Ensuring Reliability of The Gearbox during Operation Stage

Irina Makarova

, Eduard Mukhametdinov

, Larisa Gabsalikhova

, Vladimir Shepelev

Shamil Galiev

, Polina Buyvol

and Maria Drakaki

Kazan Federal University, Syuyumbike prosp., 10a, 423822 Naberezhnye Chelny, Russia

South Ural State University, Lenin Avenue, 76, 454080 Chelyabinsk, Russia

Department of Science and Technology, International Hellenic University,

14th Km Thessaloniki, N. Moudania, GR-57001, Thermi, Greece

mdrakaki@ihu.gr

Keywords: Operational Reliability, Gearbox, failure.

Abstract: A significant proportion of the costs and downtime for repairs are attributed to transmission units, including

the gearbox. One of the main reasons for such high transmission costs is the existing structure of the operating

and repair cycle, which uses a strategy of waiting for failure, as a result operability is ensured mainly through

overhaul and comprehensive maintenance with high consumption of spare parts. spare parts and repair

downtime. This article is devoted to one of the most expensive repairs for ZF gearboxes, associated with the

destruction of the front bearing of the output shaft. When inspecting gearboxes delivered with a similar defect,

the condition of the gearbox parts does not allow making an unambiguous decision on the cause of the defect

due to critical destruction of the mating parts. Based on the available research and scientific literature in the

field of gearbox operation, an analysis was carried out and the root causes of gearbox failure in operation

were identified.

1 INTRODUCTION

Today automakers are investing in smart and energy

efficient vehicles because of the fierce competition

they want to make smart and efficient mobility

options. In the context of raising urbanization and

inclusiveness of modern society, autonomous

vehicles are designed to ensure an increase in the

mobility of population all categories, while reducing

the accident rate on the roads (Makarova,

Mukhametdinov, Tsybunov,

2018

). Numerous studies

are devoted to the problems of the autonomous

vehicles operation: the advantages, prospects and

features of the transportation process organization.

Despite technological advances in design,

autonomous vehicles are still classic vehicles but with

smart abilities. Each mechanical or electrical

component of such vehicle has a limited life cycle.

https://orcid.org/0000-0002-6184-9900

https://orcid.org/0000-0003-0824-0001

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https://orcid.org/0000-0002-1143-2031

https://orcid.org/0000-0002-5241-215X

https://orcid.org/0000-0001-9322-7324

Therefore, the greater the mileage of an autonomous

vehicle, the greater the mechanical parts wear. The

higher the difficulty degree, the higher the risk of

technical problems. Until the autonomous vehicle

fleet becomes sufficient to obtain large statistical

datasets of all failure kinds, there is a significant

probability of failures during operation.

Although the vehicles produced today are reliable

and maintainable, there is still a need to further

improve their performance and fault tolerance

(Makarova, Khabibullin, Belyaev, 2012). As the

author of the paper (Bertsche, 2008) noted in his

study, the number of returns due to critical failures

and defects in automotive components and systems

has increased. This increased the manufacturer's costs

by eight times and led to the fact that warranty costs

amounted to 8-12% of the company's turnover. The

increase in the defects number can be explained by

768

Makarova, I., Mukhametdinov, E., Gabsalikhova, L., Shepelev, V., Galiev, S., Buyvol, P. and Drakaki, M.

Ensuring Reliability of the Gearbox during Operation Stage.

DOI: 10.5220/0010530707680774

In Proceedings of the 7th International Conference on Vehicle Technology and Intelligent Transport Systems (VEHITS 2021), pages 768-774

ISBN: 978-989-758-513-5

the increasing complexity of modern vehicles design.

Considering that the system for ensuring the units

operability is based on the regularities of changes in

the technical state during operation, due to the action

of various factors of a constructive, technological,

operational and organizational and technical nature

(Khabibullin et. al, 2013), the issue of researching the

vehicle components and assemblies reliability

remains relevant (Makarova, Pashkevich, Buyvol,

Mukhametdinov,

2019.).

2 METHODS FOR DEFINING

RELIABILITY: STATE OF THE

PROBLEM

A vehicle is a complex mechanical system with

several levels of hierarchy, consisting of various

subsystems and components. Ensuring the reliability

of the system can be carried out by design and

analytical methods. Design methods include defining

accurate design data, manufacturing instructions,

followed by early and extensive testing procedures to

ensure reliability. Analytical methods for ensuring

reliability include determining and / or predicting

reliability using quantitative and qualitative methods.

They are applied during the conceptual design phase

and during vehicle operation.

Faults diagnostics to identify the root cause of a

vehicle's loss of performance is the main task when

servicing a vehicle (Gritsenko, Shepelev,

Zadorozhnaya, Shubenkova, 2020, Tsybunov,

Shubenkova, Buyvol, Mukhametdinov, 2018).

Correctly and timely detected defective unit allows

not only to reduce the load on the mating parts, but

also to neutralize such negative environmental

consequences as excessive oil consumption, an

increase in pollutants in the exhaust gases (Makarova,

Shubenkova, Mavrin, Gabsalikhova, Sadygova,

Bakibayev, 2019). The use of a fault tree analysis

(FTA) as a tool for diagnosing problems with vehicle

performance has been widely used by many

researchers (James, Gandhi, Deshmukh 2018,

Makarova, Shubenkova, Mukhametdinov,

Giniyatullin, 2020). The Fishbone diagram is also

used to help identify and pinpoint the causes of

maintenance errors that can lead to failures in

automotive systems (Murugan, Ramasamy, 2015).

It is also effective to use a combination of

methods. For example, the authors of the work

(Stefana, Marciano, Alberti, 2016) used such tools as

reliability block diagram, bow-tie analysis, FTA,

Failure Mode and Effects Analysis (FMEA) and

likelihood and consequences analysis.

As one of the promising methods for

troubleshooting, many authors suggest using

vibration diagnostics, which allows to determine the

degree of parts wear in a non-disassembly way

(Makarova, Mukhametdinov, Gabsalikhova,

Garipov, Pashkevich, Shubenkova, 2019, Gritsenko,

Shepelev, Zadorozhnaya, Almetova, Burzev, 2020)

In the era of big data, the availability of

information has increased significantly, as a result of

which more sophisticated tools can be used to

determine the hidden relationships in investigated

variables. To determine the vehicle mean operating

time between failures, in addition to the classical

predictive models, the methods of intellectual

analysis are currently used. In particular, in the work

(Chong, Liu, Sun, Gilfedder, Titmus, 2019), the

authors applied the concept of deep learning in neural

networks, using data on the mileage between vehicle

faults from a geographic information system. Most of

the components in automotive systems are

mechanical, the failure time of which corresponds to

the Weibull distribution. Therefore, in their work

(Kumar, Jain, Soni, 2019), the authors proposed a

semi-Markov model suitable for repairable

mechanical systems.

The development of methods to improve the

transmission elements reliability is an urgent task,

since it affects the efficiency and driving comfort

(Roshdy, Abdelazi, 2020).

The papers (Liang, Walker, Ruan, Yang, Wu,

Zhang, 2019, Deryusheva, Kosenko, Zagutin,

Arakelyan, Krymsky, 2019, Ilyuchyk, Basalai, 2019)

are devoted to researching of changes in the technical

state and their design during transmission units’

work. As a result of using the recommendations of

these studies in production and operation, the

reliability of vehicles and other machines

transmission units has significantly increased, and the

costs of ensuring their working capacity in operation

stage have been reduced.

Within the framework of the indicated problems,

this study will analyze the defects’ causes, establish

the distribution law for the failures’ number from the

mileage, and then propose measures to improve the

reliability of this unit.

Ensuring Reliability of the Gearbox during Operation Stage

769

3 RESULTS AND DISCUSSION

3.1 Identifying the Most Common Gear

Box Defects

Since the beginning of the use of ZF gearboxes on

KAMAZ vehicles, the main reason for the failure was

the vehicle towing in neutral gear, without

disconnecting the propeller shaft. In this case, there is

no rotation of the intermediate shaft, the oil pump is

stopped, so the bearing operates under oil starvation

conditions. The most serious damage to a part occurs

if gearbox demultiplicator remains included in the

reduced range.

The classification of the ZF gearbox main faults

and failures at the initial stage of operation is shown

in Fig. 1.

Figure 1: Distribution of claims by defects’ type.

The problem under study is associated with the

destruction of the output shaft bearing, which is a

tapered roller radial thrust bearing with a size of 42.07

x 82.904 x 40.386, cm. (Fig. 2)

The bearing is installed on the output shaft pin,

fixed with two split half rings of different thickness,

depending on the clearance of the locating groove.

The bearing outer cage is the tapered surface of the

input shaft cavity, lubrication is carried out from a

centralized lubrication system, oil is supplied through

an opening in the oil bypass throttle.

As the main information source, we used the

analysis of claims for failures of the gearbox with the

defect "destruction of the output shaft bearing" due to

calls from vehicles’ owners. The analysis was carried

out for gearboxes manufactured in Brazil, China,

Russia and Germany. Fig. 3 shows photographs of the

types of bearing destruction during operation stage.

Defect analysis was carried out at the service center

of the ZF KAMA company.

One of the failure classification signs is the defect

cause, which is divided into three main types:

structural, production and operational.

Structural failure occurs due to imperfections and

structure defects, the reasons are errors in the unit’s

development and design, underestimation of safety

margins, violation of standards established by state

official standardization bodies.

A production failure is a failure due to a

production violation or human error. The reasons for

production failures are non-observance of

documentation technical standards, use of low-

quality components, insufficient level of production

quality control. In the process of analyzing the output

shaft bearing failure, the following factors are

identified: incorrect selection of the adjusting half

rings, damage to the bearing or its parts during

installation, incorrect/ non-installation of the oil

retaining ring (the consequence is oil starvation at the

time of start-up), bearing damage during storage and

transportation, installation of a poor-quality bearing,

damage when connection with the power unit, the use

of a shaft with deviations from the required

dimensions (landing with excessive or weakened

interference).

Figure 2: Output shaft bearing.

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770

Figure 3: Types of the

output

shaft bearing destruction

An operational failure is a failure caused by a

violation of established rules and/or operating

conditions. Operational failures arise due to the use of

facilities in conditions for which they were not

intended, violations of operating rules (overloading,

missing maintenance and repair, the use of non-

compliant greasing substances, non-compliance with

transportation and storage rules). For example, in case

of maintenance violations, the gear box mean

operating time between failures can be reduced by

more than 3 times as a result of air with abrasive dust

or moisture from the external environment entering

the crankcase.

The operational reasons for the failure of the

gearbox are the following factors: rolling, incorrect

load orientation (engine braking), high-speed

operation of the vehicle with low speed, violation of

towing conditions, the use of non-recommended

greasing substance.

The gearbox failure due to the bearing fault is a

grouping feature. To compile a statistical series, the

information was divided into n equal intervals. The

number of statistical series intervals was determined

by the formula of G.A. Sturgess:

n = 1 + 1,44ln(N), (1

)

where N = 30 – number of elements in the statistical

series.

n = 1 + 1,44ln(30)=5,94=6

Interval length:

= (t

max

- t

min

)/n

)

where t

max

and t

min

— the highest and lowest

reliability index values in the summary information

table.

= (91302 - 11206)/6=15029 km

At the beginning of the first interval, the

minimum mileage was taken, the results of the

calculations are shown in Table 1.

Ensuring Reliability of the Gearbox during Operation Stage

771

Table 1: Calculation results.

Interval number, i

Lower bound, t

Upper bound, t

i+1

Middle of interval, t

Frequencies, m

Cumulative frequencies

1 1126,00 16155,34 8640,67 17 17

2 16155,34 31184,68 23670,01 8 25

3 31184,68 46214,02 38699,35 3 28

4 46214,02 61243,36 53728,69 0 28

5 61243,36 76272,70 68758,03 1 29

6 76272,70 91302,04 83787,37 1 30

Amount: 30

Figure 4: Theoretical and empirical fault distribution

functions.

Based on the results of reliability analysis during

the warranty period of operation and calculations on

the output shaft bearing failure, it was established that

the sample is subject to the normal distribution law.

3.2 Proposed Events to Improve

Gearbox Reliability

3.2.1 A Design Modify

The bearing strength calculation showed that the

durability and statistical carrying capacity of the

output shaft front bearing are ensured. In the gearbox

highest transmission, the gear ratio is equal to "1,"

i.e., the input and output shafts are locked by the

fourth transmission synchronizer and rotate at the

same angular speed, respectively, the bearing is at rest

and in the absence of vibration, impact on the bearing

is minimal. A different pattern is created during

operation on the lower gears, namely when moving

on the descent, at the moment when braking occurs,

including due to the engine, the output shaft bearing

takes maximum loads, taking into account the

features of the distribution of forces in the oblique

gear, at certain moments the loads on the bearing can

be critical.

The Ecosplit gearbox lubrication system is

designed in such a way that oil is supplied to the input

shaft niche and the sliding surface of the divider gear

through a hole in the oil bypass throttle, located offset

from the output shaft rotation axis. Factors such as

exceeding the maximum permissible engine speed,

incorrect strategy for selecting gears of the main

gearbox of the gearbox, erroneous shift of the

demultiplicator gears can lead to oil starvation and

bearing overload, and, as a result, to destruction and

failure of the gearbox as a whole.

For this type of failure, researches were carried

out and it was found that one of the reasons for the

failure is a lubrication lack and high axial loads.

According to the results, a change was introduced in

the gearbox design: the diameter of the oil crossing

hole in the throttle was increased from 2.0 to 2.5 mm,

the purpose of which is to supply a larger volume of

oil.

The expansion of the oil crossing hole diameter

ensures the supply of more quantity oil, thereby

ensuring the removal of heat from the friction parts

and improving the lubrication process.

3.2.2 Replacement of Roller Radial Thrust

Bearing

Based on the analysis carried out, it can be argued that

the failure cause is operational factors, one of them is

short-term dynamic overloads arising from a change

in the direction of the power flow loading the roller

cone bearing, for example, during engine braking. For

vehicles operating in mountainous terrain, there is a

variant of the gearbox with an intarder

(hydrodynamic brake-retarder), which has proven

itself as an auxiliary braking system, but the cost of

vehicles with additional units is high and carriers, as

a rule, prefer standard vehicles. For long-term

operation in mountainous terrain with maximum load,

drivers use engine braking at high speeds at the lower

gears of the gearbox to unload the main braking

system. As noted earlier, this process is accompanied

by a maximum load of the gear box front bearings.

Vibration plays an important role in the failure

occurrence. In the highest gear, the speed of the input

and output shafts rotation is the same, that means the

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bearing does not rotate relative to the rolling

elements, and in the presence of even slight vibration

(for example, the effect of adhesion), small relative

movements between the bearing rolling elements are

generated and, under the influence of such a process,

grooves are formed on the raceways over time.

Considering the fact that the vehicle maximum

operating time is carried out in the highest gear, the

vibration effect can be critical. When the speed

decreases, switching to lower gears occurs, the

angular speeds of the input and output shafts rotation

change, the bearing starts to rotate, and the presence

of even a small depletion on the rolling elements can

lead to rolling elements’ sliding relative to the bearing

rings without rotating the rollers, which leads to

bearing seizure. As one of the solutions, to change the

output and input shafts design, by analogy with the

gearbox of the ZF Astronic and Traxon models,

where this unit has a different design solution, and use

two bearings: a cylindrical roller bearing for taking

only radial loads and a support bearing for axial

forces.

Such a design entails a change in the input and

output shafts, the introduction of new parts and

additional adjustment operations during assembly, an

increase in the labor intensity and assembly

operations time, therefore, will also lead to a

significant increase in the gearbox cost.

3.2.3 Change of Lubrication System

For bearing failure-free operation, it is necessary to

provide a bearing lubricating layer, which cannot

occur if the greasing substance amount of is

insufficient or the greasing substance has lost its

lubricating properties. Under such conditions, metal

contact occurs between the bodies and the raceways.

At the initial stage, wear implements the lapping

process: microscopic small roughness vertices

formed during machining are cut and the rolling

effect is achieved and the surface looks mirror

smooth. With a lack of greasing substance, a

significant increase in temperature occurs, which in

certain situations can lead to bearing wedging.

Additionally, with the lack of a lubricating layer,

small cracks may appear on the rolling bodies

surfaces, which increase rapidly during operation,

preventing smooth rotation of the bearing. Such

cracks accelerate the process of fatigue cracks

formation under the raceways surface, reducing the

bearing durability.

To ensure sufficient lubrication, it is proposed to

change the lubrication system using a output shaft

with minimal design changes: introduce two

additional radial holes at the installation site of the

internal bearing race, which will also prevent fretting

corrosion.

The hydrodynamic mode disruption and the peak

loads presence, possibly also a combination of both

factors, can cause the loss of bearing and gearbox

operability as a whole.

4 CONCLUSIONS

1. Based on the results of reliability analysis during

the warranty period of operation and calculations on

the output shaft bearing failure, it was established that

failures are subject to the normal distribution law.

2. It was found that the most likely cause of the failure

is short-term peak loads arising during operation,

taking into account the peculiarity of the forces

distribution in the oblique engagement.

3. An analysis of the bearing lubrication system

showed that the existing lubrication system does not

fully provide lubrication at peak loads and heat

removal from the bearing rolling bodies. Two

solutions are proposed: to change the assembly - to

use two different bearing assignments, or to change

the lubrication system in order to provide the

necessary lubrication.

ACKNOWLEDGEMENTS

The reported study was funded by RFBR, project

number 19-29-06008\19.

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