B12

The base tractor is marked as Т12.6020, and the bulldozer-loosening assemblies as B12.6020. The tractor T12.6020 and the assemblies on its base are designed to perform the large volume of earth-moving operations at wide range of the ambient temperatures (±50° С) and to develop the various grounds including the frozen soils and rock as well as the grounds of increased humidity

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Considering the modes of T12 tractor use the technologies tested on the tractors T10M as well as the proprietary engineering of the tractor critical systems are applied in its design.

The implementation of the high traction efforts is ensured by the major modifications of the tractor running gear design. The track gauge is increased by 200 mm (2080 mm). It allows mounting the track shoes of 560 or 690 mm in width. The length of the ground contact area is increased up to 3182 mm due to mounting of the track bogies with seven road wheels on the friction bearings. If increasing the track gauge up to 2280 mm, a model of high maneuverability level (marsh-crawler) with the shoe size up to 900 mm can be produced on the same base.

The six-cylinder V-type diesel engine JAMZ-236B-4 is installed on this tractor. Its size is 130х140 mm; the rated power is 230 hp at 1800 rpm. The engine is equipped with the turbo-supercharging and the liquid-oil heat exchanger designed for oil cooling. The specific fuel consumption does not exceed 162 g/hp h; the relative oil consumption vs fuel consumption, burning loss is 0.5%. The engine is installed on the tractor frame on the shock absorbers. The fan of pushing type ensures the required temperature mode of the engine cooling liquid and of the transmission oil due to the return airflow. As a result the cooler clogging is decreased as well as the heat load on a cab during the summer season. If necessary, the straight flow fan impeller can be installed when operating during the cold seasons.

The tractors Т12 are equipped with the reverse hydraulic mechanical transmission (HMT) ensuring three forward gears (maximum traverse speed 3.42; 6.07 and 9.57 km/hour, respectively) and three reverse gears (maximum traverse speed 4.25; 7.54 and 11.87 km/hour). Three-wheeled torque converter with working diameter 410 and with transformation ratio increased up to 2.95 (against 2.2 of the tractor equipped with engine D-180) is assembled as a common body with the reduction gear ensuring the tractor system hydraulic pump drive as well as the independent power take-off to the various units (for instance, the pull winches).

The planetary five-series gearbox is joined to the torque converter driven shaft with the cardan and is fastened to the front wall of the steering clutch casing. The planetary gearbox design is the same as this one applied on the tractors Т10.

The power plant equipped with the engine JAMZ and with the new torque converter was tested on the industrial tractors T10M.

The theoretical (estimated) characteristic of a tractor is given below, in Figure. The characteristics of the motor-power plant elements are aligned so that the increased traction forces can be implemented at the first gear with high efficiency coefficient (the torque converter efficiency is no less than 0.8) when the required travel speeds are achieved during the bulldozer-loosening operations.

Theoretical traction-speed characteristic

The automatic adaptability of the power train to the outer loads in wide range of their values allows the operator not to shift the gears at the assembly travel performed at the I gear in most cases. This factor as well as booster control of the tractor and attached implements makes the operator working conditions easy, and ensures increasing of the assembly capacity.

The balancing beam is hinged to the bogies connecting them as a whole system increasing the reliability of the component parts and bogie balance pivots (Fig. 5 and 6).

zoom in a) Balancing beam	zoom in  b) Mounting of the final drive and the bogies
Fig.5 Suspension system and final drive

The reliability of final drives is increased. The bogie pumping relatively to the axles outrigger from the final drive area gave an opportunity to remove the bogie braces, to ensure the easy mounting and dismounting of the final drive as well as eliminated the load transfer from the attached implements when digging and displacing the grounds thereby increasing the reliability of these critical transmission units.

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a) track bogies	b) bogie pumping axle
Fig. 6

The final drives are designed as the independent unit (module) that can be installed as a whole on the tractor frame.
These are the two-stage mechanisms: the first stage - cylindrical pair of pinions, the second one - planetary row. The final drive ratio increased up to 19.63 (Т10 tractors - 14.79) allows increasing the traction force at significant load decrease affecting all elements of power train (including the steering clutches and the brakes, the bevel drives, etc). Replacement of the driving wheels together with the sectors in case of their wear-out does not require the tractor disassembling.

The unit sealing is ensured with the self-tightening washers Duo Cone (the seals of the same type are applied in the rollers and the idlers of running gear).

The various changes in all tractor units and systems aimed to ensure the high vehicle reliability were made.

The cab equipped with the emergency and ventilation hatchway was modernized according to the up-to-date tendencies aimed to ensure the comfort operation conditions, i.e. to achieve the maximum capacity of operator for work together with his minimal tiredness. The operator seat is comfortable and safety due to ROPS/FOPS and safety belt as well as to the control levers with easy access. The harmful substance content in a cab is minimized according to the state standards due to the engine and cab installation on the shock absorbers, to the cab tightness, to the use of a heater fan, conditioner, heat-and-noise insulating mat and wall panels.

The tractors are designed with two types of bulldozer equipment: semispherical (Е) and straight blade (В). Two types of rippers can be installed: three-toothed (Р) and single-toothed ripper (Н).

The laboratory and field tests carried out with the tractors B12 discovered a high productivity of new machines during the development and displacement of various grounds.

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The B12 tractor during the rock loosening operations