Sprag Clutches Help Reduce Drag & Improve Battery Life

German-crafted GMN clutches offer a flexible solution for a variety of electric vehicle designs, including Light-Duty Commercial Trucks & People Movers. Our sprag clutches are a top choice for EV designs.

Executive Summary

GMN Bearing USA is a super precision component supplier of GMN German-manufactured bearings, clutches & seals. We are focused on improving the Electric Vehicle (EV) industry, helping to solve two of the market’s top 10 customer concerns: Mileage range & battery life. Through our exclusive FE 8000 Sprag Clutch design, GMN can help improve both issues so manufacturers & drivers can get more out of their EVs.

Read on to learn how this expertly designed, highly engineered component can offer up to 10% more battery life.

Benefits of Integrated Clutches to Light-Duty Commercial Electric Vehicles & People Movers

In a Battery Electric Vehicle (BEV), battery life can mean the difference between making it to your destination on time or being late because you had to charge your battery as it lacks the energy to make it the distance you need to go.

Apart from inconvenience, vehicle downtime also has a financial impact. For fleet managers of light-duty commercial vehicles & people movers, low battery life means fewer deliveries/pick-ups, which translates to less revenue.

A solution? GMN sprag clutches are designed to allow for an automatic disconnection of key drive train components. This allows your BEV to “coast” with minimal drag to its drive train components, decreasing battery consumption and increasing mileage longevity.

Does your electric vehicle design have multiple motors? No problem!

One way to decrease drag and increase battery longevity is to decouple one or more of the motors when it is not required. This enables the additional motors to be disconnected and not further drain the battery when the vehicle is not accelerating, while relying on one motor to maintain speed.

Likewise, decoupling any unused drive train components will reduce the overall drag on the system. Less drag means less battery consumption, which extends mileage per charge.

Where to Place A Sprag Clutch in Your EV’s Drive Train

Another benefit to the GMN FE 8000 is its versatility. Because of GMN’s simple yet effective sprag clutch design, it can be placed in multiple locations in your EV’s drive train. Here are just a few:

Wheel Hub

More recent EV technology has incorporated compact-sized motors inside of each wheel. Although this complex set-up promotes speed, the additional motors can be detrimental to overall battery life as they consume more power and introduce more drag to the system.

The integration of a GMN sprag clutch to disconnect the in-wheel hub motors allows for that overriding to protect your battery charge.

Rear Differential

The use of electric motors within the light- to medium-duty commercial vehicle sector has gained increasing popularity in recent years.

The increased load capacity of larger vehicles means more overall drag on the system to carry those loads. Here is where the ability to disconnect the rear differential becomes extremely advantageous.

Drive Train

Similar to the benefits of disconnecting the rear differential, disconnecting front and or rear drivetrain components will reduce overall system drag and allows for more mileage.

What makes a Sprag Clutch the best design for EVs?

Now that we have introduced the concept of decoupling/disconnecting drivetrain components to prolong battery life, let’s examine why sprag clutches are best suited for EV applications when compared with other clutch designs.

To start, clutch mechanisms can be either active or passive.

Active Clutches, such as dog or traditional friction plate clutches, are required to be actuated in or out of engagement.

Passive clutches, such as ratchet and pawl or sprag systems, allow the drive mechanism to disengage from the driven components when the input RPM drops below the output.

Let’s compare a few designs and learn why the GMN FE 8000 sprag clutch is the one-way bearing of choice for EVs.

Active Dog Clutches

These use an interference to couple two rotating shafts (or gears). They are typically made of two round plates—one fixed to the driving shaft or gear & the other on the shaft or gear that’s being driven.

One of these plates will have protrusions machined into the face that resemble the top of a castle wall while the other has identically shaped recesses that will receive those protrusions once engaged.

Advantages of using this type of clutch include high transient torque capabilities and being bi-directional. However, backlash between the teeth or gears can be a disadvantage in some applications.

Active dog clutches also require actuation which makes it extraordinarily complex to utilize as well as reduce energy consumption. Additionally, the delay between when the clutch is called for engagement and when the clutch is engaged can seem very rough.

Electromagnetic/Electromechanical Clutches

These actuate or engage electrically but transmit torque mechanically.

The most common design consists of THREE major parts: An electromagnetic coil, a rotor that connects to the input shaft, and an armature that connects to the output shaft via sprocket or pulley.

These types of clutches are common in today’s EVs, however many consumers have advised that the operation is not very timely or smooth.

Roller Ramp Clutches

Mainly used in heavy duty applications that require durability in a clutch, roller ramp clutches consist of FOUR main components: The outer ring, the clamping rollers, the inner ring with clamping ramps, and the spring loader for each roller.

Friction between the roller and the ramp makes each roller wedge tightly when the inner member rotates in the driving direction thus engaging the clutch.

The advantage of this type of clutch is that it is passive and requires no external actuation device. However, it is bulky in size (when compared to sprag clutches) as it requires the use of inner and outer rings to integrate the ramps.

Additionally, the amount of space needed for the ramps limits how many rollers can be used for a given clutch. Since sprags don’t need nearly as much space, numerous sprags can fit in the space required for a single roller in a roller ramp clutch. More sprags mean there are more elements to transfer torque which corresponds to a higher torque capacity.

Sprag Clutches

These clutches are designed to transfer torque when the input rotation forces the sprags to engage. The sprags themselves are taller than the radial gap between the inner & outer races in which the sprags engage. The sprags are highly engineered & tightly controlled curved surfaces on the top and bottom and use a spring to keep them in constant contact with the mating races. When the input RPM decreases below the output RPM, the frictional force generated by the engaged sprags is released and the surfaces begin to slip allowing the system to freewheel.

Why GMN Sprag Clutches are the best choice for EVs – high torque, no RPM limits

Not all sprag clutches (aka, “insert elements”) are created equal. Consider the GMN FE 8000 Sprag Clutch. There are several factors that make this clutch a stand-out:

High torque capacity

The GMN FE 8000 has more sprags in its design than most other sprag clutches on the market. This key characteristic means GMN sprag clutches consistently have up to double the torque capacity. This equivalates to possibly using a smaller size clutch for your torque needs. More torque could mean a higher safety factor for your design.

Unique sprag curvature

GMN’s distinctive geometric design of the cam sprag is a “non-lift-off design.” At a high rotation speed, centrifugal force will produce a pressing torque on the sprags, no matter how fast the spooling speed. This means there are no RPM limits!

Single cage design

Rather than a dual cage, a single cage supports the components and allows for an increased number of sprags over other brands. GMN’s clutches also operate directly against the system shaft and housing, not requiring complex mating surfaces.

No drag clips

Some sprag manufacturers use drag clips to prevent the sprags from rotating too fast and lifting off. This creates extra wear on the inner sprag surfaces. Because GMN sprags don’t have to worry about lift off, there is no need for drag clips, resulting in much less wear.

Angle of twist

One of the most important features of any sprag clutch is the rotational distance required for the sprag to engage, better known as the twisting angle.

For GMN clutches, the twisting angle is typically under 3° for nominal torque values, but if the torque is small that twisting angle can be close to 0°. Relative to other clutch mechanisms, even 3° is considered quite low.

Contact GMN Bearing USA for EV Sprag Clutch Support

Depending on your Electric Vehicle design, GMN Sprag Clutches may be the perfect solution for helping to increase your battery life & time on the road—all while also not sacrificing performance.

Let’s see if GMN sprag clutches can be the game-changing component in your EV design. GMN Bearing USA’s Mechanical Engineers are here to learn more about your EV dreams & how GMN Sprag Clutches can give you the boost to set you apart from the pack!