WO2006090946A1

WO2006090946A1 - Compact transmission preventing a vehicle from moving backward on a slope

Info

Publication number: WO2006090946A1
Application number: PCT/KR2005/000843
Authority: WO
Inventors: Seung Woo Han
Original assignee: Wooyoung Hydraulics Co.,Ltd
Priority date: 2005-02-25
Filing date: 2005-03-23
Publication date: 2006-08-31
Also published as: KR100687300B1; KR20060095045A

Abstract

Disclosed herein is a compact transmission to be used in a motor vehicle, such as a tractor, a special vehicle or a heavy vehicle, exemplified by a forklift truck and an excavator. The compact transmission of the present invention includes a subsidiary- forward clutch part which is provided in a clutch unit placed between a bevel gear and a differential pinion gear, so that the vehicle is prevented from moving backwards when shifting gears on an upward slope. Furthermore, the present invention provides a semi- permanent brake system in which both a hydraulic brake means and a parking brake means are mounted to an axle housing, thus having an extended the lifetime, and ensuring stability during parking.

Description

COMPACT TRANSMISSION PREVENTING A VEHICLE FROM MOVING BACKWARD ON A

SLOPE

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates generally to transmissions which are used in motor vehicles, such as tractors, special vehicles and heavy vehicles, exemplified by forklift trucks and excavators, and, more particularly, to a compact transmission in which a subsidiary forward clutch part is further provided in a clutch unit to prevent the vehicle from moving backwards while shifting gears on an upward slope.

2. Description of the Related Art

As well known to those skilled in the art, in a power transmission device used in a typical forklift truck, a transmission is provided along with a clutch between a torque converter and an axle shaft. Therefore, conventional power transmissions are problematic in that an engine and an axle shaft are excessively long, and most of the vibration and noise from the engine is undesirably transferred through the transmission to a driver's seat provided in a central portion of a motor vehicle.

Furthermore, in conventional power transmission devices, a transmission is provided between an engine and a bevel gear unit, which changes the direction of power transmission and conducts gear reduction. Accordingly, excessive shock occurs when shifting the gear. As a result, there are difficulties in providing durable transmissions .

In an effort to overcome the problems experienced with conventional power transmission devices, the inventor of the present invention proposed a compact transmission (Korean Patent Application No. 10-2004-02909) , which is provided between a bevel gear unit and a differential gear unit. In this compact transmission, a clutch unit is separated from a wheel reduction gear assembly and is provided between a bevel gear and a differential gear so that it is unnecessary for the bevel gear unit to change its rotational direction in order to change speed. That is, because the bevel gear unit rotates in one direction, noise and vibration are markedly decreased, and the number of elements constituting the transmission is reduced. Thereby, the weight and manufacturing costs are reduced.

In detail, the compact transmission of Korean Patent Application No. 10-2004-02909 will be explained with reference to FIG. 1. As shown in FIG. 1, power generated from the engine of a vehicle is perpendicularly transmitted through a bevel gear unit having both a bevel pinion gear 1 and a bevel ring gear 2. The power is transmitted from the bevel ring gear 2 to a clutch unit which includes a forward clutch part 3 to be connected for forward movement of the vehicle, and a backward clutch part 4 to be connected for backward movement of the vehicle. The power is transmitted from the clutch unit to a differential gear casing 10 through the forward clutch part 3 or the backward clutch part 4. The differential gear casing 10 has a differential pinion gear 11' and a differential side gear 12' . The differential gear casing 10 is coupled to a main drive shaft 13' and transmits the power to the main drive shaft 13' . The main drive shaft 13' is coupled to a reduction gear assembly 14' and transmits the power to the reduction gear assembly 14' . Thus, the vehicle moves forwards or backwards . Each of the forward and backward clutch parts 3 and 4 includes a clutch drum 7, a cylinder which is provided in the clutch drum 7, and a piston 5 which is provided at a predetermined position in the cylinder and moves using hydraulic pressure of hydraulic oil. Each of the forward and backward clutch parts 3 and 4 further includes a spring 6 which supports the piston 5, and a clutch pack 8 which is coupled to both the inner surface of the clutch drum 7 and the outer surface of a coupling 9.

However, in the case of a heavy vehicle with the conventional compact transmission having the above-mentioned construction, when the heavy vehicle is momentarily stopped, using a brake, on an upward slope or when a subsequent operation is conducted in the stopped state on the upward slope, the hydraulic pressure, which has been applied to the forward clutch part, is interrupted because of limited engine output, and the above purpose must be achieved using additional power supplied from the engine. Furthermore, to restart the vehicle from the stopped state on the upward slope, hydraulic oil must be supplied into the forward clutch part 3 to move the piston 5 in a predetermined direction, thus compressing the clutch pack 8 such that power is transmitted from the engine to the main drive shaft 13' .

However, while the pressure of the hydraulic oil supplied into the clutch unit becomes sufficient to transmit power from the engine to the main drive shaft 13' , the heavy vehicle moves backwards on the upward slope because of gravity. Furthermore, to move the heavy backward-moving vehicle forwards on the upward slope, high engine output is required. Therefore, the conventional compact transmission is problematic in that fuel consumption is excessively increased, and, because great load is applied to the elements constituting the transmission, the lifetime of the transmission is reduced.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a compact transmission in which a subsidiary forward clutch part is provided in a clutch unit, so that, when a vehicle stops at a predetermined position on an upward slope, additional hydraulic pressure is applied to the subsidiary forward clutch part before hydraulic pressure that was previously supplied to the forward clutch part is interrupted, thus transmitting forward power, thereby the vehicle does not move backwards, and in which, when the vehicle resumes moving from a stopped state, hydraulic pressure is supplied to the forward clutch part while additional hydraulic pressure is maintained in the subsidiary forward clutch part, thus markedly reducing gear shift shock.

Another object of the present invention is to provide a compact transmission in which a one-way bearing is provided in the subsidiary forward clutch part, thus fundamentally preventing backward movement of the vehicle occurring during gear shifting on the upward slope.

In an aspect, the present invention provides a compact transmission having a function of preventing a vehicle from moving backwards on an upward slope, including: a clutch unit to control power transmitted from a bevel gear unit coupled to an output shaft of an engine, the clutch unit having, a forward clutch part and a backward clutch part coupled to a forward drive gear and a backward drive gear through a forward coupling and a backward coupling, respectively, and then both coupled to a differential gear part, so that power is transmitted from the differential gear part to a reduction gear assembly through a main drive shaft and an axle assembly. The clutch unit further includes a subsidiary forward clutch part, having: at least one frictional plate coupled to an inner surface of a subsidiary clutch drum provided in the subsidiary forward clutch part; at least one frictional disk coupled to an outer surface of the forward coupling which extends into the subsidiary clutch drum; and a piston provided in the subsidiary clutch drum and supported by elastic means, so that the piston moves using hydraulic pressure and compresses both the frictional plate and the frictional disk.

In another aspect, the present invention provides a compact transmission having a function of preventing a vehicle from moving backwards on an upward slope, including: a clutch unit to control power transmitted from a bevel gear unit coupled to an output shaft of an engine, the clutch unit having a forward clutch part and a backward clutch part coupled to a forward drive gear and a backward drive gear through a forward coupling and a backward coupling, respectively, and then both coupled to a differential gear part, so that power is transmitted from the differential gear part to a reduction gear assembly through a main drive shaft and an axle assembly. The clutch unit further includes a subsidiary forward clutch part, having: at least one frictional plate coupled to an inner surface of a subsidiary clutch drum provided in the subsidiary forward clutch part; a subsidiary coupling circumscribed on the forward coupling which extends into the subsidiary clutch drum; and a piston provided in the subsidiary clutch drum and supported by elastic means, so that the piston moves using hydraulic pressure and compresses both the frictional plate and the frictional disk. The forward coupling of the subsidiary forward clutch part may be splined, keyed or screwed to both the subsidiary coupling and the forward drive gear.

In a further aspect, the present invention provides a compact transmission having a function of preventing a vehicle from moving backwards on an upward slope, including: a clutch unit to control power transmitted from a bevel gear unit coupled to an output shaft of an engine, the clutch unit having a forward clutch part and a backward clutch part coupled to a forward drive gear and a backward drive gear through a forward coupling and a backward coupling, respectively, and then both coupled to a differential gear part, so that power is transmitted from the differential gear part to a reduction gear assembly through a main drive shaft and an axle assembly. The clutch unit further includes a subsidiary forward clutch part, having: a coupling extension extending from the backward coupling into a subsidiary clutch drum provided in the subsidiary forward clutch part; at least one frictional plate coupled to an inner surface of the backward coupling extension; a one-way bearing fitted over an outer surface of the forward coupling which extends into the subsidiary clutch drum; at least one frictional disk coupled to an outer surface of an outer ring of the one-way bearing; a piston provided in the subsidiary clutch drum and supported by elastic means, so that the piston moves using hydraulic pressure and compresses both the frictional plate and the frictional disk; and a second bearing interposed between the frictional plate and the piston. The forward coupling of the subsidiary forward clutch part may be splined, keyed or screwed to the forward drive gear.

The reduction gear assembly may include: a first sun gear coupled to the main drive gear/ a plurality of first planetary gears to engage with both the first sun gear and a first ring gear fastened to the axle assembly; a first carrier shaft coupled to the plurality of first planetary gears; a second sun gear coupled to the first carrier shaft; a plurality of second planetary gears to engage with both the second sun gear and a second ring gear fastened to the axle assembly; and a second carrier shaft coupled to the plurality of second planetary gears, so that power is transmitted to a wheel at a reduced speed.

The axle assembly may include a hydraulic brake assembly, having: a brake coupling splined to the main drive shaft; a frictional brake disk coupled to an outer surface of the brake coupling; a plurality of frictional brake plates fastened to an axle housing and spaced apart from the frictional brake disk at regular intervals such that the frictional brake disk and the plurality of frictional brake plates are -alternately arranged; a first brake piston to compress both the frictional brake disk and the frictional brake plates using hydraulic pressure; and a restoring spring to provide a restoring force to the first brake piston. The axle assembly may further include a parking brake assembly, having: a parking brake piston to compress both the frictional brake disk and the frictional brake plates; and a second spring to provide an elastic force to the parking brake piston and support the parking brake piston.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. 1 is a sectional view showing a conventional transmission, which was issued by the inventor of the present invention;

FIG. 2 is a sectional view showing a clutch unit, a differential gear part and a reduction gear assembly of a compact transmission, according to a first embodiment of the present invention;

FIG. 3 is a sectional view showing an enlargement of the clutch unit of FIG. 2;

FIG. 4a is a front view of the clutch unit of FIG. 3; FIG. 4b is a sectional view of the clutch unit of FIG. 4a to show a subsidiary forward clutch part according to the present invention;

FIG. 5 is a sectional view showing an enlargement of a part of the clutch unit of FIG. 3; FIG. 6 is a sectional view showing an enlargement of the clutch unit and the differential gear part of FIG. 2;

FIG. 7 is a sectional view showing the coupling among an idle gear, a counter gear and a forward drive gear of FIG. 6;

FIG. 7b is a schematic view taken along the line A-A' of FIG. 6;

FIG. 8 is a sectional view showing a clutch unit of a compact transmission having a subsidiary coupling, according to a second embodiment of the present invention;

FIG. 9 is a sectional view showing a clutch unit of a compact transmission, according to a third embodiment of the present invention, in which a one-way bearing is provided in a subsidiary forward clutch part;

FIG. 10 is a sectional view showing a path along which power is transmitted when hydraulic pressure is applied to the forward clutch part of the compact transmission according to each of the first and second embodiments of the present invention;

FIG. 11 is a sectional view showing the path along which power is transmitted when hydraulic pressure is applied to a backward clutch part of the compact transmission according to each of the first and second embodiments of the present invention;

FIG. 12a is a sectional view of a compact transmission having a one-way bearing according to the third embodiment of the present invention, in which the power transmission path is as shown by the arrow when hydraulic pressure is applied to both a forward clutch part and a subsidiary forward clutch part of a clutch unit; FIG. 12b is a sectional view of the compact transmission of FIG. 12a, in which a power transmission path is shown by the arrow when hydraulic pressure is applied only to the subsidiary forward clutch part of the clutch unit; FIG. 13 is a sectional view of the compact transmission of FIG. 12a, in which a power transmission path is shown by the arrow when a hydraulic pressure is applied only to a backward clutch part of the clutch unit;

FIG. 14 is a sectional view showing the reduction gear assembly provided around a main drive shaft according to the present invention;

FIG. 15a is a sectional view taken along the line B-B' of FIG. 14 to show the construction of the reduction gear assembly;

FIG. 15b is a schematic view of the reduction gear assembly of FIG. 15a;

FIG. 16 is a sectional view showing both a hydraulic brake assembly and a parking brake assembly of an axle assembly according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings.

FIG. 2 is a sectional view showing the construction of a compact transmission, according to a first embodiment of the present invention.

Referring to FIG. 2, the compact transmission of the present invention receives power from a bevel gear unit 100 and changes speed using a clutch unit 200 which is perpendicularly coupled to the bevel gear unit 100. The power, changed in speed, is transmitted from the clutch unit 200 to a main drive shaft 16 through a differential gear part 60 which is coupled to the clutch unit 200. Thereafter, the power is transmitted from the main drive shaft 16 to wheels through an axle assembly 300 at reduced speed. FIG. 3 is a sectional view showing an enlargement of both the bevel gear unit 100 and the clutch unit 200 according to the first embodiment. FIG. 4a is a front view showing the clutch unit of FIG. 3.

As shown in FIG. 3, the bevel gear unit 100 includes a bevel pinion gear 11 which transmits power, generated from an engine, to the clutch unit 200. The bevel gear unit 100 further includes a bevel ring gear 12 which engages with the bevel pinion gear 11 such that the power is transmitted from the bevel pinion gear 11 to the bevel ring gear 12 in a perpendicular direction. The clutch unit 200 includes a forward clutch part 20, a subsidiary forward clutch part 30 and a backward clutch part 40.

The forward clutch part 20, which is integrated with the bevel ring gear 12, includes a forward clutch drum 21, at least one frictional plate 22 which is coupled to an inner surface of the forward clutch drum 21, and a forward coupling 25 which is provided in the forward clutch drum 21. The forward clutch part 20 further includes at least one frictional disk 23 which is coupled to an outer surface of the forward coupling 25, and a piston 24 which is provided in a cylinder 21' formed at a predetermined position in the forward clutch drum 21. The piston 24 is moved in the cylinder 21' to the left by hydraulic oil moving along an oil flow passage 17 which is connected to the forward clutch drum 21, thus compressing both the frictional plate 22 and the frictional disk 23. The forward clutch part 20 further includes an elastic means (13 of FIG. 4a) which provides restoring force to the piston 24.

The subsidiary forward clutch part 30 includes a subsidiary forward clutch drum 31, and at least one frictional plate 32 which is coupled to an inner surface of the subsidiary forward clutch drum 31. Here, the forward coupling 25 extends into the subsidiary clutch drum 31, and at least one frictional disk 33 is coupled to an outer surface of the extension of the forward coupling 25. The subsidiary forward clutch part 30 further includes a piston 34 which is provided in a cylinder 31' formed at a predetermined position in the subsidiary forward clutch drum 31. The piston 34 is moved in the cylinder 31' to the left by hydraulic oil drawn along an oil flow passage (18 of FIG. 4b) connected to the subsidiary forward clutch drum 31, thus compressing both the frictional plate 32 and the frictional disk 33. The subsidiary forward clutch part 30 further includes an elastic means (14 of FIG. 4a) which provides restoring force to the piston 34. The backward clutch part 40 includes a backward clutch drum 41, at least one frictional plate 42 which is coupled to an inner surface of the backward clutch drum 41, and a backward coupling 45 which is provided in the backward clutch drum 41. The backward clutch part 40 further includes at least one frictional disk 43 which is coupled to an outer surface of the backward coupling 45, and a piston 44 which is provided in a cylinder 41' formed at a predetermined position in the backward clutch drum 41. The piston 44 is moved in the cylinder 41' to the right by hydraulic oil moving along an oil flow passage 19 which is connected to the backward clutch drum 41, thus compressing both the frictional plate 42 and the frictional disk 43. The elastic means (14 of FIG. 4a) provides restoring force to the piston 44 of the backward clutch part 40.

Referring to FIG. 4a, the forward clutch part 20, the subsidiary forward clutch part 30 and the backward clutch part 40 constituting the clutch unit 200 are integrated by a plurality of locking bolts 15 and rotate together.

In the first embodiment, a plurality of springs, which are used as the elastic means 13 and 14, are fitted over the plurality of locking bolts 15. The springs 13, provided in the forward clutch part 20, provide elasticity to the frictional plate 22' adjacent to the piston 24 of the forward clutch part 20, thus supporting the piston 24. The springs 14, provided through both the subsidiary forward clutch part 30 and the backward clutch part 40, provide elasticity to the frictional plates 32' and 42', which are adjacent to the pistons 34 and 44 of the subsidiary forward clutch part 30 and the backward clutch part 40, respectively. Thus, the springs 14 support the pistons 34 and 44 of the subsidiary forward clutch part 30 and the backward clutch part 40. However, the elastic means is not limited to the springs 13 and 14. That is, any alternative can be used as the elastic means, so long as it is able to provide elastic restoring force to the pistons 24, 34 and 44. Furthermore, there are a variety of possible methods of installing the elastic means in the clutch unit 200. FIG. 4b is a sectional view of the clutch unit 200 to show the oil flow passage 18 which supplies hydraulic oil to the subsidiary forward clutch part 30.

As shown in FIG. 4b, the separate oil flow passage 18 is formed to the subsidiary forward clutch part 30. FIG. 5 is a sectional view showing an enlargement of a part of the clutch unit 200 according to the first embodiment.

As shown in FIG. 5, in the present invention, each frictional disk 23, 33, 43 and each frictional plate 22, 32, 42 comprise a plurality of frictional disks and a plurality of frictional plates, respectively. Furthermore, the frictional disks 23 and 33 are coupled to the forward coupling 25. The frictional disks 43 are coupled to the backward coupling 45. The frictional plates 22, 32 and 42 are coupled to the forward clutch drum 21, the subsidiary forward clutch drum 31 and the backward clutch drum 41, respectively. The frictional disks 23, 33, 43 and the frictional plates 22, 32, 42 are alternately arranged, and they are spaced apart from each other at regular intervals when not compressed by the piston 24, 34, 44, thereby acted on by a hydraulic pressure.

FIG. 6 is a sectional view showing an enlargement of both the clutch unit 200 and the differential gear part 60 according to the first embodiment.

Referring to FIG. 6, the forward coupling 25 of the forward clutch part 20 extends into the subsidiary forward clutch part 30.

The frictional disks 23 and 33 of the forward clutch part 20 and the subsidiary forward clutch part 30 are coupled to the outer surface of the forward coupling 25.

Preferably, the forward coupling 25 is splined to a forward drive gear 26.

Therefore, the forward coupling 25 and the forward drive gear 26 rotate integrally. Furthermore, the forward drive gear 26 is coupled to a differential gear casing 61 by a locking bolt so that the differential gear casing 61 rotates integrally with the forward drive gear 26.

A differential pinion gear 62 is coupled to the differential gear casing 61 and rotates along with the differential gear casing

61. The differential pinion gear 62 engages with a differential side gear 63 which is splined to the main drive shaft 16 and rotates integrally with the main drive shaft 16.

The forward drive gear 26, which rotates integrally with the differential gear casing 61, transmits power from the forward coupling 25 to the differential pinion gear 62. The power is transmitted from the differential pinion gear 62 to the main drive shaft 16 through the differential side gear 63.

The frictional disks 43 of the backward clutch part 40 are coupled to the outer surface of the backward coupling 45. The backward coupling 45 is splined to a backward drive gear 46.

FIG. 7a is a partial sectional view of FIG. 6, showing the coupling among first and second counter gears 48 and 49 and an idle gear 47, which engage with the backward drive gear 46. FIG. 7b is a schematic view taken along the line A-A' of FIG. 6.

Referring to FIGS. 7a and 7b, when the backward drive gear 46 rotates clockwise, the idle gear 47, which engages with the backward drive gear 46, rotates counterclockwise, and both the first counter gear 48, which engages with the idle gear 47, and the second counter gear 49, which is integrated with the first counter gear 48, rotate clockwise.

Then, the forward drive gear 26, which engages with the second counter gear 49, rotates counterclockwise, and the differential gear casing 61, which is coupled to the forward drive gear 26 by the locking bolt, rotates counterclockwise. The differential pinion gear 62 coupled to the differential gear casing 61 rotates counterclockwise together.

Therefore, the main drive shaft 16, which is splined to the differential side gear 63, also rotates counterclockwise. As a result, the vehicle moves backwards due to the counterclockwise rotation of the main drive shaft 16.

FIG. 8 is a sectional view showing a clutch unit 200 of a compact transmission, according to a second embodiment of the present invention. Referring to FIG. 8, the compact transmission according to the second embodiment has a subsidiary coupling 38 which is splined to the outer surface of a forward coupling 25 that extends into a subsidiary forward clutch part 30. A plurality of frictional disks 33 of the subsidiary forward clutch part 30 is coupled to the outer surface of the subsidiary coupling 38.

FIG. 9 is a sectional view showing a clutch unit 200 of a compact transmission, according to a third embodiment of the present invention.

As shown in FIG. 9, in the third embodiment, a backward coupling 45' extends into a subsidiary forward clutch part 30. A plurality of frictional plates 32 of the subsidiary forward clutch part 30 is coupled to the inner surface of the backward coupling

45' .

Furthermore, a one-way bearing 36 is fitted over the outer surface of a forward coupling 25 which extends into the subsidiary forward clutch part 30.

Moreover, an outer ring 35 is provided around the outer surface of the one-way bearing 36. A plurality of frictional disks 33 of the subsidiary forward clutch part 30 is coupled to the outer surface of the outer ring 35 of the one-way bearing 36. The one-way bearing 36 is a mechanical element that transmits both rotation and torque in only one direction. A sliding bearing, a roller bearing or any alternative having the same function as the one-way bearing 36 can be used as the one-way bearing 36. In the present invention, a sprag bearing is used as the one-way bearing 36.

The operation and effect of the compact transmission of the present invention having the above-mentioned construction will be described herein below. FIG. 10 is a sectional view of the compact transmission according to each of the first and second embodiments of the present invention, in which a forward power transmission path is shown by the arrow.

Referring to FIG. 10, power of the engine is transmitted to the bevel ring gear 12 through the bevel pinion gear 11. Subsequently, the power is transmitted to the clutch unit 200 which is integrated with the bevel ring gear 12.

Here, the power of the engine is transmitted by the rotation of the elements. In each embodiment, the bevel pinion gear 11 rotates clockwise to transmit power. The bevel ring gear 12, which engages with the bevel pinion gear 11, also rotates clockwise to transmit the power to the clutch unit 200.

As such, because the clutch unit 200, which is integrated with the bevel ring gear 12, rotates clockwise, the frictional plates 22, 32, and 42, which are coupled to the clutch drums 21, 31 and 41, also rotate clockwise.

At this time, the frictional disks 23, 33 and 43, which are coupled to the forward and backward couplings 25 and 45 provided in the clutch unit 200, are spaced apart from the frictional plates 22, 5 32 and 42 at regular intervals, respectively. Therefore, the rotating force of the clutch drums 21, 31 and 41 is transmitted neither to the forward drive gear 26 nor to the backward drive gear 46. That is, the clutch drums 21, 31 and 41 rotate freely.

When hydraulic pressure is applied to the forward clutch part

10 20, the piston 24 moves in a predetermined direction to compress both the frictional plates 22 and the frictional disks 23.

Accordingly, the frictional plates 22 and the frictional disks 23 are in close contact with each other such that the rotating force of the forward clutch drum 21 can be transmitted to the forward

15 coupling 25. As a result, the forward coupling 25 rotates clockwise.

Furthermore, because the forward drive gear 26 is splined to the forward coupling 25, the forward drive gear 26 rotates clockwise along with the forward coupling 25. The differential gear casing 0 61, which is coupled to the forward drive gear 26 by the locking bolt, also rotates clockwise and receives the power of the engine.

As well, the differential pinion gear 62, which is integrated with the differential casing 61, rotates clockwise. The differential side gear 63 also rotates clockwise. Accordingly, the 5 main drive shaft 16, which is splined to the differential side gear 63, rotates clockwise. As a result, the vehicle moves forwards.

In each embodiment of the present invention, to move the vehicle forwards, hydraulic pressure is supplied both to the forward clutch part 20 and to the subsidiary forward clutch part 30. On the other hand, to move the vehicle backwards, hydraulic pressure is supplied only to the backward clutch part 40.

In detail, when hydraulic pressure is applied to the subsidiary forward clutch part 30, the piston 34, which is provided in the cylinder 36 of the subsidiary clutch drum 31, moves to the left. Then, both the frictional plates 32 and the frictional disks 33 are in close contact with each other, so that power can be transmitted to the forward coupling 25 through both the frictional plates 32 and the frictional disks 33.

The power, transmitted to the forward coupling 25 by the hydraulic pressure supplied to the subsidiary forward clutch part 30, is transmitted to the main drive shaft 16 through both the forward drive gear 26 and the differential gear part 60 in the same manner as that described for the power transmission of the forward clutch part 20. As a result, the vehicle has forward momentum. To stop a heavy vehicle, for example, a forklift truck at a predetermined position on an upward slope, the power, which has been transmitted to the main drive shaft 16, must be interrupted. For this, the supply of hydraulic oil to the forward clutch part 20 is interrupted. Simultaneously, a driver brakes the vehicle. The engine power is supplied to other elements through other power transmission paths.

To start the vehicle again, hydraulic pressure is supplied to the forward clutch part 20 so that the engine power is transmitted to the main shaft 16. In addition, the driver releases the brake. Then, the vehicle moves forwards again.

Here, because of gravity, downward force corresponding to the weight of the vehicle is always applied to the vehicle on the upward slope. Accordingly, in the case of typical heavy vehicles, when hydraulic oil is supplied to a clutch part to move a vehicle forwards, the vehicle momentarily moves backwards before sufficient hydraulic pressure is provided in the clutch part.

However, in the present invention, when the vehicle is braked on an upward slope, additional hydraulic pressure is simultaneously supplied to the subsidiary forward clutch part 30. In this state, the hydraulic pressure, which has been applied to the forward clutch part 20, is interrupted.

Then, the vehicle does not move forwards on the upward slope, but the main drive shaft 16 still retains the forward rotating force using the power transmitted to the subsidiary forward clutch part 30. Simultaneously, because the brake is applied, the vehicle maintains its stopped state on the upward slope.

Thereafter, to move the vehicle, which was stopped, forwards again, hydraulic pressure is supplied to the forward clutch part 20.

At this time, even during a moment in which sufficient hydraulic pressure is being provided to the forward clutch part 20, the vehicle does not move backwards due to the forward rotating force which was previously provided in the subsidiary forward clutch part 30. Thus, the vehicle can smoothly move forwards.

FIG. 11 is a view showing a power transmission path of the compact transmission when hydraulic pressure is applied to the backward clutch part 40 according to each of the first and second embodiments .

Referring to FIG. 11, clockwise rotation of the engine is transmitted to the clutch drum of the clutch unit 200 through the bevel gear 100.

In this case, a hydraulic pressure, which is supplied to the backward clutch part 40, moves the piston 44. Thus, the frictional plates of the backward clutch drum 41 and the frictional disks of the backward coupling 45 are in close contact with each other, so that the power can be transmitted from the backward clutch drum 41 to the backward coupling 45. Thereby, the backward coupling 45 rotates clockwise.

Furthermore, when the backward coupling 45 rotates clockwise, the backward drive gear 46, which is splined to the backward coupling 45, also rotates clockwise. The idle gear 47, which engages with the backward drive gear 46, rotates counterclockwise.

When the idle gear 47 rotates counterclockwise, the first and second counter gears 48 and 49 rotate clockwise, and the forward drive gear 26, which engages with the second counter gear 49, rotates counterclockwise. Moreover, the differential gear casing 61, which is splined to the forward drive gear 26, rotates counterclockwise. Thereby, both the differential side gear 63 and the main drive shaft 16, which is splined to the differential side gear 63, rotate counterclockwise. As a result, the vehicle moves backwards .

FIG. 12a is a sectional view of the compact transmission having the one-way bearing 36 according to the third embodiment, in which a power transmission path is as shown by the arrow when hydraulic pressure is applied to the forward clutch part of the clutch unit 200.

In the third embodiment, to move the vehicle forwards, hydraulic pressure is simultaneously supplied to both the forward clutch part 20 and the subsidiary forward clutch part 30, unlike the first and second embodiments. When hydraulic pressure is supplied to the forward clutch part 20, a piston 24 of the forward clutch part 20 compresses both frictional plates 22 and frictional disks 23 of the forward clutch part 20. Then, a forward coupling 25, which is coupled to the frictional disks 23, rotates clockwise so that power is transmitted to a forward drive gear 26.

Furthermore, the forward drive gear 26, which is splined to the forward coupling 25, transmits the clockwise rotation from the forward coupling 25 to a differential gear part 60. When the differential gear part 60 rotates clockwise, a main drive shaft 16 also rotates clockwise. As a result, the vehicle moves forwards. Meanwhile, a second counter gear 49, which engages with the forward drive gear 26, rotates counterclockwise. A first counter gear 48, which is integrated with the second counter gear 49, also rotates counterclockwise. Simultaneously, an idle gear 47, which engages with the first counter gear 48, rotates clockwise. A backward drive gear 46, which engages with the idle gear 47, rotates counterclockwise. The backward coupling 45' , which is splined to the backward drive gear 46, also rotates counterclockwise. In other words, when hydraulic pressure is supplied to the forward clutch part 20, the clockwise rotation from the engine is transmitted to the main drive shaft 16 through both the forward coupling 25 and the forward drive gear 26. Simultaneously, the clockwise rotation of the forward drive gear 26 is transmitted to the backward coupling 45' via the second counter gear 49, which engages with the forward drive gear 26, the first counter gear 48, the idle gear 47 and the backward drive gear 46. As a result, the backward coupling 45' rotates counterclockwise.

In the third embodiment, when hydraulic pressure is applied to the forward clutch part 20, the hydraulic pressure is simultaneously applied to the subsidiary forward clutch part 30. Furthermore, a thrust bearing 37 is interposed between the piston 34 and the plurality of frictional plates 32 such that a piston 34, which is provided in the subsidiary forward clutch part 30 and rotates clockwise along with the subsidiary clutch drum 31, can compress a plurality of frictional plates 32, which are coupled to the inner surface of the backward coupling 45' and rotate counterclockwise.

When the hydraulic pressure is applied to both the forward clutch part 20 and the subsidiary forward clutch part 30, the piston 34 of the subsidiary clutch drum 31 moves in a predetermined direction. The thrust bearing 37 is moved by the piston 34. Thus, the thrust bearing 37 compresses both the frictional plates 32, which are coupled to the inner surface of the backward coupling 45' , and the frictional disks 33 which are coupled to the outer surface of the outer ring 35 of the one-way bearing 36.

Then, the outer ring 35 of the one-way bearing 36 and the backward coupling 45' integrally rotate counterclockwise, while the forward coupling 25 rotates clockwise. Thus, the vehicle moves forwards . Of course, any alternative having the same function as the thrust bearing 37 may be used in place of the thrust bearing 37, so long as it can offset relative rotation and transmit the power in an axial direction.

The one-way bearing 36 is provided between the outer ring 35 and the forward coupling 25 such that the outer ring 35 rotates only counterclockwise with respective to the forward coupling 25.

FIG. 12b is a sectional view of the compact transmission according to the third embodiment, in which a power transmission path is as shown by the arrow when hydraulic pressure is applied only to the subsidiary forward clutch part 30 of the clutch unit 200.

Hydraulic pressure is supplied only to the subsidiary forward clutch part 30 when the vehicle is stopped on an upward slope. In this case, a brake is operated and, simultaneously, the hydraulic pressure that was applied to the forward clutch part 20 is interrupted, while the hydraulic pressure applied to the subsidiary- forward clutch part 30 is maintained.

At this time, the clutch unit 200 is continuously rotated clockwise by the power transmitted from the engine. Because no hydraulic pressure is applied to the forward clutch part 20, the power is not transmitted to the forward coupling 25. Therefore, neither the forward coupling 25 nor the main drive shaft 16 rotates.

Furthermore, because the forward coupling 25 does not rotate, the backward coupling 45' , which rotates along with the forward coupling 25 and is coupled to the forward coupling 25 via the forward drive gear 26, the differential gear part 60, the first and second counter gears 48 and 49, the idle gear 47 and the backward drive gear 46, does not rotate either.

However, even when the vehicle is stopped, the clutch unit 200 is continuously rotated clockwise by the power transmitted from the bevel gear unit 100. At this time, if hydraulic pressure is applied to the subsidiary forward clutch part 30, the piston 34 of the subsidiary forward clutch part 30 rotates clockwise along with the subsidiary clutch drum 31 and compresses, using the thrust bearing 37, both the frictional plates 32, which are coupled to the inner surface of the backward coupling 45' and do not rotate, and the frictional disks 33, which are coupled to the outer surface of the outer ring 35 of the one-way bearing 36.

As such, when the vehicle is stopped on the upward slope, the forward coupling 25 does not rotate, and the frictional plates 32 of the backward coupling 45' and the frictional disks 33 of the outer ring 35 of the one-way bearing 36 are compressed by the piston 34.

Therefore, the outer ring 35 does not rotate either.

Furthermore, in this case, the one-way bearing 36 is provided between the forward coupling 25, which integrally rotates along with the main drive shaft 16, and the outer ring 35 which is coupled to the frictional plates 32 of the backward coupling 45' and does not rotate. Therefore, the one-way bearing 36 prevents the main drive shaft 16 from rotating counterclockwise. As a result, the vehicle is fundamentally prevented from moving backwards on upward slopes.

FIG. 13 is a sectional view of the compact transmission according to the third embodiment, in which a power transmission path is as shown by the arrow when hydraulic pressure is applied only to the backward clutch part 40 of the clutch unit 200. Referring to FIG. 13, when hydraulic pressure is applied to the backward clutch part 40 which rotates, a piston 44 provided in a backward clutch drum 41 moves in a predetermined direction to compress both a plurality of frictional plates 42 and a plurality of frictional disks 43. Thus, the backward coupling 45' rotates clockwise . Then, the backward drive gear 46, which is splined to the backward coupling 45', also rotates clockwise. The idle gear 47, which engages with the backward drive gear 46, rotates counterclockwise. Both the second counter gear 49, which engages with the idle gear 47, and the first counter gear 48 rotate clockwise.

The forward drive gear 26, which engages with the first counter gear 48, rotates counterclockwise. Thus, both a differential gear case 61, which is splined to the forward drive gear 26, and a differential pinion gear 62 rotate counterclockwise. Therefore, the main drive shaft 16, which is splined to the differential pinion gear 62, also rotates counterclockwise. As a result, the vehicle moves backwards.

FIG. 14 is a sectional view showing the reduction gear assembly 50 coupled to the main drive shaft 16 to drive the vehicle according to the present invention.

In each embodiment of the present invention, a planetary gear assembly is used as the reduction gear assembly 50. However, the reduction gear assembly 50 is not limited to the planetary gear assembly. In other words, various alternatives, including typical gears, are possible so long as they can reduce rotation speed. Such simple modifications are easily embodied by those skilled in the art, and thus, they must be regarded as being within the scope of the present invention. The reduction gear assembly 50 reduces the speed of the main drive shaft 16 at a ratio of 13:1 when the vehicle travels. First, the rotation of the main drive shaft 16 is transmitted to a first sun gear 51 which is splined to the main drive shaft 16.

The first sun gear 51 engages with a plurality of first planetary gears 52. The planetary gears 52 are coupled to the inner surface of a first ring gear 53 which is fastened to the housing of the axle assembly 300. A rotating center shaft 55 of the first planetary gears 52 is integrally coupled to a first carrier shaft 54. Therefore, the rotation of the engine transmitted to the first sun gear 51 is first reduced in speed by the plurality of first planetary gears 52 and is output through the first carrier shaft 54.

The first carrier shaft 54 is splined to a second sun gear 51' and transmits the rotation of the engine, which was first reduced in speed by the first planetary gears 52, to the second sun gear 51' . The second sun gear 51' engages with a plurality of second planetary gears 52' . The plurality of second planetary gears 52' is coupled to the inner surface of a second ring gear 53' which is fastened to the housing of the axle assembly 300. A rotating center shaft 55' of the second planetary gears 52' is integrally coupled to a second carrier shaft 54' .

The rotation of the engine, transmitted from the first carrier shaft 54 to the second sun gear 51' , is again reduced in speed by the plurality of second planetary gears 52' and is output through the second carrier shaft 54' . The rotating force, which is output through the second carrier shaft 54', rotates the wheels of the vehicle.

In each embodiment of the present invention, the first and second ring gears 53 and 53' are integrated into a single body and have predetermined shapes such that the first and second planetary gears 52 and 52' engage with the inner surfaces of the first and second ring gears 53 and 53' , respectively. However, alternatively, the first and second ring gears 53 and 53' may be separately manufactured and coupled to each other by a locking bolt. FIG. 15a is a sectional view taken along the line B-B' of FIG. 14 to show the construction of the reduction gear assembly 50, in which the rotation of the first and second sun gears 51 and 51' integrated with the main drive shaft 16 is reduced in speed by the plurality of first and second planetary gears 52 and 52' and the first and second ring gears 53 and 53' . FIG. 15b is a schematic view of the reduction gear assembly 50 of FIG. 15a.

The first and second rotating center shafts 55 and 55' of the first and second planetary gears 52 and 52' are integrated with the first and second carrier shafts 54 and 54' , respectively, so that the engine power is transmitted to the wheels of the vehicle by the revolution of the first and second planetary gears 52 and 52' .

FIG. 16 is a sectional view showing a brake assembly comprising a hydraulic brake assembly 70, which brakes the rotation of the main drive shaft 16, and a parking brake assembly 80, which brakes the rotation of the main drive shaft 16 for parking, according to the present invention.

The hydraulic brake assembly 70 includes a brake coupling 71 which is splined to the main drive shaft 16, a plurality of frictional brake disks 73 which is coupled to the outer surface of the brake coupling 71, and a plurality of frictional brake plates 72 which are fastened to an axle housing 76 and are spaced apart from the frictional brake disks 73 at regular intervals such that the frictional brake disks 73 and the frictional brake plates 72 are alternately arranged. The hydraulic brake assembly 70 further includes a brake piston 74 which compresses both the frictional brake disks 73 and the frictional brake plates 72 using hydraulic pressure, and a restoring spring 75 which provides restoring force to the first brake piston 74.

When the vehicle travels, the brake coupling 71, which is splined to the main drive shaft 16, rotates along with the main drive shaft 16. Furthermore, the frictional brake disks 73, which are coupled to the outer surface of the brake coupling 71, also rotate.

To brake the vehicle, hydraulic pressure is applied to the brake piston 74 so that the brake piston 74 moves to the left of FIG. 16. Thus, the brake piston 74 compresses both the frictional brake disks 73, which are rotating, and the frictional brake plates 72, which are fastened to the axle housing 76. Thereby, the frictional brake disks 73 are in close contact with the frictional brake plates 72 so that the rotation of the frictional brake disks 73 is limited. As a result, the vehicle is stopped.

The parking brake assembly 80 includes a parking brake piston

81 which compress both the frictional brake disks 73 and the frictional brake plates 72, and an elastic spring 82 which provides elastic force to the parking brake piston 81 and supports the parking brake piston 81.

When the vehicle travels, hydraulic pressure is applied to the parking brake piston 81 so that the parking brake piston 81 is placed at a predetermined position spaced apart from the frictional brake disks 73 and the frictional brake plates 72. However, during parking, the hydraulic pressure is removed from the parking brake piston 81 so that both the frictional brake disks 73 and the frictional brake plates 72 are compressed by the elastic spring 82.

As described above, the present invention provides a compact transmission in which a subsidiary forward clutch part is provided in a clutch unit, so that, when a vehicle stops at a predetermined position on an upward slope, additional hydraulic pressure is applied to the subsidiary forward clutch part before previous hydraulic pressure that was supplied to the forward clutch part is interrupted. Thus, forward power is transmitted to wheels so that the vehicle does not move backwards . Even when the vehicle resumes moving, hydraulic pressure is supplied to the forward clutch part while the additional hydraulic pressure in the subsidiary forward clutch part is maintained. Therefore, gear shift shock is markedly reduced. Furthermore, a one-way bearing is provided between the subsidiary forward clutch part and a forward drive gear coupled to the main drive shaft. As a result, backward movement of the vehicle occurring during gear shifting on the upward slope is fundamentally prevented.

In addition, the present invention provides a semi-permanent brake system in which both a hydraulic brake assembly and a parking brake assembly are mounted to an axle housing, unlike conventional arts having typical drum brakes. Therefore, even if an engine is abnormally stopped when the vehicle travels, because the parking brake is automatically operated, the vehicle is stably braked. As well, the present invention ensures stability during parking.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.

Claims

WHAT IS CLAIMED IS:

1. A compact transmission having a function of preventing a vehicle from moving backwards on an upward slope, comprising: a clutch unit to control a power transmitted from a bevel gear unit coupled to an output shaft of an engine, the clutch unit comprising: a forward clutch part and a backward clutch part coupled to a forward drive gear and a backward drive gear through a forward coupling and a backward coupling, respectively, and then both coupled to a differential gear part, so that power is transmitted from the differential gear part to a reduction gear assembly through a main drive shaft and an axle assembly, wherein the clutch unit further comprises: a subsidiary forward clutch part, comprising: at least one frictional plate coupled to an inner surface of a subsidiary clutch drum provided in the subsidiary forward clutch part; at least one frictional disk coupled to an outer surface of the forward coupling which extends into the subsidiary clutch drum; and a piston provided in the subsidiary clutch drum and supported by elastic means, so that the piston moves using hydraulic pressure and compresses both the frictional plate and the frictional disk.

2. A compact transmission having a function of preventing a vehicle from moving backwards on an upward slope, comprising: a clutch unit to control a power transmitted from a bevel gear unit coupled to an output shaft of an engine, the clutch unit comprising: a forward clutch part and a backward clutch part coupled to a forward drive gear and a backward drive gear through a forward coupling and a backward coupling, respectively, and then both coupled to a differential gear part, so that power is transmitted from the differential gear part to a reduction gear assembly through a main drive shaft and an axle assembly, wherein the clutch unit further comprises: a subsidiary forward clutch part, comprising: at least one frictional plate coupled to an inner surface of a subsidiary clutch drum provided in the subsidiary forward clutch part; a subsidiary coupling circumscribed on the forward coupling which extends into the subsidiary clutch drum; and a piston provided in the subsidiary clutch drum and supported by elastic means, so that the piston moves using hydraulic pressure and compresses both the frictional plate and the frictional disk.

3. The compact transmission as set forth in claim 2, wherein the forward coupling of the subsidiary forward clutch part is splined, keyed or screwed to both the subsidiary coupling and the forward drive gear.

4. A compact transmission having a function of preventing a vehicle from moving backwards on an upward slope, comprising: a clutch unit to control a power transmitted from a bevel gear unit coupled to an output shaft of an engine, the clutch unit comprising: a forward clutch part and a backward clutch part coupled to a forward drive gear and a backward drive gear through a forward coupling and a backward coupling, respectively, and then both coupled to a differential gear part, so that power is transmitted from the differential gear part to a reduction gear assembly through a main drive shaft and an axle assembly, wherein the clutch unit further comprises: a subsidiary forward clutch part, comprising: a coupling extension extending from the backward coupling into a subsidiary clutch drum provided in the subsidiary forward clutch part; at least one frictional plate coupled to an inner surface of the backward coupling extension; a one-way bearing fitted over an outer surface of the forward coupling which extends into the subsidiary clutch drum; at least one frictional disk coupled to an outer surface of an outer ring of the one-way bearing; a piston provided in the subsidiary clutch drum and supported by elastic means, so that the piston moves using hydraulic pressure and compresses both the frictional plate and the frictional disk; and a second bearing interposed between the frictional plate and the piston.

5. The compact transmission as set forth in claim 4, wherein the forward coupling of the subsidiary forward clutch part is splined, keyed or screwed to the forward drive gear.

6. The compact transmission as set forth in claim 2, wherein the reduction gear assembly comprises: a first sun gear coupled to the main drive gear; a plurality of first planetary gears to engage with both the first sun gear and a first ring gear fastened to the axle assembly; a first carrier shaft coupled to the plurality of first planetary gears; a second sun gear coupled to the first carrier shaft; a plurality of second planetary gears to engage with both the second sun gear and a second ring gear fastened to the axle assembly; and a second carrier shaft coupled to the plurality of second planetary gears, so that power is transmitted to a wheel at a reduced speed.

7. The compact transmission as set forth in claim 4, wherein the reduction gear assembly comprises: a first sun gear coupled to the main drive gear; a plurality of first planetary gears to engage with both the first sun gear and a first ring gear fastened to the axle assembly; a first carrier shaft coupled to the plurality of first planetary gears; a second sun gear coupled to the first carrier shaft; a plurality of second planetary gears to engage with both the second sun gear and a second ring gear fastened to the axle assembly; and a second carrier shaft coupled to the plurality of second planetary gears, so that power is transmitted to a wheel at a reduced speed.

8. The compact transmission as set forth in claim 2, wherein the axle assembly comprises: a hydraulic brake assembly, comprising: a brake coupling splined to the main drive shaft; a frictional brake disk coupled to an outer surface of the brake coupling; a plurality of frictional brake plates fastened to an axle housing and spaced apart from the frictional brake disk at regular intervals such that the frictional brake disk and the plurality of frictional brake plates are alternately arranged; a first brake piston to compress both the frictional brake disk and the frictional brake plates using hydraulic pressure; and a restoring spring to provide a restoring force to the first brake piston; and a parking brake assembly, comprising: a parking brake piston to compress both the frictional brake disk and the frictional brake plates; and a second spring to provide an elastic force to the parking brake piston and support the parking brake piston.

9. The compact transmission as set forth in claim 4, wherein the axle assembly comprises: a hydraulic brake assembly, comprising: a brake coupling splined to the main drive shaft; a frictional brake disk coupled to an outer surface of the brake coupling; a plurality of frictional brake plates fastened to an axle housing and spaced apart from the frictional brake disk at regular intervals such that the frictional brake disk and the plurality of frictional brake plates are alternately arranged; a first brake piston to compress both the frictional brake disk and the frictional brake plates using hydraulic pressure; and a restoring spring to provide a restoring force to the first brake piston; and a parking brake assembly, comprising: a parking brake piston to compress both the frictional brake disk and the frictional brake plates; and a second spring to provide an elastic force to the parking brake piston and support the parking brake piston.