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Introduction of Semi Trailer Axles

Views:0     Author:Wondee Autoparts     Publish Time: 2021-11-18      Origin:Wondee Autoparts

A trailer axle is a device that supports all or part of the vertical load of the trailer while moving (wheel rotation) and bears various external forces in other directions to ensure the normal driving of the trailer. As shown in Figure 1 below.

01-Trailer semi-trailer axle

Figure 1. Trailer/semi-trailer axle


A axle is one of the important parts of a trailer, It is mainly introduced from the following aspects:

1. Technical standards of axles

(1) The technical standard of axles assembly shall comply with China transportation industry standard JT / T475-2020.

(2) The axle welding standard shall comply with the China machinery industry standard JB / T5000.3-2018.

2. The composition of a trailer axle


A trailer axle is mainly composed of the following four assemblies: a axle body assembly, a camshaft assembly, a braking assembly and a wheel end assembly.

02-Schematic diagram of axle composition

Figure 2. Schematic diagram of axle composition

(1) Axle body assembly

It mainly includes: an axle tube, brake base plates, air chamber supports and camshaft supports, etc.


(2) Camshaft assembly

It mainly includes: camshafts, slack adjusters and a camshaft repair kit, etc.


(3) Brake assembly

It mainly includes: brake shoes, brake linings, a brake shoe accessories package, etc.


(4) Wheel end assembly

It mainly includes: hubs, brake drums, oil seals, bearings, axle nuts, and hub covers, etc.


3. Classification of axles


According to the structures of the axle, it is usually divided into the following four types:


(1) Inboard brake drum axle series:


As shown in Figure 3 below. The flange surface of the axle brake drum is located on the inner side of the hub flange surface. For the inboard axles, when maintaining and replacing the parts of the braking system, it is necessary to screw the cover and remove the bearing locknut, so that the tires, wheel hubs, brake drums and bearings can be removed together for maintenance and replacement.


Intboard brake drum axle for a semi-trailer

Figure 3.Intboard brake drum axle for a semi-trailer


(2) Outboard brake drum axle series:

As shown in Figure 4 below. The flange surface of the axle brake drum is located outside the flange surface of the hub. For the outboard axles, when maintaining and replacing brake system parts, it is only necessary to unscrew all wheel nuts and remove tires and brake drums.

Outboard brake drum axle for a semi-trailer

Figure 4.Outboard brake drum axle for a semi-trailer


(2) Spoke wheel hub series axle

As shown in Figure 4 below. The axle replaces the common wheel hubs with five spoke wheel hubs, six spoke wheel hubs, eight spoke wheel hubs and ten spoke wheel hubs, and matched with demountable wheel rims and spacers.

Spoke type axle for a semi-trailer

Figure 5. Spoke type axle for a semi-trailer


(3) Disc brake series axle

As shown in Figure 6 below. Compared with the drum axle, the overall structure of the axle is simpler, the braking friction surface is directly exposed to the air, the heat dissipation is better, and the phenomenon of heat recession is effectively avoided. The brake discs bear compressive stress on both sides, and have better crack resistance under continuous braking. The braking force of the left and right wheels is more average, and the response speed of the braking system is faster, which improves the safety of the vehicle.

08-disc brake axle

Figure 6. Disc brake type axle for semi-trailer


4. Selection of axles


The following aspects need to be considered when selecting a axle:


(1) Axle styles


Trailer axles have usually two styles: American axles and European axles.


(2) Rated axle load


The rated axle load of the trailer axle is usually 8 tons, 10 tons, 11.5 tons, 12 tons, 13 tons, 14 tons, 16 tons, 18 tons and 20 tons.


(3) Specifications of axle tube


There are usually two types of trailer axle tubes: square tubes and round tubes: square tubes usually have 150x150mm, 127x127mm and 120x120mm, and round tubes usually have Φ127mm and Φ146mm.


(4) Specifications of axle brake


The specifications of trailer axle braking are related to the rated load of the axle,

It usually have following specifications: 311x190mm, 381x220mm, 420x180mm, 420x200mm and 420x220mm.


(5) Wheel track

As shown in Figure 7 below. The wheel track is the distance between the centers of the two tires on the left and right sides of the axle. It is the core parameter of the axle. The wheel track of trailer axle usually has 1816mm, 1820mm, 1840mm, 1850mm, 1968mm, 2050mm, 2160mm, etc. And the wheel track can be adjusted according to the trailer design requirements.

Schematic diagram of axle parameters

Figure 7. Schematic diagram of axle parameters


(6) Distance of two brake chambers

As shown in Figure 7 above. The center distance of the brake chambers is the distance between the centers of the two chamber brackets, which is determined by the length of the camshafts, usually 354mm, 370mm, 390mm, etc. while the wheel track is same. The external dimensions of the brake chamber and the installation requirements determine the minimum distance between the centers of the brake chambers 223mm, otherwise it will affect the installation of the brake chambers.

(7)Matching parameters of wheel hub, wheel rim and wheel bolts


1)Matching parameters of wheel hub and wheel rim


As shown in Table 1 below. Matching parameters of axle hubs and wheel rims, which commonly used in a trailer axle.

Coordination parameters of wheel hubs and wheel rims

Table 1. Coordination parameters of wheel hubs and wheel rims


2)Bolt hole parameters of wheel rim disc


As shown in Figure 8 below. Three common parameters of wheel disc bolt holes.

Common bolt hole parameters

Figure 8. Common bolt hole parameters


3) Selection of wheel bolts


As shown in Figure 9 below. The correct selection of wheel bolts.

Selection of wheel bolt

Figure 9. Selection of wheel bolt


5. Installation of axles (on trailers)


The correct installation of the axle can make the axle give full play to the best service performance, and the following requirements shall be followed during axle installation.


(1) Assembly direction of axle


As shown in Figure 10 below. The brake chamber and the slack adjuster are in the upward direction.

Assembly direction of a trailer axle

Figure 10. Assembly direction of a trailer axle


(2) Welding of upper or lower support plates and an axle

Because the position of the upper and lower support plates is the point of the maximum bending moment and stress concentration area of the axle, if the welding method of the support plates and the axle is incorrect or excessive weld seams will increase the possibility of axle fracture. Before welding, the support plates must fits closely with the shaft tube.


1) Welding requirements of upper or lower support plates and a square tube

As shown in Figure 11 below. There must not be any weld seams or weld spotsat the joints A, B, C, and D of the upper and lower support plates and the axle, otherwise it is easy to cause fatigue fracture of the axle tube and shorten the axle service life.

Welding instructions for the upper and lower support plates of a square tube

Figure 11. Welding instructions for the upper and lower support plates of a square tube


2) Welding requirements of support seats and a round tube


As shown in Figure 12 below. There shall be no weld seams or weld spots on both sides of the mating surfaces between the support seat and the axle! Otherwise, fatigue fracture of the axle tube is easy to occur, and the service life is shortened.

Welding instructions for the upper and lower support plates of a round tube

Figure 12. Welding instructions for the upper and lower support plates of a round tube


6. Precautions for use of axles


(1) Check the tightness of the wheel nuts

As shown in Figure 13 below. After a new trailer is driven for the first time or for the first time with a heavy load and each time the wheels are replaced, the tightening of the wheel nuts must be checked and ensure that the specified torque is reached.

Tightening wheel bolts

Figure 13.Tightening wheel bolts


(2) Check the slack adjusters


As shown in Figure 14 below. The initial installation angle of the slack adjuster is 100 ~ 105 °, and the optimal braking angle is 90 °. It is recommended to adjust every 15 ~ 30 days or 5000 ~ 10000 km according to the service conditions.

Schematic diagram of adjusting a slack adjuster

Figure 14. Schematic diagram of adjusting a slack adjuster


(3) Check the brake shoe and brake lining

As shown in Figure 15 below. Every month or 10,000 kilometers, check whether the brake lining is worn to the limit step position and whether the brake lining is loose through the observation hole on the dust cover.

Brake lining inspection

Figure 15.Brake lining inspection


(4) Check brake drums

Check brake drums regularly every 3 months or according to the usage to eliminate potential safety hazards. When the brake drum wear exceeds the wear warning line or the friction surface has continuous cracks, the brake drum should be replaced in time. After prolonged or long-distance braking, rapid water cooling is prohibited.


(5) Check the hub bearing clearance


It is recommended to check the wheel hub bearing clearance frequently, which must be checked within three months for new trailer. The operation method is shown in Figure 16 below.


1) Lift the axle until the tire is off the ground, insert two crowbars between the tire and the ground, and check whether the hub bearing clearance is abnormal.


2) Turn the wheel in both directions (clockwise and counterclockwise) to check whether the noise increases with the increase of rotation speed.

Inspection of wheel hub bearing clearance

Figure 16. Inspection of wheel hub bearing clearance


7. Lubrication of axles

In order to ensure the normal operation of a axle, it is necessary to regularly refill special grease to the relevant parts. It mainly involves the following 6 parts, as shown in Figure 17 below:

Axle lubrication position

Figure 17. Axle lubrication position


(1) Camshaft bushings, spherical bearings and slack adjusters

As shown in ① ② ③ in Figure 18 below:

Suggestion: fill lubricating grease every quarter or after repair and maintenance.

Method: fill grease until there is grease overflow around.

Lubrication positions of camshaft bushes, spherical bearings, and slack adjusters

Figure 18. Lubrication positions of camshaft bushes, spherical bearings, and slack adjusters


(2) Tapered roller bearings


As shown in ④ in Figure 19 below:

Suggestion: refill special grease every half a year or after replacing the brake shoes, brake linings and wheel hubs (it can be advanced according to the actual situation).

Method: thoroughly clean the bearing and check whether the bearing has defects such as peeling and wear. In case of damage, replace the bearing and fill it with sufficient grease.

Lubrication position of tapered roller bearing

Figure 19. Lubrication position of tapered roller bearing

(3) Hub cavity


As shown in ⑤ in Figure 20 below:

Suggestion: refill special grease every six months or after maintenance and replacement of wheel hubs (it can be advanced according to actual situation)

Method: thoroughly clean the inner cavity of the wheel hub and refill an appropriate amount of grease.

Lubrication position of hub cavity

Figure 20. Lubrication position of hub cavity


8. Maintenance and service cycle of axles


The routine maintenance and service cycle of axles is shown in Table 3 below.


Maintenance items

Driving   first time

Before and after the first load driving

Every month

Every quarter

Every half a year or 5000 km

After each replacement of brake shoes, brake linings,   and wheel hubs

After every disassembly and assembly of wheels

After long-term Stop using


Check whether   the wheel nuts are tightened to the specified torque





Check the brake clearance of the slack   adjuster








Check the   thickness of the brake linings shall not be less than 6mm








Check the hub   bearing clearance and adjust it if necessary






Check that the   hub cover is tight






Check for uneven   tire wear









Visually inspect   all parts for damage and wear







Note: after the   wheel nuts are tightened each time, the anti loosening marking shall be   applied with marking glue or a mark pen!

Table 3. Axle maintenance schedule

9. Troubleshooting of axles


Troubleshooting table-problems, causes and troubleshooting methods are shown in Table 4 below:


roblems

Causes

Troubleshooting


Axle tube damaged

(1) Serious   overload and excessive instantaneous impact load

(2) The upper   and lower support plates / seats and air suspension beams were not welded   according to the specifications

(3) Unqualified   quality or serious deformation   of leaf springs

(1) Replace the   shaft body according to the rated load

(2) Replace the beam   and weld the upper and lower support plates / seats and air suspension main   beam according to the specifications

(3) Replace leaf springs

Brake drum cracked

(1) Long term heavy load operation   and poor road conditions

(2) Hot cracks occur during long-time   braking

(3) Water cooling of brake drums at   high temperature

(4) Brake drum deformation

(1) Replace the brake drum, load according to the   rated load

(2) Replace the brake drum and   standardize the use of the brake

(3) Replace the brake drum and use   the water cooling device correctly

(4) Replace the brake drum


Bearings damaged

(1) Bearing clearance changes

(2) Insufficient grease / oil

(3) There are hard foreign matters   entering the bearing

(4) Excessive impact load

(1) Replace the bearing and readjust   the bearing clearance

(2) Replace the bearing and add   grease / oil

(3) Clean the shaft head, hub cavity   and the hub cover, and replace the oil seal

(4) Replace the bearing

Poor braking

Braking lag

Wheel lock

(1) Brake shoe return spring failure

(2) Damaged brake piping system

(3) Improper brake clearance

(4) Poor operation of quick release   valve or brake chamber and insufficient air pressure

(5) Unbalanced braking

(6) Camshaft and spherical bearing   support are deformed by impact

(7) The original brake shoes  are not used when replacing the brake linings


(1) Replace the brake shoe return   spring

(2) Check the brake pipeline

(3) Readjust the brake clearance

(4) Check the   working state of quick release valve and brake chamber, and check the air   pressure, replace   relative parts

(5) Check the wear condition of   camshaft and bushing, replace relative parts

(6) Replace damaged parts

(7) Replace the brake shoes

Wheel hub overheated

(1) Bearing clearance changes

(2) Wear of the hub and the bearing

(3) Insufficient grease / oil

(1) Readjust the bearing clearance

(2) Replace the bearing and the hub

(3) Grease / oil filling

Abnormal tire wear

(1) Insufficient tire pressure

(2) Loose U-bolts

(3) Axle symmetry and centering   balance out of tolerance

(4) Incorrect suspension parallelism

(5) Beam deformation

(6) Rim deformation

(7) Improper tire selection

(1) Adjust the tire pressure

(2) Lock the nut to the specified   torque

(3) Adjust axle balance

(4) Adjust the connecting rod or   replace the connecting rod shockproof sleeve

(5) Replace the beam

(6) Replace the rim

(7) Replace the tire

Abnormal wear of brake linings

(1) Long term heavy load operation   and poor road conditions

(2) Excessive temperature due to   long-time braking

(1) Load as specified

(2) Standardized use of brakes

Wheel bolts damaged

(1) Excessive impact load

(2) Bolts and nuts are not tightened   according to the specified torque

(3) Excessive torque

(4) Thread damage during assembly

(5) The flatness of the wheel rim   spokes is out of tolerance

(1) Replace the bolts, load according to the   rated load

(2) Replace the bolts and tighten   them to the specified torque

(3) Replace the bolts and tighten   them to the specified torque

(4) Replace the bolts

(5) Replace bolts and wheel rims

Table 4. Axle troubleshooting table-problems, causes and troubleshooting methods

 Compiled by  WONDEE Autoparts


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