Here are my two cents:

The account manager is the contact with the client. The account manager's role is to keep the client happy. The account manager has the pulse of the market.

The product manager is in charge of the overall product evolution. In an R&D environment, they could be considered the project initiator.

The project manager is in charge of delivering what has been asked by the product manager or the account manager.

Often, the problems stem from who can request changes to a project, and who can approve change requests. A well detailed project charter would define each person's role.

It seems that the problem is not defining the roles of each manager but rather defining process.

The way the company operates should be clarified so that you don't feel like you're reinventing the wheel each time because its

• a) frustrating and
• b) time consuming.

You should start an initiative to set down guidelines and actual workflows about how things get done and who does what. This is a tremendous value add that a project manager can bring to the organization.

And, it can generate real cost savings in people's times.