EGR constructions for opposed-piston engines

A ported, uniflow-scavenged, opposed-piston engine including at least one cylinder with piston-controlled exhaust and intake ports and a charge air channel to provide charge air to at least one intake port of the engine, in which:

• the charge air channel includes at least one charge air cooler,
• an exhaust gas recirculation (EGR) loop has a loop input coupled to an exhaust port of the cylinder and a loop output coupled to the charge air channel in series with the at least one charge air cooler,
• the EGR loop includes a variable valve settable to a first state or to a second state, wherein the first state couples the loop output to a charge air input of the at least one charge air cooler and the second state couples the loop output to a charge air output of the at least one charge air cooler,
• the engine includes a supercharger in communication with the EGR loop to pump exhaust gas through the EGR loop into the charge air channel, and,
• the at least one charge air cooler includes a charge air cooler with an input coupled to the compressor output of a turbo-charger and an output coupled to an input of the supercharger, in which the first state couples the loop output to the input of the charge air cooler and the second state couples the loop output to the input of the supercharger.