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New level of seat performance: A comfort solution to the many hours of field harvest.

Agricultural demands for higher productivity with lower operating costs have resulted in faster transport and field operating speeds. Operators are spending more hours in the field during peak harvest seasons. Under these conditions, operator comfort and health is essential for safe operation.

The John Deere Active Seat[TM] offers a solution to help meet these challenges by unsurpassed isolation performance. Vertical vibration inputs are reduced to levels never before achieved with traditional suspension solutions. This seat is capable of isolating up to 90 percent of vertical inputs typically seen in tractors equipped with pneumatic tires.

With operator comfort being one of the most sought-after features in large agricultural tractors, the active seat was developed with comfort (fatigue reduction) and productivity (increased operating speeds) in mind.

A shared technical approach

The John Deere Active Seat[TM] was the result of a three-year, joint development by John Deere, Sears Mfg. and Parker Hannifin. While the design team consisted of a core engineering group, all facets of engineering, manufacturing and quality from each corporation were committed to the development.

The approach taken was to develop an advanced seat suspension that would target the dominant vertical inputs typically seen in agricultural tractors on pneumatic tires.

According to International Standards Organization (ISO) 5007 (Agricultural Wheeled Tractors-Operator's Seat-Laboratory Measurement of Transmitted Vibration, First Edition, 01 Jan 1990), the power spectral density (PSD) of vertical cab floor accelerations for Class 3 agricultural tractors can be seen in Figure 1.

From this figure, the majority of vertical input frequencies fall between 1 and 4 hertz with a dominant frequency of approximately 2.2 hertz. The spectral density of vertical inputs is relatively consistent for typical weights, ballast and tire configurations for tractors in this class. Development of a fully active suspension system allowed for the system to be tuned for these input frequencies while utilizing the tractor's hydraulic and electronic communication systems.

The electro-hydraulic active control system minimizes vertical seat top acceleration by sensing vertical tractor inputs and actively positioning the seat top to cancel those inputs. This results in a significantly smoother ride for the operator.

The system utilizes a proven scissors mechanism that incorporates a hydraulic actuator working in parallel with an air spring. The purpose of the air spring is to support the suspended mass (i.e. operator and seat top) while the electro-hydraulic actuator dynamically positions the seat. (See Resource cover art for suspension cutaway).

This seat utilizes an electro-hydraulic control system to control vertical seat top movement. Control of seat top position is accomplished by a hydraulic cylinder connected to an electro-hydraulic control valve assembly. A digital controller processes inputs from two sensors: a position sensor and an accelerometer. The accelerometer, mounted to the suspended seat top, measures seat top acceleration. The position sensor, mounted at the scissors hinge, measures vertical seat top position. These two signals are received by the electronic controller at 200 times per second. Based on these signals, a control algorithm determines the proper valve command needed to control vertical seat movement such that the vertical acceleration at the seat top is driven to zero.

The actuator receives oil from the tractor's hydraulic system through a control valve assembly which regulates oil pressure and controls oil flow to the actuator. Commands to the flow control valve are updated every 5 milliseconds allowing active cancellation of the vertical tractor inputs with minimal phase lag (i.e. instantaneous isolation). The hydraulic actuator ultimately controls vertical seat top position. System circuitry is shown in Figure 2.

An auxiliary air reservoir is incorporated into the air system. This increase in air volume allows for a lower spring rate in the suspension and reduces the overall actuation forces required by the hydraulic actuator. Thus, hydraulic energy requirements from the vehicle are minimized.

The active seat utilizes many of the same features as the John Deere ComfortCommand[TM] air seat: swivel, fore/aft and lateral isolation, lumbar, backrest tilt and fore/aft adjustment. The operator has two basic controls specific to the active control system: a height control switch allows the operator to adjust seat height and a ride firmness control switch allows the operator to adjust to three levels of isolation performance to suit operator preference for given operating conditions.

The John Deere Active Seat[TM] incorporates many innovative applications of existing technologies used in the industrial, mobile and automotive industries. The components for the system (i.e. valves, accelerometer, position sensor, actuator) were designed specifically for this application to meet functional and reliability demands.

Static and dynamic modeling analysis of structures, linkages and new components were performed. Analysis techniques included finite element analysis, kinematics analysis of linkages, dynamic modeling analysis of hydraulic systems, rapid controller prototyping, dynamic modeling of the electronic control system, static and dynamic stress tests, dynamic ride analysis and extensive lab testing to prove durability of the system.

Results

Conventional seat suspension systems on the market today have many limitations regarding proper isolation over all input frequencies on wheel vehicles. The active seat targets maximum isolation at the dominant input frequencies, isolating the operator from up to 90 percent of the vertical inputs in typical tractor applications.

The active suspension operates effectively at all required working speeds and applications. In addition to providing normal seat adjustments, automatic air system adjustment allows seat performance to be independent of operator weight.

Figure 3 illustrates the relative performance improvement the active seat can provide when compared to a conventional, standard air suspension seat.

These ISO standardized test results show that the active seat reduces vertical weighted RMS accelerations by 66 percent relative to typical air seat suspensions, and isolates the operator from 75 percent of the vertical weighted RMS inputs at the cab floor. These reduced acceleration levels provide the operator with increased comfort enabling more hours in the field and increasing productivity with increased field speeds.

Field data shows that in tractor applications where operating speed is not limited by the implement design, the active seat can allow for increased field speeds of 15 to 20 percent. Therefore, farmers' and machinery contractors' essential need for increasing overall work output with lower operating costs can be met.

The John Deere Active Seat[TM] is an industry first innovation which provides new levels of suspension performance unparalleled by conventional seat suspension systems. Careful execution of existing and innovative technologies have allowed this system to be viably engineered, manufactured and valued by the end customer.

[FIGURE 1 OMITTED]
Figure 3

Seat Performance Comparison

(84 kg Operator - AG 3 Input)

 Weighted RMS
 Acceleration
 ([m/s.sup.^]2)

Cab input 1.30
Typical Air Suspension 1.05
Active Suspension 0.35

Note: Table made from bar graph


ASAE member Daniel L. Dutner is a senior engineer (319-292-8001, DufnerDanielL@JohnDeere.com) and Troy E. Schick is a staff scientist (319-292-8095, SchickTroyE@JohnDeere.com) at John Deere Waterloo Works, Waterloo, IA 50701, USA.
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Title Annotation:John Deere Active Seat
Author:Dufner, Daniel L.; Schick, Troy E.
Publication:Resource: Engineering & Technology for a Sustainable World
Geographic Code:1USA
Date:Dec 1, 2002
Words:1144
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