Switches under pressure?

  • 19-Feb-2015 11:48 EST
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Broad connectivity options allow design engineers to choose how to best integrate the pressure switch into the vehicle’s control system, from direct load switching to controller interfaces.

The switch isn’t dead.

As the proliferation of and demand for “smart” technology in off-highway vehicles has risen, so has the notion that sensors are the only suitable solutions for these control loops. The switch, meanwhile, tends to be viewed as an antiquated and irrelevant technology of legacy systems. There are times and places when a sensor is the right choice. However, it turns out today’s modern switch also has a place in these next-generation control systems.

The increase in smarter heavy-duty vehicles is being driven by customer demands for efficiency and experience. A few overall industry trends have converged to accelerate vehicle intelligence integration:

•    The volume driven, trickle-down effect from automotive is making smart technologies, and associated hardware, more affordable.

•    Rising operating costs (due to fuel consumption and vehicle downtime) are driving the market to invest in intelligent machinery that improves efficiency and ultimately reduces these costs.

•    The operator’s in-cab experience is being shaped by personal experiences with technology. Computers, tablets and smart phones have dramatically impacted our personal lives and the way we function and communicate. Owners and operators are looking for that same experience on the job.

These three trends are pushing heavy-duty vehicles to operate very similar to aircraft: vehicle automation is increasing while operator manual control is minimized. The intelligence needed to achieve this type of automation requires a measureable feedback loop to the controller or ECU from a wide array of sensors and switches. This has driven a sharp rise of sensor and switch content on vehicles over the last decade.

While sensors are a necessity for measureable feedback, switch technology continues to adapt and still offers a great deal of value in this new era of vehicle control. Today’s modern pressure switches offer great integration flexibility, low design-in costs, and a successful history of protecting vehicle subsystems.

Advancements in capability and connectivity

One might think pressure sensors and switches do not compete for the same control system, but there is more overlap than meets the eye. As engineers design-in controllers and attempt to use the available I/O, there is a constant trade-off of how to connect the final system and what ports to use.

One viable method is a solid-state pressure “switch” that monitors like a sensor, but outputs similar to a switch. The modern mechanical pressure switch, however, can adequately fill this need with additional benefits in cost and flexibility. In general, the switch is a better option when a system is designed for a specific point, rather than a ranged readout. Modern connectivity options that allow the mechanical pressure switch to interface with controllers directly save the cost of moving to a solid state pressure switch.

Contrary to what some may believe, modern pressure switches can be highly flexible for integration. For example, modern pressure switches can offer low-current capability and resistive readouts to communicate with these integrated systems. This means OEM design engineers have more flexibility when selecting integration methods to the controller and overall system. Additionally, using different materials allows the switch to have a range of current-carrying capabilities. This allows the design engineer the flexibility to select whether to interface at a logic level through a controller, actuate a relay, or even directly carry the larger load of the particular circuit.

Modern pressure switches also have the ability to internally integrate other small electronics into the assembly for more functionality and interface options. One example is integrated resistors that can provide switch-health monitoring to the system for added safety and further signal differentiation. The vehicle controller can now differentiate whether the switch is online and functioning properly as well as the set point trigger for pressure setting.

Dual set point switches are another example offering multiple levels of triggering for step change readings in pressure. These dual set points can also carry loads for each switch point and call for different actions from other vehicle subsystems directly without needing to consume another I/O on the vehicle controller.

Design-In efficiency

Beyond being an affordable option, pressure switches also reduce design-in and validation costs for the OEM. The simple returned signal reduces the mating software needed for translation, allowing the OEM design engineers to focus on the decision software.

Some pressure switches—like Honeywell’s HP, HE, LP, and LE Series—use modular designs with common switch options and a broad array of connectors and ports. Keeping the switch mechanism common means less testing to validate the pressure switch.

Many OEM’s will utilize a wide range of pressure switches with unique ports and connectors. This modular approach allows the OEM design engineer to take an initial sample size for validation and replicate the design to more applications and platforms without having to repeat all the testing.

This “buildable” approach enables error-proof designs on vehicles with little-to-no design costs. Unique ports and connectors ensure that vehicles are properly wired and configured on the manufacturing line. The benefit continues to post-sale field service. Field technicians would be unable to install the incorrect switch into the system if the port and/or connector would not allow. A simple feature that improves serviceability, and minimizes the cost of mistakes and the need for additional support from the OEM team.

Proven and rugged

Construction, mining, and agriculture sites are not the most forgiving of environments for electrical components. Pressure switches have a long history of success operating in the rugged environments of heavy-duty vehicles. Tried-and-true veterans of the industry, they are designed with safety and protection in mind.

Pressure switches are called on to protect critical subsystems from unstable pressures that can lead to harmful failure modes, costly repair, and downtime. Whether monitoring minimum engine oil pressure or maximum hydraulic pressure, switches are a very reliable tool to monitor critical and costly subsystems, including transmission oil and braking systems.

Modern pressure switches continue to improve their capability of withstanding harsh environments. Examples include offering higher levels of water ingress protection, heat cycling, vibration, shock, electrical loading, and proof pressures. Additional updates in the switching mechanism also offer life-cycle capability two to four times beyond older designs. This long and reliable protection translates to value for fleet owners and operators and peace of mind to design engineers. Monitoring these systems prevents downtime and more costly failures. Not only is this real cost savings to the customer, but it furthers brand equity for the OEM.

It’s a foregone conclusion that the amount of smarter technologies will continue to grow on heavy equipment. It’s not, however, a foregone conclusion that sensors will be the best solutions to accommodate this trend. The traditional switch has evolved significantly to offer the electronic integration needs and physical characteristics of these new systems. The decades-long legacy provides confidence the pressure switch will survive and protect assigned systems. The modular designs and feedback options give design engineers electronic and physical design flexibility to optimize the control system and leverage it in other applications. Modern pressure switches provide all this with a benefit for design-in validation time and unit cost competitiveness to alternatives.

Wade Wessels, Senior Global Product Manager, Honeywell Sensing & Control, wrote this article for SAE Off-Highway Engineering.

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