Aircraft main engine fuel pump with multiple gear stages using shared journals
A multistage gear pump assembly includes first and second gear pumps that use common shafts and are axially separated by a fixed spacer within the housing. Pressurized bearings are provided at opposite axial ends of the first and second gear pumps. The second gear pump handles cruise and idle operations of the aircraft while the first gear pump stage assists in meeting higher demand modes of engine operation. Otherwise, the first gear pump is maintained at a minimal pressure to reduce energy consumption and still provide desired stability and eliminate issues associated with bearing oil whirl associated with prior known arrangements. When additional assistance is required, such as during takeoff, climb, or windmill relight, the first gear pump advantageously contributes to the increased pressure.
1. A multistage gear pump assembly comprising:
a housing having an opening of a first dimension therein;
a first gear pump received in the housing having a first drive journal shaft that rotates about a first axis and drives a first gear that operatively engages a second gear rotating about an adjacent second axis for pressurizing fluid as the first and second gears mesh with one another;
a second gear pump received in the housing having a first gear received on the first drive shaft in spaced relation along the first axis from the first gear of the first gear pump, and the first gear of the second gear pump operatively engaging a second gear rotating about the second axis for pressurizing fluid as the first and second gears mesh with one another;
a spacer fixed in the housing to prevent relative movement between the spacer and the housing, the spacer includes a bore having a second dimension less than the first dimension of the housing opening such that the first dimension of the housing opening cooperates with the spacer to form first and second recesses that receive the first and second gear pumps therein on opposite ends, respectively, of the spacer and the spacer is interposed between the first and second gear pumps;
a first seal member interposed between the first and second gear pumps; and
at least a first pressurized journal bearing supporting at least the first drive journal shaft.
2. The pump assembly of claim 1 wherein the first gears of the first and second pumps are different sizes.
3. The pump assembly of claim 2 wherein the first gear of the first pump has a greater axial length than the first gear of the second pump.
4. The pump assembly of claim 1 wherein the first gear of the first pump has a greater axial length than the first gear of the second pump.
5. The pump assembly of claim 1 wherein the spacer is an integral portion of the housing extending into the housing opening between the first and second gear pumps.
6. The pump assembly of claim 5 wherein the housing opening has first and second counterbores that terminate at the spacer.
7. The pump assembly of claim 1 wherein the housing opening is a bore open at first and second ends of the housing, and the spacer is a plate that is operatively secured to the housing against axial movement within the bore.
8. The pump assembly of claim 7 further comprising a second pressurized journal bearing axially spaced from the first pressurized journal bearing and supporting at least the first drive journal shaft.
9. The pump assembly of claim 8 wherein the first and second pressurized journal bearings are located axially outward of the first and second pumps, respectively.
10. The pump assembly of claim 9 wherein the second axis is parallel to the first axis, and the second gears of the first and second pumps are secured to a second shaft that rotates about the second axis.
11. The pump assembly of claim 1 further comprising first and second bearings disposed on opposite axial sides of the spacer to provide axial thrust load support.
12. The pump assembly of claim 11 further comprising first and second seals interposed between the spacer and the first and second bearings, respectively.
13. A multistage gear pump assembly comprising:
a housing having a bore of constant diameter therein;
a first gear pump received in the bore having a first drive journal shaft that rotates about a first axis and drives a first gear that operatively engages a second gear rotating about an adjacent second axis for pressurizing fluid as the first and second gears mesh with one another;
a second gear pump received in the bore having a first gear received on the first drive shaft in spaced relation along the first axis from the first gear of the first gear pump, and the first gear of the second gear pump operatively engaging a second gear rotating about the second axis for pressurizing fluid as the first and second gears mesh with one another;
a spacer plate received in the bore and interposed between the first and second gear pumps in the bore;
a member operatively securing the spacer plate against axial movement within the bore; and
at least a first pressurized journal bearing supporting at least the first drive journal shaft.
14. A method of assembling a multistage gear pump assembly comprising:
forming an opening having a first dimension in a housing;
fixing a spacer, having a bore of a second dimension less than the first dimension of the housing opening, in the housing against axial movement relative to the housing and thereby defining first and second recesses on opposite ends, respectively, of the spacer;
assembling first and second gear pumps in the recesses on opposite faces of the spacer;
providing a first seal member interposed between the spacer and the first pump; and
providing first and second pressurized journal bearings in the housing.
15. The method of claim 14 further comprising locating the journal bearings at opposite axial ends of the housing to support the shaft.
16. The method of claim 14 further comprising providing a second seal member interposed between the spacer and the second gear pump.
17. The method of claim 14 wherein the fixing step includes forming the spacer as an integral portion of the housing that is interposed between the first and second gear pumps to provide axial thrust load support to the gear pumps.
18. The method of claim 14 wherein the fixing step including providing a separate spacer plate and securing the spacer plate to the housing.
19. The pump assembly of claim 1 wherein the first seal member is interposed between the first gear pump and the spacer.
20. The pump assembly of claim 19 further comprising a second seal member interposed between the second gear pump and the spacer.