When Bobcat Co. developed its Toolcat 5600 utility vehicle (see January 2003 Diesel Progress), it essentially created a new class of utility vehicle. As part of the development of the Toolcat, Comer Industries said its hydromechanical transmission technology moved to a new level as well.
The Comer system developed for the Toolcat incorporated a double steering axle with hydraulic motor and integral brake, integrating hydraulic, mechanical and electronic technologies from the initial design engineering stage. This approach, said Comer, reduced prototyping lead-time and subsequent time to production.
Designed for optimum vehicle traction, the load-bearing differential axles are assembled on the front and rear of the machine. A Kubota 2203 diesel engine delivers power to each axle via two separate hydrostatic transmissions.
Two independent 28 cc/rev Bosch Rexroth axial piston hydraulic pumps drive Comer two-speed axial piston hydraulic motors flanged to the differential axles. At this point, through a reduction gear unit, the power demanded by the vehicle is transmitted to the wheels.
In addition, each axle is equipped with two sensors that, interfaced with the vehicle's electronic control unit, are used to measure the speed of the vehicle and the vehicle steering angle.
Using hydrostatic transmissions, Comer said, provides the Toolcat with infinite transmission ratios and a simplified machine layout that reduces overall vehicle size as well as lowering the weight.
One of the keys to the Toolcat was to develop a vehicle with maximum versatility while ensuring ease of use in a range of applications in the agricultural and industrial markets. Towards these ends, Comer said the use of hydrostatic transmissions has helped improve the productivity and enhance the comfort of the Toolcat leading to the versatility Bobcat desired.
The Bobcat Toolcat also features considerably improved steering performance, Comer said. Steering is power assisted by means of a steering unit connected to the steering wheel. That assembly interfaces with the axle through a cylinder mounted on the axle and hinged at the two ends of the stem with the wheel hubs.
In the cruise control mode, the operator can drive the vehicle with a multifunctional joystick installed on the control panel. Two steering sensors mounted on the axle can be used to control the machine.
As a result, with an electronic steering sensor and the double hydrostatic transmission on both axles, the vehicle theoretically can make an infinite number of steering turns. In fact, an electronic control unit can be used to preset machine trajectories or correct them during operation.
Braking is provided by a series of discs in an oil bath fitted directly on the shaft of the hydraulic motor inside the axle. This, Comer said, was a major part of developing the compact design.
One other interesting feature of the Comer system is an automotive option that allows the vehicle to be operated as if it were equipped with automatic transmission. The automotive digital control unit continuously controls the pump and hydraulic motor displacement ratio proportional to the speed of the engine.
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