Control signals for free-piston engines

A hydraulic free piston engine system, the system comprising:

• at least one engine combustion chamber;
• a piston movably disposed within at least one hydraulic chamber, the piston being operatively connected with a load device and the piston operatively connected to the at least one engine combustion chamber;
• and
• a servo valve for connecting or disconnecting the piston to the load device;
• and
• an engine controller in communication with the servo valve;
• the engine controller being programed to:
• receive a compression ratio of the engine;
• receive the desired load pressure and fluid flow rate per stroke of the piston within the at least one hydraulic chamber;
• determine a desired piston trajectory of the piston within the at least one hydraulic chamber to achieve based on:
• inputting into a dynamic trajectory model:
• the energy parameter;
• and
• the desired load pressure;
• and
• a target fluid flow rate;
• determining, from the dynamic trajectory model, a fuel injection amount;
• and
• determining, from the dynamic trajectory model, a target position of a servo valve configured to operate in a help mode configuration and a resist mode configuration;
• and
• provide a reference trajectory signal to control operation of the servo valve and a fuel injector to move the piston within the at least one hydraulic chamber at the determined desired piston trajectory, wherein the servo valve is responsive to the reference trajectory signal to switch between the help mode configuration and the resist mode configuration.

A method for operating a hydraulic free piston engine, the method comprising:

• receiving, at an engine controller for a hydraulic free piston engine, an energy parameter that is representative of an amount of fluid energy to be output by the engine, and a measured fluid pressure value of a fluid load of the engine;
• determining, by the engine controller, a piston trajectory of a piston within a hydraulic chamber of the engine;
• determining, by the engine controller, a fuel volume value and a servo valve actuation parameter, based on the energy parameter and the measured fluid pressure value;
• providing, by the engine controller, a fuel control signal to a fuel control device of the engine based on the fuel volume value;
• and
• providing, by the engine controller and based on the servo valve actuation parameter and the piston trajectory, a servo valve control signal to a servo valve in fluid communication with the hydraulic chamber and the fluid load, wherein the servo valve is responsive to the servo valve control signal to switch between a help mode configuration and a resist mode configuration.