Technical Field

The present invention relates to a service valve and, more particularly, to a service valve of the type which will prevent overfilling of and gas entrapment in an oil circuit for an integrated drive generator (IDG) and its external cooling circuit as part of a constant speed drive (CSD) when installed and serviced, for example, in aircraft by filling the CSD system when it is not operating and providing pressurization. of the oil circuit as the system is being filled.

Background Art

A CSD system of the general type referred to herein for use in aircraft installations is shown in U.S. Patent No. 3,733,924. The system disclosed therein employs a mechanical differential in conjunction with a hydrostatic transmission to rotate an aircraft alternator at constant speed via power supplied from a variable speed aircraft engine. The hydrostatic transmission is associated with a closed hydraulic circuit. Fluid is supplied to the circuit through a charge pump from a sump. Fluid pressure is regulated by a charge relief valve. An external circuit is provided for the IDG. However, this system does not address the problem of how to refill external cooling lines connected to the CSD to make up for lost fluid so that the lines are filled with fluid while being completely purged of air.

Another aircraft CSD system is shown in U.S. Patent No. 3,600,106. This system aims at reducing the required component weight in aircraft by providing a sump pressurization approach which

el iminat es the need for external engine bleed hardware . This a im is achieved by supplying air-entrained liquid into the transmission sump to attain a sufficient inlet head for the scavenge pump to maintain a desired efficiency level . A relief valve maintains a preset charge pressure in the fluid circuit . A differential pressure valve is used to maintain a sufficient pressure within a transmission sump so that there is sufficient pressure head at the inlet of a scavenge pump used for drawing leaking fluid from the transmission sump and delivering that fluid to the return conduit.

A charge pump is utilized to provide makeup , lubricating and control fluid for the system. Th charge or makeup fluid is fed through a condui connected to a port in a hydraulic drive to make up fo loss of fluid caused by leakage. Excess charge flui flows over a charge relief valve which maintains preset charge pressure in the conduit. A sump i provided in the case of the CSD to collect leakag fluid which is then pumped by means of a scavenge pum to a return conduit which passes through an externa cooling circuit, i. e. the cooler is located outside th case or housing of the CSD system, , and then to reservoir where air entrained in the fluid is separate before the fluid is returned to the charge pump However , no provision is made in this system fo filling the conduits in the external cooling circui and the rest of the system with fluid and completel purging the circuit of air during the filling proces when the system is not in operation.

Valves with movable spools have long been known for a variety of uses. For example, U.S. Patent No. 4,537,284 discloses a progressive distributor valve for distributing lubricant to heddles of weaving machines. However, this valve is not designed for the purpose of pressurizing an oil circuit at the same time that it is being filled. Also, there is no concern about purging air from the lubricant inasmuch as the lubricant is discharged through channels into an air space in the form of heddle guide grooves.

U.S. Patent No. 3,964,506 shows a pressure control system which provides for rapid filling and emptying of a clutch cylinder during engagement and disengagement of the clutch. The system uses a relief type pressure regulating valve, a solenoid-operated pilot valve and a flow control valve. However, these types of valves are not intended to operate as service valves strictly by pressure actuation and so as to provide their own pressure regulation when the system is not operating.

U.S. Patent No. 3,995,727 shows the use of a valve to provide additional cooling to the clutch of an automatic transmission. However, it will be readily appreciated that the arrangement and activation of this valve is not at all useful for service valve applications requiring high pressure fill and air purge capability.

Disclosure of the Invention

It is an object of my invention to provide a service valve which overcomes the problems _ nd disadvantages encountered with prior art devices.

More specifically, it is an object of my invention to utilize a pressure actuated service valve to provide makeup fluid for a system when the system is not in operation.

It is yet another object of my invention to provide a service valve which regulates its own pressure by virtue of being pressure activated.

It is still a further object and advantage of the service valve according to my invention which permits filling of the external cooling circuit of a CSD even when the drive is not operating.

Another object of my invention is to provide a means of pressurizing the external cooling oil circuit as it is filled in order to eliminate trapped air pockets.

Brief Description of the Drawings

These and further features, objects and advantages of my invention will become readily apparent from the following detailed description of a presently preferred embodiment when taken in conjunction with the accompanying drawings which show, for purposes of illustration only, the service valve apparatus in a CSD system for carrying out the method of my invention and, more specifically:

Fig. 1 shows a service valve installed in a CSD system (shown schematically) in a service position of the valve wherein the system is being filled with makeup fluid; and

Fig. 2 shows the service valve of Fig. 1 installed in the same CSD system but in a normal position assumed

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when the CSD system is in operation and the service valve is not being used to supply makeup fluid.

Detailed Description of a Preferred Embodiment

To assist in better understanding my invention and with a view toward conciseness, I deem it preferable not to show the entire CSD-IDG hydraulic circuit since conventional systems are shown in the U.S. Patent Nos. 3,600,106 and 3,733,924 discussed above. Under¬ standing of my invention will be facilitated by showing schematically only those parts of the CSD necessary for making and using the service valve.

A presently preferred embodiment of the service valve in accordance with my invention is designated generally by the numeral 10 in Fig. 1. It is used to fill the CSD case when the system is otherwise not operating, i.e. when the aircraft engine is not being used to drive a CSD which requires the use of fluid for control and lubrication. The valve 10 comprises an outer casing 11 and an axially movable spool 12 slidably and fluid tightly disposed within a bore in the casing 11. Again, so as not to obscure my invention, I will not describe conventional rings and packings used to make the valve fluid tight. A biasing means such as a spring 30 is placed in the valve casing 11 to abut against one face of the casing 11 and an end face of the spool 12 to bias the latter normally toward the inlet 21. It is in this normal position that the CSD will be operating as described hereinafter.

The casing 11 has a number of openings or ports for connection to various parts of the system. Port 13 near the inlet end cf the casing 11 allows fluid such

as oil to circulate through an external cooler 14 (i.e. external of the CSD case) and ^' return to the valve

10 through port 24 in the casing 11 through the line or conduit 15 as shown by arrow A. This circulation occurs both during normal operation of the CSD and when the service valve is utilized to provide makeup fluid in the system. A check valve 16 is provided in the line 15 between the opening 13 and the cooler unit 14. A case sump 17 provides fluid to the circuit line 15 during normal system operation by means of a scavenge pump 18 and a check valve 19. Oil under pressure is admitted to the bore 20 at the inlet 21 of the casing

11 having a quick disconnect for attachment to an external source of pressurized fluid for the purpose of providing makeup fluid without entrapping any gas in the system.

When it is desired to service the system, the scavenge pump 18 is shut off, and the external source of pressurized fluid is quickly hooked up to the inlet 21 forcing the spool to the leftward position shown i Fig. 1 from the rightward position shown in Fig. 2. The pressurized fluid such as oil then passes throug the port 13 communicating the bore 20 and the inle conduit for the external circuit 14. A check valve 1 is placed in the inlet conduit to prevent backflow. A the same time that the pressure fill is passing throug port 13, the piston or spool 12 is forced rearwardly i the valve casing 11 by the pressure from the oil i bore 20. The spool 12 has a narrowed portion 22 whic defines an oil-admitting space 23 which communicate with the port 24 both during normal CSD operatio (Fig. 2) and during servicing (Fig. 1) . The port 24 i

connected to the outlet conduit or line 15 of the external cooler circuit 14. As pressurized oil fills space 23 from conduit 15 in the position of spool 12 in Fig. 1, the oil exits from the valve casing 11 through a port 25 also communicating with space 23, which port 25 is connected to a conduit 26.

The conduit 26 is in communication with an air purging float valve 27. As fluid is fed into conduit 26, air is forced out through an opening 43 in the float valve 27. When the fluid reaches the level of the float valve 27, the float ball 44 rises to close off the air vent opening 43 allowing fluid pressure to build up in conduit 26. At this point a signal is sent to the operator indicating that the servicing of the external circuit is complete.

A pressure sensor 28 is located intermediate the port 25 and the float valve 27. At a predetermined point, the pressure build-up activates the pressure sensor 28 which, in turn, activates a solenoid 50 connected to an accumulator 29. Oil is fed to the accumulator 29 until a fluid level indicator (not shown) in the accumulator indicates that the accumulator is full. The solenoid to the accumulator is then deactivated.

A small amount of oil is transmitted to the IDG case by leakage across the spool 12 between bore 20 and port 42. A slight clearance too small to be shown in the drawings between the spool 12 and the casing, which communicates with the bore 20 provides for this leakage. This oil is fed into the IDG case through conduit 41. An IDG standpipe 36 is provided to allow a visual ir.dica icr. cf fill level in the IDG case. when

the oil level in the case reaches the top of the standpipe, oil overflow is directed through conduit 45 and port 37 to an overboard drain. The flowing out of oil through the overboard drain line together with the signal for external circuit service completion indicate that the operator should discontinue servicing the unit.

The operator then disconnects the quick disconnect nozzle from the inlet 21. However, some oil will still remain under pressure in the valve casing and will thus retard the spool from returning to its normal position (Fig. 2) so as to close off port 13 to the external circuit 14 and connect a deaerator 40 of conventional structure (and used in a manner similar to that shown in the transmission system in U.S. Patent No. 3,733,924 namely to remove air from the fluid during operation of the transmission) to the hydraulic circuit via a conduit 41 connected to port 42 which communicates with space 23 when the spool 12 is in its normal position (Fig. 2).

To allow the spool 12 to return to its normal non-fill position under the urging of spring 30, a bleed orifice 31 is provided through the central axis of the spool 12 to permit the fluid under pressure to bleed therethrough as a result of the leftward biasing action in the spool and into the orifice 32 arranged along the central axis of the spool. The fluid in the orifice 32 then can exit from the rear of the spool 33 which, at this time, has moved away from the wall of the casing 11. The orifice 32 is also theri ^' in communication with a space 34 surrounding the spool 12. A Dort 35 communicates the soace 34 to the IDG

standpipe 36, and a port 37 communicates the space 34 to an overboard drain for carrying away excess fluid and venting the valve.

During normal operation of the CSD system in, for example, an aircraft installation, the service valve 10 and, more particularly, the spool 12, will be in the position shown in Fig. 2 . Fluid from the IDG is pumped via the scavenge pump 18 from the case sump 17 to the external cooler circuit and from there back into the service valve casing 11 where it enters through the port 24 into the annular space 23 and thence exits through the port 42 after passing through the deaerator and is directed back toward the case (which, as previously stated, is not shown but surrounds the various parts shown in the drawing with the exception of the external cooler circuit 14) . The fluid in the standpipe 36 provides a reservoir of fluid to show that the fluid level in the case is not above a certain desired amount. If fluid emerges from the open end of the standpipe, the case has been overfilled. hile I have shown and described a presently preferred embodiment in accordance with my invention, it should be understood that the same is susceptible to numerous changes and modifications as will be apparent to one skilled in this art. I, therefore, do not wish to be limited to the details shown and described herein but intend to cover all such changes and modifications as are encompassed by the scope of the appended claims.