On June 18, 2014, a WP12 gas engine in a unit in Zibo, Shandong province suffered an accident that the main bearing pad and connecting rod pad smashed three months after the overhaul (replacing the cylinder block, crankshaft, connecting rod and piston moving components).
According to the actual damage situation fed back by customers and the accident phenomenon on site; Combined with the pictures of damaged crankshaft and bearing bush, organize relevant technicians to analyze the cause of the accident: since the damage of engine parts has different causes and manifestations, one or more causes may occur alone or simultaneously for the same damage, we must analyze the essential cause of the fault through the surface phenomenon of part damage.
However, in many cases, the essential cause can not be accurately judged only from the surface damage trace of a certain part. It is also necessary to understand the working time, working conditions, service conditions, maintenance conditions, oil quality and damage of related parts of the faulty engine, and conduct comprehensive analysis to find out the real cause of the fault.
According to the feedback information from the user, this engine is a model with relatively high maximum torque speed range:
Generally speaking, we should get used to looking at the engine partial load characteristic table of the vehicle and reading the configuration of the whole vehicle to achieve better driving habits. For the engine with high relative torque and speed, in fact, we must make rational use of the gearbox and standardize the relative shift and speed control.
As an aside, in order to meet the needs of the battlefield, early American military vehicles were marked in detail in the cab. In order to enable drivers with different skills to quickly adapt to the vehicle, usually for MT vehicles, they will mark the gear speed range and the minimum gear speed range, which can be used well on the one hand, On the other hand, it can ensure the normal use of vehicles to the greatest extent. In contrast, such labels are difficult to see in China.
To get back to business, the accident caused a lot of losses, so the pictures were sent to us to help us analyze it.
1. The bearing shells of the first and seventh main journals of the engine block are severely bitten, commonly known as strain and peeling. This bearing shell is Dafeng industry (copper lead alloy bearing shell)
2. The connecting rods of cylinders 3 and 4 of the engine smashed the bearing bush, the steel back of the bearing bush has been seriously deformed, and there is no serious strain on the piston skirt.
It takes only three months from the time the user purchased the parts to the time the car broke down, so he is in a hurry. On the one hand, he looks for the parts and on the other hand, he looks for the repair shop. From the channels he purchased, he knows that they are all regular parts of Weichai Power. At present, all service systems and roadside Express repair shops in Weichai do not have the status of data maintenance, and it is impossible to judge whether the repair shop can repair them, Therefore, under these conditions, users, repair shops and parts suppliers are very depressed.
We have learned something about the use and maintenance of this user. Compared with the heavy national highway, the vehicle configuration is unknown, and the “Meifeng” brand gas engine lubricating oil is used; Carry out simple visual analysis based on some information reflected in the accident phenomenon:
1. The main journal 1 and 7 of the engine bearing frame are stuck, and the bearing shells of other main journals are not seriously strained;
At present, the rear gear chamber of WP12 engine is used as the main transmission mode of timing drive, and the front crankshaft gear is mainly used to drive the peripheral accessories of the engine. It is not easy to realize the above situation only in terms of load and oil supply mode of engine main journal, unless there are other hidden fault features.
2. From the wear of the seventh main journal of crankshaft:
In the figure above, the half to which the red arrow belongs and the other half to which the blue arrow belongs have obvious unequal amount of wear, with less red and more blue. From the macro observation trace, the appearance is similar to that of the crankshaft, which may be caused by local deflection in the process of full floating. It is similar to the bright belt at the edge of the bearing bush or the cracking and adhesion of the coating at the edge.
3. Why did this happen? In fact, please pay attention to some of the phenomena of the connecting rod pads of cylinders 3 and 4 in the previous accident: the pads were smashed and rolled, but the pads were not held.
The oblique notched serrated connecting rod has relatively strong strength and difficult processing technology. It is widely used compared with heavy engines, especially the high strengthening type. However, for maintenance, whether it is new or old parts, it is essential in data measurement. Aside: many card friends joke that you are a typist. Where can there be a maintenance enterprise that can measure now? It often makes me speechless; At least it was like that when we repaired the car. Now society has made progress?
In the figure above, the connecting rod bodies are overheated to varying degrees. This overheating is not caused by the conduction of piston operation, but by dry grinding caused by abnormal fit clearance. Let’s look at the bearing bush.
Normally, the connecting rod is smashed from top to bottom. In fact, when we repair the engine, the strengthening types and partial structures of the connecting rod bearing bush of this kind of engine are usually different. The above state can occur because some cylinders of the engine work rough and the bearing bush fit clearance is improper, Poor lubrication and other conditions lead to dry wear of bearing bush and crankshaft connecting rod journal, resulting in sticking of pad surface coating (slight pad holding).
Under the condition of relatively high-speed operation, there is enough oil to build up pressure, resulting in the bearing shell coating being slowly stripped off, resulting in the bearing shell matching clearance exceeding the standard. Due to the large clearance, the large impact load on the steel back of the bearing shell causes extrusion deformation in the process of hitting up and down, which indirectly leads to the larger bearing shell clearance. This type indicates that the connecting rod journal of the crankshaft is only scratched and locally adhered with bearing bush coating.
4、 Many card friends say why do 3 and 4 cylinders smash the tiles (not locked) will have such a great impact. We need to start with the crankshaft of WD618 and the ignition sequence of this engine. WP12 engine is an improved version of Steyr WD618 engine. The ignition sequence of the engine is 1-5-3-6-2-4. The 3-4 crank of the crankshaft is in the same plane, the 2-5 crank is in the same plane, and the 1-6 crank is in the same plane. Let’s use soda 3D modeling to briefly demonstrate:
Because the crankshaft is made of forged steel, it is necessary to ensure sufficient strength and toughness. In case of similar problems, in fact, for this engine with combined cylinder block of upper and lower tile frame, The first and seventh main journals are very prone to similar accidents caused by improper clearance due to the failure of effective support of bearing bush caused by crankshaft bending. (aside from the topic, please ignore the wrong crank angle in the figure above, and the bug caused by the lack of proficiency in the software)
5. In some cases, the stress on the rear section of the crankshaft is very unstable and affected by various factors, but in this accident, I prefer the problem of the engine itself, which causes this phenomenon:
From the wear marks of connecting rod journal without pulling and smashing pads, it is more like transitional wear in the diagonal direction of bearing pads. There are usually several possibilities for wear:
(1) The connecting rod is twisted or bent;
(2) The crankshaft connecting rod journal is in waist drum shape;
(3) The connecting rod journal and the connecting rod big end seat hole are misaligned (inclined).
Based on the fact that the crankshaft, connecting rod, bearing bush and cylinder block in this case are allocated and sold by the central warehouse of the original factory, the serious deviation of the parts themselves can be eliminated. Moreover, if the deviation is so large, the engine cannot fail after running for 3 months.
An engine + gearbox + drive axle can pull a lot of goods, and the cab is just a carrier; Different engines, different gearboxes and different axles are also very interesting when combined, which will make you run faster, climb the slope, increase the speed, and make you unable to pull or run faster.
Based on the characteristics of the engine in the accident case of this case, if the adjustment is about 1400-1600 to achieve the relative maximum torque output (on the premise of ensuring sufficient engine output power), you will have different shift speeds and feelings with a gearbox with a range of 1.28 and a gearbox with a range of 1.36.
If the torque speed range of large displacement, high torque, medium and high speed vehicle diesel engine is 1100-1400, For example, the speed ratio interval is 1.28 (the shift speed difference is 280-350 RPM). If you want to use it more vigorously, generally speaking, if we use the same driving method to shift around 1650 in the relatively high-grade area, for this gas engine, you may have the problem that the engine speed has not reached the low value of the engine’s rated maximum torque output speed after shifting. At this time, if you add overload, you can You are still clambering forward, but for the engine, the load rate of connecting rod bearing bush and curved bearing bush is very high. If you use inappropriate engine lubricating oil at this time, if you still ignore some data statistics during maintenance and can not completely troubleshoot some problems, the consequences are similar to the phenomenon above in this case.
At present, Chinese overload + Chinese driving + Chinese maintenance are the main reasons for the problems of most Chinese trucks. If the car breaks down, it is either the car enterprise or others. They never think about how to operate a truck well. (of course, some people don’t raise trucks if they really want to understand these.) they think that trucks are just tools for low-level people. That’s a big mistake!
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