Patent Page


| December/January 2003

  • Inductive coil

  • Original igniter

  • Additional ignitor

  • Tremper's rotary valve

  • Inductive coil
  • Original igniter
  • Additional ignitor
  • Tremper's rotary valve

Gas Engine Patents of Note

Most antique engine collectors are familiar with 'make-and-break' ignition systems. In this ignition style, two contacts come together, and a spark is created when they separate. One contact carries a low-voltage current, and the other goes to ground. An inductive coil in series with the contacts builds voltage during the brief time the points are closed, producing a voltage 'kick' when the points open.

Numerous manufacturers used this rudimentary ignition scheme, but Frank E. Tremper, San Francisco, Calif., designed one of the earliest systems. In 1891 Tremper submitted a patent application on behalf of the Safety Vapor Engine Co., New York, N.Y., for 'An Improvement in Explosive Engines.' The final patent, no. 495,281, which also included Tremper's design for a rotary valve, was issued April 11, 1893.


The key feature of Tremper's igniter was a spring-loaded contact, or 'rod,' set into the crown of the piston. A pair of stationary electrodes were set into the combustion chamber, and when the piston reached the top of its travel the rod made contact with two stationary electrodes (which could be configured any number of ways), completing the ignition circuit. The rod was tapered at its contact end to encourage a self-cleaning scraping action between the rod and the electrodes.

By containing the spring-loaded contact in its own fitting in the crown of the piston, the damaging effects of heat on the rod's spring could be minimized. Additionally, Tremper's design meant there were no moving pieces outside the combustion chamber. Curiously, this design was quickly followed by another patent, but it ran along a slightly different line of thought.

Frank Tremper's original igniter patent incorporated a spring-loaded contact (item 'G' in 'Fig. 2) set in the piston head. Included in the patent was his scheme for a chain-driven rotary valve to control intake and exhaust (item 'P' in 'Fig 1').

An additional igniter patent dispensed with the spring-loaded contact and instead incorporated a 'flexible sparking strip,' which could be designed any number of ways.

Patent 503,016, granted Aug. 8, 1893, was a further development of Tremper's igniter scheme, but it dispensed with the spring-loaded rod in the piston. Instead, a bolt was firmly set protruding from the crown of the piston, and a 'flexible sparking strip' was attached to the bolt. The strip, which could be configured in any number of ways, made contact with fixed electrodes protruding into the combustion chamber at whatever position in the cylinder deemed desirable.

This design appears inherently simpler than Tremper's first patent, and is similar to other early piston-tripped igniter designs. It's not clear which design was actually more effective, but the existence of the later design suggests there may have been problems with Tremper's original scheme.

Tremper's rotary valve was integrated into his original patent. 'Fig. 3' shows the ports in the cylinder, with 'P' and P4' representing the disk valve and valve port, respectively. 'Fig. 4' shows the ports in the valve body. The valve could also be head-mounted, chain-driven through bevel gears, as shown in 'Fig. 5.'

Rotary Valve

Incorporated in Tremper's original patent was his design for a rotary valve, the most visually intriguing feature of the early Safety Vapor engines. Essentially a rotating plate that opened and closed off intake and exhaust ports on cue, Tremper's rotary valve is noteworthy.

By design, the rotary valve was set either in the cylinder wall itself or in its own compact housing bolted directly to the cylinder. With no valve chest carrying a poppet valve, and no corresponding chamber between the valve chest and the combustion chamber, combustion was confined to the cylinder proper. Further, Tremper's design meant he could dial in overlap between the intake and exhaust cycles. An endless chain running from the crankshaft connected to the rotary valve's shaft, and timing was a simple issue of gearing and porting.

Other companies experimented with rotary-type valves, but the familiar poppet valve, still with us today, eventually became the industry standard for internal combustion engines.

Know of an interesting patent? Contact Gas Engine Magazine at: 1503 SW 42nd St., Topeka, KS 66609-1265, or e-mail us at:


Gas Engine Magazine A_M 16Gas Engine Magazine is your best source for tractor and stationary gas engine information.  Subscribe and connect with more than 23,000 other gas engine collectors and build your knowledge, share your passion and search for parts, in the publication written by and for gas engine enthusiasts! Gas Engine Magazine brings you: restoration stories, company histories, and technical advice. Plus our Flywheel Forum column helps answer your engine inquiries!

Facebook YouTube


click me