DRAIN INTERVAL FOR HEAVY DUTY COMMERCIAL VEHICLES

AND A PROCESS FOR PRODUCING THE SAME

FIELD OF THE INVENTION

[001] The invention relates to lubricant oils in general, and to a novel gearbox lubricant for heavy duty commercial vehicles with enhanced drain interval in particular. The gearbox lubricant according to the present invention is a high performance lubricant which retains its original viscosity even after use and offers change of gearbox lubricant at intervals of 80,000 kms in comparison with the prior art norm of about 40,000 kms for similar applications. BACKGROUND AND PRIOR ART

[002] Commercial vehicles are subjected to ever increasing loading to achieve maximum economy of operation. This results in correspondingly increasing torque demands on their gearboxes. In addition, incorporation of integrated retardation systems in such vehicles for typical city stop-and-go operations are responsible for driving the gearbox temperatures to very high levels. These severe driving conditions demand better gearbox lubricants which offer longer lubricant drain intervals. This demand comes both from the vehicle manufacturers as well as the Original Equipment Manufacturers (OEM), as also the users of the vehicles.

[003] Hence, there is a constant need for better gearbox lubricants. Moreover, gearbox lubricants should ideally have the same drain interval as the engine lubricants so that they can be changed together. This will result in considerably reduced downtime for the vehicles, as change of engine lubricant and gearbox lubricant can be done at the same time. Presently each calls for a separate vehicle downtime.

[004] To achieve this objective, thermo-oxidative stability and viscosity-temperature balance of the lubricant need to be optimized to withstand the rising operational temperatures of gearboxes of commercial vehicles over longer periods of operation. In the Asia-Pacific region, particularly in India, mineral oil based formulations dominate the market because of the price sensitivity of buyers. Hence it becomes all the more challenging to meet the above stated demands of improved thermo-oxidative stability and viscosity-temperature balance leading to longer lubricant drain intervals in a mineral oil platform. Expectedly, there are concerted efforts by all concerned players to continuously improve the existing high performance lubricating oils. The gearbox lubricants for heavy duty commercial vehicles known in the prior art usually have a drain interval of about 40,000 kms for typical city stop-and-go operations. The present invention discloses a high performance gearbox lubricant that has a drain interval of 80,000 kms, which matches with the drain interval of the engine lubricant and makes it possible to change both lubricants together.

[005] US Application US20090062163A1 discloses a gearbox lubricant which is a composition made from isomerised base oil having less than 0.05% aromatics and additives. It has a viscosity range between 6.5 cSt and 15.5 cSt. It does not disclose any drain interval. The present invention provides a gear oil lubricant which offers drain interval of 80,000 kms, and lower change in viscosity.

[006] EP Patent number EP578435B1 and EP767236B1 disclose gear oil lubricants with improved frictional characteristics in which the base oil is, or contains a significant quantity of, a synthetic oil such as a polyalpha-olefin oil (PAO) or a synthetic ester oil. It discloses a gear oil lubricant with a broader viscosity range. The inventions are directed to a lubricant suitable for manual transmission motor vehicles. However these inventions are directed primarily to improving the friction properties of the lubricants whereas the present invention provides gear oil lubricant which has high degree of thermo-oxidative stability leading to increased drain intervals.

[007] EP patent EP1669436A1 discloses a gear oil lubricant composition which is suitable for use in heavy duty truck vehicles which are operated for at least 30,000 kms between lubricant drain intervals. Viscosity increase of less than 100% has been claimed. However, the present invention discloses a gear oil lubricant which offers drain interval of 80,000 kms, and very low change in viscosity.

[008] EP patent EP1739159A2 discloses a transmission fluid composition, which is suitable for continuously variable transmission / dual clutch transmission / automatic or manual transmissions. The fluid composition comprises maximum amount of a base oil and minimum amount of additive composition wherein the additive composition comprises alkoxylated amine, dihydrocarbyl phosphite, metallic detergent, phosphorylated succinimide, tertiary fatty amine, and ethoxylated alcohol, in respective amounts effective for providing sustained anti-NVH durability upon aging in a power transmission, which is lubricated. The present invention provides gear oil lubricant which offers very high drain intervals of 80,000 kms, and very low change in viscosity.

[009] It is therefore clear from the above that there is need for a high performance gearbox lubricant suitable for heavy duty commercial vehicles in typical city stop-and-go operations, which offers a high drain interval.

[010] The main aim of the invention is to provide a gearbox lubricant for heavy duty commercial vehicles with city start-and-go operation, which has a drain interval of 80,000 kms. This oil composition has also been termed as "candidate oil" in this specification.

[011] Another aim of the invention is to match the drain interval of the gear lubricant with that of the engine lubricant so that they can be changed at the same time and the downtime of the vehicle for change of lubricants can be minimized.

[012] Yet another aim is to balance thermo-oxidative stability and optimize viscosity- temperature of the lubricant to withstand the ever rising operational temperatures of gearboxes of commercial vehicles which have longer periods of operations.

[013] A further aim of the invention is to ensure cross compatibility of the candidate oil with similar lubricants from other sources/chemistries to eliminate the possibility of separation of the additives and their sedimentation in case of mix-up of the lubricants.

[014] Another aim is to provide a gearbox lubricant which results in cleaner gear boxes with high degree of deposit control and which can be classified as "Clean Gear Lubricant".

[015] Yet another aim is to provide a gearbox lubricant which has a high degree of thermooxidative stability.

[016] Another aim is to provide a gearbox lubricant which has extremely good EP/Anti- wear and pitting protection under low speed/high torque and non steady-state conditions, which are associated with typical city stop-and-go operations.

A further aim of the invention is to provide a process for producing the candidate oil.

[017] The above aims are attained by the present invention which relates to a high performance gear oil for heavy duty commercial vehicles as described hereunder, and the process for its production.

SUMMARY OF THE INVENTION [018] A novel high performance gearbox lubricant oil composition for heavy duty commercial vehicles and the process for producing the composition are disclosed. The composition has superior anti-wear, EP (Extreme Pressure) properties and is fortified with high degree of thermo-oxidative stability leading to longer drain intervals. The drain interval for the candidate oil is 80,000 kms, which is roughly double that of similar oils known in the prior art. Extensive field trials of the candidate oil conducted after laboratory testing have established these parameters. Visual examination of the gearbox components at the end of the trials have corroborated the test results obtained during the laboratory evaluations.

[019] The composition is prepared by a process of mechanical stirring and controlled heating of lubricating oil base stock and additives, both of which are of specified category and proportion. The candidate oil is fully compatible with oils from other sources meant for similar applications to eliminate the possibility of separation and sedimentation of the additives in case of a mix-up of such oils.

BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS

[020] Fig. 1A to Fig. ID show the photographs of various transmission parts of the heavy duty vehicles after the trial period during which the vehicles were run with the gear box lubricant of the present invention.

Fig. 1 A shows Sliding Gears

Fig. IB shows Spur Gears

Fig. 1C shows Bearings

Fig. ID shows Helical Gears

Fig. 2A Oil mixture containing candidate oil and other oil after heating to the target temperature

- no separation/sedimentation, color change or haziness

Fig. 2B Oil mixture containing candidate oil and other oil after 24 hrs of heating to the target temperature - no separation/sedimentation, color change or haziness

Fig. 3 shows the viscosity trend of field trial samples (X-Axis: Kms; Y-Axis: Vis. @100 °C in cSt)

Fig. 4 shows Fe build up of field trial samples (X-Axis: Kms; Y-Axis: Fe content in ppm) Fig. 5 shows the Cu build up of field trial samples (X-Axis: Kms; Y-Axis: Cu content in ppm) Fig. 6 shows the TAN build up of field trial samples (X-Axis: Rms; Y-Axis: TAN in mgKOH/gm)

DETAILED DESCRIPTION OF THE INVENTION

[021] The present invention discloses a high performance gearbox lubricant with enhanced drain interval for heavy duty commercial vehicles. A process for making the lubricant is also disclosed.

[022] The gearbox lubricant according to the present invention is composed of a base oil and a set of additive combinations.

[023] A combination of two base oils is used:

(i) One base oil is a solvent extracted, dewaxed, hydrofinished paraffinic base oil belonging to API -Gp-I category having viscosity of 27-34 cSt at 100 °C and viscosity index value of 90- 100 units.

(ii) The second base oil is a catalytically hydrocracked, highly paraffinic API Gp-II base oil having a viscosity range of 8-12 cSt at 100 °C and viscosity index value in the range of 100- 120 units.

(iii) Total base oil concentration is in the range of 85-94 wt% Out of this, the share of API Gp.I base oil is in the range of 30-35 wt% and that of Gp.II category base oil is in the range of 55-60 wt%.

[024] A set of additive combination as described below is added to the base oil to obtain the candidate oil. The set of additive combination comprises of the following:

(i) anti-wear additive comprising alkyl dithio phosphate, alkyl phosphonate and alkyl phosphate with alkyl chain length varying from C6-C10 carbon distribution in the range of 0.90- 1.80 wt%,

(ii) anti-wear additive comprising a long chain alkyl amine with alkyl chain length varying from C16-C20 in the concentration range of 0.075-0.19 wt%,

(iii) an extreme pressure additive- unsaturated, branched, sulphurised alkene with an active sulphur content varying from 30-45%,

(ii) a synthetic, sulphurized, alkaline earth metal sulfonate with a total base number varying from 240-290 mgKOH/gm in the concentration range of 0.2- 0.5 wt%, (iv) a hindered phenol with an alkyl chain length varying from C10-C1 in the concentration range of 200- 500 ppm,

(v) anti-oxidant additive comprising a cyclic pentadiene with minimum two aromatic rings in the concentration range of 150-250 ppm,

(vi) a metal deactivator of imidzolene type in the concentration range of 100-200 ppm and

(vii) a polymeric methacrylate with an average molecular weight of 1- 3 lakh units in the range of 1-1.5 wt%.

[025] The gearbox lubricant according to the invention is prepared by a process of mechanical stirring and controlled heating of lubricating oil base stock of specified category and proportion and additives, which are also of specified category and proportion. The steps of the process are as follows:

1. Requisite amount of base oil(s) is charged into a blending kettle and heated up to 70-80 °C for 30-45 minutes to de-moisturize the contents.

2. Next, the temperature of the kettle/contents is allowed to cool down to 60-65 °C

3. Then pour point depressant is added and the mixture is mechanically stirred for about 20-40 minutes till complete dissolution of the depressant.

4. Thereafter, a combination of performance additives, namely anti-wear/extreme pressure/anti-oxidant and detergent and metal deactivator are added in that sequence and stirred continuously for further 60-80 minutes at the same temperature for ensuring complete dissolution of the additives in the base oil.

[026] The high performance gearbox lubricant according to the present invention has several advantageous properties over conventional lubricants for similar applications. The most important advantages are listed below.

1. Longer drain intervals of up to 80,000 Kms compared to about 40,000 kms for conventional oils for similar applications.

2. High degree of thermo-oxidative stability, which is at least 40-50% higher than conventional oils.

3. Higher and sustained load carrying capacity, which is 25-30% higher than conventional oils.

4. The candidate oil yields cleaner gear boxes with high degree of deposit control and hence can be classified as "Clean Gear Lubricant". 5. Extremely good EP/ Anti-wear and pitting protection which are 25-30% higher than the conventional oils under low speed/high torque and non steady-state conditions which are representative of typical city stop-and-go operations. This is demonstrated in FZG test and gearbox component wear tests described below. 6. Exemplary temperature reduction properties in cyclic load conditions, even without any external cooling device, contributing to the overall durability of the oil in severe operating conditions.

7. Good in-service viscosity and flow characteristics (rheology) control.

8. Good in-service wear control.

Experimental:

i) Laboratory & Tribological Evaluations:

[027] All physico-chemical properties like viscosity, VI, TAN, pour point, flash point, foaming, copper corrosion and rust tests were conducted by the indicated ASTM methods. Elemental analysis was carried out by ICAEP. Thermo-oxidative stability was determined by Japanese and also by CEC methods. Condition monitoring of trial samples for viscosity, TAN and Fe content were also carried out by adopting the same methods as were for fresh oil.

[028] Tribological evaluations of 4-ball wear scar dia was determined by the respective ASTM method. Load carrying capacity was determined by FZG tester on the indicated gear ratio.

[029] Cross compatibility of the candidate oil with oils from other sources/chemistries was conducted by OEM's proprietary procedure and also by standard BIS procedure.

[030] A proprietary planetary gear test at 110 °C and with varying loads was employed to determine the overall EP/anti-wear and pitting protection attributes of the candidate oil. The test was conducted in low speed/high torque, non-steady state conditions, characteristic of typical city stop & go conditions experienced by the commercial vehicle gearboxes. The same test was also used to assess the temperature reduction characteristics of the candidate oil over reference lubricants, as the test rig did not employ any cooling devices as in the case of modern commercial vehicles.

[031] ii) Field Validation: 1. 10 buses engaged in urban transport of a metropolitan city of India, which have already run around 20,000 kms were identified.

2. The broad trial protocol adopted was as follows:

- The existing gear oil from the gear boxes of identified trial vehicles was drained and the samples collected for analysis for base line reference (zero hours)

- Flushing was done by the candidate oil (by doing a 10 mins running of the buses). Flushing oil was collected for analysis.

- Sampling for condition monitoring was done at 20K, 40K, 50K, 60K, 70K, 80K mileage accumulation of the buses.

Condition monitoring of 250 ml sample was conducted. The monitoring was done for oil parameters like viscosity, wear metals, additive metals and TAN build up. Every time, two sets of 250ml samples from each gear box were collected- one for analysis by the applicant and the second one as a control sample to be analysed by Original Equipment Manufacturer (OEM). Equal amounts of fresh oil were topped up after withdrawal of every sample for monitoring.

[032] Results and Discussion

Table 1: Laboratory performance evaluation data of candidate oil

Corrosion Prevention

a. Copper ,D-130 1 @ 121 °C/3 hb. Steel ,D-665A Pass

Foaming, Tend./stability,D-892

Seq. I , ml/ml nil/nil

Seq. II , ml/ml nil/nil

Seq. Ill , ml/ml nil/nil

ISOT , JIS 2514K

@ 135°C,96hrs

TAN increase 1.83

%Vis.Rise @100°C 4.47

Hexane Insolubles% —

0. Oxidative aging,

CEC L 48A95B (140 °C, 192 hrs)

TAN Change 4.76

KV 100 change 2.3

Blotter Test 100

1. WSD, mm, D-4172

@1500rpm,392N,80°C.lhr 0.40

2. FZG, S-A10/16.6R/90

Pass Load Stage 12

3. Rubber Aging in Oil

NBR 28,DIN 53521

Volume change,% 5.8

Hardness change,% -2

Tensile Strength,% -13

Elongation change,% -35

2. AK-6, DIN 53531

Volume change,% 1.1

Hardness change,% 8.0

Tensile Strength, % -44

Elongation change,% -69

3. 70 ACM 121433,DIN 53521

Volume change,% 0

Hardness change,% 3

Tensile Strength,% 2

Elongation change,% -4

. Elemental Analysis, ICAP P, wt% 0.060

B, wt% -

Mg, wt% 0.035

Ca, wt% -

[033] Table 1 indicates that the candidate oil possesses, besides good viscosity index

(which is an indicator of good temperature), viscosity balance, good copper and rust protection characteristics (as evidenced by 'pass ratings' in D-130 and D-665A tests) respectively. Low temperature flowability of the oil is also good as per the low pour depression temperature.

[034] Since high degree of thermo-oxidative stability is one of the targeted parameters for negotiating severe gearbox operating conditions culminating in longer drain potential, two most severe thermo-oxidative aging tests were selected during the lab screening stage. While the CEC procedure lays stress on longer drain potential, the Japanese method is severe in terms of catalyzed oxidizing conditions of the test. In both the tests, candidate oil exhibited higher degree of oxidation stability of at least 40-50% higher than the conventional oils, both in terms of controlled TAN increase, minimal viscosity rise and insoluble build up. This is one parameter, which should keep the candidate oil in good stead and impart longer drain capabilities during taxing city stop and go applications. The minimal viscosity rise was demonstrated in the 80,000 kms field tests.

[035] Tribological evaluation in 4-ball wear tester and FZG yielded low wear scar dia and 12 ^th stage pass respectively indicating good anti-wear and load carrying capacity of the oil. Elastomer compatibility of the oil was tested as per the relevant DIN methods on various seal materials like NBR, AK-6 and Acrylic rubbers. In all the cases, changes in volume, hardness, tensile strength and elongation are within the stipulated limits. This demonstrates the compatibility of the candidate oil with all the tested seal materials.

[036] Cross compatibility of the gearbox lubricant with other sources of oils meant for similar applications is of great practical importance during real time use, where there is a chance of mix-ups and top-ups with cross brands and incompatibility among them may lead to separation/sedimentation of the additives and excessive foaming problems. As per the OEM's proprietary procedure and also according to BIS's [4] standard procedure, the oil was found compatible with tested gearbox lubricants from other sources.

[037] Performance of Candidate Oil in Planetary Gear Test: Table: 2: Overall Gear Performance

[038] As described in the experimental session, this proprietary test was conducted at 110 °C and in multiple test cycles of 40 minutes duration. Oil was drawn at specified intervals and analyzed for soluble iron content. This provides a means of monitoring the wear rate during the test. The test was terminated when there is a rapid increase in the wear rate or a tooth breaks. The candidate oil is compared with a high reference oil of MB 235.0 performance credentials.

[039] Higher overall rating of candidate oil in this test as shown in Table.2 indicates that the EP/ Anti-wear and pitting protection of the oil are extremely good under low speed/high torque, non steady state conditions- representative of typical city stop and go operations.

Table: 3: Temperature Reduction Potential

[040] Table 3 indicates the temperature reduction properties of the candidate oil in comparison to the high reference oil in the same planetary gear test which is without any extra/external cooling device. A substantial decrease in the running temperature with candidate oil highlights its overall durability potential which facilitates its long drain capabilities.

[041] Fig. 3 depicts the viscosity variation of candidate oils in 10 trial buses of city operation over 80,000 KMs. From the graph, it is evident that the candidate oil did not register either too high viscosity rise or too low viscosity decline. During the entire trial duration, the viscosity remained in the SAE 80W-90 grade, same as that of fresh oil. Slight decrease in viscosity in certain buses (2056/57/58) can be attributed to the normal shearing of pour point depressant. Overall viscosity temperature balance of the oil is very good and no excessive oxidative thickening was registered.

[042] From Fig. 4, it is evident that the good anti-wear potential and overall good rating in planetary gear test exhibited by the candidate oil was vindicated by the controlled Fe build up over entire duration of field trial of 80,000 Kms. The average Fe per 1000 ms is around 2 PPM which is considered to be very controlled wear rate by industry standards. Bus no. 2058 is slightly an outlier which registered around 3 ppm which is also is very much acceptable wear rate.

[043] Cu build up for marjority of buses as depicted in Fig. 5 during the entire trial duration varied between 10-20 ppm indicating the good copper corrosion protection attributes of candidate oil.

[044] Increase in Total Acid Number (TAN) is generally construed as a measure of oxidative deterioration, for oxidation of lubricants invariably leads to acid formation. Lowever the TAN build up, lower is the oxidative degradation and superior is the durability and longer drain capability of the oil. By these yardsticks, candidate oil as depicted in Fig.6 shows nominal increase over 80,000 Kms of trial period indicating its superior oxidation stability characteristics. These data also prove the superior attributes of the oil manifested in laboratory oxidative aging experiments.

[045] Visual examination of all the essential gear components like sliding, spur and helical gears and bearings (as inspected randomly in a few buses) after the conclusion of trials revealed good EP/AW protection of the candidate oil with no scuffing, pitting, ridging or spalling marks. Even the bearing condition is very good.

[046] From the above description the following observations are made:

· A new, high performance candidate oil was developed with superior anti-wear, EP properties and fortified with high degree of thermo-oxidative stability leading to longer drain capabilities.

• As proved in the field validation, the existing drain period of 40,000 kms has been doubled to 80,000 kms to dovetail it with engine oil change frequency for a typical city stop and go operation. Field validation, condition monitoring by way of used oil analysis data of field trial samples and post trial examination of gear components revealed that the candidate oil retained its critical attributes during the entire span of trial duration and thus capable of having change frequency of 80,000 Kms.