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High-Performance Plastic Gears

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Recent Advances in Gearing

Abstract

Plastic gears have been used for decades in a wide variety of applications such as consumer articles or electromechanical actuators in the automotive sector. Plastic specific material properties such as low-density and high-damping characteristics and the possibility of mass production through injection molding are advantageous and contribute to the increasing application of plastic gears. However, the comparatively large differences in material properties compared to steel result in plastic gears mostly being used in low-power drives. In particular, the high-temperature dependency of the material properties and lower strength numbers often represent a challenge for the application of plastic gears.

In most cases, plastic gears are running dry or under starved lubrication. In the context of these operating conditions, the transmission of motion is often of principal importance as the potential to transmit power is limited due to the high level of frictional heat in combination with limited capability for heat removal. The use of a lubricant is required for the transmission of increased power. Grease lubrication offers the possibility of heat dissipation and the reduction of wear. If even higher power is to be transmitted, oil lubrication is required. Operation under oil lubrication separates the tooth flanks from each other and ensures effective dissipation of the heat generated in tooth contact.

Today, VDI 2736 is mainly used for the design and rating of plastic gears. In addition to information on the design of the wheel body and manufacturing of plastic gears, this guideline contains approaches for temperature calculation and load carrying capacity calculation. Due to the high-temperature dependency of the material properties of thermoplastic materials, knowledge of the gear temperature is of essential importance in the design of plastic gears and one of the main steps of the load carrying capacity calculation. VDI 2736 uses the basic principles of the standard DIN 3990 developed for steel gears to calculate the tooth root and tooth flank load capacity. Especially the high deflections under load compared to steel gears are currently not sufficiently considered in VDI 2736. Current research provides new knowledge on the consideration of deflection effects and their influence on the gear load carrying capacity of modern thermoplastic materials and contributes to the optimized design of plastic gears. On the material side, new high-performance plastics are constantly being developed, which further increase the temperature resistance and strength properties required. In addition to widely used materials such as polyacetal and polyamides, polyetheretherketones and other high-performance materials are increasingly being applied. Today, the low availability of standardized strength values represents a challenge for the design of ideally dimensioned components. For this reason, in addition to the investigation of the thermal and tribological operating behavior of plastic gears, the generation of standardized determined strength values is of particular interest.

The following chapter presents an overview of the state of the art and application of plastic gears, introduces existing design and calculation methods for plastic gears, and summarizes some main results of actual research work performed at FZG institute.

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Abbreviations

a (mm):

Center distance

aACR (–):

Auxiliary factor to calculate Yε, ACR

AG (m2):

Heat dissipating surface of the mechanism housing

b (mm):

Face width

bH (mm):

Hertzian semi-width

bw (mm):

Common face width of the gear pair

Cα (μm):

Amount of tip relief

c′ (N/(mm∙μm)):

Single stiffness

d1 (mm):

Reference diameter

ED (–):

Relative tooth-engagement time

FN (N):

Normal force

FR (N):

Friction force

Ft (N):

Tangential force

fzi (–):

Correction factor of Δεw

fεβ (–):

Correction factor of overlap ratio

i (–):

Transmission ratio

HV (–):

Tooth loss factor

KA (–):

Application factor

KF (–):

Application factor for tooth root load

KFα (–):

Face factor

KFβ (–):

Width factor

KH (–):

Factor for tooth flank loading

Kv (–):

Dynamic factor

kW 10−6∙mm3/(N∙m):

Wear coefficient

kϑ, Fla K∙(m/s)0.75∙mm1.75/W:

Heat transfer coefficient of the plastic gear (flank)

kϑ, Fuß K∙(m/s)0.75∙mm1.75/W:

Heat transfer coefficient of the plastic gear (root)

lFl (mm):

Profile line length of the active tooth flank

mn (mm):

Normal module

NL (–):

Number of load cycles

P (W):

Power

pet (mm):

Transverse normal base pitch

pH (N/mm2):

Hertzian pressure

Rλ, G (K∙mm2/W):

Heat transfer resistance of the mechanism housing

SFmin (–):

Required minimum safety factor (root)

SHmin (–):

Required minimum safety factor (flank)

T1, 2 (Nm):

Torque

Td (Nm):

Torque

u (–):

Transmission ratio

v1, 2 (m/s):

Circumferential speed

vg (m/s):

Sliding speed

vt (m/s):

Tangential speed

vΣ (m/s):

Sum speed

Vol (m3):

Volume

w (N/mm):

Normal line load

Wm (mm):

Averaged linear wear

Wzul (mm):

Permissible linear wear

YFa (–):

Form factor

YSa (–):

Stress correction factor

YSt (–):

Stress correction factor

Yβ (–):

Helix angle factor

Yε (–):

Contact ratio factor

Yε, ACR (–):

Modified contact ratio factor

z1, 2 (–):

Number of teeth (pinion/wheel)

ZE (–):

Elasticity factor

ZH (–):

Zone factor

ZR (–):

Surface roughness factor

Zβ (–):

Spiral angle factor

Zε (–):

Contact ratio factor

Δεw (–):

Load-induced increase in actual contact ratio

Δεzi (–):

Approximated increase in actual contact ratio due to the numbers of teeth

Δϑtooth (K):

Increase of tooth temperature

εα (–):

Transverse contact ratio

εα, w, mod (–):

Modified actual contact ratio

ϑ0 (°C):

Ambient temperature

ϑFuß (°C):

Tooth root temperature

ϑFla (°C):

Tooth flank temperature

ϑM (°C):

Bulk temperature

ϑOil (°C):

Oil temperature

μ (–):

Coefficient of friction

σF (N/mm2):

Tooth root stress

σF0 (N/mm2):

Nominal tooth root stress

σFlimN (N/mm2):

Fatigue strength

σFP (N/mm2):

Permissible root strength

σH (N/mm2):

Flank pressure

σHlimN (N/mm2):

Rolling contact fatigue strength

σHP (N/mm2):

Permissible flank pressure

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Authors and Affiliations

  1. Gear Research Centre (FZG), Technical University of Munich (TUM), Munich, Germany

    C. M. Illenberger, T. Tobie & K. Stahl

Authors
  1. C. M. Illenberger
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  2. T. Tobie
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  3. K. Stahl
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Corresponding author

Correspondence to C. M. Illenberger .

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Editors and Affiliations

  1. Mechanical Engineering, Sterling Heights, MI, USA

    Stephen P. Radzevich

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Illenberger, C.M., Tobie, T., Stahl, K. (2022). High-Performance Plastic Gears. In: Radzevich, S.P. (eds) Recent Advances in Gearing. Springer, Cham. https://doi.org/10.1007/978-3-030-64638-7_4

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  • DOI: https://doi.org/10.1007/978-3-030-64638-7_4

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