SYSTEM AND METHOD FOR ELECTRICALLY CONTROLLABLE TRANSMISSIONS
FIG5A is a graph illustrating dead times in the operation of a clutch
As with any circuit or mechanism, the ideal behavior of the electrolaminte clutches and their practical behavior differ in some aspects. In particular, as with all clutches of any type, the electrolaminate clutch may have an engagement or a disengagement delay. In other words, there may be a time delay between when an electrical signal is sent to engage the clutch and when the clutch is mechanically engaged. Similarly, there may be a delay between when an electrical signal is sent to disengage a clutch and when the clutch is actually mechanically disengaged. Some other characteristics of the time delays are that the engagement and disengagement delay may not be equal to one another. Further, the engagement (or the disengagement) delay may differ from one engagement (or disengagement) to another. There are several consequences of these time delays. One consequence is that if these delays are not accommodated for in terms of the on-off sequence of the clutches and if both clutches are effectively engaged at the same time, the result may range from a loss of efficiency to malfunction or destruction of the device. To avoid these consequences, a "dead time" may be purposely introduced in the on-off sequence of the clutches such that an engaged clutch is mechanically disengaged before an electrical signal is provided to the disengaged clutch for it to engage. FIG5A illustrates this example. The graph 800 illustrates a first clutch going from an engaged state to a disengaged state. A period of time illustrated as Tdead is allowed to elapse before the clutch in graph 810 is turned on. Although these graphs show ideal behavior of the clutches in that they turn on and off instantaneously, the approach is that Tdead may be adjusted to accommodate the engagement and disengagement delays of the clutches. The dead time may be about 0.5 to 10 msec. but other values are possible. Further, this value may be chosen based on the detailed understanding of the behavior of the clutches and other members of the device 400 as described below.
graph
865
inverter
35
Eqn.
860
bidirectional arrow inverter
810
clutch in graph
855
clutches clutch
875
gate
835
outputs output
830
outputs output
870
gate
845
hardware circuits
850
clutches clutch
840
hardware circuits
['1. A system, comprising: an electrically controllable transmission, wherein the electrically controllable transmission comprises at least one input hub, at least one electrically controllable clutch, a rotatable member, an output hub, and a bias member that couples the rotatable member to the output hub, wherein the at least one electrically controllable clutch is configured to transmit power from the at least one input hub to the rotatable member when engaged; and a control circuit configured to apply at least one control signal to the at least one electrically controllable clutch, wherein the at least one control signal comprises pulses that cause the at least one electrically controllable clutch to engage and disengage in at least one sequence of alternating engagement time intervals and disengagement time intervals, wherein a transmission ratio of the electrically controllable transmission is controlled by the at least one sequence of alternating engagement time intervals and disengagement time intervals.']