KNOCK Detection with Series Cylinder Pressure Sensors

Current legal requirements based on new driving cycles like WLTP or RDE focus on elevated power and torque from the engine. The gear ratios are chosen so as to permit low engine speeds to reduce fuel consumption and consequently CO₂ emissions by shifting the operating point to higher loads with reduced throttling and friction losses at low engine speeds. To achieve the required acceleration values the engine tends to be operated more frequently close to its power and torque limits. Thus, the knock occurring at the load limits will increase in significance. Today, in series production, knock is detected via structure-borne sound sensors and eliminated via retarded ignition. New low-cost in-cylinder pressure sensors (ICPS) suitable for series-production now permit evaluation of every single combustion cycle, thus detecting knock in the engine control unit (ECU) at all speed and load ratios independent of parasitic noise. This paper presents the potential for knock detection and knock control using series-production capable cylinder pressure sensors. First, the basic differences of the algorithm of a structure-borne sensor and a cylinder pressure sensor and the feasibility for implementation in an engine control unit are explained. Moreover, chassis dyno results are presented. They show the capability for cylinder pressure based knock control with reference ICPS and serial ICPS by comparing them with classical structure-born knock sensors. The final outcome of the investigations done is that a knock control based on serial ICPS is possible and leads to an efficiency improvement of around 0.5 % compared to a knock control based on a usual knock sensor. For a reference ICPS, the respective improvement is slightly higher at around 0.7 %.