Prof. Dr. Techn. Sci. N. GULIA
Dipl. Eng. S. KOVCHEGIN
Machine Design Department Moscow State Industrial University
Dipl. Eng. F. Martin, ЗIkarus» plant, Budapest, Hungarian Republic
Dipl. Eng. S. YURKOV, ZIL plant
At present variable speed drive (variator) application of automatic stepless transmission for a great number of cars is taking place. Great economical and ecological benefit is expected to take place by using hybrid power units in which the engine runs only at an optimal regime, and generated energy which is stored in the accumulator is used for car driving .
The most suitable automobile accumulators of mechanical energy (superflywheels) require the very mechanical stepless transmission, i.e. variator. The variable speed drive is shown to be also efficient when the sources of power are accumulators or fuel cells . New adaptive variator application in automobile transmission patented in Russia is expected to have very essential perspectives, this variator being patented in USA, England, France, Germany, Sweden, Switzerland, Hungary, Byelorussia and China now.
The most important characteristic feature of the new variator is its adaptiveness to the load that makes this transmission (having such variator) automatic one. It is required to carry out experiments as previously there were no such adaptive variators.
Moreover this adaptiveness is regulated (controlled) and it is due to this fact than the car speed is controlled. Let's clear up in brief the property of variator controlled adaptivity, and what this property can give to the car automatic transmission.
Available automobile transmissions having frictional variators are automatic, but this is done only by means of suitable sensor, electronic control units and servo-assisted units which change ratio by means of electric- or hydromotors and reducers.
It should be noted that most of the variators for automobile transmissions have frictional body clamping (pressing) mechanism supplied with servo-assisted unit.
As a result, servosystems of a variator drive can be equal to its power unit as far as volume, mass and cost are concerned. In the new variator adaptivity is a Зcongenital» or organically inherent property of its construction as in hydraulic torque converter, for example. Both in the first and in the second case when the load on the output shaft is increased (the moment of resistance), the revolution frequency of this shaft is decreased. But in each specific case this Зsmooth» characteristic of the moment versus revolution frequency function is definite and specific. In the new variator Зsmoothness» can be changed by force at the operator will.
Efficiency of the stepless gearbox having such variator is in the range of approximate by 0.85 (at the start) up to 0.95...0.96 (at minimum gear ratio) that is much more greater than that of in the gearbox with the hydraulic torque converter. Moreover gearboxes with new variator are much smaller than the hydraulic gearboxes mentioned above. They are lighter, less expensive and do not require to change steps. Such properties of new variator designed and constructed at Moscow State Industrial University are achieved by peculiarities of its construction which are described in the patent #2140028 ЗMultiplate planetary variator» (25.05.98, Russia) and #2138710 ЗAutomatic stepless gearing» (16.06.98, Russia), also in the Claim for international patent PCT/RU 99/00 162 (the author is N.V. Gulia).
The design of this automatic stepless gearbox using such adaptive variator is shown in fig. 1. According to this design the new variator includes only two rows of central friction disks – outer disks (10) and inner disks (5) with satellites (7) clamped between them by means of plate and flat disk (9) springs, correspondingly. However, it is clear according to the scheme that these rows can be as many as possible depending upon the strength and hardness of satellites axles (11) and their bearings (6). Intermediate supports on axles (11) are also can be used but when the number of rows are greater than 4. The number of satellites in the row is chiefly six, although their number can be up to 12 in case of powerful units having narrow range of variation.
Fig.1. Automatic stepless gearbox using new planetary disk adaptive variator: 1 – swinging arm axle; 2 – plate set; 3 – carrier; 4 – plate spring; 5 – inner central friction disk; 6 – satellite bearings; 7 – satellite; 8 – frictions; 9 – flat disk spring; 10 – outer central friction disks; 11 – satellite axle; 12 – counterbalance; 13 – roller; 14 – slotted disk; 15 – arm; 16 – spring; 17 – armed mechanism; 18 – carriage; 19 – output shaft; 20 – epicycle; 21 – swinging arm; 22 – disk profiled slot; 23 – lubricant feed
Axles (11) bearings (6) are on the one end of the swinging (steering) arms (21), on the other ends are counterbalances (12), one group of which being supplied with rollers (13) situated in profiled slots (22) of disc (14) connected to the output shaft (19).
Swinging arms (21) are placed on axles (1) fixed in carrier (3). Rollers (13) are depressed apart by springs (16), the effect of them can be changed by force with the help of armed mechanism (17) the action to which can be done by the arm (15) using the system of bearings. The arm can more both manually and by servo-assisted drive having flexible characteristic (for example, pneumochambers controlled by automobile pneumosystems). It should be noted, that the variator is adaptive without the mechanism of changing springs force. But in this case it will have only one Зsmooth» working characteristic for instance, as that of as in the hydraulic torque converter. The mechanism of changing spring force (both in decreasing and increasing) described above varies only the degree of Зsmoothness» characteristic of variator at any regime that is very important for automobile automatic transmission. In such a case the arm (15) will be engaged linked to the car speed control pedal either with an additional assistance or without it.
The torque from the engine flywheel to the gearbox input shaft is carried by the set of elastic steel plates (2), frictions (8) making the work of the clutch. When clamping, the right set of frictions epicycle (20) is braking that in conjunction with carriage (18) and telescopically connected to the output shaft (19) enables the driver to get the forward movement. In order to get the reverse movement of the car the left set of frictions is clamped, carrier (3) being braked.
Epicycle (20) is running in opposite direction of input shaft revolution and is engaged to the output shaft by carriage (18) traveling to the right. Intermediate or central position of the carriage (18) corresponds to neutral.
When changing the torque on the output shaft (19), the roller (13), situated in the slot (22) in balanced condition under the force of springs (4, 9, 16) which are tangential to the force of torque and other forces in the variator mechanism, changes its position in the slot and varies gear ratio. Pressing springs 4 and 9 are becoming deformed due to the wedging action of satellites, that fact is explained by the in significant resistance to the friction during friction disks running. Specially well-matched characteristics Зforce-deformation» give optimal friction disks pressing efficiency having reserve = 1,25...1,5. The slot (22) can be so profiled when it only decreases or entirely eliminates the force of roller (13) displacement during gear ratio variation. Thus the property of adaptivity is as if it were Зcongenital» which is inherent in variator construction and can be achieved only by selecting the slot form (22) and spring rigidity (16).
It should also be pointed out to the optimized automatic friction discs pressure, depending upon variator ratio. It permits us to take into consideration the changing friction coefficient in frictional contacts, which also depends on variator ratio. Such kind of pressing variator frictional elements (being much more simple from known to us) make it possible to optimize its efficiency for up-to-date automatic control system of automobile speed.
The new 2,5 kW variator was produced at the AMO ZIL plant in Moscow and undergone laboratory tests. The following characteristics were recorded:
Moreover friction coefficient and slipping values for various ratios were defined.
The whole design and inner layout of the variator (photos) are shown in works [3, 4].
Fig. 2 shown torque on output shaft T dependences upon output shaft revolution frequency n and ratio under load (accounting slipping) – i using ЗSantotrack-50» lubrication produced in USA and intended specially for variator was used in this case. Curves (1) show variator efficiency η, curves (2) show torques T.
Fig. 2. Variator efficiency (curves 1) and torque T on output shaft (curves 2) variator efficiency (curves 1)
Here it should be noted that unbroken black lines show variator characteristics when revolution frequency of the input shaft in equal to 1400 min–1; dotted red lines – 2800 min–1. Hachure green lines (dash lines) show predicted experimental characteristics of variator designed for gearbox of a bus having 100 kW engine. The torque dimension on the output shaft T for variator with small power (unbroken black and dotted red lines) is H·m for automobile variator (hachure green line) is hundred of H m.
Also it should be stressed that efficiency decrease of small powered variators having great ratios in comparison with automobile (predicted) efficiency is due to overloading and slipping which is equal to 50...70% at these regimes. The automobile variator is designed for nominal load.
Fig. 3 Зshows» friction coefficient dependencies in outer fo and inner fi contacts of variator respective by on relative slipping S%. Curves (1) and (2) show coefficients fo using lubricant ЗSantotrack-50» (in H. Vojacek experiments in Germany – 1) and motor lubricant M-8 (N. Gulia in Russia – 2) obtained in laboratory tests.
Fig. 3. Friction coefficient f dependencies on relative slipping S%
Testing grounds were equipped with frictional disks (5) having cone angle 5° that entirely corresponds to the variator frictional disks. These values of friction coefficients can be, at some extent, standard. Curves (3) characterize friction coefficients in tests using lubricant ЗSantotrack-50», curves (4) – using lubricant M-8 (upper curves (3) and (4) correspond to fo, and bottom curves correspond to fi). In this case ratio is at the range of 1,5...3. ЗSantotrack-50» lubricant proved to be advantageous according to these diagrams. Besides much greater coefficient of friction this lubricant gives less many times slipping that increases efficiency and life of friction disks. Friction disks long life lubricated by ЗSantotrack-50» in known to be measured by tens of thousands of hours and to be equal to millions of kilometers of automobile traveling.
New variator construction described above differs from previous ones by the fact that it has no Зbreak-down» of torque transmission, i.e. friction coefficient decreases at given values of slipping.
For cylindrical rollers this Зbreak-down» occurs at S ≈ 1,5...2%, for belt variators it occurs at 3...5%, sometimes greater but this Зbreak-down» takes place everywhen.
In new variator friction coefficients both fo and fi increase continuously when slipping is increased up to S = 80%, i.e. almost to full slipping (that is not permissible and in new variator it is eliminated by the brake 8, fig. 1). This feature of variator is very worth especially when this variator is used in automobiles.
In conclusion it should be said that judging by given characteristics of a variator testing model it meets all demands to stepless automatic transmissions used in automobiles. The variator is supposed to be lubricated by ЗSantotrack-50» or by its modern modification ЗSantotrack-50-S» produced by Findett Corporation (USA).