The turbocharger succumbs to the pressures of energy conservation

The turbocharger succumbs to the pressures of energy conservation

by | Wednesday, 1 July, 2020 | Automotive

For many years turbochargers were only found on expensive sports cars and diesel powered engines, but emissions regulations changed the way the world viewed forced induction. Although at the core was still the quest to improve performance, now manufacturers were looking at restoring performance and driveability to downsized fuel-sippingengines. So in the 21stCentury, almost everything from the little 999 cm3 Ford Ecoboost to the latest Ferrari’s all gained shiny new turbo technology.

But almost as soon as the tech came into its own it seems set to become redundant, upstaged by the new eCharger. Already Audi’s fitted this to the series production SQ7 and will be rolling out the technology to future production vehicles as 48 Volt electrification gains traction.

The key advantage to the electrically driven supercharger is that, as with turbochargers, there are no parasitic losses; but unlike most turbo’s there’s no turbo lag either and no need for a wastegate. The powerful electric motor can spool up the impeller to 70,000 rpm in less than a second, which eliminates turbo lag.

This naturally improves driveability and reduces consumption and emissions by between 7 and 20 percent when the device is used on a vehicle equipped with regenerative braking, which captures the car’s kinetic energy and turns it into electricity.

Pressure is key to unlocking the eCharger’s performance

Electronically controlled, the eCharger can be mapped to optimize engine performance while maximizing the energy recovered from the exhaust gas, but in order to achieve this Utopia, engineers need to create a map of the boost the engine requires by measuring manifold pressures at various engine loads and speeds. This can only be done with the aid of top quality pressure sensors.

As with any super/ turbo-charger, it’s important that the unit is matched to the engine’s requirements: Failing to do this, will either starve the engine or result in unnecessary electrical power consumption.

Being a maturing technology, not much research and testing data is available to engineers wishing to explore the boundaries of eCharge superchargers. Although fluid dynamics and electrical engineering can provide good foundations from which to build, it’s still vital that theories are validated under real-world test conditions.

In order to qualify the performance, once the baseline eCharger has been selected, the vehicle is equipped with extremely accurate pressure sensors that are readily calibrated and provide precise readings over a wide range of manifold boost pressures and temperatures. These sensors must also be resistant to vibration and chemical degradation.

Both on the engine dynamometer as well as road testing, throttle position/ engine speed/ Manifold air Pressure and temperatures are continuously recorded to ascertain the interrelationship of these key inputs.

From this information, engineers are able to verify that the correct eCharger configuration has been selected whilst at the same time ensuring that the closed loop engine management controls are able to correctly respond to the key variables.

The result of getting this right delivers a vehicle, such as the SQ7, which has stunning performance, drive ability and fuel consumption whilst still meeting future global emissions regulations.

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Accurate pressure measurement is critical to safe, cost-effective, motor vehicle development

Accurate pressure measurement is critical to safe, cost-effective, motor vehicle development

by | Wednesday, 1 July, 2020 | Automotive

The principle of hydraulic power to carry out work has been around since ancient Egyptian times, but as systems have evolved, so too have the tools required to design and develop these sophisticated, often critical circuits.

From the earliest manometer invented by Evangelista Torricelli in the 1600’s to the mechanical Bourdon gauge and finally today, the piezoresistive pressure transducer, developers have always sought the best equipment to measure pressures and optimize the design. And in recent times automotive engineers, in particular, have come to rely on these high-quality, accurate pressure sensors when carrying out vehicle testing and development.

These current pressure transducers are typically capable of recording full-scale deflections from about 350 mbar to 700 bar under sustained temperatures ranging from -40OC to 150°C; and best of all, quality sensors such as those produced by STS, are capable of a hysteresis and repeatability of typically around 0.001%!

Image 1: High precision pressure transmitter ATM.1ST with accuracy of up to 0.05% FS

High-quality pressure sensors are used in the development of key automotive systems.

This level of repeatability is critical in the design and development of cooling and fuel delivery systems, amongst others. During development, designers rely on stable pressure measuring equipment to accurately record information so that the effect of even the smallest of design changes can be documented without concerns that the sensor is incapable of repeatable results.

In a recent redesign of an engine cooling system to take advantage of the reduced parasitic losses made possible through electrification, the engineering team at a luxury OEM was initially faced with a pressure drop across the pump of around 250kPa. Before a redesign of the new electric pump was possible, accurate pressure measurements had to be recorded allowing engineers the opportunity to identify the problem. After studying the results logged by the array of pressure sensors the design was modified, reducing the drop to less than 100kPa and cutting the parasitic losses by 500W.

And although electrification and electronic controls are playing increasingly significant roles in vehicle systems, hydraulic pressure is still relied upon to guarantee smooth operation of many critical circuits.

By way of example, during the development of an automatic transmission, port line pressures have to be measured in real time and then compared to design norms to confirm that design parameters are being met. At the same time, shift times and quality are measured and subjectively evaluated to ensure drivability and performance meet customer requirements.

Notwithstanding the value of high-quality pressure sensors in recording valuable data during testing and development, in industrializing future technologies these tools can also significantly reduce design costs.

Pressure sensors make sure future technologies measure up to expectations.

In an attempt to improve the performance of severely downsized engines, manufacturers are taking advantage of the additional power 48V electrification offers, by replacing the turbocharger with an electrical supercharger.

Being a maturing technology, not much research and testing data are available to engineers wishing to optimize eCharge superchargers. Although fluid dynamics and electrical engineering provide a sound platform from which to build, it’s still vital that theories are validated under real-world test conditions.

To achieve this, manifold pressures must be mapped to optimize engine performance while maximizing the energy recovered from the exhaust gas. For this, extremely accurate pressure sensors that provide precise readings over a wide range of manifold boost pressures and temperatures are required. These sensors must also be resistant to vibration and chemical degradation.

And while manufacturers around the world continue to carry out research into electric vehicles, several groups are considering ways to harness hydrogen to generate electricity instead of relying on storage batteries.

Hydrogen fuel cells employing proton exchange membranes, also known as polymer electrolyte membrane (PEM) fuel cells (PEMFC), have already seen limited series production in vehicles such as Toyota’s Mirai.

Although small PEM fuel cells commonly operate at normal air pressure, higher powered fuel cells, of 10kW or more, usually run at elevated pressures. As with conventional Internal Combustion Engines, the purpose of increasing the pressure in a fuel stack is to increase the specific power by extracting more power out of the same size cell.

Typically the PEM fuel cell operates at pressures ranging from near atmospheric to about 3Bar, and at temperatures between 50 and 90°C. While higher power densities made possible by increasing the operating pressure, the net system efficiency may be lower due to the power needed to compress the air; hence the importance of balancing the pressure to the requirements of the particular fuel cell.

As with ICE boost pressures, this can only be done by taking accurate pressure measurements using high-quality pressure sensors. These measurements are then compared to the fuel stack outputs to minimize the parasitic losses while optimizing the gains in electrical output.

So, irrespective of the course the automotive industry chooses for future technologies, accurate pressure sensors will remain key to the development of safe and efficient vehicles.

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Manufacturers are feeling the pressure

Manufacturers are feeling the pressure

by | Wednesday, 1 July, 2020 | Automotive

With emissions regulations set to ratchet up a notch in China, Europe and North America, manufacturers are hard-pressed to optimize every engine component and function to cost effectively meet the new demands.

Although engines that are under development have always been tested to ensure they meet the most stringent quality requirements in terms of materials, emissions and efficiency, there’s a renewed focus on detailed development to unlock performance that may have previously been overlooked.

In order to do this, every time an engine is run on a test bench all the variables influencing emissions and performance have to be monitored and measured to understand their individual performance as well as how they function as part of the overall system.

This requires highly dependable, precise measuring equipment that delivers accurate readings under the extreme conditions encountered in and around the engine. Sensors of this quality and accuracy are manufactured by only a handful of suppliers around the world, which are standing out for the ability to customize quality pressure sensors to the customer’s requirements.

Pressure sensors are key to eliminating inefficiencies

STS have developed pressure sensors that meet OEM, first tier and specialist engine designers’ requirements in engine development. Using these sensors customers carry out development and design work that focuses primarily on reducing exhaust emissions and achieving a high power density, low fuel consumption, long service life and maximum reliability.

Because an engine’s efficiency depends largely on airflow and charge density into the combustion chamber and how the exhaust gases are either used to enhance the engine’s torque, by way of a turbocharger, or are able to be discharged efficiently, accurately mapping key pressure regions is critical. These pressures are often of the order of millibars, requiring extremely accurate and highly dynamic measurement.

Furthermore to obtain a reliable analysis of pressure distribution within the inlet manifold, it is important to take inlet pressure measurements as close as possible to each inlet valve. This is to accommodate the varying geometry of the manifold which often results in each cylinder being supplied with a different amount of air, which negatively impacts both performance and emissions.

When determining the performance of the exhaust system, pressure measurement becomes quite complex, as not only does the performance of the exhaust rely on pressure but also the interaction of the exhaust-gas pulses due to the engine’s firing order. STS pressure sensors are capable of measuring these processes on both the inlet and outlet sides with a high level of accuracy.

Robust sensors must remain accurate in a hostile environment

In the test environment the sensors must be resistant to the chemicals and oils associated with engines, and be able to accurately measure pressures in extreme temperatures. Moreover, the sensors need to operate reliably and not be affected by vibration or voltage fluctuations.

STS’ range of sensors also allows customers to take measurements in critical systems such as oil, fuel and water pumps, injector lines, intercoolers, and heat exchangers. All of which are vital in optimizing engine efficiency.

So although customers and regulators are increasing the demands for cleaner and better performing engines, OEMs and suppliers are well equipped to stretch the envelope and even exceed expectations.

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Hydrostatic level monitoring of tanks on piezoresistive basis

Hydrostatic level monitoring of tanks on piezoresistive basis

by | Wednesday, 1 July, 2020 | Water

Hydrostatic pressure measurement is one of the most reliable and simplest methods for fill level monitoring in liquid-carrying tanks. In the following, we explain how hydrostatic level monitoring works and what users should consider here.

In hydrostatic level measurement, the filling level of a liquid in a container is to be measured. In this case, the force of weight acting on the pressure transducer installed at the bottom of the container is measured. The weight force in this context is termed the liquid column. It increases in proportion to the filling level and acts as a hydrostatic pressure on the measuring instrument. The specific gravity of the fluid must always be considered in hydrostatic level monitoring. The filling height is thus calculated with the following formula:

h = p/sg

In this formula, h stands for the filling height, p for the hydrostatic pressure at the base of the tank and sg is the specific gravity of the liquid.

The actual quantity of fluid plays no role in hydrostatic level monitoring, since only the filling height is decisive. This means that the hydrostatic pressure is identical in a 200 liter tank narrowing towards its base and in a straight sided tank containing 150 liters of liquid, as long as the liquid and the fill height are identical (3 meters, for example).

The simplest application of hydrostatic pressure measurement is when the liquid concerned is water, since the specific gravity can be disregarded altogether here. When a fluid other than water is involved, the pressure transmitter has to be correspondingly scaled to compensate for the specific gravity of that liquid. Once this has been done, the fill level can be determined, as with water, via the hydrostatic pressure on the bottom of the tank. It becomes more complicated when different liquids are used in a single tank. In this case, not only the hydrostatic pressure at the bottom of the tank must be measured, but at the same time the specific gravity of the respective fluid also. We will leave aside the latter case at this point and instead consider hydrostatic pressure measurement in both closed and open tanks.

Hydrostatic pressure measurement in open and closed tanks

With open tanks, it does not matter whether they are above ground or set within it, as long as they have an opening that provides for a balanced air pressure inside and outside the tank. The measurement of the hydrostatic pressure can be carried out without further adjustments at the bottom of the tank. If measurement at the bottom of the tank is not possible, the filling level can also be found by means of a submersible probe, which is fed into the tank with a cable from above.

In closed tanks, higher gas pressures often prevail than in the atmosphere surrounding the tank. This gas layer above the liquid increases the pressure on the liquid itself. As a result, the liquid can flow off more quickly and there is also less loss due to evaporation. Tanks sealed from the ambient air are therefore frequently used in the oil and chemicals industries. The gas layer pushing down on the liquid also acts indirectly on the pressure transducer at the bottom of the tank and must therefore be taken into account in order to determine the correct filling level (a higher filling level than the actual would be indicated through this increased pressure). In closed containers, two pressures would therefore have to be measured: The gas pressure and the pressure at the bottom of the tank. The hydrostatic pressure of the fluid results from the difference between the measured gas pressure and the pressure measured at the base. This difference can then be converted into an indication of the fill level of the tank. For this type of application, a differential pressure sensor is generally used.

Concluding remarks

In hydrostatic level monitoring of tanks, two factors must always be considered: The type of fluid and the type of tank. The simplest application would be the monitoring of water levels in open tanks, since no adjustments have to be made for this constellation. If, however, a different liquid is involved, then the specific gravity of that liquid must also be taken into account. In addition, a measuring instrument is to be selected that can withstand the properties of the medium concerned. Whereas for most liquids stainless steel is sufficient as a housing material, highly corrosive media may also require different materials.

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Integration of piezoresistive measuring cells into existing applications

Integration of piezoresistive measuring cells into existing applications

by | Tuesday, 30 June, 2020 | OEM Integration

The core element of every pressure transmitter is the pressure measurement cell. With piezoresistive pressure transmitters, this equates essentially to the Wheatstone bridge measuring arrangement. The primary pressure measurement takes place here by way of deformations to the strain gauges. This piezoresistive measuring cell can also be integrated into existing applications such as pressure switches or pressure regulators, should this be necessary. Various possibilities exist to this end.

The most common reason for the need to integrate a sensor cell instead of a pressure transmitter into an existing application is a lack of space. In hydraulic valves, for example, there are only a few cubic centimeters of space. The integration of an entire pressure transducer is therefore not usually possible. Because of insufficient space, some users opt to employ an external sensor, which is then flange-mounted to the existing application. This approach, however, is cumbersome and not as optimal as the integration of separate measuring cells into the application.

In the selection of suitable measuring cells for individual applications, the same questions apply by and large as with the selection of an entire pressure transmitter.What needs to be established, among other things, are the pressure range to be measured, the temperature conditions and also the relevant media compatibility. In the employment of piezoresistive measuring cells into existing applications, three further selection criteria can be added: These are the mechanical and electrical considerations for integrating the sensor cells.

The mechanical selection criterion relates to actually building the measuring cells into the relevant application. Depending upon requirements, these possibilities remain open:

  • screw in
  • weld on
  • plug in
  • wedge in

On the electrical side, it must be determined which electronics are used in the application to provide the electrical signal transmission. In some circumstances, it may be that the electronics existing in the application are not equipped for the integration of pressure measurement cells. In this case, an electrical signal conversion would have to be separately integrated.

We now arrive at a real life example: An STS customer wanted to retrofit an existing precision high-pressure control valve for test bench applications with the option of pressure measurement. Since an entire pressure transmitter could not be integrated into the valve, a single pressure measurement cell had to be opted for. The demands here were that it had to display pressures up to 600 bar and it should be designed for a signal output from 0 to 100 mV/V at a supply of 10 V.

The solution selected was a measuring cell with stainless steel pressure port and miniature compensation technology. This could be screwed into the valve body below the already existing cover in a space-saving manner and also shielded from external influences. The assembly height after mounting on the valve body came to under 30 mm (including bending radius of cord strands). Apart from its minimal dimensions, there was one additional feature: The zero position and range were individually adaptable by the user with a potentiometer.

Measuring cell with stainless steel pressure port for implementation on a high-pressure control valve

Consultancy is key

Piezoresistive measuring cells are the core competency at STS. They are fully manufactured in-house, display pressure ranges from 100 mbar to 1,000 bar and are available in the materials of stainless steel, titanium and Hastelloy®. This means that, in principle, they can be employed for almost any conceivable measuring task. In collaboration with our engineers, customers receive an extensive consultancy on the integration of suitable measuring cells into existing applications.

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