Medium- and heavy-duty fleet vehicles account for 4 percent of the vehicles in use today; however, they consume 40 percent of fuel used in urban environments. Lightning Hybrids has developed a patented hydraulic hybrid system that can be retrofitted to new or existing fleet vehicles, such as shuttle busses and delivery trucks, to decrease fuel consumption by 20 percent and decrease NOx (the key component of smog) by up to 50 percent. Our system provides a new method for fleet operators to reduce fuel costs, brake wear, engine wear, and pollution. The Lightning Hybrids Energy Recovery System (ERS) uses LabVIEW software paired with a SOM for control. The NI platform has been key to the success of Lightning Hybrids from the beginning. We have used several versions of CompactRIO and Single-Board RIO devices to develop the technology both on and off of vehicles.
The ERS uses high-pressure hydraulic fluid to store energy that would otherwise be lost as heat during braking. The ERS includes the subsystems outlined below:
• Hydraulic Pump/Motor—Converts vehicle kinetic energy into hydraulic energy and then back.
• Power Transfer Module (PTM)—Mechanical interface from the hydraulic motor to the vehicle’s drivetrain, which includes a gear reduction and a clutch pack.
• Hydraulic Accumulators—These “hydraulic batteries” store energy as high-pressure hydraulic fluid, via nitrogen filled bladders.
o High Pressure—The high-pressure accumulator has a working pressure of up to 6,000 PSI
o Low Pressure—The low-pressure accumulator has a working pressure of up to 300 PSI
• Hydraulic Manifold—Valve body that acts as an interface between the hydraulic motors and hydraulic accumulators. It is populated with multiple electrically actuated hydraulic valves that proportionally control the amount and direction of fluid flow.
• Controller—Used to control every aspect of the ERS.
o Actuate hydraulic and pneumatic valves
o Interface to the vehicle via CAN to send and receive messages
o Record data for use in a telematics system and communicate the data to servers
o Provide an interface through an in-vehicle wireless network to a user interface for debug and development
o Monitor system performance and ensure safe operation
During installation, the ERS is installed under the vehicle and incorporated into the driveline between the transmission and the differential. We developed a modular framework so we can quickly retrofit the ERS to most medium and heavy-duty vehicles with minimal new design work or modification to the vehicle. We mount the PTM/manifold combination between the frame rails and the accumulators are placed remotely where space is available. We used high-pressure hydraulic lines to connect the accumulators to the manifold. A custom wire harness is run into the cab and allows for quick integration with the vehicle’s wire harness. The system is designed for easy installation. We can typically commission a new system onto a vehicle in less than a day, which limits downtime for the fleet.
A key component that makes the ERS successful is the high-pressure accumulator. Hydraulic accumulators, typically made from steel, have been around for decades. Traditional accumulators make a poor choice for mobile applications as their high weight impacts the vehicle load capacity and offset much of the economy gains from the hybrid system. Lightning Hybrids uses an accumulator that is composed of an aluminum shell wrapped in carbon fiber and fiberglass. This construction drastically reduces the weight of the accumulator but still allows for high working pressures. Inside the accumulator shell is a nitrogen-filled bladder that functions as a gas spring. As the incompressible hydraulic fluid enters the accumulator, it compresses the nitrogen inside the bladder to store energy.
The ERS control application has three modes of operation:
• Hydraulic Idle—The ERS is idle as there is no command for braking/accelerating or the necessary hydraulic charge is not present.
• Hydraulic Braking—The driver slows the vehicle. The proper valves are actuated and the ERS applies a torque to the drive shaft to create an acceleration opposite the direction of travel. The work of slowing the vehicle is used to build pressure. The hydraulic motors move fluid from low pressure to high pressure so that it can be used to accelerate the vehicle at a later time. The factory brakes are only needed for emergency stops, traction control, or other non-typical stopping requirements.
• Hydraulic Accelerating—The driver is accelerating the vehicle. The proper valves are actuated and high-pressure hydraulic fluid rotates the hydraulic motors to accelerate the vehicle. The available hybrid torque is calculated and used to reduce the throttle signal sent to the engine reducing fuel, emissions, and engine wear. Under some conditions, the ERS can provide up to 100 percent of the torque used to accelerate the vehicle with no engine power needed.
NI software and hardware have been key for us since early in Lightning Hybrids history. After some initial experimentation, we quickly focused our efforts on a CompactRIO solution. Our first NI controller was an 8-slot cRIO-9024. We used it for internal prototype development and deployed it in the field in the first pilot systems. We later transitioned to a 4-slot cRIO-9075 as our second-generation controller. We used the CompactRIO controllers to quickly prototype our system. The CompactRIO is flexible enough for the quick changes needed for a prototype, yet still rugged enough to be placed on a vehicle and survive real-world conditions.
Our third-generation controller used an sbRIO-9626 paired to a custom-designed daughterboard. The Single-Board RIO was a great option for us. We used it to take our prototype code with minimal modification and run on a different, much more cost efficient, controller. There are approximately 100 of these controllers in the field on hybrid systems, and they were used on our first commercial-scale order. The Single-Board RIO helped us to scale to a controller that was viable for mass production.
In 2016 we upgraded again to our fourth-generation controller. The new version uses an NI SOM paired with a custom-designed daughterboard. Using the SOM, we could reduce the cost of our controller by almost 60 percent over the Single-Board RIO solution while gaining a significant amount of FPGA and real-time processing power. Additionally, we transitioned from VxWorks to NI Linux Real-Time to improve security as well as implement a remote update feature. We can update vehicles in the field without sending personnel to the truck or having any downtime for the operator. This ensures that existing vehicles get software updates in as little as a day instead of weeks or months.
Our experience with the SOM has been great. NI helped along the way by making sure we had the information we needed during the daughterboard design and addressed the few minor issues we experienced. We could quickly transition our code base to the SOM because of the ease of use of the NI ecosystem. One engineer was able to modify the code base to work with the SOM while maintaining backward compatibility with the Single-Board RIO in approximately two weeks. The additional processing power of the SOM empowered us to implement new features and algorithms into our software that has increased the fuel saved.
As Lightning Hybrids moves forward, we will continue focus on improving efficiency and reducing emissions. Our use of NI hardware and software will help us drive this continued improvement.