A boost type digital hydraulic brake system and a control method thereof

Abstract

The application provides a boost type digital hydraulic braking system and a control method thereof. The system comprises a pedal device, a brake cylinder, a displacement detection system, a pressure detection system, a controller, a hydraulic pump, an accumulator, a hydraulic inertia pipe, a first digital on-off valve and a second digital on-off valve. The control method comprises three modes of braking preparation, braking and closing. The controller determines the mode of the system according to a detection signal. In the braking preparation mode, the brake cylinder is not pre-charged, and the brake block and the brake disc keep a safe distance. The hydraulic pump charges the accumulator and the inertia pipe in the brake hydraulic circuit. When the braking mode is entered, the energy storage element instantaneously releases energy, which is superimposed with the output of the hydraulic pump. At this time, the digital on-off valve increases the opening, rapidly increases the flow in the circuit, increases the liquid charging speed in the brake cylinder and reduces the braking time.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of hydraulic braking, and particularly relates to a pressure-boosting digital hydraulic braking system and a control method thereof. BACKGROUND

[0002] A braking system refers to a series of devices for forcibly reducing the running speed of a vehicle, and mainly functions to reduce the speed of a running vehicle to even a stop and to keep the speed of a downhill running vehicle stable. The highest technology of current full hydraulic braking is an electro-hydraulic proportional braking control technology. Since a proportional valve has a dead zone in the middle, the pressure response of a brake is slow, and the braking process lags. The proportional valve has internal leakage, which makes it difficult to stabilize the braking pressure for a long time and reduces the control accuracy. At the same time, the slide valve structure of the proportional valve has a very high requirement for the cleanliness of oil, and oil pollution can cause the sticking of the valve core, resulting in the inability of the brake to effectively brake, poor reliability, and difficulty in meeting the requirements of full hydraulic braking under complex working conditions. The digital hydraulic technology uses a digital on-off valve as the core control element, has a fast frequency response, and the discrete fluid generated by high-frequency opening and closing can be fused in the pipeline to achieve the effect of continuous fluid control, has high control accuracy, is not sensitive to the cleanliness of oil, and therefore has stronger anti-pollution ability and faster response.

[0003] Among the many schemes for optimizing the braking system by using a digital on-off valve, there is a preloading braking scheme that applies a preloading pressure to make the brake in a pre-braking state in advance, thereby improving the braking response speed. However, such a scheme reduces the safety distance between the brake block and the brake disc, resulting in erroneous braking of the system. In addition, since the digital on-off valve only has two states of "on" and "off", there is inevitably flow pulsation and impact pressure, which often causes the braking pressure of the hydraulic system to deviate from the required pressure when the hydraulic cylinder brakes.

[0004] In addition, the commonly used vehicle braking assist system is a vacuum pump assist system. Since the inside of the vacuum assist pump needs to be pre-vacuumed by a vacuum pump or an engine, when the vehicle has an accident such as rolling, skidding, etc., and is turned off, the braking assist system cannot continuously provide braking assist, which is dangerous SUMMARY

[0005] In order to overcome the deficiencies of the prior art, the present application provides a pressure-boosting digital hydraulic braking system and a control method thereof.

[0006] The technical scheme of the present application is as follows:

[0007] In one aspect, the application provides a boost type digital hydraulic braking system, comprising a pedal device, a brake cylinder, a displacement detection system for detecting the position of the pedal device, and a pressure detection system for detecting the hydraulic oil pressure in the brake cylinder, the boost type digital hydraulic braking system further comprising: a controller, a hydraulic pump, an accumulator, a hydraulic inertia pipe, a first digital on-off valve, and a second digital on-off valve; the first digital on-off valve is a two-position three-way valve, and the second digital on-off valve is a two-position two-way valve;

[0008] The inlet end of the hydraulic inertia pipe is connected to an external oil tank through the hydraulic pump, and the outlet end is connected to the inlet of the first digital on-off valve; the first outlet of the first digital on-off valve is connected to the brake cylinder and the inlet of the second digital on-off valve, respectively, and the second outlet of the first digital on-off valve is connected to an external return tank as a return port; the accumulator is connected to the inlet end of the hydraulic inertia pipe; the return port of the second digital on-off valve is connected to an external return tank;

[0009] The controller is connected to the displacement detection system, the pressure detection system, the accumulator, and the hydraulic inertia pipe to obtain the position of the pedal device, the pressure signal of the brake cylinder rodless chamber, the pressure of the accumulator, and the flow signal of the hydraulic inertia pipe, and outputs control instructions to the hydraulic pump, the first digital on-off valve, and the second digital on-off valve; the controller controls the first digital on-off valve according to the flow signal in the hydraulic inertia pipe and the actual pressure demand of the brake cylinder, and matches the actual flow in the brake pipe with the actual pressure demand of the brake cylinder based on the liquid sensing principle of the inertia pipe.

[0010] In a second aspect, the application provides a brake control method based on the boost type digital hydraulic braking system, wherein the controller controls the system to be in a brake preparation mode, a brake mode, or an off mode according to the detection signals of the displacement detection system and the pressure detection system;

[0011] When the controller does not receive the brake instruction signal of the displacement detection system, the system is in the brake preparation mode; at this time, the controller controls the first digital on-off valve to keep the right position and the second digital on-off valve to be closed; the hydraulic pump is in a low-power working state to save power consumption, the controller always transmits the most suitable driving frequency f1 and the most suitable duty ratio size β1 to the first digital on-off valve and keeps a small valve opening degree γ1, so as to ensure that the hydraulic circuit keeps a high pressure P1 under the condition of low-power working of the hydraulic pump, and the high-pressure hydraulic oil flows into the inlet and outlet ports of the bladder accumulator through the pipeline, compresses the air bag in the accumulator shell, and stores hydraulic energy; the rodless chamber of the brake cylinder has no hydraulic oil flow, and the brake block is located at the left limit position;

[0012] When the controller receives the brake instruction signal of the displacement detection system, the system enters the brake mode; the controller controls the first digital switch valve to switch to the left position, and the external oil tank flows into the rodless cavity of the brake cylinder through the hydraulic pump, the accumulator, the hydraulic inertia tube and the left position of the first digital switch valve, pushes the piston rod to act right, makes the brake block and the brake disc friction to achieve the brake effect;

[0013] After the brake is completed, the controller controls the first digital switch valve to switch back to the right position, and controls the second digital switch valve to switch to the left position to open, the hydraulic oil in the brake cylinder flows back to the oil tank through the second digital switch valve, the brake block returns to the initial limit position, and a brake cycle is completed;

[0014] When the controller detects that the vehicle is parked and stationary, the brake system enters the closed mode, and the hydraulic pump is closed.

[0015] Compared with the prior art, the application has the beneficial effects including:

[0016] (1) The application does not pre-charge the brake cylinder before braking, so that the brake block is located at the initial limit position and maintains a safe distance from the brake disc, avoiding the occurrence of false braking and improving driving safety.

[0017] (2) The application is based on the energy storage characteristics of the traditional hydraulic components accumulator and inertia tube. When the vehicle is driving normally, the hydraulic pump charges the accumulator and inertia tube in the brake hydraulic circuit. When the brake instruction is issued, the energy storage elements release energy instantaneously, which is superimposed with the output of the hydraulic pump. At this time, the digital switch valve increases the opening, rapidly increases the flow in the circuit, and increases the liquid charging speed in the brake cylinder, thereby reducing the braking time.

[0018] (3) The application is integrated into the hydraulic brake control circuit and does not depend on the engine and vacuum pump independent system. The hydraulic pump is separately powered for the hydraulic control circuit, and the digital switch valve, accumulator and inertia tube are directly installed on the brake. When the power of the vehicle hydraulic system energy supply element is insufficient, the brake can still effectively brake.

[0019] (4) The application utilizes the liquid sensing principle of the hydraulic inertia tube to reduce the flow pulse in the hydraulic circuit. At the same time, the pressure detection system detects the pressure data in the rodless cavity of the brake cylinder in real time and transmits it to the controller. The controller adjusts the duty ratio and drive frequency of the inertia tube in real time, so that the actual flow in the tube is highly matched with the required flow of the brake cylinder. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 It is a structure schematic diagram of the boost type digital hydraulic brake system of the application;

[0021] Figure 2 It is a principle schematic diagram in the brake preparation mode;

[0022] Figure 3 The principle diagram of the brake system in the braking mode;

[0023] Figure 4 The principle diagram of the brake system in the pressure relief state at the end of braking;

[0024] Figure 5 The timing diagram of the brake system.

[0025] In the figure, 1 is a hydraulic inertia tube, 2 is an accumulator, 3 is a first digital on-off valve, 4 is a brake cylinder, 5 is a brake block, 6 is a brake disc, and 7 is a second digital on-off valve. DETAILED DESCRIPTION

[0026] The application will be further described and illustrated with reference to the specific embodiments. The embodiments are only exemplary and do not limit the scope of the disclosure. The technical features of the various embodiments of the application can be combined accordingly without conflict.

[0027] The principle diagram of the brake system of the boost type digital hydraulic brake system is shown in FIG. 1, wherein 1 is an inertia tube, 2 is an accumulator, 3 is a first digital on-off valve, 4 is a brake cylinder, 5 is a brake block, 6 is a brake disc, and 7 is a second digital on-off valve. Figure 1 The controller is connected with a displacement detection system, a pressure detection system, the accumulator, and the hydraulic inertia tube to obtain detection signals. The controller inputs a signal α to the hydraulic pump, an on-off duty modulation signal β1 (0-100%) of the first digital on-off valve 3, a driving frequency signal f1 (100-300 Hz), an on-off duty modulation signal β2 (0-100%) of the second digital on-off valve 7, and a driving frequency signal f2 (100-300 Hz).

[0028] The accumulator is filled with liquid by an external oil tank through a hydraulic pump to ensure that the accumulator can provide sufficient brake pressure. When the controller detects that the accumulator pressure is insufficient, the hydraulic pump fills the accumulator with liquid to supplement the pressure by transmitting a control signal α. The size of the target brake pressure P0 is determined by the stroke of the pedal device, that is, the greater the stroke distance, the greater the target brake pressure P0.

[0029] The controller is connected with a displacement detection system, a pressure detection system, the accumulator, and the hydraulic inertia tube to obtain pedal device position, brake cylinder rodless cavity pressure signal, accumulator pressure, and hydraulic inertia tube flow signal in real time. The controller outputs control instructions to the hydraulic pump, the first digital on-off valve, and the second digital on-off valve. The controller controls the first digital on-off valve according to the flow signal in the hydraulic inertia tube and the actual pressure demand of the brake cylinder, and matches the actual flow in the brake tube with the actual pressure demand of the brake cylinder based on the liquid sensing principle of the inertia tube.

[0030] In this embodiment, the inlet end of the hydraulic inertia pipe 1 is connected to an external oil tank via a hydraulic pump, and the outlet end is connected to the inlet of the first digital switch valve 3. The first outlet of the first digital switch valve 3 is connected to the inlets of the brake cylinder 4 and the second digital switch valve 7, respectively, and the second outlet of the first digital switch valve 3 serves as a return port connected to an external return oil tank. The accumulator 2 is connected to the oil line at the inlet end of the hydraulic inertia pipe 1. The return port of the second digital switch valve 7 is connected to an external return oil tank. When the first digital switch valve 3 is in the right position, the inlet of the first digital switch valve 3 is connected to the second outlet. When the first digital switch valve 3 is in the left position, the inlet of the first digital switch valve 3 is connected to the first outlet. The brake cylinder 4 is equipped with a brake block 5 with a return spring. When no hydraulic oil flows into the rodless chamber of the brake cylinder, the brake block is located at the left limit position under the action of the spring and maintains a sufficient safe distance from the brake disc 6 to prevent the braking system from braking incorrectly. After the rodless chamber of the brake cylinder is filled with fluid greater than a set value, the brake block rubs against the external brake disc to brake the vehicle.

[0031] The braking control method of the present invention based on the above system mainly utilizes the controller to control the system to be in braking preparation mode, braking mode or off mode according to the detection signals of the displacement detection system and the pressure detection system; the three modes are described below.

[0032] Braking preparation status (braking preparation mode):

[0033] When the controller does not receive a braking command signal from the displacement detection system, the system is in a braking preparation state, such as... Figure 2 As shown, the controller acquires the corresponding detection signals in real time through the displacement detection system and the pressure detection system. The controller de-energizes the relay of the first digital switching valve 3 and keeps it in the right position. The external oil tank returns to the external oil tank through the hydraulic pump, accumulator 2, hydraulic inertia pipe 1 and the right position of the first digital switching valve 3.

[0034] In this mode, the hydraulic pump operates at low power to save power consumption. The controller always transmits the optimal drive frequency f1 and the optimal duty cycle β1 to the first digital switching valve 3 and maintains a small valve opening γ1 to ensure that the hydraulic circuit maintains a high pressure P1 when the hydraulic pump operates at low power. High-pressure hydraulic oil flows into the inlet and outlet of the bladder accumulator through the pipeline, compressing the air bladder in the accumulator housing and storing hydraulic energy.

[0035] In this mode, the loop is in steady state, the controller monitors the flow signal in the inertia tube in real time and controls the first digital on-off valve 3 according to the actual pressure demand of the brake cylinder (at this time the pressure demand is 0 MPa), based on the liquid sensing principle of the inertia tube, so that the actual flow in the brake pipe matches the brake cylinder pressure demand. The left end pressure of the hydraulic inertia tube is P1, and the right end is connected to the oil tank with a pressure of 0 MPa. In theory, the hydraulic inertia tube will store the hydraulic energy of P1.

[0036] At the same time, the controller controls the relay of the second digital on-off valve 7 to lose power and keep the right bit, that is, the second digital on-off valve 7 is closed.

[0037] In the brake preparation mode, the rodless cavity of the brake cylinder has no hydraulic oil flow, and the brake block is located at the left limit position and keeps a sufficient safety distance from the brake disc to prevent false braking of the brake system. Compared with the preloading brake scheme in which the preloading pressure makes the brake block approach the brake disc in advance before the brake command is issued to improve the brake response speed, this scheme effectively increases the safety distance, avoids false braking and other phenomena, and improves safety.

[0038] Braking state (braking mode):

[0039] When the controller receives the brake command signal of the displacement detection system, the system enters the braking mode. As shown in Figure 3 , the controller controls the relay of the first digital on-off valve 3 to be powered and switches to the left bit, and the external oil tank flows into the rodless cavity of the brake cylinder through the hydraulic pump, accumulator, inertia tube and left bit of the first digital on-off valve 3, pushing the piston rod to act right, making the brake block rub with the brake disc to achieve the braking effect.

[0040] In this mode, the hydraulic pump is in high-power working state to improve the response speed of the system braking. The controller always transmits the optimal driving frequency f2 and the optimal duty ratio size β2 to the first digital on-off valve 3 and keeps a larger valve opening γ2, so that high-speed high-pressure large-flow hydraulic oil passes through.

[0041] In this mode, hydraulic oil quickly flows into the rodless cavity of the brake cylinder, and the air bag in the accumulator housing expands, pressing the hydraulic oil remaining in the housing out of the inlet and outlet. The accumulator and the hydraulic inertia tube both input the energy stored in the brake preparation mode back to the circuit, making the cylinder front pressure P2 quickly rise to the target brake pressure value. At the same time, the controller further speeds up the pressure rising speed and improves the pressure control precision by modulating the duty ratio and driving frequency of the first digital on-off valve 3, and reduces the hydraulic impact of the oil on the hydraulic system.

[0042] The controller monitors the flow signal in the inertia tube in real time and controls the first digital on-off valve 3 according to the actual pressure demand of the brake cylinder, based on the liquid sensing principle of the inertia tube, so that the actual flow in the brake pipe matches the brake cylinder pressure demand.

[0043] After braking is completed, the controller de-energizes the relay of the first digital switch valve 3 and switches it back to the right position, while simultaneously energizing the relay of the second digital switch valve 7 and switching it to the left position. Under the action of the spring, the hydraulic oil in the brake cylinder flows back to the oil tank through the second digital switch valve 7, and the brake pads return to their initial limit positions, completing one braking cycle.

[0044] Off state (off mode):

[0045] When the controller detects that the vehicle is parked, the braking system switches back to the off state, and the hydraulic pump is turned off.

[0046] The following section uses a specific example to illustrate the timing of a braking system, such as... Figure 5 As shown, at time t1, the vehicle starts, and the external oil tank returns to the external oil tank through the hydraulic pump, accumulator, inertia tube, and the right position of the first digital switch valve 3. Due to the action of the external oil tank assembly and the first digital switch valve 3, the pressure at the front end of the hydraulic inertia tube in this circuit begins to rise, reaching P1 at time t2, and the hydraulic inertia tube and accumulator are charged. At time t3, the braking signal is issued, the relay of the first digital switch valve 3 is energized and switches to the left position, and the external oil tank, through the hydraulic pump, accumulator, and hydraulic inertia tube, causes the pressure at the front end of the inertia tube to rise rapidly to P2 at time t4. The oil then flows into the rodless chamber of the brake cylinder through the upper position of the first digital switch valve 3. After a short delay, the pressure in the rodless chamber of the brake cylinder reaches P2 at time t5, pushing the piston rod to the right, causing the brake pads to rub against the brake disc to achieve the braking effect.

[0047] At time t6, the braking signal disappears, the relay of the first digital switch valve 3 is de-energized and switches back to the right position, while the relay of the second digital switch valve 7 is energized and switches to the left position. Under the action of the spring, the hydraulic oil in the brake cylinder flows back to the oil tank through the second digital switch valve 7, and the brake pads return to their initial limit positions. The pressure in the rodless chamber of the brake cylinder and the pressure at the front end of the inertia tube drop to 0 MPa at time t7. Subsequently, at time t8, the pressure in the circuit (hydraulic pump, accumulator, inertia tube, lower position of the first digital switch valve 3, and external oil tank) rises back to P1, and the accumulator and inertia tube are recharged, ready for the next braking. When the vehicle is parked at time t9, the pressure at the front end of the inertia tube gradually drops to 0 MPa, and the braking system is shut off.

[0048] Through the above control timing, before braking, the brake cylinder is not pre-charged, so that the brake block is located at the initial limit position and keeps a safe distance from the brake disc. When the vehicle is normally running, the hydraulic pump charges the accumulator and the inertia tube in the brake hydraulic circuit. When the brake command is issued, the energy storage element instantaneously releases energy, which is superimposed with the output of the hydraulic pump. At this time, the digital on-off valve increases the opening, rapidly increases the flow in the circuit, and increases the liquid filling speed in the brake cylinder, thereby reducing the braking time. The application utilizes the liquid sensing principle of the hydraulic inertia tube to reduce the flow pulse in the hydraulic circuit. At the same time, the pressure detection system detects the pressure data in the rodless cavity of the brake cylinder in real time and transmits it to the controller. The controller adjusts the duty cycle and driving frequency of the inertia tube in real time, so that the actual flow in the tube is highly matched with the required flow of the brake cylinder.

[0049] The above-described embodiments only express several embodiments of the present application, and the description is more specific and detailed, but it cannot be understood as a limitation on the scope of the patent of the present application. For ordinary skilled persons in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which are within the scope of protection of the present application.

Claims

1. A brake control method based on a boost type digital hydraulic brake system, characterized by, The booster type digital hydraulic brake system comprises a pedal device, a brake cylinder, a displacement detection system for detecting the position of the pedal device, and a pressure detection system for detecting the hydraulic oil pressure in the brake cylinder; the booster type digital hydraulic brake system further comprises a controller, a hydraulic pump, an accumulator, a hydraulic inertia pipe, a first digital on-off valve, and a second digital on-off valve; the first digital on-off valve is a two-position three-way valve, and the second digital on-off valve is a two-position two-way valve; The inlet end of the hydraulic inertia pipe is connected to an external oil tank through the hydraulic pump, and the outlet end is connected to the inlet of the first digital on-off valve; the first outlet of the first digital on-off valve is connected to the brake cylinder and the inlet of the second digital on-off valve, respectively, and the second outlet of the first digital on-off valve is connected to an external return tank as a return port; the accumulator is connected to the oil circuit at the inlet end of the hydraulic inertia pipe; the return port of the second digital on-off valve is connected to an external return tank; The controller is connected to the displacement detection system, the pressure detection system, the accumulator, and the hydraulic inertia pipe to obtain the position of the pedal device, the pressure signal of the rodless chamber of the brake cylinder, the pressure of the accumulator, and the flow signal of the hydraulic inertia pipe, and outputs control instructions to the hydraulic pump, the first digital on-off valve, and the second digital on-off valve; The controller controls the system to be in a brake preparation mode, a brake mode, or a closed mode according to the detection signals of the displacement detection system and the pressure detection system; When the controller does not receive the brake instruction signal of the displacement detection system, the system is in the brake preparation mode; at this time, the controller controls the first digital on-off valve to keep the right position and the second digital on-off valve to close; the hydraulic pump is in a low-power working state to save power consumption, and the controller always transmits the optimal driving frequency to the first digital on-off valve and the optimal duty cycle size and keeps a small valve opening to ensure that the hydraulic circuit maintains a high pressure under the condition of low-power working of the hydraulic pump The high-pressure hydraulic oil flows into the inlet and outlet ports of the bladder accumulator through the pipeline, compresses the air bag in the accumulator shell, and stores hydraulic energy; the rodless chamber of the brake cylinder has no hydraulic oil flow, and the brake block is located at the left limit position; When the controller receives a brake instruction signal from the displacement detection system, the system enters the brake mode; the controller controls the first digital on-off valve to switch to the left position, and the external oil tank flows into the rodless chamber of the brake cylinder through the hydraulic pump, the accumulator, the hydraulic inertia pipe, and the left position of the first digital on-off valve, pushes the piston rod to move to the right, and makes the brake block rub against the brake disc to achieve the brake effect; In the braking mode, hydraulic oil rapidly flows into the rodless cavity of the brake cylinder, the air bag in the accumulator housing expands, and the hydraulic oil remaining in the housing is pressed out from the inlet and outlet; the accumulator and the hydraulic inertia tube both input the energy stored in the braking preparation mode back to the circuit, so that the pressure before the cylinder Rises rapidly to the target braking pressure value; at the same time, the controller further accelerates the pressure rising speed, improves the pressure control precision, and reduces the hydraulic impact of oil on the hydraulic system by modulating the duty ratio and driving frequency of the first digital on-off valve. After the brake is completed, the controller controls the first digital on-off valve to switch back to the right position, and controls the second digital on-off valve to open, so that the hydraulic oil in the brake cylinder flows back to the tank through the second digital on-off valve, and the brake block returns to the initial limit position, completing a brake cycle; When the controller detects that the vehicle is parked and stationary, the brake system enters the closed mode, and the hydraulic pump is closed.

2. The brake control method according to claim 1, characterized by, The accumulator is a bladder accumulator, which stores hydraulic energy by compressing the air bag in the accumulator shell.

3. The brake control method according to claim 1, characterized by, When the first digital on-off valve remains in the right position, the inlet and the second outlet of the first digital on-off valve are in conduction, and when the first digital on-off valve remains in the left position, the inlet and the first outlet of the first digital on-off valve are in conduction.

4. The brake control method according to claim 1, characterized by, The brake cylinder is provided with a brake block; when the rodless chamber of the brake cylinder has no hydraulic oil flowing in, the brake block is located at the left limit position and maintains a sufficient safety distance from the brake disc to prevent the brake system from braking by mistake; when the rodless chamber of the brake cylinder is filled with liquid greater than a set value, the brake block rubs against the external brake disc to brake the vehicle.

5. The brake control method according to claim 1, characterized by, In the brake preparation mode, the hydraulic circuit is in a steady state, the actual pressure demand of the brake cylinder is 0 MPa, the pressure at the inlet end of the hydraulic inertia tube is , the outlet end is connected to the oil tank, the pressure is 0 MPa, and the hydraulic inertia tube will store hydraulic energy.

6. The brake control method according to claim 1, characterized by, In the braking mode, the hydraulic pump is in high-power working state to improve the response speed of the system braking; the controller always transmits the most suitable driving frequency to the first digital on-off valve and the most suitable duty cycle size and keeps a larger valve port opening so that high-speed high-pressure large-flow hydraulic oil passes through.

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