Worm gearboxes with countless combinations
Ever-Power offers an extremely wide range of worm gearboxes. Because of the modular design the typical programme comprises countless combinations in terms of selection of gear housings, mounting and connection options, flanges, shaft styles, type of oil, surface therapies etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is simple and well proven. We just use high quality components such as residences in cast iron, aluminum and stainless steel, worms in case hardened and polished metal and worm tires in high-grade bronze of special alloys ensuring the the best possible wearability. The seals of the worm gearbox are given with a dust lip which efficiently resists dust and normal water. Furthermore, the gearboxes happen to 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 single step or 10.000:1 in a double reduction. An equivalent gearing with the same gear ratios and the same transferred electricity is bigger than a worm gearing. Meanwhile, the worm gearbox is definitely in a more simple design.
A double reduction may be composed of 2 standard gearboxes or as a particular gearbox.
Compact design
Compact design is one of the key phrases of the typical gearboxes of the Ever-Power-Series. Further optimisation can be achieved by using adapted gearboxes or exceptional gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is due to the very clean working of the worm gear combined with the application of cast iron and high precision on component manufacturing and assembly. Regarding the our accuracy gearboxes, we have extra attention of any sound which can be interpreted as a murmur from the apparatus. Therefore the general noise level of our gearbox can be reduced to an absolute minimum.
Angle gearboxes
On the worm gearbox the input shaft and output shaft are perpendicular to each other. This often proves to be a decisive edge producing the incorporation of the gearbox significantly simpler and smaller sized.The worm gearbox can be an angle gear. This can often be an advantage for incorporation into constructions.
Strong bearings in sturdy housing
The output shaft of the Ever-Power worm gearbox is very firmly embedded in the apparatus house and is suitable for self locking gearbox Direct suspension for wheels, movable arms and other parts rather than having to create a separate suspension.
Self locking
For larger equipment ratios, Ever-Electricity worm gearboxes provides a self-locking effect, which in many situations can be used as brake or as extra secureness. Likewise spindle gearboxes with a trapezoidal spindle will be self-locking, making them well suited for a wide selection of solutions.
In most gear drives, when driving torque is suddenly reduced consequently of vitality off, torsional vibration, electric power outage, or any mechanical failure at the tranny input aspect, then gears will be rotating either in the same way driven by the system inertia, or in the contrary way driven by the resistant output load due to gravity, planting season load, etc. The 
latter state is known as backdriving. During inertial action or backdriving, the motivated output shaft (load) becomes the generating one and the generating input shaft (load) turns into the motivated one. There are several gear drive applications where outcome shaft driving is undesirable. To be able to prevent it, various kinds of brake or clutch products are used.
However, additionally, there are solutions in the gear tranny that prevent inertial action or backdriving using self-locking gears with no additional gadgets. The most typical one is certainly a worm equipment with a low lead angle. In self-locking worm gears, torque used from the load side (worm gear) is blocked, i.e. cannot drive the worm. Nevertheless, their application includes some limitations: the crossed axis shafts’ arrangement, relatively high gear ratio, low velocity, low gear mesh performance, increased heat era, etc.
Also, there happen to be parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can use any equipment ratio from 1:1 and higher. They have the traveling mode and self-locking setting, when the inertial or backdriving torque is put on the output gear. Originally these gears had suprisingly low ( <50 percent) generating proficiency that limited their app. Then it had been proved [3] that excessive driving efficiency of such gears is possible. Requirements of the self-locking was analyzed in the following paragraphs [4]. This paper explains the basic principle of the self-locking method for the parallel axis gears with symmetric and asymmetric pearly whites profile, and reveals their suitability for diverse applications.
Self-Locking Condition
Number 1 presents conventional gears (a) and self-locking gears (b), in case of backdriving. Figure 2 presents conventional gears (a) and self-locking gears (b), in the event of inertial driving. Almost all conventional gear drives possess the pitch level P located in the active portion the contact series B1-B2 (Figure 1a and Body 2a). This pitch level location provides low particular sliding velocities and friction, and, due to this fact, high driving effectiveness. In case when this kind of gears are influenced by end result load or inertia, they happen to be rotating freely, as the friction minute (or torque) is not 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, put on the gear
T’1 – driven torque, put on the pinion
F – driving force
F’ – driving force, when the backdriving or inertial torque put on 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 should be located off the energetic portion the contact line B1-B2. There are two options. Choice 1: when the idea P is placed between a middle of the pinion O1 and the point B2, where the outer size of the apparatus intersects the contact collection. This makes the self-locking possible, but the driving proficiency will become low under 50 percent [3]. Choice 2 (figs 1b and 2b): when the idea P is positioned between the point B1, where the outer diameter of the pinion intersects the line contact and a center of the apparatus O2. This sort of gears could be self-locking with relatively excessive driving proficiency > 50 percent.
Another condition of self-locking is to truly have a sufficient friction angle g to deflect the force F’ beyond the center of the pinion O1. It creates the resisting self-locking moment (torque) T’1 = F’ x L’1, where L’1 can be a lever of the induce F’1. This condition could be offered as L’1min > 0 or
(1) Equation 1
or
(2) Equation 2
where:
u = n2/n1 – gear 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 custom. They cannot become 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 functionality and after that defines tooling parameters.
Direct Gear Style presents the symmetric gear tooth shaped by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is produced by two involutes of two diverse base circles (Figure 3b). The tooth tip circle da allows avoiding the pointed tooth tip. The equally spaced the teeth form the gear. The fillet profile between teeth was created independently to avoid interference and offer minimum bending stress. The operating pressure angle aw and the get in touch with ratio ea are described by the next 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 high pressure and high 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. Because of this, the transverse speak to ratio ea < 1.0 (typically 0.4 - 0.6). Insufficient the transverse speak to ratio should be compensated by the axial (or face) contact ratio eb to guarantee the total contact ratio eg = ea + eb ≥ 1.0. This can be achieved by using helical gears (Determine 4). On the other hand, helical gears apply the axial (thrust) force on the gear bearings. The dual helical (or “herringbone”) gears (Determine 4) allow to compensate this force.
High transverse pressure angles bring about increased bearing radial load that could be up to four to five situations higher than for the traditional 20o pressure angle gears. Bearing assortment and gearbox housing design ought to be done accordingly to hold this increased load without abnormal deflection.
App of the asymmetric tooth for unidirectional drives allows for improved performance. For the self-locking gears that are used to avoid backdriving, the same tooth flank can be used for both generating and locking modes. In this instance asymmetric tooth profiles present much higher transverse get in touch with ratio at the granted pressure angle than the symmetric tooth flanks. It creates 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 traveling and locking modes. In cases like this, asymmetric tooth account with low-pressure position provides high efficiency for driving setting and the opposite high-pressure angle tooth account is employed for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype units were made based on the developed mathematical types. The gear info are shown in the Desk 1, and the test gears are presented in Figure 5.
The schematic presentation of the test setup is shown in Figure 6. The 0.5Nm electric engine was used to operate a vehicle the actuator. A acceleration and torque sensor was installed on the high-rate shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was connected to the low rate shaft of the gearbox via coupling. The source and end result torque and speed information were captured in the info acquisition tool and additional analyzed in a computer employing data analysis application. The instantaneous efficiency of the actuator was calculated and plotted for an array of speed/torque combination. Ordinary driving performance of the personal- locking equipment obtained during tests was above 85 percent. The self-locking real estate of the helical equipment occur backdriving mode was likewise tested. During this test the external torque was put on the output gear shaft and the angular transducer demonstrated no angular movements of insight shaft, which verified the self-locking condition.
Potential Applications
Initially, self-locking gears were used in textile industry [2]. Even so, this kind of gears has a large number of potential applications in lifting mechanisms, assembly tooling, and other gear drives where in fact the backdriving or inertial generating is not permissible. One of such app [7] of the self-locking gears for a continuously variable valve lift system was suggested for an automobile engine.
Summary
In this paper, a theory of operate of the self-locking gears has been described. Design specifics of the self-locking gears with symmetric and asymmetric profiles are shown, and screening of the apparatus prototypes has proved fairly high driving proficiency and dependable self-locking. The self-locking gears could find many applications in various industries. For example, in a control systems where position stability is vital (such as for example in motor vehicle, aerospace, medical, robotic, agricultural etc.) the self-locking allows to attain required performance. Like the worm self-locking gears, the parallel axis self-locking gears are very sensitive to operating circumstances. The locking reliability is influenced by lubrication, vibration, misalignment, etc. Implementation of these gears should be finished with caution and needs comprehensive testing in every possible operating conditions.