| The bulldozer is the main type of the engineering machinery products, it can find wide application in mine, water conservancy, construction, highway, harbor and national defence engineering, it is used for excavating the riverbed, piling up the dune, constructing the roadbed by means of piling up, backfilling the ditch, leveling the road, loosening the uncultivated land, removing the roadblock, aiding the scraping operation, etc..The bulldozer is the circulating operation machinery, its operation circumstances are adverse, the driver needs adjusting the position of the operating device continuously and frequently changing the speed of the bulldozer, changing the running direction in the process of operation. At present, the concentrated linkage bar part and flexible shaft control mechanism are mostly adopted for the steering & braking system of the bulldozer produced at home and abroad, gear-shifting, steering and braking controls of the bulldozer are performed on the control lever in a concentrated way. This structure needs more control lever parts and the operating force is greater, this case can divert the driver's attention on the occasion of frequent steering and braking and affect the operation quality, the labor intensity is higher, the system reliability is lower as well. Space inside the driver's cab of the bulldozer is narrow and the highlighted contradiction between the simplified structure and proper arrangement of each control lever exists. In addition, the mechanical drive and hydraulic drive are mainly adopted for current steering & braking system of the bulldozer. Whichever type is adopted, it is necessary to adjust each linkage, adjusting bolt etc. relating to the steering & braking system. In case the dimension can't conform to the requirement or the adjustment is not proper, the steering & braking system will be out of order. All levers will be worn out as well due to relative movement for a long period of time, this disadvantage will lead to abnormal dimensions, and thus cause the steering & braking system to be out of order.In order to maintain the advanced level in the bulldozer industry at home and enhance the operating performance, reliability, serviceability, repairability and the automation level of the bulldozer as well, the original steering & braking control system of the bulldozer has been improved, the single-handle steering & braking control system of the bulldozer has been developed.The electrical & hydraulic proportion control is adopted for this system, its design train of thought is: control the handle to send out the pulse width modulation (PWM) electrical signal being proportional to the angle according to magnitude and direction of the angle for the handle, the single-chip device will receive this signal and conduct operation, amplification and the logic judgment to control the pressure signal of the electrical & hydraulic proportional valve, then control the correspondent steering & braking oil cylinder via the change-over valve and finally control the actuator to drive rotation of the crank arm for the steering & braking valve to fulfill steering and braking.The electrical & hydraulic proportion control scheme is: the control handle inside the driver's cab is connected with the electrical & hydraulic proportion control valve placed on the cross beam via the wire by means of the electrical & hydraulic proportion control, the proportion control valve is connected with the control oil cylinder via the oil pipe, all connections are of flexible type. This scheme makes it be very easy to design and arrange the driver's cab. Meanwhile, the force to operate the handle is less, and thus the driver's labor intensity is greatly reduced. In addition, steering & braking control process is controlled by the single-chip device, and thus its control feature can conveniently be changed by changing the control program. Because of adoption of the computerized control, the uncontrolled areas caused by the clearance between the linkage bars in the traditional scheme of mechanical scheme can completely eliminated, so the control accuracy and control sensitivity can be enhanced.After determining the hydraulic control circuit for the electrical & hydraulic proportion control of the system and the hardware circuit of the control system, the loop opening and loop closing transmission functions of the system are set up on the basis of composition of the system, stabilization of the system and the step response feature in the time area are described with simulation, the study for the PID (proportional-integral-differential) self-set control arithmetic is fulfilled. After fulfilling self-set of the parameters, the regulating time of the system is shortened, it is advantageous to enhancing follow-up feature of the system, improving the dynamic performance of the system to the greater extent, the control effect can satisfy the design requirement. Meanwhile, this system has been installed and tested on the bulldozer Type TY230 and feasibility of the system has been further verified. |
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