Single-Orifice Restrictors in eAxles and EDUs

using single-orifice restrictors withIn Electric vehicles

In eAxles and EDU, single-orifice restrictors can be used to lubricate or cool certain portions of the system. These components (single-orifice restrictors) are called many different things depending on the company and include restrictors, orifices, lube jets, lube orifices, lubrication orifices, targeting orifice/restrictor, or oil spray nozzle. Specifically, these restrictors typically will lubricate where gears mesh together, creating friction and heat that needs to be dissipated, and bearings which need lubrication. The lubrication and cooling oil are typically also used to cool other parts of the system like the electric motor as well. There can be restrictors in there as well, but the feed will require more flow than we can provide with our precision micro orifices.

Common electric vehicle design engineer questions

• How do you lubricate and cool the gear train in your eAxle/EDU/EDU? Do you use splash cooling, or do you have a forced lubrication system?
• If forced lubrication, what do you currently use to target or spray the lubrication oil and what is the system pressure of this portion of the system?
• If splash cooling, do you intend to move towards forced lubrication on the next generation system to reduce weight and improve efficiency? And if so, what will you use as lubrication orifice?
• Have they thought about ways to reduce the weight of the entire system? For example, could they downsize their oil pump by using smaller more precisions orifices that have a lower flow requirement, but higher fluid velocity to lubricate and cool the system as effectively? This would also reduce the fluid requirements of the system which would also reduce weight.
• How is the electric motor, rotor, bearing and stator cooled and lubricated in their eAxle/EDU/EDM?
• Do they utilize any directed cooling/lubrication in their electric motor, rotor, stator and bearings? Are their spots that get hotter and need more cooling under certain driving conditions?

Lee Advantage

Lubrication jets are not new to the automotive industry and have been used in ICE (internal combustion engine) vehicles for years. In those ICE transmissions though, the internal pressure of the system is typically in the range of 35-70 bar (500-1000 psi), with the lubrication being slightly lower, but still high enough where very large holes can be used or even cup plugs with a pierced hole will work. Since these solutions are relatively low-cost, Lee restrictors have not been able to replace these components.

On electric vehicles, the pressures inside the eAxles or EDU typically max out around 35 bar (500 psi) and the lubrication system can be as high as 20 bar (290 psi), and we’ve seen as low as 1 bar (14.5 psi). At these pressures, very large holes or pierced holes won’t create a uniform straight stream of fluid and in many instances cannot be used anymore.

If the customer is at the higher end of the lubrication system pressure range, they may be able to use some of these larger drilled holes on the range of ∅1.5 mm to ∅5 mm. The compromises designers will have to make though is they will have to size their electric oil pump big enough to accommodate flow through all these orifices continuously. They previously had to do with ICE vehicles as well, but the oil pump was driven off the crankshaft so the energy to power the pump was already available. In an electric vehicle, that pump is powered by the batteries in the vehicle so the larger the pump, the more energy it requires, and that directly reduces the range of the vehicle.

To reduce the energy needs of the pump, designers could instead design smaller Lee restrictors in their system that could accomplish the same lubrication and cooling function as larger holes. Our restrictors would have reduced fluid flow, but increased fluid velocity to penetrate the small gaps in the gear meshes or bearings better. This creates two major benefits for designers:

• Reduce the size of electric oil pump – Lower flow needs so they can downsize to a smaller pump saving on electricity to run the pump as well as lower weight of the system due to the smaller pump.
• Less fluid in the system – Lower flow needs also means they don’t need as much fluid in the system. This is a benefit to the total weight of the system as well as the environmental aspect of using less oil which many companies in the automotive space are trying to do.

These benefits are directly related to the efficiency of the electric vehicle and contribute positively to increase vehicle range. Vehicle range or consumers having range anxiety is a key factor for electric vehicles.

Vehicle range can only be increased by three factors right now: increase number or size of batteries, different battery chemistry that could potentially store more energy or more efficient use of energy stored in the batteries. Increasing the size of the battery is not ideal as it increases the weight and therefore diminishing returns, and the battery material is somewhat scarce so ideally, they would want to use smaller batteries. Many companies are currently researching different battery chemistries, but these solutions will take years if not decades before they will have completed all their studies and would be commercially available. But being more efficient with the use of energy in the vehicle is something they can do right now, and it will carry forward to any future developments.