- Detail

At present, there are two major developments and two major trends in the design of the braking system of wheel loaders. One is that the service brake is developing towards the closed wet type. The brake is fully enclosed, waterproof and dustproof, with stable braking performance, wear resistance and long service life, and does not need to be adjusted. The heat dissipation effect is good, and the temperature of the friction pair is significantly reduced. Changing the number of friction discs without increasing the radial size can adjust the braking torque and realize serialization and standardization. The second is the development of brake transmission device from air to oil to full hydraulic power braking. The brake pedal of this brake device directly operates the brake hydraulic valve, which can save pneumatic components, has a simple and compact structure, won't freeze in winter, doesn't need to drain water for maintenance, won't rust the valve and pipeline, and improves the braking reliability. Therefore, it is more and more used in the braking system of wheel loaders. This paper briefly introduces the design and calculation methods and steps of this system. The principle of full hydraulic service braking system is shown in Figure 1, and the principle of parking braking system is shown in Figure 2

1 hypothetical conditions reduce machine failure and braking performance requirements 1.1 hypothetical conditions ignore air resistance, and assume that the braking torque of the four wheels is equal and works at the same time; The parking brake braking torque acts on the output end of the transmission or the input end of the drive axle. 1. Section 32 braking performance requirements 1.2.1 the requirements for braking distance are in accordance with GB (equivalent to ISO), and the requirements for braking distance (horizontal road surface) of off highway machinery are shown in Table 1. Table 1 braking distance of off highway machinery maximum speed

(km/h) maximum mass

(kg) braking distance of service braking system

(m) braking distance of auxiliary braking system

(m) ≥ 32/θ ≤32000V2/68+（V2/124）. （G/32000）V2/39+（V2/130）. （G/32000）≥32000V2/44V2/30≤32/ θ ≤32000V2/68+（V2/124）. （G/32000）+0.1(32-V)V2/39+（V2/130）. (g/32000) + 0.1 (32-v) ≥ 32000v2/44+0.1 (32-v) v2/30+0.1 (32-v) * V - initial braking speed (km/h) g - working mass of the whole machine (kg) 1.2.2 the performance requirements of the driving system not only meet the requirements of braking distance, but also require that the driving braking system can meet the requirements of the loader to stop on the slope of 25% (14.0) without load. 1.2.3 when the auxiliary braking system is fully loaded, it is required to park on a 15% (8.5) ramp without sliding; When no-load, there should be no slippage on the ramp of 18% (1 is the industrial form of socialized cooperation in the industrial chain and realizing cross-border cooperation 0.2). When the service braking system fails, it shall be used as emergency braking. 2 Calculation of braking torque 2.1 calculate the total braking torque mb1:mb1 of four-wheel braking wheel loaders on horizontal roads according to the required braking distance= δ. (N.m)

a1=v02/[25.92 (s0-v0.t1/3.6)] (m/s2)

where G - working mass of the whole machine (kg)

a1 - braking deceleration (m/s2)

rk - wheel rolling radius (m)

δ— Slewing mass conversion coefficient

δ= 1+[4Jk+ Σ (2) ]/(RK2. G)

jk - moment of inertia of tire and rim (kg.m2)

jm__ M moment of inertia of rotating parts (kg.m2)

im - M transmission ratio from rotating parts to wheels

if JK and JM are not known, approximation can be taken δ= 1.1

v0 - initial braking speed (km/h)

wheel loader v0=20km/h

s0 - braking distance (m) when v=v0 in Table 1

t1 - braking system lag time (s)

for full hydraulic braking system, take t1=0.22.2 to calculate the total braking torque according to parking on the ramp (1) when using service brake, the total braking torque

mp1=n14 RK) (N.m)

where G - gravitational acceleration (m/s2)

(2) total braking torque when parking brake is unloaded

mp2=n10.2 RK) (N.m)

(3) total braking torque when parking brake is fully loaded

mp3= (g+w) n8.5 . RK) (N.m)

where W - rated load mass of loader (kg)

according to the calculation of 2.1 and 2.2, the required total braking torque of service braking

m'b=max{mb1, mp3}

required parking brake total braking torque

m'p=max{mp1, mp3}; 2.3 check the total braking torque according to the attached long parts (1) horizontal road service braking

mbu=g.g δ. (N.m)

u - the sliding friction coefficient between the tire and the cement pavement is generally taken as u=0.6 (2) no-load parking brake on the ramp

mpu1=cos10.2/() (N.m)

f - the static friction coefficient between the tire and the cement pavement

id - the transmission of the main drive of the axle

if - the transmission of the final drive of the axle (3) the full load parking brake on the ramp always produces differential error

mpu2 (g+w) Cos8.5/() (N.m)

in fact, mpu1 mpu22.4 braking torque determination, taking into account the calculation results of 2.1, 2.2 and 2.3, the total braking torque MB of service braking should meet

MB = min{m'b, MBU}

the total parking braking torque MP should meet:

MP = min{mp, mpu1}

after determining MB2, recalculate the braking deceleration a and braking distance s:

A = mb/.G δ. rk)=(0..37)g (m/s2)

S=V02/(25.92a)+V0. T/3.6 (m)

after determining MP, the braking deceleration AE and brake distance se of parking brake as emergency braking can also be calculated:

ae= (G δ.） 0.25g (m/s2)

Se=V02/(25.92ae)+V0. T/3.6 (m)

s and se should meet the requirements of Table 1. 3 brake design calculation the structure of the service brake is shown in Figure 3. Four wheel brake can

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