Aerodynamically Induced Loads on Hood Latch and Hood Retention Systems 2019-01-0657

Hood Latch Systems are regulated to have a secondary latch or secondary latching position, in order to retain the hood in case of partial or incomplete closure by the operator while driving the vehicle. On a vehicle with a front-opening hood, an incompletely closed hood can be lifted by incoming air flow and cause a 'hood fly-up' condition where the hood obscures the driver's vision and could lead to a higher risk of loss of vehicle control or forward collision. Many vehicles are equipped with hood ajar switches that will provide a warning to the driver if the hood is not latched, however most of these systems require some hood displacement from the full latch condition in order to provide a signal to the vehicle's driver. There have been instances documented of a "false latch" conditions whereby the latch appears to be fully closed based on apparent hood flushness to the body, however the latch was not fully engaged and the hood was prevented from moving to the pop-up or secondary latch position due to latch-striker misalignment, corrosion, or dirt/dust buildup in the latch mechanism. The latch may then suddenly move from flush to secondary position at high speeds due to aerodynamic lift acting on the closed hood, or shocks due to road surface inputs. It is of interest then for the hood and latch engineer to understand the load applied to the hood latch, striker and hood structure when this condition occurs over a range of anticipated vehicle speeds & usage conditions in order to ensure that the structural requirements applied to the component parts are adequate to prevent a hood fly-up from occurring. A method of collecting this data will be demonstrated as well as the results obtained from several different types of vehicles will be discussed.