Engine

1. An engine comprising an EGR cooler without a bypass, an EGR valve, a common rail type fuel injector, an upstream exhaust gas temperature sensor upstream of the EGR cooler, a downstream exhaust gas temperature sensor downstream of the EGR cooler and upstream of the EGR valve, and a controller controlling an opening of the EGR valve,

the controller being configured to fully close the opening when a cut condition is satisfied and variably control the opening when a cut release condition is satisfied,

wherein

an operating zone is defined as a zone surrounded by a characteristic curve indicating a relationship between rotation speed and torque,

the operating zone comprises a high operating zone containing an NTE zone, and a low operating zone that is set at a lower torque side and at a lower rotation speed side with respect to the high operating zone,

the cut condition is that an operating condition specified by the rotation speed and the torque is kept within the low operating zone for a predetermined time period or more,

the cut release condition is that the operating condition falls within the high operating zone, and

the controller is configured to:

specify a first estimated torque based on a load factor, a second estimated torque based on an injection amount, and a third estimated torque based on a rail pressure,

determine which of the first, second and third estimated torques is a maximum estimated torque,

determine whether an upstream temperature sensed by the upstream temperature sensor exceeds a predetermined upstream temperature,

determine whether a downstream temperature sensed by the downstream temperature sensor exceeds a predetermined downstream temperature,

determine whether the cut condition exists and control the EGR valve to a closed position if the predetermined time period has been exceeded in which the maximum estimated torque is below a predetermined torque, and

determine the cut release condition exists and control the EGR valve to an at least partially open position if the maximum estimated torque exceeds the predetermined torque, or the upstream temperature exceeds the predetermined upstream temperature, or the downstream temperature exceeds the predetermined downstream temperature.

2. The engine according to claim 1 , wherein

the controller is configured to set a target value of the rotation speed to a low speed or a high speed,

the low speed is the rotation speed at which the torque takes its peak value in the characteristic curve, and

the high speed is the rotation speed higher than the low speed, the entirety of the torque at the high speed being contained in the high operating zone.

3. A freezing machine comprising:

an engine; and

a compressor driven by the engine,

the engine comprising an EGR cooler without a bypass, an EGR valve, a common rail type fuel injector, an upstream exhaust gas temperature sensor upstream of the EGR cooler, a downstream exhaust gas temperature sensor downstream of the EGR cooler and upstream of the EGR valve, and a controller controlling an opening of the EGR valve,

wherein

the controller is configured to fully close the opening when a cut condition is satisfied and variably control the opening when a cut release condition is satisfied, wherein

an operating zone is defined as a zone surrounded by a characteristic curve indicating a relationship between rotation speed and torque,

the operating zone comprises a high operating zone containing an NTE zone, and a low operating zone that is set at a lower torque side and at a lower rotation speed side with respect to the high operating zone,

the cut condition is that an operating condition specified by the rotation speed and the torque is kept within the low operating zone for a predetermined time period or more,

the cut release condition is that the operating condition falls within the high operating zone, and

the controller is configured to:

specify a first estimated torque based on a load factor, a second estimated torque based on an injection amount, and a third estimated torque based on a rail pressure,

determine which of the first, second and third estimated torques is a maximum estimated torque,

determine whether an upstream temperature sensed by the upstream temperature sensor exceeds a predetermined upstream temperature,

determine whether a downstream temperature sensed by the downstream temperature sensor exceeds a predetermined downstream temperature,

determine whether the cut condition exists and control the EGR valve to a closed position if the predetermined time period has been exceeded in which the maximum estimated torque is below a predetermined torque, and

determine the cut release condition exists and control the EGR valve to an at least partially open position if the maximum estimated torque exceeds the predetermined torque, or the upstream temperature exceeds the predetermined upstream temperature, or the downstream temperature exceeds the predetermined downstream temperature.

4. The freezing machine according to claim 3 , wherein

the controller is configured to set a target value of the rotation speed to a low speed or a high speed,

the low speed is the rotation speed at which the torque takes its peak value in the characteristic curve, and

the high speed is the rotation speed higher than the low speed, the entirety of the torque at the high speed being contained in the high operating zone.