Hydraulic cooperative braking control system for large-gradient and heavy-load auxiliary transportation robot

Abstract

The invention discloses a hydraulic cooperative brake control system for a large-gradient and heavy-load auxiliary transport robot. The hydraulic cooperative brake control system comprises a brake cylinder, an oil tank, a pump unit, a first electromagnetic directional valve and a first electro-hydraulic proportional overflow valve. The brake oil path module is arranged between the brake cylinder and the pump unit; the brake oil path module comprises a second electromagnetic directional valve, a second electro-hydraulic proportional overflow valve and a pressure sensing unit; the second electromagnetic directional valve is connected in series between the brake cylinder and the pump unit; the second electro-hydraulic proportional overflow valve is arranged between the second electromagnetic directional valve and the brake cylinder in parallel and used for controlling oil pressure of the brake cylinder; the pressure sensing unit is arranged at a brake shoe and is used for detecting the braking force; the signal input end of the control module is connected with the pressure sensing unit, the signal output end of the control module is connected with the second electro-hydraulic proportional overflow valve, and the control module controls the generated braking force to be maintained at a set preset value; braking force is dynamically adjusted by means of multiple sets of non-interfering braking oil way modules, accurate constant speed reduction is conducted on the braking force, and the device adapts to the large-gradient heavy-load descending working condition.

Description

Technical Field

[0001] The invention relates to the field of auxiliary transport robots, and in particular to a hydraulic cooperative braking control system for large-slope, heavy-load auxiliary transport robots. Background Art

[0002] Monorail cranes, as a common auxiliary transport robot, are usually responsible for carrying objects hanging from below. At present, monorail cranes are mostly used for conventional operation conditions with small slopes, low loads and low operating speeds; there is no monorail crane transport robot in the prior art that can operate under large slopes and heavy loads, which leads to low transport efficiency of existing monorail cranes.

[0003] When operating under steep slope and heavy load conditions, technicians usually control the monorail crane to perform constant deceleration braking; however, when braking, the existing monorail crane will experience fluctuations in braking force due to friction and heat generated by the brake shoes, which leads to drastic speed fluctuations during braking, making it impossible to accurately control the monorail crane.

[0004] The existing monorail crane brake module, in which the brake shoes are extended synchronously and the braking force is maintained at the same size, has inconsistent wear conditions of different brake shoes under actual working conditions. Therefore, during braking, it is often the case that different brake shoes are braked synchronously, with some being too tight and some being too loose, further causing deviations in the braking response time of each brake shoe. Furthermore, deviations occur in the braking force of each brake shoe, resulting in deviations in the braking effect, which will also aggravate the situation of drastic speed fluctuations.

[0005] Therefore, the existing technology cannot achieve the function of precise control of the monorail crane through the constant deceleration braking of the monorail crane, and the monorail crane transport robot cannot adapt to operation under large slopes and heavy loads, which further limits the application of the monorail crane transport robot. Summary of the invention

[0006] In response to the above technical problems, the present invention provides a hydraulic collaborative braking control system for a large-slope, heavy-load auxiliary transport robot. By coordinating the braking oil circuit module with the control module, it ensures that the braking force of the control brake shoe is always stably maintained at a preset value, thereby achieving constant deceleration braking on a single track. The present invention can effectively solve the limitation that the traditional monorail crane hydraulic braking system cannot adapt to large-slope and heavy-load downward conditions.

[0007] In order to achieve the above technical objectives, the present invention adopts the following technical means: A hydraulic cooperative braking control system for a large-slope, heavy-load auxiliary transport robot, comprising a plurality of brake cylinders for braking the auxiliary transport robot, an oil tank for providing pressure oil to the brake cylinders, a pump unit for pumping pressure oil from the oil tank into the brake cylinders, a first electromagnetic reversing valve for controlling whether the brake cylinders unload oil, and a first electro-hydraulic proportional relief valve for controlling the hydraulic oil to return to the oil tank; Wherein, a main oil outlet pipe is provided at the outlet of the oil tank, and the pump unit is connected in series in the main oil outlet pipe; the brake cylinder realizes braking of the auxiliary transport robot by controlling the release and closing states of the brake shoe; include: A plurality of brake oil circuit modules with the same structure are connected in parallel to the main oil outlet pipe, and are arranged one by one between the plurality of brake cylinders and the pump unit; wherein each of the brake oil circuit modules comprises at least a second electromagnetic reversing valve, a second electro-hydraulic proportional relief valve and a pressure sensing unit; the second electromagnetic reversing valve is connected in series between the brake cylinder and the pump unit, and is used to control the brake cylinder to be disconnected from the pump unit during constant deceleration braking; the second electro-hydraulic proportional relief valve is arranged in parallel between the second electromagnetic reversing valve and the brake cylinder, and is used to receive the oil output from the brake cylinder to control the braking force generated by the brake cylinder; the pressure sensing unit is arranged at the position corresponding to the brake shoe, and is used to detect the braking force of the corresponding brake shoe; A control module, whose signal input end is connected to the control pressure sensing unit, and whose signal output end is electrically connected to the second electro-hydraulic proportional overflow valve, is used to control the braking force generated by the brake cylinder to maintain it at a preset value set in advance to achieve constant deceleration braking of the brake cylinder.

[0008] The main oil outlet pipe is connected in series with a one-way valve at the outlet direction of the pump unit, and the one-way valve is used to ensure that the hydraulic oil cannot pass through the pump unit in reverse.

[0009] The brake oil circuit module also includes: The accumulator is arranged in parallel between the second electromagnetic reversing valve and the brake cylinder, and is used to adjust the oil pressure difference between the brake cylinder and the second electro-hydraulic proportional relief valve.

[0010] The oil inlet of the brake cylinder is connected to the pump unit through an oil filter, and the oil filter is used to filter and remove impurities from the hydraulic oil passing through.

[0011] The pressure sensing unit comprises: The pressure sensor is arranged at the brake shoe and is used for converting the braking force generated by the friction of the brake shoe into a data signal.

[0012] A control method for a hydraulic cooperative braking control system for a large-slope, heavy-load auxiliary transport robot comprises the following steps: S1: The control module controls the control current of the first electro-hydraulic proportional relief valve to gradually decrease, the pump unit maintains the output flow unchanged, and the pressure sensor measures the braking force generated by the brake shoe; S2: The control module controls the pump unit to stop working, and the second electromagnetic reversing valve is powered on to disconnect the oil passage between the brake cylinder and the oil tank, ensuring that the brake cylinder controlled by each brake oil circuit module is controlled by the second electro-hydraulic proportional relief valve to control the extension and contraction length, thereby controlling the brake shoe holding force; S3: The control module controls the second electro-hydraulic proportional relief valve to be at the maximum working current and gradually decreases until the pressure reaches the set value; the brake cylinder controls the braking force of the brake shoe to be maintained at the preset value, keeping the braking force constant, thereby assisting the transport robot to maintain a uniform deceleration, thereby performing constant deceleration braking; S4: The control module compares the real-time braking force obtained by the pressure sensor with the preset braking force value calculated in advance based on the measured traction force; when the real-time braking force is small, the control module controls the current of the second electro-hydraulic proportional overflow valve to increase accordingly, reduces the internal oil pressure of the brake cylinder, and increases the braking force of the brake shoe; otherwise, the control module controls the current of the second electro-hydraulic proportional overflow valve to decrease accordingly.

[0013] Beneficial effects: First, during emergency braking, the control module of the present invention can control the flow change of the second electro-hydraulic proportional relief valve according to the signal of the pressure sensor, so that the brake shoe controlled by the brake cylinder generates a preset braking force; thereby, the monorail crane performs constant deceleration braking, and when the monorail crane is operating on a large slope and under heavy load conditions, during emergency braking, there will be no large vibration and impact caused by fluctuations in the braking force due to rapid braking.

[0014] Second, during emergency braking, the hydraulic brake circuit designed in the present invention can independently control the braking force of the corresponding brake shoe because the three brake modules are independent of each other, ensuring that they can more accurately correspond to their own braking force and will not cause excessive initial speed deviation, resulting in drastic speed fluctuations during constant deceleration braking and serious deviation from the expected deceleration curve. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is the principle diagram of the brake hydraulic circuit of the present invention; Figure 2 This is a block diagram of the brake control structure of the present invention.

[0016] In the figure: 1, oil tank; 2, pressure indicator; 3, liquid level gauge; 4, thermometer; 5, safety valve; 6.0, accumulator D; 6.1, accumulator A; 6.2, accumulator B; 6.3, accumulator C; 7.1, pressure sensor A; 7.2, pressure sensor; 7.3, pressure sensor C; 8.0, first electro-hydraulic proportional relief valve; 8.1, second electro-hydraulic proportional relief valve A; 8.2, second electro-hydraulic proportional relief valve B; 8.3, second electro-hydraulic proportional relief valve Flow valve C; 9. Pump unit; 10.0. Oil inlet filter A; 10.1. Oil inlet filter B; 10.2. Oil inlet filter C; 10.3. Oil inlet filter D; 11. One-way valve; 12. Overflow valve; 13.0. First solenoid reversing valve; 13.1. Second solenoid reversing valve A; 13.2. Second solenoid reversing valve B; 13.3. Second solenoid reversing valve C; 14.1. Brake cylinder A; 14.2. Brake cylinder B; 14.3. Brake cylinder C. DETAILED DESCRIPTION

[0017] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0018] A hydraulic cooperative braking control system for a large-slope, heavy-load auxiliary transport robot, comprising a plurality of brake cylinders for braking the auxiliary transport robot, an oil tank for providing pressurized oil to the brake cylinders, a pump unit for pumping pressurized oil from the oil tank into the brake cylinders, a first electromagnetic reversing valve for controlling whether the brake cylinders unload oil, and a first electro-hydraulic proportional overflow valve for controlling the return of hydraulic oil to the oil tank; specifically, there are at least three brake cylinders, including brake cylinder A, brake cylinder B and brake cylinder C.

[0019] Among them, the brake cylinder realizes braking of the auxiliary transport robot by controlling the release and closing states of the corresponding brake shoes; multiple brake cylinders are arranged in parallel and connected to the oil outlet of the pump unit; a main oil outlet pipe is arranged at the outlet of the oil tank, which is connected to the brake cylinder through the main oil outlet pipe, and the pump unit is connected in series in the main oil outlet pipe; it also includes that multiple brake oil circuit modules with the same structure are connected in parallel to the main oil outlet pipe, which are arranged one by one between the multiple brake cylinders and the pump unit.

[0020] Among them, each of the brake oil circuit modules includes at least a second electromagnetic reversing valve, a second electro-hydraulic proportional overflow valve and a pressure sensing unit; the second electromagnetic reversing valve is connected in series between the brake cylinder and the pump unit, and is used to control the brake cylinder to be disconnected from the pump unit during constant deceleration braking; the second electro-hydraulic proportional overflow valve is arranged in parallel between the second electromagnetic reversing valve and the brake cylinder, and is used to receive the oil output of the brake cylinder, control the oil pressure of the brake cylinder to control the braking force generated by the brake cylinder; the pressure sensing unit is arranged at the corresponding brake shoe, and is used to detect the braking force of the corresponding brake shoe.

[0021] Furthermore, according to the corresponding brake oil circuit module, the second solenoid reversing valve is divided into a second solenoid reversing valve A, a second solenoid reversing valve B and a second solenoid reversing valve C; the second electro-hydraulic proportional overflow valve is divided into a second electro-hydraulic proportional overflow valve A, a second electro-hydraulic proportional overflow valve B and a second electro-hydraulic proportional overflow valve C.

[0022] Furthermore, the pressure sensing unit includes: a pressure sensor, which is arranged at the brake shoe and is used to convert the braking force generated by the friction of the brake shoe into a data signal.

[0023] The pressure sensors are respectively arranged on each corresponding brake oil circuit module, including pressure sensor A, pressure sensor B and pressure sensor C.

[0024] The control module has a signal input end electrically connected to the pressure sensing unit and a signal output end electrically connected to the second electro-hydraulic proportional relief valve, and is used to control the braking force generated by the brake cylinder to maintain a preset value set in advance to achieve constant deceleration braking of the brake cylinder. Specifically, the control module adopts a PLC controller.

[0025] Thereby, during emergency braking of the present invention, the control module can control the flow change of the second electro-hydraulic proportional overflow valve according to the signal of the pressure sensor, so that the brake shoe controlled by the brake cylinder generates a preset braking force; thereby, the monorail crane performs constant deceleration braking, and when the monorail crane is operating on a large slope and under heavy load conditions, during emergency braking, there will be no large vibration and impact caused by fluctuations in the braking force due to rapid braking.

[0026] Furthermore, in order to adjust the oil pressure difference between the brake cylinder and the overflow valve, an accumulator is arranged in parallel between the second electromagnetic reversing valve and the brake cylinder. The accumulator is divided into accumulator A, accumulator B and accumulator C.

[0027] Furthermore, in order to prevent the hydraulic system from clogging after long-term operation, the oil inlet of the brake cylinder is connected to the pump unit through an oil filter, and the oil filter is used to filter and remove impurities from the hydraulic oil passing through. Among them, the oil filter is divided into an oil inlet filter A arranged at the outlet of the pump unit, and an oil inlet filter B, an oil inlet filter C and an oil inlet filter D respectively arranged at the corresponding brake cylinders.

[0028] Furthermore, a relief valve and a first electro-hydraulic proportional relief valve are provided in parallel with the first electromagnetic reversing valve; the relief valve is provided with a fixed relief pressure to prevent overpressure and overload of the brake control system; the first electro-hydraulic proportional relief valve is used to ensure the stability of the working pressure of the brake cylinder in the released state.

[0029] Furthermore, in order to ensure the stability of the entire hydraulic circuit, an accumulator D is also provided in the pipeline; and in order to facilitate the monitoring of conventional data such as temperature, liquid level and pressure in the hydraulic circuit, improve control accuracy and prevent safe manipulation, a thermometer, liquid level gauge and pressure indicator are also provided in the pipeline; and in order to prevent the dangerous situation of excessive pressure in the entire hydraulic circuit, a safety valve is also provided in the pipeline.

[0030] Specifically, the pump source device that drives the brakes of the monorail crane includes an oil tank, a thermometer, a liquid level gauge, a pressure indicator, an oil inlet filter, a one-way valve, and a pump unit; these provide a pressure source for the system to supply oil to the brake cylinder during the travel of the monorail crane, so that the brake cylinder shoe opens and the monorail crane is braked by the braking force.

[0031] The brake oil circuit module is divided into brake oil circuit module A, brake oil circuit module B and brake oil circuit module C; wherein, all three include a second electromagnetic reversing valve with two-position two-way, an accumulator, a pressure sensor, an electro-hydraulic proportional relief valve, and an oil outlet filter; and, the brake oil circuit modules A, B and C have the same structure.

[0032] Among them, the pump unit is connected to the oil inlet of three groups of parallel second electromagnetic reversing valve A, second electromagnetic reversing valve B, and second electromagnetic reversing valve C through the oil inlet filter A and the one-way valve; furthermore, the second electromagnetic reversing valve A, the second electromagnetic reversing valve B, and the second electromagnetic reversing valve C are directly connected to the brake cylinder A, the brake cylinder B, and the brake cylinder C respectively; the oil outlet of the brake cylinder is connected to the oil inlet of the second electro-hydraulic proportional overflow valve A, the second electro-hydraulic proportional overflow valve B, and the second electro-hydraulic proportional overflow valve C, and the corresponding oil outlets of the second electro-hydraulic proportional overflow valve A, the second electro-hydraulic proportional overflow valve B, and the second electro-hydraulic proportional overflow valve C are all connected to the oil tank; on the connection circuit between the brake cylinder and the second electromagnetic reversing valve, pressure sensor A, the first and second pressure sensors, the pressure sensor C and the accumulator A, the accumulator B, and the accumulator C are respectively arranged.

[0033] At the same time, the overflow valve, the first electro-hydraulic proportional overflow valve, and the first electromagnetic reversing valve are connected in parallel, the oil inlets of the two are connected to the oil outlet of the pump unit, and the corresponding oil outlets of the two are directly connected to the oil tank; and an accumulator D and a pressure sensor D are also arranged on the pipeline.

[0034] A control method of a hydraulic cooperative braking control system for a large-slope, heavy-load auxiliary transport robot, the method adopts the above-mentioned hydraulic cooperative braking control system, and the control method comprises: The monorail crane hydraulic cooperative braking control system has three working modes: working release, constant deceleration braking, and parking braking.

[0035] First, when releasing the brake: At this time, the system pressure has reached the set value; in the initial state, the relief valve, the first electro-hydraulic proportional relief valve, the second electro-hydraulic proportional relief valve A, the second electro-hydraulic proportional relief valve B, and the second electro-hydraulic proportional relief valve C are energized; among them, the current signal of the first electro-hydraulic proportional relief valve gradually increases from 0.

[0036] Furthermore, at this time, the first solenoid reversing valve loses power and is in a disconnected state, and the second solenoid reversing valve A, the second solenoid reversing valve B, and the second solenoid reversing valve C lose power and are in a connected state; therefore, at this time, the return oil channels of the brake cylinder A, the brake cylinder B, and the brake cylinder C are all closed.

[0037] Then, the pump unit starts to work, pumping out the hydraulic oil, which passes through the second electromagnetic reversing valve and the oil inlet filter in sequence until it enters the brake cylinder; at this time, the brake cylinder quickly builds up working pressure, and the piston rod extends to cause the brake shoe to release; Next, when the working pressure of the brake shoe reaches the set value, the pump unit enters the low-speed working mode to ensure the stability of the brake cylinder pressure; then, the PLC controller performs PID control according to the feedback signal of the pressure sensor D, and adjusts the control current of the first electro-hydraulic proportional relief valve to ensure the stability of the working pressure of the brake cylinder in the working release state; at the same time, the relief valve is set with a fixed relief pressure to prevent the system from over-pressure.

[0038] When constant deceleration braking is performed immediately afterwards, the PLC controller executes the constant deceleration braking procedure: First, the control current of the first electro-hydraulic proportional relief valve gradually decreases, and the pump unit maintains the output flow unchanged, thereby reducing the oil pressure in the brake cylinder, causing the brake shoe to clamp the moving wheel of the monorail crane, thereby generating braking force; at this time, the braking force is measured by pressure sensor A, pressure sensor B, and pressure sensor C.

[0039] Next, the pump unit stops working, and the second solenoid reversing valve A, the second solenoid reversing valve B, and the second solenoid reversing valve C are energized and disconnected; at this time, the second electro-hydraulic proportional overflow valve A, the second electro-hydraulic proportional overflow valve B, and the third electro-hydraulic proportional overflow valve C are at the set maximum working current and gradually decrease; as the overflow volume of the three gradually increases, the internal oil pressure of the brake cylinder begins to gradually decrease, and then the piston rod of the brake cylinder retracts, driving the brake shoe to further tighten the brake, increasing the braking force of the brake shoe; until the braking force reaches the pressure setting value calculated by the PLC controller-the preset value, so that the originally dynamically changing braking force is kept within a constant range as much as possible, and then the deceleration is kept constant, and the speed is reduced at a uniform speed, so as to complete constant deceleration braking; conversely, when the braking force is higher than the preset value, the internal oil pressure of the brake cylinder is increased to reduce the braking force of the brake shoe.

[0040] Among them, the PLC controller measures the traction force of the single track through the conventionally set sensors, calculates it according to the preset value of 1.5 times the traction force, and then obtains the changed preset value.

[0041] At the same time, since the brake oil circuit module adopts a multi-group collaborative braking mode, the several groups of brake oil circuit modules are independent of each other; therefore, accumulators A, accumulator B, and accumulator C respectively added to the brake oil circuit module provide hydraulic energy for the constant deceleration braking circuit, thereby improving the control accuracy, realizing dynamic adjustment of the braking force, and completing constant deceleration braking.

[0042] When the parking brake is finally reached: First, the acceleration sensor detects the running speed of the monorail crane. When the PLC controller detects that the running speed of the monorail crane approaches zero, the first electro-hydraulic proportional overflow valve loses power and is disconnected, the second electro-hydraulic proportional overflow valve A, the second electro-hydraulic proportional overflow valve B, and the second electro-hydraulic proportional overflow valve C lose power and are connected, and the second solenoid reversing valve A, the second solenoid reversing valve B, and the second solenoid reversing valve C lose power and are disconnected.

[0043] At this time, the first electromagnetic reversing valve is electrically connected, the three groups of brake cylinders are directly connected to the oil tank, the brake shoes are closed and locked, and the machine enters a shutdown state.

Claims

1. A hydraulic cooperative braking control system for a large-slope, heavy-load auxiliary transport robot, comprising a plurality of brake cylinders for braking the auxiliary transport robot, an oil tank for providing pressure oil to the brake cylinders, a pump unit for pumping pressure oil from the oil tank into the brake cylinders, a first electromagnetic reversing valve for controlling whether the brake cylinders unload oil, and a first electro-hydraulic proportional relief valve for controlling the hydraulic oil to return to the oil tank; in, A main oil outlet pipe is provided at the outlet of the oil tank, and the pump unit is connected in series in the main oil outlet pipe; the brake cylinder realizes braking of the auxiliary transport robot by controlling the release and closing states of the brake shoe; The invention is characterized by comprising: A plurality of brake oil circuit modules with the same structure are connected in parallel to the main oil outlet pipe, and are arranged one by one between the plurality of brake cylinders and the pump unit; wherein each of the brake oil circuit modules comprises at least a second electromagnetic reversing valve, a second electro-hydraulic proportional relief valve and a pressure sensing unit; the second electromagnetic reversing valve is connected in series between the brake cylinder and the pump unit, and is used to control the brake cylinder to be disconnected from the pump unit during constant deceleration braking; the second electro-hydraulic proportional relief valve is arranged in parallel between the second electromagnetic reversing valve and the brake cylinder, and is used to receive the oil output from the brake cylinder to control the braking force generated by the brake cylinder; the pressure sensing unit is arranged at the position corresponding to the brake shoe, and is used to detect the braking force of the corresponding brake shoe; A control module, whose signal input end is electrically connected to the pressure sensing unit, and whose signal output end is electrically connected to the second electro-hydraulic proportional overflow valve, is used to control the braking force generated by the brake cylinder to maintain it at a preset value set in advance to achieve constant deceleration braking of the brake cylinder.

2. The hydraulic cooperative braking control system for a large-slope, heavy-load auxiliary transport robot according to claim 1 is characterized in that: The main oil outlet pipe is connected in series with a one-way valve at the outlet direction of the pump unit, and the one-way valve is used to ensure that the hydraulic oil cannot pass through the pump unit in reverse.

3. The hydraulic cooperative braking control system for a large-slope, heavy-load auxiliary transport robot according to claim 1 is characterized in that: The brake oil circuit module also includes: The accumulator is arranged in parallel between the second electromagnetic reversing valve and the brake cylinder, and is used to adjust the oil pressure difference between the brake cylinder and the second electro-hydraulic proportional relief valve.

4. The hydraulic cooperative braking control system for a large-slope, heavy-load auxiliary transport robot according to claim 1 is characterized in that: The oil inlet of the brake cylinder is connected to the pump unit through an oil filter, and the oil filter is used to filter and remove impurities from the hydraulic oil passing through.

5. The hydraulic cooperative braking control system for a large-slope, heavy-load auxiliary transport robot according to claim 1 is characterized in that: The pressure sensing unit comprises: The pressure sensor is arranged at the brake shoe and is used for converting the braking force generated by the friction of the brake shoe into a data signal.

6. A control method for a hydraulic cooperative braking control system for a large-slope, heavy-load auxiliary transport robot, the method adopts the hydraulic cooperative braking control system described in any one of claims 1 to 5, characterized in that: The control method comprises the following steps: S1: The control module controls the control current of the first electro-hydraulic proportional relief valve to gradually decrease, the pump unit maintains the output flow unchanged, and the pressure sensor measures the braking force generated by the brake shoe; S2: The control module controls the pump unit to stop working, and the second electromagnetic reversing valve is powered on to disconnect the oil passage between the brake cylinder and the oil tank, ensuring that the brake cylinder controlled by each brake oil circuit module is controlled by the second electro-hydraulic proportional relief valve to control the extension and contraction length, thereby controlling the brake shoe holding force; S3: The control module controls the second electro-hydraulic proportional relief valve to be at the maximum working current and gradually decreases until the pressure reaches the set value; the brake cylinder controls the braking force of the brake shoe to be maintained at the preset value, keeping the braking force constant, thereby assisting the transport robot to maintain a uniform deceleration, thereby performing constant deceleration braking; S4: The control module compares the real-time braking force obtained by the pressure sensor with the preset braking force value calculated in advance based on the measured traction force; when the real-time braking force is small, the control module controls the current of the second electro-hydraulic proportional overflow valve to increase accordingly, reduces the internal oil pressure of the brake cylinder, and increases the braking force of the brake shoe; otherwise, the control module controls the current of the second electro-hydraulic proportional overflow valve to decrease accordingly.

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