TECHNICAL FIELD

This invention relates generally to vehicle steering and more particularly to a steering system which improves performance of log haulers operating on rough terrain or in forests.

BACKGROUND ART

Highway vehicles and many off-highway vehicles have used stub axles to support steerable wheels. Typically, in such a construction, a pair of stub axles are pivotally connected on nearly vertical axes to opposite ends of a transverse axle. The U.S. Pat. No. 3,903,983 issued to Laurel R. Yeske for Steering System for Vehicles shows a vehicle having four stub axle supported steerable wheels together with a control system for selectively choosing front steering, rear steering, front and rear steering, crab steering and parallel steering. Some off-highway vehicles are provided with central steering wherein front and rear sections of a vehicle are pivoted about a central vertical pivot. The previously used or suggested steering arrangements are not satisfactory for steering a multiple section log hauler or forwarder in a serpentine fashion through a tree harvesting area. Also they do not provide satisfactory adjustment of the support wheels of a multiple section log hauler to maintain a satisfactory load center as the various sections of the log hauler traverse the uneven terrain usually associated with wood lands and forests.

The present invention is directed to overcoming one or more of the problems or disadvantages associated with the prior art.

DISCLOSURE OF THE INVENTION

A steering arrangement is provided for a log hauler having a tractor and a plurality of log trailers joined by central vertical pivot connections. The steering arrangement includes steering mechanism for causing steering about the central vertical pivots and steering mechanism for steering each of the support wheels. All the support wheels are steerable relative to a chassis of the tractor or the log trailer they support, thereby providing a very maneuverable vehicle for moving in serpentine fashion over irregular terrain often found in wooded areas. The lateral stability of the log hauler is greatly enhanced by also making the steerable support wheels vertically adjustable relative to the chassis of the log hauler sections. Each of the steerable support wheels is rotatably supported on one end of a pendulum arm which has its other end pivotally connected to a chassis through a connector which allows the pendulum arm to swing vertically relative to the connector. The connector is pivotally connected to the chassis of the tractor or one of the log trailers for pivotal steering movement about a vertical pivot axis. Power operated actuators are used to control the swinging movement of the pendulum arm and to control the pivotal steering movement of the carrier relative to the chassis structure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1

is a side view of a multi-section, tractor powered log hauler;

FIG. 2

is a top view of the tractor shown in

FIG. 1

with structure broken away to show the pendulum arms connected to the tractor chassis; and

FIG. 3

is a top view similar to

FIG. 2

but showing the pendulum arms pivoted relative to the vehicle chassis.

BEST MODE FOR CARRYING OUT THE INVENTION

The log hauler or forwarder illustrated in

FIG. 1

is primarily used to load and transport cut timber or logs out of the woodland or forest to a storage, shipping or processing location. Although the log hauler may at times be operated on hard surfaces roads, it is especially designed to travel on uneven terrain and in forests to load logs near the point of harvesting, thereby minimizing the building of logging roads and the expense and damage incurred in skidding the logs long distances. The illustrated log hauler includes a train of vehicle sections interconnected on vertical pivot axes. The log hauler includes a two wheel tractor

11

which is powered by an internal combustion engine, not shown, and is equipped with an operator's station or cab

12

. The tractor

11

has a chassis

13

extending in the direction of travel which is pivotally connected to the chassis

14

of a first log trailer

16

for steering movement about a vertical pivot axis

17

. A hydraulic actuator

18

for effecting steering of the tractor about the axis

17

has a cylinder end pivotally connected to the chassis

13

of the tractor

11

and a rod end pivotally connected to the chassis

14

of the log trailer

16

. The tractor

11

includes a pair of traction wheels

21

,

22

which are driven by an engine, not shown, mounted on the chassis

13

of the tractor

11

. The chassis

14

of the log trailer

16

is supported at its front end by a pair of laterally spaced wheels

23

,

24

and is supported at its rear end by a pair of laterally spaced wheels

26

,

27

.

A second log trailer

31

includes a chassis

32

which is supported by a pair of laterally spaced wheels

33

,

34

. The second log trailer

31

is connected in towed relation to the first log trailer

16

by a longitudinally extending link or tongue

36

. The front end of the tongue

36

is pivotally connected on a vertical pivot axis

37

to the chassis

14

of the first log trailer

16

. The rear end of the tongue

36

is pivotally connected to the chassis

32

of the second log trailer

31

on a vertical pivot axis

38

. Steering movement of the tongue

36

relative to the second log trailer

31

is controlled by a hydraulic actuator

42

having a cylinder end pivotally connected to the tongue

36

and a rod end pivotally connected to the chassis

32

of the second log trailer

31

.

A logging crane

43

includes a mast

44

rigidly mounted on the chassis

14

of the first log carrier

16

, a first boom

45

having a rear end pivotally connected to the top of the mast

44

and a second boom

46

which has an upper end pivotally connected to a front end of the first boom

45

. A hydraulic actuator

47

is interconnected between the mast

44

and the first boom

45

. A hydraulic actuator

48

has its cylinder end pivotally connected to the first boom

45

and its rod end pivotally connected to the upper ends of a pair of links

49

,

50

. The link

49

is pivotally connected at its lower end to the rear end of the first boom

45

and a lower end of link

50

is pivotally connected to the second boom

46

. The second boom

46

includes a hollow casing

51

and an extensible part

52

telescopically fitted in the hollow casing

51

. A log grapple

53

is pivotally connected to the extensible part

52

. A hydraulic actuator

54

has a cylinder end pivotally connected to the hollow casing

51

and has a rod end pivotally connected to the extensible part

52

.

Referring also to

FIGS. 2 and 3

, the traction wheels

21

,

22

are rotatably supported on the front ends of a pair of pendulum arms

61

,

62

and the rear ends of the pendulum arms

61

,

62

are pivotally supported on a pair of horizontal transverse axes

63

,

64

by a pair of carriers

66

,

67

. The carriers

66

,

67

are pivotally connected to the chassis

13

of the tractor

11

on a pair of vertical pivot axes

68

,

69

. The vertical swinging movement of the pendulum arm

61

about the axis

63

is controlled by a hydraulic actuator

71

having a cylinder end pivotally connected to the tractor chassis

13

and a rod end pivotally connected to the front end of the pendulum arm

61

. The vertical swinging movement of the pendulum arm

62

about the axis

64

is controlled by a hydraulic actuator

72

interconnected between the front end of the pendulum arm

62

and the tractor chassis

13

. The pendulum arm

61

is steered by operation of a hydraulic actuator

76

interconnected between the tractor chassis

13

and the carrier

66

and the pendulum arm

62

is steered by operation of a hydraulic actuator

77

interconnected between the tractor chassis

13

and the carrier

67

.

As shown in

FIG. 1

, the first log trailer

16

is carried on its left hand side, as viewed in the direction of travel, by the wheels

23

,

26

which are mounted, respectively, on steerable and vertically adjustable pendulum arms

81

,

82

. The pendulum arms

81

,

82

are supported on the chassis

14

of the first log trailer

16

in the same manner as the pendulum arms

61

,

62

are supported on the tractor chassis

13

. Vertical swinging movement of the pendulum arms

81

,

82

is controlled by a pair of hydraulic actuators

83

,

84

which have their cylinder ends pivotally connected to the first log trailer chassis

14

and their rod ends pivotally connected to pendulum arms

81

,

82

. The wheels

24

,

27

on the right hand side of the first log trailer

16

are positioned in transversely opposite relation to the wheels

23

,

26

and are mounted on steerable and vertically adjustable pendulum arms, not shown, in the same manner as the pendulum arms

61

,

62

. The carriers for the transversely opposite pendulum arms carrying the wheels

23

,

24

are steered by hydraulic actuators, not shown, in the same manner as the traction wheels

21

,

22

.

The wheels

26

,

27

are mounted on the chassis

14

of the first log trailer

16

in the same manner as the wheels

23

,

24

are mounted on the first log trailer

16

. In a similar manner, the second log trailer

31

is supported at its laterally opposite sides by the wheels

33

,

34

. As illustrated in

FIG. 1

, the wheel

33

is rotatably mounted on a pendulum arm

86

, the vertical swinging adjustment of which is controlled by a hydraulic actuator

87

interconnected between the chassis

32

and the pendulum arm

86

. The two sets of wheels

23

,

24

and

26

,

27

supporting the first log trailer

16

and the single set of wheels

33

,

34

supporting the second log trailer

31

are reverse images of the set of wheels

21

,

22

supporting the tractor

11

.

A hydraulic control system, not shown, is provided for the steering actuators which causes the trailing sections

16

,

31

of the log hauler to follow the steered path of the tractor

11

. An automatic control, not shown, adjusts the vertical swinging movement of the pendulum arms to keep the chassis of the log hauler sections level.

Industrial Applicability

A log hauler constructed in accordance with this invention is a multiple section vehicle which is capable of traveling over uneven terrain and through forest or wooded areas where tree harvesting operations are carried out. Heretofore, logging roads were built in the forests and wooded areas being harvested so that logging trucks, primarily of on-highway design, could be used to travel into the harvesting area to be loaded with logs assembled at a pick-up point by log skidders. Building roads is expensive and is detrimental to the environment because of the necessary ditches, cuts and fills. Road building activity causes soil erosion and makes reforestation more difficult in those areas disturbed by the road building activity. The log hauler of this invention minimizes the need for logging roads because it can safely travel over uneven terrain even when loaded and therefore it can travel to and load logs near the point where the trees are cut down in the harvesting operation. By loading the logs close to the point of tree cutting, there is reduced skidding or dragging of logs to a pick up point.

The ability to control the articulation of the vehicle sections and steer the support wheels

21

,

22

,

23

,

24

,

26

,

27

,

33

,

34

, permits the log hauler to move in a serpentine path through forests and cut over areas with stumps. When uneven terrain is encountered, an automatic leveling control adjusts the vertical position of the support wheels to compensate for the ground irregularity. Each section of the log hauler is provided with an automatic leveling control system to maintain the load center near a laterally centered position between its support wheels. The control system for steering and the control system for adjusting the vertical position of the support wheels are designed to operate at the same time, as is necessary when traveling in a winding path over uneven ground surface. The control system for vertically adjusting the support wheels also permits the vehicle sections to be raised when traveling over stumps or boulders during a tree harvesting operation.

The crane

44

is capable of loading logs on both log trailers

16

,

31

. The extensible boom

53

of the crane

44

allows the crane

44

to load logs on the second trailer

31

and extends the reach of the crane

44

for picking up logs and unloading logs.

Other aspects and features of the present invention can be obtained from a study of the drawings, the disclosure, and the appended claims.