A turbocharger is disclosed. The turbocharger includes a seal plate facing a front portion outer periphery of an oil thrower arranged between a bearing portion and an impeller in front thereof, integral with a bearing housing. An oil-thrower facing part formed in the bearing housing faces a rear portion outer periphery of the oil thrower to provide an oil sump. The seal plate is in the form of press-fit plate, a diameter of the press-fit plate being smaller than an outer diameter of the impeller and being at least equal to a minimum working bore diameter for machining of an outer periphery or oil discharge openings of the oil-thrower facing part.

TECHNICAL FIELD

The present invention relates to a turbocharger which prevents lubricant from a bearing portion from leaking to an impeller.

BACKGROUND ART

Generally, as shown inFIGS. 1 and 2, a turbocharger has a bearing housing3integrally arranged between turbine and compressor housings1and2, a turbine shaft5being rotatably supported by the bearing housing3via a bearing portion4. The turbine shaft5is provided on its one (front) side with an impeller6surrounded by the compressor housing2and on its other (rear) side with a turbine rotor7surrounded by the turbine housing1.

The bearing portion4in the bearing housing3is composed of a thrust bearing comprising floating bushes4aarranged as rotary bearings on the turbine shaft5and spaced apart from each other axially of the shaft5, an inner plate4bwhich restrict axial movement of the floating bush4a,an outer thrust bracket4cfixed in the bearing housing3via a bolt8and a thrust collar4darranged between the inner plate4band the outer thrust bracket4cand abutting on a stepped portion5aof the turbine shaft5.

The bearing housing3is formed with a supply opening9directed toward the turbine shaft5and a first branch flow passage10branched from the opening9to the floating bush4a,lubricant fed to the opening9being supplied via the flow passage10to between the bush4aand the housing3and to between the bush4aand the shaft5, thereby forming oil films for support of rotation of the shaft5. In this regard, for formation of the oil film between the bush4aand shaft5, the floating bush4ais formed with an oil passage11diametrically passing through the bush4a.

The bearing housing3is further formed with a separate second branch flow passage12branched from the opening9, lubricant fed to the opening9being supplied via the flow passage12and an oil passage13in the outer thrust bracket4cto between the bracket4cand thrust collar4dfor formation of oil film to receive thrust load.

Arranged at an outer periphery of the turbine shaft5and between the thrust collar4dof the bearing portion4and the impeller6is a tubular oil thrower14which has a front portion14aformed at its outer periphery with an annular groove14breceiving a piston-ring-like seal ring15. The oil thrower14has a rear portion14cfitted in an inner periphery of the outer thrust bracket4cwith a slight gap16.

Arranged to face the outer periphery of the front portion14aof the oil thrower14is a seal plate18fixed via a bolt17to the bearing housing3, the piston-ring-like seal ring15in the groove14bof the oil thrower14abutting on an inner periphery of the seal plate18by its expansive spring force. The seal plate18is positioned at a back of the impeller6, is sized to be greater than an outer diameter of the impeller6and provides a part of a flow passage20on a diffuser19for flow straightening of compressed air from the compressor.

When such turbocharger is driven, the turbine rotor7is rotated for example by exhaust gas from the engine, the impeller6being driven by the rotated turbine shaft5to suck and compress air via a suction port21. The compressed air is flow-straightened by the flow passage20of the diffuser19and is supercharged into the downstream engine for enhanced output performance of the engine (see, for example, Reference 1).

In this case, when lubricant is supplied via the supply opening9to the bearing portion4, oil films are formed between the floating bush4aand bearing housing3and between the floating bush4aand turbine shaft5; the lubricant having formed the oil films is flowed out via a gap between the inner plate4band turbine shaft5and via a gap between the inner plate4band thrust collar4d. Lubricant is also supplied to between the outer thrust bracket4cand thrust collar4dfor formation of oil film; the lubricant having formed the oil film is flowed out via the gap16between the rear portion14cof the oil thrower14and the outer thrust bracket4c.

SUMMARY OF THE INVENTION

Problems to be Solved by the Invention

However, in the conventional turbocharger with the bearing housing3assembled with the separate seal plate18, the flow passage20of the diffuser19is formed with irregularities22and23due to a head17aof the bolt17and due to a boundary of the seal plate18, respectively, which may cause turbulence of the air to lower the supercharging efficiency. Moreover, when the seal plate18is assembled, the flow passage20of the diffuser19to which air is supercharged from the impeller6may be flawed for example by assembling tools; the flaws formed may similarly cause turbulence of the air to lower the supercharging efficiency. Furthermore, thread machining and the like of the bearing housing3may increase machining cost and increased number of parts such as bolt17used for assembling of the seal plate18may increase production cost.

It is preferred that the lubricant discharged via the gap16between the rear portion14cof the oil thrower14and outer thrust bracket4cis discharged outside via a space24between the bracket4cand the seal plate18. However, because of the turbine shaft5and oil thrower14being rotated at high velocity, the lubricant may be accumulated as mist around the bracket4c,running down to the seal ring15and disadvantageously leaking via the ring15to the impeller6.

The invention was made in view of the above and has its object to provide a turbocharger which has enhanced supercharging efficiency and reduced product cost and prevents oil from a bearing portion from leaking to an impeller.

Means or Measures for Solving the Problems

The invention is directed to a turbocharger with an oil thrower arranged between a bearing portion for support of a turbine shaft in a bearing housing and an impeller in front thereof, a seal plate facing a front portion outer periphery of the oil thrower for prevention of oil from leaking from the bearing portion to the impeller and being integral with the bearing housing to be positioned at a back of the impeller, an oil-thrower facing part formed in the bearing housing to face a rear portion outer periphery of said oil thrower to provide an oil sump, said turbocharger comprising said seal plate in the form of press-fit plate, a diameter of said press-fit plate being smaller than an outer diameter of said impeller and being at least equal to a minimum working bore diameter for machining of the outer periphery of said oil-thrower facing part or machining of oil discharge openings provided in said oil-thrower facing part.

In the invention, it is preferable that the oil sump is defined by first and second projections peripherally extending from the rear portion at an end and axially intermediate portion of the oil thrower, respectively, and first and second facing portions on said oil-thrower facing part which face the first and second projections, respectively.

Thus, according to a turbocharger of the invention, the seal plate is in the form of press-fit plate for unification with the bearing housing, so that fixture by bolt is not required to provide no irregulars due to bolt head and the diameter of the press-fit plate is made smaller than that of the impeller so that the irregulars due to for example the boundary of the press-fit plate can be positioned at a back of the impeller different from the flow passage of the diffuser, thus preventing turbulence of the air due to the irregularities and preventing the supercharging efficiency from being lowered. Even if there are any flaws caused upon press-fitting of the press-fit plate due to for example tools, such flows can be positioned at the back of the impeller different from the flow passage of the diffuser, so that the air is prevented from being turbulent due to irregularities of the flaws, thereby preventing the supercharging efficiency from being lowered. Moreover, because of the seal plate being formed by the press-fit plate, for example thread machining for fixing to the bearing housing becomes unnecessary to suppress the machining fee, and assembling by bolt becomes unnecessary to reduce in number the parts, consequently reducing the production cost.

Since the oil sump is constituted by the oil thrower and oil-thrower facing part and the lubricant from the bearing portion is flowed into the oil sump where it is discharged outside through the oil discharge opening, thereby minimizing the amount of the lubricant leaking from between the oil thrower and oil-thrower facing part to the impeller. Moreover, the diameter of the opening on the seal plate into which the press-fit plate is pressed is that enabling machining of the outer periphery of the oil-thrower facing part, so that the outer periphery of the oil-thrower facing part can be properly shaped to prevent the lubricant from being directed toward the seal plate and thus leaking to the impeller by making the lubricant leaking from between the oil thrower and the oil-thrower facing part to flow along the outer periphery of the oil-thrower facing part. Moreover, the bore diameter of the opening on the seal plate into which the press-fit plate is pressed is that enabling machining of the outer periphery of the oil-thrower facing part, so that the lubricant flowed from the bearing portion into the oil sump can be directly discharged through the oil discharge opening, thus preventing the lubricant from being directed to the seal plate and preventing the lubricant from leaking to the impeller.

In the invention, the oil sump may be easily formed by defining the same by the first and second projections peripherally extending from the rear portion at the end and axially intermediate portion of the oil thrower, respectively, and first and second facing portions on said oil-thrower facing part facing the first and second projections, respectively.

Effects of the Invention

A turbocharger of the invention can exhibit excellent effects and advantages. Provision of the seal plate in the form of press-fit plate can improve the supercharging efficiency and reduce the production cost. By the structure of the oil sump arranged between the oil thrower and oil-thrower facing part, the oil sump can receive the lubricant flowed out from the bearing portion to instantly discharge the same through the oil discharge openings, thus preventing the lubricant from leaking to the impeller.

EXPLANATION OF THE REFERENCE NUMERALS

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the invention will be described in conjunction with the attached drawings.

FIGS. 3-10show the embodiment of the invention in which parts similar to those inFIGS. 1 and 2are represented by the same reference numerals. The turbocharger according to the embodiment of the invention is constructed as mentioned below so as to overcome the problems in discharge of lubricant from the conventional bearing portion4.

A bearing portion31as shown inFIGS. 3 and 4which supports a turbine shaft5within a bearing housing3comprises a floating bush32which has unitary construction and supports the turbine shaft5at two portions. The floating bush32is supplied with lubricant from a supply opening33formed in the bearing housing3via a flow passage34extending from the opening33so that oil films are formed between the bush32and the housing3and between the bush32and the shaft5for support of rotation of the shaft5. In this regard, for formation of the oil film between the bush32and the shaft5, the floating bush32is formed with an oil passage35diametrically passing through the bush32.

The floating bush32of the bearing portion31is provided on its one (front) side with an oil thrower36which is positioned at an outer periphery of the turbine shaft5and between the bush32and an impeller6in front thereof and functions also as a thrust bearing for the shaft5. The oil thrower36has a front portion36aformed at its outer periphery with an annular groove36bwhich in turn receives a piston-ring-like seal ring37. The oil thrower36has a rear portion36cwith an outer periphery which faces a cylindrical oil-thrower facing part39formed on an inner periphery38of the bearing housing3for support of the bearing portion31and extends forward axially of the turbine shaft5.

Defined between the rear portion36cof the oil thrower36and the oil-thrower facing part39is an oil sump40. More specifically, the oil sump40is defined by first and second projections36dand36eperipherally extending from the rear portion36cat an end and an axially intermediate portion of the oil thrower36a,respectively, and first and second facing portions39aand39bon the oil-thrower facing part39facing the first and second projections36dand36e,respectively. The oil sump40comprises grooves40aand40bbetween the first and second projections36dand36eand between the first and second facing portions39aand39b,respectively. The oil sump40has a plurality of oil discharge openings41extending from the groove40band passing through the oil-thrower facing part39to outside, the openings41extending from the groove40bto outside being slant in directions away from the impeller6.

A forward end outer periphery42of the oil-thrower facing part39is two-step machined with a working tool43shown inFIG. 7to have the forward end with an ensured thickness and set back outward and rearward so that the lubricant may be flowed outward along the outer periphery42of the facing part39and away from the impeller6.

Just like the conventional bearing portion4, lubrication of the floating bush32in the bearing portion31causes the lubricant to be flowed out through between the bush32and the housing3and between the bush32and the shaft5. The outflow lubricant is flowed between the first projection36dof the oil thrower36and the first portion39aof the facing part39into the oil sump40where the lubricant is temporarily reserved and is discharged via the discharge openings41in directions away from the impeller6. As a result, with the turbine shaft5and the oil thrower36rotated at high velocity, lubricant may barely leak between the second projection36eof the oil thrower36and the second portion39bof the facing part39, and the barely leaking lubricant is flowed along the outer periphery42of the facing part39in directions away from the impeller6. Thus, the lubricant is totally prevented from being directed toward the impeller6.

The turbocharger of the invention is further constructed as mentioned below so as to overcome the problem in the conventional seal plate18separating from the bearing housing3.

Arranged to face the outer periphery of the front portion36aof the oil thrower36is a seal plate44positioned at a back of the impeller6and integral with the bearing housing3. The seal plate44comprises a fixed seal plate45integral with the bearing housing3and extending to a required potion at the back of the impeller6and a press-fit plate47snuggly pressed in an inner opening46of the fixed seal plate45. On an inner periphery of the press-fit plate47, a seal ring37in the groove36bof the oil thrower36abuts with its expansive spring force.

An outer diameter of the press-fit plate47is smaller than that of the impeller6and is at least equal to a minimum working bore diameter necessary for machining of the outer periphery42of the oil-thrower facing part39or machining of the oil discharge openings41by the tool43through the opening46of the fixed seal plate45. The press-fit plate47inFIGS. 3 and 4has the outer diameter equal to or slightly greater than that of the outer periphery of the oil-thrower facing part39. The opening46with greater diameter would contribute to easy machining of the outer periphery42of the facing part39and oil discharge openings41by the tool43; however, this would bring about increase in diameter of the press-fit plate47and would require greater force for press-fitting. Thus, it is preferable that the bore diameters of the opening46and the press-fit plate47are of smaller diameters.

When the press-fit plate47is to be pressed into the opening46of the fixed seal plate45, firstly, as shown inFIG. 8, the oil thrower36is arranged in the inner periphery of the press-fit plate47through the seal ring37. Then, as shown inFIG. 9, the bearing housing3is arranged on a seat48so as to direct the compressor upward. The press-fit plate47with the oil thrower36arranged is temporarily arranged for alignment with the opening46of the fixed seal plate45. Using the press-fit jig49shown inFIG. 10, press-fitting is conducted by a press (not shown). This causes the first and second projections36dand36eof the oil thrower36to be aligned with the first and second facing portions39aand39bin the bearing housing3, respectively, the arrangement being such that no steps are produced with respect to (or at the boundary to) the fixed seal plate45of the bearing housing3. Reference numeral50inFIG. 10denotes a pressing collar projecting peripherally for applying pressing force to the press-fit jig49for press-fitting of the seal plate44.

After the press-fit plate47and the oil thrower36are arranged in the bearing housing36, the turbine shaft5, impeller6, turbine rotor7, turbine housing1, compressor housing2and the like are assembled together into a total structure. Upon driving, the turbine rotor7is driven for example by the exhaust gas of the engine to drive the impeller6connected to the turbine shaft5, the impeller6sucking the air via the suction port21for compression, the compressed air being straightened in flow in the flow passage20of the diffuser19and is supercharged into the downstream engine.

Thus, according to the turbocharger of the embodiment of the invention, the press-fit plate47is pressed into the fixed seal plate45for unification with the bearing housing3, so that no fixture by bolt is required to provide no irregulars due to bolt head; and the diameter of the press-fit plate47is made smaller than the outer diameter of the impeller6so that the irregulars due to for example the boundary of the press-fit plate47can be positioned at the back of the impeller6differently from the flow passage20of the diffuser19, thus preventing turbulence of the air due to the irregularities and preventing the supercharging efficiency from being lowered. Even if there are any flaws caused upon press-fitting of the press-fit plate47due to tools such as press-fit jig49, such flaws can be positioned at the back of the impeller6differently from the flow passage20of the diffuser19, so that the air is prevented from being turbulent due to the irregularities of the flaws, thereby preventing the supercharging efficiency from being lowered. Moreover, because of the seal plate44being formed by the press-fit plate47, thread machining for fixing to the bearing housing3becomes unnecessary to suppress the machining fee, and assembling by bolt becomes unnecessary to reduce in number the parts, consequently reducing the production cost.

Since the oil sump40is constituted by the oil thrower36and oil-thrower facing part39and the lubricant from the bearing portion31is flowed into the oil sump40where it is instantly discharged outside through the oil discharge openings41. Thus, even if the turbine shaft5and oil thrower36are rotated at higher velocity, the lubricant may barely leak from between the oil thrower36and the oil-thrower facing part39into the seal plate44, the lubricant from the bearing portion31being prevented from leaking to the impeller6via the seal ring37. Moreover, the bore diameter of the opening46of the fixed seal plate45corresponding to the diameter of the press-fit plate47is that enabling machining of the outer periphery42of the oil-thrower facing part39, so that the outer periphery42of the oil-thrower facing part39can be properly shaped to prevent the lubricant from being directed toward the seal ring37by making the lubricant leaking from between the oil thrower36and the oil-thrower facing part39to flow along the outer periphery42of the oil-thrower facing part39. Moreover, the bore diameter of the opening46on the fixed seal plate45corresponding to the diameter of the press-fit plate47is that enabling machining of the oil discharge openings41in the oil-thrower facing part39, so that the oil discharge openings41are machined for the oil sump40formed between the oil thrower36and the oil-thrower facing part39for instant discharge of the lubricant flowed into the oil sump40to outside, thereby preventing the lubricant from being directed toward the seal plate44and thus preventing the lubricant from leaking via the seal ring37to the impeller6.

In the embodiment of the invention, the oil sump40is defined by first and second projections36dand36eperipherally extending from the rear portion36cand axially intermediate portion of the oil thrower36, respectively, and first and second facing portions39aand39bon the oil-thrower facing part39facing the first and second projections36dand36e,respectively. Thus, the oil sump40can be easily formed and the lubricant flowed out from the bearing portion31can be easily flowed into the oil sump40. As a result, even with the turbine shaft5and oil thrower36being rotated at higher velocity, the oil may barely flow out from between the oil thrower36and the oil-thrower facing part39to the seal plate44, thus preventing the lubricant from the bearing portion31from leaking to the impeller6through the seal ring37.

It is to be understood that a turbocharger according to the invention is not limited to the above-mentioned embodiment and that various changes and modifications may be made without departing from the scope of the invention. For example, the shape of the bearing portion is not limited to that shown in the embodiment; the bearing portion may be of a conventional shape or of any other shape.