Optimizing Cooling Circuit for Expansion Reservoir Volume and Rubber Hose Manufacturability

Overview

Our sponsor, Volvo Group North America, tasked us with running tests to conceptualize if a reduced expansion tank size is feasible for battery-electric class A trucks. Currently, these electric trucks are created using standards based on engine-powered trucks and so with an increased number of electrical components, the amount of coolant required is becoming excessive and the expansion tank size is large. The team’s model must meet pressure and flow requirements to be able to theoretically create a new standard for Volvo’s electric vehicles. Also, the coolant system includes a variety of rubber hoses needed to flow coolant to the hottest parts of the engine and the feedback response time from vendors on whether these hoses are manufacturable can take anywhere from a few days to a few weeks. Volvo asked the team to construct a guideline tool to significantly reduce the production time of coolant circuits, in which it will educate the employer early on whether the hose desired can be fabricated.  

Objectives

* Minimize the working volume of expansion tanks in Battery-Electric Vehicles (BEV) trucks based on Internal Combustion Engines (ICE) standard and extract findings. ​
* Generate a guideline tool for rubber hose manufacturability that will accelerate production time regarding coolant circuits.  

Approach

* Customer needs were gathered directly from the Volvo team via email and weekly meetings.  
* The conceptual design was directly based on Volvo engine-powered coolant systems and the size of the circuit was constructed with the assistance of the Volvo team. The design of the hose calculator consisted of equations and formatting from a pre-existing Excel tool from Volvo. 
* The team visited the Mack Trucks facility in Macungie, Pa, and acquired knowledge about how trucks are built from beginning to end along with insight into the size and application of the present expansion tank and rubber hoses necessary.  
* The Volvo team provided a CAD model for the team to understand the connection points required and the power-flow innovations team 3D printed a display tank for the showcase using this CAD. Due to printer size constraints available to the team, the display tank was unable to be printed large enough to be used in the actual prototype.  
* Alpha, beta, and final prototypes were fabricated. The alpha prototype consisted of a cardboard layout of the circuit to visualize the application later in the design process. The beta prototype was built on a 3ft by 5ft piece of plywood with vinyl hoses in locations that allow water to flow from the water pump at the bottom of the board to the tank eventually placed at the top. The beta prototype consisted of a small 3D printed version of the expansion tank model provided by Volvo. This allowed the team to calculate the approximate size of the entirety of the system and view the possible sizes of tanks. The final prototype and test rig consisted of a purchased 2L tank placed at the top of the board along with 3 deaeration lines, a static fill line, a circuit of clear vinyl hoses, and a water pump to circulate the red-dyed water. There were flow meters and pressure gauges added for data readings and valves to allow constraint. Wooden inserts were made to take up volume in the tank to allow multiple sets of data. For the guideline tool, a calculator was created in Excel using equations from Volvo, images of a variety of hoses, and data from pre-existing hoses. 
* Tests were run on the final prototype by getting flow meter and pressure readings when the tank was empty and then incrementally reduced the working volume of the tank and recording how the variables changed. Testing on the calculator consisted of our team and our sponsor inputting necessary variables for individual hoses and observing if the calculator agreed with data from vendors.  
* The results generated showed that the pump pressures remained relatively constant until the working volume was reduced to 14%. There was a spike in pressure changes around 12-10.5% indicating that theoretically a new standard could be set for battery electric trucks at around 14-16% working tank volume. The guideline tool results indicated that the calculator was accurate and is a good step in the right direction toward decreasing production time for cooling circuits in Volvo’s battery-electric vehicles.  

Outcomes

* The working volume expansion tanks implemented in Volvo’s battery-electric class A trucks could be reduced to around 14-16% compared to 18-22% based on our team’s findings.  
* Production of coolant systems for battery-electric and engine-powered trucks can be reduced possibly by weeks with the application of the rubber hose manufacturability calculator.  
* This project opens an opportunity for a new procedure to be followed for battery-electric vehicles in Volvo due to less material needed.