Section 101 Examples
Example 26: Internal Combustion Engine

This is an example provided by the U.S. Patent and Trademark Office for analyzing Section 101 patent subject matter eligibility issues. This example is taken from Appendix 2 of the July 2015 Update on Subject Matter Eligibility.

This example should be viewed in light of the introduction that was provided with it.

Index to USPTO's Section 101 Examples
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Example 26: Internal Combustion Engine

This hypothetical example demonstrates the use of the streamlined analysis. The claim below is based on the technology from U.S. Pat. 5,533,489. As a streamlined analysis would not result in a written rejection, the discussion sets forth exemplary reasoning an examiner might use in drawing a conclusion of eligibility.


Nitrogen oxides are constituents of exhaust gas that are produced during the operation of an internal combustion engine. It is generally understood that nitrogen oxides are harmful to our atmosphere and cause air pollution. The amount of nitrogen oxides produced in the exhaust gas is relative to the temperature that the fuel and air mixture burns in the engine. Therefore, exhaust gas recirculation (EGR) has been developed to recirculate the exhaust gas back to the air intake, which reduces the amount of oxygen in the combustion mixture and causes it to burn at a lower temperature, thereby reducing the amount of nitrogen oxides produced. However, as the amount of EGR increases there may be a resulting decline in engine performance (e.g., a decrease in power output).

The invention is an internal combustion engine that solves this problem by automatically modifying the amount of EGR based upon current engine operations. In particular, the inventor has discovered that engine performance can be optimized by turning off the EGR during acceleration, which permits the engine to operate at maximum power output while retaining the reduction in nitrogen oxides. Therefore, the invention uses a control system to control the opening and closing of an exhaust gas recirculation valve based upon a rate of change of the engine throttle, in order to modify the amount of EGR.


1. An internal combustion engine providing exhaust gas recirculation comprising:
• an air intake manifold;
• an exhaust manifold;
• a combustion chamber to receive air from the air intake manifold, combust a combination of the received air and fuel to turn a drive shaft, and output resulting exhaust gas to the exhaust manifold;
• a throttle position sensor to detect the position of an engine throttle;
• an exhaust gas recirculation valve to regulate the flow of exhaust gas from the exhaust manifold to the air intake manifold; and
• a control system, comprising a processor and memory, to receive the engine throttle position from the throttle position sensor, calculate a position of the exhaust gas recirculation valve based upon the rate of change of the engine throttle position and change the position of the exhaust gas recirculation valve to the calculated position.


Claim 1: Eligible.

The claim recites an internal combustion engine with an intake manifold, exhaust manifold, combustion chamber, throttle position sensor, exhaust gas recirculation valve and a control system comprising a processor and memory. Thus, the claim is directed to a machine (a combination of mechanical parts), which is one of the statutory categories of invention (Step 1: YES).

Next, the claim must be evaluated to determine if the claim is directed to a law of nature, natural phenomenon or abstract idea. But when the claim is reviewed, it is immediately evident that although the claim operates by calculating the rate of change, which is a mathematical relationship describing how a variable changes over a specific period of time, the claim clearly does not seek to tie up this mathematical relationship so that others cannot practice it. In particular, the claim’s description of an internal combustion engine having manifolds, valves, and sensors forming a specific structure that uses the control system to optimize exhaust gas recirculation makes it clear that the claim as a whole would clearly amount to significantly more than any recited exception. The claim as a whole adds meaningful limitations to the use of the mathematical relationship. Additionally, use of the mathematical relationship improves engine technology. Thus, eligibility of the claim is self‐evident, and there is no need to perform the full eligibility analysis (e.g., Steps 2A and 2B). The claim is patent eligible.

If the examiner believes that the record would benefit from clarification, remarks could be added to an Office action or reasons for allowance indicating that while the claim may recite a mathematical relationship, the claim clearly amounts to significantly more than the rate of change by providing meaningful limitations to the mathematical relationship and improving engine technology.