Engine supercharger drive device

A supercharger drive device (1) for a combustion engine (E) includes a gear carrier shaft (6) operable to rotate in unison with a crankshaft (2) of the combustion engine (E), a high speed gear (8) and a low speed gear (10) provided in the gear carrier shaft (6), a drive shaft (14) of a supercharger (12) which is rotatable when coupled with either one of the high speed gear (8) and the low speed gear (10), a gear shifter (16) for selecting one of the high speed gear (8) and the low speed gear (10) for transmitting a motive force from the gear carrier shaft (6) to the drive shaft (14) through the selected one of the high and low speed gears (8) and (10), and a shifter drive unit (18) for actuating the gear shifter (16) in dependence on the rotational speed of the combustion engine (E).

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a supercharger drive device for variable transmission of a supercharger driven by a combustion engine.

2. Description of Related Art

The supercharger connected with and driven by the combustion engine has such a tendency that if it is adjusted to be suitable for a low-to-medium speed region, the supercharged pressure (the amount of charged air) in a high speed region will increase too much, but if it is adjusted to be suitable for the high speed region the supercharged pressure in the low-to-medium speed region will become insufficient. The patent document listed below discloses the drive device operable to switch the supercharger, which is operatively linked with a transmission connected with the combustion engine, on or off in dependence of a gear shifting of the transmission. The drive device disclosed in the patent document has, however, been found having such a problem that the change gear ratio of the supercharger itself remains constant and is therefore insufficient.

PRIOR ART LITERATURE

SUMMARY OF THE INVENTION

The present invention has been devised to substantially eliminate the foregoing problems and inconveniences inherent in the prior art and is intended to provide a supercharger drive device of a type, in which a change gear ratio of the supercharger can be selected in dependence on the number of revolutions, or rotational speed, of the combustion engine.

In order to accomplish the foregoing object of the present invention, there is provided a supercharger drive device for a combustion engine designed in accordance with the present invention includes a gear carrier shaft operable to rotate in unison with a rotary shaft of the combustion engine, a plurality of speed change gears mounted on the gear carrier shaft, a drive shaft of a supercharger connected directly or indirectly with the speed change gears for rotation, a gear shifter for selecting one of the plural speed change gears to transmit a motive force from the gear carrier shaft to the drive shaft by way of such selected one of the speed change gears, and a shifter drive unit for actuating the gear shifter in dependence on the rotational speed of the combustion engine.

According to the construction, the shifter drive unit selects one of the speed change gears by actuating the gear shifter in dependence on the rotational speed or the number of revolutions of the combustion engine and, therefore, the rotational speed of the supercharger can be adjusted to an optimum value in dependence on the rotational speed of the combustion engine.

In a preferred embodiment of the present invention, each of the speed change gears may be a speed-up gear, in which case the shifter drive unit is preferably operable to actuate the gear shifter to select one of the plural speed change gears such that the speed-up ratio becomes low with an increase of the rotational speed of the rotary shaft. This structure makes it possible to provide the optimum speed-up ratio dependent on the rotational speed of the combustion engine.

In another preferred embodiment of the present invention, the plural speed change gears may include a low speed gear and a high speed gear, both of the low and high speed gears being mounted on the gear carrier shaft for rotation relative to the latter, in which case the gear shifter is interposed between the low speed gear and the high speed gear and mounted on the gear carrier shaft for movement in a direction axially of the gear carrier shaft, but relatively non-rotatable to such gear carrier shaft, whereby upon axial movement of the gear shifter, the latter is selectively engaged with one of the low speed gear and the high speed gear for rotation together therewith.

In a further preferred embodiment of the present invention, the gear carrier shaft may be engaged with a crankshaft gear mounted on the rotary shaft for driving a balancer shaft. According to this structure, the crankshaft gear is concurrently used to drive the supercharger and therefore, an undesirable increase of the number of component parts can be suppressed. Also, the gear carrier shaft, the gear shifter and other components can be arranged with the utilization of the dead space available on one side of the crankshaft remote from the balancer shaft.

In a still further preferred embodiment of the present invention, the gear carrier shaft may be coupled with a starter through a one-way clutch. According to this structure, a change in engine torque incident to gear shifting can be absorbed by a slide friction taking place in the one-way clutch and therefore, it is possible to avoid a transmission thereof to the supercharger.

In a yet still further preferred embodiment of the present invention, the supercharger may include the drive shaft, an impeller shaft connected with the drive shaft through a planetary gear assembly, an impeller fixedly mounted on the impeller shaft, a housing for supporting the impeller shaft, and a casing fitted to the housing for enclosing the impeller, the planetary gear assembly being supported by the housing. According to this structure, the supercharger and the planetary gear assembly can be unitized together as a single unit and, therefore, an undesirable increase of assembling steps can be suppressed while an undesirable increase of the number of component parts is also suppressed. Also, since a relatively large speed-up can be obtained due to the use of the planetary gear assembly, a speed increasing machine can be compactized.

DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, the present invention will be described in detail in connection with preferred embodiments thereof with reference to the accompanying drawings.

FIG. 1is a longitudinal sectional view showing a combustion engine E equipped with a supercharger drive device1designed in accordance with a first preferred embodiment of the present invention. The combustion engine E shown therein includes a crankshaft2which is a rotary shaft, a balancer shaft4disposed so as to extend parallel to the crankshaft2, and a crankshaft gear5formed in an outer periphery of one of paired webs3of the crankshaft2for driving a balancer shaft4. A gear carrier shaft6, which is one kind of an idle shaft, is disposed on one side of the crankshaft2remote from the balancer shaft4, which shaft6is rotatable in unison with the crankshaft2through an engagement of a drive gear7, formed integrally with the gear carrier shaft6, with the crankshaft gear5.

The gear carrier shaft6is provided with a high speed gear8and a low speed gear10, each of which is a kind of a speed change gear. Both of the high speed gear8and the low speed gear10are speed increasing gears and are mounted on the gear carrier shaft6for rotation relative to, but axially immovably relative to such gear carrier shaft6. It is to be noted that although in the illustrated embodiment, the two speed change gears, i.e., the high and low speed gears, are shown and described as employed, three or more speed change gears may be employed.

The combustion engine E is equipped with a supercharger12for compressing and forcibly supplying air to the combustion engine E. This supercharger12includes a drive shaft14drivingly connected with one of the high and low speed gears8and10, which have large and reduced diameters, respectively. More specifically, the supercharger drive shaft14has a low speed drive gear14aof a reduced diameter and a high speed drive gear14bof a large diameter, which are mounted on such drive shaft14for rotation together therewith. Those high speed gear8, low speed gear10, high speed drive gear14aand low speed drive gear14bcooperate with each other to define a speed increasing gear train. In the embodiment now under discussion, the drive shaft14and the gear carrier shaft6are connected directly with each other, but they may be connected indirectly with each other through, for example, an idle gear. While the details of the supercharger12will be described later, the drive shaft14is rotatably supported by an engine casing EC, which forms a part of an engine body, through three bearings15.

A gear shifter16is interposed between the high speed gear8and the low speed gear10. This gear shifter16is made up of a shifting drum17having its opposite side faces formed with first and second dogs17aand17aeach protruding the corresponding side face of the shifting drum17in a direction parallel to the axial direction of the gear carrier shaft6, and a shifting fork19for operating the shifting drum17. This shifting drum17is so splined to the gear carrier shaft6that the shifting drum17can be axially movable along the gear carrier shaft6, but cannot rotate independently of the gear carrier shaft6. The shifting fork19referred to above is driven by a shifter drive unit18in the axial direction of the gear carrier shaft6to move the shifting drum17in such axial direction so that the first and second dogs17aand17arigid or integral with the shifting drum17can be selectively engaged in engagement holes8aand10a, which are defined in the high speed gear8and the low speed gear10, to selectively interlock the shifting drum17with one of the high speed gear8and the low speed gear10one at a time.

Through the selected one of the speed change gears8and10, rotation of the gear carrier shaft6is transmitted to the drive shaft14. In other words, when the shifting drum17and the high speed gear8are dogged together in the manner described above, the rotation of the gear carrier shaft6, that is, the rotation of the crankshaft2is transmitted to the drive shaft14at a large speed-up ratio, but when the shifting drum17and the low speed gear10are dogged together, the rotation of the gear carrier shaft6is transmitted to the drive shaft14at a small speed-up ratio. The shifter drive unit18is of a type including, for example, a servo motor, but may not be necessarily limited thereto. By this shifter drive unit18, the rotational drive of the crankshaft2is transmitted from the gear carrier shaft6to the drive shaft14of the supercharger12through the selected speed change gear8or10. Those gear carrier shaft6, high speed gear8, low speed gear10, drive shaft14of the supercharger12, gear shifter16and shifter drive unit18altogether constitute the supercharger drive device1of the kind referred to previously.

The supercharger12is disposed outside the engine casing EC forming a part of the engine body and, as shown inFIG. 2in a sectional view thereof, one end14cof the drive shaft14of the supercharger12is connected with one end22aof an impeller shaft22through a planetary gear assembly20while an impeller24mounted on the opposite end22bof the impeller shaft22for rotation together therewith. Hereinafter, one end of the supercharger12is referred to as an engine E side and the opposite end thereof is referred to as a counter engine side.

The impeller shaft22is rotatably supported by a tubular housing26. The housing26has one end side fixed to the engine casing EC, forming a part of the combustion engine, through an anchoring casing28by means of housing fastening members60such as, for example, bolts and also has the opposite end side to which a casing30for enclosing the impeller24is fitted with the use of a plurality of casing fastening member62such as, for example, bolts. In this way, a portion of the impeller shaft22, except for that end thereof where the impeller24is mounted, is enclosed by the housing26and that portion thereof, where the impeller24is mounted, and the impeller24itself are enclosed by the casing30. The anchoring casing28has a shaft support portion28asupporting an input shaft29of the planetary gear assembly20through two bearings31, and the drive shaft14referred to previously is relatively non-rotatably connected with the input shaft29.

As hereinabove described, the planetary gear assembly20is interposed between the drive shaft14and the impeller shaft22and is supported by one end portion of the housing26. In the embodiment shown and now under discussion, the supercharger12and the planetary gear assembly20are supported by the housing26to form a supercharger unit, which is in turn fitted to the engine casing EC, forming a part of the engine body, by means of the housing fastening members60.

An internal gear32of a large diameter is meshed with the input shaft29of the planetary gear assembly20, a plurality of planetary gears38are meshed with this internal gear32, and a gear34mounted on one end portion22aof the impeller shaft22as a sun gear is meshed with those planetary gears38. Accordingly, the rotational drive of the drive shaft14is transmitted from the input shaft29of the planetary gear assembly20to the impeller shaft22, which serves as an output shaft, through the internal gear32and the planetary gears38.

The gear shifter16of the structure described above and shown inFIG. 1operates in the following manner. As best shown inFIG. 3, a rotation sensor40for measuring the rotational speed of the combustion engine E and an hand operated switch SW for manually setting an operating mode of the combustion engine E are connected with an engine control unit ECU. The shifter drive unit18is operable to move the gear shifter16in a direction axially of the gear carrier shaft6in dependence on the rotational speed of the combustion engine E. More specifically, the engine control unit ECU determines either a normal (low speed) mode42or a high speed mode44in reference to an increase of the rotational speed of the crankshaft2, which is made available from the rotation sensor40, and then control the shifter drive unit18so that the latter drives the gear shifter16to select one of the speed change gears8and10, which is appropriate to one of the modes42and44which has been determined by the engine control unit ECU.

The low speed mode42referred to above is a mode, under which the speed-up ratio of the supercharger12during a predetermined low speed region of the combustion engine E is increased to increase a supercharge pressure, that is, the amount of supercharged air so that the engine torque at the low speed can be gained. Once the engine control unit ECU determines the low speed mode42, the gear shifter16is dogged with the high speed gear8. On the other hand, the high speed mode44referred to above is a mode, under which the speed-up ratio of the supercharger12during a predetermined high speed region is reduced to prevent the amount of the supercharged air from being excessive so that a proper engine torque and a stabilized rotation can be obtained. Once the engine control unit ECU determines the high speed mode44, the gear shifter16is dogged with the low speed gear10.

The engine control unit ECU controls the amount of fuel to be injected, the ignition timing and other parameters on the basis of a sensor signal, fed from the rotation sensor40and indicative of the rotational speed of the combustion engine E, to thereby control the rotational speed of the combustion engine E. The engine control unit ECU is also operable to increase the rotational speed of the supercharger12during the low speed mode42as hereinabove described, but to suppress the rotational speed of the supercharger12from becoming excessive on the basis of the sensor signal from the rotation sensor40during the high speed mode44.

In addition to the determination of the operating mode in dependence on the rotational speed of the combustion engine E as hereinabove described, the operating mode can be switched even with the hand operated switch SW. Accordingly, the operator can select one of the modes at his or her will. Also, an eco mode46may be employed, during which the drive of the supercharger12is switched off. During the eco mode46, the gear shifter16is held at an intermediate position at which the gear shifter16is engaged neither with the high speed gear8nor with the low speed gear10.

According to the embodiment, the shifter drive unit18shown inFIG. 1actuates the gear shifter16in dependence on the rotational speed of the combustion engine E to select one of the speed change gears8and10and, accordingly, the rotational speed of the supercharger12can be adjusted to an optimum value in dependence on the rotational speed of the engine E. In other words, during the low speed mode42, the gear shifter16is dogged with the high speed gear8to increase the speed-up ratio of the supercharger12so that control can be made to gain the engine torque during the medium-to-low speed region as shown inFIG. 4. As a result, the shaft output of the combustion engine during the medium-to-low speed region also increases.

On the other hand, during the high speed mode44, the gear shifter16is dogged with the low speed gear10by the shifter drive unit18shown inFIG. 3to reduce the speed-up ratio of the supercharger12so that control can be made to prevent the amount of the supercharged air during the high speed region from becoming excessive to thereby secure the proper engine torque and the stabilized revolution as shown inFIG. 4. As a result, the high shaft output of the combustion engine during the high speed region is maintained.

Also, since the crankshaft gear5is concurrently used to drive the supercharger12, an undesirable increase of the number of component parts can be suppressed. In addition, the gear carrier shaft6, the gear shifter16and other components can be arranged with the utilization of the dead space available on one side of the crankshaft2remote from the balancer shaft4.

Yet, since the supercharger12and the planetary gear assembly20are unitized together to provide the supercharger unit, not only can the number of assembling steps be reduced while the undesirable increase of the number of component parts is avoided, but also a large speed-up can be obtained by the use of the planetary gear assembly20and, therefore, the supercharger drive device1can be downsized advantageously.

In a second preferred embodiment of the present invention, which will now be described with particular reference toFIG. 5showing a longitudinal sectional view, the supercharger drive device now identified by1A according to this second embodiment includes a gear carrier shaft6A having the high speed gear8and the low speed gear10mounted thereon for rotation together therewith, and an electrically drive starter50is operatively coupled with the gear carrier shaft6A through a one-way clutch48and a starter drum49. The starter drum49is specifically mounted on an outer periphery of the gear carrier shaft6A for rotation relative to such gear carrier shaft6a, and has a starter gear49amounted on one end thereof for engagement with the electrically operated starter50. The one-way clutch48referred to above is interposed between a cylindrical portion49bof the other end of the starter drum49, remote from the starter gear49a, and a drive gear7A that is formed integrally with the gear carrier shaft6A.

According to the second preferred embodiment, only when the starter drum49that is driven by the electrically operated starter50attains a speed higher than that of the drive gear7A, the one-way clutch48is brought into a coupled position to enable the transmission of the rotational force from the starter drum49to the drive gear7A. Conversely, when the drive gear7A attains a speed higher than that of the starter drum49subsequent to the start of the combustion engine, the one-way clutch48is brought into a decoupled position to interrupt the transmission of the rotational force from the drive gear7A to the starter drum49.

Although the present invention has been fully described in connection with the preferred embodiments thereof with reference to the accompanying drawings which are used only for the purpose of illustration, those skilled in the art will readily conceive numerous changes and modifications within the framework of obviousness upon the reading of the specification herein presented of the present invention. By way of example, the use may be made of a rubber damper on the drive gear7or7A of the gear carrier shaft6to reduce an undesirable transmission of a change in engine torque to the planetary gear assembly20.

Also, in place of the planetary gear assembly20, the use may be made of a variable transmission for driving the supercharger12therethrough so that the speed-up ration can be changed in such a way as to increase the speed-up ratio at a low speed rotation but to reduce the speed-up ratio at a high speed rotation. Accordingly, a relatively high engine torque can be obtained from the low speed rotation and an undesirable occurrence of an excessive engine torque at the high speed rotation can be suppressed advantageously.

Accordingly, such changes and modifications are, unless they depart from the scope of the present invention as delivered from the claims annexed hereto, to be construed as included therein.

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