Moving linear piezoelectric motor for vehicle applications

A piezoelectric moving linear motor consists of three piezoelectric actuators which are controlled relative to each other. One piezoelectric actuators causes two blocks to move away from each other in opposition to a spring force. The other two piezoelectric actuators selectively clamp a block to a guide shaft. By cyclically controlling the actuation of the three piezoelectric actuators, the motor is able to move the blocks axially along the guide shaft. Preferably, a vehicle component such as a window is fixed to one block and is caused to move along the guide shaft.

BACKGROUND OF THE INVENTION 
This application relates to a moving linear piezoelectric motor. In 
preferred applications, the motor is utilized to drive a vehicle 
component. 
In the prior art, piezoelectric multilayer stack actuators are utilized in 
many applications to provide a motor. Piezoelectric actuators of this type 
are generally formed from specific materials that can expand or contract 
in response to electrical charges. The expansion and contraction occurs 
quite rapidly, and with proper control, piezoelectric actuators can be 
utilized to move other members. Generally, piezoelectric actuators have 
not been utilized to transmit heavy elements that require high torque. 
Vehicle components have typically utilized rotary electric motors to drive 
their components. The rotary motors are sometimes connected through 
transmissions which change the rotary movement into linear movement. 
Examples of the type of vehicle components routinely driven by electric 
motors are window lift motors, sunroof lift motors, door lock mechanisms, 
seat position drives, and any other moving elements. The electric motors 
and gear boxes typically utilized for vehicle applications have been 
somewhat bulky and expensive. 
Piezoelectric motors can be relatively small compared to electric motors. 
In addition, piezoelectric motors can be relatively inexpensive. However, 
piezoelectric motors have not been utilized to drive vehicle components in 
the past. Again, piezoelectric actuators have typically been utilized to 
drive low-torque requiring applications. 
SUMMARY OF THE INVENTION 
In a disclosed embodiment of this invention, piezoelectric actuators are 
utilized to provide a moving linear motor for moving a component between 
spaced positions. In a preferred application, the component is a vehicle 
component, and most preferably a vehicle window. 
In a preferred embodiment, three piezoelectric actuators are utilized and 
controlled in combination to achieve the linear motor. A first block is 
spaced from a second block. A piezoelectric actuator is associated with 
each of the blocks and is operable to move a clamping finger towards and 
away from a guide shaft. The two blocks move along the guide shaft. One of 
the two blocks is fixed to the component. That is, if a window is being 
lifted by this motor, the window is fixed to move with one of the two 
blocks. 
The two blocks are spaced by a small axial distance. Pins extend through 
one of the blocks, and are fixed to the other block. A spring biases the 
pin, and the block fixed to the pin, toward the other block. A 
displacement piezoelectric actuator is associated with one of the two 
blocks, and drives a push lever toward and away from the other block. 
To achieve the inventive linear movement, a first of the two blocks has its 
clamp finger clamped on the guide shaft. The other block has its clamp 
finger moved to the unclamped position. The clamp finger moves to the 
unclamped position by expanding or contracting an associated piezoelectric 
actuator. After one of the blocks is clamped and the other block is 
unclamped, the displacement piezoelectric actuator drives the lever such 
that it forces the unclamped block away from the clamped block. The 
clamped block is fixed on the guide shaft and does not move. The lever 
pivots relative to the blocks, and the unclamped block moves axially along 
the guide shaft by a small amount. The lever creates a mechanical 
advantage providing more movement of the unclamped block than would be 
otherwise achieved by the expansion of the piezoelectric actuator. The 
same is true for the clamp finger movement. Preferably, the lever has arms 
spaced on both sides of the guide shaft which force the block along the 
guide shaft. By placing the arms on opposed sides of the guide shaft, any 
torque about the guide shaft is negated. In this way, the inventive motor 
achieves smooth and reliable movement. 
Once the unclamped block has moved, its clamp is closed. The clamp 
associated with the previously clamped block is then unclamped. The 
displacement piezoelectric actuator is then de-energized or relaxed. A 
spring bias on the pins then draws the now unclamped block toward the now 
clamped block. In this way, the two blocks rapidly move in small 
increments along the guide shaft. Since the vehicle component is fixed to 
one of the blocks, the vehicle component also moves along the guide shaft. 
In preferred embodiments of this invention, the basic motor is utilized 
either singularly, or in pairs to drive a window. If the motor is utilized 
in pairs, the relative movement of the two motors on spaced guide shafts 
can be controlled to operate at different speeds such that the window may 
move into its associated seat in the door frame from a variety of angular 
orientations. This facilitates the soft and safe movement of the window 
into its seat. 
The linear motor is smaller than the prior art motors. Moreover, since the 
motor achieves direct linear movement, no rotary-to-linear transmission is 
needed. 
These and other features of the present invention can be best understood 
from the following specification and drawings, of which the following is a 
brief description.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 1 shows a system 20 that provides a linear motor for movement along a 
shaft 22. A first block 23 has pins 24 extending through the block, which 
are then fixed to a second block 25 at 27. Springs 26 are received on pins 
24 and bias the pin 24 and the block 25 toward the block 23. 
The blocks 23 and 25 are similar, and each include a lower fixed portion 28 
and clamping arm portion 30. A component, here a window 31, is fixed to 
one block, here block 23. The clamping arm portions 30 are movable under 
the influence of a multilayer stack piezoelectric actuator 32, which can 
expand or contract to move the clamp 30 between clamped and unclamped 
positions on the guide shaft 22. A worker in the piezoelectric motor art 
would know how to achieve such movement with the application of 
appropriate voltages. Fixed portion 34 is a guide bushing provided about 
the guide shaft 22 and spaced from the clamp portion 30. A lever 36 pivots 
on a pin 38 in a displacement element 40 which is fixed to the lower 
portion 28 (not shown) of block 23. A piezoelectric actuator 42 expands or 
contracts to drive the lever 36 to pivot about the point 38 through a 
transmission element 44. 
In the position shown in FIG. 1, the blocks 23 and 25 are not spaced by any 
influence of the lever 36. Instead, the piezoelectric element 42 has been 
de-energized or moved to its contracted or relaxed position. The force of 
springs 26 has caused the pin 24 and block 25 to be moved toward the block 
23. The two blocks are spaced by the distance D.sub.1. 
As shown in FIG. 2A, the clamping portion 30 includes a finger 44 spaced on 
one side of the guide shaft 22 from guide bushing 34. The piezoelectric 
actuator 32 expands or contracts to move finger 44 from the open unclamped 
position as shown in FIG. 2A to a closed clamped position such as shown in 
FIG. 3. 
As shown, pins 43 connect finger 44 to block 34. Springs 45 bias finger 44 
toward the FIG. 3 position. In the position shown in FIG. 2A, the 
piezoelectric actuator 32 is expanded, thus causing finger 44 to pivot 
about point 47, and away from the guideshaft 22 against the force of 
spring 45. Set screw 46 provides the actual contact between the 
piezoelectric actuator 32 and the clamp finger 44. Set screw 46 can be 
adjusted to adjust the amount of movement of the finger 44 based on the 
expansion of the actuator 32. By utilizing the pivot mount 47, the finger 
44 achieves a mechanical advantage at the location of shaft 22. That is, 
the actuator 32 need only move a relatively small amount, and the finger 
44 will move a greater amount. This will insure good clamping force even 
if there are some slight manufacturing tolerances resulting in an 
unexpectedly large amount of clearance between the finger 44 and the shaft 
22. In the FIG. 3 position, the piezoelectric actuator 32 has moved to its 
contracted or de-energized position, and the spring force 45 now forces 
the finger 44 onto guideshaft 42 to provide the clamped position. 
Note, shaft 22 is shown to have a truncated upper surface. This will 
prevent the blocks from rotating on the shaft 22. In certain applications, 
it may not be necessary to have the truncated surface, and yet the motor 
will still not rotate relative to the shaft. As an example, if the blocks 
are attached to a window, the mount to the window will prevent any 
rotation relative to the shaft. Other shaft shapes are within the scope of 
this invention. 
As shown in FIG. 2B, the clamp arm 30 is biased toward the shaft 22 by the 
spring 45. The guide bushing 34 includes a opening at a central location 
to receive the clamp arm 30 and allow access to the shaft 22. 
It should be understood the details illustrated in FIGS. 2A and 2B are 
exemplary, and other arrangements for clamping on the guide shaft 22 may 
be utilized. Further, while the invention is shown here with the actuated 
position of the piezoelectric actuator 32 resulting in the unclamped 
position, it should be understood that an alternative arrangement could be 
provided in which the finger is moved to the locked position when actuator 
32 is actuated. The embodiment shown in FIG. 2A, 2B and 3 wherein the 
de-energized position is clamped is preferred, as this will result in 
clamping when the system is shut down, thus locking the window. 
FIG. 4 shows a detail of the lever 36, which has arms 48 formed on each 
side of the guide shaft 22, and associated with corresponding surfaces on 
the guide surface 34 of the fixed portion 28. 
As shown in FIG. 4, since the arms 48 are spaced on each side of the guide 
shaft 22, any torque about the shaft center line will be negated. The 
lever provides mechanical amplification of the amount of expansion of 
displacement actuator 42. This allows a substantially lower operating 
frequency than what would be otherwise required to achieve practical 
window movement rates. 
The movement of an element with motor 20 will now be described with 
reference to FIGS. 5 and 1. As shown in FIG. 5, the motor has now caused 
upward movement. Block 25 has its clamp 30 clamped on the guide shaft 22, 
such as shown in FIG. 3. Block 23 has its clamp 30 moved to the unclamped 
position as shown in FIG. 2A. The piezoelectric actuator 42 is expanded to 
drive the lever 36 to pivot upwardly as shown in FIG. 5. This movement 
forces block 23 along guide shaft 22. The movement spaces the blocks 23 
and 25 by a distance D.sub.2, which is greater than the distance D.sub.1 
as shown in FIG. 1. 
Once an incremental amount of movement has been achieved by this step, the 
clamp 30 associated with block 23 is moved to the clamped position as 
shown in FIG. 3. Block 25 has its clamp portion 30 moved to the unclamped 
portion as shown in FIG. 2A, and the piezoelectric actuator 42 is moved to 
its relaxed position. At that point, springs 26, which have been 
compressed by movement of block 23, move to a relaxed position by forcing 
pins 24 and block 25 upwardly. The motor now returns to the position shown 
in FIG. 1, where blocks 23 and 25 ar spaced by a distance D.sub.1. The 
method is then repeated on a quick cycle. By quickly repeating these two 
steps, the motor moves incrementally and smoothly along the shaft 22. By 
controlling the operation of piezoelectric actuators 32 and 42, the 
overall movement of the combined blocks is very smooth, and is effectively 
continuous. 
The force capability of the motor is determined by the frictional force of 
the individual clamps 30, and by the force capability and mechanical 
stiffness of the piezoelectric actuator 42 and the lever mechanism. This 
force capability is proportionally reduced by the mechanical amplification 
caused by the lever. The mechanical stiffness of the displacement 
mechanism is also reduced by the square of the amplification effect. Thus, 
the amount of amplification of the lever arm is limited by other design 
features. Even so, force capabilities ranging up to several hundred pounds 
are easily obtainable with this motor design. 
The motor speed is governed by the operating frequency and the amount of 
motion achieved on each cycle. Actuator heating due to dielectric losses 
in the piezoelectric actuator material increases with operating frequency. 
Thus, continuous operation of the motor would require a typical operating 
frequency of below 1-2 kHz depending on the overall size and geometry of 
the piezoelectric actuators used. For a one inch long piezoelectric 
displacement actuator 42 having a .002" nominal stroke (i.e.,0.2% strain) 
amplified by a 5:1 ratio lever arm, the motor speed at 500 Hz operation is 
5 inches per second. Operation below 1 kHz also reduces the radiated 
acoustic noise by the motor. The stroke amplification is a unique feature 
of this motor which permits high speed operation without the use of 
excessively large piezoelectric actuators or excessively high operating 
frequencies. 
To operate the motor in a reverse direction, clamp 30 associated with block 
23 is locked. The clamp 30 associated with block 25 is open. The 
piezoelectric element 42 is moved to its expanded position such that the 
lever 36 pivots about point 38. Since block 23 is fixed to guide shaft 22, 
block 25 is forced downwardly as shown in FIG. 5. Once an incremental 
amount of movement has been achieved, clamp 30 associated with block 25 is 
moved to its clamped position. The clamp 30 associated with block 23 is 
moved to its unclamped position and piezoelectric element 42 is moved to 
its contracted position. At this time, the spring force from the 
compressed springs 26 causes block 23 to move downwardly such that the two 
blocks return to the position as shown in FIG. 1. Again, by rapidly 
repeating these two steps, the present invention is able to achieve smooth 
movement of the blocks. Note that motor reversal is virtually 
instantaneous, since it involved only the electrical reversal of the 
timing sequence for the two actuators. 
FIG. 6 shows an embodiment 49 wherein a single motor 20 is mounted on a 
single shaft 22 to drive a window 47 upwardly. A motor control 50 controls 
the motor to achieve the desired movement. 
FIG. 7 shows an alternative embodiment 49. A control 50 controls movement 
of a window 52 through two linear motors 20, as disclosed above. One block 
from each motor is fixed to move with the window 52 such that as the 
motors move incrementally along the guide shaft 22, the window 52 also 
moves. 
FIG. 8 shows another embodiment 56 having two guide shafts 58 which are 
somewhat curved. In this application, the window 60 is driven towards a 
position 62 where a forward end 64 initially contacts the door frame 65. 
By controlling the speed of the two motors 20 such that the leftwardmost 
motor in FIG. 8 is driven more rapidly initially, this movement can be 
achieved. With this movement, the window can be brought into smooth and 
safe abutment with its seat in the door frame 65. This is especially 
beneficial for windows having relatively complex configurations. 
FIG. 9 shows another embodiment 66 wherein one guide shaft 67 is provided 
beneath the window 68 and a second guide shaft 70 is provided on the side. 
Of course, motors 20 can be provided at any of several locations on the 
window including the side or bottom. In addition, while there may be two 
guide shafts, it may be possible to only utilize a single motor, with the 
second guide shaft receiving a slide bearing arrangement to provide 
guidance only. 
Preferred embodiments of this invention have been disclosed, however, a 
worker of ordinary skill in the art would recognize certain modifications 
come within the scope of this invention. For that reason, the following 
claims should be considered to determine the true scope and concept of 
this invention.