Engine system with EGR over-pressure protection

1. An engine system for an engine having at least a first cylinder, a second cylinder, a third cylinder, and a fourth cylinder, the engine system comprising:

a first exhaust manifold fluidly connected to the first cylinder;

a second exhaust manifold fluidly connected to the second cylinder;

a third exhaust manifold fluidly connected to the third cylinder;

a fourth exhaust manifold fluidly connected to the fourth cylinder, the fourth exhaust manifold being distinct from the third exhaust manifold;

a recirculation passage extending from the first exhaust manifold to at least one of the first and second cylinders;

a recirculation control valve disposed in the recirculation passage;

a first restricted orifice connecting the first exhaust manifold to the second exhaust manifold;

a second restricted orifice connecting the third exhaust manifold to the fourth exhaust manifold;

a first pressure relief passage extending from the first exhaust manifold;

a second pressure relief passage extending from the third exhaust manifold;

a first valve disposed within the first pressure relief passage and movable to selectively reduce a back pressure of the first exhaust manifold, the first valve being a relief control valve configured to move between a flow-passing position and a flow-blocking position;

a second valve disposed within the second pressure relief passage and movable to selectively reduce a back pressure of the third exhaust manifold; and

a controller in communication with the relief control valve and the recirculation control valve, the controller being configured to effect an opening motion of the relief control valve automatically based on a closing motion of the recirculation control valve and simultaneously with the closing motion of the recirculation control valve.

2. The engine system of claim 1 , wherein the recirculation passage extends from the first exhaust manifold to both of the first and second cylinders.

3. The engine system of claim 1 , wherein the recirculation passage is a first recirculation passage,

the engine system further comprising a second recirculation passage extending from the first exhaust manifold to at least one of the third and fourth cylinders.

4. The engine system of claim 3 , further comprising

a first intake manifold connecting the first and second cylinders; and

a second intake manifold connecting the third and fourth cylinders,

wherein the first recirculation passage is fluidly connected to the first intake manifold, and the second recirculation passage is fluidly connected to the second intake manifold.

5. The engine system of claim 1 , wherein the recirculation passage is connected to the first and third exhaust manifolds in parallel.

6. The engine system of claim 1 , further comprising a turbocharger connected downstream of the second exhaust manifold, wherein the first pressure relief passage extends from the first exhaust manifold to the turbocharger.

7. The engine system of claim 1 , further comprising a turbocharger connected downstream of the second exhaust manifold, wherein the first pressure relief passage extends from the first exhaust manifold to a location downstream of the turbocharger.

8. The engine system of claim 1 , further comprising:

a high-pressure turbocharger connected downstream of the second exhaust manifold; and

a low-pressure turbocharger connected downstream of the high-pressure turbocharger,

wherein the first pressure relief passage extends from the first exhaust manifold to a location downstream of the high-pressure turbocharger and upstream of the low-pressure turbocharger.

9. The engine system of claim 1 , further comprising:

a high-pressure turbocharger connected downstream of the second exhaust manifold; and

a low-pressure turbocharger connected downstream of the high-pressure turbocharger,

wherein the first pressure relief passage extends from the first exhaust manifold to a location downstream of the low-pressure turbocharger.

10. The engine system of claim 1 , wherein the first restricted orifice is a fixed orifice.

11. The engine system of claim 1 , further comprising a cooler disposed in the recirculation passage, wherein the recirculation control valve is located downstream of the cooler.

12. The engine system of claim 1 , wherein the controller is further configured to cause the relief control valve to move based on a pressure of exhaust in the first exhaust manifold.

13. A method for operating an engine having a first cylinder, a second cylinder, a third cylinder, and a fourth cylinder, the engine further including

a first exhaust manifold fluidly connected to the first cylinder;

a second exhaust manifold fluidly connected to the second cylinder;

a third exhaust manifold fluidly connected to the third cylinder;

a fourth exhaust manifold fluidly connected to the fourth cylinder, the fourth exhaust manifold being distinct from the third exhaust manifold;

a recirculation passage extending from the first exhaust manifold to at least one of the first and second cylinders;

a recirculation control valve disposed in the recirculation passage;

a first pressure relief passage extending from the first exhaust manifold;

a relief control valve disposed within the first pressure relief passage and movable to selectively reduce a back pressure of the first exhaust manifold, the relief control valve being configured to move between a flow-passing position and a flow-blocking position; and

a controller in communication with the recirculation control valve and the relief control valve,

the method comprising:

directing air into the first cylinder, the second cylinder, the third cylinder, and the fourth cylinder;

directing exhaust from the first cylinder into the first exhaust manifold;

directing exhaust from the second cylinder into the second exhaust manifold;

directing exhaust from the third cylinder into the third exhaust manifold;

directing exhaust from the fourth cylinder into the fourth exhaust manifold;

restricting a flow of exhaust from the first exhaust manifold into the second exhaust manifold;

restricting a flow of exhaust from the third exhaust manifold into the fourth exhaust manifold;

directing exhaust from the first exhaust manifold to mix with air entering at least one of the first and second cylinders by effecting an opening motion of the recirculation control valve via the controller;

directing exhaust from the third exhaust manifold to mix with air entering at least one of the third and fourth cylinders;

selectively relieving a pressure of exhaust in the first exhaust manifold by effecting an opening motion of the relief control valve via the controller, the controller being configured to effect the opening motion of the relief control valve automatically based on a closing motion of the recirculation control valve and simultaneously with the closing motion of the recirculation control valve; and

selectively relieving a pressure of exhaust in the third exhaust manifold.

14. The method of claim 13 , wherein selectively relieving the pressure of exhaust in the first exhaust manifold includes directing exhaust from the first exhaust manifold to join exhaust from the second exhaust manifold entering a turbocharger.

15. The method of claim 13 , further including directing exhaust from the second exhaust manifold through a turbocharger, wherein selectively relieving the pressure of exhaust in the first exhaust manifold includes directing exhaust from the first exhaust manifold to a location downstream of the turbocharger.

16. An engine, comprising:

an engine block at least partially defining a first cylinder, a second cylinder, a third cylinder, and a fourth cylinder;

a first intake manifold fluidly connected to the first and second cylinders;

a first exhaust manifold fluidly connected to the first and second cylinders;

a second intake manifold fluidly connected to the third and fourth cylinders;

a second exhaust manifold fluidly connected to the third and fourth cylinders;

a third exhaust manifold fluidly connected to the third cylinder;

a fourth exhaust manifold fluidly connected to the fourth cylinder, the fourth exhaust manifold being distinct from the third exhaust manifold;

a turbocharger fluidly connected to only the second exhaust manifold, such that all exhaust gas entering the turbocharger exited from the second exhaust manifold;

at least one recirculation passage extending from the first and second exhaust manifolds to the first and second intake manifolds;

a recirculation control valve disposed in the at least one recirculation passage;

a restricted orifice connecting the first exhaust manifold to the second exhaust manifold;

a pressure relief passage extending from the first exhaust manifold to at least one of the second exhaust manifold and a location downstream of the turbocharger;

a relief control valve disposed within the pressure relief passage and movable to selectively reduce a back pressure of the first exhaust manifold; and

a controller in communication with the relief control valve and the recirculation control valve, the controller being configured to effect an opening motion of the relief control valve automatically based on a closing motion of the recirculation control valve and simultaneously with the closing motion of the recirculation control valve.