Hydraulic pump

A hydraulic pump having a pump body formed by stacked plates mounted end-to-end. First and second ports for delivery and return of hydraulic fluid are formed through a port plate that is surmounted by a valve plate through which first and second main valve passages, each aligned with the first and second ports respectively, are formed. The valve plate is surmounted by a manifold plate in which first and second fluid distribution chambers, fluidly communicated with the first and second main valve passages respectively, are formed. A pump plate atop the manifold plate contains a gear assembly in a pumping chamber formed in the ends of the pump and manifold plates that draws fluid from one fluid distribution chamber and discharges it to the other. Each main valve passage contains a main pump valve that is biased for movement toward a sealing position that blocks fluid flow from through the main valve passage and each main pump valve is engaged by pistons in piston chambers that intersect the main valve passage in which the valve is disposed and opens to the fluid distribution chamber communicated with the other main valve passage.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to improvements in hydraulic pumps. 
2. Brief Description of the Prior Art 
Hydraulic pumps and actuating cylinders provide an effective means for 
positioning an object with respect to its surroundings and are, 
accordingly, in widespread use. For example, as disclosed in U.S. Pat. No. 
4,482,330 issued Nov. 13, 1984 to Cook, there are advantages to adjusting 
the height of an outboard motor on the transom of a boat during operation 
of the boat and such positioning can be efficiently carried out by 
mounting the motor on a motor bracket that is slidably mounted on a 
transom bracket that is, in turn, mounted on the transom of the boat. 
Vertical movement of the motor can then be effected by a hydraulic 
actuating cylinder that is connected between the two brackets and operated 
by pressurized hydraulic fluid supplied by a hydraulic pump. 
U.S. Pat. No. 4,482,330 provides an illustration of demands that are often 
made on hydraulic pumps. In order for the pump used in the motor mounting 
apparatus described in U.S. Pat. No. 4,482,330 to carry out the purpose 
intended, it must meet a number of requirements. Not only must the pump be 
reversible (that is, capable of delivering hydraulic fluid under pressure 
from either of two ports while receiving return fluid into the other 
port), it must also provide a positive seal against fluid flow once the 
motor has been placed at a desired position. Moreover, these requirements 
must be reliably met by a pump of reasonable size that can be mounted on 
the transom bracket. Of equal importance, these characteristics must be 
met by a pump that can be obtained at a reasonable cost from a dependable 
source of supply. Since the outboard motor mounting apparatus is a 
consumer item, excessively expensive components will limit the market for 
the apparatus; similarly, if the source is not dependable, difficulties 
will arise in meeting the demand to again affect the market for the 
product. 
In the past, the totality of these requirements has created a problem for 
the manufacturer of a product in which a hydraulic pump would be well 
suited for carrying out the operation of the product. The manufacturer may 
not be able to obtain a suitable pump at a price that will make its 
product competitive, or low cost pumps that are available may not be well 
suited for its product. Moreover, the manufacturer may very well not be in 
a position to manufacture the pumps itself to meet its requirements. If 
the product is a specialty item, the cost of tooling up to manufacture the 
pump (primarily the cost of casting pump bodies to include various 
chambers and flow passages) may not be recoverable from sales of the 
product. The net result is that the manufacturer may have to use a pump 
that is not optimally suited for its product but that is available at a 
reasonable price. Moreover, should the source of pumps dry up, for 
example, by a discontinuance of manufacture of the pump, the manufacturer 
must find a new source of supply, requiring a compromise between pump 
characteristics and pump costs. In the worst case, the manufacturer may 
not be able to find a suitable pump at a suitable price. 
SUMMARY OF THE INVENTION 
The present invention provides a hydraulic pump that can be economically 
manufactured in small lots to a pump user's specifications. To these ends, 
the hydraulic pump of the present invention is comprised of a pump body 
that, in turn, is comprised of a plurality of stacked plates that can be 
manufactured using nothing but machine tools found in any machine shop and 
then connected end-to-end to form the pump body. Chambers and flow 
passages that contain operating elements of the pump that control the 
movement of fluid into and out of the pump body as well as movement 
therein are formed, for the chambers, in the ends of the plates and, for 
the passages, through the plates so that the pump can be manufactured 
using nothing more than standard turning, milling and drilling operations 
that can be carried out at low cost in any machine shop. Thus, in 
particular, costly casting operations, which have made the manufacture of 
prior art pumps in small lots economically unfeasible, are eliminated in 
the manufacture of pumps constructed in accordance with the present 
invention. 
Such construction is, in part, enabled by a novel valving assembly of which 
the pump of the present invention is comprised. More specifically, control 
of fluid flow to and from the pump and sealing of the pump against fluid 
flow when the pump is not operating is effected by two main pump valves 
that are located in main valve passages that communicate with ports that 
deliver hydraulic fluid from the pump and receive the return of fluid to 
the pump. These valves are biased for movement to sealing positions in the 
main valve passages so that fluid flow into the pump is prevented at such 
times that the pump is not operating to deliver and receive hydraulic 
fluid from and to the pump. During operation, hydraulic fluid is 
transferred between two fluid distribution chambers, each of which is 
fluidly communicated with a main valve passage, so that pressure in one 
fluid distribution chamber will force one main pump valve open to permit 
delivery of hydraulic fluid from the pump. The return of fluid to the pump 
is then effected by a piston assembly that responds to fluid pressure in 
the fluid distribution chamber to which hydraulic fluid is transferred and 
mechanically engages the main pump valve in fluid communication with the 
other fluid distribution chamber to force such main pump valve away from 
the sealing position thereof and open the main valve passage wherein such 
valve is located to fluid flow. 
An object of the present invention is to provide a hydraulic pump that can 
be economically manufactured in small lots. 
Another object of the invention is to provide a low cost hydraulic pump 
that will enable manufacturers of products wherein pumps are used to 
manufacture the pumps used in their products. 
Yet a further object of the invention is to provide a hydraulic pump that 
can be inexpensively manufactured using machine tools and without the use 
of castings. 
Other objects, features and advantages of the present invention will become 
apparent from the following detailed description when read in conjunction 
with the drawings and appended claims.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Referring now to the drawings in general and to FIG. 1 in particular, shown 
therein and designated by the general reference number 20 is a hydraulic 
pump constructed in accordance with the present invention. In general, the 
pump 20 is comprised of a pump body 22 that has first and second ports 24, 
26 (FIG. 12) formed therein for delivering hydraulic fluid to an external 
device (not shown) such as a hydraulic actuating cylinder and receiving a 
return of fluid therefrom. A gear assembly 28 (FIG. 4), forming a 
conventional gear pump, is mounted within the pump body 22 to draw fluid 
from a selected one of the ports and discharge it, under pressure, to the 
other port as will be described below. Atop the pump body 22, the pump 20 
is comprised of a reservoir member 30 that has an open lower end 32 (also 
referred to herein as a second end 32 of the reservoir member) and a 
closed upper, or first, end 34. The interior of the reservoir member forms 
a reservoir for hydraulic fluid that can be used to provide additional 
fluid to the discharge from the pump 20 or receive a portion of the fluid 
returned to the pump 20 in a manner to be described below. A reversible 
electric motor 36 is mounted atop the reservoir member 30 and has an 
elongated shaft 38 that extends through the reservoir member 30 when the 
pump is assembled and into the pump body 22 to engage and drive the gear 
assembly 28. 
In accordance with one aspect of the present invention, the construction of 
the pump body 22 and reservoir 30 are such that the pump 20 can be 
economically manufactured using machine tools that are available in any 
machine shop and FIGS. 1 and 2 illustrate in part the manner in which this 
construction is achieved. As shown in FIG. 2, the pump body 22 is 
comprised of a stack of plates that can be bolted end-to-end so that 
manufacture of the pump body 22 can be readily effected by manufacturing 
the plates and then assembling the pump body 22 from them. More 
specifically, the pump body 22 is comprised of: a pump plate 40 having a 
first end 42, a second end 44 and an outer periphery 46 that intersects 
the ends 42, 44 and extends therebetween; a manifold plate 48 having a 
first end 50, a second end 52 and an outer periphery 54 that intersects 
the ends 50, 52 and extends therebetween; a valve plate 56 having a first 
end 58, a second end 60 and an outer periphery 62 that intersects the ends 
58, 60 and extends therebetween; and a port plate 64 having a first end 
66, a second end 68 and an outer periphery 70 that intersects the ends 66, 
68 and extends therebetween. As shown in the drawings, a selected one of 
the plates; for example, the manifold plate 48, can be machined from angle 
stock so that one web of the stock forms the plate and the other web 
extends from the periphery of the plate to form a convenient bracket 72 
for mounting the assembled pump 20 on an apparatus in which the pump 20 
might be used. 
Before describing the construction of each of the plates 40, 48, 56 and 64, 
it will be useful to first describe the assembly of the pump 20 once the 
plates have been independently manufactured. Referring first to FIG. 2, 
threaded holes 74, 76, 78, 80, 82, 84 are formed through the manifold 
plate 48 and aligning, unthreaded holes 75, 77, 79, 81, 83, and 85 (FIG. 
10) are formed through the valve plate 56 and unthreaded holes 87, 89, 91, 
93, 95, 97 (FIG. 13) through the port plate 70. (For clarity of 
illustration, the holes 75, 77, 79, 81, 83 and 85 through the valve plate 
56 and holes 87, 89, 91, 93, 95 and 97 through the port plate 64 have not 
been numerically designated in FIG. 2.) Assembly of lower portions of the 
pump body 22; specifically, the manifold plate 48, the valve plate 56 and 
the port plate 64, is effected by mating the first end 66 of the port 
plate 64 with the second end 60 of the valve plate 56, mating the first 
end 58 of the valve plate 56 with the second end 52 of the manifold plate 
48, and passing bolts 86, 88, 90, 92, 94, 96 through the port and valve 
plates to screw into the holes 74-84 in the manifold plate 48. Similarly, 
as shown in FIG. 1, threaded holes 98, 100, 102 and 104 are formed through 
the pump plate 40 to receive bolts 106, 108, 110 and 112 that pass through 
aligning holes 99, 101, 103, 105 (FIG. 8) through the manifold plate 48, 
holes 107, 109, 111, and 113 (FIG. 10) through the valve plate 56 and 
holes 115, 117, 119 and 121 (FIG. 13) through the port plate 64 to 
complete assembly of the pump body 22. Sealing of the bolt holes to 
prevent leakage from the pump body 22 can be effected as indicated on the 
bolts 106, 108, 110 and 112; specifically, as indicated in FIG. 14, the 
holes 87, 89, 91, 93, 95 and 97 for the bolts 86, 88, 90, 92, 94 and 96 
and holes 115, 117, 119 and 121 for the bolts 106, 108, 110 and 112 are 
countersunk, as shown at 114 for the hole 115, at the second end 68 of the 
port plate 64 and each of the bolts is provided with an O-ring and washer, 
numerically designated at 116 and 118 respectively for the bolt 106 in 
FIG. 1, that fit within countersunk portions of the holes through the port 
plate 64. 
With continuing reference to FIG. 1, a shoulder 120 is formed on the first 
end 42 of the pump plate 40 to mate with the open lower end of the 
reservoir member 30 and assembly of the reservoir member 30 to the pump 
body 22 is effected via bolts 122, 124 that are passed through unthreaded 
holes 126 and 128 formed through the closed first end of the reservoir 
member 30 to screw into threaded holes 130 and 132 formed through the pump 
plate 40. Sealing between the reservoir member 30 and the pump plate 40 is 
effected by an O-ring 134 that mounts on the shoulder 120 and sealing of 
the holes that receive the bolts 122, 124 is effected in the same manner 
that sealing of the holes that receive the bolts through plates of the 
pump body 22 is effected; that is, by means of washers and O-rings (not 
numerically designated in the drawings) mounted on the bolts. 
A shoulder 136 is formed on the first end 34 of the reservoir member 30 to 
mate with the open lower end of the case 138 of the motor 36 and the motor 
36 is bolted to the reservoir member 30 via bolts 140 and 142 that pass 
through holes 144 and 146 formed through the motor case 138 to screw into 
threaded holes 148 and 150 formed in the first end 34 of the reservoir 
member 30. Sealing between the reservoir member 30 and the motor 36 is 
effected by an O-ring 152 that mounts on the shoulder 136 and seals about 
the bolts 140 and 142 is formed by O-ring and washers (not numerically 
designated in the drawings) in the manner described above. 
Before continuing, it will be useful to summarize the assembly of the pump 
20. Initially, the manifold, valve and port plates, 48, 56 and 64 
respectively, and pump components contained in these plates as will be 
described below is effected via the bolts 86, 88, 90, 92, 94 and 96 and 
the pump plate 40 is then secured to the manifold plate 48 via the bolts 
106-112. As part of this assembly, O-rings 154, 156 and 158 are placed in 
grooves 160 (FIG. 11), 162 (FIG. 10) and 164 (FIG. 4) formed in the second 
end of the valve plate 56, the first end of the valve plate 56 and the 
second end of the pump plate 48, respectively, to provide seals between 
the plates of the pump body 22. Thereafter, the reservoir member 30 is 
mounted on the pump body 22 and bolted thereto. Finally, the shaft 38 of 
the motor 36 is passed through a bore 166 formed through the upper end of 
the reservoir member 30 and a rotating seal 168 about such bore and into 
the pump body 22 to engage the gear assembly 28 as will be discussed 
below. 
It will thus be seen that, as a result of the above-described construction 
of the pump 20, the interior of the pump body 22; specifically, the ends 
of the plates 40, 48, 56 and 64, will be accessible to the pump 
manufacturer for machining operations so that chambers and flow passages 
to be discussed below can be formed by milling, turning and drilling 
operations in which chambers are cut into the ends of the plates of which 
the pump body 22 is comprised and flow passages are formed through such 
plates. Once these chambers and passages have been formed, the assembly 
described above will completely seal the pump 20 from the environment so 
that the pump can be protected from environmental damage by a suitable 
surface coating applied to the reservoir member and pump body after 
assembly. 
With this introduction, details of the construction of the pump 20 and 
additional components of which it is comprised may now be considered. 
Referring first to FIG. 1, the reservoir member 30 can be conveniently 
constructed from aluminum bar stock by external machining to form the 
shoulder 136 and internal boring and machining from the second end 32 to 
form a cavity 170 that will become a reservoir when the reservoir member 
30 is mounted atop the pump body 22 as described above. A port for filling 
the reservoir is formed by a threaded hole (not shown) formed laterally 
through the wall about such cavity to receive a plug 172. A smaller cavity 
(not numerically designated in the drawings) is machined into the upper 
wall 173 of the cavity 170, about the bore 166, to receive the rotating 
seal 168. Holes described above and used in the assembly of the pump 20 
are formed by conventional drilling and tapping operations. 
The pump plate 40, more particularly shown in FIGS. 3 through 7, can 
similarly be manufactured from aluminum bar stock using external machining 
to form the shoulder 120 and milling and drilling to form remaining 
features of such plate. More particularly, as shown in FIGS. 4 through 6, 
a body portion 174 of a pumping chamber (not generally designated in the 
drawings) is milled into the second end 44 of the pump plate 40 to receive 
meshing gears 176 and 178 of which the gear assembly 28 is comprised. The 
body portion 174 of the pumping chamber has the general form of two 
interlocking circular cavities, one centered on a bore 180 that is drilled 
through the pump plate 40 to align with the axis of the motor 36 in the 
assembled pump and the other centered on a bore 182 offset from the bore 
180. In the assembly of the pump 20, the motor shaft 38 is extended 
through the bore 180 and has a flat 184 formed on one side thereof to 
engage a semicircular bore formed through the gear 176 so that the gear 
176 can be rotated in either direction on the shaft 38. The gear 178 is 
mounted on a pin 186 supported in the bore 182. The lower end of the body 
portion 174 of the pumping chamber, at the second end 44 of the pump plate 
40, is closed by the first end 50 of the manifold plate 48 when the pump 
body 22 is assembled and, as shown in FIGS. 6 and 8, first and second 
inlet-outlet portions, 188 and 190, of the pump chamber are milled into 
the first end 50 of the manifold plate 48 to underlie opposite sides of 
the body portion 174 of the pumping chamber. Such relationship between the 
portions of the pumping chamber have been shown in dashed line in FIG. 3 
for a purpose that will become clear below. 
As shown in FIG. 6, fluid make-up passages 192 and 194 are bored through 
the pump plate 40 in alignment with portions of the inlet-outlet portions 
188 and 190 respectively to fluidly communicate the pumping chamber with 
the reservoir member cavity 170 in the assembled pump 20. Each of the 
passages 192 and 194 contains a fluid make-up valve, 196 for the passage 
192 and 198 for the passage 194, that will open to permit fluid to flow 
into the pumping chamber from the reservoir but will close in response to 
fluid pressure in an inlet-outlet portion of the pumping chamber to 
prevent fluid flow through the passages 192 and 194 from the pumping 
chamber to the reservoir formed in the reservoir member 30. More 
specifically, each make-up valve is comprised of a ball 197 that is driven 
by fluid pressure in the inlet-outlet portion of the pumping chamber 
against a seat (not numerically designated in the drawings) formed in the 
passage wherein the ball 197 is located and a spring 199 that displaces 
the ball 197 from the seat in the absence of such pressure. 
Referring to FIG. 7, relief passages 200 and 202 are formed through the 
pump plate 40 to align with passages 204 and 206 formed through the 
manifold plate 48. The passages 200 and 202 contain conventional pressure 
relief valves 208 and 210 respectively, each comprised of a ball 201, the 
balls 201 being driven partially into the passages 204, 206 through the 
manifold plate 48 by springs 203. The valves 208, 210 open at a 
preselected pressure in the passages 204 and 206 to discharge hydraulic 
fluid to the reservoir formed in the reservoir member 30 for a reason that 
will become clear below. 
With continuing reference to FIGS. 6 and 7 and with additional reference to 
FIGS. 8 and 9, first and second fluid distribution chambers 212 and 214 
are formed in the pump body 22 by milling channels in the second end 52 of 
the manifold plate 48 as specifically shown in FIG. 9, such channels being 
closed to become chambers by abutment of the first end 58 of the valve 
plate 56 with the second end 52 of the manifold plate 48 when the pump 
body 22 is assembled. As shown in FIG. 9, each chamber 212, 214 so formed 
has an elongated body portion, 216 for the chamber 212 and 218 for the 
chamber 214, and the body portions 216, 218 extend parallel to each other 
across the second end of the manifold plate 48. Lateral extensions 220, 
222 and 224 are formed from the body portion 216 of the first fluid 
distribution chamber 214, the extensions 220, 222 and 224 terminating 
along a centerline 226 of the manifold plate 48 between the body portions 
216 and 218 of the fluid distribution chambers 212 and 214 respectively. 
Similar lateral extensions 228, 230 and 232 are formed from the body 
portion 218 of the fluid distribution chamber 214. 
The chambers 212 and 214 have been superimposed in dashed line on the first 
end 42 of the pump plate 40 in FIG. 3 and on the first end 50 of the 
manifold plate 48 in FIG. 8 to illustrate fluid communication between the 
reservoir, the pumping chamber and the fluid distribution chambers when 
the pump 20 is assembled and it will be useful to consider this 
communication before continuing with the description of remaining portions 
of the pump body 22. As shown in FIGS. 3 and 6, the body portion 216 of 
the first fluid distribution chamber 212 underlies the inlet-outlet 
portion 188 of the pump chamber so that fluid communication between the 
first fluid distribution chamber 212 and one side of the pumping chamber 
can be established by a passage 234 (see also FIG. 8) drilled through the 
manifold plate 48 to intersect the inlet-outlet portion 188 of the pumping 
chamber and the body portion 216 of the first fluid distribution chamber. 
Similarly, the body portion 218 of the second fluid distribution chamber 
underlies the inlet-outlet portion 190 of the pumping chamber to establish 
fluid communication between the opposite side of the pumping chamber and 
the second fluid distribution chamber 214 via a passage 236 drilled 
through the manifold plate to intersect the inlet-outlet portion 190 of 
the pumping chamber and the body portion 218 of the second fluid 
distribution chamber. As noted above, the motor 36 that drives the gears 
176 and 178 is reversible. Thus, the gears can be turned by operating the 
motor 36 to turn the gear 176 in a direction 238 in FIG. 4 to draw 
hydraulic fluid from the second fluid distribution chamber 214 and 
discharge such fluid into the first fluid distribution chamber 212. 
Alternatively, the motor 36 can be operated to turn the gear 176 in a 
direction 240 to draw hydraulic fluid from the first fluid distribution 
chamber 212 and discharge such fluid into the second fluid distribution 
chamber 214. Further, as shown in FIGS. 3 and 7, the passage 200 formed 
through the pump plate 40 and containing the pressure relief valve 208 and 
the passage 204 formed through the manifold plate 48 are aligned with the 
body portion 216 of the first fluid distribution chamber 212 so that the 
pressure relief valve 208 serves to limit the pressure in the first fluid 
distribution chamber 212. Similarly, the passage 202 formed through the 
pump plate 40 and containing the pressure relief valve 210 and the passage 
206 formed through the manifold plate 48 are aligned with the body portion 
218 of the second fluid distribution chamber 214 so that the pressure 
relief valve 210 serves to limit the pressure in the second fluid 
distribution chamber 214. The purpose of such limitation will become clear 
from the description of the operation of the pump 20 to be discussed 
below. 
Referring now to FIGS. 10, 11 and 12, the valve plate 56 has a first main 
valve passage 242 and a second main valve passage 244 formed therethrough 
to intersect the first and second ends, 58 and 60 respectively, of the 
valve plate 56. As particularly shown in FIG. 12, each of these passages 
is bored to have: a small diameter portion, 246 for the passage 242 and 
248 for the passage 244, intersecting the first end 58 of the valve plate 
56; a large diameter portion, 250 for the passage 242 and 252 for the 
passage 244, intersecting the second end 60 of the valve plate 56; and an 
intermediate diameter portion, 254 for the passage 242 and 256 for the 
passage 244, between the large and small diameter portions. Shoulders 258 
and 260 are formed between the large and intermediate diameter portions of 
the passages 242 and 244 respectively to form primary valve seats, and 
shoulders 262 and 264 are similarly formed between the intermediate and 
small diameter portions of the passages 242 and 244 respectively to form 
secondary valve seats that close the valve body to fluid flow at such 
times that the motor 36 is not operating in a manner to be discussed 
below. 
The passages 242 and 244 provide interruptible fluid communication between 
the fluid distribution chambers 212 and 214 and the ports 24 and 26 
respectively. To this end, and as shown in FIG. 10 wherein the fluid 
distribution chambers have been drawn in dashed line on the first end of 
the valve plate 56, the intersections of the passages 242 and 244 with the 
first end of the valve plate 56 lie along a line 266 that coincides with 
the centerline 226 of the manifold plate (FIG. 9) in the assembled pump 
body 22 and the passage 242 is aligned with the extension 220 of the fluid 
distribution chamber 212 while the extension 228 of the second fluid 
distribution chamber 214 is aligned with the passage 244. The centers of 
the ports 24 and 26 are similarly disposed along a line 268 (FIG. 13) that 
parallels the centerline 226 and the centers thereof are spaced a distance 
equal to the spacing of the centers of the passages 242, 244 so that, as 
shown in FIG. 12, the first port 24 is coaxial with the first main valve 
passage 242 and the second port 26 is coaxial with the second main valve 
passage 244 in the assembled pump body 22. 
Control of the delivery and return of fluid from and to the pump body 22 is 
effected by a valve assembly (not generally designated in the drawings) 
comprised of a first main pump valve 270 located in the first main pump 
valve passage 242 and second main valve 272 located in the main valve 
passage 244. As shown for the first main pump valve 270, each of the main 
pump valves 270, 272 is comprised of a central body portion 274 that is 
located in the intermediate diameter portion 254 or 256 of the passage 242 
or 244 that contains the valve 270 or 272. A flange 276 is formed on the 
end of the body portion 274 of each valve 270, 272 to engage, for the 
valve 270, the primary valve seat 258 and, for the valve 272, the primary 
valve seat 260 in a sealing position shown for the valves 270, 272 wherein 
the valves are driven to their maximal extent within the passages 242 and 
244 toward the first end 58 of the valve plate 56, On the opposite end of 
the body portion 274 of each valve 270, 272, an axial extension 278 (for 
clarity of illustration, the axial extension 278 for the valve 272 has not 
been illustrated in the drawings) is formed to extend into the small 
diameter portions 246, 248 of the valve passages 242, 244 wherein the 
valve is located. As shown for the valve 270, an O-ring 280 is mounted on 
the axial extension 278 of each of the valves 270, 272 to engage the 
secondary seat 262 or 264 of the passage 242 or 244 wherein the valve is 
the located when the valves are in the sealing position thereof shown in 
FIG. 12. Springs 282 and 284 are mounted in enlarged portions 286, 288 of 
the ports 24 and 26 respectively and engage the valves 270 and 272 in the 
assembled pump 20 to bias the valves to ward the sealing positions 
thereof. 
With the pump 20 constructed as has so far been described, the ports 24 and 
26 will neither deliver nor receive hydraulic fluid from a device, such as 
a hydraulic actuating cylinder, attached to the ports 24, 26. Instead, the 
valves 270 and 272 provide a positive seal against fluid flow from such 
device that serves as a safety feature of the invention. For example, 
should the pump be used with the outboard motor mounting apparatus 
described in the aforementioned U.S. 4,482,330 to Cook and should the 
first port 24 be connected to the end of the hydraulic actuating cylinder 
in such apparatus that receives pressurized hydraulic fluid to raise the 
outboard motor, the weight of the motor and motor bracket on which it is 
mounted will tend to drop the motor at such times that the pump is turned 
off. However, such tendency will give rise to a hydraulic pressure in the 
first port 24 that will drive the valve 270 firmly against the seats 258 
and 262 to capture hydraulic fluid in one end of the hydraulic actuating 
cylinder and provide a positive lock against any movement of the motor on 
the transom of the boat. Indeed, any tendency to move of a device that is 
positioned by hydraulic fluid from the pump 20 will cause one of the 
valves 270, 272 to be more firmly seated in the sealing position thereof 
in one of the main valve passages to cause a positive lock against such 
movement. 
As will be discussed below with respect to the operation of the pump, fluid 
flow between the fluid distribution chambers and the ports is effected by 
displacing the valves 270, 272 away from the sealing positions thereof and 
grooves 290 and 292 (FIGS. 11 and 12) are formed in the walls of the 
intermediate portions 254, 256 of the passages 242, 244 to enable fluid to 
flow about the valves 270, 272. Specifically, fluid flows about the 
extensions 278 of the valves 270, 272, through the grooves 290, 292, over 
the upper sides of the flange 276 and between the flanges and the walls of 
the enlarged portions 250, 252 of the passages 242, 244. 
With continuing reference to FIG. 12 and with further reference to FIG. 10, 
two first piston chambers 294 and 296 are formed in the first end 58 of 
the valve plate 56 to extend thereinto and intersect the enlarged portion 
252 of the second main valve passage 244. As can be seen in FIG. 10, 
wherein the fluid distribution chambers 212 and 214 have been superimposed 
on the first end of the valve plate in dashed lines, the first piston 
chambers 294 and 296 are overlain by the extensions 224 and 222 
respectively of the first fluid distribution chamber 212 so that fluid 
pressure in such chamber at such times that the pump 20 is operated to 
transfer fluid from the second fluid distribution chamber to the first 
fluid distribution chamber is transmitted to the first piston chambers 
294, 296. First pistons 298 and 300, slidably mounted in the first piston 
chambers 294 and 296 respectively and having conventional O-ring seals 
(not numerically designated in the drawings) to prevent fluid flow through 
the first piston chambers, extend to and engage the flange 276 of the 
second main pump valve 272 and the pistons 298 and 300 respond to pressure 
in the first fluid distribution chamber 212 to exert a force on the second 
main pump valve 272 for a purpose to be discussed below. Two second piston 
chambers 302 and 304 are similarly formed in the first end 58 of the valve 
plate 56 to underlie the extensions 230, 232 of the second fluid 
distribution chamber 214 and the second pistons chambers 302, 304 
similarly contain second pistons 306 and 308 that are slidably mounted in 
the chambers 302, 304 to engage the portion 276 of the first main pump 
valve 270. 
OPERATION OF THE PUMP 
In order to discuss the operation of the pump 20, a schematic 
representation of portions of the hydraulic circuit of the pump 20 has 
been added to FIG. 12 and such portions of the circuit have been drawn in 
relation to the valves 270, 272 and pistons 298, 300, 306, and 308 mounted 
in the valve plate 56. Features of the representation have been indicated 
using numerical designations of the features of the pump that have been 
described above; specifically, the fluid distribution chambers 212 and 214 
have been represented by horizontal lines so designated in FIG. 12 with 
the extensions 220, 222, 224, 228, 230 and 232 from the body portions of 
the first fluid distribution chambers being represented as vertical lines 
to the main valve passage bores and the piston chambers. Similarly, 
passages formed through the manifold and pump plates have been represented 
by lines bearing the numerical designations of such passages in FIGS. 6 
and 7, the gear assembly 28 and valves 196, 198, 208 and 210 have been 
represented by common hydraulic symbols bearing the numerically 
designations of such components in FIGS. 4, 6 and 7 and the reservoir 
formed by the reservoir member 30 as described above has been indicated as 
a block bearing the numerical designation 30. 
As has been discussed above, at such times that the motor 36 is not 
operating, the springs 282 and 284 bias the main pump valves 270, 272 into 
the sealing position in the main pump valve passages 242 and 244 so that 
return of fluid to the pump 20 cannot occur. Specifically, fluid pressure 
in the ports 24 and 26 tending to establish a return flow to the pump 20 
will drive the valves 270 and 272 more firmly against seats formed in the 
passages 242, 244 to provide a positive lock against any return of fluid 
to the pump 20 in a nonoperating condition of the pump 20. 
To establish fluid flow from and to the pump 20, it is necessary only to 
commence operation of the motor 36 and, moreover, the direction of flow at 
the ports 24, 26 is determined by the direction of rotation of the shaft 
38 of the motor 36. More specifically, if the motor shaft 38 is rotated in 
the direction 238 shown in FIG. 4, hydraulic fluid will be drawn from the 
second fluid distribution chamber 214 and delivered to the first fluid 
distribution chamber 212 to build up hydraulic pressure in the chamber 
212. As can be seen in FIG. 12, such pressure is transmitted by the 
chamber extension 220 to the first main valve passage 242 to force the 
first main pump valve 270 away from the sealing position thereof and 
establish fluid communication from the first fluid distribution chamber 
212 to the first port 24 for delivery of hydraulic fluid from the port 24. 
Moreover, the extensions 222 and 224 of the first fluid distribution 
chamber 212 will transmit pressure in the chamber 212 to the first pistons 
298 and 300 that, as shown in FIG. 12, bear against the second main pump 
valve 272. Thus, the pressure in the first fluid distribution chamber 
exerts a force on the second main pump valve 272 to force the second main 
pump valve away from the sealing position thereof. Thus, the second main 
valve passage 244 is opened to fluid flow for the return of fluid via the 
second port 26 to the second fluid distribution chamber 21 and thence to 
the gear assembly 28. Thus, operation of the motor 36 to turn the shaft 38 
thereof in the direction 238 establishes a fluid circulation in which 
hydraulic fluid is drawn from a device connected to the ports 24, 26 via 
the port 26 and transmitted back to the device via the port 24. 
If the motor shaft 38 is turned in the reverse direction, i.e., the 
direction 240 in FIG. 4, the reverse result is obtained. In this case, 
fluid is drawn from the first fluid distribution chamber 212 and delivered 
to the second fluid distribution chamber 214 to build up pressure therein 
that will directly force the second main pump valve 272 away from the 
sealing position thereof while forcing the first main pump valve 270 away 
from its sealing position via pressure exerted against the second pistons 
306 and 308. Thus, again a fluid circulation is established between the 
pump 20 and a device connected to the ports 24 and 26; however, such 
circulation will draw hydraulic fluid from the side of the device 
connected to the first port 24 and deliver fluid to the side of the device 
connected to the second port 26. 
It will be noted that the above-described operation of the pump 20 is 
self-regulating. Should the pressure in one fluid distribution chamber be 
insufficient to cause the pistons fluidly communicated therewith to force 
the main pump valve in the main pump valve passage communicated with the 
other fluid distribution chamber away from its sealing position, flow from 
the pump 20 will cease to cause fluid pressure in the fluid distribution 
chamber which is receiving fluid from the gear assembly 28 to increase 
indefinitely. Thus, at some point, the main pump valve in the return main 
valve passage must, at some point, be forced from its sealing position to 
establish the above described fluid circulation. 
The present invention also contemplates that the pump 20 will, at times, be 
used with a single-ended hydraulic actuating cylinder; that is, a 
hydraulic actuating cylinder in which the piston rod extends from the 
piston of the cylinder through only one end portion of the cylinder. In 
this case, the quantity of fluid that must be received at one side of the 
hydraulic actuating cylinder to effect a movement of the piston rod 
thereof will differ from the quantity that is driven from the other side. 
In the case in which delivery must exceed return and delivery is from the 
first port 24 via the first fluid distribution chamber 212 so that the 
pressure in the second fluid distribution chamber is, in effect, negative, 
the make-up valve 198 to the second fluid distribution chamber will open 
to provide additional fluid to the intake side of the gear assembly 28 to 
make up the difference. Similarly, should a larger delivery of fluid be 
required from the second port 26 than is drawn from the first port 24, the 
difference is supplied from the reservoir 30 via the make-up valve 196. 
Finally, should fluid flow from the pump 20 be externally blocked for any 
reason, pressure in the high pressure fluid distribution chamber 212, 214 
will force the relief valve 208 or 210 from such chamber to the reservoir 
to open and thereby shunt hydraulic fluid from the gear assembly 26 to the 
reservoir member 30 to prevent damage to the pump 20. 
It will be clear that the present invention is well adapted to carry out 
the objects and attain the ends and advantages mentioned as well as those 
inherent therein. While a presently preferred embodiment has been 
described for purposes of this disclosure, numerous changes may be made 
which will readily suggest themselves to those skilled in the art and 
which are encompassed in the spirit of the invention disclosed and as 
defined in the appended claims.