A variable combustion cylinder ratio control method variably controls a combustion cylinder ratio of an engine during an intermittent deactivation operation, in which cylinder deactivation is intermittently performed. The method includes, when setting N to an integer greater than or equal to 1, repeatedly performing a cylinder deactivation in a pattern in which combustion is consecutively performed in N cylinders in the order of cylinders entering a combustion stroke, and then a subsequent cylinder is deactivated. The method further includes changing the combustion cylinder ratio by changing the pattern such that the value of N is changed by one at a time.

A method for monitoring a pressure sensor in a direct injection system including at least one common rail, a high-pressure fuel pump, a hydraulic circuit connecting the high-pressure pump to the common rail, a passive pressure-limiting valve connected to the hydraulic circuit, configured to open once the pressure in the hydraulic circuit is greater than a threshold pressure, so as to discharge the fuel, including the steps of detecting the opening of the pressure-limiting valve, measuring the pressure P.sub.MES corresponding to the time of opening of the pressure-limiting valve and comparing the measured pressure P.sub.MES to the threshold pressure P.sub.1 in order to detect a drift in the pressure sensor.

A method for monitoring a pressure sensor in a direct injection system including at least one common rail, a high-pressure fuel pump, a hydraulic circuit connecting the high-pressure pump to the common rail, a passive pressure-limiting valve connected to the hydraulic circuit, configured to open once the pressure in the hydraulic circuit is greater than a threshold pressure, so as to discharge the fuel, including the steps of detecting the opening of the pressure-limiting valve, measuring the pressure P.sub.MES corresponding to the time of opening of the pressure-limiting valve and comparing the measured pressure P.sub.MES to the threshold pressure P.sub.1 in order to detect a drift in the pressure sensor.

A control device for controlling an engine provided with a fuel pump including a pressurizing chamber, a plunger inserted into the pressurizing chamber and which changes a volume of the pressurizing chamber, and an on-off valve configured to open and close a suction port, is provided. When a pressurizing cycle consists of a period of pressurizing stroke in which the volume of the pressurizing chamber is reduced to allow fuel to be pressurized and a period of suction stroke in which the volume of the pressurizing chamber is increased to allow fuel to be drawn into the pressurizing chamber, a closing cycle of the on-off valve is controlled so that a ratio of the closing cycle to the pressurizing cycle becomes smaller in a second combustion mode where a partial compression-ignition combustion is performed than in a first combustion mode where SI combustion is performed.

A control device for controlling an engine provided with a fuel pump including a pressurizing chamber, a plunger inserted into the pressurizing chamber and which changes a volume of the pressurizing chamber, and an on-off valve configured to open and close a suction port, is provided. When a pressurizing cycle consists of a period of pressurizing stroke in which the volume of the pressurizing chamber is reduced to allow fuel to be pressurized and a period of suction stroke in which the volume of the pressurizing chamber is increased to allow fuel to be drawn into the pressurizing chamber, a closing cycle of the on-off valve is controlled so that a ratio of the closing cycle to the pressurizing cycle becomes smaller in a second combustion mode where a partial compression-ignition combustion is performed than in a first combustion mode where SI combustion is performed.

The error diagnosis device has: an input unit that receives detected values for pressure inside the common rail; a calculation unit that, if the detected values are less than a target common rail pressure, calculates the pressure differences and the fuel pump discharge amounts, and a determination unit that determines whether or not a set time has lapsed in a slate in which the pressure differences are at least a first threshold value and less than a second threshold value and the discharge amounts are at least a third threshold value and less than a fourth threshold value. The determination unit determines that an error has occurred in the high-pressure pump if the set time has lapsed and determines that an error has occurred in the flowrate adjustment valve if the set time has not lapsed.

The error diagnosis device has: an input unit that receives detected values for pressure inside the common rail; a calculation unit that, if the detected values are less than a target common rail pressure, calculates the pressure differences and the fuel pump discharge amounts, and a determination unit that determines whether or not a set time has lapsed in a slate in which the pressure differences are at least a first threshold value and less than a second threshold value and the discharge amounts are at least a third threshold value and less than a fourth threshold value. The determination unit determines that an error has occurred in the high-pressure pump if the set time has lapsed and determines that an error has occurred in the flowrate adjustment valve if the set time has not lapsed.

A system for pump assist to maximize fuel consumption in a natural gas powertrain includes a fuel delivery system including a natural gas storage tank supplying a first natural gas flow, a pressure sensor disposed to provide data regarding a natural gas pressure within the storage tank, and a natural gas pump operable to selectively boost the first natural gas flow to create a second natural gas flow with increased pressure. The system further includes an engine operable to utilize one of the natural gas flows to provide an output torque and including a fuel injector and a computerized fuel system controller programmed to monitor the data regarding the natural gas pressure within the storage tank, compare the data regarding the natural gas pressure within the storage tank to a threshold cut-off pressure for the fuel injector, and command activation of the natural gas pump based upon the comparing.

A system for pump assist to maximize fuel consumption in a natural gas powertrain includes a fuel delivery system including a natural gas storage tank supplying a first natural gas flow, a pressure sensor disposed to provide data regarding a natural gas pressure within the storage tank, and a natural gas pump operable to selectively boost the first natural gas flow to create a second natural gas flow with increased pressure. The system further includes an engine operable to utilize one of the natural gas flows to provide an output torque and including a fuel injector and a computerized fuel system controller programmed to monitor the data regarding the natural gas pressure within the storage tank, compare the data regarding the natural gas pressure within the storage tank to a threshold cut-off pressure for the fuel injector, and command activation of the natural gas pump based upon the comparing.

A fuel pressure control system for a fuel supply system of an injector of an engine includes: a booster pump for increasing a high-pressure system fuel pressure; a pressure reducing valve for reducing the high-pressure system fuel pressure; and a control device for controlling the booster pump and the pressure reducing valve. The control device includes a valve opening necessity determination unit for the pressure reducing valve. The control device executes a valve opening control for opening the pressure reducing valve. The control device further includes a restriction execution unit for performing a valve opening restriction control in the valve opening control to prevent a pressure exceeding a predetermined target portion threshold pressure from being applied to a target portion.