EP2941569B1

EP2941569B1 - Lubrication system for a rotary vacuum pump

Info

Publication number: EP2941569B1
Application number: EP13824385.2A
Authority: EP
Inventors: Leonardo Cadeddu
Original assignee: VHIT SpA
Current assignee: VHIT SpA
Priority date: 2012-12-27
Filing date: 2013-12-13
Publication date: 2017-06-28
Anticipated expiration: 2033-12-13
Also published as: CN104919182A; EP2941569A1; WO2014102650A1; ITTO20121157A1; US20150345496A1

Description

Technical field

The present invention relates to rotary vacuum pumps, and more specifically it concerns a lubrication system for a rotary vacuum pump as defined in the preambles of claims 1 and 5. Such pumps are known of from any of EP 1850007 , JP 2006118424 , GB 2069610 , DE 2011005464 .
Preferably, but not exclusively, the invention is applied in the so-called single-vane pumps, i.e. pumps where the rotor includes a single vane with constant length, and the following description will mainly refer to this preferred application.

Prior art

Single-vane pumps are often used as vacuum pumps, for instance in the automotive field. They comprise a body defining a chamber, for instance with approximately elliptical cross section, in which the rotor rotates, in tangential contact, about an eccentric axis. The rotor has a diametrical slot where the vane is mounted and the vane is radially movable in the slot so that, while the rotor is rotating, the vane ends slide substantially in contact with the internal wall of the chamber. The chamber is divided by the rotor and the vane into a suction room and a pressure room, between which a pumped fluid is displaced.
In pumps used in motor car engines, when the rotor and the vane rotate air is sucked from the power brake through non-return one-way valves and is mixed with oil sent to the pump by the engine lubrication pump. The mixed air and oil are subsequently compressed in the chamber and then discharged into the engine, where oil is separated by means of an oil separator and collected in the oil sump.
Lubrication systems for rotary vacuum pumps used in the automotive field and mounted on the thermal engine are known, in which the pump is lubricated by the engine lubrication oil under pressure. An example is disclosed in ES 2340182 .
In another known lubrication system, disclosed for instance in DE 3841329 , lubrication oil coming under pressure from the pump drive shaft is sprayed into or sent to a coaxial bore in the rotor and conveyed inside the pump by the latter.
A first problem encountered in such pumps and in their lubrication systems is the oil return, under particular speed conditions of the engine, towards the power brake through the non-return valve, with consequent damages, in particular, of the parts made of elastomeric material and incompatible with the engine oil.
Oil return is caused by depression variations occurring upstream and downstream the valves under particular speed conditions of the engine. Those depressions are such that they nullify the forces generated by the pressure difference and by the resilient means, and have the effect of making the sealing element operate in "weak" manner, thereby allowing oil migration towards the power brake.
The same kind of problem may occur when the engine is off and oil is present inside the pump, if the suction valve(s) do(es) not have a perfect seal.
The solution of sucking atmospheric pressure between the non-return valves in order to prevent oil return to the power brake is known, for instance as disclosed in DE 102011005464 .
A second problem may occur when the engine is turned off: such a problem is the oil suction into the pump when the engine stops and the oil return to the power brake when the engine is off.
The phenomenon of oil suction, in this second case, is due to the permanence of a depression inside the pump for relatively short but significant periods, occurring when the engine is turned off.
A third technical problem may occur in case the engine on which the pump is mounted, after having been turned off, rotates in reverse direction, driven by the vehicle drive system. If oil suction occurred as disclosed with reference to the second problem, such a third problem may cause a hydraulic block with consequent pump breaking. A known solution for avoiding the occurrence of the second problem and the third problem related thereto is disclosed in document WO 2007003215 , which teaches applying non-return valves to the exhaust, which valves have the task of favouring a quick restoration of the atmospheric pressure inside the pump, when the engine is stopped.
Use of a safety valve in the suction chamber, arranged to discharge oil under pressure toward the oil sump thereby solving the third problem, is also known in the art.

Description of the invention

It is an object of the present invention to provide a lubrication system for a rotary vacuum pump which solves the problems of the prior art.
According to the invention, this is achieved by means of a lubrication system as definet in Claim 1.
In a further option a valve for protection in case of counter-rotation, discharging oil towards the engine oil sump, is provided in the lubricating system.
The invention also concerns a rotary vacuum pump as defined in Claim 5.
In a further aspect, the invention also provides a lubrication method as defined in Claim 10.

Brief Description of the Figures

The above and other features and advantages of the present invention will become apparent from the following description of preferred embodiments given by way of nonlimiting examples with reference to the accompanying drawings, which show the invention applied to a single-vane pump and in which:

Fig. 1 shows a diagram of a conventional lubrication system for a single-vane rotary vacuum pump;
Fig. 2 shows a diagram of a lubrication system according to the invention;
Fig. 3 is a cross-sectional view of a pump for the lubrication system according to the invention.

Description of Preferred Embodiments

The invention will be described in detail with reference to its application in a single-vane pump, as defined above. In order to make understanding of the invention easier, Fig. 1 shows a diagram of a conventional lubrication system for a rotary vacuum pump. In the example, a lubrication system for a single-vane pump is illustrated. The present invention can however be employed in any pump with vane rotor.
Referring to Fig. 1, pump 10 comprises a casing 40 defining a pumping chamber 44, for instance with an approximately elliptical cross-section, having an internal wall 42. Chamber 44 houses a rotor 12 that, in known manner, rotates substantially tangent to wall 42. The rotor has a radial slot 46 where a vane 22, radially slidable within the same slot, is mounted. During the clockwise rotation of rotor 12, the vane and the rotor divide chamber 44 into a suction chamber 13 and a compression chamber 18. Moreover a lubrication channel 11, connected to an engine lubrication pump 17, is formed in casing 40.
Lubrication system 100 comprises, besides pump 10, a suction duct 50, which connects pump 10 to a power brake 16 and through which pump 10 sucks air from the power brake. Duct 50 is equipped with one- way valves 14 and 15.
In the operation of a single-vane pump in a known lubrication system, when rotor 12 and vane 22 rotate clockwise, air is sucked from power brake 16 through valves 14 and 15 of suction duct 50 and is mixed in pumping chamber 44 with oil sent through channel 11 by an engine lubrication pump 17, sucking the engine oil from oil sump 20. The mixed air and oil are subsequently compressed in compression chamber 18 and then exhausted into the engine through a stop valve 19, known in the art as "check valve". Inside the engine, oil is separated from air by means of an oil separator and is then collected in oil sump 20.
During such operation, the problem described above of the oil return towards the power brake when the engine is on can occur, since, under particular speed conditions of the engine, depression variations are generated upstream and downstream valves 14, 15, which variations are such as to nullify the forces generated by the pressure difference and the resilient means. Thus the sealing elements in the valves are made to operate in "weak" manner, resulting in an oil migration towards the power brake and in damages, in particular, of the parts thereof made of an elastomeric material incompatible with the engine oil.
As said before, when the engine is turned off, other problems can arise: oil suction into the pump when the engine stops and oil return towards the power brake when the engine is off.
Oil suction is due to the permanence of a depression inside pumping chamber 44 of pump 10 for relatively short but significant periods when the engine is turned off. Such a depression causes oil suction from lubrication channel 11.
A known solution to this problem consists in using a valve 21 for protection in case of counter-rotation, discharging oil towards oil sump 20 when the engine on which pump 10 is mounted, after having been turned off, rotates in reverse direction, driven by the vehicle drive system.
Oil return towards the power brake when the engine is off may take place when, after the engine has been turned off, depression is maintained for relatively long periods in suction chamber 13 and in the portion of suction duct 50 between one- way valves 14 and 15. This phenomenon may give rise to two different problems: oil suction from the pump towards power brake 16, occurring if valves 14 and 15 perform a "weak" sealing, or sticking of the sealing element in valve 14, favoured by the soiling by oil residuals, when the valve sealing is good and hence the depression is maintained for very long periods, when the engine is off, with a consequent cooling that worsens the phenomenon.
Said sticking is due to the force generated by the flexible member of the valve, in addition to the pressure difference acting on the sealing member of the valve.
A lubrication system 200 according to the invention will now be described with reference to Figs. 2 and 3. In Figs. 2 and 3, elements corresponding to those illustrated in Fig. 1 are denoted by the same reference numerals.
Fig. 2 shows a diagram of lubrication system 200 according to the invention, and Fig. 3 shows an exemplary embodiment of a pump 300 for lubrication system 200 according to the invention.
Lubrication system 200 according to the invention includes, like prior art lubrication system 100, a pump 300, for instance a single-vane pump.
The lubrication system according to the invention can be applied also to a multi-vane pump.
The system according to the invention further comprises suction duct 50, which connects pump 300 to power brake 16 and through which pump 300 sucks air from power brake 16. More particularly, air is sucked through valves 14 and 15. Preferably, duct 50 is equipped with two one- way valves 14, 15. Preferably, valve 14 is arranged to connect pump 300 with suction duct 50. Preferably, system 200 includes, like prior art system 100, lubrication channel 11 of pump 300, connected to engine lubrication pump 17, and check valve 19 located at the exit from a discharge duct 26, connecting the pumping chamber 44 with the inside of the engine and introducing the air-oil mixture into the engine after compression in compression chamber 18.
As shown in Fig. 2, valve 21 for protection in case of counter-rotation has been eliminated in system 200 according to the invention.
In a second embodiment of the invention, not shown in the Figures, the lubrication system further includes valve 21 for protection in case of counter-rotation, discharging oil towards oil sump 20, similarly to the prior art system shown in Fig. 1.
Lubrication system 200 according to the invention includes a connecting duct 23 connecting the inside of the engine with suction duct 50, in turn connecting pump 300 to power brake 16.
Connecting duct 23 has a narrowing 24 in its end portion, in correspondence of suction duct 50. Preferably, connecting duct 23 is connected to suction duct 50 in a portion comprised between one- way valves 14, 15. Preferably, connecting duct 23 is connected to suction duct 50 in a region downstream of and close to valve 14, and is arranged to connect suction duct 50 with the inside of the engine, preferably with an exhaust region 25 of the oil-air mixture, adjacent to check valve 19 and to the outlet of a discharge duct 26 connecting it.
During operation, an oriented flow of the air-oil mixture, shown by the arrows in Figs 2, 3, is generated. That flow starts from compression chamber 18 of pump 300 and, through connecting duct 23 and narrowing 24, reaches suction duct 50, returning then to pump 300, in particular to suction chamber 13, through valve 14.
Advantageously, the provision of the oriented flow of the air-oil mixture flowing through connecting duct 23 eliminates the problem of the oil return towards the power brake when the engine is on, since pressure variations upstream and downstream valves 14, 15 and the resulting oil migration towards the power brake are eliminated, and prevents the permanence of a depression inside the pump when the engine is off, which depression could cause oil suction into the pump. The flow of the air-oil mixture sucked from the inside of the engine, passing through connecting duct 23 and narrowing 24, has moreover the advantage of optimising lubrication of the pumping assembly of pump 300 and of reducing the oil amount taken from the lubrication circuit, thereby reducing the overall energy utilised.
The phenomenon of oil suction into the pump when the engine is off can no longer occur in lubrication system 200 according to the invention, and hence valve 21 for protection in case of counter-rotation is no longer necessary, since the depression can no longer be established in pumping chamber 44 of pump 300 and in suction duct 50, which are at atmospheric pressure or at a slight temporary overpressure existing in the inside of the engine.
Advantageously, oil return towards the power brake or the sticking of the sealing element in valve 14 when the engine is off can no longer occur in system 200, since, when the motor is turned off, atmospheric pressure is established in pumping chamber 44 of pump 300 and between valves 14, 15, thanks to the provision of connecting duct 23.
In the second embodiment of the invention, valve 21 for protection in case of counter-rotation is provided to solve the problem caused by oil inflow generated by other phenomena, such as for instance accumulation of oil under pressure in the engine or oil draining, occurring in rare kinds of engines. In such cases, valve 21 for protection in case of counter-rotation is maintained.
Fig. 3 shows an exemplary embodiment of a pump 300 for lubrication system 200 according to the invention.
Pump 300 according to the invention includes, in known manner, casing 40 and pumping chamber 44 with its internal wall 42. Chamber 44 houses rotor 12, which, in known manner, rotates substantially tangent to wall 42. The rotor has radial slot 46 where vane 22, radially slidable within the same slot, is mounted. During the clockwise rotation of rotor 12, the vane and the rotor divide chamber 44 into suction chamber 13 and compression chamber 18. Lubrication channel 11, connected to engine lubrication pump 17, is preferably formed in casing 40.
Pump 300 according to the invention further includes connecting duct 23 connecting the inside of the engine with suction duct 50, in turn connecting pump 300 to power brake 16.
Preferably, pump 300 is connected to suction duct 50 by means of one-way valve 14.
Connecting duct 23 is formed, for instance drilled, in casing 40 and it has a narrowing 24 in its end portion, in correspondence of suction duct 50. Preferably, connecting duct 23 is connected to suction duct 50 between one- way valves 14, 15, downstream of and close to valve 14, and is arranged to connect suction duct 50 with the inside of the engine, preferably with the exhaust region of the oil-air mixture.
Preferably, connecting duct 23 has a funnel-shaped end portion 27, which is formed in correspondence of the portion of casing 40 facing the engine, in region 25 adjacent to check valve 19 and to the outlet of discharge duct 26 where the air-oil mixture is exhausted.
The funnel shape of end portion 27 of connecting duct 23 assists in collecting oil particles at the suction.

Claims

Lubrication system (200) for a rotary vacuum pump (300) connectable to a thermal engine, comprising a rotary vacuum pump (300), a suction duct (50) connected to the pump (300) and adapted to be connected to a power brake (16), characterized in that said lubrication system (200) further comprises a connecting duct (23) connected to the suction duct (50) and adapted to be connected to the inside of the engine in order to generate through the connecting duct (23) a flow of an air-oil mixture sucked from the inside of the engine.
Lubrication system (200) according to claim 1 in which the suction duct (50) is provided with two one-way valves (14, 15), characterized in that the connecting duct (23) is connected to the suction duct (50) in a portion of the duct (50) comprised between the two one-way valves (14, 15).
Lubrication system (200) according to claim 2, characterized in that the connecting duct (23) is connected to the suction duct (50) in a region downstream of and close to the valve (14).
Lubrication system (200) according to any one of the preceding claims, characterized in that the connecting duct (23) has a narrowing (24) in its end portion terminating in the suction duct (50).
Rotary vacuum pump (300) connectable to a suction duct (50) of a power brake (16), said pump comprising a casing (40) which defines a pumping chamber (44); a rotor (12) and a vane (22) mounted on the rotor (12), said rotor and vane being suitable to divide the chamber (44) into a suction chamber (13) and a compression chamber (18); characterized in that the pump (300) further comprises a connecting duct (23) formed in the casing (40) and adapted to connect the inside of the engine to the suction duct (50).
Rotary vacuum pump (300) according to claim 5 and connected to the suction duct (50) by means of a one-way valve (14), characterized in that the connecting duct (23) is connected to the suction duct (50) downstream of and close to the valve (14).
Rotary vacuum pump (300) according to claim 6, characterized in that the connecting duct (23) has a narrowing (24) in its end portion terminating in the suction duct (50).
Rotary vacuum pump (300) according to any one of claims 5 to 7, characterized in that the connecting duct (23) is made by drilling.
Rotary vacuum pump (300) according to any one of claims 5 to 8, characterized in that the connecting duct (23) has a funnelled shape at its end portion oriented towards the part of the casing (40) facing the engine.
Lubrication method for a rotary vacuum pump (300) according to any one of claims 5 to 9, wherein an oriented flow of an air-oil mixture starting from the compression chamber (18) of the pump (300) is generated, said flow passing through the connecting duct (23), reaching the suction duct (50) and returning to the suction chamber (13) of the pump (300).