CN112721895B - IEHB system master cylinder hydraulic pressure estimation method based on friction model - Google Patents

IEHB system master cylinder hydraulic pressure estimation method based on friction model Download PDF

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CN112721895B
CN112721895B CN202110104823.9A CN202110104823A CN112721895B CN 112721895 B CN112721895 B CN 112721895B CN 202110104823 A CN202110104823 A CN 202110104823A CN 112721895 B CN112721895 B CN 112721895B
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史彪飞
熊璐
余卓平
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Tongji University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T13/00—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems
    • B60T13/74—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with electrical assistance or drive
    • B60T13/745—Transmitting braking action from initiating means to ultimate brake actuator with power assistance or drive; Brake systems incorporating such transmitting means, e.g. air-pressure brake systems with electrical assistance or drive acting on a hydraulic system, e.g. a master cylinder
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B60—VEHICLES IN GENERAL
    • B60T—VEHICLE BRAKE CONTROL SYSTEMS OR PARTS THEREOF; BRAKE CONTROL SYSTEMS OR PARTS THEREOF, IN GENERAL; ARRANGEMENT OF BRAKING ELEMENTS ON VEHICLES IN GENERAL; PORTABLE DEVICES FOR PREVENTING UNWANTED MOVEMENT OF VEHICLES; VEHICLE MODIFICATIONS TO FACILITATE COOLING OF BRAKES
    • B60T17/00—Component parts, details, or accessories of power brake systems not covered by groups B60T8/00, B60T13/00 or B60T15/00, or presenting other characteristic features
    • B60T17/18—Safety devices; Monitoring
    • B60T17/22—Devices for monitoring or checking brake systems; Signal devices

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  • Mechanical Engineering (AREA)
  • Regulating Braking Force (AREA)
  • Testing Of Devices, Machine Parts, Or Other Structures Thereof (AREA)

Abstract

The invention relates to an IEHB system master cylinder hydraulic pressure estimation method based on a novel friction model, which comprises the following steps: 1) establishing a kinetic equation of the IEHB system; 2) testing the friction force of the IEHB system; 3) establishing a novel recursion friction model according to a friction force test result; 4) estimating the master cylinder hydraulic pressure according to the dynamic equation of the IEHB system obtained in the step 1) and the novel recursive friction model obtained in the step 3). Compared with the prior art, the invention has the advantages of reducing the IEHB cost, improving the safety and reliability and the like.

Description

IEHB system master cylinder hydraulic pressure estimation method based on friction model
Technical Field
The invention relates to the technical field of automobile brake-by-wire, in particular to an IEHB system master cylinder hydraulic pressure estimation method based on a friction model.
Background
An Integrated Electro-Hydraulic brake (IEHB) system integrates a servo electric supercharging device and a master cylinder, can quickly and accurately adjust output brake pressure through a combined Hydraulic adjusting unit while ensuring compact integral structure, and can integrate the active safety function of the novel whole vehicle more conveniently.
Because the IEHB system has the main and wheel cylinder hydraulic pressure decoupling capability and the active pressure building function, the braking energy recovery maximization of the electric vehicle and the automatic driving functions of the intelligent driving vehicle, such as AEB (automatic braking system), ACC (Adaptive cruise control) and the like, can be realized, and the IEHB system has become the development trend of the future vehicle braking system. At present, mass-produced IEHB systems are equipped with a master cylinder hydraulic pressure sensor to realize feedback control on master cylinder hydraulic pressure, but increase product cost and risk of sensor failure. Part of the IEHB systems utilize a method of mutual detection of two master cylinder hydraulic pressure sensors to solve the problems of sensor failure detection and backup, but the system cost is further increased.
In order to improve the sensor failure safety of the IEHB system under the condition of not increasing the cost as much as possible and ensure the market competitiveness of products, a master cylinder hydraulic pressure estimation algorithm is particularly important. At present, research on the IEHB system at home and abroad mainly focuses on the aspects of configuration design and hydraulic pressure control of a master cylinder and a wheel cylinder, and research on master cylinder hydraulic pressure estimation is not common. The domestic thesis is not available, a small amount of research is carried out abroad, the hydraulic pressure control is mainly aimed at, the hydraulic pressure estimation is only aimed at control service, and the estimation precision is not high.
In the aspect of master cylinder hydraulic pressure control, domestic and foreign scholars have conducted extensive research on the core problem of friction nonlinearity. And hydraulic pressure control strategies based on flutter signal compensation, Stribeck friction model compensation, LuGre friction model compensation and the like are provided, and the system linearity and the hydraulic pressure control precision are improved. However, the dither signal causes vibration and noise of the brake system, reduces riding comfort and increases power consumption of the system, and thus the system cannot be put into mass production. The method for compensating the traditional friction model has the contradiction between the model precision and the engineering practicability, the high-precision friction model usually needs large test amount and parameter identification workload, in addition, an IEHB system usually comprises a plurality of friction links of different types, and whether the overall friction characteristic still accords with the traditional friction model needs to be further verified. In conclusion, the development of master cylinder hydraulic pressure estimation of the brake-by-wire system is of great significance, and in addition, the core difficulty of hydraulic pressure estimation, namely modeling of friction force, is also required to be further researched.
Disclosure of Invention
The invention aims to overcome the defects of the prior art and provide an IEHB system master cylinder hydraulic pressure estimation method based on a friction model.
The purpose of the invention can be realized by the following technical scheme:
the IEHB system master cylinder hydraulic pressure estimation method based on the friction model comprises the following steps:
s1: and establishing a kinetic equation of the IEHB system. The kinetic equation is a mathematical model of the IEHB system established according to newton's second law. The dynamic equation comprises five items, namely inertia force, motor thrust, hydraulic thrust, friction force and rack return spring elasticity of the IEHB system.
S2: the IEHB system was tested for friction. The friction force of the IEHB system is tested by acquiring all unknown items except the friction force in the kinetic equation of the IEHB system, including some mechanical parameters and sensor information, so that the friction force can be tested through experiments.
S3: and establishing a recursion friction model according to the friction force test result. Namely, after the friction force is obtained, a novel friction model is established according to the specific change rule of the friction force.
S4: the master cylinder hydraulic pressure is estimated from the IEHB kinetic equation of step S1 and the recursive friction model of step S3.
Estimating the master cylinder hydraulic pressure refers to calculating an unknown term, i.e., the master cylinder hydraulic pressure, based on known terms in the IEHB system dynamics equation, such as the friction model created in step S3, and the like.
Compared with the prior art, the friction model-based IEHB system master cylinder hydraulic pressure estimation method provided by the invention at least has the following beneficial effects:
the invention fills the domestic blank in the estimation of the main cylinder hydraulic pressure of the IEHB system, can reduce the dependence of the IEHB on the hydraulic pressure sensor under the condition of not increasing the cost of the IEHB system, improves the failure safety of the hydraulic pressure sensor, or further omits the main cylinder hydraulic pressure sensor, thereby further reducing the cost of the IEHB and improving the safety and the reliability.
The novel friction model provided by the invention consists of a linear function, and compared with a Stribeck model which contains an index term and a LuGre model which contains a differential equation set, the novel friction model is simpler in form, simple in calculation and low in requirement on a controller; secondly, the novel friction model provided by the invention is easy to identify parameters, and compared with the Stribeck model and the LuGre model which require a large number of tests, the identification test workload is greatly reduced because the speed is basically irrelevant.
The novel friction model provided by the invention is obtained according to the rule of IEHB friction characteristics, and directly gives the rule that the friction force changes along with the motor torque, so that the method is more visual and credible, and has higher accuracy for master cylinder hydraulic pressure estimation.
The novel friction model and the master cylinder hydraulic pressure estimation method provided by the invention are reasonable and feasible, have typicality and universality, and the whole set of methodology for acquiring the novel friction model according to the change rule of the friction force along with the motor torque has guiding significance.
Drawings
Fig. 1 is a schematic diagram of the main structure of an IEHB system employed in the embodiment;
as indicated by the reference numbers in fig. 1:
1. the system comprises an electric control unit, 2, a permanent magnet synchronous motor, 3, a speed reduction transmission mechanism, 4, a liquid storage tank, 5, a normally open electromagnetic valve, 6, a hydraulic pressure sensor, 7, a brake wheel cylinder, 8, a brake master cylinder, 9, a decoupling cylinder, 10, a pedal simulator, 11, a pedal displacement sensor, 12 and a brake pedal;
FIG. 2 is a schematic diagram of a main cylinder hydraulic pressure estimation method of an IEHB system based on a friction model in an embodiment;
FIG. 3 is a schematic diagram of a motor torque signal for a friction test in an embodiment, wherein different point types represent different time courses for clearly expressing a change rule of the motor torque along with time;
FIG. 4 is a schematic diagram of a test result of the friction force in the embodiment, wherein different point types represent different time courses for clearly expressing a change rule of the friction force along with the motor torque;
fig. 5 is a schematic diagram of a test result of rack displacement varying with a target motor torque in the embodiment, wherein different point types represent different time courses in order to clearly express a variation rule of rack displacement varying with the target motor torque;
FIG. 6 is a diagram illustrating a test result of master cylinder hydraulic pressure varying with rack displacement in an embodiment, wherein different point types represent different time courses in order to clearly express a variation rule of master cylinder hydraulic pressure varying with rack displacement;
FIG. 7 shows the friction test results and fitting results of the motor torque signals with different frequencies in the embodiment;
fig. 8 is a graph showing the bench test effect of master cylinder hydraulic pressure estimation in the embodiment, in which fig. 8(a) shows the test effect of the maximum pressure 65bar at the pressure rise time 2.3 seconds, fig. 8(b) shows the test effect of the maximum pressure 72bar at the pressure rise time 1.4 seconds, fig. 8(c) shows the test effect of the pressure rise time 0.8 seconds, and the maximum pressure 86bar at the pressure rise time 86bar, fig. 8(d) shows the test effect of the pressure rise time 1 seconds, and the maximum pressure 82bar at the pressure rise time 0.6 seconds, fig. 8(e) shows the test effect of the maximum pressure 82bar at the pressure rise time 2 seconds, and fig. 8(f) shows the test effect of the maximum pressure 65bar at the pressure rise time 2 seconds.
Detailed Description
The invention is described in detail below with reference to the figures and specific embodiments. It is to be understood that the embodiments described are only a few embodiments of the present invention, and not all embodiments. All other embodiments, which can be obtained by a person skilled in the art without any inventive step based on the embodiments of the present invention, shall fall within the scope of protection of the present invention.
Examples
The invention relates to an IEHB system master cylinder hydraulic pressure estimation method based on a friction model, the main structure of the IEHB system adopted in the embodiment is shown in figure 1, and the IEHB system comprises the following components:
a brake pedal unit: the brake pedal 12 assembly is included and reflects the driving intention of a driver;
an active voltage building unit: the brake system comprises a motor (a permanent magnet synchronous motor 2 in the embodiment), a worm gear, a worm and a gear rack (a speed reduction transmission mechanism 3 in the embodiment), wherein the motor is used for converting the rotating torque of the motor into translational thrust on the rack so as to push a master cylinder to generate corresponding brake hydraulic pressure;
a brake execution unit: the brake system comprises a brake master cylinder 8, brake wheel cylinders 7, electromagnetic valves (normally open electromagnetic valves 5 in the embodiment), a liquid storage tank 4 and a hydraulic pipeline, wherein the brake master cylinder is used for converting thrust on a rack of an active pressure building unit into hydraulic pressure of each wheel cylinder, and finally, a friction pad at the end of each brake wheel cylinder acts on a brake disc to generate corresponding brake torque;
a control unit: the system comprises an IEHB controller (an electronic control unit 1 in the embodiment), a hydraulic pressure sensor 6, a pedal displacement sensor 11, a pedal force sensor (a pedal simulator 10 in the embodiment) and related circuits, and is used for obtaining pedal force and pedal travel signals, then calculating the braking intention of a driver, calculating target braking pressure, and calculating target motor torque through feedback signals of the pressure sensors to realize pressure closed-loop control. Note: in the test, the IEHB can respond to the braking intention of a driver and can also respond to the target hydraulic pressure or the target motor torque directly given by the upper computer. That is, in the friction force test of the present embodiment, it is mainly performed by directly giving the target motor torque. When the master cylinder hydraulic pressure is estimated, the IEHB system calculates the target motor torque according to an internal algorithm and then outputs the target motor torque by stepping on a brake pedal by a driver.
Aiming at the IEHB system, the specific implementation steps of the IEHB system master cylinder hydraulic pressure estimation method based on the friction model are as follows:
step one, from a motor rotor, a worm wheel and a gear shaft of the IEHB system to a rack and a master cylinder piston, the system friction force (including a mechanical part and a hydraulic part) is considered in a centralized way and is equivalent to the rack for modeling, and a dynamic equation of the IEHB system can be obtained according to a Newton second law, wherein the equation is shown as a formula (1):
Figure GDA0003351535450000051
in the formula: mgGeneralized rack mass;
Figure GDA0003351535450000052
the acceleration of the rack is adopted, the pressure building direction is positive, and the acceleration can be obtained by an angular position sensor arranged on the permanent magnet synchronous motor; t ismThe pressure building direction is positive for the motor moment, and the response speed of the motor is far higher than the hydraulic pressure, so that the target motor moment can be obtained; i is the worm gear transmission ratio; r isgIs the gear engagement radius; a. themIs the master cylinder piston area; p is a radical ofmThe hydraulic pressure of the main cylinder is obtained by a hydraulic pressure sensor when the friction force is tested; ffFor system friction force, during pressure build-upPositive, negative when pressure is released; fmsThe value of the elastic force of the return spring of the main cylinder is always positive due to the existence of the pretightening force.
Step two, after obtaining variables except the friction force in a dynamic equation of the IEHB system, testing the friction force according to the formula (2);
Figure GDA0003351535450000053
step three, in the bench test, a target motor torque signal of the IEHB system shown in fig. 3 is given through the upper computer, and a test result is shown in fig. 4. The change rule of the friction force of the system along with the target motor torque is vividly shown, and different time schedules are shown in different point types.
In fig. 5, when the target motor torque increases from zero to about 0.2Nm, the rack displacement rapidly increases from an initial value (about 0.64mm) to about 7mm, and fig. 6 shows that the change in the master cylinder hydraulic pressure during this period is small, and if the inertial force is ignored
Figure GDA0003351535450000054
And return spring force (F)ms) The increase amplitude of the friction force of the system is almost equal to the target motor thrust force
Figure GDA0003351535450000055
The same is true.
In fig. 6, after the rack displacement exceeds 7mm, the master cylinder hydraulic pressure increases as the rack displacement increases, and therefore the system friction force and the speed of increase of the rack displacement with the target motor torque become slow.
Fig. 5 shows that when the target torque is reduced, the rack displacement is almost constant, and the master cylinder hydraulic pressure is also almost constant, and the system friction force is changed from the previous dynamic friction to the static friction state, namely, the friction force is greatly opposite to the external force and the like. Therefore, as the target torque decreases, the system frictional force immediately decreases, and as shown in fig. 4, if the inertial force and the return spring elastic force are ignored, the magnitude of the decrease in the system frictional force is almost the same as the target motor thrust.
When the target motor torque is reduced to about 1.8Nm, the system friction is reduced to 0 and starts to increase reversely; when the target motor torque is reduced to about 1Nm, the rack displacement starts to be obviously reduced, and the static friction is changed into dynamic friction. Thereafter, as the motor torque is further reduced, the system friction is reduced.
When the target motor torque is increased again, the rack displacement is almost unchanged, the main cylinder hydraulic pressure is also almost unchanged, and the system friction force is changed into a static friction state from dynamic friction. Therefore, the system friction force increases immediately as the target motor torque increases, and if the inertia force and the return spring force are neglected, the increase range of the system friction force is almost the same as the target motor thrust force.
As the target motor torque increases, to about 1.2Nm, the rack displacement begins to increase significantly and the static friction becomes kinetic friction. At this time, the master cylinder hydraulic pressure increases as the rack displacement increases, and therefore the system friction force and the rack displacement become slower as the increase speed of the target torque increases.
The change law of the friction force along with the motor torque can be summarized as follows: when the target motor torque is increased, the system friction force is increased from the current value by the slope of the 2 line, and when the system friction force is increased to meet the 1 line, the system friction force changes along the 1 line. When the target motor torque is reduced, the system friction force is reduced from the current value by the slope of the 2 line, when the system friction force is reduced to be intersected with the 3 line, the system friction force changes along the 3 line, and when the target motor torque is increased, the system friction force is increased from the current value by the slope of the 2 line, when the system friction force is increased to be intersected with the 1 line, the system friction force changes along the 1 line. And the process is repeated in a reciprocating way.
In order to further study the influence of the operating speed of the IEHB system on the system friction, the relationship between the system friction and the target motor torque under the IEHB common working condition (the maximum value of the target motor torque triangular wave signal is 2.25Nm, and the periods are 45s, 22.5s, 11.25s, 4.5s and 2.25s, respectively) was tested.
Therefore, the system friction force and the target motor torque are in a strong piecewise linear function relationship and are not greatly influenced by the change of the operation speed of the IEHB system. Therefore, the linear function is used to perform a piecewise fitting on the system friction, and the result is shown in fig. 7. Wherein, the expressions of the 1 line, the 2 line and the 3 line are respectively expressed as formulas (3), (4) and (5).
Ff＝424.8Tm+120.204 (3)
Ff＝2334.4Tm-4133.4 (4)
Ff＝-953.256Tm-91.216 (5)
Designing a recursive friction model according to the change rule of the system friction force along with the target motor torque, wherein the change rule of the system friction force along with the target motor torque is as follows: when the target motor torque is increased, the system friction force is increased from the current value by the slope of the 2 line, and when the system friction force is increased to meet the 1 line, the system friction force changes along the 1 line. When the target motor torque is reduced, the system friction force is reduced from the current value by the slope of the 2 line, when the system friction force is reduced to be intersected with the 3 line, the system friction force changes along the 3 line, and when the target motor torque is increased, the system friction force is increased from the current value by the slope of the 2 line, when the system friction force is increased to be intersected with the 1 line, the system friction force changes along the 1 line. And the process is repeated in a reciprocating way.
The expression of the generated recursive friction model is as follows:
when k is 1:
Ff(1)＝424.8Tm(1)+120.204 (6)
when k is more than or equal to 2:
Figure GDA0003351535450000073
or
Figure GDA0003351535450000071
Wherein k is the number of discrete system operations. And (3) when the friction force is on a 1 line (namely formula (6)) at the step 1, and the friction force at the step 2 and later is counted, determining the friction force at the step according to the change situation of the current motor torque relative to the motor torque at the last step and the magnitude of the friction force at the last step, namely formula (7), and calculating step by step to obtain a recursion friction model, namely, because the friction force at each moment is related to the friction force at the last moment, the friction force at each moment is recurred step by step after the friction force at the given initial moment. This given friction is given by the formula (6), and the formula (7) is recurred step by step.
Compared with the conventional friction model, the conventional friction model is a formula with a specific form, describes one or more specific characteristics of the friction force according to the friction principle, and is a model specially researched for the friction force. The novel recursive friction model provided by the embodiment of the invention is novel in that a model based on a test data 'rule' is provided. Specifically, for example, a coulomb friction model in a conventional model, which basically has the friction force proportional to the positive pressure, the friction force can be calculated given the positive pressure and the friction coefficient. The friction force of the model of the invention is only related to the motor torque, and the motor torque is neither positive pressure nor friction coefficient, but the change rule of the friction force along with the motor torque described by the model of the invention can be explained by the conversion of dynamic and static friction force, and the model is a semi-empirical model.
And step four, after a dynamic model and a recursive friction model of the IEHB system are obtained, estimating the master cylinder hydraulic pressure according to the formula (8).
Figure GDA0003351535450000072
The quantity which can be directly obtained according to the IEHB system is the rack displacement of a rack displacement sensor (or a motor rotor angular position sensor), and in addition, the rack acceleration can also be obtained by solving two guide meters. The motor torque may be obtained from the target motor torque. Other variables, e.g. rack mass MgWorm gear transmission ratio i and gear meshing radius rgMaster cylinder piston area AmEtc. are all design parameters, known terms. The return spring force can be obtained by testing alone in earlier experiments, and is a function of rack displacement and is also a known item. The friction force is a known item by establishing a novel friction model, namely, only the hydraulic pressure in a dynamic equation is unknown, so that the hydraulic pressure can be estimated.
The specific verification is implemented as follows:
in order to verify the universality of the main cylinder hydraulic pressure estimation algorithm, a driver steps on a brake pedal according to normal driving habits, an electric control unit of an IEHB system responds to the braking intention of the brake pedal, the hydraulic pressure estimation algorithm calculates an estimated value of the main cylinder hydraulic pressure through an IEHB dynamic model including a recursion friction model according to target motor torque calculated by the electric control unit and IEHB motor angular position sensor information, and the actual hydraulic pressure is obtained by a hydraulic pressure sensor. The test results are shown in fig. 8(a) to 8 (f). Fig. 8(a) shows the test effect of the pressure rise time of 2.3 seconds and the maximum pressure of 65bar, fig. 8(b) shows the test effect of the pressure rise time of 1.4 seconds and the maximum pressure of 72bar, fig. 8(c) shows the test effect of the pressure rise time of 0.8 seconds and the maximum pressure of 86bar, fig. 8(d) shows the test effect of the pressure rise time of 1 second and the maximum pressure of 82bar, fig. 8(e) shows the test effect of the pressure rise time of 0.6 seconds and the maximum pressure of 82bar, and fig. 8(f) shows the test effect of the pressure rise time of 2 seconds and the maximum pressure of 65 bar. Therefore, the estimated value of the hydraulic pressure can stably and accurately track the actual hydraulic pressure under the normal driving working condition. And counting the estimated value and the actual value when the hydraulic pressure is greater than zero to obtain the root mean square error of 2.05 bar. Typically, the pressure variation that the driver can feel is 5bar, so the accuracy of the hydraulic pressure estimation meets the engineering application requirements.
While the invention has been described with reference to specific embodiments, the invention is not limited thereto, and those skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope of the invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the claims.

Claims (4)

1. An IEHB system master cylinder hydraulic pressure estimation method based on a friction model is characterized by comprising the following steps:
1) establishing a kinetic equation of the IEHB system;
2) testing the friction force of the IEHB system;
3) after the friction force of the IEHB system is obtained, a recursion friction model is established according to the specific change rule of the friction force;
4) estimating the master cylinder hydraulic pressure according to the dynamic equation of the IEHB system obtained in the step 1) and the recursive friction model obtained in the step 3); the concrete contents are as follows:
estimating an unknown item, namely the master cylinder hydraulic pressure according to the known item in the kinetic equation of the IEHB system and the recursive friction model established in the step 3);
the estimation formula of the master cylinder hydraulic pressure is as follows:
Figure FDA0003351535440000011
in the formula: p is a radical ofmFor master cylinder hydraulic pressure, MgIn the sense of the generalized rack mass,
Figure FDA0003351535440000012
is the acceleration of the rack, the pressure building direction is positive, TmIs motor torque, the pressure build-up direction is positive, i is the worm gear transmission ratio, rgIs the gear engagement radius, AmIs the master cylinder piston area, FfIs the friction force of the system, positive when building pressure, negative when releasing pressure, FmsThe value of the elastic force of the return spring of the main cylinder is always positive.
2. The friction model based IEHB system master cylinder hydraulic pressure estimation method of claim 1, wherein the equation of dynamics of the IEHB system is a mathematical model of the IEHB system established according to newton's second law.
3. The friction model based IEHB system master cylinder hydraulic pressure estimation method of claim 2, wherein the equation of dynamics of the IEHB system is expressed as:
Figure FDA0003351535440000013
in the formula: mgIn the sense of the generalized rack mass,
Figure FDA0003351535440000014
is the acceleration of the rack, the pressure building direction is positive, TmIs motor torque, the pressure build-up direction is positive, i is the worm gear transmission ratio, rgIs the gear engagement radius, AmIs the master cylinder piston area, pmIs master cylinder hydraulic pressure, FfIs the friction force of the system, positive when building pressure, negative when releasing pressure, FmsThe value of the elastic force of the return spring of the main cylinder is always positive.
4. The friction model based IEHB system master cylinder hydraulic pressure estimation method of claim 1, wherein the specific content of step 2) is:
all unknown items except the friction force in the IEHB system kinetic equation are obtained, including mechanical parameters and sensor information, the unknown items are converted into known items, and the friction force is tested through experiments according to all the known items.
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