On the problems with the onboard gearboxes of T-80 tanks in the USSR
Since its adoption tanks The T-80 tank type and its initial mass production were plagued by numerous problems with various systems and components failing. A significant number of these were gearbox failures, which required repeated modifications during production.
A fairly detailed article, published in the USSR in 1987, was written about the improvements that were introduced to increase the fault tolerance of the gearboxes, as well as the impact of tank operating conditions on their durability. It is very interesting both from a technical and a simple point of view. historical plan, that's why we're publishing it here.
The influence of operating conditions on the durability of the T-80 tank's armored personnel carrier
During the operation of the T-80 tank, it was discovered that onboard gearbox (OG) failures account for a significant portion of the tank's overall failure rate. One of the reasons for this is the unsteady production process, accompanied by a large number of design changes, which is typical at the beginning of serial production and tank fielding.
Fig. 1. Change in the frequency of failures of the T-80 tank’s air defense system by year of its production (1) and by year of detection of failures (2)
Thus, from 1980 to 1985, the highest failure rate was in the BKPs manufactured between 1981 and 1983 (Fig. 1). During this period, numerous design changes were introduced by industry plants. Among them, we note the following:
Improved bolt locking (1982);
cancellation of cooling of the axles of the 1st and 2nd planetary gear sets with nitrogen during assembly (1983);
improved lubrication of the F3 clutch and T4 brake (1983);
introduction of ultrasonic testing of the steel base of metal-ceramic friction discs (MCF) (1983);
introduction of TSZP-8 oil instead of B-3V (1984);
introduction of a 6-row loose bearing for the satellite of the 1st–2nd planetary rows (1984);
introduction of the MKD with modified geometry of lubrication grooves (1984);
introduction of a second watering point for the friction discs of T4 and T5 brakes (1984);
introduction of a new design of lubrication system pipelines, eliminating their damage during installation (1984);
introduction of modified profile distribution mechanism cams with reduced resistance to returning the steering levers to their original position (1984);
elimination of booster feed valves in the distribution mechanism (1985);
improvement of the technology for manufacturing friction multilayer composite materials (1986);
strengthening of the F3 clutch (1986);
introduction of hydraulic brakes (1986).
Improvements to the BKP design, however, had little impact on a number of failures resulting from insufficient consideration of the operational characteristics of the VGM. Based on complaint materials, data from controlled military use, control, warranty, and other tests, the following BKP failure distributions were obtained:
By type of operation:
Military exploitation..................................................... 86%
Tests ..................................................................................... 14%
By nature (place) of military operation:
Training centers (TC) ..................................................... 50%
Combat training groups (CTG) ............................................... 40%
Linear divisions..................................................... 10%
An analysis of the T-80 tank's BKP failures that occurred during control tests (CT) (Table 1) shows that they are mainly related to production failures.
The greatest number of failures occurred due to excessive wear, sintering, warping, and destruction of friction discs in the friction devices, loosening of bolts, wear of axles, and destruction of the bearings of the first and second planetary gear sets' satellites, as well as destruction of the final drive bearings. Friction disc failures accounted for 62% of the total number of FCT failures, distributed as follows: F3 clutch - 31%, T1 brakes - 16%, T5 - 10%, T4 - 3%, and F2 clutch - 2%. It should also be noted that, in military use, a large number of FCT failures occur after 300–3000 km of operation.
Research and observations of the controlled tanks made it possible to identify the features of their operation in the training centers, combat groups, and in line units, and to establish differences in the operating conditions of these tanks from the conditions during testing (for example, control) (Table 2).
Operating tanks in the training center and in the combat group is characterized by low engine power utilization rates, infrequent use of higher gears and frequent use of lower gears, low average speed, long engine idling times, and a large number of transient conditions. For example, when operating in the training center, the T-80 tank spent 89% of its time in first and second gears (compared to 40% in the combat group). The number of starts was 20 times greater than in the combat group, the total number of gear changes was 2,5 times greater (including 4-10 times greater in lower gears), and the number of braking operations was 5-6 times greater.
To assess the impact of the aforementioned differences in operating conditions on the reliability of the ICP, computational studies were conducted on the loading and service life of the ICP's main components under operating modes corresponding to these conditions. The ICPs of two variants were calculated: 1 — corresponding to the design and technological documentation of 1980, 2 — 1986 (Tables 3–5). An assessment of the ICP's service life for the conditions of the training center was also conducted using actual statistical data on the operating modes in one of the training centers. The assessment using the methodology showed that under operating conditions typical of the testing center, the ICP of variant 1 ensures the specified service life with a non-destruction probability of 98%, while that of variant 2 is 96%.
When operating tanks in the UBG and UC, the operating time corresponding to the established warranty is ensured for both BKP variants with a probability of over 98%. This estimate is valid for operation without deviations from the instructions.
Typical tank operation in the UBC involves three roughly equal types of training: firearms training, tactical training, and driving, as well as various types of exercises. However, there are often cases where individual tanks are used predominantly for one type of training, for example, only firearms training or only driving training. For example, in some units, drivers and gunners are trained in different training battalions, each with its own tanks. In these cases, the load on some transmission components increases sharply while the utilization of others decreases, leading to inefficient resource utilization and a decrease in the reliability of the transmission as a whole.
During the training process, due to the lack of proper skills and knowledge among trainees, the following deviations from the operating instructions are typical:
movement with the steering levers not brought to their original position;
starting from a standstill without using the stopping brakes (at a power turbine speed different from zero);
operation of a tank with malfunctions or with incorrect control drive adjustments;
failure to comply with maintenance deadlines.
Starting a tank without following the operating instructions (IE) leads to a significant increase in load and, consequently, wear on the friction components. According to calculations, wear over 1000 km of the F3 clutch in gears 1, 2, and 3 is 0,041, 0,520, and 0,010 mm, respectively. The T1 brake experiences particularly increased load.
When starting off in second gear with a violation of the EI, it exceeds the load on the parking brakes during emergency braking of the tank in fourth gear with a deceleration of 4 m/cm² (Fig. 2). Repeated, frequent starting in first gear and in reverse while attempting to pull the tank out by rocking is no less dangerous.
Tank starting conditions that violate the IE can lead to significant wear, overheating, warping, sintering, and failure of the T1 brake friction discs and F3 clutch. Calculations show that if the T-80 tank's steering control levers are not returned to their initial position, resulting in a pressure drop in the hydraulic control system to 0,3–0,5 MPa, then when driving in second gear, which is most typical for training units, the T1 brake in the leading side of the tank will fail, and after the tank exits the turn, it will continue to slip for a considerable time.
When driving in first gear, in this case, prolonged slippage of the F3 clutch (for up to 20 s) occurs both in the Lagging Side CVT when exiting a turn, and in the Leading Side CVT, it also breaks down and slips for a long time. Although the specific friction powers in these slipping modes are relatively low (45–75 W/cm²), significant slippage duration leads to damage to the T1 brake and the F3 clutch, similar to that seen when starting off with a violation of the IE (see Fig. 2). It should be noted that failure to engage the steering levers reduces the CVT's performance not only due to prolonged slippage of the friction devices, but also due to deterioration of the CVT's component lubrication due to the increased oil supply to the hydraulic control system.
The deviations from the IE considered are possible not only during training, but also, for example, in a stressful situation, and under-adjustment of the levers can be used by drivers intentionally as a special technique to improve the controllability of the VGM in a turn.
The enhancement of the F3 clutch implemented by the manufacturers (improving its lubrication and increasing the number of disks, increasing the wear and heat resistance of the MKD by improving the geometry of the lubrication grooves and manufacturing technology), as well as increasing the efficiency of the hydraulic control system (by changing the profile of the distribution mechanism cams and the design of the oil system pipelines, improving the quality of the end seals) increased the performance and reliability of friction devices, including the F3 and T1.
However, this is not sufficient to completely eliminate the possibility of F3 and T1 clutch failure during tank operation with potential deviations from the IE requirements. It is necessary to develop and implement measures to automatically maintain full control pressure (increasing it to the nominal value in the leading side control unit during turning to prevent friction element failure both when the steering levers are not fully engaged and when turning during gear shifting).
Additionally, it is necessary to develop and implement a gearshift interlock when the tank starts moving, triggered when the power turbine speed is different from zero (e.g., by controlling the drain valve using tank speed and power turbine speed sensors). It would also be advisable to increase the service life of the T1 brake, for example, by installing an additional pair of friction discs and improving the lubrication of this brake and the F2 clutch, similar to the previously improved lubrication of the F3 clutch and the T4 brake.
Increased wear, warping, sintering, and failure of the friction discs of the T5 and T4 brakes are primarily due to the high thermal load on the parking brakes and the increased frequency of their use during tank operation in training units. The use of hydraulic retarders on the T-80 tank approximately doubles the service life of the friction discs of the T4 and T5 brakes (by reducing the number of parking brake engagements and reducing the amount of slippage per engagement).
However, as control tests in 1986 showed, this resulted in transmission overheating and accelerated clogging of oil filters by the decomposition products of TSZP-8 oil. This was apparently facilitated by the increased frequency of braking when tanks were moving at high speeds in a column in dusty conditions and the combination of hydraulic brake controls and the engine's variable nozzle assembly (VNA), which precluded engine braking using the VNA without the use of hydraulic retarders.
To assess the influence of hydraulic retarders on the thermal state of the T-80 tank transmission, a calculation of this state was carried out for hydraulic retarders of the 1986 design, as a result of which, for the average operating mode of movement under KI conditions at an ambient air temperature of 40 °C, the following values of heat removal of the transmission cooling system radiator were obtained, MJ/h:
Actual ..................................................................................... 149
Required (according to road conditions) for transmissions with hydraulic retarders controlled by:
combined control system¹ ............................................................... 163
system with a separate control unit .............................................. 129
Required for transmission without hydraulic retarder ................................. 121
The data provided shows that using hydraulic retarders with a separate control unit will not result in significant transmission overheating. However, the oil outlet temperature may increase significantly, which will negatively impact oil quality.
The combination of hydraulic retarder and engine RSA controls virtually eliminates the possibility of engine braking without hydraulic retarders and leads to a 4-8-fold increase in their use frequency, which, in turn, leads to an increase in heat generation that exceeds the heat dissipation capabilities of the transmission cooling system radiator.
The temperature of the oil in the transmission lubrication system increases significantly and, under unfavorable conditions, can go beyond the permissible limits, as was the case during the 1986 test when tanks were moving in a column in conditions of high temperature and dusty air.
To improve the reliability of the stopping brakes and hydraulic retarders without deteriorating other transmission characteristics, it is necessary:
develop and implement measures to eliminate the frequent use of hydraulic retarders and overheating of transmissions by introducing rational characteristics of hydraulic retarders and separating the controls of hydraulic retarders and the engine RSA;
improve the operation of the transmission lubrication and cooling systems to prevent clogging of oil filters with oil decomposition products;
increase the heat resistance of friction discs by using 40Х3М2ФА steel;
Provide for limiting the engine torque when operating in reverse gear (for example, by limiting the fuel supply) to prevent T5 brake slippage under extreme conditions.
Conclusion. To improve the reliability of the T-80 tank's combat control system (BCS) across a wide range of operating conditions, it is advisable to continue developing a reinforced BCS, as well as work on developing an automatic gearshift system.
1 - on a production vehicle.
Source:
"The Impact of Operating Conditions on the Durability of the T-80 Tank's BKP." M.G. Zhuchkov, V.A. Kolesov, R.N. Korolkov, V.S. Fantalov. Journal "Bulletin of Armored Equipment" No. 10, 1987.
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