Worm gearboxes with many combinations
Ever-Power offers a very wide range of worm gearboxes. Because of the modular design the typical programme comprises countless combinations when it comes to selection of gear housings, mounting and connection options, flanges, shaft designs, type of oil, surface therapies etc.
Sturdy and reliable
The design of the Ever-Power worm gearbox is simple and well proven. We simply use top quality components such as homes in cast iron, lightweight aluminum and stainless, worms in case hardened and polished metal and worm wheels in high-quality bronze of unique alloys ensuring the the best wearability. The seals of the worm gearbox are provided with a dust lip which effectively resists dust and drinking water. In addition, the gearboxes happen to be greased for life with synthetic oil.
Large self locking gearbox reduction 100:1 in a single step
As default the worm gearboxes enable reductions as high as 100:1 in one step or 10.000:1 in a double reduction. An equivalent gearing with the same equipment ratios and the same transferred ability is bigger when compared to a worm gearing. At the same time, the worm gearbox is normally in a far more simple design.
A double reduction could be composed of 2 common gearboxes or as a particular gearbox.
Compact design
Compact design is probably the key words of the typical gearboxes of the Ever-Power-Series. Further optimisation may be accomplished by using adapted gearboxes or particular gearboxes.
Low noise
Our worm gearboxes and actuators are extremely quiet. This is because of the very easy running of the worm gear combined with the utilization of cast iron and large precision on component manufacturing and assembly. In connection with our precision gearboxes, we consider extra treatment of any sound which can be interpreted as a murmur from the gear. Therefore the general noise degree 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 one another. This typically proves to be a decisive benefits producing the incorporation of the gearbox substantially simpler and more compact.The worm gearbox is an angle gear. This can often be an edge for incorporation into constructions.
Strong bearings in stable housing
The output shaft of the Ever-Power worm gearbox is very firmly embedded in the gear house and is ideal for direct suspension for wheels, movable arms and other parts rather than having to create a separate suspension.
Self locking
For larger equipment ratios, Ever-Electric power worm gearboxes will provide a self-locking result, which in lots of situations can be used as brake or as extra protection. As well spindle gearboxes with a trapezoidal spindle are self-locking, making them ideal for a wide range of solutions.
In most gear drives, when traveling torque is suddenly reduced therefore of power off, torsional vibration, electrical power outage, or any mechanical failing at the transmission input area, then gears will be rotating either in the same direction driven by the machine inertia, or in the contrary path driven by the resistant output load due to gravity, planting season load, etc. The latter state is called backdriving. During inertial action or backdriving, the motivated output shaft (load) turns into the traveling one and the traveling input shaft (load) turns into the driven one. There are several gear drive applications where outcome shaft driving is unwanted. As a way to prevent it, various kinds of brake or clutch devices are used.
However, there are also solutions in the gear transmitting that prevent inertial movement or backdriving using self-locking gears with no additional devices. The most typical one is certainly a worm equipment with a low lead angle. In self-locking worm gears, torque used from the strain side (worm equipment) is blocked, i.e. cannot travel the worm. Nevertheless, their application comes with some constraints: the crossed axis shafts’ arrangement, relatively high gear ratio, low swiftness, low gear mesh performance, increased heat era, etc.
Also, there are parallel axis self-locking gears [1, 2]. These gears, unlike the worm gears, can make use of any equipment ratio from 1:1 and larger. They have the driving mode and self-locking method, when the inertial or backdriving torque is definitely put on the output gear. At first these gears had very low ( <50 percent) driving effectiveness that limited their app. Then it had been proved [3] that large driving efficiency of such gears is possible. Requirements of the self-locking was analyzed on this page [4]. This paper explains the theory of the self-locking process for the parallel axis gears with symmetric and asymmetric teeth profile, and reveals their suitability for diverse applications.
Self-Locking Condition
Determine 1 presents conventional gears (a) and self-locking gears (b), in case of backdriving. Figure 2 presents standard gears (a) and self-locking gears (b), in the event of inertial driving. Practically all conventional gear drives have the pitch point P situated in the active part the contact brand B1-B2 (Figure 1a and Physique 2a). This pitch level location provides low certain sliding velocities and friction, and, due to this fact, high driving efficiency. In case when such gears are influenced by end result load or inertia, they happen to be rotating freely, as the friction instant (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 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 should be located off the effective portion the contact line B1-B2. There will be two options. Option 1: when the point P is positioned between a center 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, however the driving efficiency will always be low under 50 percent [3]. Option 2 (figs 1b and 2b): when the point P is put between the point B1, where the outer diameter of the pinion intersects the collection contact and a middle of the apparatus O2. This type of gears can be self-locking with relatively substantial driving performance > 50 percent.
Another condition of self-locking is to have a ample friction angle g to deflect the force F’ beyond the center of the pinion O1. It generates the resisting self-locking moment (torque) T’1 = F’ x L’1, where L’1 is usually a lever of the power F’1. This condition could be shown 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 customized. They cannot be fabricated with the requirements tooling with, for example, the 20o pressure and rack. This makes them very well suited for Direct Gear Design® [5, 6] that provides required gear 
performance and from then on defines tooling parameters.
Direct Gear Design presents the symmetric gear tooth shaped by two involutes of 1 base circle (Figure 3a). The asymmetric gear tooth is formed by two involutes of two distinct base circles (Figure 3b). The tooth tip circle da allows avoiding the pointed tooth suggestion. The equally spaced the teeth form the gear. The fillet profile between teeth was created independently in order to avoid interference and provide minimum bending anxiety. The functioning pressure angle aw and the get in touch with ratio ea are identified 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 large sliding friction in the tooth get in touch with. If the sliding friction coefficient f = 0.1 – 0.3, it requires 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 speak to ratio should be compensated by the axial (or face) get in touch with ratio eb to ensure the total speak to ratio eg = ea + eb ≥ 1.0. This could be achieved by using helical gears (Shape 4). On the other hand, helical gears apply the axial (thrust) induce on the gear bearings. The twice helical (or “herringbone”) gears (Number 4) allow to pay this force.
Substantial transverse pressure angles bring about increased bearing radial load that may be up to four to five times higher than for the traditional 20o pressure angle gears. Bearing variety and gearbox housing design should be done accordingly to hold this improved load without extreme deflection.
Application of the asymmetric teeth for unidirectional drives permits improved overall performance. For the self-locking gears that are used to prevent backdriving, the same tooth flank is utilized for both traveling and locking modes. In this case asymmetric tooth profiles present much higher transverse get in touch with ratio at the granted pressure angle compared to the symmetric tooth flanks. It creates it possible to reduce the helix position and axial bearing load. For the self-locking gears which used to prevent inertial driving, several tooth flanks are being used for traveling and locking modes. In this instance, asymmetric tooth profile with low-pressure position provides high performance for driving method and the opposite high-pressure angle tooth profile is used for reliable self-locking.
Testing Self-Locking Gears
Self-locking helical gear prototype sets were made based on the developed mathematical products. The gear info are offered in the Table 1, and the check gears are shown 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. An integrated speed and torque sensor was mounted on the high-velocity shaft of the gearbox and Hysteresis Brake Dynamometer (HD) was linked to the low quickness shaft of the gearbox via coupling. The input and output torque and speed info were captured in the info acquisition tool and further analyzed in a pc employing data analysis software program. The instantaneous efficiency of the actuator was calculated and plotted for a broad range of speed/torque combination. Normal driving productivity of the personal- locking equipment obtained during examining was above 85 percent. The self-locking home of the helical gear occur backdriving mode was also tested. During this test the external torque was put on the output equipment shaft and the angular transducer confirmed no angular movements of input shaft, which confirmed the self-locking condition.
Potential Applications
Initially, self-locking gears were found in textile industry [2]. On the other hand, this kind of gears has many potential applications in lifting mechanisms, assembly tooling, and other equipment drives where in fact the backdriving or inertial generating is not permissible. One of such program [7] of the self-locking gears for a consistently variable valve lift program was suggested for an car engine.
Summary
In this paper, a principle of function of the self-locking gears has been described. Style specifics of the self-locking gears with symmetric and asymmetric profiles will be shown, and examining of the gear prototypes has proved fairly high driving efficiency and trusted self-locking. The self-locking gears could find many applications in a variety of industries. For example, in a control devices where position balance is important (such as in automotive, aerospace, medical, robotic, agricultural etc.) the self-locking will allow to achieve required performance. Like the worm self-locking gears, the parallel axis self-locking gears are hypersensitive to operating conditions. The locking reliability is influenced by lubrication, vibration, misalignment, etc. Implementation of the gears should be finished with caution and requires comprehensive testing in all possible operating conditions.