Anti-pinch window drive circuit

[0001] This application claims the benefit of U.S. Provisional Application No. 60/350,192, filed Jan. 21, 2002.

[0002] This invention relates to control circuits and more specifically relates to a novel anti-pinch circuit for sensing obstacles in an automotive window path.

[0003] Motor driven automotive windows should stop while closing if an obstacle (such as a person's hand or finger or the like) is pressed between the top of the window and the top of the window frame. Mechanical sensors (transducers) can be used for this purpose but these increase the number of parts needed and increase the cost of the window control system. The use of added parts also reduces the reliability of the system.

[0004] It would be desirable to eliminate the need for such sensor transducers in an anti pinch control system.

[0005] In accordance with the invention, the motor current (of a d-c motor in an H bridge control circuit) is monitored and the distortion in the motor current wave shape due to an obstacle in the window path when closing is monitored to stop the motor. The sensing circuit can be integrated into an IC control chip, such as the IR3220 chip of the International Rectifier Corporation. This circuit is shown in copending application Ser. No. 10/091,194, filed Mar. 4, 2002 entitled H-BRIDGE WITH SINGLE LEAD FRAME (IR-1853), which is incorporated by reference in this application.

[0014] The present invention offers to automotive power window manufacturers a “full silicon” platform for an integrated low cost anti pinch solution without external sensors.

[0015] Referring first to FIG. 3, the overall circuit of the invention is shown for the anti pinch control of d-c motor 20 which is connected to drive a window within automotive door frame. The inputs M1 and M2 to the motor 20 are the terminals between high side MOSFETs 21 and 22 (FIG. 1) and low side MOSFETs 23 and 24 (FIGS. 2 and 3). MOSFETs 21 and 22 are integrated into IC 25 (FIG. 1) which has the general structure of the integrated H Bridge chip of copending application Ser. No. 10/091,194 (ER-1853) which is modified, as will be described hereinafter to contain the control functions of the invention. The low side MOSFETs 23 and 24 may be discrete 40 volt, 7 mohm MOSFETs in an SO8 package.

[0016] Capacitors 30 and 31 are input capacitors connected across the input terminals +V_cc and GND of the automotive system. Resistors 32 and 33 are connected in the gate circuits of MOSFETs 23 and 24 respectively.

[0017] The components of the system of FIGS. 1 and 3 may be mounted on a common circuit board 35 as shown in FIG. 2. Board 35 may be a thin FR4 type printed circuit board or the like and may have a width of about 21 mm as shown in FIG. 2. This assembly can be conveniently mounted in the chassis of d-c motor 20 or in any other desired way.

[0018] With the two additional regular MOSFETS, 23 and 24 the circuit drives DC motor in either of two directions and features over-current and over temperature protection circuits 40 and 40a (FIG. 1). Other relevant circuit blocks include High Side Current sensing circuits 41 and a Programmable Logic Array (P.L.A.) 42. The “H bridge I.C.” 25 is able to house at the same time a P.L.A. 42 and Current Sensing High Side Switches 21, 22 so that all the basic blocks for the Anti-pinch function are integrated in a single part. FIG. 1 shows the typical architecture for device 25.

[0019] The architecture of IC 25 of FIG. 1 includes:

• • [0020] (a) embedded short-circuit protection circuits 40;
  • [0021] (b) overload protection by sensing the junction temperature at function block 40a;
  • [0022] (c) the inner 20 kHz PWM Soft Start circuit 50 which provides a sequence which avoids the inrush current of the motor;
  • [0023] (d) the High Side Current Sensing switches 21 and 22 offer the benefit of a direct and simple feedback of the motor current. Each direction is sensed in a single feedback circuit and the signal includes the free-wheeling step;
  • [0024] (e) the speed of the motor is evaluated by “sampling on request” the back EMF of the motor;
  • [0025] (f) PWM circuitry offers the capability of controlling either the speed or the torque of the motor;
  • [0026] (g) The P.L.A. allows the I.C. 42 to become “intelligent” by supporting the State Machine of the whole anti-pinch function.
    The Sensorless Detection

[0027] The sensorless detection goal of the invention is to identify different mechanical stops among several possibilities (the top of the door, an arm or a finger . . . etc.). Each has a defined and unique “Torque/Speed vs Time” characteristic when used as a mechanical stop in a power window. A simple and accurate way to differentiate each characteristic consists in sampling “specific points” of the Torque/Time or Speed/Time profiles when the window encounters an obstacle as will be described. When the profile “sampled” doesn't correspond to the “Top of the door” model then the window is immediately powered downward in order to release the obstacle.

[0028] Torque measurement can be done by the inner current sensing High Side Switch(Swit). A 100 kHz bandwidth and the 5% precision of the current feedback available with the IC 25 are good enough for the torque evaluation even while switching at 20 kHz.

[0029] The shaft speed of Motor 20 is measured by sensing the back E.M.F. of the motor. Sampling the speed is accomplished by in the following sequence that is executed on request during the window motion:

• • [0030] 1) turn off the 4 Mosfets 21, 22, 23, 24 of the H bridge;
  • [0031] 2) wait for 2 milliseconds to demagnetize the motor;
  • [0032] 3) turn on a Low Side Mosfet 23 or 24 to connect the motor to Ground;
  • [0033] 4) sample the Back EMF on the open terminal M1 or M2 of the motor;
  • [0034] 5) turn off the Low Side Mosfet 23, 24 and repower the motor.

[0035] The whole sequence lasts no longer than 3 ms and the H-Bridge is then switched back to its initial state. The sampled value is then used in the Anti-Pinch Algorithm as a speed feedback.

Torque & Speed Profiles

[0036] The basic aim is to identify the “top of the door” characteristic with a sufficient definition in order to not confuse it with any “flesh obstacle”. The characterization is done by looking at the “Torque vs. Time” and the “Speed vs. Time” curves when the window approaches the top of the door. Monitoring the “Torque vs. Time” curve could cover 80% of the “anti-pinch” function but the “Speed vs. Time” profile helps in identifying some of the most difficult cases like a thin finger or a child's neck or head. The waveforms of FIGS. 4 and 5 show the torque profiles for the top of the door and for a hand pinched in the window respectively. The current of the motor is monitored and represents the torque.

[0037] The small plateau on the curve of FIG. 4 is the “signature” of the top of the door. In this example, it corresponds to the rubber seal that the window has to go through before being blocked. The slope and the shape of the current and the slope and the shape of the motor speed (not represented here) clearly characterize the door top compared to the “flesh” profiles (body obstacles) as shown in FIG. 5. If needed, the door top “signature” is easily improved by adding a very small spring (laminated or regular) directly inside the rubber window seal. By doing so, the plateau is higher and more exaggerated (due to added torque needed to compress the spring) and the “signature” becomes really typical even with ageing or temperature effects. The spring may be added either in the door or embedded in the mechanical system.

[0038] FIG. 6 shows the torque profile monitored over a given sample time. If, during the sample time, the window reaches the top of the door frame, the torque (as measured by motor current), will have the shape shown in solid lines, and if an obstacle is engaged, it will have the shape shown in dotted lines. The current (torque) will be constant, and below a preset threshold, if neither the door top or obstacle is reached in the interval.

[0039] FIG. 7, shows the motor shaft speed (as measured by the motor back EMF) during the interval. The motor speed drops to zero if the door top is reached, as shown in solid lines in FIG. 7; or reduces more gradually as shown in dotted lines if an obstacle is encountered.

[0040] The torque and speed profiles of FIGS. 6 and 7 respectively need not to be monitored all the time. Selecting two or three samples in the “typical zone” is enough to identify the door top. One of the algorithms is presented hereafter. It monitors the motor current during the window motion and starts a two sample acquisition sequence when the current exceeds a pre-determined threshold. The sequence is composed of two (optionally three) series of the current and speed samples. They are compared to a current threshold and a speed threshold (optionally two current and speed thresholds).

[0041] An example of a three series sequence is described in the flow chart of FIG. 8. The thresholds and temporization have to be adapted depending on the mechanical system and the motor characteristics. The sequence architecture itself remains identical whatever the window type.

[0042] The flow chart of FIG. 8 shows how the “door top signature” of FIG. 4 is identified thanks to a 3 point characterization. The anti-pinch detection can be summarized with reference to FIG. 8 as follows:

• • [0043] If the torque exceeds the nominal value for more than 50 ms and if it corresponds to the door top signature then the window is stopped.
  • [0044] If the torque exceeds the nominal value for more than 50 ms and doesn't show a door top profile, then the motor power is reversed and the window goes down until the second current threshold definitely stops it at the bottom position.

[0045] More specifically, and as seen in FIGS. 6, 7 and 8, the circuit of FIG. 1 defines two motor current threshold values I_th1 and I_th2 (which are motor torque threshold values); and two EMF threshold values V_th1 and V_th2, corresponding to motor speed threshold values.

[0046] In a first sample, the motor torque is measured in 50 ms intervals until the motor current exceeds I_th1) which can be caused either because of the beginning of the door top profile or hand profile in FIG. 6.

[0047] A comparison is next made of the motor current to threshold I_th2, If I_th2 has not been reached, then the “hand profile” and not the door top profile is the cause of the increase in motor torque, and the motor power is reversed. However, if the current exceeds I_th2, the back EMF (or shaft speed) is acquired (in a second phase) to determine if the EMF is between V_th1 and V_th2. If it is not this indicates, in FIG. 7, a “soft” obstacle, and the motor is reversed. If the motor speed is between V_th1 and V_th2, the motor may be stopped, or subsequent measurements may be made in a third phase to either stop or reverse the motor as shown in FIG. 8.

Temperature Effects

[0048] The door signature is not adversely affected by temperature variations. Temperature effects can be virtually eliminated when the signature is enhanced by the use of a spring. At low temperature, the torque level during motion is higher and may reach the obstacle detection threshold. The corresponding current threshold (I_th1) is then pre-programmed depending on the outside temperature. This can be done by a temperature sensor directly interfaced with the I.C. It is also possible to measure the average current of the motor during the first downward going motion and to predict the proper “anti-pinch” current level when the window will be going upward.

[0049] The H bridge I.C. of FIG. 1 may use a 20 kHz PWM oscillator. Speed or torque could be momentarily controlled as desired and help in the “anti-pinch” function (for example, a reduction of the speed when the current threshold is reached to help to differentiate the profiles) and to simplify the “anti-pinch detection.

[0050] Although the present invention has been described in relation to particular embodiments thereof, many other variations and modifications and other uses will become apparent to those skilled in the art. It is preferred, therefore, that the present invention be limited not by the specific disclosure herein.