Toyota’s assembly pallet patent (US9604755B2) is a jig patent designed with folding positioning members so that a single pallet can accommodate battery cell stacks of multiple shapes.
Problem Definition
This patent was granted on March 28, 2017 (filed 2013-10-03, priority JP2012-227718, priority date 2012-10-15, inventors Takashi Ouchi and Atsunori Hattori, applicant Toyota Motor Corp, family JP5754432B2). Vehicle battery packs have differing cell-stack shapes depending on mounting location and specification, but conventional pallets had fixed support blocks, requiring the entire pallet to be replaced whenever the pack type changed. The core question of this patent is how a single pallet, using folding positioning members, can accommodate cell stacks of multiple shapes.
Kinematic Analysis
According to claim 1, the pallet consists of a row of folding pins, a row of positioning engagement members, and boss locating pins. The positioning engagement member has a concave support surface and folds toward or unfolds away from the pallet body about a rotation axis. When a rotation-restricting pin is inserted into a rotation-restricting hole, the support position is fixed; when it is withdrawn, rotation is permitted and the member switches to the non-support position (based on specification drawings 3A–3C, 4A–4C). By folding away unused rows and unfolding only the rows matching a given pack shape to support the restraining rod, a single pallet accommodates multiple cell-stack shapes.
Calculation / Formula Verification
Since the claims do not specify concrete dimensions, the rotation-lock mechanism described in the specification is verified from a structural-mechanics perspective. The load on the rotation-restricting pin is the reaction force generated when the restraining rod (lower restraining rod) rests on the support surface. Letting this reaction force be $R$ (N) and the distance between the support surface and the rotation axis be $l$ (mm), the moment applied to the rotation-restricting pin is as follows.
$$M = R \times l$$
$M$ is the moment in N·mm, and the rotation-restricting pin must withstand this moment as axial shear for the locked position to remain secure. Since the specification does not state a load value (undisclosed), concrete figures for safety-factor calculation should be confirmed after field measurement. However, because the structure is a single-member design in which one rotation-restricting pin bears the entire support-surface reaction force in shear, applying this patent’s structure to a reference design requires verifying both the yield (primary) and fatigue (secondary) safety factors when selecting pin diameter and material.
Shop-notes
An alternative mechanism without folding members — permanently placing dedicated pins on the pallet for each chemistry/shape — could be considered, but the specification itself lists as a non-adoption reason that this increases pin count and cost, and that in multi-model lines the labor cost of folding and unfolding reduces labor efficiency. Machinability note: since the rotating member and the support surface are subject to repeated rotational friction, wear-resistant treatment (hard anodizing or surface hardening) is needed, along with managing the fit tolerance of the rotation-axis hole as a clearance fit to avoid binding during assembly. This folding structure is a reference case, presented as an alternative contrasting with the single clearance-fit pin approach reviewed in the separately covered multi-model battery pack assembly pallet design article, illustrating the trade-off between part count and maintainability.
Design-Reflection Checklist
- Doubly verify the yield and fatigue safety factors of the rotation-restricting pin when adopting a folding member
- Review minimizing the support-surface-to-rotation-axis distance $l$ to reduce the moment
- Reflect wear-resistant treatment specification for the rotating member in the drawing
- Prepare a comparison table of part count and maintainability trade-offs between the folding approach and the fixed clearance-fit approach
One-Line Summary: Toyota’s assembly pallet patent’s folding positioning structure increases multi-model adaptability, but it carries the structural trade-off of concentrating the entire reaction force onto a single rotation-restricting pin.