GB2198481A - Rotary vacuum pump - Google Patents

Abstract

The pump has a number of sliding blades 15 the outer ends of which are thrust into contact with an inner surface 43 of a working chamber 10 formed in the pump body 2 so as to form variable-volume duty chambers 48 between the blades 15, and has an air intake opening 24 and an air exhaust and lubricating oil drain opening 44. The exhaust/drain opening 44 communicates with an exhaust/drain duct (26, 35, 40, 41, Fig. 1) formed in the body 2, the angle subtended at the rotor axis by the exhaust/drain opening 44 (i.e. between ends 45, 46) being greater than the angle subtended by the initial portion 26 of the exhaust/drain duct. <IMAGE>

Description

PERFECTED ROTARY BLADE VACUUM PUMP The present invention relates to a rotary blade vacuum pump conveniently for use on diesel engine vehicles for creating, in particular, the vacuum required for operating a power brake.

Such rotary vacuum pumps are known to comprise a supporting body for a shaft controlled by the engine for turning an eccentric rotor in a duty cavity, which rotor presents a number of blades sliding inside cavities formed on the rotor itself and inside which oil under pressure is supplied so as to thrust the outer ends of the blades into contact with the inner surface of the duty cavity which is thus divided by the said blades into a number of variable-volume duty chambers.The strong hydrostatic thrust exerted on the inner ends of the blades, in contrast with the blade re-entry force exerted together with rotary sliding on the inner surface of the duty cavity which is eccentric in relation to the rotor, results in the blades oscillating and knocking sharply on the surface of the duty cavity and, consequently, severe, uneven ear on tie surface t itself.

The ain of the present invention is to provide a perfected rotary blade vacuum pump of tile aforementioned type designed to overcome the aforementioned drawback.

ith this aim in view, according to the present invention, there is provided a rotary blade vacuum pump comprising a supporting bod for a shaft turning a rotor Having a number of blades sliding inside cavities formed in tulle said rotor and the outer ends of which are thrust into contact with tie inner surface of a duty cavity formed in tie said body so as to form variable-volume duty chambers between the said blades, and having an air intake opening and an air exhaust and lubricating oil drain opening; tie said exlwaust/drain opening communicating with an exEzaust/drain duct formed in the said supporting body; characterised by the fact that the angle of the said ex haust/drain opening is greater than that of an initial portion of tie said exhaust/drain duct.

Thus by the present invention the exhaust/drain opening subtends an angle at the rotor axis greater than the angle at the rotor axis subtended by the initial portion of the exhaust/drain duct, so that the exhaust/drain opening extends further around the periphery of the duty cavity than does the exhaust/ drain duct.

One embodiment of the present invention will be described, by way of a non-limiting example, with reference to the accompanying drawings, in which Fig.1 shows a partially-sectioned side view of a rotary blade vacuum pump according to the present invention; Fig.s 2 and 3 show sections along lines Il-Il and III-III respectively of the rotary vacuum pump in Fig.l; Fig.4 shows a side view of an internal component on the Fig.I vacuum pump; Fig.5 shows a section along line V-V of the Fig.4 component.

With reference to Fig.s 1 to 3, rotary blade vacuum pump 1 comprises a supporting body 2, conveniently of die-cast aluminium, closed at the front by a cover 3 secured to body 2 by three bolts 4 with'an annular seal 5 inbetween.

At the rear end opposite the end closed by cover 3, body 2 presents a flanged part 6 designed to fit onto an engine block (of known type not shown) witP1 an annular seal 7 inbetween. The said body 2 presents a small-section central portion 8 which, in the direction of cover 3, widens out into a portion 9 forming, internally, a duty cavity 10. Portion 8 of body 2 supports a shaft 11 which, at one end, projects beyond flanged part 6 so as to be turned, in known manner not shown, by the engine, and, at the other end, is fitted, in rotary manner, with a rotor 13 housed inside duty cavity 10 and having four grooves 14 housing respective blades 15 designed to slide inside the said grooves 14 and the outer ends of which are designed to contact the inner surface of cavity 10.Inside shaft 11 there is formed an axial channel 16 for the passage of lubricating oil under pressure. The said shaft ii also presents a radial hole 17 enabling communication between channel 16 and the surface of shaft ii in portion 8 of body 2, for the purpose of lubricating shaft 11. The said channel 16 therefore presents an sxial end hole 19 for enabling communication between channel 16 and a circular cham- ber 20 formed on the top surface of rotor 13 facing cover 3, the said chamber 20 communicating with an end portion of grooves 14. Towards a lateral portion of cover 3, there originates an outer annular wall 22 housing a connecting pipe 23 comprising internally, and in known manner, a check valve enabling only air intake from the known outer pipe (not shown).The said connecting pipe 23 communicates with duty cavity 10 via an intake opening 24 formed in cover 3 and shown by the dotted line in Fig.3. In supporting body 2, in a bottom portion 25 facing downwards with vacuum pump 1 arranged as shown in Fig.1, there is formed a first portion 26 of an exhaust/drain duct communicating with a bottom compartment 35 closed by means of a disc 37 secured circumferentially to the edge of an annular wall 38 of portion 25 via the interposition of a sealing ring 36. Along the axis of body 2, there extends upwards from compartment 35 a duct 40 which, together with duct 26, has its axis parallel with that of compartment 35 and communicates at the top with the end of an exhaust/drain duct 41 formed in supporting body 2, parallel with the longitudinal axis of the same, and coming out beyond flanged part 6.

According to the perfected design of the present inven- tion, duty cavity 10 is fitted inside with a hollow cylindrical body 43, shown more clearly in Fig.s 4 and 5, which, towards the end of its lateral wall, presents an opening 44 having a channel-shaped profile and which acts as an exhaust/drain opening for duty cavity 10 on vacuum pump 1. In more detail, the said exhaust/drain opening 44 communicates with the first portion 26 of the exhaust/ drain duct and, as shown in Fig.3, presents a much larger angle.The angle of the said exhaust/drain opening 44, in fact, is substantially equal to the angular distance between the outer ends of two successive sliding blades 15, and the initial portion 45 of the said opening 44 is positioned in such a manner as to be affected by tlle outer end of a blade 15 substantially as soon as the compressed adjacent duty chamber 48 ceases to communicate with intake opening 24. The end portion'46 of tV1e said exPlaust/drain opening 44, on the other hand, is substantially aligned with the angularly end portion of tiie underlying exhaust/ drain duct 26.

Vacuum pump 1 according to the present invention operates as follows. Rotation of shaft 11 turns rotor 13 with the result that blades 15 define, in known manner, variablevolume chambers 48, the volume of which increases gradually from exhaust/drain opening 44 towards intake opening 24, and then decreases down to a minimum at exhaust/drain opening 44. Air is therefore sucked in through opening 24 from connecting pipe 23 and exhausted through opening 44, first portion 26, compartment 35 and ducts 40 and 41.

Furthermore, oil under pressure is supplied through channel 16 in shaft 11, which oil, via hole 19 and circular chamber 20, forces blades 15 rearwards, which are thus maintained contacting the inner surface of hollow cylindrical body 43 in duty cavity 10. During re-entry of blades 15, lubricating oil flows out of rotor 13, which oil is also expelled, together with the air, through opening 44 and duct 41 and collected in the engine oil sump.

According to the present invention, and as shown in Fig.3, as a blade 15 moves past the intake opening 24 area, it closes and gradually compresses a variable-volume chamber 48. Subsequent to further slight rotation, the blade 15 defining the front of the said chamber 48 moves up to tlie initial portion 45 of exhaust/drain opening 44, thus en abling communication between chamber 48 and first portion 26 of the exhaust/drain duct. This provides for eliminating damaging overpressure of the oil on blades 15 which, by no longer oscillating sharply, are free to slide smoothly on the inner surface of body 43, thus considerably reducing wear on the said surface which is rendered more uniform. Forming the said exhaust/drain opening 44 as described with a channel-shaped profile determines a relatively small-section initial portion 49, limited by the wall of duty cavity 10, thus preventing a sharp fall in pressure inside chamber 48. End portion 46 of exhaust/ drain opening 44 angularly aligned with the end portion of first portion 26 of the exhaust/drain duct in no way reduces suction during depression of vacuum pump 1.

To those skilled in the art it will be clear that changes may be made to the embodiment described herein without, however, departing from the scope of the present invention.

Claims (1)

1) - A rotary blade vacuum pump comprising a support ing bbdy for a shaft turnihg a rotor having å number of blades sliding ihside cavities form d in the said rotor and the outer ends of which are thrust into contact kith the inner surface of a duty cavity formed in the said body so as to form variable-volume duty chambers between the said blades, and having an air intake opening and an air exhaust and lubricating oil drain opening the said exhaust/drain opening communicating with an exhaust/ drain duct formed in the said supporting body characterised by the fact that the angle of the said exhaust/drain opening is greater than that of an initial portion of the said exhaust/drain duct.

2) - A vacuum pump as claimed in Claim 1, characterised by the fact that the said exhaust/drain opening presents an angle substantially equal to the angular d4gtance between the outer ends of two successive blades 3) - A vacuum pump as claimed in Claim 1 or 2, characterised by the fact thAt the initial portion of the said exhåust/dfain opening is positioned in such a manner as to be affected by the outer end of a blade when the compressed adjacent duty chamber ceases to communicate with the said intake opening 4) - A vacuum pump as claimed in Clam 3, characterised by the fact that the initial portion of the said ethaust/dràin opening is positioned in such a manner ds to be affected by the outer end of a blade sub stantially as soon as tle compressed adjacent duty chamber ceases to communicate with the said intake opening 5) - A vacuum pump as claimed in one of the foregoing Claims; characterised by the fact that the end portion of the said exhaust/drain opening is substantially aligned with the angularly end portion of the said initial portion of the said exhaust/drain duct.

6) - A vacuum pump es claimed in one of the foregoing Claims, characterised by the fact that the said exhaust/ drain opening is formed laterally in relaton to the duty cavity on the said supporting body 7J - A vacuum pump as claimed in Claim 6, characterised by the fact that the said exhaust/drain opening is formed in a hollow cylindrical body positioned coaxially in the said duty cavity 8) - A vacuum pump as claimed in one of the foregoing Claims, characterised by the fact that the said exhaust/ drain opening presents a channel-shaped profile.

9) - A vacuum pump as claimed in one of the foregoing Cltim8 eharacterised by the fact that the said exhaust/ drain opening presents n relatively small-section first portion 10) - A rotary blade vacuum pump as claimed in claim 1 and as herein described with reference to the accompanying illustrative drawings.