Enclosure design for portable on-board vehicle recorder

Customer

An American developer of innovative products and services for mobile communication devices.

Objective

The objective is to create the design and enclosure of a portable on-board vehicle recorder, a device for monitoring parameters of the vehicle as well as for recording car route and audio in the vehicle. All the information transfers all wirelessly to a dispatch and coordination center.

The size and shape of the enclosure should make it possible to plug the device into the OBD-II connector (it is supported by all cars made after 1996). Additional requirements for the enclosure include impact and vibration resistance, as well as resistance to temperature differences.

The device should target the end user, so its enclosure should not be just a sophisticated engineering design, but an aesthetic solution – it should protect the stuffing of the device and at the same time serve as an incentive in making a decision to purchase.

The target audience includes individuals who are car owners.

The scope of the product’s application is quite wide – tracking vehicle parameters if there is no on-board computer available, mobile vehicle diagnostics, monitoring a rental car park, etc. An option customers expect to find in the product is parental control of their children’s vehicles (for this purpose, the device should be fitted with a special lock that prevents unauthorized disabling).

Basic Enclosure Design Requirements

The enclosure should allow for reliable clamping of the hardware inside the device and prevent its operational failure

• The enclosure should withstand high temperature fluctuations (the customer has taken the responsibility to ensure hardware operability at high temperatures)
• The device should be fitted with the reset option using a special button on the board
• Access should be provided to the mini USB port in the process of operation
• A special hole should be implemented in the enclosure for recording audio from a microphone on the board
• Connectors on the device should be protected by a cover
• The enclosure design should be fitted with a special lock, which makes it impossible to disconnect the black box from the diagnostic OBD-II port without a special key
• The device should have the appearance of both an engineering and aesthetic solution (it is possible to use glossy material in manufacturing the enclosure)
• It is necessary to use a certified connector used to connect the device to the OBD-II port

Solution

Enclosure Design Development

The size of the device enclosure, as well as the position of the connectors and control elements, was determined based on the size of the provided PCB and size-forming elements found on the board.

In the development process, changes were made in the vision of the enclosure design as well as the characteristics of the hardware, along with the connectors mounted on it. Therefore, the initially developed drawings differ from the final ones.

Based on the hardware data provided by the customer, five options of the enclosure were offered:

The choice of colors is conventional in the design options (originally, shades of gray and black were offered). This color solution will help associate the product with mobile devices (black is the most popular color in their design). The drawings show a reset button as a button proper as well as a hole.

Enclosures 1 and 4 are glossy, while 2, 3 and 5 are matt-surface.

The corrugated surface in Options 2 and 3 was made for easy removal of the device from the diagnostic port. In Options 1, 4 and 5, this solution is presented as a groove for easy hand grip.

Also, at the initial stages of development, the customer considered different connector placement options – open connectors or with a protective cover. Later it was decided to abandon two big-size connectors and use only the mini USB connector.

At the next stage of the project, after the other hardware solutions were introduced, a new series of drawings were considered, which were tailored to the customer’s preferences:

The customer made a decision to develop a design based on Option 15, using a three-dimensional big-size hardware model. As a result, experts from the Promwad electronics design center presented the following enclosure design (this option was approved by the customer and sent over for design development):

Enclosure Structure Development

A major design challenge was development of a mechanism to block disabling of the device. This is a special engineering task because the OBD-II connector design does not allow for locking any devices on it and is designed in such a way that the user can easily connect / disconnect necessary equipment / cables.

Despite the fact that finding a solution to fit the customer’s preference is a purely engineering task, this had to be done at the design stage. Using a locking mechanism involved specific engineering requirements, which had a big impact on the design.

After studying the OBD-II connector design, the enclosure developers were assured of the possibility of implementing a clamping mechanism. The operating principle of the lock is based on the connector design, which allows for a clamping element in form of a metal strip. The device can be locked by jamming the strip:

A clamping mechanism in the OBD-II connector

Three clamping options were offered to the customer:

Option 1. Locking (jamming the locking element) by turning in a special key

Option 2. Locking by turning the latch (lock) by the hand, without a key

Option 3. Locking by moving the locking device (red) by the hand, without a key

Each of the solutions offered was tested. Based on the results, a decision was made together with the customer to use Option 1. It is easy to manufacture (no need to make a press mold because the mechanism is cut on a special machine) and meets the customer's requirement of using a key to disable the device.

Enclosure 3D Modeling and Prototyping

After the design in terms of manufacturability (design and manufacturing of press molds, assemblability in production) was agreed on, components of the enclosure were designed using 3D modeling. Structurally, the enclosure design includes the following elements:

• Upper and lower enclosure parts, major load-bearing structures
• Decorative cover that covers the connector and the hole with a node for blocking the disabling of the device without a key
• A mechanism for clamming the device, implemented in the OBD-II connector

The enclosure parts and the decorative cover of the device were made of polybutylene terephthalate (PBT). The clamping mechanism was made of steel by milling. Based on the developed mathematical enclosure model, prototypes were manufactured.

Stereo lithography images of the prototypes are shown below:

Assembled and disassembled prototypes to the design (pic. 1—2). Rear view with the protective cap removed (pic. 3)

Testing model of the device: board and enclosure

After the approval of the manufactured prototypes, a set of design documentation was created for manufacturing a production batch. The design documentation was successfully delivered to the customer and handed over for production.

Assembly tests were conducted on the basis of the manufactured prototypes. Based on the testing results, changes were introduced

Benefits

• Low cost of a set of enclosure parts in mass production
• Easy assembly
• Mcro vibration resistance

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