Discussion on the Design and Evaluation Method of the Follow-up Force Characteristics of Vacuum Booster Chen Wenquan (Chongqing Hongyu Precision Industry Co., Ltd., Chongqing 402760) Method to improve the braking efficiency of the automobile and improve the comfort of braking. The article addresses different vacuum boosters. The input force and output force characteristics of the structure type are changed. The new design and evaluation methods of input force, output force follow-up section initial force, jump force, minimum assist point input force and output force are mainly proposed.
1 vacuum booster structure and working principle 1.1 vacuum booster and the relationship between the car brake system and its function Vacuum booster is an important component of the car brake system. In the automotive brake system, the vacuum booster is directly connected to the brake master cylinder, and then the vehicle brake system is formed by the brake line and front brake, rear brake, and hydraulic adjustment device (proportional valve or anti-lock device).
During braking, the vacuum booster is the primary actuator for the driver's braking operation. Therefore, the design quality and manufacturing quality of the vacuum booster will directly affect the braking performance of the car. In order to improve the reliability, stability, and operability of vehicle braking, it is necessary to become more familiar with and master the working principle and structural design and performance evaluation of the vacuum booster. In particular, with the continuous improvement of vehicle braking performance requirements, the design and accurate evaluation of the follow-up force characteristics of the vacuum booster is particularly important.
1.2 vacuum booster control valve assembly structure and working principle of the reaction disk type single diaphragm vacuum booster structure as an example, the vacuum booster is mainly from the front shell, rear shell, tray, diaphragm, control valve assembly and other zero Components. The diaphragm divides the vacuum booster cavity into a front cavity and a rear cavity. The main function of the control valve assembly is to control the input force and output force characteristics of the vacuum booster, and its structure is as shown.
The control valve assembly is the core component of the vacuum booster. It is mainly composed of valve body, reaction plate, vacuum valve spring, air valve spring, air valve plunger and control valve.
Under the action of the spring force of the vacuum valve spring and the air valve spring, the locking piece restricts the air valve plunger and the input force pushing rod to a relatively fixed ideal position through the limiting action of the locking piece, so that the control valve inner ring The end face is in close contact with the end of the air valve plunger to form an air valve. At the same time, the end plane of the control valve and the plane of the ring end of the valve body constitute a vacuum valve, and a certain clearance S is maintained so that the air valve plunger and the reaction disk are in a power transmission and output. The required clearance position for the force characteristics s-pillar, as shown.
Control valve assembly structure shows a reaction plate seat; 2 - reaction plate; 3 - air valve plunger; 4 a bun; 5 valve body; 6 air valve spring; 7 control valve; 8 * vacuum valve spring; 9 a lose The relationship between the structure and performance of the manipulator pusher 2 valve and the characteristics of the follow-up section force curve are different. During the design and use of the vacuum booster, due to the differences in the structure and performance of the control valve, the force characteristics of the control valve will change greatly, especially The change of the manpower and output force characteristics of the moving section is most obvious, and the influence on the booster is also greater. By analyzing the structure and force characteristics of the vacuum booster control valve, vacuum boosters can be classified into three categories according to the shape of the resulting characteristic curve: a. Standard force type vacuum booster; b Non-standard jump force type vacuum booster C; c non-standard jump-free vacuum booster. Its characteristic curve is as shown.
2.1 Input manpower, output force characteristic curve characteristic section definition According to the basic requirement of vacuum booster design, to accurately grasp the performance of the vacuum booster is to master the characteristics of the vacuum booster transmission manpower, output force characteristic curve linear transformation. Through the above analysis of the working relationship of the brake state control valve and the relationship between the vacuum booster input force and the output force characteristic curve, we can see that the lift curve of the input force and output force curve can be divided into 3 characteristic segments: 1st, 0st The C segment is the input force from the initial rise, the output force follows the growth and does not reach the characteristic section of the set assist ratio (minimum boost point below point C), is defined as the follow-up segment; the second segment is output force and output The proportional amplification relationship (set assist ratio) increases the characteristic segment, defined as the booster segment; the 3rd, £1-f segment output force increases the characteristic segment with the input manpower and is defined as the no-assistance segment.
In the actual application process, the manpower and output force of the follow-up segment are mainly applicable to the deceleration brake and the condition to be braked. According to different models and user groups, starting from the design requirements of the entire vehicle's braking performance, and starting from the requirements for vehicle comfort of different models, the input force and output force characteristics follow the initial force of the moving section and the jump force value. The minimum power input point F4 and the output force is a key design of vacuum booster performance.
2.2 Standard force characteristics The formation of the vacuum booster force characteristic curve The standard force characteristic vacuum booster control valve vacuum valve spring and air valve spring pre-pressure than the booster return spring pre-pressure / small. The displacement of the vacuum valve is less than the displacement of the air valve plunger, that is, the provisions of Article 31 of 37-1999 "Technical Conditions of Vacuum Booster". At this time, the input force acting on the vacuum booster is the initial force Fa. Because of the vacuum valve spring and The pre-pressure of the air valve spring is much smaller than the pre-pressure of the booster return spring/smaller, and the displacement of the vacuum valve is smaller than the displacement of the air valve plunger, ie ~
37-1999 "Technical Conditions of Vacuum Booster", Article 3.3, when the input force fA of the vacuum booster is in a state factory, the maximum output force is the jumping force.
As the input force acting on the delivery manipulator increases again, the air valve plunger continues to contact the reaction disk, and the compression reaction disk is generated according to the elastic modulus of the reaction disk rubber body and linearly related to the elastic force characteristics of the reaction disk. Displacement, so that the air valve is opened gradually and evenly, so that the pressure difference between the front and rear chambers of the vacuum booster is generated, thereby achieving a proportional servo assist effect.
With the action, the input manpower of the transmission manipulator increases, the air valve plunger continues to generate displacement, and the reaction plate is compressed until the air valve is fully opened. The vacuum booster front cavity and rear cavity achieve the negative pressure difference of the booster. That is to say, the maximum boost point of the vacuum booster is reached, and the segment C output manpower and output force characteristic curve are formed.
As the input force F acting on the delivery manipulator increases, the air valve plunger continues to displace, and continues to compress the reaction plate to open the air valve. However, the vacuum booster front cavity and rear cavity have been reached since they have been fully opened before. Saturated negative pressure difference. Therefore, at this time, the output force of the vacuum booster and the increase in delivery force are only a linear and equal increase in the servo relationship, resulting in a segment of the input force and output force curve of £.
The standard force characteristic vacuum booster delivers manpower and output force characteristics as shown in (a).
2.3 Formation of non-standard force-type vacuum booster force characteristic curve The pre-pressure of the vacuum valve spring and air valve spring of the non-standard jump force vacuum booster is greater than the pre-pressure/V of the booster return spring and the vacuum valve displacement Less than the air wide piston displacement stt (ie, with the increase in the human input, the force of the human effort and the booster return spring force / balance, but also because the booster return spring stiffness is greater than the vacuum valve spring and air The stiffness of the valve spring (ie, >p'*), the vacuum valve is not closed, the force of the delivery manpower can only cause the vacuum valve spring and the air valve spring to compress, and the delivery manipulator will produce a displacement until the vacuum valve is closed. The output power of the segment is basically a linearly increasing relationship with the input force L, forming a segment of the input manpower and output force characteristics.
As the input force increases, until the vacuum valve is closed, the booster front and rear chambers are isolated. In addition, the characteristics of the manpower and output force of the Ss non-standard jump force vacuum booster are shown in (b).
2.4 Formation of non-standard forceless vacuum booster force characteristic curve Non-standard non-jump force vacuum booster air valve plunger end structure is generally designed as a frustum, in the control valve assembly and the frustum The top surface remains in contact with the reaction disk, and the displacement of the air valve plunger is zero (ie, = 0).
At the beginning of the braking, the input manpower/acting on the delivery manipulator, due to = 0, the top surface of the air valve plunger truncated cone contact with the reaction plate, the displacement of the air valve plunger with the input force increases and the displacement occurs. . Because the vacuum valve is still at the distance of AS =Ss, the vacuum valve is closed. At this time, the original state of the vacuum valve and the air valve is not changed, so the reaction disk can only play a force transmission role. Until the force of the manpower is balanced with the force of the booster return spring, the output force mandrel has the tendency of displacement so as to generate the output force, forming a ―/1 section input force, output force characteristic curve segment.
With the increase in the amount of manpower, the air valve plunger will continue to displace the reaction plate until the vacuum valve is closed, and the front and rear chambers of the booster are isolated. The output force of this segment is basically linearly related to the input labor force fA, forming a /1 C segment input force and output force characteristic curve segment.
With the increase of the human power, the air valve plunger will continue to compress the reaction disk, and then the displacement will occur, and the air valve will gradually be opened to achieve the power-assist effect. The characteristics of the input manpower and output force of the non-standard jumpless vacuum booster are shown in (c).
3 vacuum booster follow-up section main performance design parameters vacuum booster follow-up section main performance design parameters are: starting power and jumping force, the minimum power point of the power transmission and the minimum power output point.
According to the physico-mechanical split, the free-to-work foot weight is 2~5N, the initial comfort pedal force is 10~25N, and the driving force of the human body's maximum power point is the input force at 130 3*1 minimum power point. The heart performance parameter design first sets the initial comfort pedal force according to the vehicle model ("the default is 15N"). The constant force (lever ratio) requires a constant force of 50NFt at 110N in the specific design process. 3.2 The starting dynamic performance parameter design is based on the input manpower and output. The force characteristics require that the starting power should be less than or equal to the minimum power point, ie, manpower.
The initial force Fa of the jump force non-standard manpower transmission and output force characteristic curve is smaller than the constant force F6, ie. Main (Main Cylinder Working Cross Section Area) 3.4 Minimum Boost Point Output Force 'Performance Parameter Design Minimum Boost Point Output Force*// Mainly to ensure the hydraulic pressure at the initial braking of the brake system. According to the initial braking of the brake The design principle of the hydraulic pressure is mainly to ensure the stability of the initial braking state, so as to adapt to the force requirements of the braking driver. Therefore, the general design P′ is not a linear relationship for the standard transmission manpower and output force characteristic curve at first. There is still some difference between the evaluation value and the actual status. Therefore, using the output manpower-output force test method to evaluate the starting force and jumping force of the follow-up segment can only be a stereotypical evaluation.
In order to accurately reflect the follow-up dynamic characteristics of each type of vacuum booster, it is necessary to analyze the relationship between follow-up displacement and force (transmission force, output force). For the starting force of the vacuum booster 8, the jump force, the relationship between the manpower of the minimum assistance point and the output force/p' of the minimum assist point, the displacement-input force and output force characteristic test method can be used to determine the follow-up starting torque. , Jumping power, minimum power input point and minimum power point output force J;: accurate evaluation.
4.1 Non-standard force-type vacuum booster displacement manpower, output force characteristic curve form For non-standard jump force type vacuum booster, according to the output manpower output force characteristic test method to evaluate its initial force and jump force are respectively The displacement-input manpower and output force characteristics test methods are shown in (b). By correspondingly finding out the position relationship between follow-up segment input force and output force follow-up displacement feature point, it is possible to accurately evaluate the starting force of the follow-up segment, the jumping force, the manpower of the minimum assist point and the output force of the minimum assist point.
The comparison of the characteristic curves of the two evaluation methods can be seen as follows: the minimum power output point is the input power F, and the output power greater than the minimum power supply point at the initial power is greater than the original standard evaluation jump force. That is, F6 = F6 >々; A person-person.
4.2 Standard force characteristics Type of vacuum booster manpower, output force curve For the standard force type vacuum booster, according to the output manpower an output force test method to evaluate the starting force, jump force and 7P '. According to the displacement An input force, output force characteristics test method, characteristic curve shown in (a). The comparison of the characteristic curves of the two evaluation methods can be seen: At this time, the starting dynamical center of the two characteristic curves is equal to the minimum assisting point output manpower center, that is, the factory = heart, the jumping force value and the output power of the minimum boosting point. Equivalence, ie /p, can further prove that when the displacement-input manpower and output force characteristic test method is used to evaluate the initial force and the jump force, the standard force and the starting force and the jumping force of the output force characteristic curve can be considered. The value is considered as a special case of the initial force and the jumping force of the jump force non-standard curve.
4.3 The formation of the input force and output force characteristic curves of non-standard non-maneuvering vacuum booster For the non-standard non-jumping vacuum booster, the initial force and jumping force are evaluated according to the test method of the output manpower output force. And '. According to the displacement of an input force, output force characteristics of the test method, its initial power, the minimum power point of the human input force, the minimum power output point power man'. Its characteristics as shown in (c).
There is a big difference between the two evaluation methods. The starting force and jumping force of the evaluation using the input force and output force characteristic curve are all very small, and the jumping force also shows a negative value. The initial force of the displacement-input manpower and output force curve evaluation is consistent with the former, but the output manpower and output force characteristics of the vacuum booster are evaluated as a function of the manpower of the linear transformation feature of the motion segment and the output force of the input force point. In order to further improve the maneuverability and safety reliability of the car, and improve the structure and performance design of the vacuum booster control valve, the force characteristics of the follower section of the vacuum booster can be changed. Through the analysis of the test results of the three types of vacuum booster follow-up force characteristics, it is proved that the displacement-input manpower and output force characteristics test method is used to carry out the initial force f, the jumping force center, and the minimum power point to deliver human support. The evaluation of the minimum power output point is feasible and reasonable, and the evaluation result is scientific and accurate.
Member level engineer, engaged in the development and design of automotive brake systems for more than 20 years.
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