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Anti-trap windows prevent injury and death

Smart Close® anti-trap automotive windows prevent injury and death. We create a new standard of care for automotive power closures. NHTSA estimates that 500 people, approximately 50% of children, are treated in hospital emergency rooms each year. Due to injuries related to power windows [1].

Smart Close® technology is easy to install and works. All applications, are helped independent of window shape or geometry. The system is ideally suited for power automotive windows, sunroofs, tailgates, sliding doors, trunks, and other power closures. Furthermore, this paper describes the design and operation of Smart Close® anti-trap windows. We include the experience of sensitivity response to both animate and inanimate objects. Also discussed are vehicle installation, performance test results, and competitive performance comparisons.

Anti-trap Automotive Windows Federal Standards

The Federal Motor Vehicle Safety Standard (FMVSS-118) “Power-operated window, partition, and roof panel systems” defines the minimum requirements for power closure systems to prevent accidental injury or death. Because this standard was written over 30 years ago. It fails to account for today’s fast-paced lifestyle, the general attitude of trust in-vehicle safety technologies. Also, the advent of new convenience features (such as express close).

The premise of FMVSS-118 divides its requirements into one of two implicitly designated groups: 
  1. “Supervised Operation” classified as “S4” and 
  2. “Unsupervised Operation,” “S5” [2].

The “S4” classification allows closure of the window or panel when the vehicle ignition key is in the “ON,” “START,” or “ACCESSORY” position. Only as long as an operator intentionally trying to activate the window is present in and around the vehicle up to a distance of 6 meters. 

The “S5” classification excludes the operator’s presence while activating window closure.

Window closure forces allowed by FMVSS-118 are high enough to injure or cause the deaths of children. 

Power window closing facts:

  1. In today’s world, people trust their vehicle safety systems. In a 2003 Harris poll, 75% of respondents were unaware that power windows kill and injure children [3].
  2. Children are often left alone in vehicles. Adults leave them there for “just a minute.” In addition, with all of the modern electronic attractions in today’s vehicles, children are prone to enter it as a place to play.
  3. Many vehicles allow the power windows to remain operational for up to 10 minutes after turning off the vehicle. Operation is allowed with the keys removed, as long as the doors remain closed.

These facts, coupled with the deadly forces generated by a power closure system, make obvious the necessity for a change to the FMVSS-118 standard.

Anti Trap Goals – reduce injuries caused by car windows

The number of injuries caused by automotive window lift systems increases each year. A contributing factor is the increased use of electrical motor-driven windows now available as standard equipment in most automotive vehicles. These systems provide powerful and rapid closure of automobile windows at the touch of a button. The ease of their use gives adults and children alike the convenience of operating a window with no more than the touch of a finger. Yet most of the reported injuries involve children who are either unaware of the dangers of the window lift system or too young to understand the danger.

The Smart Close® system addresses the entrapment safety concerns while also meeting the functional requirements of the window lift system.

The goals of the Smart Close® design are:

  1. Produce a window lift system that will prevent children from being trapped, injured, or killed
  2. Provide safe window operation without sacrificing functionality
  3. Work in all applications, independent of window shape or geometry 
  4. Cost-effective for use on all vehicles

Anti-trap child injuries

  1. With the anti-trap system, when a child places a finger or neck in an opening, the closing window reverses without injury to the child. A space-charge field detects the child’s presence in the window opening and won’t allow the window to close. 
  2. This cost-effective anti-trap system has three unique operating modes.
  3. The non-contact mode relies on an object’s size and electrical conductivity for detection as it enters into proximity of the space-charge field. Detection causes the automotive window to reverse before physical contact.
  4. Contact mode (redundant sensing) reacts to forces created between the obstruction and sensor strip embedded in the weather seal to reverse the window.
  5. Speed mode (redundant sensing) monitors window speeds to identify the presence of an obstruction in the path of the closing window.

Redundant Entrapment Detection

Together, these three modes provide redundant entrapment detection, resulting in a dramatic safety improvement over other anti-trap systems. In addition, the technology meets or exceeds all FMVSS-118 S5 requirements [3].

 The system has two components. The first component is a module that integrates the (1) control electronics, (2) motor, and (3) speed reduction gearing into a single package for driving the window lift mechanism, as shown in Figure 1. The second component is a sensor strip positioned longitudinally onto the weather seal against the window seals. The sensor consists of two conductors separated by a foam dielectric, all extruded with a surrounding elastomeric jacket. The system works by measuring the change in capacitance of the sensor either as: 

  1. an object comes into its proximity or as 
  2. the distance between the conductors is reduced when compressed. 
anti-trap Automotive window
Figure 1: Smart Close™ on Vehicle Door

Smart Close® An 8-way electrical connector provides the unit with battery, ground, ignition, window command inputs, and a diagnostic output for monitoring system status. A second connector provides a 2-wire connection of the sensor strip to the control module.


The system operates from 9 to 16 Volts D.C., and vehicle wiring errors are protected. It also meets automotive EMC standards.

Anti Trap Power Window Operation

Smart Close® will immediately reverse direction during normal window operation following a close command upon detection of an obstruction to prevent entrapment.

While vehicle ignition is off, the automotive window lift module maintains power through unswitched battery power. A switched ON vehicle ignition turns the window lift module from its low power mode to operate the window. The removed ignition input will allow the window lift module to remain active until all pending functions are complete. Once the window has stopped moving and a no-entrapment condition is determined, the module will enter low power mode until the ignition is again applied. The feature is significant should entrapment occur when removal of the ignition signal.

The control module will accept the (window UP) switch input command to close the window as long as an obstruction is not detected. If an obstruction is detected when the command to raise the window is received, the window will retract. Likewise, if an obstruction is detected when the window is being closed, the window will reverse.


Smart Close® is unique in that it provides three redundant modes of obstruction detection:

  1. The non-contact mode relies on the size and conductive properties of the obstruction reacting to a space-charge proximity field produced around the sensor strip. A distorted field as an object (such as a finger or hand) enters. Smart Close® detects this distortion and reverses the window either (a) before the obstruction actually contacts the sensor or (b) with a force of fewer than five Newtons on an animate object (such as a child). Note: One Newton (N) is approximately equal to 0.22 pounds of force (lb-f).
  2. Contact mode responds to the forces created between obstruction and the sensor strip as the window rises. The feature is required when the sensor strip does not develop enough signal strength to distort the space charge for non-contact function — a characteristic of a small non-conductive object (such as a pencil). The obstruction will compress the sensor strip, moving the conductors closer together. The obstruction causes the necessary changes in the space-charge field for detection. Minimal compression is required before detection occurs, and forces of less than 40 Newtons will be imparted on an inanimate, non-conductive object before retracting the window using the cylindrical test rod (FMVSS-118 S5 method).
  3. Speed mode monitors window travel time fluctuations using hall-effect sensors to identify the presence of obstructions in the path of the closing window. This method senses obstructions that do not contact the sensor strip.

Through advanced algorithms, the control module uses information from speed and contact modes to adjust the detection sensitivity of the system. The feature prevents the sensor strip from detecting normal forces exerted by the window.

If either the sensor strip or hall-effect sensors do not function properly, the control lift module will continue to operate with limited, safe functionality until performing service. Together, the three modes provide redundancy in obstruction detection to greatly enhance the performance and reliability of the system.


Power Window Performance Comparisons

Torque Sensing:

Automobile component manufacturers have electronic control circuitry to indirectly sense when an object is in the path of a moving window. This circuitry monitors the window lift motor to sense the motor’s torque to the window. Historically, Implement this as either a (1) motor current sense or a (2) motor speed sensor circuit. The window is either stopped or reversed when a pinched object is detected.

Only after a squeezing force occurs can this method determine that an obstruction is present in the path of the moving window. This method cannot address the environmental conditions that could mimic an obstacle. Snow, ice, or dirt buildup on a window can cause the window lift motor to labor and experience resistance similar to that produced by an obstruction. These factors prevent an otherwise unobstructed window from closing properly. Forces to move the window in these systems must be set to dangerously high levels to overcome all eventualities.


Contact Strip Switches:

Another existing technology uses a designed contact strip switch where electrical conductors contact one another when compressed by an obstruction, closing the switch [4]. This system generates 80 to 100 Newtons of force before retraction occurs. Even after the switch is closed, the inertia of the moving window (system latency) allows the forces on the obstruction to rise even higher. The performance is also highly dependent on the angle at which the obstruction contacts the switch. Additionally, the switch cannot detect obstacles in the corners or bends in the window frame.

Bypassing with no anti-trap protection 

Inadequacies in the above technologies have necessitated temporarily shutting down their safety systems. The operator is permitted to temporarily bypass the safety feature and force window closure with no anti-trap protection.

The safety feature bypass procedure is so simple that a child operating the window switches can accidentally activate it. The result is a system that falls short of providing complete entrapment protection while maintaining necessary automotive window functionality. Typical vehicle owner’s manual warning statements alert operators to the possible injury of occupants when overriding window lift systems.

Overriding – (be careful) serious injury or death could occur

“To override the safety feature…follow this procedure…the window will then travel up with no protection.” They also warn of unattended children operating power windows in the automotive vehicle. “Children should not be left unattended in the vehicle and should not be allowed to operate the power windows. They may injure themselves seriously. If someone’s neck, head, or hands get caught in a closing window, it could result in death or serious injury.”

These warnings are unnecessary with Smart Close® since the window cannot injure a child entering the closure area.


Vehicle Testing – car truck or bus – anything automotive

Figure 2 shows force comparisons between Smart Close™ and an existing torque-sensing product [5]. Tables 1-4 show the graph as developed the raw data. C

anti-trap Automotive window
Figure 2: Force Comparisons

A force data were recorded at 3 points (A, B, & C). The average creates the graph values. These points lay along the weatherstrip shown in Figure 3.Then were measured while closing the window. A positioned human finger is on a 25mm force gauge probe (in the first test). The second test used only the 25mm force gauge probe per FMVSS-118 S5 cylindrical rod requirement.

anti-trap Automotive window
Figure 3: Test Points

Existing Torque-Sensing Technology

Table 1: Torque-Sensing: Amount of Force (Newtons) for AUTO CLOSE

Table 2: Torque-Sensing: Amount of Force (Newtons) for MANUAL CLOSE

Smart Close™ Technology

Table 3: Smart Close™: Amount of Force (Newtons) for

* 5 N is the minimum reading possible for the force gauge.


Table 4: Smart Close®: Amount of Force (Newtons) for MANUAL CLOSE
The performance results demonstrate that Smart Close® can detect the presence of a human obstruction (as small as a finger) without generating high pinch forces. Likewise, Smart Close® responds with much lower pinch forces than those recorded with the torque sensing technology when using the force probe.

In another test example, several obstruction objects demonstrate the superior performance of Smart Close® over the existing torque sensing system.

In Figure 4, the torque sensing system allowed window closure on an empty aluminum beverage can without retracting. In this example, the torque sensing system completely undetected the obstruction.

The Figure 4 Smart Close® system reversed the window in the instance shown. No visual deformation occurred. Figures 4 and 5 show that Smart Close® detects the object before entrapment or exerting force. The result is far less force applied to the obstruction, reducing any chance of injury.

sensing Smart Close
Figure 4: Aluminum Beverage Can
Smart Close Sensors
Figure 5: Human Hand

The Moment of Peak Force Shown


New Power window closing possibilities

With the additional safety provided by Smart Close® technology, new features become possible, such as:

  • Global window close – closing all windows with one button
  • Window close by remote key fob
  • Window close by rain sensor command
  • Window close by cabin temperature sensor command

Without a fully protecting anti-trap system, implemented features in an automobile are NOT safe.


Car, truck, bus (any vehicle) will be made safer with Smart Close®!

  1. Power windows pose a clear and unexpected danger to the public, especially children.
  2. The industry is not using the safest available technology (injury-free).
  3. Existing federal standards do not adequately address the dangers of power closure systems.
  4. The federal standard (FMVSS-118 S4) “Power-operated window, partition, and roof panel systems” needs improvement. 

FMVSS-118 S5 (which requires window direction reversal before contacting or exerting a squeezing force of 100 Newtons) should become the standard for power closures. Change FMVSS-118 requirements from 100 Newtons (22 Lbs.-force) to 40 Newtons (8 Lbs.-force) of squeezing force to be safe. Eliminate FMVSS-118 S4.

Smart Close®


The Smart Close® technology offers a significant safety improvement over existing power closure systems. Smart Close® provides unmatched safety improvements without compromising closure functionality.

  1. Protects children from injury, i.e., less than 5 Newtons of force
  2. Eliminates false reversals caused by environmental and installation factors
  3. Stops the override condition now required to effect closure
  4. Provides new convenience features without compromising safety



  1. Injuries Associated With Hazards Involving Motor Vehicle Power Windows. Research Note, May 1997, National Highway Traffic Safety Administration 
  2. FMVSS 571.118 Standard No; 118: Power-operated window, partition, and roof panel systems: 49 CFR Ch. V (10-1-00 Edition)
  3. A Study About Power Windows in Automobiles. Telephone Survey, July 2003, Harris Interactive, Inc.
  4. Sollmann, Matthias, Guido Schurr, and Deirdre Duffy-Baumgaertner. Anti Pinch Protection for Power Operated Features. SAE International 2004-01-1108 
  5. Cadillac STS 2006 force measurements, Current production data®
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