Fuel pressure control system

A fuel pressure control system for a fuel supply system that supplies fuel to an injector of an engine, the fuel pressure control system comprising:

• a booster pump for increasing a high-pressure system fuel pressure as a fuel pressure of a high-pressure system as a part of the fuel supply system by discharging the fuel to the high-pressure system;
• 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, wherein:
• the control device includes a valve opening necessity determination unit for determining whether the pressure reducing valve needs to be opened;
• the control device executes a valve opening control for opening the pressure reducing valve to release the high-pressure system fuel pressure to an outside of the high-pressure system under a condition that the valve opening necessity determination unit determines that the pressure reducing valve needs to be opened;
• the control device further includes a restriction execution unit for performing a valve opening restriction control in the valve opening control for opening the pressure reducing valve with restricting a valve opening degree of the pressure reducing valve to prevent a pressure exceeding a predetermined target portion threshold pressure from being applied to a target portion as a release destination or a release passage of the high-pressure system fuel pressure in the valve opening control;
• the control device further includes a valve opening degree calculation unit that calculates a target valve opening degree when the valve opening necessity determination unit determines that the pressure reducing valve needs to be opened;
• the control device controls the valve opening degree of the pressure reducing valve so as to approach a calculated target valve opening degree;
• in the valve opening restriction control, the valve opening degree calculation unit calculates a predetermined optimum valve opening degree and an allowable valve opening degree as the opening degree of the pressure reducing valve equal to or lower than an upper limit within a range in which there is no risk that the pressure exceeding the target portion threshold pressure is applied to the target portion as the target valve opening degree;
• and
• in the valve opening restriction control, smaller one of the optimum valve opening degree and the allowable valve opening degree is set as the target valve opening degree.

A fuel pressure control system for a fuel supply system that supplies fuel to an injector of an engine, the fuel pressure control system comprising:

• a booster pump for increasing a high-pressure system fuel pressure as a fuel pressure of a high-pressure system as a part of the fuel supply system by discharging the fuel to the high-pressure system;
• 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, wherein:
• the control device includes a valve opening necessity determination unit for determining whether the pressure reducing valve needs to be opened;
• the control device executes a valve opening control for opening the pressure reducing valve to release the high-pressure system fuel pressure to an outside of the high-pressure system under a condition that the valve opening necessity determination unit determines that the pressure reducing valve needs to be opened;
• the control device further includes a restriction execution unit for performing a valve opening restriction control in the valve opening control for opening the pressure reducing valve with restricting a valve opening degree of the pressure reducing valve to prevent a pressure exceeding a predetermined target portion threshold pressure from being applied to a target portion as a release destination or a release passage of the high-pressure system fuel pressure in the valve opening control;
• in the valve opening restriction control, a balance valve opening control for opening the pressure reducing valve to prevent the high-pressure system fuel pressure from exceeding a predetermined high-pressure system threshold pressure and to prevent the pressure exceeding the target portion threshold pressure from being applied to the target portion;
• the control device further includes a target fuel pressure calculation unit that calculates a predetermined high-pressure system target fuel pressure;
• the control device controls the high-pressure system fuel pressure so as to approach a calculated high-pressure system target fuel pressure;
• the control device further incudes a state determination unit that determines whether it is in a caution required state in which there is a risk that the balance valve opening control is not executable in the valve opening restriction control if a predetermined anomaly increase of the high-pressure system fuel pressure;
• and
• the control device starts executing a predetermined fuel pressure restriction control when the state determination unit determines that it is in the caution required state to set the high-pressure system target fuel pressure to be lower than a case where the fuel pressure restriction control is not performed, so that the balance valve opening control is executable even if the predetermined anomaly increase occurs.