AU2017100717A4 - Oil pump and engine lubrication system - Google Patents

Abstract

An oil pump 100 provides positive displacement of oil through a valve member 112 by actuation of a solenoid moving a piston (or plunger) 106. The piston 106 incorporates a one way or 'check valve 112 allowing oil to flow into a pumping chamber 120 during the return stroke of the piston under influence of a return spring 110 when solenoid field windings 108 are sufficiently de-energised. As the piston 106returns, the outlet 122 valve is closed by its valve closing spring 124 and oil flows from the pump's inlet 102, through the piston and past the unseated valve member 112a of the valve 112 in the piston 106 and into the pumping chamber 120. The valve member 112a can have a valve face 114 unseated from a valve seat 116 during this return stroke of the piston. For a pumping stroke (Figure 3B), the valve member 112a in the piston 106 is closed with the valve face 114 seated against the valve seat 116 under influence of a return spring 118. During a pumping stroke (Figure 3B), the valve member 11 2a remains closed by its return spring 118, and the oil in the pumping chamber is forced under pressure to open the outlet valve 122, overcoming the outlet valve closing spring 124, and positively displacing a metered amount of oil from the pump through the outlet 104. The valve 112 can be a piston valve or 'poppet valve', an umbrella or reed type valve. The pump 100 can form part of a lubrication system including a reservoir 126 supplying an engine 10. 118 108 116 100 11 6 1201 102 106 0\ 104 10 0 0104 Fig 3A 112 112a 114 Fig 3B 112 112a 114 Fig 4

Description

1 2017100717 14 Jun2017

OIL PUMP AND ENGINE LUBRICATION SYSTEM

FIELD OF THE INVENTION

[0001] The present invention relates to an oil pump, such as for use in supplying or controlling oil flow to an engine, for example, by metering quantities of lubrication oil to the engine.

[0002] More particularly, the invention concerns a system for delivering lubrication oil for use by an engine.

[0003] The present invention finds application for delivering metered quantities of lubrication oil to an internal combustion engine (ICE), such as a two-stroke or four-stroke internal combustion piston engine (ICPE) or rotary (Wankel) type ICE.

[0004] Furthermore, the present invention has been devised particularly, although not necessarily solely, for use with an engine of an unmanned aerial vehicle (UAV).

[0005] More specifically, the present invention has been devised particularly, although not necessarily solely, for use with UAV engines where low oil flow rates are required for the desired operation of the UAV.

BACKGROUND TO THE INVENTION

[0006] The following discussion of the background art is intended to facilitate an understanding of the present invention only. The discussion is not an acknowledgement or admission that any of the material referred to is or was part of the common general knowledge as at the priority date of the application.

[0007] As mentioned above, the invention is particularly applicable to a lubrication system for a two-stroke internal combustion engine of a UAV. Accordingly, the invention will primarily be discussed in relation to that application. However, it should be understood that the invention may have application to various other 2 2017100717 14 Jun2017 machines, apparatus and devices having internal combustion engines which require lubrication.

[0008] The lubrication requirements for a two-stroke engine of a UAV are provided by way of a lubrication system comprising a pump for delivering lubrication oil to various parts of the engine, including for example the engine crankcase. The pump is connected to an oil supply, typically in the form of a reservoir such as a tank. The reservoir provides a supply of oil to the pump as required.

[0009] Typically, the pump is a positive displacement pump actuated by a solenoid.

[0010] It has been found that in such an engine lubrication system, the pump may not necessarily supply oil in a reliable manner to the engine in certain circumstances. This can lead to engine failure and may have catastrophic consequences for the UAV. It will be appreciated that engine failure at altitude can result in loss or destruction of the UAV.

[0011] Equally, rapid failure of the oil pump supplying oil in other vehicle engine applications can cause loss or destruction of such vehicles, either through oil starvation and possible engine seizure, or by loss of control of the vehicle.

[0012] In certain positive displacement type oil pumps which are known within the industry, it has been found that these pumps can fail to flow any oil or have greatly reduced flow under low pressure inlet conditions such as may exist due to high suction lift operation.

[0013] It is against this background, and the problems and difficulties associated therewith, that the present invention has been developed.

SUMMARY OF THE INVENTION

[0014] With the aforementioned in mind, an aspect of the present invention provides an oil pump having an inlet to receive oil into the pump, an outlet for oil to exit the pump, and a piston operable to force oil under pressure from the outlet, 3 2017100717 14 Jun2017 the piston including a valve to permit the oil into a pumping chamber, wherein the valve is closed during a pumping stroke of the piston when displacing oil from the pump.

[0015] For consistency, the term ‘piston’ will be used in this specification. However, it will be appreciated that the piston can be termed a ‘plunger’. In this specification, the terms piston and plunger are considered interchangeable.

[0016] The piston or plunger provides a reciprocating device enabling positive displacement of the oil. The piston or plunger incorporates therein the valve facilitating the oil to enter the pumping chamber (which can optionally be called a ‘compression chamber’) when the valve within the piston/plunger is open, and which valve is closed during the pumping stroke of the piston/plunger.

[0017] The piston may preferably be, or form part of, an armature of a solenoid forming part of a solenoid type pump.

[0018] Alternatively, or in addition, the piston may form part of a mechanical pump arrangement whereby actuation of the piston results from a direct mechanical coupling to a rotating or moving part of the engine.

[0019] The pump may be a metering pump to deliver metered amounts of lubrication oil to the engine. Control of the operating frequency of the pump can therefore be used to control the flow rate of lubrication oil to the engine.

[0020] The pump may include an outlet valve (also known as an outlet check valve) to allow oil to exit the pump via the outlet and prevent backflow of oil from the inlet into a pumping chamber of the pump.

[0021] Preferably the outlet valve includes a biasing means operated one way valve between the pumping chamber and the outlet. More preferably, the outlet valve is the only valve between the pumping chamber and the pump’s outlet.

[0022] Preferably the biasing means of the outlet valve includes a spring, such as a coil spring, to return a ball valve to a seat to seal the valve during a return stroke of the piston. 4 2017100717 14 Jun2017 [0023] The valve in the pump’s piston may be provided by one or more of a poppet type valve, an umbrella valve or reed type valve.

[0024] Preferably, the valve in the pump’s piston is arranged and configured so as to reduce the clearance volume or ‘dead volume’ between inlet and outlet valves.

[0025] The clearance volume or ‘dead volume’ is the volume taken up between the face of the piston (including the valve in the piston) and the opposing fixed face of the compression chamber toward which the piston approaches during a pumping stroke. This volume is ‘dead’ because it defines a volume of oil that cannot be pumped during a given stroke.

[0026] A clearance distance between the face of the piston and the opposing wall of the compression chamber (and hence a clearance ‘volume’ is consequently defined) is typically required to prevent, at the very least, noise from the pump if the piston and wall come into contact, but also to prevent likely damage to the piston and rapid failure of the pump due to impact between these two elements. Minimising this clearance volume also maximises the volume of oil that can be pumped and increases pumping efficiency of the pump.

[0027] It should be noted that in certain designs using a ball and spring inlet check valve downstream of the piston inlet valve seat, there is often a substantial addition to the clearance volume by virtue of the need to house the ball and spring surrounds. Reduction of this clearance volume by using alternative inlet valve designs in certain applications, such as a poppet valve and upstream spring, reed valve or umbrella valve, can improve the volume of oil that is pumped and the suction capability of the pump.

[0028] Preferably the pump is controlled to deliver oil at a pumping frequency of between 0.1 Hz and 20Hz, preferably between 0.1 Hz and 15Hz, and more preferably between 0.1 Hz and 12Hz. However, the pump may preferably be operated to deliver oil at a pumping frequency of between 0.1 Hz and 3Hz.

[0029] Control and/or adjustment of the pumping frequency can be used to manage the flow rate of the oil to the engine. Pumping frequency relates to the 5 2017100717 14 Jun2017 number of pumping cycles (i.e. the number of piston pumping and return strokes) per second.

[0030] With the valve included in the pump’s piston, and therefore eliminating the need for two valves (pressure side inlet and outlet check valves) on the outlet side of the pump’s piston (i.e. on the pressure side of the pump), the pump does not have to displace the volume of oil between those inlet and outlet check valves. This enables the pump to maintain inlet prime.

[0031] Thus, one or more forms of the present invention provide a compression ratio of >1.5:1 (greater than 1.5:1). The pump according to one or more embodiments of the present invention thereby has improved suction at the inlet. Preferably the internal compression ratio is greater than 2.0:1 and more particularly is around 2.8:1.

[0032] Furthermore, because of the ability to pump oil even with air present, the pump of at least one embodiment of the present invention is able to self prime. Therefore, the pump can expel air whilst taking in the oil and commencing to pump the oil, without the dry failure problem of non-self priming oil pumps which otherwise simply do not start to pump the oil or seize due to lack of oil for heat dispersion and lubrication.

[0033] It will be appreciated that one or more forms of the present invention provides for optimisation of pump operating characteristics, particularly suitable for customised or specific vehicle applications.

[0034] For example, with the ability to self prime, the oil pump of one or more forms of the present invention can be positioned above the oil reservoir.

[0035] Other oil pumps that do not have the ability to self prime, must either be pre-primed, or must be below, at the same level or within a very short height above the oil reservoir, which severely limits the options for positioning the oil reservoir and pump relative to one another on the vehicle.

[0036] Thus, oil pumps that cannot self prime can limit packaging options for the engine and lubrication system, and thereby may compromise the overall 2017100717 14 Jun2017 6 packaging volume and may result in compromised vehicle performance e.g. due to an increased packaging volume causing additional drag (and therefore potentially limiting maximum speed, flight manoeuvrability, or increasing fuel consumption).

[0037] The oil pump of the present invention may be a micro-pump configured to deliver relatively small quantities of oil. For example, displacement of the piston over a full stroke may be around 0.20-0.25mm, and total displacement of oil in one stroke may be around 6.5mm3. These features provide the oil pump with the ability to handle low oil flow rates, which make the oil pump of the present invention particularly suited for application in certain UAV engine configurations.

[0038] Clearance volume (i.e. the volume of oil retained in the pumping chamber at full stroke of the piston) may be as little as 3.6mm3 or less. This is at least in part due to lack of need for two check valves downstream of the piston.

[0039] A pump according to one or more forms of the present invention may not require a flexible diaphragm to separate a solenoid mechanism from the oil flow path; rather, the oil may flow through the flow path in the piston, via the valve in the piston, and into the pumping chamber (compression chamber). This avoids the risk of a split or damaged diaphragm causing pump failure and a potential catastrophe for the vehicle.

[0040] Preferably an oil pump of the present invention or oil lubrication system incorporating an oil pump embodying the present invention meters a defined quantity of oil per stroke. For example, oil delivery per stroke may be around 6mg ±10%.

[0041] With improved compression ratio, the pump is able to lift oil a height of >2 metres. This is a significant increase on known pumps of comparable physical size and application (i.e. electronic solenoid pumps for oil lubrication systems on vehicles). 7 2017100717 14 Jun2017

BRIEF DESCRIPTION OF THE DRAWINGS

[0042] One or more embodiments of the present invention will hereinafter be described with reference to the accompanying Figures, in which: [0043] Figure 1 shows a general arrangement of an oil supply system including an oil pump to supply lubrication oil to the engine; [0044] Figure 2A shows a cross section through a known oil pump with its piston at the most forward position in the pumping stroke of a pumping cycle; [0045] Figure 2B shows a cross section as shown in Figure 2A but with the piston returned to a position prior to the piston’s forward pumping stroke; [0046] Figure 3A shows a cross section of an embodiment of a pump of the present invention, with the pump’s piston at its most forward position in the pumping stroke of a pumping cycle; [0047] Figure 3B shows a cross section as shown in Figure 3B but with the piston returned to a position prior to the piston’s forward pumping stroke; and [0048] Figure 4 shows an arrangement of an oil lubrication system according to an embodiment of the present invention, the lubrication system arranged to supply oil to an engine.

DESCRIPTION OF PREFERRED EMBODIMENT

[0049] One or more embodiments of the present invention are each directed to an oil pump 100 applicable to an engine lubrication system for supplying lubricating oil to an engine 10.

[0050] Such an oil pump, oil lubrication system and engine are particularly applicable for use in unmanned aerial vehicles (UAVs).

[0051] Figure 1 shows an example of a basic engine lubrication system to supply lubrication from a reservoir to the engine 10. In the arrangement shown in Figure 8 2017100717 14 Jun2017 1, the engine 10 is a two-stroke engine with a crankcase 12 connected to an oil reservoir 16.

[0052] The lubrication system 14 includes the oil reservoir 16 and a pump 18 to supply oil from the reservoir 16 to the crankcase 12. The pump 18 is an electrically powered solenoid type pump connected to a supply 28 of electricity.

[0053] Figures 2A and 2B show cross sections through a known type of electric solenoid pump 18 for use in supplying lubricating oil for such an engine 10 and lubricating system of Figure 1.

[0054] As shown in greater detail with reference to Figures 1, 2A and 2B, the known type of oil pump 18 is a solenoid type pump powered by an electrical supply 28.

[0055] The known oil pump has an inlet 20 for the supply of oil into the pump via a conduit 24 connecting the pump to the reservoir 16, and an outlet 22 to supply oil from the pump 18 to the engine crankcase via conduit 26.

[0056] The pump has a piston 36. During a pumping stroke, the piston 36 drives forward toward the outlet 22 under influence of an electromagnetic field coil produced by energised field windings 46 surrounding the piston.

[0057] A piston return spring 48 causes the piston to return when the field windings are de-energised. Thus, through cyclical energisation and deenergisation of the field windings (field coil), the piston is caused to reciprocate backwards and forwards within the pump 18.

[0058] During the return stroke, oil enters a pumping chamber 42 between the piston face 50 and an inlet check valve 38. The inlet check valve is retained closed by pressure from an inlet check valve return spring 44.

[0059] During a pumping stroke, the piston forces oil from the pumping chamber 42 under pressure. This overcomes the inlet check valve return spring 44, thereby forcing the oil from the pumping chamber into an outlet volume 54 (which houses the inlet check valve return spring). The outlet volume is between the 9 2017100717 14 Jun2017 inlet check valve and an outlet check valve 40. The outlet check valve retains oil within the outlet volume until sufficient pressure overcomes the outlet check valve return spring 52.

[0060] Thus, during a pumping stroke, the piston 36 has to overcome the inlet check valve return spring and the outlet check valve return spring pressures, as well as pumping not only the volume of oil within the pumping chamber 42 but also the volume of oil within the outlet volume 54.

[0061] It will be appreciated that the stroke distance of the piston is relatively small, typically being 0.20-0.25mm (the distance from the piston’s maximum returned position to its maximum forward position). Thus, with the pressure of both the inlet and outlet check valves to overcome, and the volumes of oil in the pumping chamber and in the outlet volume to pump through the outlet, the pump draws a significant amount of current for its size.

[0062] Furthermore, such a pump may not prime when initially trying to pump oil (i.e. at engine start-up), particularly when the oil is viscous at low temperatures or the pump is drawing oil and air (e.g. when there may be a low oil level in the reservoir).

[0063] In addition, such a pump may not prime if the pump has to draw the oil during dry priming (initial priming) from a height exceeding a few centimetres, such as >10cm.

[0064] It will be appreciated that a pump that can overcome one or more of these problems would be beneficial.

[0065] It will further be appreciated the engine lubrication system incorporating an oil pump embodying the present invention can be applied to other types of engines, including other two-stroke engines and also four-stroke engines.

[0066] An oil pump embodying the present invention and/or engine lubrication system incorporating an oil pump embodying the present invention need not necessarily be limited to application with an engine for a UAV and may find other applications. 10 2017100717 14 Jun2017 [0067] Other applications of embodiments of the present invention can be in relation to aircraft, as well as other machines, apparatus and devices which have engines with lubrication requirements.

[0068] As shown with reference to Figures 3A and 3B, an oil pump 100 according to at least one embodiment of the present invention provides positive displacement of oil actuated by a solenoid.

[0069] In Figures 3A and 3B, solid arrows show flow of the oil, short dashed lines show direction of movement of the piston/plunger 106, and dash-dot lines show direction of movement of the valve member 112 during the return stroke (Figure 3A) and the pumping stroke (Figure 3B).

[0070] The solenoid is operable to actuate the piston 106 (also known as a ‘plunger’) within the pump 100 to perform an oil delivery stroke. The piston or plunger 106 can therefore provide or be part of the solenoid caused to move when the solenoid field windings/coil 108 are energised.

[0071 ] The piston 106 incorporates a one way valve or ‘check valve’ that allows oil to flow into a pumping chamber 120 during the return stroke of the piston under influence of a return spring 110 when the field windings are sufficiently deenergised. It will be appreciated that the field windings need not be fully deenergised, but so long as they are sufficiently de-energised that the spring force can return the piston to its return position to commence a subsequent pumping stroke.

[0072] As shown in the embodiment represented in Figure 3A, as the piston 106 moves to its return position (i.e. moves to the left in the figure shown), the outlet 122 valve is closed by its valve closing spring 124.

[0073] During this return movement, oil flows from the pump’s inlet 102, through the piston and past the unseated valve member 112a of the valve 112 in the piston 106 and into the pumping chamber 120.

[0074] In the embodiment shown, the valve member 112a has a valve face 114 unseated from a valve seat 116 during this return stroke of the piston. 11 2017100717 14 Jun2017 [0075] For a pumping stroke (Figure 3B), the valve member 112a in the piston 106 is closed with the valve face 114 seated against the valve seat 116 under influence of a return spring 118.

[0076] During a pumping stroke, as shown in Figure 3B, the valve member 112a of the valve is maintained closed by its return spring 118 and the oil in the pumping chamber is forced under pressure to open the outlet valve 122, overcoming the outlet valve closing spring 124, thereby positively displacing a metered amount of oil from the pump through the outlet 104, preferably around 6mg.

[0077] It will be appreciated that, while Figures 3A and 3B show a valve 112 within the piston, the valve itself having a small piston valve or ‘poppet valve’ (e.g. valve member 112a), that valve could be another type of valve in the pump’s piston, such as an umbrella or reed type valve specifically arranged and configured to reduce the volume of the pumping chamber 120. An umbrella valve or reed valve would serve the same purpose as a poppet valve (i.e. to control flow from the inlet into, and prevent backflow out of, the pumping chamber 120, and to overcome the need for two valves downstream of the pumping chamber and avoid the inefficient need to pump the associated volume of oil between those two check valves).

[0078] The purpose of the valve in the pump’s piston or plunger 106 is to open to permit oil flow into the pumping chamber 120 during the return stroke of the pump’s piston, and to close to prevent flow back through the pump’s piston during a pumping stroke to thereby enable the pump’s piston to positively displace the oil from the pumping chamber 120, overcome the outlet valve and force oil out of the pump 100.

[0079] The pump 100 can be a metering pump to output a metered amount of oil per pumping stroke. For example, in at least one particular embodiment, approximately 6mg of oil per stroke can be output.

[0080] Controlling the operating frequency of the pump can therefore be used to adjust the flow rate of oil delivered to the engine. Operating (pumping) frequency 2017100717 14 Jun2017 12 can, for example, be controlled or adjusted to be between 0.1 Hz and 20Hz, though frequencies between 0.1 Hz and 3Hz may be preferred. It will be appreciated that at a pumping frequency of 3Hz and a metered output of 6mg of oil, the pump can deliver an oil flow rate of 1080mg per minute. Electronic/electrical control of the pump can be used to adjust oil flow rate to match lubrication requirements for engine speed and load demands.

[0081] Figure 4 shows an oil lubrication system according to an embodiment of the present invention.

[0082] The lubrication system provides lubrication oil from a reservoir 126 to the crankcase 12 of the engine 10.

[0083] The pump 100 of an embodiment of the present invention is positioned above the reservoir 126. A supply conduit 128 provides a flow path for oil from the reservoir to the inlet of the pump. A pressure conduit 130 provides a flow path from the outlet of the pump to the engine. A controller 132 controls operation of the pump (i.e. ON, OFF and the cycle/duty time).

[0084] A pump according the present invention facilitates optimisation of various internal features of the pump which in turn can assist in minimising the clearance volume between the inlet and outlet valves of the pump. Minimising this volume has been found to be a key feature of the pump and one which increases inlet suction allowing for self-priming and the ability to draw oil into the pump from a significant height.

[0085] Whilst the present invention has been described in terms of a preferred embodiment in order to facilitate a better understanding of the invention, it should be appreciated that various modifications can be made without departing from the principles of the invention. Therefore, the invention should be understood to include all such modifications within its scope.

Claims (5)

1. THE CLAIMS DEFINING THE INVENTION ARE AS FOLLOWS:

   1. An oil pump having an inlet to receive oil into the pump, an outlet for oil to exit the pump, and a piston operable to force oil under pressure from the outlet, the piston including a valve to permit the oil into a pumping chamber, wherein the valve is closed during a pumping stroke of the piston when displacing oil from the pump.
2. 2. The oil pump according to claim 1 including an outlet valve to allow oil to exit the pump via the outlet and to prevent substantial backflow of oil into a pumping chamber of the pump between the outlet valve and the valve in the piston.
3. 3. The oil pump according to claim 2, wherein the valve in the piston of the pump is arranged and configured to reduce clearance volume or 'dead volume’ between that valve of the piston and the outlet valve.
4. 4. The oil pump according to any one of the preceding claims, providing a compression ratio greater than 1.5:1.
5. 5. The oil pump according to any one of the preceding claims, the oil pump being self priming.