GB/T 24648.1-2009 English PDF (GBT24648.1-2009)

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GB/T 24648.1-2009: Assessment of tractor reliability
GB/T 24648.1-2009
NATIONAL STANDARD OF THE
PEOPLE’S REPUBLIC OF CHINA
ICS 65.060.10
T 60
Assessment of tractor reliability
ISSUED ON: NOVEMBER 15, 2009
IMPLEMENTED ON: MAY 01, 2010
Issued by: General Administration of Quality Supervision, Inspection and
Quarantine;
Standardization Administration of the People's Republic of
China.
Table of Contents
Foreword ... 3 
1 Scope ... 4 
2 Normative references ... 4 
3 Terms and definitions ... 4 
4 Fault classification and judgement rules ... 6 
5 Evaluation indicator system ... 8 
6 Evaluation methods ... 11 
7 Use test methods ... 12 
Annex A (Informative) Tractor test summary ... 18 
Annex B (informative) Examples of tractor faults ... 26 
Assessment of tractor reliability
1 Scope
This Part of GB/T 24648 specifies terms and definitions, fault classification and
judgment rules, evaluation indicator system, evaluation method for assessment
of tractor reliability as well as test methods for tractor reliability during use.
This Part is applicable to reliability assessment and evaluation of shaped tractor.
Reliability assessment of prototype tractor may refer to this Part.
2 Normative references
The provisions in following documents become the provisions of this Part of
GB/T 24648 through reference in this Part. For dated references, the
subsequent amendments (excluding corrigendum) or revisions do not apply to
this Part, however, parties who reach an agreement based on this Part are
encouraged to study if the latest versions of these documents are applicable.
For undated references, the latest edition of the referenced document applies.
GB/T 3871.3, Agricultural tractors - Test procedures - Part 3: Power tests for
power take-off (GB/T 3871.3-2006, ISO 789-1:1990, MOD)
GB/T 3871.4, Agricultural tractors - Test procedures - Part 4: Rear three-point
linkage lifting capacity (GB/T 3871.4-2006, ISO 789-2:1993, MOD)
GB/T 3871.6, Agricultural tractors - Test procedures – Part 6: Determination
of braking performance (GB/T 3871.6-2006, ISO 5697: 1982, Agricultural
and forestry vehicles - Determination of Braking Performance, IDT)
GB/T 3871.12, Agricultural tractors - Test procedures - Part 12: Working tests
GB/T 6229, Test methods for walking tractors
GB/T 24648.2-2009, Reliability assessment of engineering and agricultural
machine - Evaluation parameter system and failure classification code
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
3.1 operating time
The time for a product to complete various defined functions. For tractor,
operating time includes tractor load operation time, turning time at turn-row and
conversion time for tractor’s null operation (5h null operation time is converted
to 1h working time), but excluding tractor running-in time, performance test time
and engine idle time.
3.2 fault correction time
The time required from fault is found to product function is recovered, that is,
the sum of fault diagnosis time, repair time and commissioning time, but
excluding time delayed by human or natural factors.
3.3 maintenance time
The operating time required to complete maintenance specified in user manual.
It includes shift maintenance and time spent on maintenance at all levels, but
excluding time delayed by human or natural factors.
3.4 fault
All phenomena that a product or its component cannot perform its specified
functions or performance indicators are deteriorated beyond specified range
(see 2.2 in GB/T 24648.2-2009).
For example, parts damage, wear overrun, weld cracking, paint peeling, loose
fasteners, sign off and difficulty in starting, power reduction, fuel consumption
increase, slow rise and other phenomena that exceed specified values.
3.5 inherent weakness fault
Under specified conditions of use, the fault that is caused by defect inherent in
product itself.
For example, excessive deformation, fracture, early wear and fatigue of parts,
abnormal corrosion and aging, loosening or failure of fasteners, performance
degradation, and "three leaks" (see 2.3 in GB/T 24648.2-2009).
3.6 secondary fault
The fault of other parts of product that is directly or indirectly caused by fault of
some part of product, or the derived fault caused by inherent weakness fault.
For example, when engine is broken due to broken connecting rod bolts and
damages of a series of parts such as connecting rods, bushings, pistons and
cylinders, broken connecting rod bolts shall be inherent weakness fault, and
damages of a series of parts shall be secondary fault (see 2.4 in GB/T 24648.2-
2009).
See formula (2) for mean interval time between faults.
Where,
MTBF - Mean interval time between faults of tractor, in hours (h);
tci - Timing end test time of the ith tractor to be tested, in hours (h); for tractor to
be investigated, it is accumulated operating time, in hours (h);
ra - Total number of faults (except minor faults) of tractors to be tested or
investigated during use or test period (including during run-in and performance
test).
If all tested tractors have no faults (except minor faults), it is specified to use
to represent.
5.4 Mean interval time between downtime faults
See formula (3) for mean interval time between downtime faults.
Where,
DTMTBF - Mean interval time between downtime faults of tractor, in hours (h);
rd - Total number of downtime faults (i.e., fatal faults and severe faults) of
tractors to be tested or investigated during use or test period (including during
run-in and performance test).
If all tested tractors have no faults (except minor faults), it is specified to use
to represent.
5.5 Trouble-free comprehensive score
Within specified test time, if one of tractors to be tested has fatal fault, this type
of tractor shall fail in trouble-free comprehensive score. Its Q value shall not be
calculated.
For tractor to be tested that has no fatal fault, its trouble-free comprehensive
score is calculated according to formula (4):
or total cost of troubleshooting of this type of tractor (including replacement and
repair costs) during test period specified in 7.3.3.2, in RMB;
Ct - Unit price of this type of tractor, in RMB.
6 Evaluation methods
6.1 Data sources
Sources that are used to evaluate tractor reliability may come from the following
three aspects.
6.1.1 Use test
According provisions of Clause 7, perform reliability test, combing with
production use.
6.1.2 Laboratory or test site reliability test
According to method specified in relevant standard, perform reliability test in
laboratory or on test site where conditions are controllable. However, equivalent
relationship between such test time and actual use time of user shall be known
in advance.
6.1.3 User survey
Conduct sample surveys or full follow-up surveys among users to obtain
reliability data for actual use of tractor.
6.2 Fault determination
For all faults of tractor, according to provisions of Clause 4, determine the nature
of each fault and its category one by one, which are used as basis to calculate
relevant indicators.
6.3 Marking methods for indicator
Marking format for tractor’s reliability indicators is specified as follows:
Indicator code = indicator value (data source)
For example: reliability indicators for tractor of which ××× type engine calibration
power is less than 18kW are as follows:
MTTFF=150h (3×500h ...