Audi A6L car forward gear start jitter maintenance
A 2016 FAW Audi A6L sedan equipped with 3.0T engine and matched with the second-generation OB5 type 7-shift wet DCT transmission was repaired for the first time because of the weakness of the reverse gear and the erosion of the K2 clutch controlling the even and reverse gears.However, about a month after the delivery of the car, the user complained that the transmission and abnormal phenomenon: forward gear start jitter, 1-2 gear and 2-3 gear tremble and sound, after the second return to the factory, three pieces of valve body was continuously replaced, but the fault phenomenon is still the same.Fault diagnosis: after picking up the car, the author did find the starting jitter and the low speed range was not very comfortable after the road test.When we returned to the factory to collect the relevant dynamic data, we found that the engagement was smooth and there was no impact feeling when we put reverse gear and forward gear in place, and the driving current of the clutch and the feedback oil pressure of the clutch also met the standards (as shown in FIG. 1 and 2).However, when observing and analyzing the current clutch matching value, it is found that the lower matching point of K1 clutch is somewhat low (as shown in FIG. 3) : ① Only the lower matching value is incorrect (low) when K1 is analyzed alone;(2) There is no problem when analyzing K2 alone;③ When comparing and analyzing K1 and K2, the matching value on K2 should not be higher than the matching value on K1 under normal circumstances.According to the clutch matching value analysis, neither of the two clutches should be ablated, but there may be other problems, which can only be known by removing the transmission and decomposing the clutch.Removing the transmission and disassembling the dual clutch did find that the friction plates were in good condition, without any ablative marks.After careful inspection, some problems were indeed found: First, the two sets of friction plates were not original (as shown in FIG. 4);Second, the friction plate is wrongly installed (the oil groove direction of all friction plates should be consistent), as shown in FIG. 5.Second, the gap between the two groups of friction plates is somewhat large (K1: about 3.2mm, K2: about 2.2mm).There were no other problems.Since no obvious problems were found, it was decided to replace the original friction plate, piston and clutch hub (using only the original steel plate) for commissioning.Just load the car test (cold car can not meet the matching conditions) forward gear and reverse gear start feeling is good, but with the temperature rise found: (1) forward gear start (1) there is a shake;02 gear to 3 gear also slightly shake.After matching the clutch engagement point, it was found that the lower limit value of K1 was abnormal (as shown in FIG. 6). After matching, the fault phenomenon was still the same (mainly due to the severe start jitter of gear 1 and stiff suspension).The key is that after only replacing a dual clutch hub and a set of original friction plates, nothing else is moved. How did the lower matching value of K1 clutch change so much?In place to hang forward gear stiff and small throttle start or idle crawl have a shake?The point is why is the match under K1 clutch so big?Does it have to do with drive matching (clutch adaptive)?Then a better road condition was found for driving matching.After 20-30min time road test drive matching (manual mode 4 or 6 gear learning K1 clutch, manual mode 5 or 7 gear learning K2 clutch), the drive matching task of the two clutches in the factory is successfully completed soon and the current drive matching value is displayed, but the fault phenomenon is still the same.The key is that the matching value of K1 clutch rises again (as shown in Figure 7).It is really too strange, the failure phenomenon did not reduce, the matching value increased again, is what data is not good?In the continuous test run (the fault phenomenon was obviously in gear 1), a little abnormality was indeed found through dynamic data. When gear 1 was idling or the brake pedal was pressed lightly, the jitter was obvious. At this time, it was found that the K1 clutch pressure fed back by G193 was unstable (as shown in FIG. 8).However, the pressure information of K2 clutch is very stable during reverse idling (as shown in FIG. 9). Of course, the vehicle itself is not abnormal during reverse idling.Because there is also a stiff and uncomfortable feeling in gear 12-3 of the driving blade, the dynamic data is not normal when there is a fault in gear 2-3 during driving (as shown in FIG. 10).Again: How could a single clutch hub and a set of friction plates change the data?Is it the short test time of pickup, or the data analysis is not in place?Starting from gear 1 and performance in gear 2-3, combined with dynamic data analysis, should be K1 clutch pressure instability or abnormal.If there’s nothing wrong with the clutch, is there something wrong with the valve?To verify whether the hydraulic valve was faulty, we happened to have a new valve that we tried.However, after shi tried the new valve body of the car, the fault phenomenon still did not change, on the contrary, the matching value of the clutch is more abnormal (as shown in Figure 11).First, why is the matching value high when the original friction piece K1 is replaced?Second, why is the matching value higher under the replacement of the new valve K1?Is it the control unit or the valve body?Is it the clutch, or the oil between the valve body and the clutch?After the replacement of the control unit, the data and symptoms remain unchanged.Analysis by elimination method: first, there is no problem with the valve body 100%;Second, there must be no problem with the control unit;Third, is it the clutch?What else didn’t we think about the clutch?If there is no problem with the clutch, there is no problem with the friction plate, and there is no problem with the piston. Is it the problem of the steel plate?Is there that much deviation in the data from the steel plate (clutch matching letter)?On second thought, I’m not 100% sure there’s nothing wrong with the dual clutch at this point, so it looks like we’re going to start with the clutch, because everything else is fine.Again, the transmission was removed and the clutch was disassembled. At the same time, in order to make sure the clutch was safe, we decided to replace a set of original steel plates.The sealing of the dual clutch was retested, including the standard clearance, and was reloaded without any problems. At the same time, the filter inside and outside the converter was replaced again, and the new DCTF was also replaced.But after loading, there was a more serious problem: that is, when preparing for the test, we found that the forward gear and reverse gear can not run, and the instrument alarm.Two fault codes are read after detection: P17D600 – Clutch 1 pressure is too high, P17D700 – clutch 2 pressure is too high (as shown in Figure 12).It’s really strange that the clutch was moved again and only a set of steel plates were replaced. How could there be a more serious problem?It is worth mentioning that this repair did not use the new body of the tested car.Troubleshooting:From the current fault code to stone, forward and reverse gear are not driving is the cause of the transmission control unit records the two fault code launched the “safe cutting function”, after being hung forward gears or hang a reverse gear, the control unit will not through N435 and N439 two clutch pressure solenoid valve output, so this time even to the fault code to delete,Read dynamic data actually do not see abnormal data.Information about the clutch pressure mainly to white G193 and G194 two pressure sensors feedback, so the two fault code issue only two possibilities: first, two from the pressure of medium is “false” is not really high, if it is a “false”, that is either lying two pressure sensors, or control unit calculation error;Second, the pressure on both clutches is really too high. If so, what’s the problem?The clutch itself is not possible, nor can the oil circuit, is it the valve body problem?Finally, I had to load the new valve body of the tested car again for a test run, and the results were all normal, not only the fault phenomenon disappeared, but also the clutch data returned to normal (as shown in Figure 13). So far, the transmission that had been maintained for more than a month was finally repaired.Fault summary: This case is obviously a repair caused by the quality of accessories. In fact, the most important part is the fault diagnosis link 1 clutch data analysis. At present, most peers still rely on the method of replacing parts to troubleshoot one by one, and suspect what to replace what;In addition, the quality of remanufactured parts is not up to the standard required for remanufacturing.So how to solve the transmission failure at one time, without high quality accessories support is difficult to do.Strengthening data analysis ability can improve the accuracy of fault diagnosis, thus improving maintenance efficiency and maintenance quality.