Such metal salts generally include the metal in a stoichiometric or in an excess amount, i.e. in a concentration greater than the stoichiometric concentration. Same are then overbased detergents; the excess of metal involving the overbased nature of the detergent additive is generally in the form of an oil-insoluble metal salt, e.g. carbonate, hydroxide, oxalate, acetate, glutamate, preferentially carbonate.

Advantageously, the lubricating composition used according to the invention can comprise from 0.5% to 8% or from 2% to 4% by weight with respect to the total weight of the lubricating composition, of an overbased detergent additive.

Further advantageously, the lubricating composition used according to the invention can further comprise an additive which lowers the pour point.

By slowing down the formation of paraffin crystals, the pour point lowering additive generally improves the behavior under cold conditions of the lubricating composition, according to the invention.

Examples of additives lowering the pour point include alkyl polymethacrylates, polyacrylates, polyarylamides, polyalkylphenols, polyalkylnaphthalene, alkyls polystyrenes.

Advantageously, the lubricating composition according to the invention can further comprise a dispersing agent.

The dispersing agents can be chosen from Mannich bases, succinimides and derivatives thereof.

Further advantageously, the lubricating composition according to the invention can comprise from 0.2% to 10% by weight with respect to the total weight of lubricating composition, of dispersing agent.

The lubricating composition according to the invention can further comprise at least one thickening agent.

The lubricating composition according to the invention can further comprise an antifoaming agent and a demulsifying agent.

The present invention further relates to the use of base oil with a viscosity less than or equal to 4 in an engine lubricating composition, so as to reduce particle emissions of said engine.

The present invention further relates to the use as defined hereinabove, wherein the reduction of particle emissions relates to the WLTC cycle or the RDE cycle, and more particularly to the reduction of emissions of particles with a size greater than or equal to 10 nm, e.g. comprised between 10 nm and 40 nm.

The present invention further relates to a method for reducing the emission of particles in an engine, preferentially a gas, gasoline, diesel or further hybrid engine, comprising the use of a lubricating composition comprising a base oil with a viscosity less than or equal to 4.

The present invention also relates to a method for reducing the emission of particles in an engine, in particular a controlled ignition engine, e.g. a combustion engine, preferably a gas, gasoline, diesel or hybrid engine, comprising the use of a lubricating composition comprising a base oil or a mixture of base oils, wherein said base oil or said mixture of base oils has a kinematic viscosity (BOV or base oil viscosity) measured at 100° C., as per the standard ASTM D445, less than or equal to 4.5 mm²/s, and wherein said lubricating composition has a viscosity at 150° C. and under constant shear greater than or equal to 2.4 mPa.s⁻¹.

The present invention further relates to a method for reducing the emission of particles in an engine, preferably a gas, gasoline, diesel or hybrid engine, lubricated by a lubricating composition comprising the addition of a base oil with a viscosity less than or equal to 4, to said lubricating composition.

The present invention further relates to a method for reducing the emission of particles in an engine, preferably a gas, gasoline, diesel or hybrid engine, lubricated by a lubricating composition comprising a base oil or a mixture of base oils, wherein said base oil or said mixture of base oils has a kinematic viscosity (BOV or base oil viscosity) measured at 100° C., as per the standard ASTM D445, less than or equal to 4.5 mm²/s, and wherein said lubricating composition has a viscosity, at 150° C. and under constant shear, greater than or equal to 2.4 mPa.s⁻¹.

In such methods, the particles, the base oil and the lubricating composition are as defined hereinabove.

The present invention covers all motor vehicles, in particular vehicles comprising a 2-stroke or 4-stroke engine, gasoline, diesel, hybrid or gas engines.

The present invention covers all motor vehicles, preferably comprising at least one controlled ignition engine, preferably a combustion engine, in particular heavy vehicles or light vehicles, preferably heavy goods vehicles.

The present invention will now be described with the help of non-limiting examples.

EXAMPLE 1
Lubricating Compositions

The following lubricating compositions were prepared according to Table 2 below.

TABLE 2

Composition 2
Composition 3
Composition 4
Composition 5

Reference
Composition 1
(according to
(according to
(according to
(according to

composition
(comparative)
the invention)
the invention)
the invention)
the invention)

((in % with
(in % with
(in % with
(in % with
(in % with
(in % with

respect to
respect to
respect to
respect to
respect to
respect to

the total
the total
the total
the total
the total
the total

weight of the
weight of the
weight of the
weight of the
weight of the
weight of the

composition)
composition)
composition)
composition)
composition)
composition)

Grade
10W-40
10W-40
5W-30
5W-30
0W-40
0W-30

Additive
21.4
11.3
21.4
11.3
21.4
21.4

package

Mineral base
76.1
84.5
76
82.8
68.8
73.1

oil (group III)

(mixture of

two base

oils)

Base oil
6
8
4
4
3
2.9

viscosity

Hydrogenated
2.5
4.2
2.6
5.9
9.8
5.5

styrene

butadiene

polymer

The characteristics of the lubricating compositions are collated in Table 3 below:

TABLE 3

Composition 2
Composition 3
Composition 4
Composition 5

Reference
Composition 1
(according to
(according to
(according to
(according to

composition
(comparative)
the invention)
the invention)
the invention)
the invention)

KV 40° C.
91.57
94.32
56.76
52.45
74.22
50.3

ASTM

D445-97

or ISO3104

(mm²/s)

KV 100° C.
13.49
13.8
9.747
9.751
13.53
9.674

ASTM

D445-97

or ISO 3104

(mm²/s)

VI
147
149
158
174
188
181

(ISO 3104)

HTHS 150° C.
4
3.86
3.14
2.99
3.83
3.85

CEC L14-90

(mPa · s)

Noack 1 h
6.5
4.6
12.2
13.6
31.5
32

250° C.

CEC L-040-93

(%)

EXAMPLE 2
Measurement of the Number of Emitted Particles and of Fuel Eco

The compositions of example 1 were tested over the WHTC cycle and the quantity of particles having a size greater than or equal to 10 nm emitted at the end of each cycle was measured.

The engine tests were carried out on turbocharged straight-six engines. The tests were carried out at the same starting temperature of the engine. All other test bench conditions were kept constant as well. Sampling for the exhaust gas measurements was carried out from raw exhaust gases ahead from the exhaust system but after the treatment systems. Thereby, the effects observed are indeed due solely to the use of the lubricating composition and not to any other criterion such as the temperature, the humidity, etc.

The particle size distribution was measured in parallel by a Cambustion differential mobility spectrometer (DMS500). Same uses a high voltage discharge for charging every particle proportionally to the surface thereof. The charged particles are introduced into a classification section with a strong radial electric field. Such field causes particles to drift through a flow inside a column, toward the electrometer detectors. The particles are detected at different distances in the column, depending on the aerodynamic resistance/Icharge ratio thereof. The outputs of the 22 electrometers are processed in real-time at 10 Hz, so as to provide spectral data and other measurements.

Fuel consumption was also measured and calculated by the following equation:

Fuel
⁢

consumption

=

Total
⁢

mass
⁢

of
⁢

fuel
⁢

injected

[
g
]

cycle

[
kWh
]

The emissions of particles were calculated as follows:

Emissions
⁢

of
⁢

particles

=

Total
⁢

number
⁢

of
⁢

particles

[
#
]

cycle

[
kWh
]

The results are given in Table 4 hereinbelow:

TABLE 4

Composition 2
Composition 3
Composition 4
Composition 5

Reference
Composition 1
(according to
(according to
(according to
(according to

composition
(comparative)
the invention)
the invention)
the invention)
the invention)

Fuel
248
249
246
249
249
245

consumption

(g/kWh)

Emissions of
5.75 × 10¹²
3.78 × 10¹²
2.52 × 10¹²
2.18 × 10¹²
1.72 × 10¹²
1.56 × 10¹²

particles

(number/kWh)

The results clearly show that the choice of the base oil according to the invention (viscosity less than or equal to 4) clearly reduces particle emission. The results also show that the choice of the base oil according to the invention has no impact on the consumption of fuel (Fuel Eco), thereby showing that a reduction in particle emissions is not synonymous with an improvement of Fuel Eco.

EXAMPLE 3
1^stTesting Campaign
Preparation of Lubricating Compositions The lubricating compositions were prepared according to Table 5 hereinafter.

TABLE 5

Composition 6
Composition 7
Composition 8
Composition 9
Composition 10

(comparative)
(comparative)
(reference oil)
(invention)
(invention)

Grade
0W12
0W20
0W20
0W20
0W20

Package of
14
14
14
14
14

additives

Base oil
BOV 4
Mixture of
BOV 4
Mixture of 90%
Mixture of

Group III
group III base
Group III
BOV 4 Group III
group III base

Base oil
oils: 43% BOV
Base oil
base oil and
oils: 70% BOV

4 oil and 57%

10% BOV 6
4 oil and 30%

BOV 6

Group IV
BOV 3

base oil

PISH
0.4
0
4
4.4
5.6

polymer

PMA
0
0
0
0
0

polymer

Composition 11
Composition 12
Composition 13
Composition 14

(invention)
(invention)
(invention)
(invention)

Grade
0W20
XW30
XW30
XW30

Package of
14
14
14
14

additives

Base oil
BOV 3
BOV 3
BOV 4
BOV 4

Group III
Group III
Group III
Group III

Base oil
Base oil
Base oil
Base oil

PISH
7
12.5
10.2
0

polymer

PAMA
0
0
0
10.0

polymer

The numbers in Table 5 correspond to percentages by weight with respect to the total weight of composition.

The characteristics of the lubricating compositions are given in Table 6 below:

TABLE 6

Compo. 6
Compo. 7
Compo. 8
Compo. 9
Compo. 10

(comp.)
(comp.)
(reference oil)
(invention)
(invention)

HTHS 150
2.17
2.55
2.64
2.6
2.6

(mPa · s⁻¹)

CEC L-036-90 or

ASTM D4683

Base oil viscosity
4.324
5.578
4.324
4.304
3.918

(100° C.)

ASTM D445-97

(mm²/s)

Noack volatility
10.7
7.7
11.1
10.8
15.2

ASTM D5800 or

CEC L-040-93

Compo. 11
Compo. 12
Compo. 13

(invention)
(invention)
(invention)

HTHS 150
3.49
3.52
3.42

(mPa · s⁻¹)

CEC L-036-90 or

ASTM D4683

Base oil viscosity
3.320
4.324
4.324

(100° C.)

ASTM D445-97

(mm²/s)

Noack volatility
21
10.7
11.4

ASTM D5800 or CEC

L-040-93

Measurement of the Number of Emitted Particles

The compositions of example 3 were subjected to the WLTC or RDE tests and the quantity of particles per kilometer traveled having a size greater than or equal to 10 nm emitted at the end of each cycle was measured. An EB2ADTS (PSA Peugeot Citroën) engine with a displacement of 1.2 I (maximum power of 60 KW) was used.

The engine tests were carried out on turbocharged straight-three engines. The tests were carried out at the same starting temperature of the engine (20° C.). All other test bench conditions were kept constant as well. Sampling for the exhaust gas measurements was carried out from raw exhaust gases at the outlet of the turbocharger and upstream of the post-treatment system.

The particle number was measured using a Horiba MEXA2000-SPCS particle counter equipped with an overhead diluter. Each lubricating composition was tested 10 times on a WLTC cycle (with forced cooling at 20° C. at the beginning of each cycle). The first 3 cycles were deliberately discarded to allow the injection system to stabilize. The other 7 cycles were taken into account for the results. Particle numbers were expressed as average particle numbers (PN10 and PN23) per kilometer over the cycle considered.

The test campaign was thus carried out on an iso-additivation matrix.

The results are given in Tables 7 and 8 hereinafter, which relate to the WLTC and RDE cycles, respectively.

The test of a reference oil (composition 8) provides a framework for each test. The test results are expressed with respect to the result of the last reference oil passed.

TABLE 7

Change of the number of particles

(PN10) in comparison with the

WLTC cycle
composition 8

Composition 6
+23%

(comparative)

Composition 7
+34%

(comparative)

Composition 9
−8%

(invention)

Composition 10
−18%

(invention)

Composition 11
−46%

(invention)

Composition 12
−28%

(invention)

Composition 13
−26%

(invention)

TABLE 8

Change of the number of particles

(PN10) in comparison with the

RDE cycle
composition 8

Composition 6
+5%

(comparative)

Composition 7
+12%

(comparative)

Composition 9
−11%

(invention)

Composition 10
−17%

(invention)

Composition 11
−24%

(invention)

Composition 12
−4%

(invention)

Composition 13
−22%

(invention)

The results of Tables 7 and 8 demonstrate that the compositions used according to the invention effectively serve to reduce the number of particles with a size greater than or equal to 10 nm, over a WLTC or RDE cycle.

Tables 9 and 10 hereinafter summarize the results obtained on an RDE or WLTC cycle for composition 8 as regards the particles with a size of 10 nm. The results show the repeatability of the effect of decreasing the emission of PN10 particles.

TABLE 9

Tests

1
2
3
4
5
6
7
8

#PN10 per
2.26 ×
2.04 ×
2.23 ×
1.89 ×
1.61 ×
1.64 ×
1.84 ×
1.64 ×

km traveled
10¹²
10¹²
10¹²
10¹²
10¹²
10¹²
10¹²
10¹²

over WLTC

cycle

#PN10 per
4.88 ×
4.34 ×
4.32 ×
4.17 ×
3.57 ×
3.52 ×
3.75 ×
3.63 ×

km traveled
10¹²
10¹²
10¹²
10¹²
10¹²
10¹²
10¹²
10¹²

over RDE

cycle

TABLE 10

Reference oil
PN10
PN10

Composition 8
WLTC
RDE

Mean value
1.88^E12
3.97^E12

Standard deviation
0.25^E12
0.48^E12

Standard Deviation/mean
13%
12%

Repeatability (IC95)
0.69^E12
1.34^E12

Repeatability/average
37%
34%

EXAMPLE 4
2^ndTesting Campaign

A second testing campaign was carried out. Lubricants differ in viscosity grade but also in the composition of additives and of base oils. Table 11 shows the characteristics of the lubricating compositions which demonstrate an influence of the viscosity grade on the reduction of the PN10 number, independently of the composition:

TABLE 11

Compo. 14
Compo. 15
Compo. 16
Compo. 9
Compo. 17

(Inv.)
(inv.)
(inv.)
(inv.)
(inv.)

Grade
0W20
0W20
0W20
0W20
0W30

Package of
A (14%)
A (14%)
A (14%)
A (14%)
B (12%)

additives

Base oil
BOV 4
BOV 4
BOV 4
Mixture of
Mixture of

Group III
Group III
Group III