Douglas Dynamics sued Buyers Products for infringement of three patents related to snowplow mounting assemblies. The three patents that were owned by Douglas included Re: 35,700, US Patent Number 5,353,530, and US Patent Number 6,944,978. The court of appeals reviewed the district court’s denial of Douglas’s request for permanent injunction against Buyer, and the district court’s infringement analysis of Douglas’s patents based con claim construction.

Both Douglas and Buyers are producers of snowplows that can be maintained in front of trucks, with Douglas owning a market share in this field and Buyer being a much smaller company. The ‘700 patent has claims directed towards a snowplow assembly that can be mounted onto a vehicle and removed as a single unit. Therefore, heavy portions of the snowplow man not be mounted to the vehicle during use. Additionally, the ‘700 patent describes that the mounting frame may not extend past the bumber of the vehicle, which could cause damage.

Claim 1 of the 5,353,530 patent is reproduced below (emphasis added)

1. For use with a vehicle having a frame and a front bumper, a snow plow assembly, comprising:

a mount frame for connection to the vehicle frame behind the bumper,

a mount frame for connection to the vehicle frame behind the bumper,

a lift assembly including an A-frame, a lift frame and a snow blade,

the snow blade mounted on the forward end of the A-frame,

the lift frame including means for pivotally connecting the rear end of the A-frame to the lift frame whereby the A-frame is free to rotate relative to the lift frame and means for releasably connecting the lift frame to the mount frame affording removal of the lift assembly from the mount frame as a single unit so as to leave the mount frame on the vehicle, and

the releasably connecting means including a U-shaped channel located at a position behind the vehicle bumper when the lift frame is connected to the mount frame, the channel defined by a pair of upstanding legs connected by a lower bight portion with the legs extending in the direction of travel of the vehicle.

The district court held that the limitation of the “life frame including means for pivotally connecting the rear end of the A-frame to the lift frame” requires that that A frame must be required to support the lift frame in both the mounted and the unmounted states. Because Buyers’ snowplow have a lift frame spporting the A-frame (the opposite of the claimed configuration) the district court held that Buyers’ snowplow did not infringe. Further, the district court held that the A-frame and the lift frame had to be directly connected to each other. In Buyers’ snowplow there was only an indirect connection because they had an additional interface between the support frame and the lift frame.

On appeal, the court of appeals held that the district court erred in their construction of the term “connected to.” The court reasoned that although the ordinary meaning of the term “connected to” encompasses indirect linkages, the specification uses variations of the term “connect” to describe indirect connections. The court of appeals also stated that the patent does not at any point limit the connection to a “direct” connection. In summary, the court of appeals held that the term “connected to” is not limited to direct connections.


  1. Instead of using the term “connect,” I prefer to use softer words such as: coupled to, or “communicatively coupled to” when talking about patent claims for software and mobile applications. This is because most of the times devices are connected over a network, which can be wireless. Additionally, many times there is no need to limit the standard and/or protocols that the devices are communicating with each other.
  2. When writing patent claims dealing with mechanical devices, I prefer to use terms such as “supported by” if there may not be a direct connection between two parts of the device, and the term “interface” when there is a direct connection. I feel like the term “supported by” in most circumstances will be broader then “connected to” because there only needs to be some sort of connection. However, when using the term supported by it is very important to write the claims in a way such that element A is supported by element B, and not vice vesa.
  3.  When writing patent claims for a device that is directly connected to another device, it may be important to specifically state that the device is “directly connected to” or “interfaced to.” One such example may be in data storage networks where devices have to be directly connected to each other for data transfer rate reasons. Without stating that the devices are directly connected, one could read that any sort of wireless interface between two devices may be “connected.”
  4.  If an Examiner has a rejection in an office action that states that a “connection” must be a direct connection, this would be a perfect case to site. More so, this is a good case to site where the specification may clarify the meaning of a term, where the term may have a broader scope.
  5. This case may also be a good case to site in office actions if a claim states that two devices are “directly connected.” Using this case, you can show an examiner that directly connected means via physically means and not with an adapter.
By | 2013-06-07T21:29:54+00:00 June 7th, 2013|Patent Attorney Takeaways|Comments Off on AN AUSTIN PATENT ATTORNEY’S REVIEW: DOUGLAS DYNAMICS V. BUYERS PRODUCTS