with regard to the application of High-Torque Variable-Speed Drives (HTVSD) of non-friction type
This work is aimed at the resolution of the task of effective transfer of mechanical power from engine to the executive unit (EU), for example, to driven units of the farm tractor.
Any machine unit (MU) consists of the engine (EU) and kinematic-dynamic converter (KDC), which is intended for coordination of operation of engine and EU (figure 1), i.e. with the help of this unit the user is to obtain from the engine the mechanical power of the “required quality”.
Figure 1. Diagram of machine unit (MU)
1 – kinematic-dynamic converter (KDC);
2 and 3 – input and output shaft of KDC; 4 – engine;
5 – executive unit (EU); ω – angular speed; M - torque
It is known that in most cases, about which V.P. Goryachkin wrote, the optimal characteristic for EU is the line (figure 2) that takes the shape of hyperbola for torque at the constant consumed power. In the figure it is a continuous line, which corresponds to the characteristics of so-called constant power engine (CPE). The actually obtained optimal characteristic is shown by the dotted line, on which it should be noted the stop torque Mst at a zero speed of shaft 3 that ensures operation in “shutdown mode”. It is the most important property, necessary for effective operation of EU in the dynamic mode.
Figure 2. Speed characteristics
These considerations form the basis for two directions of MU improvement: they are the development and improvement of engines or KDC.
The improvement of engines cannot be called successful. Among heat engines, the most common is the internal combustion engine (ICE), which can not directly ensure “shutdown mode”, because it can’t operate at small speeds (figure 2) and needs complicated and expensive KDCs, such as: friction clutch with multiply-speed gearbox (power transfer can be interrupted); hydraulic transmission (losses make up more than 20%); electric transmission (it is metal-intensive and costly).
The foregoing considerations allow to make conclusion about the necessity of development and application as KDC of the cheap, economical, reliable and compact mechanical variable-speed drive, which is able to ensure “shutdown mode” and vary, i.e. to change gradually speed and torque without breaking the transmitted power.
Let us assume that a High-Torque Variable-Speed Drive (HTVSD) is the variable-speed drive, the design of which allows to transfer effectively power more than 50 kW at the acceptable value of irregularity factor
δ = (ω3, max - ω3, min) / ω3, СР .
The variable-speed drives are divided into friction and non-friction ones. In friction ones, variable-speed drives rotation is transferred at the expense of friction forces (tangential forces), for creation of which the contact load between friction pairs is to be greater by 10 – 25 times than the working load, which prevents the development of friction HTVSD.
According to the definition of A. A. Blagonravov , we will assume that non-friction variable-speed drives are units, the kinematic pairs of which have holonomic constraints. In this case working loads are transferred by normal forces, which form grounds for HTVSD development.
Considering in theory the matters of design of the variable-speed drive, the components of which have only holonomic constraints, A. A. Blagonravov came to the conclusion about mandatory existence in such structure of the oscillatory mechanism (OM), the operation of which depends on the input shaft, with oscillatory shaft (OS) and rectifier (R) that transfers oscillations into unidirectional rotation of the output shaft. The variation of gear ratio is obtained at the expense of change of the amplitude λ of OS oscillations, while the rectifier is to have non-friction overrunning clutches (ORC).
The sufficiency of above-mentioned conditions is proved by well-known designs of kinematic and dynamic variable-speed drives, while their necessity can be refuted by reference to variable-speed drives without the specified peculiarities, but such designs are not known.
In kinematical variable-speed drives OS has rigid kinematics, which is set by cam or non-cam OM. In variable-speed drives (torque converters), the OS oscillations appear at the expense of inertia forces due to eccentric weight. The considerable disadvantage of well-known variable-speed drives is their great value of δ, unacceptable for practical application.
The represented work touches upon only kinematical variable-speed drives, the improvement of which is to be carried out in the direction of the development of effective OM and rectifiers.
Figure 3. Diagram of pulse HTVSD
G and 4 – gear and toothed wheel; 5 – elastic clutch;
CH – control handle; α, γ, φ – rotation angles;
ω – angular speed
Figure 3 represents the design of HTVSD with rectifier of V2 type, i. e. with two ОМ, which ensures (as it is shown on figure 4) rectification at any position of the input shaft, the δ value of the unit with such rectifier makes up two or somewhat less at the expense of overrunning operation of clutches (section b-d on the diagram). The gear ratio of the rectifier V2 makes up
u = ω4 / |ωК| .
Figure 4. Angular speeds of the OS ωК and
output shaft ωВ of the rectifier V2
The variable-speed drives with rectifier V2 are called pulse ones (HTVSD2), and their field of application is limited. The possibility of HTVSD2 application, in which reduction of δ is obtained at the expense of the elastic clutch is described in . The author manufactured the pilot model of the pulse HTVSD2 with unique OM .
The comprehensive solution of the problem of δ reduction is suggested in the German patent application of Rindfleisch . Figure 5 represents the diagram of such variable-speed drive, in which two rectifiers V2 are used and operate with phase shift 90°. The follower gears G of rectifiers rotate wheels 4 of three-shaft differential, the bevel-pinion cage 6 with pinion 5 is fixed on output shaft 3 of the variable-speed drive. The output shaft speed is equal to the average speed of differential wheels.
ω3 = 0,5 (ωa + ωb) , (1)
i.e. the differential averages irregular velocities on the output elements of rectifiers. Let call such rectifier D-rectifier (RD), while name the variable-speed drive as HTVSDD.
Figure 5. Diagram of HTVSDD with D-rectifier (RD)
1 – case; 2 – input shaft; 3 – output shaft;
4 – differential wheel; 5 – pinion;
6 – bevel-pinion cage
In order to obtain the value δ = 0, we use cam OM, which ensure the following speed without overrunning operation of the overrunning clutch (OC):
ωa = 2ω2λu sin²α ,
where λ is amplitude of OS oscillations. Proceeding from (1), we obtain (figure 6)
ω3 = ω2λu [sin²α + sin²(α + 90°)] = ω2λu ,
consequently, at the constant speed of the input shaft ω2, the speed of the output one ω3 = const, and gear ratio of the variable-speed drive will make up
i = ω3 / ω2 = u (λ / π) = 0 … imax = u (λmax / π) . (2)
Figure 6. Speeds of differential elements
The mathematical modeling of HTVSDD operation with the help of Lagrange equations of the second order showed  that if OC operates in overrunning mode, speed ω3 changes automatically, i.e. without control handle (СH): if М3 increases, speed omega;3 can be decreased approximately twice and vice versa; at the same time the rotation uniformity is saved (δ ≈ 0).
If we designate the critical amplitude of oscillations λ0, at which unidirectional rotation of the output shaft starts, we will obtain the value of stop torque
Mst = M2π / (λ0u) ,
from which the unique feature of HTVSD follows – very large torque on the output shaft: HTVSD can increase the transfer torque by hundred and more times. The speed characteristics are shown on figure 7. The torque on the output shaft near М3 is limited by strength of HTVSD components, consequently,
M3 ≤ M3st = M3max < Mst ,
and the operating capacity of the variable-speed drive can be ensured by reduction of power, received from engine, at low “i” at following velocities:
0 ≤ ω3 < ω3п = N3н / M3st ,
where power, received from the HTVSD shaft, N3н = М3н ω3max = М3 ω3 at velocities
ω3п ≤ ω3 < ω3max = ω2λmaxu .
u, λmax, М3st are the main parameters of HTVSD.
Figure 7. Speed characteristics on the HTVSD output shaft
There are many structure diagram of HTVSDD, for example [4 – 7].
Figure 8 represents the most rational structure of the reversing HTVSDD, developed by the author, which has the following characteristics: u = 1, λmax = π / 3 = 60°, М3st = 1600 Nm. The gear ratio range (2) makes up i = 0 … 0,33. The reverse is ensured at the expense of OC reversal.
Figure 8. Structure of HTVSDD with Mst3 = 1,6 kNm
The variable-speed drive consists of case 1, in which input 2 and output 3 shafts, pair of rectifiers 15, installed perpendicularly, with OS 14 and output gears 16 are mounted. The pair of spatial cams 6 are installed on trunnions 7 of the input shaft and can be turned to angle 0 … 30° with the help of CH 9 via pin 8 and slider 12 (10 – nut, 11 – screw). The two-arm rockers 13 with rollers, which contact with cams, are fixed on the OS. The gears 16 are engaged into the wheels of shafts 4 of conic differential, bevel-pinion cage 17 of which is fitted tightly on output shaft splines (5 – pinions). Position 18 is the oil supply coupling, intended for lubrication of axes of rollers and turn on the reversing unit of OC.
The variable-speed drive operates in the following manner. Figure 8 shows the “shutdown mode”, in which rotation to shaft 3 is not transferred. In operating variable-speed drive, if CH turns, cams shift and transfer oscillatory spins via rockers to oscillatory shafts (OS), speeds of which are rectified by rectifiers. The rotation is transferred through gears 16 and differential, and the output shaft begins to rotate.
The pilot model of HTVSD with М3st = 200 Nm, represented on the photo (figure 8), is designed and manufactured according to the analogous diagram. In this design the unique toothed overrunning clutches are used, which ensure HTVSD operation at the speed of the input shaft n = 6000 rpm, with efficiency coefficient of the gear drive.
High-Torque Variable-Speed Drive
The following photo represents the unit, which consists of two overrunning clutches, fixed on the differential side shaft.
Pulse rectifier of V2 type
Figure 9 represents the diagram of installation of variable-speed drives in the grain combine, for which the author designed two variable-speed drives: pulse HTVSD2  with power 120 kW, with torsion bar that operates as the elastic clutch and HTVSDD with power 30 kW, with sliding spatial cams , while the wheel differential is built into the differential of the variable-speed drive .
Figure 9. Diagram of the variable-speed drive unit of the grain combine
1 – combine body; 2 – axles; 3 – drive wheels;
4 – final reduction gear; 5 – brakes
Figure 10 represents the diagram of the variable-speed drive unit for motor-car , which in addition to reversing HTVSDD is equipped with a gearbox. Its necessity is due to the fact that because of the overrunning nature of the output shaft operation, the variable-speed drive does not support the engine braking mode. In this mode the variable-speed drive is turned off, and rotation is transferred via the gearbox, which can also be used during motion in the steady-state speed mode.
Figure 10. Diagram of the variable-speed drive unit of the motor-car
GB – gearbox; HGB – handle of GB;
7 and 8 – driving and driven shafts of GB;
12 and 13 – friction clutches with handles 14, 15;
6 – input shaft of HTVSD
The figure 11 represents the diagram of variable-speed drive unit of the caterpillar, every drive sprocket of which is equipped with reversing HTVSDD. It allows to simplify considerably transmission and improve maneuverability.
Figure 11. Diagram of variable-speed drive unit of the caterpillar
Let estimate economic efficiency of ICE with HTVSD, using methods represented in [8 and 9].
It is proved that in the test dynamic mode, in the course of which the flywheel accelerated from the stationary position to the speed that corresponds to ICE maximum power, the maximum installed power of engine with HTVSD was less more than thrice as compared with ICE, connected with the flywheel by the friction clutch (FC). It can be explained by good traction and dynamic characteristics of MU with HTVSD and availability of stop torque in it.
Using MU efficiency coefficient as assessment of its efficiency
ηmach = Аmach / (GtHi)
(Amach is the effective work of the vehicle; Gt is the mass of consumed fuel; Hi is the low heat value of fuel), the relative fuel efficiency (FE) was identified
Efuel = (ηv − ηmach) / ηv = (Gt − Gvt) / Gt ,
where ηv = ηmach for ICE with HTVSDD, Gvt и Gt are the mass of fuel, consumed by ICE with HTVSD and other MU.
The values of Efuel are represented by the histogram in figure 12.
For the dynamic mode the test mode of the flywheel acceleration from the stationary position was used. The acceleration finish corresponds to the ICE speed, at which the indicated efficiency coefficient of the engine is maximal. The coefficient of mechanical efficiency of the variable-speed drive in calculations is accepted to be ηHTVSD = 0,85.
According to the histogram, in the dynamic mode ICE with HTVSD is more efficient than all MU by 50 … 30%. In the static one their efficiency is approximately equal at the maximum speed of ICE.
It should be noted that the variable-speed drive allows to support the operation of ICE in the optimal mode with regard to the fuel efficiency, maximal torque or power, as well as minimum toxicity of exhaust gases, which can be carried out with the help of automatic control.
If there are no strict requirements to the uniformity of rotation of the output shaft of variable-speed drive, in the design of HTVSDD non-cam OM [3, 13 – 15] can be applied, in such case δ ≈ 0,2 . Such design is simpler, cheaper and more compact, than one with cam OM.
The most prospective way is application of HTVSD at dynamic operation modes: off-highway and urban transport, processing equipment, construction and agricultural engineering units.
List of references
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