International Journal of Advanced Computer Science, Vol. 2, No. 7, Pp. 250-253, Jul., 2012.

Manuscript Received: 1, Sep., 2011

Revised:

2, Oct., 2011

Accepted:

9, Jun., 2012

Published: 15,Aug., 2012

Keywords

off-road

vehicles,

hydraulic

brake

systems,

bench

experiments,

Abstract The full power hydraulic

brake system has several advantages over

traditional brake actuation systems. These

systems are capable of supplying fluid to a

range of very small and large volume service

brakes with actuation that is faster than

air/hydraulic brake systems. Implementation

of full power hydraulic brake system in

off-road vehicles calls for good

understanding of its dynamic characteristics.

In this paper, we consider the problem of

dynamic modeling of the brake system and

develop a dynamic model for a hydraulic

brake valve. First, the dynamic

characteristics of full power hydraulic brake

system are analyzed theoretically. The effects

of varying design parameters (brake valve,

accumulator and so on) and the different

operating conditions are then analyzed.

Second, we investigate the dynamic

characteristics of a full power hydraulic

brake system using a test bench, which is a

loader brake system specifically designed for

one construction Machinery Company.

Finally, based on the experimental results,

the mathematical models are amended and

verified. The result shows that the

model-calculated dates agree well with tested

dates. The dynamic behavior of hydraulic

valve can be well predicted with the model.

The simplified models can be applied to the

studies of full power hydraulic brake system

dynamics.

1. Introduction

With its excellent brake performance and high reliability,

the full power hydraulic brake system has been widely

applied for the large-scale off-road vehicles abroad.

Compared with the domestic widely used air/hydraulic

brake system, the full power hydraulic brake system has the

properties of simpler circuit, closer structure, faster brake

and easier maintenance [1-8]. Thus the transference from

the air/hydraulic brake system to the full power hydraulic

brake system is the new development tendency for the brake

system of off-road wheel vehicles. Brake valves, as the key

hydraulic part in the full power hydraulic brake system its

Muyi Lin and Wenfeng Qu are with Mechanical and Electronic

Engineering School，Beijing Information Science & Technology University, Beijing, China. ( Lin.muyi@bistu.edu.cn, qu.wenfengxy@sina.com)

property is closely related to the safety and running

properties of the vehicles. Only when the dynamic behavior

and other related factors in the brake valves and the brake

system are kept under control during the braking can the

basis be supplied to the anticipation and analysis of the

brake system design and match and the whole brake

property.

2. Brake System and Hydraulic Brake

Valve

The main properties required by the double-circuit full

power hydraulic brake system of the off-road vehicles: The

pedal force is to be proportional to the pressure of the brake

system. The maximum pedal force is under 350N.The

operation is sensitive, the responsive time short and the

delay small. All the circuits can work simultaneously

without interfering with one another.

Fig. 1 Structure of brake valve

The parts that affect the property of the off-road vehicle

brake system are brake valves, accumulators, checking

cylinders and pipes; the most critical part is brake valve.

There are two kinds of hydraulic brake valves usually

applied by off-road vehicles. One is series adjustable brake

valve (Fig. 1). It is mainly applied in the double-circuit

hydraulic brake system. Another is pedal-controlled

reverse-adjusted brake valve that is mainly used for the

spring brake system. When the braking process is

commenced by the series hydraulic brake valve, Upper

Spool 2 moves downward under the action of the spring1,

and at the same time, the hydraulic power exerted by Upper

Spool 2 will push Lower Spool 3 downward. The two

spools will first close Return Port 4, and then connect

Accumulator Port 5 and Press Port 6 of the wheel brake

cylinder. The pedal force through the balance with the brake

Hydraulic Brake System Analysis Using Bench

Experiments for Off-Road Vehicles Muyi Lin, & Wenfeng Qu

Lin et al.: Hydraulic Brake System Analysis Using Bench Experiments for Off-Road Vehicles.

International Journal Publishers Group (IJPG) ©

251

pressure decides the brake force, and keeps the spool at the

controlling position until the brake pressure reaches the

required amount, which is remained by the spools at the

same time. The arrangement of the spools has the effect that

the failure of one circuit will not affect the function of

another only if the pedal travels slightly further.

The Mathematics Model of the operation process of the

brake valve is (1)-(6): 2

1 1 32

v vt f v

d x dxF m B k x A p

dt dt (1)

2

0 2 3 4 2 2

v vt v f v

d x dxk x x A p p m B k x

dt dt (2)

12 3 230 1 313

1 3 12

0196

a dpVdp p A

l dt K dt

(3)

12 3 230 1 2 43

2 4 22

0196

a V dpdp p A

l dt K dt

(4)

3 20

V dpdpC

dt K dt (5)

4 20

V dpdpC

dt K dt (6)

Where: Ft is component force of pedal. m is mass of

moving part. xv is spool displacement. B is moving damp

coefficient of spool. K is modulus of elasticity. kf is steady

state flow force constant. kt is return spring constant. x0 is

pre-compression of return spring. A1 is area of upper spool

land. A2 is area of lower spool land. P is accumulator supply

pressure. p1 is export pressure at upper spool. p2 is export

pressure at lower spool.p2 is export pressure at lower spool.

p3 is pressure at upper spool land. p4 is pressure at lower

spool land. δ is jaw opening. φ0 is restriction diameter. α1 is

restriction area. ν is kinematics viscosity. l0 is restrictive

length. C0 is volume coefficient of accumulator. V1 is

control volume of upper spool. V2 is control volume of

lower spool. V3 is volume of upper brake cylinder. V4 is

volume of lower brake cylinder.

On the basis of theoretic mathematics model of

hydraulic brake system, analysis is performed on the

dynamic property of the brake system, the result of which

leads to the design of double-circuit brake valve for the

off-road vehicles. It is an easy and effective approach to

analyze the vehicle brake dynamic property through the

study of dynamic property of the vehicle hydraulic brake

system. It is helpful to the analysis and improvement of the

whole brake system to make a theoretic study of the

dynamic property of the brake valve. However, the theoretic

analysis involves too many calculating parameters, some of

which are too hard to obtain, so theoretic model cannot

accurately anticipate the dynamic property of the system.

The experimental study of the brake valves can not only get

to know the dynamic property of the brake valves but also

simplify the calculating model of the brake system in the

study of the whole vehicle brake dynamics.

3. Bench Experiments of Brake System

The double-circuit full power hydraulic brake system

mainly consists of hydraulic pump, accumulators, brake

valve, charging valve and brakes. Based on the common

structure of off-road vehicle double-circuit full power

hydraulic brake system, the experimental system on the

brake system dynamic property is established through the

theoretic analysis of brake valves (Fig. 2).

Fig. 2 The experimental system

As required by the double-circuit brake valve property,

the brake valve pedal, the brake cylinder entrance and brake

valve entrance are respectively taken as the experimental

points, to which the payload sensors and pressure sensors

are attached. The resulting signals are indicated and

recorded on the dynamic strain gauge.

The dynamic property experiment mainly refers to

simulating the two representative situations of speed-down

and urgency brake to test the dynamic relation between the

brake valve pedal force and the brake cylinder pressure

under the conditions of system pressure as the brake valve

pressure rating; testing the brake valve dynamic property

after the system stops supplying oil; testing the

independence property of the double-circuit brake valve, i.e.

the dynamic property of brake valve after any of the inputs

or outputs of the brake valve is switched off.

4. The Experimental Results and

Analyses

Figure 3 shows the dynamic relation between the brake

pedal force and the brake cylinder pressure under the

speed-down brake condition with the system pressure of

14Mpa; Fig. 4 shows the dynamic relations among the brake

pedal force, input pressure and brake cylinder pressure after

the pump is stopped with the system pressure of 14Mpa.

The pressure undulation at the beginning of braking is

caused by the empty displacement of brake pistons. To start

moving, the pistons have to resist the sealing friction, which

will lead to the temporary decrease of pressure.

International Journal of Advanced Computer Science, Vol. 2, No. 7, Pp. 250-253, Jul., 2012.

International Journal Publishers Group (IJPG) ©

252

Fig. 3 Dynamic relation between the brake pedal force and the brake

cylinder pressure

Fig. 4 Dynamic relations among the brake pedal force, input pressure and

brake cylinder pressure

According to the results of experiment on dynamic

property of the brake valve, under different braking

conditions, the braking speed is the same fast and there is

almost no phase difference between pedal forces and

braking pressure, the braking pressure is proportionate to

pedal force to meet the requirements of the off-road vehicles

to brake system and brake valve. When the brake pump

stops supplying oil, though the brake pressure decreases

rapidly, the 70% of the required pressure can still be met

after three repeated brakes to meet the requirement of

IS03450 to the system.

Fig. 5 Independence property of the double-circuit brake valve

According to the results of the experiment on the

independence property of the double-circuit brake valve, at

the same pressure of oil supply system (14Mpa) and when

the input and output circuits are cut off respectively, the

braking speed of each leftover single circuit is fast, the

brake pressure is proportionate to the pedal force and there

is seldom phase difference between pedal force and brake

pressure to meet the property requirement of .double-circuit

brake valve with each independent circuit working

simultaneously and not interfering each other. Due to the

different demarcate values of pressure sensor; there is

difference in the scope of test curve under the same pressure

(Fig. 5).

5. Conclusion

It is the first step as well as an important basis in

evaluating the safety of the running vehicles to know the

dynamic property of the brake valve in the study of the

whole vehicle brake property; it is also significant to the

optimum match of the brake system and the other parts or

other system of the car, to the design of the whole hydraulic

brake system and to the longer use of parts and components.

The experiment on the dynamic property of brake valve is

also helpful to obtaining some calculating parameters that

are impossible in theoretic analysis, so that the total analysis

is possible on the effect of brake valve structure parameters

and application conditions on the hydraulic property, and

the foundation for further theoretic analysis and model

imitation is established. The results of the experiment

indicates that it is feasible to design the brake valve and

experiment system, proves the theoretic model, meets the

requirements of dynamic property analysis and research of

the brake valve and system, and offers important reference

to the design and quality improvement of the off-road

vehicle full power hydraulic brake system.

Acknowledgment

This project was supported by the Key Technologies

Research and Development programmer of ShanXi

province, China. The support is gratefully acknowledged.

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