Worm gearboxes with many combinations
Ever-Power offers a very wide selection of worm gearboxes. Because of the modular design the standard programme comprises many combinations in terms of selection of gear housings, mounting and interconnection options, flanges, shaft designs, type of oil, surface remedies etc.
Sturdy and reliable
The look of the Ever-Power worm gearbox is simple and well proven. We just use top quality components such as houses in cast iron, aluminium and stainless, worms in case hardened and polished steel and worm wheels in high-quality bronze of specialized alloys ensuring the the best wearability. The seals of the worm gearbox are given with a dust lip which effectively resists dust and drinking water. In addition, the gearboxes will be greased for life with synthetic oil.
Large reduction 100:1 in one step
As default the worm gearboxes allow for reductions of up to 100:1 in one step or 10.000:1 in a double lowering. An equivalent gearing with the same gear ratios and the same transferred electric power is bigger when compared to a worm gearing. Meanwhile, the worm gearbox is normally in a far more simple design.
A double reduction could be composed of 2 standard gearboxes or as a special gearbox.
Compact design
Compact design is self locking gearbox probably the key phrases of the typical gearboxes of the Ever-Power-Series. Further optimisation can be achieved by using adapted 
gearboxes or special gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is due to the very even running of the worm gear combined with the application of cast iron and high precision on component manufacturing and assembly. In connection with our precision gearboxes, we take extra care of any sound which can be interpreted as a murmur from the gear. Therefore the general noise degree of our gearbox is usually reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This frequently proves to be a decisive edge producing the incorporation of the gearbox considerably simpler and more compact.The worm gearbox can be an angle gear. This can often be an advantage for incorporation into constructions.
Strong bearings in sound housing
The output shaft of the Ever-Power worm gearbox is quite firmly embedded in the gear house and is suitable for direct suspension for wheels, movable arms and other areas rather than having to build a separate suspension.
Self locking
For larger gear ratios, Ever-Electrical power worm gearboxes will provide a self-locking impact, which in many situations can be utilised as brake or as extra protection. As well spindle gearboxes with a trapezoidal spindle happen to be self-locking, making them well suited for a variety of solutions.
In most gear drives, when driving torque is suddenly reduced because of this of ability off, torsional vibration, vitality outage, or any mechanical failing at the transmission input aspect, then gears will be rotating either in the same route driven by the system inertia, or in the contrary route driven by the resistant output load due to gravity, planting season load, etc. The latter state is known as backdriving. During inertial movement or backdriving, the powered output shaft (load) turns into the driving one and the driving input shaft (load) becomes the influenced one. There are several gear drive applications where result shaft driving is undesirable. So as to prevent it, various kinds of brake or clutch units are used.
However, there are also solutions in the apparatus tranny that prevent inertial movement or backdriving using self-locking gears with no additional equipment. The most typical one is definitely a worm equipment with a minimal lead angle. In self-locking worm gears, torque used from the strain side (worm gear) is blocked, i.e. cannot travel the worm. Even so, their application comes with some restrictions: the crossed axis shafts’ arrangement, relatively high gear ratio, low rate, low gear mesh efficiency, increased heat generation, etc.
Also, there happen to be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can make use of any gear ratio from 1:1 and larger. They have the generating mode and self-locking function, when the inertial or backdriving torque is put on the output gear. Originally these gears had very low ( <50 percent) driving effectiveness that limited their software. Then it had been proved [3] that high driving efficiency of such gears is possible. Criteria of the self-locking was analyzed in the following paragraphs [4]. This paper explains the principle of the self-locking method for the parallel axis gears with symmetric and asymmetric teeth profile, and displays their suitability for numerous applications.
Self-Locking Condition
Determine 1 presents conventional gears (a) and self-locking gears (b), in case of backdriving. Figure 2 presents typical gears (a) and self-locking gears (b), in the event of inertial driving. Almost all conventional equipment drives possess the pitch level P situated in the active portion the contact range B1-B2 (Figure 1a and Figure 2a). This pitch stage location provides low particular sliding velocities and friction, and, subsequently, high driving productivity. In case when this sort of gears are motivated by output load or inertia, they will be rotating freely, because the friction point in time (or torque) isn’t sufficient to avoid rotation. In Figure 1 and Figure 2:
1- Driving pinion
2 – Driven gear
db1, db2 – base diameters
dp1, dp2 – pitch diameters
da1, da2 – outer diameters
T1 – driving pinion torque
T2 – driven gear torque
T’2 – driving torque, applied to the gear
T’1 – driven torque, put on the pinion
F – driving force
F’ – generating force, when the backdriving or perhaps inertial torque applied to the gear
aw – operating transverse pressure angle
g – arctan(f) – friction angle
f – average friction coefficient
To make gears self-locking, the pitch point P ought to be located off the effective portion the contact line B1-B2. There are two options. Alternative 1: when the point P is placed between a centre of the pinion O1 and the point B2, where in fact the outer size of the apparatus intersects the contact line. This makes the self-locking possible, however the driving proficiency will end up being low under 50 percent [3]. Option 2 (figs 1b and 2b): when the idea P is put between your point B1, where the outer diameter of the pinion intersects the line contact and a center of the apparatus O2. This sort of gears can be self-locking with relatively high driving effectiveness > 50 percent.
Another condition of self-locking is to truly have a satisfactory friction angle g to deflect the force F’ beyond the center of the pinion O1. It creates the resisting self-locking point in time (torque) T’1 = F’ x L’1, where L’1 is usually a lever of the push F’1. This condition could be offered as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – equipment ratio,
n1 and n2 – pinion and gear number of teeth,
– involute profile angle at the tip of the gear tooth.
Design of Self-Locking Gears
Self-locking gears are customized. They cannot end up being fabricated with the benchmarks tooling with, for example, the 20o pressure and rack. This makes them incredibly suited to Direct Gear Design® [5, 6] that provides required gear performance and from then on defines tooling parameters.
Direct Gear Design presents the symmetric equipment tooth shaped by two involutes of one base circle (Figure 3a). The asymmetric equipment tooth is produced by two involutes of two distinct base circles (Figure 3b). The tooth hint circle da allows avoiding the pointed tooth suggestion. The equally spaced teeth form the apparatus. The fillet profile between teeth was created independently in order to avoid interference and provide minimum bending tension. The working pressure angle aw and the contact ratio ea are described by the following formulae:
– for gears with symmetric teeth
(3) Equation 3
(4) Equation 4
– for gears with asymmetric teeth
(5) Equation 5
(6) Equation 6
(7) Equation 7
where:
inv(x) = tan x – x – involute function of the profile angle x (in radians).
Conditions (1) and (2) show that self-locking requires ruthless and huge sliding friction in the tooth get in touch with. If the sliding friction coefficient f = 0.1 – 0.3, it needs the transverse operating pressure angle to aw = 75 – 85o. As a result, the transverse get in touch with ratio ea < 1.0 (typically 0.4 - 0.6). Lack of the transverse get in touch with ratio should be compensated by the axial (or face) get in touch with ratio eb to guarantee the total get in touch with ratio eg = ea + eb ≥ 1.0. This is often attained by using helical gears (Physique 4). Nevertheless, helical gears apply the axial (thrust) power on the gear bearings. The twice helical (or “herringbone”) gears (Number 4) allow to pay this force.
Large transverse pressure angles lead to increased bearing radial load that may be up to four to five situations higher than for the traditional 20o pressure angle gears. Bearing selection and gearbox housing design should be done accordingly to hold this increased load without high deflection.
Application of the asymmetric teeth for unidirectional drives permits improved performance. For the self-locking gears that are used to prevent backdriving, the same tooth flank is used for both driving and locking modes. In this case asymmetric tooth profiles give much higher transverse contact ratio at the presented pressure angle compared to the symmetric tooth flanks. It makes it possible to reduce the helix angle and axial bearing load. For the self-locking gears that used to prevent inertial driving, distinct tooth flanks are being used for driving and locking modes. In this case, asymmetric tooth account with low-pressure position provides high performance for driving function and the contrary high-pressure angle tooth profile is employed for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype pieces were made based on the developed mathematical designs. The gear data are presented in the Table 1, and the test gears are offered in Figure 5.
The schematic presentation of the test setup is displayed in Figure 6. The 0.5Nm electric engine was used to operate a vehicle the actuator. A built-in swiftness and torque sensor was attached on the high-velocity shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low swiftness shaft of the gearbox via coupling. The type and productivity torque and speed info were captured in the info acquisition tool and additional analyzed in a computer applying data analysis program. The instantaneous efficiency of the actuator was calculated and plotted for a broad range of speed/torque combination. Normal driving performance of the self- locking gear obtained during assessment was above 85 percent. The self-locking property of the helical gear set in backdriving mode was as well tested. During this test the external torque was applied to the output gear shaft and the angular transducer revealed no angular motion of source shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears had been found in textile industry [2]. On the other hand, this kind of gears has various potential applications in lifting mechanisms, assembly tooling, and other equipment drives where the backdriving or inertial traveling is not permissible. Among such program [7] of the self-locking gears for a continually variable valve lift system was suggested for an vehicle engine.
Summary
In this paper, a basic principle of function of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles are shown, and tests of the gear prototypes has proved relatively high driving productivity and trusted self-locking. The self-locking gears may find many applications in various industries. For instance, in a control devices where position stability is vital (such as for example in automotive, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to achieve required performance. Similar to the worm self-locking gears, the parallel axis self-locking gears are very sensitive to operating conditions. The locking reliability is affected by lubrication, vibration, misalignment, etc. Implementation of these gears should be done with caution and needs comprehensive testing in all possible operating conditions.
