hydraulic brake system analysis using bench experiments for off-road vehicles
DESCRIPTION
Muyi Lin, Wenfeng QuInternational Journal of Advanced Computer Science, Vol. 2, No. 7, Pp. 250-253, Jul., 2012.TRANSCRIPT
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. ( [email protected], [email protected])
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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Lin et al.: Hydraulic Brake System Analysis Using Bench Experiments for Off-Road Vehicles.
International Journal Publishers Group (IJPG) ©
253
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