Sliding element for lubricated sliding system

Abstract

The invention relates to a chain guide, respectively a chain tensioner for use in a lubricated sliding system, comprising a surface layer or bearing or comprising a sliding element comprising a surface layer, the surface layer being mainly made of a polymeric material containing a matrix polymer and optionally other components dispersed in said matrix polymer, wherein the matrix polymer consists of a semi-crystalline polyamide (SCPA) having a tensile modulus at 140? C. of at least 800 MPa (measured by the method according to ISO 527-1A). The invention also relates to a power train drive system comprising an engine, a transmission differential and a drive shaft system, a drive chain and a plastic component comprising a sliding element in contact with the lubricated drive chain, wherein the chain guide, the chain tensioner, respectively the sliding element has a coefficient of friction (Co F), measured in lubrication oil at 140? C. at a nominal contact pressure of 1 MPa and a speed of 1 m/s, of at most 0.07.

Claims

1. A chain guide or chain tensioner for use in a lubricated sliding system, wherein the chain guide or chain tensioner comprises: a sliding element which includes (i) a plastic body supporting the sliding element, and (ii) a surface layer on the plastic body having a thickness in a range of 50 ?m-5 mm, wherein the plastic body and the surface layer are formed of different injection molded polymeric materials, and wherein the injection molded polymeric material forming the surface layer comprises: (A) a matrix polymer which consists of a semi-crystalline polyamide (SCPA) having a tensile modulus at 140? C. of at least 800 MPa (measured by the method according to ISO 527-1A) and, optionally, (B) other components dispersed in and/or blended with said matrix polymer, wherein the SCPA comprises: (A.1) a semi-crystalline aliphatic polyamide, and (A.2) 0.01-10 wt. % relative to the total weight of the polymeric material of a semi-crystalline semi-aromatic polyamide having a Tg of at least 110? C. and a melting enthalpy of at least 70 J/g.

2. The chain guide or chain tensioner according to claim 1, wherein the SCPA has a tensile modulus at 140? C. which is in a range of 850-1050 MPa.

3. The chain guide or chain tensioner according to claim 1, wherein the semi-crystalline aliphatic polyamide (A.1) has a glass transition temperature (Tg) of at least 80? C. and a melting enthalpy (?H) of at least 70 J/g.

4. The chain guide or chain tensioner according to claim 1, wherein the SCPA has a melting temperature (Tm) and the sliding element has been annealed at a temperature between 100 and 20? C. below Tm for at least 1 hour.

5. The chain guide or chain tensioner according to claim 1, wherein the injection molded polymeric material comprises at least one other component selected from the group consisting of: (B.a) 0.01-20 wt. % of polymers other than the semi-crystalline polyamide; (B.b) 0.01-20 wt. % of solid lubricant particles comprising a material chosen from the group consisting of molybdenum disulfide, graphite, boron nitride and silane nitride, and any mixtures thereof; (B.c) 0.01-5 wt. % of an inorganic nucleating agent comprising micro-talc and/or carbon black; and (B.d) 0.01-10 wt. % of inorganic fillers other than (B.b) and (B.c) and/or fibrous reinforcing agents; wherein the wt. % are all relative to the total weight of the polymeric material.

6. The chain guide or chain tensioner according to claim 1, wherein the plastic body of the sliding element consists of a fibre reinforced thermoplastic material and wherein the surface layer of the sliding element consists of the injection molded polymeric material which is non-reinforced.

7. The chain guide or chain tensioner according to claim 1, wherein the sliding element has a coefficient of friction (CoF) in a range of 0.005-0.07 as measured in lubrication oil Shell Helix Super Mineral Motor Oil 15W-40 at a contact temperature of 140? C., a nominal contact pressure of 1 MPa and a sliding speed of 1 m/s.

8. A lubricated sliding system comprising a power train drive system which includes an engine, a transmission differential, a drive shaft system and the chain guide or chain tensioner according to claim 1.

9. A power train drive system comprising: an engine, a transmission differential, a drive shaft system, a drive chain, and a sliding element comprising (i) a plastic body supporting the sliding element, and (ii) a surface layer on the plastic body having a thickness in a range of 50 ?m-5 mm in sliding contact with a lubricated drive chain, wherein the sliding element has a coefficient of friction (CoF) of at most 0.07 as measured in lubrication oil Shell Helix Super Mineral Motor Oil 15W-40 at a contact temperature of 140? C., a nominal contact pressure of 1 MPa and a sliding speed of 1 m/s, and wherein the surface layer of the sliding element being comprised of an injection molded matrix polymer which consists of a semi-crystalline polyamide (SCPA) having a tensile modulus at 140? C. of at least 800 MPa (measured by the method according to ISO 527-1A), wherein the SCPA comprises: (A.1) a semi-crystalline aliphatic polyamide, and (A.2) 0.01-10 wt. %, relative to the total weight of the matrix polymer, of a semi-crystalline semi-aromatic polyamide having a Tg of at least 110? C. and a melting enthalpy of at least 70 J/g, and wherein the plastic body is formed of an injection molded polymeric material which is different from the injection molded matrix polymer of the surface layer.

10. The power train drive system according to claim 9, further comprising a chain guide or chain tensioner which includes the sliding element.

Description

FIGURES

(1) FIG. 1: cross sectional view of a cylindrically symmetrical plastic cup as used in the friction test.

(2) FIG. 2: Schematic view of the friction test set-up.

(3) FIG. 1 shows a cross section through the central axis of a cylindrically symmetrical plastic cup (1) as used in the friction test. The cup has an inner diameter of 24 mm, an outer diameter of 27.5 mm, and a height of 5 mm, as indicated in FIG. 1.

(4) The cups used in the friction test were injection moulded from the respective plastic materials.

(5) The friction test set-up is shown in FIG. 2. The plastic cup (1) is installed in an upper specimen holder (2) of the testing machine (not shown). An SKF WS 81104 shaft washer (3), which is used as the steel counter surface, is mounted on a lower specimen holder (4). The washer has an inner diameter of 20 mm, an outer diameter of 35 mm, and a height of 2.75 mm. It has a hardness of 60 on the Rockwell-C scale (60 HRc) and an average surface roughness (Ra) of 2 ?m. A hole (5) is machined 0.5 mm below the contact surface to mount a thermo-couple for temperature logging. Heating oil (Shell Helix Super Mineral Motor Oil 15W-40) is circulated through a channel (6). The washer was provided with a thermocouple, positioned 0.5 mm underneath the contact surface between the washer and the cup. The oil (6) is used to keep the contact temperature, as measured by the thermocouple, at 140? C. The washer and the lower part of the cup are submerged in a testing oil (7) (Nissan Motor Oil Strong Save-X 5W-30 SM KLAM3-05304).

(6) Contact normal pressure is applied by a force F on the lower specimen holder (4). The nominal contact pressure was 1 MPa, respectively 5 MPa. The upper specimen holder (2) rotates at an angular velocity of 742 rpm corresponding with a sliding velocity of 1 m/s at the contact surface. This sliding velocity is the sliding velocity calculated for the centre of the cup wall, which also corresponds with the average sliding velocity calculated over the wall thickness. The friction torque T is measured by a load cell (8). The coefficient of friction was calculated from the ratio T/F.

(7) Materials and Test Results

(8) The materials used in the test, the thermal and mechanical properties and the tests results have been collected in table 1.

(9) TABLE-US-00001 TABLE 1 Materials and test results CoF [] CoF [] Modulus at at Tg Tm ?Hm at 140? C. NCP of NCP of Material (? C.) (? C.) (J/g) [MPa] 1 MPa 5 MPa PA6 55 225 ~70 0.145 PA66 60 265 80 400 0.13 0.075 PA46 80 290 80 700 0.09 0.06 PA46 annealed 930 0.05 0.07 PA46/PPA 120 325 85 950 0.01 0.05 blend (97.5/2.5 wt. %) NCP = nominal contact pressure