06-11-2012, 11:47 AM
EFFECTS OF MULTI.MODE FOUR.WHEEL STEERING ON SPRAYER MACHINE PERFORMANCE
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ABSTRACT.
A self.propelled agricultural sprayer with four.wheel steering (4WS) was developed. A digital controller was designed
and built to control the rear steering angle based on that of the front wheels through electrohydraulic control valves. Three
modes of steering were enabled and investigated. Experimental methods were developed to determine what potential 4WS has
in improving machine performance. In particular, machine performance of the sprayer was evaluated by measuring turning
radius and performance metrics in headland turning and lateral path shift procedures. Coordinated 4WS resulted in smaller
turning radii than conventional two.wheel steering (2WS). In the headland turning tests, significant mean increases in aligning
distance of 5.58 m and significant mean decreases in rear wheel off.tracking area of 9.3 m2 were observed in 4WS over 2WS.
In lateral path correction tests, crab 4WS substantially decreased the area and magnitude of estimated application errors over
conventional 2WS, while coordinated 4WS resulted in increased application errors. These results provide evidence that 4WS
could enable improvement in sprayer machine performance.
386 TRANSACTIONS OF THE ASAE
The application of 4WS to road vehicles has been studied
since the mid.1980s as a means to provide better handling and
stability (Crolla, 1996). In 1985, Nissan introduced the first
practical 4WS system in a passenger car (Irie and Kuroki,
1990). In addition, 4WS has been implemented on automobiles
to improve low.speed maneuverability. Delphi¡¯s Quadrasteer
4WS, for example, reduces the turning radius of an
SUV or pickup truck by 20% (Holt, 2001). Adachi et al. (1991)
developed 4WS control strategies to improve low.speed
maneuverability with the objective of reducing turning radius
and rear end swing out. Driving test results showed that an
18% reduction in turning radius with only a 14% increase in
rear end swing out could be achieved with 4WS operating
under a front.end path memorizing control method. Watanabe
and Katoh¡¯s (1990) study of low.speed 4WS maneuverability
showed performance advantages in several performance
metrics. While off.road vehicles typically have operating
conditions and functional objectives that differ from those of
automobiles, these results indicate that 4WS has potential to
improve low.speed maneuverability in agricultural vehicles.
In addition, they provide inspiration for how to experimentally
measure performance.
METHODS
4WS CONTROLLER DESIGN
Control Valves and Sensor Hardware
The self.propelled sprayer used for this work was modified
from the production unit (model 4710, Deere and Co., Moline,
Ill.), which has hydraulic 2WS. The modified sprayer had a
rear axle with steerable wheels, hydraulic steering cylinders,
and non.contact rotary potentiometer sensors to measure the
steering angle at the front and back. The sensors were
calibrated to relate sensor voltage output to steering angle.
Two electrohydraulic proportional control valves (PVG 32,
Sauer Danfoss, Ames, Iowa) were added to the sprayer and
were controlled with an analog voltage signal. The valve for
the front wheels could be actuated electronically or by
hydraulic pilot pressure provided by the steering unit at the
steering wheel. For this research, the front wheels were
controlled hydraulically by the steering unit, and the rear
wheels were controlled electronically. The PVG 32 valves had
a linear response with pressure compensation and a narrow
deadband region, which eliminated many of the problems with
valves used in previous work (Qui et al., 1999).