Coolant Flow Measurement with a Precision Pressure Monitor｜Pressure Loss Testing for EV Cooling

EV Coolant Pressure Loss Measurement

Electric vehicles (EVs) are equipped with many heat-generating devices, including motors, batteries, inverters, and power control units. Since each device generates different amounts of heat and has a different optimal operating temperature, a single vehicle is typically equipped with multiple cooling systems. In the development and design phase of such water-cooled devices, accurately understanding the pressure loss in the coolant flow paths is essential.

The MT300 differential pressure model is a liquid-compatible differential pressure measurement instrument used to measure pressure loss in the cooling flow paths of various devices with high accuracy using a single unit. It can be applied to flow path design evaluation of a wide range of water-cooled devices placed in cooling circuits, including the water jackets located on top of battery packs.

Challenges in Flow Path Design

With the expanding adoption of EVs and the progress of decarbonization, improving driving range and energy efficiency has become a key competitive factor in the automotive industry. Efficiently cooling heat-generating devices such as motors and batteries is an indispensable factor in reducing overall vehicle power consumption and extending driving range. The efficiency of the cooling system is greatly influenced by flow path design and the measurement accuracy that supports it.

Reducing Cooling Pump Power Consumption

The power consumption of a cooling system is determined by the magnitude of the pressure loss generated within the flow paths. Since greater losses contribute to reductions in a vehicle's energy efficiency and driving range, optimizing the flow path design requires capturing minute pressure losses with high accuracy.

Difficulty of Low-Pressure Measurement in Liquids

Coolants are liquids, and in optimized flow paths, pressure losses fall into a very small range. Many conventional high-accuracy pressure monitors are designed for gases only, and their accuracy may not be guaranteed in the low-pressure range for liquids. As a result, available measurement options for thoroughly evaluating cooling flow paths are limited.

Streamlining Evaluation Systems

EVs are equipped with multiple devices that generate different amounts of heat and have different optimal temperatures, each requiring individual evaluation of its cooling flow path. This places many demands on the measurement side as well, including support for the appropriate pressure range for each device and flow path, as well as efficient measurement data acquisition.

Solution with the MT300 Precision Pressure Monitor

Direct Differential Pressure Measurement with a Single Unit

The MT300 differential pressure model adopts a method that directly measures differential pressure (ΔP) using a single built-in sensor. In the common method of using two pressure monitors to measure each pressure and then calculating the difference, the accuracy of each sensor accumulates (e.g., 0.01% × 2 = 0.02%), which tends to reduce the accuracy of differential pressure measurement. With the single-sensor method, no accuracy accumulation occurs, leading to a simplified measurement system, space saving, and more efficient data acquisition.

Compatible with Both Liquids and Gases

The MT300 differential pressure model is compatible with gases and liquids (non-flammable, non-explosive, non-toxic, and non-corrosive fluids) as the measurement medium. Four ranges are available — 1 kPa, 10 kPa, 130 kPa, and 700 kPa — allowing the appropriate combination of range and resolution to be selected based on the design conditions of the coolant flow path and the expected magnitude of pressure loss.

Liquid compatibility is enabled by a structure in which a metal diaphragm receives the pressure and silicone oil sealed inside transmits only the pressure to the sensor. Since the highly sensitive semiconductor-based sensor is designed not to come into direct contact with the measurement fluid, stable measurement is possible for both gases and liquids.

Yokogawa's Proprietary Silicon Resonant Sensor

The MT300 is equipped with a silicon resonant sensor developed by Yokogawa. Pressure is applied to resonators formed on a silicon wafer, and pressure is detected from the change in resonant frequency. By using a differential method that determines pressure from the difference in the natural frequencies of two resonators, external environmental influences such as ambient temperature are canceled out, achieving both low temperature dependency and high resolution. The sensor is also adopted as a Transfer Standard for international comparisons of pressure standards, which further supports its long-term stability.

High-Accuracy Capture of Minute Pressure Losses

The smallest 1 kPa differential pressure model features a display resolution of 0.00001 kPa and a relative accuracy of ±(0.01% of reading + 0.00025 kPa), providing fine measurement conditions. Even the small pressure losses that result from highly efficient cooling flow paths can be captured stably, contributing to improved accuracy in flow path design evaluation.

Expected Benefits of Using the MT300

By utilizing the MT300 differential pressure model, the following benefits can be expected in EV cooling system development.

Reduced Cooling Pump Power Consumption

The ability to capture even minute pressure losses with high accuracy makes it easier to identify bottlenecks in flow path design. By enabling a design with reduced flow path resistance, optimization in the direction of lowering the driving power required by the cooling pump can be expected.

Contribution to Improved Driving Range and Energy Efficiency

The power consumption of the cooling system affects the overall energy efficiency of an EV. Reducing cooling system power consumption through optimized coolant flow paths is expected to improve the overall energy efficiency of the vehicle, contributing to extended driving range and improved energy efficiency.

Improved Evaluation Efficiency in the Development Phase

Because differential pressure can be measured directly with a single unit, the measurement system can be simplified and made more compact. Even at development sites where flow path evaluation of multiple devices is performed in parallel, the system configuration can be rationalized while maintaining the required accuracy.

Reliability Through Long-Term Stable Operation

The MT300 guarantees a measurement accuracy of 0.01% for 12 months and offers long-term stability thanks to its silicon resonant sensor. For example, accuracy drift between annual recalibration cycles is small, supporting long-term use as a continuous measurement foundation at development sites.