Lubricant pump and method of producing

FIELD OF THE INVENTION

The invention relates to a lubrication pump and a method of producing the lubrication pump, and more particularly to a lubrication pump for a vehicle transfer case which pumps a lubricant through a passageway in an axial bore of a shaft.

BACKGROUND OF THE INVENTION

A four wheel drive vehicle includes a vehicle transfer case for distributing a driving force from a transmission connected to a prime mover such as an internal combustion engine to front and rear wheels through a vehicle drive train assembly. The transfer case is adapted to be secured to one end of the vehicle transmission. An input shaft is rotatably supported within the transfer case for coupling with an output shaft of the vehicle transmission. The input shaft of the transfer case is coupled to a speed change mechanism which is then coupled to an output shaft of the transfer case. The output shaft of the transfer case is then coupled with the vehicle drive train assembly. Lubrication of a plurality of bearings within the transfer case is accomplished by a pumping mechanism, such as a gerotor pump, which is mounted on the input shaft of the transfer case and pumps a lubricant through an axial bore of the input shaft.

Typically, pumping mechanisms have been constructed of cast aluminum which has been precision machined. Restriction of the total weight, durability, and temperature resistance of materials used to produce the pumps are a concern for design of the pumping mechanism.

It would be desirable to produce a lubrication pump for a vehicle transfer case in which weight is minimized and durability and temperature resistance are maximized.

SUMMARY OF THE INVENTION

Consistent and consonant with the present invention, a lubrication pump for a vehicle transfer case in which weight is minimized and durability and temperature resistance are maximized has surprisingly been discovered. The lubrication pump for a vehicle transfer case comprises:

a pump body having a generally hollow cylindrical shape and a central longitudinal axis, one end of the pump body having a radial wall with a centrally disposed aperture;

a synthetic polymer pump insert having a generally cylindrical main body with a central aperture, an inlet channel, and an outlet channel, the inlet channel in fluid communication with a source of lubricating fluid and the outlet channel in fluid communication with the central aperture of the main body, the pump insert inserted in the pump body;

a synthetic polymer outer gear, the outer gear being generally ring shaped with an inner surface forming an aperture, the inner surface having a generally sinusoidal shape which forms a plurality of peaks and valleys, the outer gear received in the pump body adjacent the pump insert;

a synthetic polymer inner gear, the inner gear being generally disc shaped with a central aperture formed by an inner surface, the inner surface having a shaft engaging portion to drivingly engage the inner gear with a shaft of a vehicle transfer case, an outer surface of the inner gear having a generally sinusoidal shape which forms a plurality of peaks and valleys, the number of peaks and valleys of the outer surface of the inner gear being at least one less than the number of peaks and valleys of the inner surface of the outer gear, the inner gear rotatingly received in the central aperture of the outer gear adjacent the pump insert; and

a generally disc shaped pump cover having a central aperture, the pump cover attached to the pump body to enclose the pump insert, the outer gear and the inner gear within the pump body and form a substantially liquid tight seal with the pump body.

BRIEF DESCRIPTION OF THE DRAWINGS

The above, as well as other objects, features, and advantages of the present invention will be understood from the detailed description of the preferred embodiments of the present invention with reference to the accompanying drawings, in which:

FIG. 1

is an exploded perspective view of a lubrication pump for a vehicle transfer case incorporating the features of the invention;

FIG. 2

is a schematic view of the lubrication pump for a vehicle transfer case illustrated in

FIG. 1

;

FIG. 3

is a partial elevation view of the inner gear of the lubrication pump taken along line

3

—

3

of

FIG. 1

; and

FIG. 4

is a partial elevation view of the inner gear, the outer gear, the pump insert, and the inlet adapter of the lubrication pump taken along line

4

—

4

of FIG.

1

.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings, and particularly

FIG. 1

, there is shown generally at

10

a lubrication pump for a vehicle transfer case incorporating the features of the invention. The lubrication pump

10

includes a pump body

12

, a pump insert

14

, an outer gear

16

, an inner gear

18

, and a pump cover

20

.

The pump body

12

has a hollow cylindrical shape with an outer wall

22

. One end of the pump body

12

has a radial wall

24

surrounding a central aperture

26

. A lip

28

is formed at an inner edge of the radial wall

24

surrounding the central aperture

26

. An inlet aperture

30

is formed in the outer wall

22

. A radial ledge

32

extends radially outward from the end of the outer wall

22

opposite the radial wall

24

. The radial ledge

32

is ring shaped, having an inner portion of the ring attached to the outer wall

22

. An annular array of spaced apart extensions

34

are formed at an outer edge of the ring shaped radial ledge

32

. The extensions

34

extend in an axial direction from the outer edge of the radial ledge

32

. In the embodiment shown, the pump body

12

is produced from stamped steel. It is understood that other methods such as precision machining, for example, or other materials, such as a synthetic polymer, for example, could be used to produce the pump body

12

.

The pump insert

14

has a cylindrical main body

36

with a centrally disposed aperture

38

. An arcuate inlet channel

40

is disposed in the main body

36

and is in fluid communication with an inlet aperture

42

. The inlet aperture

42

is adapted to receive an inlet adapter

44

which is in fluid communication with a source of lubricating fluid

104

, as illustrated in FIG.

2

. An arcuate outlet channel

46

is disposed in the main body

36

radially opposite the inlet channel

40

. An outlet opening

48

facilitates fluid communication between the outlet channel

46

and the aperture

38

. An annular ridge

50

is disposed on the inner surface of the main body

36

which forms the aperture

38

.

The outer gear

16

consists of an annular ring having a generally sinusoidal inner surface

52

which forms an aperture

54

. A front face

56

and a rear face

58

contain a plurality of recessed portions

60

defined by the peaks

62

and the valleys

64

of the sinusoidal inner surface

52

. In the embodiment shown, there are fifteen peaks

62

and fifteen valleys

64

formed on the sinusoidal inner surface

52

. It is understood that an inner surface

52

having more or fewer peaks

62

and valleys

64

can be used without departing from the scope and spirit of the invention.

The inner gear

18

consists of a disc having a central aperture

66

. In the embodiment shown, the inner surface

68

of the inner gear

18

is serrated to receive a serrated portion

70

of a shaft

72

. It is understood that other engaging surfaces between the inner gear

18

and the shaft

72

can be used such as a single D or a double D, for example, without departing from the scope and spirit of the invention. A front face

74

of the inner gear

18

has an annular ring

76

surrounding the central aperture

66

. An outer surface

80

has a generally sinusoidal shape or annular array of lobes having a plurality of peaks

82

and valleys

84

. In the embodiment shown, there are fourteen peaks

82

and fourteen valleys

84

formed in the sinusoidal outer surface

80

of the inner gear

18

. It is understood that an outer surface

80

having more or fewer peaks

82

and valleys

84

can be used without departing from the scope and spirit of the invention. The number of peaks

82

and valleys

84

formed on the outer surface

80

will ideally be one less than the number of peaks

62

and valleys

64

formed on the inner surface

52

of the outer gear

16

. It is understood that the difference between the number of peaks

82

and valleys

84

formed on the outer surface

80

of the inner gear

18

and the number of peaks

62

and valleys

64

formed on the inner surface

52

of the outer gear

16

can be greater than one. As illustrated in

FIG. 3

, a rear face

78

has an annular ring

86

formed thereon adjacent and radially inward of the outer surface

80

.

In the embodiment shown, glass filled nylon is used to produce the pump insert

14

, the inlet adapter

44

, the outer gear

16

, and the inner gear

18

. Glass percentages up to 60 percent have been found to perform satisfactorily. A glass percentage of 35 percent has been found to provide optimal performance. Additionally, nylon without a glass filler has also been found to perform satisfactorily as a material of construction for the pump insert

14

, the inlet adapter

44

, the outer gear

16

, and the inner gear

18

. It is also understood that other synthetic polymers could be used without departing from the scope and spirit of the invention.

The pump cover

20

consists of a disc having a central aperture

88

formed in an annular ring

90

which is offset in the direction of a front face

92

. A plurality of protuberances

94

form an anti-rotation structure and extend radially from the pump cover

20

. It is understood that the anti-rotation structure could be formed on the pump body

12

as well. In the embodiment shown, the pump cover

20

is produced from stamped steel. It is understood that other methods such as precision machining, for example, or other materials, such as a synthetic polymer, for example, could be used to produce the pump cover

20

.

The shaft

72

includes an axial bore

96

as illustrated in

FIG. 2. A

radial aperture

98

which communicates with the axial bore

96

is disposed in one end of the shaft

72

adjacent the serrated portion

70

. A plurality of spaced apart lubrication apertures

100

are in fluid communication with the axial bore

96

and extend radially therefrom.

To assemble the lubrication pump

10

, the pump insert

14

is inserted into the hollow portion of the pump body

12

in the orientation shown in FIG.

1

. The inner gear

18

is mated to the outer gear

16

as illustrated in FIG.

4

and inserted into the pump body

12

adjacent the pump insert

14

. The pump cover

20

is mated to the pump body

12

such that the protuberances

94

are disposed between the extensions

34

. The extensions

34

of the pump body

12

are then hemmed to join the pump body

12

and the pump cover

20

to enclose the pump insert

14

, the outer gear

16

, and the inner gear

18

therein. The inlet adapter

44

is then inserted through the inlet aperture

30

of the pump body

12

and releasably fastened to the inlet aperture

42

of the pump insert

14

. Once the lubrication pump

10

is assembled, the lubrication pump

10

is placed on the shaft

72

by sliding the shaft

72

through the central aperture

88

of the pump cover

20

. The serrated portion

70

of the shaft

72

is mated with the inner surface

68

of the inner gear

18

. The radial aperture

98

of the shaft

72

is disposed adjacent the inner surface of the pump insert

14

to facilitate fluid communication with the outlet opening

48

of the outlet channel

46

. The end of the shaft

72

is then slid through the central aperture

26

of the pump body

12

. The shaft

72

forms a substantially liquid tight seal with the pump body

12

and the pump cover

20

.

In the embodiment shown, the inlet adapter

44

is releasably fastened to the inlet aperture

42

of the pump insert

14

by a screwed connection. It is understood that other connection methods could be used. A conduit

102

fluidly connects the inlet aperture

42

with a source of lubricating fluid

104

, as schematically illustrated in

FIG. 2. A

typical lubricating fluid used is automatic transmission fluid with or without additives, although it is understood that other lubricating fluids may be used.

In operation, the shaft

72

is caused to rotate in the clockwise direction, as depicted by the arrow

106

in

FIG. 2

, by connection to a driving mechanism such as a transmission of an automobile (not shown). In turn, the inner gear

18

is caused to rotate within the outer gear

16

. Since there are fewer peaks

82

and valleys

84

in the inner gear than there are peaks

62

and valleys

64

in the outer gear

16

, the inner gear

18

is permitted to rotate without causing the outer gear

16

to rotate. As the inner gear

18

rotates, lubrication fluid is caused to be pumped from the source of lubrication fluid

104

, through the conduit

102

, and into the lubrication pump

10

. Within the lubrication pump

10

, the fluid moves through the inlet aperture

42

, through the inlet channel

40

, through the outer gear

16

and the inner gear

18

, through the outlet channel

46

and the outlet opening

48

, through the radial aperture

98

and through the axial bore

96

. The lubrication fluid is then caused to flow through the plurality of lubrication apertures

100

to lubricate bearings (not shown). The protuberances

94

militate against rotation of the lubrication pump

10

with the shaft

72

by abutting surfaces of the vehicle transfer case (not shown) adapted to receive the protuberances

94

.

Since the lubrication pump

10

is typically hidden from view and not easily inspected, it is critical that the lubrication pump

10

be reliable in its operation. The nature of the design of the lubrication pump

10

is such that pump prime must be maintained, or insufficient lubrication fluid may be pumped to the bearings. The extent of the prime required for the lubrication pump

10

to operate efficiently is a function of the amount of clearance between the outer gear

16

and the inner gear

18

and the pump body

12

and pump cover

20

. Since the operating temperature of the lubrication pump

10

is typically approximately 250 degrees Fahrenheit, the thermal expansion of the lubrication pump

10

components becomes important. Nylon having 35 percent glass filler has an expansion coefficient of approximately 0.00008 inches per inches-degree Fahrenheit. Nylon with 60 percent glass filler has an expansion coefficient of approximately 0.00004 inches per inches-degree Fahrenheit. Due to the expansion characteristics of nylon and glass filled nylon versus that of steel, the efficiency of the lubrication pump

10

increases as the operating temperature increases. This is not true with pumps of the prior art using an aluminum pump body and cover with powdered metal gears.

By using molded parts produced from nylon and glass filled nylon, machining costs are minimized. No precision machining is required. Lubrication pumps having inner and outer gears produced from powdered metal typically require precision machining, adding to cost and complexity of production.

From the foregoing description, one ordinarily skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications to the invention to adapt it to various usages and conditions.