This truck uses a newly developed pneumatic valve in its transmission to replace electrical switches.

A repeated glitch in the field performance of its 18-speed electropneumatic transmission systems was causing quality control and product warranty issues for Transmissiones TSP (Transmissions TSP), Quertaro, Mexico. Electrical switches used to indicate the position of steel bars that move gears and send appropriate signal commands had a short service life and triggered low transmission response. Parker Hannifin Corp.’s technical specialists discovered the problem was low electrical shielding and high stress on the steel bars, which allowed dust and grease to penetrate the switch chamber’s body casing.

To increase sales and reduce warranty hassles, an alternative system was needed for the transmission, which would be actuated by pneumatic valves instead of electrical switches.

Pinning down the problem
This particular transmission, produced by TSP Transmissions, has s ix manual speed changes controlled by a steel handle along with two double-effect pneumatic pistons controlled by electro-valves. These valves were driven by three electrical switches in the shift knob — with one of the positions sited in neutral. The electrical switches routinely failed as a result of low electrical protection level s and high plunger s t res s . Switches tended to flame in lowtemperatures due to false contact between internal plates. The problem resided in the transmission housing.

David Jurez, TSP Transmissions developer engineer, contacted his sales representative, Guillermo Rodrguez, Parker Motion Control Mxico, to help relieve the problem. Parker proposed eliminating the electrical switch entirely. They first provided TSP with a pneumatic valve for initial testing purposes and, as an alternative, designed a totally new pneumatic system based on an existing product unrelated to the transportation market.

“It's a dirty environment,” Jurez commented, “with grease, water, and dust penetrating internal mechanisms and wreaking havoc. It needed to operate in the 130° C temperature range at half a million cycles.”

The ultimate mechanism that resolved the performance issues for TSP Transmissions was a totally new pneumatic sensory valve tailored to perform in very hostile operating environments.

Tried, tested, and true
Rigorous tests conducted in engineering labs located i n Mexico and Australia demonstrated that dust and grease entering the switch housing unit were the culprit. Parker Motion & Control Mxico engineers, interfacing with Parker Pneumat ic Sweden, then developed the new pneumatic sensing valve, based on lab results from Parker’s Australian Division, to replace the electrical switches.

The valve system is a 3-way, 2-position unit designed to replace three electrical switches. Used as a pair, the pneumatic sensing valves detect steelbar position inside the transmission housing. The position combination of these valves sends pneumatic signals to slave valves that actuate splitter/ range cylinders in tandem with shift/ speed change knob positions. Parker also supplied slave valves for the TSP Transmissions system.

Under high-temperature test conditions, the newly-engineered pneumatic valve demonstrated rapid response times, easy speed/gear changes, and increased vehicle control while remaining wholly robust in hazardous operating environments. It also enhanced endurance levels and radically improved transmission field performance. These characteristics led to improved driver control and confidence along with dramatically reduced product warranty claims. As an added bonus, transmission production costs were reduced by 7%.

The Parker pneumatic sensing valve proved to be highly stress-resistant, even while functioning at peak performance. Transmission service requirements were also reduced due to easy valve assembly/disassembly. According to Jurez, the defining valve performance characteristic is its ability to function flawlessly under extremely hostile operating conditions.

“We were able to eliminate the repeated failures of the previous electrical components with the new pneumatic system,” Jurez continued, “and in the process, got measurable performance improvements in transmission shifting at a significant production cost reduction.”

For more informat ion, contact Guillermo Rodriguz, automation product manager, Parker Hannifin Mexico, at grodriguez@parker.com, or Paxton Augustine, at Parker’s Transportation Pneumatic Div. at paugustine@parker.com or call (269) 629-5000.