DESCRIPTION OF THE PRIOR ART <BR> <BR> <BR> <BR> <BR> [0002]<BR> <BR> <BR> <BR> <BR> <BR> Track-laying vehicles such as a bulldozer and a scrape dozer which run to work raove by transmuting engine power mechanically.

A scrape dozer with both functions oo a scraper and a bulldozer can be operated forward for excavating, loading, conveying, removing earth, and preparing land and successively arien backward to the excavation position, like a shuttle. This charac. eristic leads to the use of scrape dozers for constructi : : g roads, develo ing building lots and the golf links and carrying out agrarian reform.

[0003] As shown in Fig. 4, a scrape dozer has a bowl 51 between right and left caterpillar bands 50 for exca'.'ating and loading earth and sand, a bic-de 52 for preparing land on the front thereof and a cab seat 53 on the top of the body.

In the power system for moving this machine, power is transmitted from an engine 1, through a torque converter 2, a

transmission 3 and a steering system 4, to right and left driving wheels 6a and 6b by gears.

[0004] The steering system 4 changes a direction of the vehicle, so that the power transmitted from an output shaft 3a of the transmission through a shaft coupling 8 is transmitted to right and left pinions 10a and 10b via clutches 7a and 7b.

When the vehicle turns, the clutch 7a (or 7b) on the turning direction is released and power is transmitted only to the pinion 10b (or 10a) on the other side. Consequently, the vehicle turns in the direction of which power is shut off to the pinion. Additionally, even if power is shut off to the driving wheel 6a on one side (or 6b), the power to the other side causes the vehicle to turn a little into the gentle-turn.

Then, a brake 5a (or 5b) is used to stop the turning of the side that power is shut off.

[0005] As a result, when the vehicle turns, the speed is suddenly decreased. Not only the shock is heavy, but also the traction lowers.

Some types of bulldozer have a steering system with a differential mechanism combining bevel gears, so that the speed is kept when a vehicle turns.

[0006] This steering system is like one shown in Fig. 5. An output shaft of transmission 3 is provided with a bevel gear 61 which is connected to an input shaft 62 of a working gear 60. Output shafts 63

and 64 on the right and left sides of the working gear are connected to right and left driving wheels which are not shown in the figure. The output shafts 63 and 64 are provided with brakes 66a and 66b respectively. Numeral 65 indicates a clutch for difflock.

[0007] In this steering system, when the vehicle turns, actuation of the brake 66a (or 66b) reduces revolution numbers of the output shaft 63 (or 64). This reduction enables the other output shaft 64 (or 63) to revolve higher than is in straight-ahead motion. Therefore, the vehicle can turn smoothly without reducing of the speed. Since in this steering system some energy is lost by the brake, the output shaft may be provided with a type of hydraulic pump motor which is changeable in capacity (for example, unexamined Japanese Patent Publication No. 6- 183366).

[0008] An engine of a bulldozer is placed lengthwise (the output shaft is placed in the moving direction). The output shaft of a transmission is provided almost at the center and right-angled between right and left driving wheels. Therefore, the length of a steering system can be extended to a maximum space between caterpillar bands.

[0009] However, since an engine of scrape dozer cannot but be structurally mounted sideways, both the transmission and the steering system need to be put in the space between the caterpillar bands (see Fig. 3). Consequently, within the dimension A, it is necessary to place

the portion from a shaft coupling 8 coupling with the transmission to the center between the pinion 10a and 10b on the output of the steering system, namely the center between the caterpillar bands. As a result, it is impossible to use the aforesaid differential mechanism combining bevel gears.

[0010] An object of the present invention is to provide a compact steering system having differential mechanism suitable for track-laying vehicles on which an engine is mounted sideways.

[0011] In the present invention, to achieve the above purpose, the following system is applied; A steering system comprises an input shaft connected to an output shaft of a transmission, output shafts for transmitting power respectively to driving wheels of right and left caterpillar bands. In the steering system for track-laying vehicles turned by changing speed of one of the output shafts by a hydraulic motor, the input shaft is inserted through a hollow shaft on which each sun gear of first, second and third planetary gear mechanisms is fixedly installed. The end of the input shaft is connected to a planetary carrier of the first planetary gear mechanism. A ring gear of the second planetary gear mechanism is connected to the hydraulic motor. A planetary carrier of the second planetary gear mechanism is connected to a ring gear of the first planetary gear mechanism and one output shaft. A ring gear of the third planetary gear mechanism is fixed on a case. A planetary carrier

of the third planetary gear mechanism is connected to the other output shaft.

[0012] The steering system according to the present invention is applied to track-laying vehicles wherein engine power is transmitted via a transmission mechanically to the driving wheels of caterpillar bands such as bulldozers, scrape dozers, combines and the like, but not intended for track-laying vehicles which move by using a hydraulic pump and a hydraulic motor such as mobile cranes and pile drivers.

[0013] The steering system according to the present invention works well especially for track-laying vehicles wherein an engine is mounted sideways. Even if an engine is mounted lengthwise, however, when the engine cannot be mounted at the center of the body, the steering system can be applied.

Since a track-laying vehicle is conveyed to a constructing site by such a vehicle as trailer-track, the size between the caterpillar bands is limited for transport. If the width of steering system between the caterpillar bands is limited by placement of working devices and the like, as described in Claim 2, it is preferable that both output shafts actuating pinions are outwardly engaged with a hollow shaft between second planetary gear mechanism and third planetary gear mechanism.

In other words, the third planetary gear mechanism may be arranged on the side to be limited in order to set the steering system in a manner that the center between the both pinions is the center position of the

body. Moreover, it is especially effective that an engine is mounted sideways with the transmission and the steering system placed between the caterpillar bands on the right and left sides, such as a scrape dozer (Refer to Claim 3).

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a diagrammatic view showing the composition of the steering system of track-laying vehicle as one embodiment of the present invention.

Fig. 2 is a partial sectional view of the steering system of track-laying vehicle as one embodiment of the present invention.

Fig. 3 is an explanatory view showing the power system of a conventional scrape dozer.

Fig. 4 is a side view of a scrape dozer.

Fig. 5 is an explanatory view of a conventional steering system.

Fig. 6 is a perspective view of the steering system shown in Fig. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0014] An embodiment according to the present invention is now explained referring to Fig. 1 and 2.

This steering system is applied to the scrape dozer explained in the aforementioned prior art. With respect to the parts also shown in Fig. 3 and 4, same numerals are used and explanation is omitted. An

output shaft 3a of a transmission 3 and a shaft coupling 8 and pinions 10a, 10b are provided at the conventional positions.

[0015] As shown in Fig. 1, an input shaft 11 is provided via the output shaft 3a of the transmission 3 and the shaft coupling 8 and inserted through a hollow shaft 25 on which a first sun gear 13, a second sun gear 18 and a third sun gear 26 are fixedly installed. The end of the input shaft 11 is connected with a first planetary carrier 12. Namely, the hollow shaft 25 is the common shaft of three planetary gear mechanisms 37,38 and 39.

[0016] The first planetary carrier 12 is provided with a planetary gear 14 with which the first sun gear 13 and a first ring gear 15 are engaged.

The second planetary gear mechanism 38 is comprised of the second sun gear 18 fixedly installed on the hollow shaft 25, a second planetary gear 17 which is provided with a second planetary carrier 16a connected with the first ring gear 15, and a second ring gear 19 which is connected with a gear 22 engaged with a gear 21 connected with an output shaft of a hydraulic motor 40. The second planetary gear 14 is connected with a right output shaft 20b by a second planetary carrier 16b. The circuit of the hydraulic motor 40 is constituted so that the hydraulic motor 40 can rotate normally and inversely and revolution numbers can be changed.

[0017] The third planetary gear mechanism 39 is comprised of the

third sun gear 26 fixedly installed on the hollow shaft 25, a third planetary gear 27 and a third ring gear 30 fixedly installed on a case 35.

A third planetary carrier 28 is connected with a left output shaft 20a.

The numbers of teeth on corresponding gears are same between the second planetary gear mechanism 38 and the third planetary gear mechanism 39. Therefore, the numbers of teeth are same between the second sun gear 18 and the third sun gear 26, the second planetary gear 17 and the third planetary gear 27, the second ring gear 19 and the third ring gear 30.

[0018] The left output shaft 20a and the right output shaft 20b are provided, facing each other, between the second planetary gear mechanism 38 and the third planetary gear mechanism 39. The pinion 10a and the pinion 10b are installed adjacently and fixedly to the output shafts 20a, 20b.

Numerals 33 and 34 show brake mechanisms fixedly installed within the case 35. The brake mechanism 33 is engaged with the first ring gear 15 and the brake mechanism 34 is engaged with the third planetary carrier 28. The operation of the steering system is now explained.

[0019] In straight-ahead motion, the hydraulic motor 40 is in the stopped state. The power of an engine 1 is transmitted, via the shaft coupling 8 connected with the output shaft 3a of the transmission 3, to the input shaft 11 and rotates the first planetary carrier 12 of the first

planetary gear mechanism 37. This turns the first ring gear 15 and the first sun gear 13. Then, the second ring gear 19 is in the fixed state and the rotation of the first ring gear 15 rotates the second planetary carrier 16a and then the right output shaft 20b via the second planetary carrier 16b.

[0020] Meanwhile the rotation of the first sun gear 13 rotates the second sun gear 18 and the third sun gear 26, via the hollow shaft 25.

This causes the rotation of the third carrier 28, and the left output shaft 20a, since the third ring gear 30 is fixed on the case 35. The numbers of teeth of gears are same between the second planetary gear mechanism 38 and the third planetary gear mechanism 39, so the right output shaft 20b and the left output shaft 20a rotate at the same revolution numbers and respectively turn the pinions lOb, 10a at the same speed.

[0021] Next, in turning motion, the hydraulic motor 40 is rotated. A direction for turning depends on the turning direction of the hydraulic motor 40. A radius for turning depends on the revolution numbers of the hydraulic motor 40.

The rotation of the hydraulic motor 40 turns the gear 22 via the gear 21. This rotates the second ring gear 19 and changes the revolution numbers of the right output shaft 20b. If the right output shaft 20b is increased more than is in straight-ahead motion, the rotation of the second sun gear 18 is decreased more than is in

straight-ahead motion.

[0022] Accordingly, the left output shaft 20a is decreased as the right output shaft 20b is increased. Conversely, as the right output shaft 20b is decreased (the hydraulic motor 40 is reversed), the right output shaft 20b is decreased and the rotation of the second sun gear 18 is increased more than is in straight-ahead motion. Therefore, the left output shaft 20a is increased as the right output shaft 20b is decreased.

[0023] As aforementioned, the turning is performed by increasing and decreasing the revolution numbers of the right output shaft 20a by the hydraulic motor 40. The speed in turning motion is same as the speed in straight-ahead motion, however.

Additionally, the brake mechanisms 33,34 are not related to the planetary gear mechanism. The brake mechanisms 33,34 are simultaneously operated, and decrease speed of the vehicle, and work to stop and park the vehicle.

[0024] As explained above, the present invention realizes smooth turning of the vehicle without decreasing the speed thereof, since the input shaft is inserted through the hollow shaft on which each sun gear of the first, second and third planetary gear mechanisms is fixedly installed, and the end of the input shaft is connected to the planetary carrier of the first planetary gear mechanism, and the ring gear of the second planetary gear mechanism is connected to the hydraulic motor

and one output shaft. Furthermore, since the engine can be placed sideways so that the transmission and the steering system can be arranged between the caterpillars bands, the present invention can be effectively applied to not only track-laying vehicles which an engine cannot be placed lengthwise but also vehicles which an engine cannot be arranged at the center of the body.