WO1993006389A1 - Piston for use in an engine or motor - Google Patents

Piston for use in an engine or motor Download PDF

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Publication number
WO1993006389A1
WO1993006389A1 PCT/GB1992/001678 GB9201678W WO9306389A1 WO 1993006389 A1 WO1993006389 A1 WO 1993006389A1 GB 9201678 W GB9201678 W GB 9201678W WO 9306389 A1 WO9306389 A1 WO 9306389A1
Authority
WO
WIPO (PCT)
Prior art keywords
piston
pads
skirt
thrust
thrust surface
Prior art date
Application number
PCT/GB1992/001678
Other languages
French (fr)
Inventor
David Alec Parker
Michael Ledsham Price Rhodes
Original Assignee
T&N Technology Limited
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by T&N Technology Limited filed Critical T&N Technology Limited
Publication of WO1993006389A1 publication Critical patent/WO1993006389A1/en

Links

Classifications

    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16J—PISTONS; CYLINDERS; SEALINGS
    • F16J1/00—Pistons; Trunk pistons; Plungers
    • F16J1/02—Bearing surfaces
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02F—CYLINDERS, PISTONS OR CASINGS, FOR COMBUSTION ENGINES; ARRANGEMENTS OF SEALINGS IN COMBUSTION ENGINES
    • F02F3/00—Pistons 

Definitions

  • This invention is concerned with a piston for use in an engine or motor, the piston comprising a crown and a skirt projecting from the crown.
  • a piston is considered to have a longitudinal axis disposed generally centrally of the crown and the skirt, which axis extends along the cylinder in which the piston reciprocates.
  • pistons are not generally truely cylindrical about their central axis, the term "circumferential" is used herein to indicate a direction generally around the longitudinal axis in a plane extending normal to said longitudinal axis.
  • the skirt of a piston has two thrust surfaces disposed on opposite sides of the longitudinal axis of the piston. These thrust surfaces engage the wall of the cylinder and guide the piston in its motion. It is known from GB Patent Specification 2104188 to provide the skirt of a piston with pads on each of two thrust surfaces thereof, the pads being arranged to transmit lateral thrust forces between the piston and the wall of a cylinder in which the piston reciprocates. The pads are provided with ramps at their circumferentially-extending edges to cause lubricant to be forced over the pad by hydro-dynamic action during reciprocation of the piston. Thus, not only is there a reduction in the contact area between the skirt and the wall of the cylinder but also there is a consequential reduction of the viscous losses in the oil lubricating the skirt. This effectively reduces friction and thereby increases the efficiency of the engine or motor.
  • the invention provides a piston for use in an engine or motor, the piston comprising a crown and a skirt projecting from the crown, the skirt having two substantially continuous thrust surfaces disposed on opposite sides of a longitudinal axis of the piston, at least one of the thrust surfaces having pads projecting therefrom to transmit lateral thrust forces between the piston and the wall of a cylinder in which the piston reciprocates, the pads being integral with the remainder of the thrust surface and having ramps at their circumferentially-extending edges to cause lubricant to be forced over the pad by hydro-dynamic action during reciprocation of the piston, characterised in that there are two such pads on said at least one of the thrust surfaces and each pad extends circumferentially substantially completely across the thrust surface and has the ratio of its circumferential width to its axial length substantially greater than unity.
  • a piston according to the invention by comparison with the piston known from GB 2104188, the same total area of pad can be achieved but with pads having substantially less axial length. This enables better oil film formation to be achieved and gives the possibility of shorter piston skirts.
  • the ratio of the circumferential width to the axial length of each pad is at least 4:1, more preferably at least 6:1.
  • apertures through the skirt may be provided between the two pads.
  • Such apertures may be in the form of a row of holes extending parallel to said pads.
  • a piston according to the invention may have two similar pads on its other thrust surface so that both thrust faces are the same.
  • the thrust surfaces may have different arrangements of pads to suit the different conditions experienced thereby.
  • one thrust surface may have two pads as described above while the other has three pads as described in GB 2104188 in relation to Figure 2 thereof.
  • the two pads on a thrust surface differ dimensionally from each other.
  • skirt is not a full skirt, i.e., does not occupy the full circumference of the piston, it is possible for the shorter edges of the pads to correspond with edges of portions of the skirt, thereby avoiding the necessity for machining side ramps as described in GB Patent Specification 2104188.
  • the pads preferably, project by between 12 and 125 microns beyond the remainder of the skirt and the ramps are, preferably, inclined at an angle of less than 2 degrees.
  • Figure 1 is a side elevational view of a first illustrative piston
  • Figure 2 is a side elevational view of a second illustrative piston.
  • the first illustrative piston 10 is for use in an internal combustion engine and comprises a crown 12 provided with the usual grooves 14 for the reception of piston rings.
  • the piston 10 also comprises a skirt 16 projecting from the crown 12 and providing support bosses (not shown) in which a gudgeon pin can be mounted to connect the piston to a connecting rod (not shown) .
  • the skirt 16 is, in this case, a partial skirt. In other words, it occupies only a proportion of the circumferential extent of the piston, this proportion being made up of two diametrically opposed portions.
  • the skirt 16 provides two substantially continuous thrust faces 20 which are disposed on opposite sides of the longitudinal axis 22 of the piston 10. Projecting from each thrust surface 20 are two pads 24 which are arranged to transmit lateral thrust forces between the piston 10 and the wall of a cylinder in which the piston reciprocates (not shown) .
  • Each pad 24 is integral with the remainder of the thrust surface 20, i.e. they are cast and machined from the same piece of metal. Each pad 24 extends circumferentially substantially completely across the thrust surface 20. Furthermore, the ratio of the circumferential width W to the axial length L of each of the pads 24 is substantially greater than unity, being in this case approximately 6.
  • Each pad is also provided with ramps 25 at its circumferentially-extending edges in the same manner as is described in GB Patent Specification No. 2104188 to cause lubricant to be forced over the pad by hydro-dynamic action during reciprocation of the piston.
  • the pads 24 are also provided with ramps 27 at their axially edges as is also described in GB 2104188. It will be observed that the pads 24 are mutually similar and arranged one above the other. The pads 24 project approximately 100 microns beyond the remainder of the thrust surface 20 and the ramps 25 and 27 are inclined at angles of approximately 1.5 degrees.
  • each thrust surface 20 is provided between the pads 24, apertures through the skirt 16 in the form of a row of holes 26 extending parallel to the pads 24. These holes 26 have the purpose of enabling lubricant to enter the space between the pads 24 so that it can augment the oil left on the cylinder wall after passage of the leading pad
  • the second illustrative piston 40 shown in Figure 2 has a crown 42 with grooves 44, and a partial skirt 46.
  • the piston 40 has two pads 54 on each of two thrust surfaces 50 thereof. These pads 54 extend circumferentially substantially completely across the thrust surface 50.
  • the ratio of the circumferential width to the axial length of each of the pads 54 is substantially greater than unity but this ratio differs between the upper and lower pads 54 because the pads 54 extend right to the edges of the portion of the skirt 46 on which they are formed so that, because of a taper in the skirt 46, the upper pad 54 has a greater circumferential width than the lower pad 54.
  • the pads 54 are not provided with ramps as described in GB 2104188 at their axial edges but do have such ramps 55 at their circumferential edges. Holes 56, similar to the holes 26, are provided between the pads 54 to augment the oil supply.

Abstract

A piston (10; 40) for an engine or motor has a skirt (16; 46) with integral pads (24; 54) projecting from at least one thrust surface (20; 50) thereof. The pads are arranged to transmit lateral thrust forces between the piston and the wall of the cylinder in which the piston reciprocates. There are two pads and each extends circumferentially substantially completely across the thrust surface and has the ratio of its circumferential width (W) to its axial length (L) substantially greater than unity. Ramps (25; 55) at the circumferential edges of the pads cause lubricant to be forced over the pads.

Description

PISTON FOR USE IN AN ENGINE OR MOTOR
This invention is concerned with a piston for use in an engine or motor, the piston comprising a crown and a skirt projecting from the crown.
For the purposes of this specification, a piston is considered to have a longitudinal axis disposed generally centrally of the crown and the skirt, which axis extends along the cylinder in which the piston reciprocates. Although pistons are not generally truely cylindrical about their central axis, the term "circumferential" is used herein to indicate a direction generally around the longitudinal axis in a plane extending normal to said longitudinal axis.
The skirt of a piston has two thrust surfaces disposed on opposite sides of the longitudinal axis of the piston. These thrust surfaces engage the wall of the cylinder and guide the piston in its motion. It is known from GB Patent Specification 2104188 to provide the skirt of a piston with pads on each of two thrust surfaces thereof, the pads being arranged to transmit lateral thrust forces between the piston and the wall of a cylinder in which the piston reciprocates. The pads are provided with ramps at their circumferentially-extending edges to cause lubricant to be forced over the pad by hydro-dynamic action during reciprocation of the piston. Thus, not only is there a reduction in the contact area between the skirt and the wall of the cylinder but also there is a consequential reduction of the viscous losses in the oil lubricating the skirt. This effectively reduces friction and thereby increases the efficiency of the engine or motor.
It is an object of the present invention to provide pistons in which the pads on the thrust surfaces of the skirt are arranged to optimise the reductions in friction.
The invention provides a piston for use in an engine or motor, the piston comprising a crown and a skirt projecting from the crown, the skirt having two substantially continuous thrust surfaces disposed on opposite sides of a longitudinal axis of the piston, at least one of the thrust surfaces having pads projecting therefrom to transmit lateral thrust forces between the piston and the wall of a cylinder in which the piston reciprocates, the pads being integral with the remainder of the thrust surface and having ramps at their circumferentially-extending edges to cause lubricant to be forced over the pad by hydro-dynamic action during reciprocation of the piston, characterised in that there are two such pads on said at least one of the thrust surfaces and each pad extends circumferentially substantially completely across the thrust surface and has the ratio of its circumferential width to its axial length substantially greater than unity.
In a piston according to the invention, by comparison with the piston known from GB 2104188, the same total area of pad can be achieved but with pads having substantially less axial length. This enables better oil film formation to be achieved and gives the possibility of shorter piston skirts.
Preferably, the ratio of the circumferential width to the axial length of each pad is at least 4:1, more preferably at least 6:1.
In order to augment the supply of oil, apertures through the skirt may be provided between the two pads. Such apertures may be in the form of a row of holes extending parallel to said pads. A piston according to the invention may have two similar pads on its other thrust surface so that both thrust faces are the same. Alternatively it may be advantageous if the thrust surfaces have different arrangements of pads to suit the different conditions experienced thereby. For example, one thrust surface may have two pads as described above while the other has three pads as described in GB 2104188 in relation to Figure 2 thereof. Furthermore, it may be advantageous if the two pads on a thrust surface differ dimensionally from each other.
Where the skirt is not a full skirt, i.e., does not occupy the full circumference of the piston, it is possible for the shorter edges of the pads to correspond with edges of portions of the skirt, thereby avoiding the necessity for machining side ramps as described in GB Patent Specification 2104188.
The pads, preferably, project by between 12 and 125 microns beyond the remainder of the skirt and the ramps are, preferably, inclined at an angle of less than 2 degrees.
There now follow detailed descriptions, to be read with reference to the accompanying drawings, of two pistons which are illustrative of the invention.
In the drawings:
Figure 1 is a side elevational view of a first illustrative piston; and
Figure 2 is a side elevational view of a second illustrative piston.
The first illustrative piston 10 is for use in an internal combustion engine and comprises a crown 12 provided with the usual grooves 14 for the reception of piston rings. The piston 10 also comprises a skirt 16 projecting from the crown 12 and providing support bosses (not shown) in which a gudgeon pin can be mounted to connect the piston to a connecting rod (not shown) . The skirt 16 is, in this case, a partial skirt. In other words, it occupies only a proportion of the circumferential extent of the piston, this proportion being made up of two diametrically opposed portions. In particular, the skirt 16 provides two substantially continuous thrust faces 20 which are disposed on opposite sides of the longitudinal axis 22 of the piston 10. Projecting from each thrust surface 20 are two pads 24 which are arranged to transmit lateral thrust forces between the piston 10 and the wall of a cylinder in which the piston reciprocates (not shown) .
Each pad 24 is integral with the remainder of the thrust surface 20, i.e. they are cast and machined from the same piece of metal. Each pad 24 extends circumferentially substantially completely across the thrust surface 20. Furthermore, the ratio of the circumferential width W to the axial length L of each of the pads 24 is substantially greater than unity, being in this case approximately 6. Each pad is also provided with ramps 25 at its circumferentially-extending edges in the same manner as is described in GB Patent Specification No. 2104188 to cause lubricant to be forced over the pad by hydro-dynamic action during reciprocation of the piston. The pads 24 are also provided with ramps 27 at their axially edges as is also described in GB 2104188. It will be observed that the pads 24 are mutually similar and arranged one above the other. The pads 24 project approximately 100 microns beyond the remainder of the thrust surface 20 and the ramps 25 and 27 are inclined at angles of approximately 1.5 degrees.
Between the pads 24, apertures through the skirt 16 are provided in each thrust surface 20 in the form of a row of holes 26 extending parallel to the pads 24. These holes 26 have the purpose of enabling lubricant to enter the space between the pads 24 so that it can augment the oil left on the cylinder wall after passage of the leading pad
24.
It will be observed that, as a result of the natural rocking action of the piston during reciprocation in the cylinder, the thrust forces on the pads 24 will be unequal for most of the engine operating cycle. The pads 24 are located in such a way as to minimise the extent of the rocking action.
The second illustrative piston 40 shown in Figure 2 has a crown 42 with grooves 44, and a partial skirt 46. The piston 40 has two pads 54 on each of two thrust surfaces 50 thereof. These pads 54 extend circumferentially substantially completely across the thrust surface 50. The ratio of the circumferential width to the axial length of each of the pads 54 is substantially greater than unity but this ratio differs between the upper and lower pads 54 because the pads 54 extend right to the edges of the portion of the skirt 46 on which they are formed so that, because of a taper in the skirt 46, the upper pad 54 has a greater circumferential width than the lower pad 54. Because they extend to the edges of the skirt portions, the pads 54 are not provided with ramps as described in GB 2104188 at their axial edges but do have such ramps 55 at their circumferential edges. Holes 56, similar to the holes 26, are provided between the pads 54 to augment the oil supply.

Claims

A piston (10; 40) for use in an engine or motor, the piston comprising a crown (12; 42) and a skirt (16; 46) projecting from the crown, the skirt having two substantially continuous thrust surfaces (20; 50) disposed on opposite sides of a longitudinal axis (22; 52) of the piston, at least one of the thrust surfaces having pads (24; 54) projecting therefrom to transmit lateral thrust forces between the piston and the wall of a cylinder in which the piston reciprocates, the pads being integral with the remainder of the thrust surface and having ramps (25; 55) at their circumferentially-extending edges to cause lubricant to be forced over the pad by hydro-dynamic action during reciprocation of the piston, characterised in that there are two such pads (24; 54) on said at least one thrust surface (20; 50) and each pad extends circumferentially substantially completely across the thrust surface and has the ratio of its circumferential width (W) to its axial length (L) substantially greater than unity.
A piston according to Claim 1, characterised in that said ratio is at least 4:1.
A piston according to Claim 1, characterised in that said ratio is at least 6:1.
A piston according to any one of Claims 1 to 3, characterised in that apertures (26; 56) through the skirt (16; 56) are provided between the two pads (24; 54) .
A piston according to Claim 4, characterised in that the apertures (26; 56) are in the form of a row of holes extending parallel to said pads (24; 54) . A piston according to any one of Claims 1 to 5, characterised in that the piston has two similar pads on its other thrust surface.
A piston according to any one of claims 1 to 6, characterised in that the pads project by between 12 and 125 microns.
A piston according to any one of claims 1 to 7, characterised in that said ramps (25; 55) are inclined at an angle of less than 2 degrees.
AMENDED CLAIMS
[received by the International Bureau on 28 December 1992 (28.12.92); original claims 7 and 8 deleted; original claim 1 amended; remaining claims unchanged (2 pages)]
A piston (10; 40) for use in an engine or motor, the piston comprising a crown (12; 42) and a skirt (16; 46) projecting from the crown, the skirt having two substantially continuous thrust surfaces (20; 50) disposed on opposite sides of a longitudinal axis (22; 52) of the piston, at least one of the thrust surfaces having pads (24; 54) projecting therefrom by between 12 and 125 microns, the pads being arranged to transmit lateral thrust forces between the piston and the wall of a cylinder in which the piston reciprocates, the pads being integral with the remainder of the thrust surface and having ramps (25; 55) at their circumferentially-extending edges, the ramps being inclined at an angle of less than 2o so that they cause lubricant to be forced over the pads by hydro-dynamic action during reciprocation of the piston, characterised in that there are two such pads (24; 54) on said at least one thrust surface (20; 50) and each pad extends circumferentially substantially completely across the thrust surface and has the ratio of its circumferential width (W) to its axial length (L) substantially greater than unity.
A piston according to Claim 1, characterised in that said ratio is at least 4:1.
A piston according to Claim.1, characterised in that said ratio is at least 6:1.
A piston according to any one of Claims 1 to 3, characterised in that apertures (26; 56) through the skirt (16; 56) are provided between the two pads (24; 54) . A piston according to Claim 4, characterised in that the apertures (26; 56) are in the form of a row of holes extending parallel to said pads (24; 54).
A piston according to any one of Claims 1 to 5, characterised in that the piston has two similar pads on its other thrust surface.
PCT/GB1992/001678 1991-09-21 1992-09-14 Piston for use in an engine or motor WO1993006389A1 (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB9120187.1 1991-09-21
GB919120187A GB9120187D0 (en) 1991-09-21 1991-09-21 Piston for use in an engine or motor

Publications (1)

Publication Number Publication Date
WO1993006389A1 true WO1993006389A1 (en) 1993-04-01

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PCT/GB1992/001678 WO1993006389A1 (en) 1991-09-21 1992-09-14 Piston for use in an engine or motor

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WO (1) WO1993006389A1 (en)

Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0072228A2 (en) * 1981-08-11 1983-02-16 Ae Plc Pistons
DE3428490A1 (en) * 1984-08-02 1986-02-13 Mahle Gmbh, 7000 Stuttgart Trunk piston for internal combustion engines
WO1986005249A1 (en) * 1985-03-02 1986-09-12 Ae Plc Pistons
EP0201116A1 (en) * 1985-04-12 1986-11-12 AE BORGO S.p.a. Internal-combustion engine piston with oil cushion lubrication
EP0240092A1 (en) * 1984-08-04 1987-10-07 Ae Plc Improvements in or relating to pistons for internal combustion engines
EP0373516A1 (en) * 1988-12-10 1990-06-20 T&N TECHNOLOGY LIMITED Pistons
DE4113773A1 (en) * 1990-07-23 1992-01-30 Alcan Gmbh Piston with reduced free play for internal combustion engine - has specific areas coated with low friction graphite and polymer dispersion and non-coated areas which are set back compared to coated areas

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE3273182D1 (en) * 1981-07-31 1986-10-16 Ae Plc Pistons for internal combustion engines
ZA825602B (en) * 1981-08-11 1984-03-28 Ae Plc Pistons
BR8500574A (en) * 1984-02-17 1985-09-24 Deere & Co LOW FRICTION PISTON FOR USE IN A CYLINDER
DE3531801A1 (en) * 1985-09-06 1987-03-19 Kolbenschmidt Ag LIGHT METAL PISTON
GB2246833B (en) * 1990-06-23 1994-05-25 T & N Technology Ltd Pistons for engines or motors

Patent Citations (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0072228A2 (en) * 1981-08-11 1983-02-16 Ae Plc Pistons
DE3428490A1 (en) * 1984-08-02 1986-02-13 Mahle Gmbh, 7000 Stuttgart Trunk piston for internal combustion engines
EP0240092A1 (en) * 1984-08-04 1987-10-07 Ae Plc Improvements in or relating to pistons for internal combustion engines
WO1986005249A1 (en) * 1985-03-02 1986-09-12 Ae Plc Pistons
EP0201116A1 (en) * 1985-04-12 1986-11-12 AE BORGO S.p.a. Internal-combustion engine piston with oil cushion lubrication
EP0373516A1 (en) * 1988-12-10 1990-06-20 T&N TECHNOLOGY LIMITED Pistons
DE4113773A1 (en) * 1990-07-23 1992-01-30 Alcan Gmbh Piston with reduced free play for internal combustion engine - has specific areas coated with low friction graphite and polymer dispersion and non-coated areas which are set back compared to coated areas

Also Published As

Publication number Publication date
GB2259748A (en) 1993-03-24
GB9219408D0 (en) 1992-10-28
GB9120187D0 (en) 1991-11-06

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