Some vehicles are equipped with a closure panel, such as a lift gate, which is driven between an open position (position 2) and a closed position (position 1) using an electric drive system. Hold systems have been proposed to provide such vehicles with the capability of assisting the operator of the closure panel, in order to maintain a third position hold (or position 2) during opening and closing operations, so as to help counteract the weight of the closure panel itself. Without these hold systems, the closure panel may sag back down at the top end of the operational opening range due to the closure panel weight providing a closure torque greater than an opening torque provided by the electric drive system. Such proposed hold systems are, in some instances, complex and expensive and may not offer adequate failsafe modes (in the event of electric motor failure or loss of power) while at the same time maintaining adequate manual efforts by the operator. Also recognized is a need to provide a counterbalance mechanism that can offer efficient counterbalance force customization for different closure panel weights and configurations (e.g. differing centers of gravity), including the ability to accommodate for third position hold or stop and hold functionality of the closure panel.
Further disadvantages of current hold systems include bulky form factors which take up valuable vehicle cargo space, requirement to have additional lift support systems in tandem such as gas struts and other counterbalance mechanisms, unacceptable impact on manual open and close efforts requiring larger operator applied manual force at the panel handle, undesirable force spikes that do not provide for smoother manual force/torque curves, requirement to use vehicle battery power to maintain third position hold, and/or temperature effects resulting in variable manual efforts required by the operator due to fluctuations in ambient temperature.
It is recognized that constantly applied forces in a counterbalance mechanism can be problematic due to variations in the geometry and/or operator positioning during the complete raise and lowering cycle of a closure panel, including the ability to provide for third position hold where desired.