opening ramp and from the end of the closing ramp to 180 u00b0 between the two ramps lies a typical valve acceleration curve often called an acceleration profile that is composed of three large acceleration pulses these are the positive opening pulse 230 the negative valve spring pulse 232 and the positive closing pulse 234 observe that the acceleration over the two positive pulses is always positive except at their boundaries where the acceleration is zero similarly the acceleration throughout the negative pulse is always negative except at its boundaries where it is zero for purposes of discussion throughout this description it is assumed that draft acceleration curves between the square wave ramps always consist of a positive pulse followed immediately by a negative pulse finally ending with a second positive pulse there are no zero acceleration values except those occurring at the boundaries of the three pulses in typical cam design processes only the three pulses 230 232 and 234 between the two opening and closing ramps 220 and 222 are adjusted to create a desirable valve motion ramps and their positioning within the acceleration profile once set are not typically varied a design engineer will add delete and move points that sketch out a desired acceleration curve or profile a curve fitting routine or spline generates a curve passing through these points of the designer 39 s choosing to define the cam acceleration profile a u03b8 between ramps the designer 39 s initial rough sketch 200 connects the acceleration data points shown as small circles in fig2 such as 240 242.