Controller and control method for injection using function map

A method of controlling an injector (1) or the like suitable for use in an internal combustion engine, includes providing a first data map having a plurality of first data map points, each of the first data map points representing a first data map output value, and providing a function map (40) comprising a second data map (46; 146) having a plurality of second data map points, each corresponding to a respective one of the first data map points, and wherein the second data map is divided into at least a first-type data map region containing second data map points representing second data map output values only of a first type (Y, O) and a second-type data map region containing second data map points representing second data map output values only of a second type (Y, O), wherein a portion of the second data map (46; 146) defines a hysteresis region (52). The method also includes determining an operating point on an operating path (50; 150) within the second data map (46; 146) in dependence upon first and second engine operating parameters (4a, 4b) and determining a control function for the injector (1) based on a first data map output value determined from the first data map and the second data map output value determined from the second data map (46; 146), in dependence upon whether the operating point in the second data map (46; 146) lies in a part of the first-type data map region which is outside the hysteresis region (52), or whether the operating point in the second data map (46; 146) lies in a part of the first-type data map region which is within the hysteresis region (52).