CA1334368C

CA1334368C - Steering effort and responsiveness adjustment

Info

Publication number: CA1334368C
Application number: CA000616715A
Authority: CA
Inventors: David Roy Holm
Original assignee: Deere and Co
Current assignee: Deere and Co
Priority date: 1988-07-29
Filing date: 1993-09-09
Publication date: 1995-02-14
Anticipated expiration: 2009-07-06
Also published as: CA1335421C; CA1334369C; CA1334816C; CA1335422C; CA1336105C

Abstract

A tractor steering system includes a pitman arm coupled to an output shaft emanating from a steering gear box into which a steering wheel operated input shaft extends. The pitman arm has inner and outer points of connection, as considered relative to the output shaft and a steering drag link is selectively coupled to the pitman arm at the inner point of connection when it is desired that steering effort be minimized and is selectively coupled to the pitman arm at the outer point of connection when it is desired that steering responsiveness be maximized.

Description

~ 8TEERING FFFORT AND RE8PON8IVENE88 ADJU8T~FNT
Related Application This is a divisional of Canadian application Serial Number 604,977 filed on 06 July 1989.
Backqround of the Invention The typical tractor steering system includes a gear box having an input shaft coupled for being driven by the tractor steering wheel and having output shaft which is coupled to the steering linkage by a pitman arm. The effective length of the pitman arm determines how much effort must be used in turning the steering wheel in a given situation and determines steering responsiveness, i.e., how many turns lock-to-lock of the steering wheel are required to move the wheels between maximum right-hand and left-hand turning positions. Usually, the effective length of the pitman arm is a fixed length chosen as a compromise between that length which would be most desirable for operations where the steerable front wheels are heavily loaded and considerable turning resistance must be overcome, as when a snowblower is mounted to the tractor, for example, and that length which would be most desirable for operations where the tractor must be quickly turned, as when a mower is mounted to the tractor, for example.
Summary of the Invention According to the present invention, there is provided an improved tractor steering system.
A broad object of the invention is to provide a tractor steering system incorporating a simple mech~n;sm which may be selectively adjusted for minimizing steering effort when considerable weight is being carried by the steerable wheels or for maximizing steering responsiveness when quick maneuverability of the tractor is desired.
A more specific object of the invention is to provide a steering system incorporating a pitman arm having its effective length adjustable, whereby steering effort is at a minimum when the pitman arm is at its shortest effective length and steering responsiveness is at its maximum when the pitman arm is at its longest effective length.

` A

~ A still more specific object of the invention is to provide a steering system having a pitman arm, as described in the immediately pr~c~;ng object, wherein the pitman arm is provided with at least two connecting points for selective connection to a drag link with one of the two connection points resulting in the effective length of the pitman arm being longer when the drag link is connected thereto as compared to its effective length when the drag link is connected to the other connection point.
These and other objects will become apparent from a reading of the ensuing description together with the appended drawings.
Brief Description of the Drawings FIG. 1 is a right front perspective view of a lawn and garden tractor of the type with which the present invention is particularly adapted for use.
FIG. 2 is a left rear perspective view of a lawn and garden tractor, shown in phantom lines, incorporating a steering system embodying the present invention.
FIGS. 3 and 4 are right side and rear views respectively of the steering pitman arm shown in FIG. 2.
Descri~tion of the Preferred Embodiment Referring now to FIG. 1, therein is shown a lawn and garden tractor 20 including a longitudinally extending main frame 22 including right and left side frame members 24 and 26, respectively. A front axle 28 is coupled to central location of a front frame member (not shown) by a pin defining a fore-and-aft pivot axis about which the axle is free to oscillate. Coupled to the axle 28, in a manner described below, are a front pair of steerable wheels 30 and 32. The rear end of the frame 22 is supported on a rear pair of drive wheels 46 and 48. An engine (not shown) is supported on a forward portion of the frame 22 in a compartment defined in part by a hood 50. Mounted to the frame 22 rearwardly of the hood 50 is a combined operator platform and fender deck structure 68. A seat assembly 76 is mounted to the structure 68 so as to position an operator within easy reach of a ` A

~ steering wheel 38 located forwardly of the seat and forming part of a steering system 36 (FIG. 2).
Referring now also to FIGS. 2, 3 and 4, it can be seen that the front axle 28 has upright cylindrical receptacles 174 fixed to its opposite ends and that the steering system 36 includes a pair of L-shaped spindles 176 having upright portions swivelly received in the receptacles. The front wheels 30 and 32 are respectively mounted to out-turned portions of the spindles 176. Left and right arms 180 and 181 are respectively fixed to the respective upright portions of the spindles 176 at locations below the receptacles 174, the arms 180 and 181 being interconnected by a tie rod 184 and limited in their turning movement by stop blocks 249 fixed to the underside of the axle 28. A steering control arm 186 is fixed to an upper end of the upright portion of the left spindle 176. A drag link 190 has a forward end connected to the arm 186 by a ball joint connector 191 and has a rearward end connected to a lower end of a pitman arm 192 having an upper end fixed, as at 246, to an output shaft of a conventional steering gear box 188. An input shaft 194 extends into the gear box 188 and has an upper end universally coupled, as at 198, to a lower end of a steering column 200 having the steering wheel 38 fixed to the upper end thereof.
It will be appreciated that steering is accomplished in the usual way by turning the steering wheel 38 one way or the other for steering the wheels 30 and 32 within a range of movement determined by the stop blocks 249, with lock-to-lock movement of the steering wheel corresponding to that for moving the wheels 30 and 32 between maximum right- and left-turn positions.
The amount of turning resistance of the wheels 30 and 32 is dependent upon the weight carried by the wheels and thus may change when different implements are mounted on the vehicle. For example, considerably more weight is carried by the wheels when a snowblower is mounted to the forward end of the tractor than when a mower is mounted to the midsection of the tractor. Therefore, it is desirable to have a steering A

~ system which will require only a reasonable amount of effort to be exerted when operating a snowblower, for example. On the other hand, mowing operations are normally done at higher speeds than snowblowing operations and in areas containing more obstacles than areas where snowblowing is done.
Therefore, it is desirable to have a steering system which will be responsive so that the tractor may be quickly maneuvered during mowing operations.
For the purpose of optimizing the steering effort when operating a snowblower, for example, and the steering responsiveness when operating a mower, for example, the effective length or radius arm of the pitman arm 192 is made adjustable. Specifically, with respect to the connection 246, the arm 192 is provided with inner and outer points of connection 240 and 242, respectively. The inner connection 240 is connected to the drag link 190 when it is desired that the effort be optimized while the outer connection 242 is connected to the drag link when it is desired that the responsiveness be optimized. It is noted that with one arrangement of the invention, the steering wheel 36 required 3.0 turns lock-to-lock when using the shorter effective length of the pitman arm 192 and 2.25 turns lock-to-lock when using the longer effective length of the pitman arm.

Claims

1. In a steering system including a steering wheel coupled to a shaft connected to an input shaft projecting into a steering gear box and a pitman arm having one end connected to an output shaft, emanating from said steering gear box, and having another end coupled to a steering drag link, the improvement comprising: said pitman arm, with respect to the output shaft, having inner and outer points of connection for optional connection to said drag link, with the inner point being selected when it is desired that effort be minimized and with the outer point being selected when it is desired that responsiveness be maximized.

2. The steering system defined in claim 1 wherein said inner and outer points of connection are spaced apart approximately 23.5 millimeters.

3. The steering system defined in claim 1 wherein said outer point of connection is formed in said pitman arm such that said steering wheel has 2.25 turns lock-to-lock when the drag link is coupled to said outer point of connection.

4. The steering system defined in claim 1 wherein said outer point of connection is formed in said pitman arm such that said steering wheel turns 3.0 turns lock-to-lock when the drag link is coupled to said inner point of connection.