Power unit for a vehicle

A power unit for a vehicle including an engine configured to drive the vehicle, a transaxle coupled to a drive wheel, a power transmission system which is coupled to the engine and to the transaxle and is configured to transmit a rotational force output from the engine to the transaxle, and a base plate fastened to the engine and to the transaxle so as to cover a lower surface of the engine and a lower surface of the transaxle.

TECHNICAL FIELD

The present invention relates to a power unit mounted in a vehicle such as a golf cart that travels at a low speed.

BACKGROUND ART

Conventionally, in lightweight and small vehicles such as a golf cart, an inexpensive, lightweight and small power unit is desirably mounted. One example of such a power unit includes an engine and a transaxle in which a reduction gear, a differential gear, and an axle are integral with each other, both the engine and transaxle being unitarily mounted to a frame member. For example, in a golf cart disclosed in U.S. Pat. No. 4,821,827, a transaxle with an axle oriented rightward and leftward and an engine disposed forward of the transaxle are mounted to a vehicle body in such a manner that they are supported by a frame of pipe-shaped and other frame members. In a vehicle disclosed in U.S. Pat. No. 5,915,495, an engine is held from below by a plate-shaped support member bent in an L-shape in a side view, and a transaxle disposed behind the engine is fastened to a rear panel section of the support member by bolts.

In the golf cart disclosed in U.S. Pat. No. 4,821,827, since it is difficult to handle one pipe frame in a bent state, it becomes necessary to weld a plurality of pipe frames to each other, causing poor productivity and increasing the number of components. Furthermore, a number of gaps formed in the pipe frames make it difficult to protect the engine and the transaxle.

In the vehicle disclosed in U.S. Pat. No. 5,915,495, the plate-shaped support member is located only below the engine, and thus the transaxle is exposed from below. Therefore, obstacles and others from below are likely to contact a lower surface of the transaxle during traveling of the vehicle, degrading durability of the transaxle.

SUMMARY OF THE INVENTION

The present invention addresses the above described condition, and an object of the present invention is to provide a lightweight and compact power unit for a vehicle which includes an engine and a transaxle unitarily mounted and has high durability and productivity.

According to the present invention, there is provided a power unit for a vehicle comprising an engine configured to drive the vehicle; a transaxle coupled to a drive wheel; a power transmission system which is coupled to the engine and to the transaxle and is configured to transmit a rotational force output from the engine to the transaxle; and a base plate fastened to the engine and to the transaxle so as to cover a lower surface of the engine and a lower surface of the transaxle.

In such a construction, since the engine and the transaxle are unitarily fastened by using the plate-shaped base plate, rather than a pipe frame, productivity of the power unit is improved. Furthermore, since the plate-shaped base plate covers the lower surface of the transaxle as well as the lower surface of the engine, obstacles and others from below will not contact the lower surface of the transaxle during traveling of the vehicle. As a result, durability of the power unit is improved.

The base plate may include a planar bottom wall portion configured to cover the lower surface of the engine and the lower surface of the transaxle, and a pair of side wall portions respectively protruding upward from both end portions of the bottom wall portion.

In such a construction, since the base plate formed by the bottom wall portion and the side wall portions has a concave cross-section, stiffness of the base plate is improved in contrast to a base plate formed only by the flat plate.

The power unit for a vehicle may further comprise a side plate laterally fastened to the engine, to the transaxle, and to the base plate; wherein an output shaft of the engine and an input shaft of the transaxle protrude laterally in the same direction; and wherein the side plate may have a first insertion portion into which the output shaft is inserted to position the engine and a second insertion portion into which the input shaft is inserted to position the transaxle.

In such a construction, since the engine, the transaxle, and the base plate are coupled to each other by the side plate, stiffness of the entire power unit can be improved. Furthermore, since the output shaft of the engine and the input shaft of the transaxle are positioned by the side plate, the power transmission system can be easily and surely mounted to the output shaft and the input shaft.

The side plate may be a flat plate, and may be fastened to a side surface of the engine, to a side surface of the transaxle, and to a side surface of the base plate by bolts.

Since the side plate is a flat plate and can be easily manufactured by punching or the like, a manufacturing cost can be reduced. In addition, stiffness of the power unit can be increased in a direction of a plane of the side plate (direction parallel to a surface of the side plate). In addition, since the side plate couples the engine, the transaxle, and the base plate, stiffness of the power unit can be further increased.

The power unit for a vehicle may further comprise a generator configured to be driven by the engine to generate electric power; wherein a transmission belt is installed around a pulley of the output shaft of the engine and a pulley of an input shaft of the generator. The generator may be fastened to a generator bracket configured to couple the engine to the transaxle and to the side plate.

In such a configuration, since the engine and the transaxle are coupled to each other via the generator bracket and the generator fastened to the generator bracket is fastened to the side plate, stiffness of the entire power unit can be increased.

The generator may be rotatably mounted on a common axis to the generator bracket and to the side plate; and the power unit may further comprise a tensioner configured to apply a force to cause the generator to be rotated around the common axis in a direction to apply a tension to the transmission belt.

The tensioner may include a side bracket coupled to the side plate and to the engine, and an extensible rod protrusible from the side bracket. The extensible rod may be coupled to the generator and is extensible and retractable to cause the generator to be rotated.

In such a construction, merely by adjusting a protruding amount of the extendible rod protruding from the side bracket, the generator is rotated, so that a distance between the output shaft of the engine and the input shaft of the generator is changed. This makes it easy to adjust the tension to be applied to the transmission belt.

The power unit may further comprise a joint bracket fastened to the base plate to couple the power unit to the vehicle body frame. The joint bracket may be provided to couple the pair of right and left side wall portions to each other.

In such a construction, since the right and left side wall portions are coupled to each other by the joint bracket, stiffness of the base plate can be increased. In addition, since the joint bracket is separate from the base plate and position or the like of mounting portions of the vehicle body frame can be addressed by changing only the joint bracket, flexibility of design change or the like is improved.

The power unit may further comprise a muffler coupled to the engine through an exhaust pipe; wherein the muffler may be coupled to the base plate and/or to the transaxle by a muffler bracket, and the muffler bracket may be bent so as to have elasticity.

In such a construction, even if the exhaust pipe is thermally deformed by heat of the exhaust gas, the resulting load is absorbed by the muffler bracket coupling the muffler to the base plate and/or the transaxle, because of its elasticity. This makes it possible to avoid an event that the exhaust pipe is subjected to undesired stress.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Thereinafter, an embodiment of the present invention will be described with reference to the drawings.FIG. 1is a perspective view of a power unit1for a vehicle according to an embodiment of the present invention.FIG. 2is a plan view of the power unit1ofFIG. 1.FIG. 3is a right side view of the power unit1ofFIG. 1.FIG. 4is a left side view of the power unit1ofFIG. 1. As shown inFIGS. 1 to 4, the power unit1is mounted in a low-speed vehicle such as a golf cart (not shown) and includes an engine2configured to drive the vehicle, a transaxle3coupled to a drive wheel (not shown), and a continuously variable transmission (CVT)4which is coupled to the engine2and to the transaxle3and serves as a power transmission system configured to transmit a rotational force output from the engine2to the transaxle3.

The engine2includes a crankcase6from which an output shaft (crankshaft)10protrudes rightward in the lateral direction, a cylinder block7protruding obliquely forward from the crankcase6, a cylinder head8located on an upper portion of the cylinder block7, and a cylinder head cover9located over the cylinder head8to cover the cylinder head8from above.

The transaxle3includes a gear box11from which an input shaft14protrudes rightward, i.e., in the same direction as the output shaft10of the engine2protrudes, an axle pipe12protruding rightward and leftward from the gear box11, an axle12′ inserted into the axle pipe12, and brake units13which are mounted to right and left ends of the axle12′ and are coupled to drive wheels (not shown) of the vehicle. The transaxle3is disposed behind the engine2. The gear box11contains a reduction gear (not shown) coupled to the input shaft14and a differential gear (not shown) through which a rotational force of the reduction gear is transmitted to the axle12′.

The CVT4includes a drive pulley17mounted on the output shaft10of the engine2, a driven pulley18mounted on the input shaft14of the transaxle3, and a transmission belt19installed around the drive pulley17and the driven pulley18, and is configured to change the speed of the rotational force from the engine2and to transmit the resulting rotational force to the transaxle3.

A metal base plate5is fastened to the gear box11of the transaxle3and to the engine2by bolts B1and B2so as to cover a lower surface of the gear box11and a lower surface of the engine2.

FIG. 5is a perspective view of the base plate5of the power unit1ofFIG. 1. As shown inFIG. 5, the base plate5includes a flat bottom wall portion5acovering the lower surface of the engine2and the lower surface of the gear box11of the transaxle3, a first left side wall portion5b1protruding upward from a front portion of a left end of the bottom wall portion5a, a second left side wall portion5b2protruding upward from a rear portion of the left end of the bottom wall portion5a, and a right side wall portion5cprotruding upward over an entire length of a right end of the bottom wall portion5a. Bolt holes5fto fasten the engine2and openings5jand5kare formed on the bottom wall portion5a. A pair of elongate bolt holes5hare formed at a front region of the right side wall portion5cto fasten a metal flat side plate32(FIG. 3) thereto as described later. Bolt holes5gare formed at a rear region of the right side wall portion5cand the second side wall portion5b2to fasten the transaxle3. An elongate bolt hole5iis formed on the second left side wall portion5b2to fasten a first muffler bracket44(FIG. 9) as described later. Mounting portions5dand5eare formed at a front end portion of the first left side wall portion5b1and a front end portion of the right side wall portion5c, respectively in such a manner that they are bent close to each other. Bolt holes5mand5nare respectively formed on the mounting portions5dand5eto fasten a metal joint bracket34(FIG. 1) by which the power unit1is coupled to a vehicle body frame (not shown). The bolt hole5mis an elongate hole to allow for dimensional tolerance.

As shown inFIGS. 1 to 5, the metal joint bracket34is fastened to the mounting portions5dand5eof the base plate5by bolts B14and is coupled to a vehicle body frame (not shown). The joint bracket34includes a vertical plate portion34afastened by the bolts B14to the mounting portion5eof the right side wall portion5cand to the mounting portion5dof the first left side wall portion5b1to couple them to each other and a coupling plate portion34bprotruding horizontally forward from a center region of an upper end of the vertical plate portion34aand being inserted into a coupling hole (not shown) formed on the vehicle body frame to restrict movement of the front portion of the power unit1.

A generator21, which also serves as a starter motor, is mounted above a region between the engine2and the transaxle3. The generator21is provided with a second driven pulley23mounted on an input shaft22thereof protruding rightward. A second drive pulley20for the generator21is mounted on the output shaft10of the engine2and is located inward of the drive pulley17of the CVT4. A transmission belt24is installed around the second drive pulley20and the second driven pulley23to transmit a part of the rotational force from the engine2to the generator21.

An upstream end of a first exhaust pipe28in a flow direction of exhaust gas is coupled to the cylinder head8of the engine2. A downstream end of the first exhaust pipe28is coupled to an upper surface of a muffler29disposed in front of the left axle pipe12and on the left side of a rear portion of the base plate5. The muffler29is disposed such that its axis is oriented vertically. An upstream end of a second exhaust pipe30is coupled to the upper surface of the muffler29, and a downstream end thereof extends to a region in close proximity to a lower portion of the muffler29. An air cooling fan36(FIG. 4) is mounted on the left side of the engine2.

FIG. 6is a perspective view of the power unit1ofFIG. 1, from which the CVT4and the generator21are removed. As shown inFIG. 6, the metal flat side plate32manufactured by punching is fastened to the engine2, to the transaxle3, and to the base plate5. The side plate32is fastened to a front portion of the right side wall portion5cof the base plate5by bolts B3. The side plate32extends upward and rearward, toward the transaxle3, from a location where the side plate32is fastened to the right side wall portion5cof the base plate5. The side plate32has a through hole (first insertion portion)32ainto which the output shaft10of the engine2is loosely inserted and to which an outer periphery of a boss protruding from a right side wall of the crankcase6(FIG. 1) of the engine2to extend concentrically with the output shaft10is fitted for enabling positioning between the engine2and the side plate32, and a cut portion (second insertion portion)32binto which the input shaft14of the transaxle3is loosely inserted and to which an outer periphery of a boss protruding from a right side wall of the gear box11(FIG. 1) of the transaxle3to extend concentrically with the input shaft14is fitted for enabling positioning between the transaxle3and the side plate32.

The side plate32is fastened to a right side wall of the engine2by bolts B4at four locations in close proximity to and outside the through hole32aand to a right side wall of the transaxle3by a stud B5and a nut at two locations in close proximity to and outside the cut portion32b. Since the side plate32fastened to the engine2and the transaxle3is fastened to the base plate5by bolts B3, improving stiffness of the power unit1. In this embodiment, bolt mounting portions of the engine2, the transaxle3and the base plate5to which the side plate32is fastened by bolts are on the same plane.

A metal generator bracket38is mounted on an upper region at the left side between the engine2and the transaxle3and is configured to couple an upper portion of the engine2to an upper portion of the transaxle3. The generator bracket38is fastened to the engine2by bolts B6and to the gear box11of the transaxle3by bolts B7. As shown inFIG. 1, the generator21is rotatably mounted to the generator bracket38(FIG. 6) by a bolt B8and is rotatably mounted to the side plate32of the vehicle by the bolt B9. The bolt B8and the bolt B9are aligned on a common axis in the lateral direction. The generator21is mounted to the generator bracket38and the side plate32to be rotatable around the common axis of the bolts B8and B9aligned coaxially.

Turning toFIG. 6again, a metal side bracket40is mounted on an upper region at the right side between the engine2and the transaxle3and is configured to couple the side plate32to the engine2. The side bracket40is fastened at one end portion thereof by a bolt B10to an upper region of a center part in the longitudinal direction of the side plate32and at an opposite end portion thereof to the engine2by a bolt B11. A L-shaped extensible rod41is protrusibly attached to the side bracket40by a double nut42. As described later, the extensible rod41is coupled at an upper end portion thereof to the generator21(FIG. 7). The side bracket40, the extensible rod41, and the double nut42constitute a tensioner39. By extending the extensible rod41, the generator21is rotated, thereby applying tension to the transmission belt24.

FIG. 7is a right side view of the power unit1for the vehicle ofFIG. 1, showing the generator21and the tensioner39.FIG. 8is a front view thereof. As shown inFIGS. 7 and 8, the generator21has, on right and left side surfaces thereof, support flanges25protruding downward. As described above, the left support flange25is rotatably fastened to the generator bracket38(FIG. 6) by the bolt B8. The right support flange25is rotatably fastened to the side plate32(FIG. 6) by the bolt B9. A protruding portion26is formed to protrude forward from a right side surface of the generator21. The extensible rod41of the tensioner39is coupled to the protruding portion26.

To be specific, the tensioner39includes the side bracket40, the extensible rod41, and the double nut42. The side bracket40includes a vertical plate portion40ahaving a bolt hole40dto fasten the side bracket40to the side plate32(FIG. 6), a horizontal plate portion40bprotruding inward in the lateral direction from an upper end of the vertical plate portion40aand having an elongate hole40e,and a vertical plate portion40cprotruding forward and upward from an inner end portion of the horizontal plate portion40band having an elongate bolt hole40fto fasten the side bracket40to the engine2. The extensible rod41includes a vertical rod portion41aand a horizontal rod portion41bprotruding outward in the lateral direction from an upper end of the vertical rod portion41a. A male threaded portion41cis formed on an outer peripheral surface of a lower end side of the vertical rod portion41a. With the vertical rod portion41aof the extensible rod41inserted into the elongate hole40eof the horizontal plate portion40bof the side bracket40, the double nut42is threadedly engaged with the male threaded portion41c. The horizontal rod portion41bof the extensible rod41is fastened at an upper end thereof to the protruding portion26of the generator21. By rotating the double nut42, the protruding amount of the extensible rod41protruding upward from the side bracket40is adjusted. Thereby, the generator21is rotated around the bolts B8and B9, applying tension to the transmission belt24(FIG. 1).

FIG. 9is a perspective view showing in large part the muffler29and the base plate5of the power unit1ofFIG. 1.FIG. 10is a perspective view showing in large part the muffler29of the power unit1ofFIG. 1. As shown inFIGS. 9 and 10, the muffler29is cylindrical, and is disposed on the left side of a rear portion of the base plate5in such a manner that its longitudinal direction conforms to a vertical direction, i.e., its center axis is oriented vertically. The downstream end of the first exhaust pipe28and the upstream end of the second exhaust pipe30are respectively coupled to the upper surface of the muffler29. The downstream end of the second exhaust pipe30, at which an exhaust gas outlet is formed, extends to the region in close proximity to the lower portion of the muffler29. The muffler29is fastened to the second left side wall portion5b2of the base plate5via the first metal muffler bracket (lower muffler bracket)44by threading a bolt B12into the bolt hole5iformed on the second left side wall portion5b2. The muffler29is fastened to the gear box11of the transaxle3via a second metal muffler bracket (upper muffler bracket)45by bolts B13.

The first muffler bracket44has an extra length to be bent in substantially a U-shape between the muffler29and the base plate5as viewed from above so that the first muffler bracket44has elasticity like a spring. The second muffler bracket45has an extra length to be slightly bent between the muffler29and the gear box11of the transaxle3as viewed from above, and its tip end portion is substantially U-shaped as viewed from the side so that the second muffler bracket45has elasticity like a spring. Whereas the muffler29is fastened to the base plate5and to the transaxle3by the first and second muffler brackets44and45, respectively, it may alternatively be fastened to one of them.

In accordance with the above described power unit1, since the engine2and the transaxle3are unitarily fastened to each other by using the base plate5rather than a pipe frame, productivity increases. In addition, since the base plate5covers the lower surface of the gear box11of the transaxle3as well as the lower surface of the engine2, unwanted substances and so on from below do not contact the lower surface of the gear box11of the transaxle3during travel of the vehicle. As a result, durability of the gear box11improves.

Since the base plate5formed by the bottom wall portion5a,and the side wall portions5b1,5b2, and5chas a concave cross-section, its stiffness improves in contrast to a flat plate.

Since the engine2, the transaxle3, and the base plate5are coupled to each other by the side plate32, stiffness of the entire power unit1improves. Since the side plate32enables the output shaft10of the engine2and the input shaft14of the transaxle3to be positioned, the CVT4can be mounted to the output shaft10and to the input shaft14easily and surely. Since the side plate32is formed of the flat plate, it can be manufactured easily by punching. As a result, a manufacturing cost can be reduced. In addition, stiffness of the power unit1in a direction of a plane of the side plate32improves.

Since the engine2and the transaxle3are coupled to each other by the generator bracket38and the generator21fastened to the generator bracket38is fastened to the side plate32, stiffness of the whole power unit1improves.

Since the left side wall portion5b1and the right side wall portion5cof the base plate5are coupled to each other by the joint bracket34, stiffness of the base plate5further improves. Since the joint bracket34is separable from the base plate5, change of the structure, position or the like of mounting portions of the vehicle body frame can be addressed by changing only the joint bracket34. Thus, design changes can be achieved flexibly.

Since the muffler29is disposed in the space which is lateral of a rear portion of the base plate5to extend vertically, and the muffler29is fastened to the base plate5and to the transaxle3, the power unit with the muffler29can be formed with a compact configuration. Even if the exhaust pipe28is thermally deformed by heat of the exhaust gas, the resulting load is absorbed by the muffler brackets44and45coupling the muffler29to the base plate5and the transaxle3, because of their elasticity. This makes it possible to avoid an event that the exhaust pipe28is subjected to undesired stress.