HST contributes to award-winning design

Deere's 700H tractor capturing the prestigious Red Dot Award, leaves its competitors green with envy.

Deere's 700H captured the prestigious Red Dot Desgin Award, in part, because of its dual-path hydrostatic propulsion drive.

Jim Manor, engineering manager, crawlers, of John Deere's Construction and Forestry (C&F) Division, explains that the hydraulic system on the 700H tractor is really two separate systems. "The transmission is a dual-path hydrostatic (HST) system, which has a hydraulic motor mounted to each the two final drives. This was a key consideration in our capturing the Red Dot Award." (See description on page 46.)

In fact, on the website for the awards program, www.red-dot-world.com, the hydraulic system tops the list of design innovations for the 700H: "The new John Deere 700H Crawler has many new design features and innovations. The manual gearbox has been replaced with hydrostatic motors mounted directly to the final drive. This allows the operator to control all directional and speed commands with a single joystick."

Marjorie Ballina, supervisor, crawler powertrain, also with Deere's C&F division, further explains, "The propulsion drive is an electronically controlled, dual-path hydrostatic transmission system with two separate pump-motor sets. Each set independently drives each track. This not only provides a wide versatility of control, but enables us to maximize productivity and fuel economy." She says this is the same concept used on Deere's successful C-series dozers, loaders, and H-series crawler dozers sized less than 100 hp.

Controlling the transmission

Ballina continues, "An electronic transmission control unit (TCU) is used to take full advantage of the versatility of independent track drive. Mounted in the operator's station, the TCU is a Sauer-Danfoss S2X micro controller. All operator control inputs use familiar automotive-style Halleffect sensors. Three independent control loops in the dual-path hydrostatic system also rely on the Hall-effect sensors for feedback: speed, tracking/steering, and power management.

A key innovation to Deere 700H crawler tractor is its dual-path hydrostatic drive, which drives each track thorugh a separate hydrostatic transmission. This allows the operator to control all directional and speed commands with a single joystick.

"During vehicle calibration, the TCU determines controller output to each track for a given speed command. In doing so, it allows for power turns, pivot turns, and counter-rotate turns. For tracking and steering, track speed is monitored through a speed pickup in each motor. The TCU automatically adjusts left and right speed commands to maintain straight-ahead travel or a constant turning radius — whatever is commanded by operator." The 700H can achieve a top speed of 6 mph, with an optional maximum of 6.8 mph.

Power management plays an important role not only in performance and productivity, but in fuel consumption and to prevent stalling the engine. To accomplish this, actual engine speed is monitored via a speed pickup in the tandem pump. Engine speed command is monitored by a position sensor mounted to the accelerator pedal. If the engine speed feedback signal drops below a parameter based on the command feedback signal, the TCU controls pumps and motors to reduce the hydraulic load, thereby preventing engine stall.

The power train

The 700H is powered by a John Deere 6068T turbocharged six-cylinder diesel engine, which produces 115 net hp at 2100 rpm. Pumps are mounted directly to the engine's flywheel housing as a tandem unit. They are coupled to the engine by a torsional damping coupling. Displacement of each of the two axial-piston HST pumps ( Sauer Danfoss Series 90 with 75-cc displacement) is controlled electronically.

Ballina explains that a two-stage electrohydraulic pump displacement control uses mechanical feedback to establish closed-loop control of each pump's swashplate angle. Each HST pump is fitted with a gerotor style pump to provide pilot pressure for swashplate angle (displacement) control and to provide charge pressure for preventing cavitation of the HST pump.

System relief pressure is set at 440 bar (6400 psi).). Each pump has its own system forward and reverse relief. A single neutral charge relief valve serves both HST pumps. Each track is driven by a 160-cc Sauer-Danfoss Series 51 bent-axis piston motor. Each of these two HST motors is mounted to a final drive with integral disc brakes and a 33:1 gear reduction. Each motor contains a Hall-effect speed pickup for sensing track speed and direction.

Data communications
As with any of today's sophisticated construction equipment, data transmission has become a necessity for preventive maintenance, fault diagnosis, and productivity monitoring, and quality control. To this end, the 700H is equipped with an alpha-numeric module. With this module, a service technician can:
perform a calibration routine that accounts for normal component variability,
customize machine responses, such as speed limiting or to optimize performance or sensitiviy for individual operator preferences,
access service codes (all hydrostatic transmission system wiring and electric component faults generate individual service codes), and
diagnose operating conditions, such as live and calibrated values for engine, pump, and motor speeds, control currents, and operator control sensor values.

The 700H also has an RS-232 interface, which is especially valuable in the engineering development phase. Through this interface, technicians can:
upgrade application software
conduct real-time data logging,
completely customize machine responses, and
access WebGPI (interface software from Sauer-Danfoss) to monitor and control specific characteristic of pump operation.

Importance of light weight

Light weight often is not perceived as an attribute of construction equipment. After all, these machines fall under the general category of heavy equipment. But light weight does have its advantages with construction equipment. First, because machines must be carried by truck to the work site, lighter weight translates to lower fuel consumption when transporting equipment to the construction site. Second, ground compaction is an important issue at many construction sites. Compacted earth resists penetration of rain water into the soil, so rain water instead flows on the surface. This runoff promotes erosion and lowers the water, both of which continue to be environmental concerns.

The 700H ranges in weight anywhere from 26,000 to 28,000 lb, dependingon options. Ballina says that "because its transmission generates a drawbar pull of 40,600 lb, the 700H has a pull-to-weight ratio of about 1.6. This ratio is important because it allows buyers to compare drawbar pull between two machines with the same weight. For two machines of the same weight, the one with the higher ratio will have a greater drawbar pull. This ratio gives potential buyers an easy benchmark for comparison."

Hydraulics for implements

Donaldson's HMK04 hydraulic filter provides Deere's 700H with the ease of spin-on installation with high pressure capability to withstand pressure spikes.

Jeff Bauer, hydraulics engineer with Deere's C&F division, offers that the 700H's hydraulic system for driving implements does not break new ground as far componentry goes. "Primary control is provided by a Husco 6000 series open-center valve, and power is supplied by a Parker Hannifin 330 standard gear pump. This pump delivers 25 gpm at a maximum pressure of 3200 psi with the engine running at 2100 rpm. If the customer wants the optional winch drive, we specify Parker's 350 drive-through gear pump.

"To produce a blade control system that outperforms the competition, we borrowed our patented blade control linkage from our model 450H. We've also had great success with the Donaldson HMK04 hydraulic filters on our 400H, 500H and 650H machines, so we stuck with those. And rounding out the implement system is a pair of our own Series 120 cylinders."

Bauer continues, "The only thing that makes the implement hydraulic system stand apart is attention to detail. We created a valve development process during the tail end of designing the 650H. This process established detailed steps to follow to end up with a valve that met all the metering constraints with minimal iterations. Much work was done up front to benchmark our competition and establish metering goals, which was the most important step in the process. Based on this success, we rfelied on the same process for the 700H."

Red Dot Award: the best in international design

The Red Dot design award is one of the leading international design competitions. Its label is hotly contested; its jury, recognized experts. Its winners are welcomed into the Red Dot Design Museum, and its award ceremony attracts over 1200 guests from design, industry, politics and culture to Essen, Germany each year.

Since 1955, the Design Zentrum Nordrhein Westfalen has highlighted internationally outstanding product design with its famous Dot. In 2000, Design Innovations, as the competition was previously called, received a new, international name: Red Dot Award: Product Design. Manufacturers and designers of a broad range of industrial products compete for the prestigious Red Dot Award in 11 product groups all the year round. And the competition is growing every year.

Designworks is the graphics and styling consultant for John Deere's Construction and Forestry Division. They submitted the 700H to the Red Dot design competition. Greg Brew of Designworks, explained, "In our eyes, capturing the Red Dot will allow Deere to truly declare their industrial design as world class. They can feel comfortable in overseas markets, knowing that their basic design need not need be altered to be accepted in all their markets. Understanding what the brand and design stand for is fundamental to the translation of the brand in the world market. But having proof of this — in the form of a prestigious international award — should allow Deere to pursue other elements of their strategy and be comfortable with the international acceptance of their brand efforts.