shuttle valve. Its rodless chamber is connected to port A of the second proportional directional valve, the rod chamber of the left steering cylinder of the second axle, and the other oil inlet of the second shuttle valve.

[0035] The second check valve has its inlet connected to the T port of the first proportional directional valve and the T port of the second proportional directional valve, respectively, and its outlet connected to the module return port and the outlet of the second solenoid ball valve, respectively.

[0036] The module oil inlet is used to supply hydraulic oil to the overall actuator module;

[0037] The module return port is used to transport the hydraulic oil in the return line back to the hydraulic oil tank through the cooler.

[0038] Based on the aforementioned steering system of a bridge-type heavy-duty AGV, this application also proposes a steering method for a bridge-type heavy-duty AGV, which includes the following stages:

[0039] 1) Startup initialization;

[0040] After the AGV is powered on and started, the pressure sensor detects and feeds back the hydraulic system pressure to the whole machine controller;

[0041] If the oil pressure is less than the first preset threshold of the system, the whole machine controller sends a command to the motor to execute the high-speed pressure mode. At the same time, the solenoid DT1 of the first solenoid ball valve is energized and the solenoid DT16 of the second solenoid ball valve is energized. Both pressure relief circuits in the hydraulic pump station module and the action module are closed. The hydraulic oil is drawn by the hydraulic pump and input to the oil outlet filter for filtration before flowing into the action module.

[0042] When the oil pressure is higher than the preset pressure of the high-pressure ball valve, some hydraulic oil is charged into the accumulator;

[0043] Subsequently, the electromagnet DT1 of the first solenoid ball valve is de-energized. At this time, the hydraulic oil flows through the first solenoid ball valve to the cooler, and then returns to the hydraulic oil tank after being filtered by the return oil filter.

[0044] 2) Steering control;

[0045] It includes three types of state control: vehicle steering, single-axle steering, and diagonal operation; the whole machine controller sends a command to the motor to execute the high-speed pressurization mode, the electromagnet DT1 of the first solenoid ball valve is energized, and the hydraulic oil is controlled to stop flowing back into the return oil line. The hydraulic oil is drawn by the hydraulic pump and input to the oil outlet filter for filtration before flowing into the action module.

[0046] 3) Stress compensation;

[0047] During the aforementioned steering control phase, if the pressure sensor detects that the oil pressure is less than the second threshold preset by the system, the whole machine controller determines the action type and implements the pressure compensation process.

[0048] 4) Oil temperature adjustment;

[0049] During the aforementioned steering control phase, the oil temperature in the hydraulic tank is continuously monitored by a temperature sensor.

[0050] 5) Depressurize;

[0051] When the AGV stops running, the hydraulic system automatically depressurizes.

[0052] Furthermore, in stage 1), if the accumulator is fully charged and the oil pressure is still not less than the preset pressure value of the high-pressure ball valve, the pressure sensor will feed back the pressure value to the vehicle controller, thereby controlling the motor to enter the low-speed pressurization mode, and at the same time, the excess pressure will be released through the overflow valve.

[0053] Furthermore, in stage 1), a second check valve is provided in the return oil line of the action module to unidirectionally guide the return oil line, and a first check valve is provided in the inlet oil line to unidirectionally guide the inlet oil line, so as to prevent the hydraulic oil entering the action module from directly entering the return oil line.

[0054] Furthermore, stage 2) includes:

[0055] 2.1) The entire vehicle turns to the left;

[0056] When the solenoid DT5 of the first proportional directional valve is energized, its P port is connected to its B port, and hydraulic oil flows to the rodless chamber of the left steering cylinder of the first axle and the rod chamber of the right steering cylinder of the first axle, so that the wheels of the first axle vehicle turn to the left; at the same time, when the solenoid DT8 of the second proportional directional valve is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder of the second axle and the rodless chamber of the right steering cylinder of the second axle, so that the wheels of the second axle vehicle turn to the right, thus realizing the left steering control of the vehicle.

[0057] 2.2) The entire vehicle turns right;

[0058] When the solenoid DT6 of the first proportional directional valve is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder of the first axle and the rodless chamber of the right steering cylinder of the first axle, so that the wheels of the first axle vehicle turn to the right; at the same time, when the solenoid DT7 of the second proportional directional valve is energized, its P port is connected to its B port, and hydraulic oil flows to the rodless chamber of the left steering cylinder of the second axle and the rod chamber of the right steering cylinder of the second axle, so that the wheels of the second axle vehicle turn to the left, thus realizing the right steering control of the vehicle.

[0059] 2.3) Single front axle steering;

[0060] When the solenoid DT5 of the first proportional directional valve is energized, its P port is connected to its B port, and hydraulic oil flows to the rodless chamber of the left steering cylinder of the first axle and the rod chamber of the right steering cylinder of the first axle, so that the wheels of the first axle vehicle turn to the left; if so, when the solenoid DT6 of the first proportional directional valve is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder of the first axle and the rodless chamber of the right steering cylinder of the first axle, so that the wheels of the first axle vehicle turn to the right.

[0061] 2.4) Single rear axle steering;

[0062] When the solenoid DT8 of the second proportional directional valve is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder of the second axle and the rodless chamber of the right steering cylinder of the second axle, so that the wheels of the second axle vehicle turn to the right; or, when the solenoid DT7 of the second proportional directional valve is energized, its P port is connected to its B port, and hydraulic oil flows to the rodless chamber of the left steering cylinder of the second axle and the rod chamber of the right steering cylinder of the second axle, so that the wheels of the second axle vehicle turn to the left.

[0063] 2.5) Moving diagonally to the right;

[0064] When the solenoid DT6 of the first proportional directional valve is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder of the first axle and the rodless chamber of the right steering cylinder of the first axle, so that the wheels of the first axle vehicle turn to the right; at the same time, when the solenoid DT8 of the second proportional directional valve is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder of the second axle and the rodless chamber of the right steering cylinder of the second axle, so that the wheels of the second axle vehicle turn to the right, thus realizing the rightward diagonal movement of the vehicle;

[0065] 2.6) Moving diagonally to the left;

[0066] When the solenoid DT5 of the first proportional directional valve is energized, its P port and B port are connected, and hydraulic oil flows to the rodless chamber of the left steering cylinder of the first axle and the rod chamber of the right steering cylinder of the first axle, thus turning the wheels of the first axle vehicle to the left. At the same time, the solenoid DT7 of the second proportional directional valve is energized, and its P port and B port are connected, and hydraulic oil flows to the rodless chamber of the left steering cylinder of the second axle and the rod chamber of the right steering cylinder of the second axle, thus turning the wheels of the second axle vehicle to the left, thereby realizing the vehicle's diagonal leftward movement.

[0067] Furthermore, stage 3) includes:

[0068] 3.1) Steering pressure compensation for the axle;

[0069] When the AGV performs a left turn on one axle, the rod chamber of the left turn cylinder of the first axle is unloaded and its rodless chamber is filled with oil, while the rod chamber of the right turn cylinder of the first axle is filled with oil and its rodless chamber is unloaded. The hydraulic oil flowing out of the two sets of unloaded chambers flows to the first shuttle valve. First, the first shuttle valve is activated to block the oil inlet connecting the rodless chamber of the left turn cylinder of the first axle and the rod chamber of the right turn cylinder of the first axle. Then, the hydraulic oil flowing out of the two sets of unloaded chambers is filled into the P port of the first proportional directional valve through the pressure compensation port of the first pressure compensator to supplement the left turn pressure of the first axle.

[0070] When the AGV performs a right turn on one axle, the rodless chamber of the left turn cylinder of the first axle is unloaded and its rod chamber is filled with oil, while the rodless chamber of the right turn cylinder of the first axle is filled with oil and its rod chamber is unloaded. The hydraulic oil flowing out of the two sets of unloaded chambers flows to the first shuttle valve. First, the first shuttle valve is activated to block the oil inlet connecting the rod chamber of the left turn cylinder of the first axle and the rodless chamber of the right turn cylinder of the first axle. Then, the hydraulic oil flowing out of the two sets of unloaded chambers is filled into the P port of the first proportional directional valve through the pressure compensation port of the first pressure compensator to supplement the right turn pressure of the first axle.

[0071] 3.2) Second axle steering pressure compensation;

[0072] When the AGV performs a left turn on the second axle, the rod chamber of the left turn cylinder of the second axle is unloaded and its rodless chamber is filled with oil, while the rod chamber of the right turn cylinder of the second axle is filled with oil and its rodless chamber is unloaded. The hydraulic oil flowing out of the two sets of unloaded chambers flows to the second shuttle valve. First, the second shuttle valve actuates to block the oil inlet connecting the rodless chamber of the left turn cylinder of the second axle and the rod chamber of the right turn cylinder of the second axle. Then, the hydraulic oil flowing out of the two sets of unloaded chambers is filled into the P port of the second proportional directional valve through the pressure compensation port of the second pressure compensator to supplement the left turn pressure of the second axle.

[0073] When the AGV performs a right turn on the second axle, the rodless chamber of the left steering cylinder of the second axle is unloaded and its rod chamber is filled with oil, while the rodless chamber of the right steering cylinder of the second axle is filled with oil and its rod chamber is unloaded. The hydraulic oil flowing out of the two unloading chambers flows to the second shuttle valve. First, the second shuttle valve actuates to block the oil inlet connecting the rod chamber of the left steering cylinder of the second axle and the rodless chamber of the right steering cylinder of the second axle. Then, the hydraulic oil flowing out of the two unloading chambers is filled into the P port of the second proportional directional valve through the pressure compensation port of the second pressure compensator to supplement the right steering pressure of the second axle.

[0074] 3.3) Energy accumulator replenishment;

[0075] If the steering pressure compensation of the first or second axle still fails to meet the steering action requirements and the pressure at both ends of the high-pressure ball valve is lower than the pressure of the accumulator, oil is injected into the pipeline from the accumulator to supplement the pressure.

[0076] Once the system pressure reaches the steering action requirements, replenish the accumulator with hydraulic oil.

[0077] Furthermore, stage 4) includes:

[0078] When the oil temperature is higher than the system's preset temperature range, the AGV should not run and / or turn; the whole machine controller sends a command to the motor to execute the high-speed pressurization mode, and the cooler performs cooling and temperature reduction work; at the same time, all solenoid valves of the hydraulic system are de-energized, and the hydraulic oil flows to the cooler through two return oil lines, and after being cooled by the cooler, it flows back to the hydraulic oil tank until the oil temperature is lower than the system's preset third threshold, at which point the AGV resumes normal operation and the cooler stops working;

[0079] When the oil temperature is higher than the optimal operating temperature range of the hydraulic oil, if there is a need for steering, steering will be performed; if there is no need for steering, the whole machine controller will send a command to the motor to execute the high-speed pressurization mode, and the cooler will perform cooling and temperature reduction work; until the oil temperature is lower than the fourth threshold preset by the system, the motor enters the low-speed circulation operation mode, and the cooler stops working.

[0080] When the oil temperature is below the operating temperature range, the AGV should not run and / or turn; the whole machine controller sends a command to the motor to execute the high-speed pressurization mode, and the hydraulic oil circulates rapidly to generate friction and increase the temperature during the flow; at the same time, all solenoid valves of the hydraulic system should not be energized, and the hydraulic oil flows back to the hydraulic oil tank through two return oil lines until the oil temperature is higher than the optimal operating temperature range of the hydraulic oil, at which point the motor enters the low-speed circulation mode.

[0081] Furthermore, stage 5) includes:

[0082] When the second and first solenoid ball valves are de-energized, the inlet and outlet oil lines are connected; the battery stops running and the hydraulic pump stops pumping oil; the hydraulic oil inside the first and second proportional directional valves flows back into the hydraulic return oil line and cooler through their respective T ports, and is filtered by the return oil filter and returned to the hydraulic oil tank.

[0083] If the pressure inside the accumulator is higher than the system pressure, the hydraulic oil inside will flow out and pass through the second solenoid ball valve, cooler, and then be filtered by the return oil filter back to the hydraulic oil tank.

[0084] In summary, this application has the following beneficial effects and advantages compared with the prior art;

[0085] 1. This application can continuously maintain the internal pressure of the system through the accumulator and pressure compensator, thereby effectively ensuring the effective and smooth supply of the pressure required for vehicle steering, with a short and timely response time.

[0086] 2. This application ensures continuous circulation of hydraulic oil through temperature control and motor speed mode switching, thereby maintaining smooth switching between high-speed pressurization mode and low-speed circulation mode. This ensures the optimal viscosity of the hydraulic oil, preventing the hydraulic oil from becoming too thick due to low temperature, which could prevent steering or cause steering jamming. It also prevents the seals from aging, deforming, and losing elasticity due to excessive temperature, which could lead to oil leakage and hydraulic system failure. Attached Figure Description

[0087] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. Some specific embodiments of this application will be described in detail below with reference to the accompanying drawings in an exemplary and non-limiting manner. The same reference numerals in the drawings designate the same or similar parts or components. It should be understood by those skilled in the art that these drawings are not necessarily drawn to scale.

[0088] Figure 1 This is a block diagram of the hydraulic pump station module structure of the steering system;

[0089] Figure 2 This is a block diagram of the steering system's action execution module structure; Detailed Implementation

[0090] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions will be clearly and completely described below in conjunction with the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0091] like Figure 1 and Figure 2 As shown, this application proposes a steering system for a bridge-type heavy-duty AGV. The system includes a whole machine controller, a hydraulic pump station module that is connected by pipelines to realize hydraulic oil circulation, and an action execution module, which is implemented by the whole machine controller for data acquisition and command issuance.

[0092] The overall controller is used to receive data detection signals and send control commands;

[0093] The hydraulic pump station module is composed of the following components connected together:

[0094] Hydraulic oil tank 1 is used to store hydraulic oil running in the overall circulation pipeline. For example, 46# wear-resistant hydraulic oil can be used. Its working temperature is -10° to 80°, and its optimal operating temperature is 40 to 60°.

[0095] Temperature sensor 2 is installed at the bottom of hydraulic oil tank 1 to detect the temperature of hydraulic oil. Its detection rod extends into the oil tank and its temperature detection range is between -40°C and 65°C.

[0096] The level sensor 3 is installed on the top of the hydraulic oil tank 1 to detect the level of the hydraulic oil, and its detection rod extends into the interior of the tank.

[0097] The return oil filter 4 is used to filter impurities in the hydraulic oil in the return oil pipeline. Its inlet is connected to the outlet of the cooler 5, and its outlet is connected to the return oil port of the hydraulic oil tank 1.

[0098] Cooler 5 is used to cool hydraulic oil. Its outlet is connected to the inlet of return oil filter 4. Its inlet is connected to the outlet of the first solenoid ball valve 11, the outlet of the first relief valve 12, and the return oil port 40 of the pump station.

[0099] Motor 6 is used to provide power for the hydraulic oil circulating within the overall hydraulic pump station module. Its output end drives the mechanical bushing connected to the hydraulic pump 7. Motor 6 has two speed modes: a high-speed pressurization mode with a working frequency of 1600r / min and a low-speed circulation mode with a working frequency of 600r / min. Through these two working modes, the continuous flow of hydraulic oil can be controlled while maintaining good viscosity and temperature.

[0100] Hydraulic pump 7 is used to draw hydraulic oil from hydraulic oil tank 1 and provide pressure for the hydraulic oil circulation. Its oil inlet is connected to the oil outlet of hydraulic oil tank 1, and its oil outlet is connected to the oil inlet of oil filter 9.

[0101] Oil filter 9 is used to filter impurities in hydraulic oil in the oil outlet pipeline. Its oil inlet is connected to the oil outlet of hydraulic pump 7, and its oil inlet is connected to the oil inlet of first solenoid ball valve 11, the oil inlet of first relief valve 12, and the oil outlet 30 of pump station respectively.

[0102] The first solenoid ball valve 11 is controlled by the overall controller through the on / off state of its electromagnet DT1 to regulate the working state of the valve. It is used to realize the circulation of hydraulic oil in a small circulation cooling mode, thereby ensuring that the hydraulic oil maintains an appropriate oil temperature and viscosity. The oil inlet of the first solenoid ball valve 11 is connected to the oil inlet of the first relief valve 12, the oil outlet of the oil filter 9, and the oil outlet of the pump station 30, respectively. Its oil outlet is connected to the oil outlet of the first relief valve 12, the oil inlet of the return oil filter 4, and the return oil outlet of the pump station 40, respectively.

[0103] The first relief valve 12 is used to monitor the oil pressure of the overall hydraulic pump station module to prevent failures such as oil leakage and pipe bursting caused by excessive pressure. The oil inlet of the first relief valve 12 is connected to the oil inlet of the first solenoid ball valve 11, the oil outlet of the oil filter 9 and the oil outlet 30 of the pump station, respectively. Its oil outlet is connected to the oil outlet of the first solenoid ball valve 11, the oil inlet of the return oil filter 4 and the return oil outlet 40 of the pump station, respectively.

[0104] The level gauge 8 is installed on the side of the hydraulic oil tank 1 and is connected to the inside of the tank. It is used for manual observation of the oil level in the tank.

[0105] The pump station outlet 30 is connected to the module inlet 50 to supply hydraulic oil to the overall actuator module;

[0106] The pump station return port 40 is connected to the module return port 60 to deliver hydraulic oil back to the hydraulic oil tank 1;

[0107] The execution action module is composed of the following connected components:

[0108] The first one-way valve 28 has its inlet connected to the module inlet 50, and its outlet connected to the high-pressure ball valve 15, the inlet of the first pressure compensator 22, the inlet of the second pressure compensator 19, and the inlet of the second solenoid ball valve 16, respectively, so as to ensure that the oil inlet pipeline of the action module has a one-way conduction function and prevent hydraulic oil from flowing back through the oil inlet pipeline.

[0109] The high-pressure ball valve 15 has two interfaces that determine the direction of hydraulic oil flow based on the pressure at both ends. Each interface can be used as an oil inlet or an oil outlet. One end interface is connected to the oil inlet of the first pressure compensator 22, the oil inlet of the second pressure compensator 19, the oil inlet of the second solenoid ball valve 16, and the oil outlet of the first check valve 28, respectively. The other end interface is connected to the oil outlet of the accumulator 10, thereby ensuring the oil storage capacity of the accumulator 10 while controlling the accumulator 10 to supply hydraulic oil to the hydraulic circuit of the overall action module.

[0110] Accumulator 10 is used to store hydraulic oil and replenish hydraulic oil according to the actual oil pressure of the hydraulic pipeline. Its oil outlet is connected to high-pressure ball valve 15.

[0111] The second solenoid ball valve 16 is controlled by the overall controller through the opening and closing of its solenoid DT16 to regulate the working state of the valve. It is used to disconnect the oil circuit when the overall execution module is in normal operation to ensure the pressure of the oil inlet pipeline, and to release pressure when the overall execution module is in a stopped state to ensure that the hydraulic oil stored in the accumulator 10 flows back to the hydraulic oil tank 1. Its oil inlet is connected to the oil inlet of the high-pressure ball valve 15, the oil inlet of the first pressure compensator 22, the oil inlet of the second pressure compensator 19, and the oil outlet of the first check valve 28. Its oil outlet is connected to the oil outlet of the second check valve 17 and the module return oil port 60.

[0112] Pressure sensor 14 is used to detect the hydraulic circuit pressure of the overall execution module and feed it back to the whole machine controller. It is installed between the oil inlet of the second solenoid ball valve 16 and the oil outlet of the first check valve 28.

[0113] Pressure gauge 13 is used to detect the hydraulic circuit pressure of the overall actuator module. It is installed between the oil inlet of the second solenoid ball valve 16 and the oil outlet of the first check valve 28.

[0114] The first pressure compensator 22 is used to collect the hydraulic oil returning from the first shuttle valve 21 and supply it to the first proportional directional valve 23 to quickly respond to the steering action; its oil inlet is connected to the oil inlet of the high-pressure ball valve 15, the oil inlet of the second pressure compensator 19, the oil inlet of the second solenoid ball valve 16, and the oil outlet of the first check valve 28, respectively; its oil outlet is connected to the P port of the first proportional directional valve 23; and its pressure compensation port is connected to the oil outlet of the first shuttle valve 21.

[0115] The second pressure compensator 19 is used to collect the hydraulic oil returning from the second shuttle valve 18 and supply it to the second proportional directional valve 20 to quickly respond to the steering action; its oil inlet is connected to the oil inlet of the high-pressure ball valve 15, the oil inlet of the first pressure compensator 19, the oil inlet of the second solenoid ball valve 16, and the oil outlet of the first check valve 28, respectively; its oil outlet is connected to the P port of the second proportional directional valve 20; and its pressure compensation port is connected to the oil outlet of the second shuttle valve 18.

[0116] The first shuttle valve 21 is used to collect hydraulic oil from the return ports of the left steering cylinder 24 and the right steering cylinder 25 of the first axle and supply it to the first pressure compensator 22 for use in the next steering action; it has two oil inlets and one oil outlet. When oil enters one oil inlet, the other oil inlet is blocked; its oil outlet is connected to the pressure compensation port of the first pressure compensator 22, and its two oil inlets are connected to the A port and the B port of the first proportional directional valve 23, respectively.

[0117] The second shuttle valve 18 collects hydraulic oil from the return ports of the left steering cylinder 26 and the right steering cylinder 27 of the second axle and supplies it to the second pressure compensator 19 for use in the next steering action. It has two inlets and one outlet. When oil is entering through one inlet, the other inlet is blocked. Its outlet is connected to the pressure compensation port of the second pressure compensator 19, and its two inlets are connected to the A port and the B port of the second proportional directional valve 20, respectively.

[0118] The first proportional directional valve 23 is energized and its opening degree is adjusted by the overall controller through the on / off switching of its electromagnets DT5 and DT6. It has four oil circuit interfaces: P, T, A, and B. It has two reversing modes: the first mode is that the P port is connected to the A port, and the connection between the B port and the T port is controlled by the electromagnet DT6; the second mode is that the P port is connected to the B port, and the connection between the A port and the T port is controlled by the electromagnet DT5. Its P port is connected to the oil outlet of the first pressure compensator 22, its T port is connected to the T port of the second proportional directional valve 20 and the oil inlet of the second check valve 17, its A port is connected to one of the oil inlets of the first shuttle valve 21, the rod chamber of the left steering cylinder 24 and the rodless chamber of the right steering cylinder 25, and its B port is connected to the other oil inlet of the first shuttle valve 21, the rodless chamber of the left steering cylinder 24 and the rod chamber of the right steering cylinder 25.

[0119] The second proportional directional valve 20 is energized and its opening degree is adjusted by the overall controller through the on / off switching of its electromagnets DT7 and DT8. It has four oil circuit interfaces: P, T, A, and B. It has two reversing modes: the first mode is that the P port is connected to the A port, and the connection between the B port and the T port is controlled by the electromagnet DT8; the second mode is that the P port is connected to the B port, and the connection between the A port and the T port is controlled by the electromagnet DT7. Its P port is connected to the oil outlet of the second pressure compensator 19, its T port is connected to the T port of the first proportional directional valve 23 and the oil inlet of the second check valve 17, its A port is connected to one of the oil inlets of the second shuttle valve 18, the rod chamber of the left steering cylinder 26 of the second bridge and the rodless chamber of the right steering cylinder 27 of the second bridge, and its B port is connected to the other oil inlet of the second shuttle valve 18, the rodless chamber of the left steering cylinder 26 of the second bridge and the rod chamber of the right steering cylinder 27 of the second bridge.

[0120] The left steering cylinder 24 of the first axle is installed on the left side of the first axle and is used to achieve left and right turns by controlling the oil inlet and outlet of its two oil chambers. Its rod chamber is connected to port A of the first proportional directional valve 23, the rodless chamber of the right steering cylinder 25 of the first axle, and one of the oil inlets of the first shuttle valve 21. Its rodless chamber is connected to port B of the first proportional directional valve 23, the rod chamber of the right steering cylinder 25 of the first axle, and the other oil inlet of the first shuttle valve 21.

[0121] The right steering cylinder 25 of the first axle is installed on the right side of the first axle and is used to achieve left and right turns by controlling the oil inlet and outlet of its two oil chambers. Its rod chamber is connected to port B of the first proportional directional valve 23, the rodless chamber of the left steering cylinder 24 of the first axle, and one of the oil inlets of the first shuttle valve 21. Its rodless chamber is connected to port A of the first proportional directional valve 23, the rod chamber of the left steering cylinder 24 of the first axle, and the other oil inlet of the first shuttle valve 21.

[0122] The left steering cylinder 26 of the second axle is installed on the left side of the second axle and is used to achieve left and right turns by controlling the oil inlet and outlet of its two oil chambers. Its rod chamber is connected to port A of the second proportional directional valve 20, the rodless chamber of the right steering cylinder 27 of the second axle, and one of the oil inlets of the second shuttle valve 18. Its rodless chamber is connected to port B of the second proportional directional valve 20, the rod chamber of the right steering cylinder 27 of the second axle, and the other oil inlet of the second shuttle valve 18.

[0123] The right steering cylinder 27 of the second axle is installed on the right side of the second axle and is used to achieve left and right turns by controlling the oil inlet and outlet of its two oil chambers. Its rod chamber is connected to port B of the second proportional directional valve 20, the rodless chamber of the left steering cylinder 26 of the second axle, and one of the oil inlets of the second shuttle valve 18. Its rodless chamber is connected to port A of the second proportional directional valve 20, the rod chamber of the left steering cylinder 26 of the second axle, and the other oil inlet of the second shuttle valve 18.

[0124] The second check valve 17 has its oil inlet connected to the T port of the first proportional directional valve 23 and the T port of the second proportional directional valve 20, respectively, and its oil outlet connected to the module return oil port 60 and the oil outlet of the second solenoid ball valve 16, respectively.

[0125] The module oil inlet 50 is used to supply hydraulic oil to the overall action module;

[0126] The module return port 60 is used to transport the hydraulic oil in the return oil line back to the hydraulic oil tank 1 through the cooler 5.

[0127] Based on the aforementioned steering system of a bridge-type heavy-duty AGV, this application proposes a steering method for a bridge-type heavy-duty AGV that includes the following control phase:

[0128] 1) Startup initialization;

[0129] After the AGV is powered on and started, the pressure sensor 14 detects and feeds back the hydraulic system pressure to the whole machine controller;

[0130] If the oil pressure is less than the first threshold preset by the system, the whole machine controller sends a command to the motor 6 to execute the high-speed pressure mode. At the same time, the electromagnet DT1 of the first electromagnetic ball valve 11 is energized, and the electromagnet DT16 of the second electromagnetic ball valve 16 is energized. Both pressure relief circuits in the hydraulic pump station module and the action module are closed. The hydraulic oil is drawn by the hydraulic pump 7 and input to the oil outlet filter 9 for filtration before flowing into the action module.

[0131] When the oil pressure is higher than the preset pressure of the high-pressure ball valve 15, some hydraulic oil is charged into the accumulator 10;

[0132] If the accumulator 10 is fully charged and the oil pressure is still not less than the preset pressure value of the high-pressure ball valve 15, the pressure sensor 14 will feed back the pressure value to the vehicle controller, thereby controlling the motor 6 to enter the low-speed pressurization mode, and at the same time, the excess pressure will be released through the overflow valve 12.

[0133] Subsequently, the electromagnet DT1 of the first solenoid ball valve 11 is de-energized. At this time, the hydraulic oil flows through the first solenoid ball valve 11 to the cooler 5, and then returns to the hydraulic oil tank 1 after being filtered by the return oil filter 4. In this cycle, the hydraulic oil can continuously maintain the optimal viscosity.

[0134] In addition, a second check valve 17 is provided in the return oil line of the action module to guide the return oil line in one direction, and a first check valve 28 is provided in the inlet oil line to guide the inlet oil line in one direction, so as to prevent the hydraulic oil entering the action module from directly entering the return oil line and causing damage to the system.

[0135] 4) Steering control;

[0136] It includes three types of state control: vehicle steering, single-axle steering, and diagonal operation. Specifically,

[0137] 2.1) The entire vehicle turns to the left;

[0138] The whole machine controller sends a command to the motor 6 to execute the high-speed pressurization mode. The electromagnet DT1 of the first solenoid ball valve 11 is energized, which controls the hydraulic oil to stop flowing back into the return oil pipeline. The hydraulic oil is drawn by the hydraulic pump 7 and input to the oil outlet filter 9 for filtration before flowing into the action module.

[0139] When the electromagnet DT5 of the first proportional directional valve 23 is energized, its P port is connected to its B port, and hydraulic oil flows to the rodless chamber of the left steering cylinder 24 of the first axle and the rod chamber of the right steering cylinder 25 of the first axle, so that the wheels of the first axle vehicle turn to the left; at the same time, when the electromagnet DT8 of the second proportional directional valve 20 is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder 26 of the second axle and the rodless chamber of the right steering cylinder 27 of the second axle, so that the wheels of the second axle vehicle turn to the right, thus realizing the left steering control of the vehicle;

[0140] 2.2) The entire vehicle turns right;

[0141] When the AGV needs to turn right, the following action control process is executed:

[0142] The whole machine controller sends a command to the motor 6 to execute the high-speed pressurization mode. The electromagnet DT1 of the first solenoid ball valve 11 is energized, which controls the hydraulic oil to stop flowing back into the return oil pipeline. The hydraulic oil is drawn by the hydraulic pump 7 and input to the oil outlet filter 9 for filtration before flowing into the action module.

[0143] When the electromagnet DT6 of the first proportional directional valve 23 is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder 24 of the first axle and the rodless chamber of the right steering cylinder 25 of the first axle, so that the wheels of the first axle vehicle turn to the right; at the same time, when the electromagnet DT7 of the second proportional directional valve 20 is energized, its P port is connected to its B port, and hydraulic oil flows to the rodless chamber of the left steering cylinder 26 of the second axle and the rod chamber of the right steering cylinder 27 of the second axle, so that the wheels of the second axle vehicle turn to the left, thus realizing the right steering control of the vehicle;

[0144] 2.3) Single front axle steering;

[0145] The controller sends a command to motor 6 to execute high-speed pressurization mode, energizing the electromagnet DT1 of the first solenoid ball valve 11.

[0146] The hydraulic oil is controlled to stop flowing back into the return oil line. The hydraulic oil is drawn by the hydraulic pump 7 and input to the oil outlet filter 9 for filtration before flowing into the action module.

[0147] When the electromagnet DT5 of the first proportional directional valve 23 is energized, its P port is connected to its B port, and hydraulic oil flows to the rodless chamber of the left steering cylinder 24 of the first axle and the rod chamber of the right steering cylinder 25 of the first axle, so that the wheels of the first axle vehicle turn to the left; if so, when the electromagnet DT6 of the first proportional directional valve 23 is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder 24 of the first axle and the rodless chamber of the right steering cylinder 25 of the first axle, so that the wheels of the first axle vehicle turn to the right.

[0148] 2.4) Single rear axle steering;

[0149] The whole machine controller sends a command to the motor 6 to execute the high-speed pressurization mode. The electromagnet DT1 of the first solenoid ball valve 11 is energized, which controls the hydraulic oil to stop flowing back into the return oil pipeline. The hydraulic oil is drawn by the hydraulic pump 7 and input to the oil outlet filter 9 for filtration before flowing into the action module.

[0150] When the electromagnet DT8 of the second proportional directional valve 20 is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder 26 of the second axle and the rodless chamber of the right steering cylinder 27 of the second axle, so that the wheels of the second axle vehicle turn to the right; or, when the electromagnet DT7 of the second proportional directional valve 20 is energized, its P port is connected to its B port, and hydraulic oil flows to the rodless chamber of the left steering cylinder 26 of the second axle and the rod chamber of the right steering cylinder 27 of the second axle, so that the wheels of the second axle vehicle turn to the left.

[0151] 2.5) Moving diagonally to the right;

[0152] The overall controller sends a command to motor 6 to execute the high-speed pressurization mode. The solenoid DT1 of the first solenoid ball valve 11 is energized, controlling the hydraulic oil to stop flowing back into the return oil line. The hydraulic oil is drawn by the hydraulic pump 7 and input to the outlet oil filter 9 for filtration before flowing into the action module. The solenoid DT6 of the first proportional directional valve 23 is energized, and its P port is connected to its A port. The hydraulic oil flows to the rod chamber of the left steering cylinder 24 of the first axle and the rodless chamber of the right steering cylinder 25 of the first axle, realizing the rightward rotation of the wheels of the first axle vehicle. At the same time, the solenoid DT8 of the second proportional directional valve 20 is energized, and its P port is connected to its A port. The hydraulic oil flows to the rod chamber of the left steering cylinder 26 of the second axle and the rodless chamber of the right steering cylinder 27 of the second axle, realizing the rightward rotation of the wheels of the second axle vehicle. Thus, the vehicle is diagonally driven to the right.

[0153] 2.6) Moving diagonally to the left;

[0154] The overall controller sends a command to motor 6 to execute the high-speed pressurization mode. The solenoid DT1 of the first solenoid ball valve 11 is energized, controlling the hydraulic oil to stop flowing back into the return oil line. The hydraulic oil is drawn by the hydraulic pump 7 and input to the oil filter 9 for filtration before flowing into the action module. The solenoid DT5 of the first proportional directional valve 23 is energized, and its P port is connected to its B port. The hydraulic oil flows to the rodless chamber of the left steering cylinder 24 of the first axle and the rod chamber of the right steering cylinder 25 of the first axle, realizing the left rotation of the wheels of the first axle vehicle. At the same time, the solenoid DT7 of the second proportional directional valve 20 is energized, and its P port is connected to its B port. The hydraulic oil flows to the rodless chamber of the left steering cylinder 26 of the second axle and the rod chamber of the right steering cylinder 27 of the second axle, realizing the left rotation of the wheels of the second axle vehicle. Thus, the vehicle can move diagonally to the left.

[0155] 5) Stress compensation;

[0156] During the aforementioned steering control phase, if the pressure sensor 14 detects that the oil pressure is less than the system's preset second threshold (e.g., when the pressure cannot be met in time due to the AGV's steering requirements being too fast), the overall controller determines the action type and implements the following pressure compensation process:

[0157] 3.1) Steering pressure compensation for the axle;

[0158] When the AGV performs a left turn on one axle, the rod chamber of the left turn cylinder 24 is unloaded and its rodless chamber is filled with oil, while the rod chamber of the right turn cylinder 25 is filled with oil and its rodless chamber is unloaded. The hydraulic oil flowing out of the two sets of unloaded chambers flows to the first shuttle valve 21. First, the first shuttle valve 21 is activated to block the oil inlet connecting the rodless chamber of the left turn cylinder 24 and the rod chamber of the right turn cylinder 25. Then, the hydraulic oil flowing out of the two sets of unloaded chambers is filled into the P port of the first proportional directional valve 23 through the pressure compensation port of the first pressure compensator 22 to supplement the left turn pressure of the first axle.

[0159] When the AGV performs a right turn on one axle, the rodless chamber of the left turn cylinder 24 of the first axle is unloaded and its rod chamber is filled with oil, while the rodless chamber of the right turn cylinder 25 of the first axle is filled with oil and its rod chamber is unloaded. The hydraulic oil flowing out of the two sets of unloaded chambers flows to the first shuttle valve 21. First, the first shuttle valve 21 is activated to block the oil inlet connecting the rod chamber of the left turn cylinder 24 of the first axle and the rodless chamber of the right turn cylinder 25 of the first axle. Then, the hydraulic oil flowing out of the two sets of unloaded chambers is filled into the P port of the first proportional directional valve 23 through the pressure compensation port of the first pressure compensator 22 to supplement the right turn pressure of the first axle.

[0160] 3.2) Second axle steering pressure compensation;

[0161] When the AGV performs a left turn on the second axle, the rod chamber of the left turn cylinder 26 of the second axle is unloaded and its rodless chamber is filled with oil, while the rod chamber of the right turn cylinder 27 of the second axle is filled with oil and its rodless chamber is unloaded. The hydraulic oil flowing out of the two sets of unloaded oil chambers flows to the second shuttle valve 18. First, the second shuttle valve 18 is activated to block the oil inlet connecting the rodless chamber of the left turn cylinder 26 of the second axle and the rod chamber of the right turn cylinder 27 of the second axle. Then, the hydraulic oil flowing out of the two sets of unloaded oil chambers is filled into the P port of the second proportional directional valve 20 through the pressure compensation port of the second pressure compensator 19 to supplement the left turn pressure of the second axle.

[0162] When the AGV performs a right turn on the second axle, the rodless chamber of the left-hand steering cylinder 26 of the second axle is unloaded and its rod chamber is filled with oil, while the rodless chamber of the right-hand steering cylinder 27 of the second axle is filled with oil and its rod chamber is unloaded. The hydraulic oil flowing out of the two sets of unloading chambers flows to the second shuttle valve 18. First, the second shuttle valve 18 is activated to block the oil inlet connecting the rod chamber of the left-hand steering cylinder 26 of the second axle and the rodless chamber of the right-hand steering cylinder 27 of the second axle. Then, the hydraulic oil flowing out of the two sets of unloading chambers is filled into the P port of the second proportional directional valve 20 through the pressure compensation port of the second pressure compensator 19 to supplement the right-hand steering pressure of the second axle.

[0163] 3.3) Energy accumulator replenishment;

[0164] If the steering pressure compensation of the first or second axle still fails to meet the steering action requirements and the pressure at both ends of the high-pressure ball valve 15 is lower than the pressure of the accumulator 10, oil is injected into the pipeline from the accumulator 10 to supplement the pressure.

[0165] Once the system pressure reaches the steering action requirements, hydraulic oil is replenished to the accumulator 10.

[0166] 4) Oil temperature adjustment;

[0167] During the aforementioned steering control phase, the temperature sensor 2 continuously monitors the oil temperature in the hydraulic oil tank 1.

[0168] When the oil temperature is higher than the system's preset temperature range (e.g., 80°C), the AGV should not run and / or turn; the whole machine controller sends a command to motor 6 to execute high-speed pressurization mode, and cooler 5 performs cooling work; at the same time, all solenoid valves of the hydraulic system are de-energized, and hydraulic oil flows to cooler 5 through two return oil lines, and after being cooled by cooler 5, it flows back to hydraulic oil tank 1 until the oil temperature is lower than the system's preset third threshold (e.g., 60°C), the AGV resumes normal operation, and cooler 5 stops working;

[0169] When the oil temperature is higher than the optimal operating temperature range of hydraulic oil (e.g., 60°), if there is a need for steering, steering will be performed. If there is no need for steering, the whole machine controller sends a command to motor 6 to execute high-speed pressurization mode, and cooler 5 performs cooling and temperature reduction work. Until the oil temperature is lower than the fourth threshold preset by the system (e.g., 50°), motor 6 enters low-speed circulation mode, and cooler 5 stops working.

[0170] When the oil temperature is below the operating temperature range (e.g., below -10°C), the AGV should not run and / or turn; the whole machine controller sends a command to motor 6 to execute the high-speed pressurization mode, the hydraulic oil circulates rapidly to generate friction and increase temperature during the flow; at the same time, all solenoid valves of the hydraulic system are not energized, and the hydraulic oil flows back to the hydraulic oil tank 1 through two return oil lines until the oil temperature is above the optimal operating temperature range of the hydraulic oil (e.g., 60°C), motor 6 enters the low-speed circulation operation mode;

[0171] By controlling the temperature as described above, the hydraulic oil can maintain its optimal viscosity. This prevents risks such as leakage due to aging, deformation, or loss of elasticity of seals caused by excessively high temperatures, and also prevents excessively low viscosity caused by excessively low temperatures, which could lead to difficulties in oil pump suction, potentially resulting in cavitation, pump wear or damage, decreased system efficiency, and increased energy consumption.

[0172] 5) Depressurize;

[0173] When the AGV stops running, the hydraulic system automatically depressurizes;

[0174] At this time, the second solenoid ball valve 16 and the first solenoid ball valve 11 are de-energized, and the oil inlet pipe and the oil outlet pipe are connected; the battery 6 stops running, and the hydraulic pump 7 stops pumping oil; the hydraulic oil inside the first proportional directional valve 23 and the second proportional directional valve 20 flows back into the hydraulic return pipe and cooler 5 through their respective T ports, and is filtered by the return oil filter 4 and returned to the hydraulic oil tank 1.

[0175] If the pressure inside the accumulator 10 is higher than the system pressure, the hydraulic oil inside will flow out and pass through the second solenoid ball valve 16, the cooler 5, and then be filtered by the return oil filter 4 before returning to the hydraulic oil tank 1.

[0176] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of this application; at the same time, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. The content of this specification should not be construed as a limitation of this application.

Claims

1. A steering system for a bridge-type heavy-duty AGV, characterized in that, It includes a whole machine controller, a hydraulic pump station module connected by pipelines to realize the circulation of hydraulic oil, and an action execution module; The overall controller is used to receive data detection signals and send control commands; The hydraulic pump station module is composed of the following components connected together: Hydraulic oil tank, used to store hydraulic oil running in the overall circulation pipeline; A temperature sensor is installed at the bottom of the hydraulic oil tank to detect the temperature of the hydraulic oil. The return oil filter is used to filter impurities in the hydraulic oil in the return oil pipeline. Its inlet is connected to the outlet of the cooler, and its outlet is connected to the return oil port of the hydraulic oil tank. The cooler is used to cool the hydraulic oil. Its outlet is connected to the inlet of the return oil filter. Its inlet is connected to the outlet of the first solenoid ball valve, the outlet of the first relief valve, and the return oil port of the pump station. The motor is used to provide power for the hydraulic oil circulating within the overall hydraulic pump station module, and its output end drives the mechanical bushing connected to the hydraulic pump. A hydraulic pump is used to draw hydraulic oil from a hydraulic oil tank and provide pressure for the hydraulic oil circulation. Its inlet is connected to the outlet of the hydraulic oil tank, and its outlet is connected to the inlet of the oil filter. The oil outlet filter is used to filter impurities in the hydraulic oil of the oil outlet pipeline. Its oil inlet is connected to the oil outlet of the hydraulic pump, and its oil inlet is connected to the oil inlet of the first solenoid ball valve, the oil inlet of the first relief valve, and the oil outlet of the pump station. The first solenoid ball valve is controlled by the whole machine controller through the on and off of its electromagnet DT1 to adjust the working state of the valve; the oil inlet of the first solenoid ball valve is connected to the oil inlet of the first overflow valve, the oil outlet of the oil filter and the oil outlet of the pump station respectively, and its oil outlet is connected to the oil outlet of the first overflow valve, the oil inlet of the return oil filter and the return oil outlet of the pump station respectively. The first relief valve is used to monitor the oil pressure of the overall hydraulic pump station module. The oil inlet of the first relief valve is connected to the oil inlet of the first solenoid ball valve, the oil outlet of the oil filter, and the oil outlet of the pump station, respectively. Its oil outlet is connected to the oil outlet of the first solenoid ball valve, the oil inlet of the return oil filter, and the return oil outlet of the pump station, respectively. The pump station's oil outlet is connected to the module's oil inlet to supply hydraulic oil to the overall actuator module; The pump station return port is connected to the module return port to deliver hydraulic oil back to the hydraulic oil tank 1.

2. The steering system of the bridge-type heavy-duty AGV according to claim 1, characterized in that, The execution action module is composed of the following connected components: The first check valve has its inlet connected to the module inlet, and its outlet connected to the high-pressure ball valve, the inlet of the first pressure compensator, the inlet of the second pressure compensator, and the inlet of the second solenoid ball valve, respectively. The high-pressure ball valve has two interfaces that determine the direction of hydraulic oil flow based on the pressure at both ends. Each interface can be used as an oil inlet or an oil outlet. One end interface is connected to the oil inlet of the first pressure compensator, the oil inlet of the second pressure compensator, the oil inlet of the second solenoid ball valve, and the oil outlet of the first check valve, respectively. The other end interface is connected to the oil outlet of the accumulator. The accumulator is used to store hydraulic oil and replenish hydraulic oil according to the actual oil pressure of the hydraulic pipeline. Its oil outlet is connected to the high-pressure ball valve 15. The second solenoid ball valve is controlled by the whole machine controller through the on / off state of its solenoid DT16 to regulate the working state of the valve; its oil inlet is connected to the oil inlet of the high pressure ball valve, the oil inlet of the first pressure compensator, the oil inlet of the second pressure compensator, and the oil outlet of the first check valve, respectively; its oil outlet is connected to the oil outlet of the second check valve and the module return oil port, respectively. A pressure sensor, used to detect the hydraulic circuit pressure of the overall actuator module and feed it back to the whole machine controller, is installed between the oil inlet of the second solenoid ball valve and the oil outlet of the first check valve. A pressure gauge is used to detect the hydraulic circuit pressure of the overall actuator module. It is installed between the oil inlet of the second solenoid ball valve and the oil outlet of the first check valve. The first pressure compensator is used to collect the hydraulic oil returning from the first shuttle valve and supply it to the first proportional directional valve to quickly respond to the steering action; its oil inlet is connected to the oil inlet of the high-pressure ball valve, the oil inlet of the second pressure compensator, the oil inlet of the second solenoid ball valve, and the oil outlet of the first check valve, respectively; its oil outlet is connected to the P port of the first proportional directional valve; and its pressure compensation port is connected to the oil outlet of the first shuttle valve. The second pressure compensator is used to collect the hydraulic oil returning from the second shuttle valve and supply it to the second proportional directional valve to quickly respond to the steering action; its oil inlet is connected to the high-pressure ball valve, the oil inlet of the first pressure compensator, the oil inlet of the second solenoid ball valve, and the oil outlet of the first check valve, respectively; its oil outlet is connected to the P port of the second proportional directional valve; and its pressure compensation port is connected to the oil outlet of the second shuttle valve. The first shuttle valve is used to collect hydraulic oil from the return ports of the left steering cylinder of the first axle and the right steering cylinder of the first axle and supply it to the first pressure compensator. It has two oil inlets and one oil outlet. When oil enters one oil inlet, the other oil inlet is blocked. Its oil outlet is connected to the pressure compensation port of the first pressure compensator, and its two oil inlets are connected to the A port and B port of the first proportional directional valve, respectively. The second shuttle valve collects hydraulic oil from the return ports of the left and right steering cylinders of the second axle and supplies it to the second pressure compensator for use in the next steering action. It has two inlets and one outlet. When oil enters one inlet, the other inlet is blocked. Its outlet is connected to the pressure compensation port of the second pressure compensator, and its two inlets are connected to the A and B ports of the second proportional directional valve, respectively. The first proportional directional valve is energized and its opening degree is adjusted by the overall controller through the on / off switching of its electromagnets DT5 and DT6. It has four oil circuit interfaces: P, T, A, and B. It has two reversing modes: the first mode is that the P port is connected to the A port, and the connection between the B port and the T port is controlled by the electromagnet DT6; the second mode is that the P port is connected to the B port, and the connection between the A port and the T port is controlled by the electromagnet DT5. Its P port is connected to the oil outlet of the first pressure compensator, its T port is connected to the T port of the second proportional directional valve and the oil inlet of the second check valve, its A port is connected to one of the oil inlets of the first shuttle valve, the rod chamber of the left steering cylinder of the first bridge and the rodless chamber of the right steering cylinder of the first bridge, and its B port is connected to the other oil inlet of the first shuttle valve, the rodless chamber of the left steering cylinder of the first bridge and the rod chamber of the right steering cylinder of the first bridge. The second proportional directional valve is energized and its opening degree is adjusted by the overall controller through the on / off switching of its electromagnets DT7 and DT8. It has four oil circuit interfaces: P, T, A, and B. It has two reversing modes: the first mode is that the P port is connected to the A port, and the connection between the B port and the T port is controlled by the electromagnet DT8; the second mode is that the P port is connected to the B port, and the connection between the A port and the T port is controlled by the electromagnet DT7. Its P port is connected to the oil outlet of the second pressure compensator, its T port is connected to the T port of the first proportional directional valve and the oil inlet of the second check valve, its A port is connected to one of the oil inlets of the second shuttle valve, the rod chamber of the left steering cylinder of the second bridge and the rodless chamber of the right steering cylinder of the second bridge, and its B port is connected to the other oil inlet of the second shuttle valve, the rodless chamber of the left steering cylinder of the second bridge and the rod chamber of the right steering cylinder of the second bridge. The left steering cylinder of the first axle is installed on the left side of the first axle and is used to achieve left and right turns by controlling the oil inlet and outlet of its two oil chambers. Its rod chamber is connected to port A of the first proportional directional valve, the rodless chamber of the right steering cylinder of the first axle, and one of the oil inlets of the first shuttle valve. Its rodless chamber is connected to port B of the first proportional directional valve, the rod chamber of the right steering cylinder of the first axle, and the other oil inlet of the first shuttle valve. The right steering cylinder of the first axle is installed on the right side of the first axle and is used to achieve left and right turns by controlling the oil inlet and outlet of its two oil chambers. Its rod chamber is connected to port B of the first proportional directional valve, the rodless chamber of the left steering cylinder of the first axle, and one of the oil inlets of the first shuttle valve. Its rodless chamber is connected to port A of the first proportional directional valve, the rod chamber of the left steering cylinder of the first axle, and the other oil inlet of the first shuttle valve. The left steering cylinder of the second axle is installed on the left side of the second axle and is used to achieve left and right turns by controlling the oil inlet and outlet of its two oil chambers. Its rod chamber is connected to port A of the second proportional directional valve, the rodless chamber of the right steering cylinder of the second axle, and one of the oil inlets of the second shuttle valve. Its rodless chamber is connected to port B of the second proportional directional valve, the rod chamber of the right steering cylinder of the second axle, and the other oil inlet of the second shuttle valve. The right steering cylinder of the second axle is installed on the right side of the second axle and is used to achieve left and right turns by controlling the oil inlet and outlet of its two oil chambers. Its rod chamber is connected to port B of the second proportional directional valve, the rodless chamber of the left steering cylinder of the second axle, and one of the oil inlets of the second shuttle valve. Its rodless chamber is connected to port A of the second proportional directional valve, the rod chamber of the left steering cylinder of the second axle, and the other oil inlet of the second shuttle valve. The second check valve has its inlet connected to the T port of the first proportional directional valve and the T port of the second proportional directional valve, respectively, and its outlet connected to the module return port and the outlet of the second solenoid ball valve, respectively. The module oil inlet is used to supply hydraulic oil to the overall actuator module; The module return port is used to transport the hydraulic oil in the return line back to the hydraulic oil tank through the cooler.

3. A steering method for a bridge-type heavy-duty AGV using the steering system of the bridge-type heavy-duty AGV as described in claim 2, characterized in that, Includes the following stages, 1) Startup initialization; After the AGV is powered on and started, the pressure sensor detects and feeds back the hydraulic system pressure to the whole machine controller; If the oil pressure is less than the first preset threshold of the system, the whole machine controller sends a command to the motor to execute the high-speed pressure mode. At the same time, the solenoid DT1 of the first solenoid ball valve is energized and the solenoid DT16 of the second solenoid ball valve is energized. Both pressure relief circuits in the hydraulic pump station module and the action module are closed. The hydraulic oil is drawn by the hydraulic pump and input to the oil outlet filter for filtration before flowing into the action module. When the oil pressure is higher than the preset pressure of the high-pressure ball valve, some hydraulic oil is charged into the accumulator; Subsequently, the electromagnet DT1 of the first solenoid ball valve is de-energized. At this time, the hydraulic oil flows through the first solenoid ball valve to the cooler, and then returns to the hydraulic oil tank after being filtered by the return oil filter. 2) Steering control; It includes three types of state control: vehicle steering, single-axle steering, and diagonal operation; the whole machine controller sends a command to the motor to execute the high-speed pressurization mode, the electromagnet DT1 of the first solenoid ball valve is energized, and the hydraulic oil is controlled to stop flowing back into the return oil line. The hydraulic oil is drawn by the hydraulic pump and input to the oil outlet filter for filtration before flowing into the action module. 3) Stress compensation; During the aforementioned steering control phase, if the pressure sensor detects that the oil pressure is less than the second threshold preset by the system, the whole machine controller determines the action type and implements the pressure compensation process. 4) Oil temperature adjustment; During the aforementioned steering control phase, the oil temperature in the hydraulic tank is continuously monitored by a temperature sensor. 5) Depressurize; When the AGV stops running, the hydraulic system automatically depressurizes.

4. The steering method for a bridge-type heavy-duty AGV according to claim 3, characterized in that, In stage 1), if the accumulator is fully charged and the oil pressure is still not less than the preset pressure value of the high-pressure ball valve, the pressure sensor will feed back the pressure value to the vehicle controller, thereby controlling the motor to enter the low-speed pressurization mode, and at the same time, the excess pressure will be released through the overflow valve.

5. The steering method for a bridge-type heavy-duty AGV according to claim 3, characterized in that, In stage 1, a second check valve is provided in the return oil line of the action module to unidirectionally guide the return oil line, and a first check valve is provided in the inlet oil line to unidirectionally guide the inlet oil line, so as to prevent the hydraulic oil entering the action module from directly entering the return oil line.

6. The steering method for a bridge-type heavy-duty AGV according to claim 3, characterized in that, Phase 2) includes, 2.1) The entire vehicle turns to the left; When the solenoid DT5 of the first proportional directional valve is energized, its P port is connected to its B port, and hydraulic oil flows to the rodless chamber of the left steering cylinder of the first axle and the rod chamber of the right steering cylinder of the first axle, so that the wheels of the first axle vehicle turn to the left; at the same time, when the solenoid DT8 of the second proportional directional valve is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder of the second axle and the rodless chamber of the right steering cylinder of the second axle, so that the wheels of the second axle vehicle turn to the right, thus realizing the left steering control of the vehicle. 2.2) The entire vehicle turns right; When the solenoid DT6 of the first proportional directional valve is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder of the first axle and the rodless chamber of the right steering cylinder of the first axle, so that the wheels of the first axle vehicle turn to the right; at the same time, when the solenoid DT7 of the second proportional directional valve is energized, its P port is connected to its B port, and hydraulic oil flows to the rodless chamber of the left steering cylinder of the second axle and the rod chamber of the right steering cylinder of the second axle, so that the wheels of the second axle vehicle turn to the left, thus realizing the right steering control of the vehicle. 2.3) Single front axle steering; When the solenoid DT5 of the first proportional directional valve is energized, its P port is connected to its B port, and hydraulic oil flows to the rodless chamber of the left steering cylinder of the first axle and the rod chamber of the right steering cylinder of the first axle, so that the wheels of the first axle vehicle turn to the left; if so, when the solenoid DT6 of the first proportional directional valve is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder of the first axle and the rodless chamber of the right steering cylinder of the first axle, so that the wheels of the first axle vehicle turn to the right. 2.4) Single rear axle steering; When the solenoid DT8 of the second proportional directional valve is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder of the second axle and the rodless chamber of the right steering cylinder of the second axle, so that the wheels of the second axle vehicle turn to the right; or, when the solenoid DT7 of the second proportional directional valve is energized, its P port is connected to its B port, and hydraulic oil flows to the rodless chamber of the left steering cylinder of the second axle and the rod chamber of the right steering cylinder of the second axle, so that the wheels of the second axle vehicle turn to the left. 2.5) Moving diagonally to the right; When the solenoid DT6 of the first proportional directional valve is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder of the first axle and the rodless chamber of the right steering cylinder of the first axle, so that the wheels of the first axle vehicle turn to the right; at the same time, when the solenoid DT8 of the second proportional directional valve is energized, its P port is connected to its A port, and hydraulic oil flows to the rod chamber of the left steering cylinder of the second axle and the rodless chamber of the right steering cylinder of the second axle, so that the wheels of the second axle vehicle turn to the right, thus realizing the rightward diagonal movement of the vehicle; 2.6) Moving diagonally to the left; When the solenoid DT5 of the first proportional directional valve is energized, its P port and B port are connected, and hydraulic oil flows to the rodless chamber of the left steering cylinder of the first axle and the rod chamber of the right steering cylinder of the first axle, thus turning the wheels of the first axle vehicle to the left. At the same time, the solenoid DT7 of the second proportional directional valve is energized, and its P port and B port are connected, and hydraulic oil flows to the rodless chamber of the left steering cylinder of the second axle and the rod chamber of the right steering cylinder of the second axle, thus turning the wheels of the second axle vehicle to the left, thereby realizing the vehicle's diagonal leftward movement.

7. The steering method for a bridge-type heavy-duty AGV according to claim 3, characterized in that, Stage 3) includes, 3.1) Steering pressure compensation for the axle; When the AGV performs a left turn on one axle, the rod chamber of the left turn cylinder of the first axle is unloaded and its rodless chamber is filled with oil, while the rod chamber of the right turn cylinder of the first axle is filled with oil and its rodless chamber is unloaded. The hydraulic oil flowing out of the two sets of unloaded chambers flows to the first shuttle valve. First, the first shuttle valve is activated to block the oil inlet connecting the rodless chamber of the left turn cylinder of the first axle and the rod chamber of the right turn cylinder of the first axle. Then, the hydraulic oil flowing out of the two sets of unloaded chambers is filled into the P port of the first proportional directional valve through the pressure compensation port of the first pressure compensator to supplement the left turn pressure of the first axle. When the AGV performs a right turn on one axle, the rodless chamber of the left turn cylinder of the first axle is unloaded and its rod chamber is filled with oil, while the rodless chamber of the right turn cylinder of the first axle is filled with oil and its rod chamber is unloaded. The hydraulic oil flowing out of the two sets of unloaded chambers flows to the first shuttle valve. First, the first shuttle valve is activated to block the oil inlet connecting the rod chamber of the left turn cylinder of the first axle and the rodless chamber of the right turn cylinder of the first axle. Then, the hydraulic oil flowing out of the two sets of unloaded chambers is filled into the P port of the first proportional directional valve through the pressure compensation port of the first pressure compensator to supplement the right turn pressure of the first axle. 3.2) Second axle steering pressure compensation; When the AGV performs a left turn on the second axle, the rod chamber of the left turn cylinder of the second axle is unloaded and its rodless chamber is filled with oil, while the rod chamber of the right turn cylinder of the second axle is filled with oil and its rodless chamber is unloaded. The hydraulic oil flowing out of the two sets of unloaded chambers flows to the second shuttle valve. First, the second shuttle valve actuates to block the oil inlet connecting the rodless chamber of the left turn cylinder of the second axle and the rod chamber of the right turn cylinder of the second axle. Then, the hydraulic oil flowing out of the two sets of unloaded chambers is filled into the P port of the second proportional directional valve through the pressure compensation port of the second pressure compensator to supplement the left turn pressure of the second axle. When the AGV performs a right turn on the second axle, the rodless chamber of the left steering cylinder of the second axle is unloaded and its rod chamber is filled with oil, while the rodless chamber of the right steering cylinder of the second axle is filled with oil and its rod chamber is unloaded. The hydraulic oil flowing out of the two unloading chambers flows to the second shuttle valve. First, the second shuttle valve actuates to block the oil inlet connecting the rod chamber of the left steering cylinder of the second axle and the rodless chamber of the right steering cylinder of the second axle. Then, the hydraulic oil flowing out of the two unloading chambers is filled into the P port of the second proportional directional valve through the pressure compensation port of the second pressure compensator to supplement the right steering pressure of the second axle. 3.3) Energy accumulator replenishment; If the steering pressure compensation of the first or second axle still fails to meet the steering action requirements and the pressure at both ends of the high-pressure ball valve is lower than the pressure of the accumulator, oil is injected into the pipeline from the accumulator to supplement the pressure. Once the system pressure reaches the steering action requirements, replenish the accumulator with hydraulic oil.

8. The steering method for a bridge-type heavy-duty AGV according to claim 3, characterized in that, Stage 4) includes, When the oil temperature is higher than the system's preset temperature range, the AGV should not run and / or turn; the whole machine controller sends a command to the motor to execute the high-speed pressurization mode, and the cooler performs cooling and temperature reduction work; at the same time, all solenoid valves of the hydraulic system are de-energized, and the hydraulic oil flows to the cooler through two return oil lines, and after being cooled by the cooler, it flows back to the hydraulic oil tank until the oil temperature is lower than the system's preset third threshold, at which point the AGV resumes normal operation and the cooler stops working; When the oil temperature is higher than the optimal operating temperature range of the hydraulic oil, if there is a need for steering, steering will be performed; if there is no need for steering, the whole machine controller will send a command to the motor to execute the high-speed pressurization mode, and the cooler will perform cooling and temperature reduction work; until the oil temperature is lower than the fourth threshold preset by the system, the motor enters the low-speed circulation operation mode, and the cooler stops working. When the oil temperature is below the operating temperature range, the AGV should not run and / or turn; the whole machine controller sends a command to the motor to execute the high-speed pressurization mode, and the hydraulic oil circulates rapidly to generate friction and increase the temperature during the flow; at the same time, all solenoid valves of the hydraulic system should not be energized, and the hydraulic oil flows back to the hydraulic oil tank through two return oil lines until the oil temperature is higher than the optimal operating temperature range of the hydraulic oil, at which point the motor enters the low-speed circulation mode.

9. The steering method for a bridge-type heavy-duty AGV according to claim 3, characterized in that, Stage 5) includes the de-energization of the second solenoid ball valve and the first solenoid ball valve, and the connection between the oil inlet pipeline and the oil outlet pipeline. When the battery stops running, the hydraulic pump stops pumping oil; the hydraulic oil inside the first and second proportional directional valves flows back into the hydraulic return pipe and cooler through their respective T ports, and is filtered by the return oil filter before returning to the hydraulic oil tank. If the pressure inside the accumulator is higher than the system pressure, the hydraulic oil inside will flow out and pass through the second solenoid ball valve, cooler, and then be filtered by the return oil filter back to the hydraulic oil tank.

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