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Operations involving excavation of bedrock in large-scale civil engineering projects, or quarrying works for limestone or crushed rock can be broadly divided into two methods: blasting, and excavation using mechanical power. Ripping operation using bulldozers is typical example of the second method, and this method is superior because it is safe and does not cause pollutions. For this reason, its applicable range is being expanded including areas where the blasting method was being used. However, ripping operation using bulldozers demands a high level of training from the operator, and in addition to this, shoe slippage causes premature wear of the undercarriage and low fuel economy. The shoe slip control system that we have developed carries out sensing of the acceleration of the machine in forward and reverse directions, and sensing of the input / output speed of the torque converter, and in this way it always knows the traction and the slip ratio of the machine.

A higher versatility is required from medium size bulldozers as vehicles other than large size bulldozers. Therefore the design concept of the transmission for medium size bulldozers has to be changed to that of large size bulldozers. We adopted combination of high capacity torque convertor and low reduction (high output speed) cross ratio gear train for medium size bulldozers' transmission. We also evaluated the advantages and disadvantages of rotating clutches, and decided not to use the rotating clutches in new transmission for medium size bulldozers, because of their disadvantages. By these design concepts and material technology, we can reduce the transmission size and improve the efficiency.

A new transmission control system which realizes almost the same high level of operability as of a TORQFLOW (T/F) transmission (see Note 1) has been developed and introduced on an efficient HYDROSHIFT (H/S) transmission (see Note 2) for bulldozers. To develop the system, comparison and evaluation were made between H/S transmission machines without torque converter and T/F transmission machines with torque converter to ascertain the advantages and disadvantages of H/S transmission machines. As a result, the disadvantages inherent to H/S transmission machines, such as poor shifting characteristics, fine travel characteristics at low travel speed, and anti engine-stall characteristics were solved by electronically and synthetically controlling all clutches including those incorporated into the steering brake system, without sacrificing any advantages.

Of all the parts used on crawler-type construction equipment, the track bushings in the undercarriage of large bulldozers are subjected to particularly severe load conditions. A new and innovative heat treatment technology has been developed in order to improve the durability of these bushings from the point of their wear and fatigue crack characteristics. A new steel material has also been specified to match this heat treatment technology. The bushings thus developed have been extensively tested on bulldozers in customer service and proved to be successfully applied for production. They also offer a possibility for considerable reduction in manufacturing cost.

Conventional medium to large-sized bulldozers have a powertrain comprised of a manually operated powershift transmission connected in series with a torque converter. There is a growing need, however, for a power train that is more efficient and easy to operate, thereby increasing bulldozer productivity. One answer to this growing demand is the hydromechanical transmission (HMT) developed by Komatsu for medium to large-sized bulldozers. The HMT consists of a powershift transmission combined in parallel with a hydrostatic transmission (HST) featuring a pair of hydraulic units. The HMT has a continuously variable shifting ratio and achieves high efficiency and automatic shifting. Additionally, it has an electronic controller that controls the transmission ratio to maintain engine speed at the maximum power point. As a result, bulldozers with the HMT demonstrate greatly improved productivity over bulldozers with the conventional powertrain.

KOMATSU has successfully developed and marketed the HYPER GX series computer-controlled, intelligent hydraulic excavators. The development concepts of the HYPER GX series are as follows: 1. To improve safety at construction sites by use of measuring functions which reduce the number of ancillary workers. 2. To improve working environment and the quality of work by use of automatic functions which reduce operator fatigue and time required to complete a job. 3. To solve the problem of shortage of experienced workers by the use of operator support functions which allow easy operation even for inexperienced or older operators. Representative of these is the fully automatic grading function, with which the movement of boom, arm and bucket is computer-controlled to enable automatic excavation at a predetermined gradient.

As a direct result of the mining industries need to improve efficiency and production in open pit type operations, the size of dump trucks has increased. In addition, the increase in vertical lift and resultant grades, and the in crease in hauling distances are making the demand for mechanical drive dump trucks. With these mining requirements, we have developed the mechanical automatic transmission, controlled by microprocessor, with 8 forward speeds and 1 reverse speed, which suit 120 mton class dump trucks and 160 mton class dump trucks. This paper shows the design concept and progress made in development of these transmissions.

Torqflow transmission, which is composed of planetary gear mechanism, multiple disk clutches and a hydraulic control unit, has been adapted for Construction Machine because it allows an easy selection of speeds (forward or reverse). Recently a rubber facing material with high coefficient friction has been used disk clutch's facing parts for compact design. Meanwhile, it's heat conduction is inferior to metalic disk to be usually used, so at engage time temperature of rubber facing disk is higher than metalic and it's ablasive wear ratio, which is verified to have influence on facing temperature by experiments, is increased far more than before. Therefore prediction of facing temperature has been more important than before. Now, in this report, study on transient thermal analysis is introduced because it's accuracy has come to practical level.

After new transmission lubricants are developed there is an extensive validation program where friction durability testing is performed on multiple clutch materials. Each durability test can run for long terms and the entire validation program can take much longer terms. A well designed lubricant and friction material will deliver the necessary friction control for construction equipment to operate at optimum level. A mechanistic construct has been evaluated to calculate friction durability in clutch systems based on fluid and surface tribological properties. Fluid properties include both boundary frictional and rheological effects. Surface properties include elastic modulus, surface roughness, asperity density and asperity tip radius. Using this mechanistic construct friction durability has been predicted.