Electric forklifts are certainly not new technology, with the first ride-on electric machine marketed in the 1920’s by Yale. Development of transistor-enabled power electronics in the 1980’s enabled a transition from legacy DC systems to higher efficiency, lower maintenance AC induction motor technologies across most of the market by the end of the ‘90’s. The improvements helped achieve a 60% market share for electric forklifts by 2020,forecast is to grow to 70% within the decade per Interact Analysis. Further strengthening the positioning of the electric drive solutions are additional technology developments, including alternative energy storage sources, such as Lithium Ion or Fuel Cell; the market is also just starting to realize the benefits of advance motor technologies of the type of PM or ASRPM (Assisted Reluctance Permanent Magnet).
The most compelling reason for a stronger presence of electric-only trucks is the need for a large percentage of the 6t and smaller trucks to operate within enclosed work areas. Of course, the underlying issue with any indoor operation is the need to manage tail pipe emissions. Even when utilizing a lower-emission fuel such as LP, it is still necessary to manage emissions such as CO, and oxides of both sulfur and nitrogen. Considering the increasingly important green house emissions, total CO2 reductions of almost 40% can be achieved, assuming typical carbon intensity of the United States electric grid. Another distinctive characteristic for electric powered vehicles is the orders of magnitude lower noise emissions as compared to equivalent ICE-power machines. Within the realm of forklifts, it is not uncommon for a BEV version to demonstrate 10dB(a) lower sound pressure levels at the operator’s ear. While many warehouses may have dedicated use cases for fork trucks, increasing the flexibility of a particular machine configuration adds value to the marketability of a particular vehicle configuration for the OEM. For example, when considering the need to operate within environmentally controlled areas such as freezers, it may be required to have a zero-emissions power source for the material handling systems to avoid contamination.
Speaking of operating costs, A significant contributor to both nominal costs and reduced operational productivity is maintenance – both scheduled and unscheduled. It is easy to for an ICE configuration to utilize 20 times more moving parts vs.an electric drivetrain and that reduction leads to simpler maintenance schedules and reduced costs. Normal maintenance savings of 20 to 40% each year are typically cited for electric trucks vs. ICE variants.
Downsides to the BEV variants? What can become a constraint to more and larger trucks adapting to electric is a concern and constraint the automotive world has been wrestling with for well over a decade already –vehicle working range, or “range anxiety”. Enhancing system efficiency reduces the constraints and risks of this concern.
If we start with a simple comparison, showing average efficiency of an induction motor versus a hybrid ASRPM motor, the potential becomes self-evident. Across a full range of working speeds, the ASRPM motor yields more than4% better efficiency; what is particularly exciting is in the lower speed ranges, which is where a vehicle such as a forklift can operating extensively due to high numbers of accel/decel cycles, the ASRPM efficiency advantage is maximized.
To develop real-life assessments, we partnered with the University of Trieste, Italy to evaluate energy consumption on a simplified variant of the VDI forklift work cycle - ignoring energy recover/regeneration for most of the cycle. Applying two different methodologies for calculating the energy consumption for an induction motor configuration as compared to an equivalently-sized ASRPM system - and assuming minimal optimization of the ASRPM configuration – we would predict energy savings of 7.5%.
Supplementing this analysis, we compared actual energy consumption when performing a simple accel/decel + reversals work cycle over 120 total cycles. Taking the average energy consumed/cycle, we saw the ASRPM system saved 12%. If we convert that into real life numbers from a VDI cycle, per a study from Wroclaw (Poland)University of Science and Technology, approximately 75% of the energy consumed within the VDI work cycle is consumed by the ground drive, thereby the 12%ground drive savings would equate to 9% realized total energy consumption savings for the work cycle. For a 36kWh Li-Ion type battery and assuming €300/kWh product cost for the battery pack, the OEM is provided the opportunity of saving almost €1000 in batteries for their machine while keeping the same range – OR- extending the working range of thetruck by about 45 minutes (assuming 36kWh can complete an 8 h r work shift today).
The base motor technology is only apart of the picture. By looking at the overall system as an integrated solution, including the gearing efficiency, gearbox speed ratings, and motor performance curves, PMP Industries develops vehicle-level performance prediction models and based upon the targeted duty cycle(s), we can rapidly iterate motor features optimizing motor performance – placing the weighted average motor “sweet spot” where optimum actual working efficiency is needed. While we are early realizing these benefits in real world installations with fully tuned control software, initial estimates are predicting we could see ground drive power loss reductions of 20%or more as compared to legacy induction motor systems – almost doubling what “simple” ASRPM implementations would be achieving.
Concentrating on integration aspects - more than pure energy savings.
If we simply modify the pump drive motor and axle drives to be integrated with the controller, speed sensor, thermal sensors, and park brakes (axles), the installation becomes drastically simplified, with essentially only the voltage regulator being connected to all three motors by power and ground wires – the only other connections needed would be inputs from the VCU – minimal other difference from the more complex legacy configuration.
This integrated solution reduces part count by 25% or more, reduces the total amount of copper used in the system, requires fewer parts to be purchased, while also contributing to lower complexity and assembly labor. Optimization through simplification.
Integrating power cables and power controller into the drive motors provides other benefits due to the physics at play within the control circuit. Referencing the induced current field between the motor and power controller and influences on the vehicle, operator, and work environment, studies show the induced current levels in the frequency domain with longer cables exhibited multiple significant excitation frequencies as compared to an equivalent version with short cables. While there is active debate regarding the effects of EMF in the typical frequency range of ~1MHz on human biology, these frequencies fall directly within typical ranges for radio transmissions and can contribute to interference within networks and in extreme circumstances medical devices. When we look at the typical results within the time domain, it’s evident that not only are there more points of EMF interference risk, but peak current dissipated is an order of magnitude less with short cables – dissipating less energy = lower losses.
Some of the affects from reduced cabling lengths are quite straightforward; simply looking at the amount of resistance and dissipated power between two different installations – one with 2m long cables and another with a relatively generous 0,5m estimate for motors and controllers integrated onto the drive axle, the power savings realized can be meaningful. For example, assuming 3mm diameter, with 250Arms peak; 130 Arms average, the resulting wire resistance would yield peak power savings of 139 Watts; 61 on average for the 0,5m version. Alternatively, reducing wire diameter becomes more viable, reducing the overall amount of copper needed for the installation even further while still achieving reduced losses.
The intriguing potential the industry has yet to fully assess with reduced wire impedance is the overall control system between the power controller and motor becomes more rigid, providing for a higher level of control capability within the motion control system. This is due to the improved signal to noise ratio between the motor status (signal) and varying non-value added impedance(wires/noise); coupling the controller and motor more effectively untaps higher overall system efficiency and performance.
Macro market drivers within the material handling industry are driving an accelerated implementation of zero emission, electric drive solutions – yielding higher use case flexibility, reduced maintenance, and better working environments. Creative implementation of new technologies and methods, such as ASRPM-type electric motors with novel integration and optimized control methodologies – yields extended vehicle range and performance while enhancing the workplace environment and reducing total cost of ownership– adding value throughout the product lifecycle – from the OEM to the end user.