Control principle of electric control system for Komatsu 200 excavator
In recent years, with the development of electro-hydraulic control technology, electronic control systems have become a component of electronic load sensing control systems and have been widely used in the field of construction machinery in developed countries. The various series of track type hydraulic excavators from Komatsu are widely used in the engineering field in China, among which some models such as Komatsu 200 excavator and PC120-6 are equipped with electronic control systems. This article systematically introduces the structure, principle, and adjustment of Komatsu's electronic control system, and analyzes its common faults to help understand such systems.
1. Structure, Principle, and Adjustment of Electronic Control System
The Komatsu electronic control system has data information transmission with other control systems but is relatively independent. The hardware system includes left and right electronic control levers, control device ECU, and pilot control proportional valve.
1.1 System Structure (1) Joystick.
The joystick is a resistance type electronic control joystick, with a structure of 2 coaxial connected potential sensors on each axis X and Y, which serve as position signals for forward and reverse operation of each axis. Each joystick has 4 analog signal outputs, mainly outputting position command signals for the 4 operating positions of the joystick to the control ECU. When the joystick is in the neutral position, the voltage of each sensor is 2.5 ± 0.2V. During operation, the output of the sensor in the operated position is between 2.5-4.6V, while the output of the sensor in the opposite position is between 2.5-0.6V. Their output signals vary with the operating position.
(2) Control device ECU.
In addition to receiving 8 operation position command signals from the left and right joystick, the control device ECU also obtains engine and pump operation status information from the power control ECU, and transmits system control and fault information to the display; Use various control information to control the eight action pilot control proportional valves of four action mechanisms, including rotation, boom, arm, and bucket.
(3) Pilot controlled proportional valve.
The pilot control proportional valve is an electromagnetic control type, which controls the pilot turbidity pressure of each action under the control of the ECU current of the control device, thereby controlling the opening and reversing of each reversing valve.
1.2 Control principle
(1) The signal emitted by the position sensor of the joystick changes with the position of the joystick. When the joystick is in the neutral or reverse position, its output signal is between 0.6 and 2.8V. The ECU controls the corresponding proportional valve current to be about 90mA, and the proportional valve is in the closed state. The corresponding pilot control oil pressure is zero (does not operate); When operating this control position, its output signal is between 3.0 and 4.4V, which increases with the increase of operation amplitude. The ECU controls the corresponding proportional valve current to vary proportionally between 300 and 1000mA, and the corresponding pilot control oil pressure to vary between 0.5 and 2.9MPa, thereby controlling the opening of the corresponding action reversing valve.
(2) The output signal voltage of the forward and reverse position sensors on the X-axis (or Y-axis) of the joystick should be within the range of 0.4-4.6V, and there should be a Upositive=5-Ureverse relationship, with a relationship error within 0.3V. Otherwise, it is considered that the sensor on that axis is faulty. The controller ECU will safely lock the current of the two control proportional valves of the action mechanism, making the action mechanism unable to work and issuing a fault alarm.
(3) To ensure safety, before turning on the power and starting, the control unit ECU needs to confirm that each control position is in the neutral position (the voltage of the sensing signals for all 8 positions should be 2.5 ± 0.3V). Otherwise, if the control handle is not in the neutral position, the current of the control proportional valve for all actions such as the boom, arm, bucket, and rotation will be locked and protected, and its operation will be prohibited.
1.3 System Adjustment
The adjustment of the system mainly involves the adjustment of the joystick position sensor and the adjustment of the pilot oil pressure.
The position sensor is a potential type, with a power supply of 5V and a shaft that can rotate 360 °. Each joystick has 4 position sensors. When adjusting, make the joystick stand in the center position. First, adjust the distance between the joystick disc and the plunger (1-2mm), and then adjust the output signal voltage of each sensor to be within the range of 2.5 ± 0.2V. Operate each individual to the maximum and check that the sensor output signal voltage should be greater than 4.2V. Otherwise, the distance between the handle disc and plunger, as well as the wear of the handle universal joint, should be checked again and repaired.
Whether the pilot oil pressure is normal or not is related to whether the pilot control oil pressure of the system action is normal, and its standard value is 2.9 MPa.
2. Fault diagnosis system
The fault diagnosis system is accessed through a display and is divided into service programs and fault diagnosis programs. The service program can detect the output voltage signal parameters of various sensors in the system and the control current parameters of solenoid valves; The fault diagnosis program can query the fault codes of past or current faults.
3. Common Fault Analysis
(1) Common fault one: The bucket, arm, boom, and slewing cannot move and there is a fault alarm.
Fault analysis: ① Incorrect operation. Opening the key and the control handle before starting are not in the neutral position, causing the control unit ECU to perform safety lock protection. As long as the two control handles are in the neutral position and the power switch is turned on again to start, normal operation can be restored The joystick is malfunctioning. If the rocker arm of a certain group of position sensors breaks or deforms, even if the joystick is in the neutral position, the sensors of that group are not in the neutral position (the transmission signal is not within the range of 2.5 ± 0.2V), causing the control device ECU to perform safety lock protection.
Fault detection method: When both left and right operating handles are in the neutral position, enter the service program, check the service codes of each operating position [50, 51 (boom); 52, 53 (bucket); 54, 55 (swing); 56, 57 (boom)], and check the output voltage of its position sensor. The normal value should be 2.5 ± 0.3V, in order to determine the fault point and replace or repair it.
Due to the traditional hydraulic control of the walking operation, it is not affected by the system.
(2) Common fault 2: Some actions cannot be performed and there is a fault alarm.
Fault analysis: ① The two sensor circuits of the operating handle of the action mechanism are short circuited or open circuited. ② The two pilot control proportional valves of the action mechanism are faulty or their circuits are faulty. Specifically, the fault point can be determined and repaired or replaced by retrieving the fault code and combining it with actual measurements.
(3) Common fault three: The bucket, boom, boom, and rotation movements are relatively slow.
Fault analysis: The most likely fault is that the total hydraulic pressure of the pilot is lower than the normal value. Due to the traditional hydraulic operation of walking, the impact is not significant, while the pilot pressure of other actions is controlled by a proportional valve, and its impact is more obvious. It was determined by detecting the pilot oil pressure.
(4) Common fault four: Some actions are relatively slow
All Komatsu excavator components will become weak and slow after installing hydraulic oil separators during operation: some problems with the active overflow valve are due to the need to adjust the position of its key components, the old problem of the hydraulic oil pump needing to control the system to power off, and the previous navigation system also had many issues. Most of the problems with Komatsu excavators are not too difficult to solve as long as the root cause of the problem is identified.
What is the reason why the power assist valve of the entire machine's power system is pressed, but the effectiveness of the second-hand excavator does not increase? It is mainly the main cause of the engine power assist switch. There will be a momentary short circuit in the wire between the power assist valve and the DG, and there is a problem with the overflow flow valve. The KB diversion solenoid valve has a gap, and there is a wire connection failure between the DG diversion solenoid valve and the KB bearing.
Most hydraulic cylinders cannot move freely or their speed slows down: the sealing sleeve on the hydraulic cylinder is severely damaged, the bearing of the front oil distribution valve has malfunctioned, the operating system valve chip of the main circuit board is stuck, the first exported valve has abnormal phenomena, and the damper valve chip is stuck in the distribution valve.
The descent operation of the boom of the Komatsu excavator is too monotonous, and the working speed is quite fast: the reason is that when it walks, the diversion valve selected by the active arm to execute the descent command fails, causing the hydraulic oil separator to not work properly.
