Skid-Steer Controlled Differential Layout for Lower Parasitic Loss
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Solution Overview
Problem
Existing skid-steered vehicle drive configurations face inefficiencies due to high parasitic losses, bearing stress, and complexity, particularly at high speeds, and require oversized motors and specialized bearing cages, which increase weight, cost, and complexity.
Innovation Solution
A novel controlled differential configuration that couples two shafts with a pair of planet carriers and ring gears, allowing direct connection to the transmission output without gear mesh losses, and includes a locking mechanism for independent steer motor control, reducing load on bearings and parasitic losses, and enabling standard bearings to be used.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a conventional differential gear mechanism is used with steer motors mounted on half shafts, then steering control is achieved, but oversized motors are required handling high torque and high power, increasing weight and cost
Solution Approach 1:
The invention separates the steering function from the propulsion function by using a controlled differential mechanism that allows independent speed control of half shafts. The steer motor only needs to provide the speed differential rather than full propulsion power, enabling segmentation of functional requirements and reduction of motor size.
Solution Approach 2:
The controlled differential mechanism acts as an intermediary between the steer motor and the half shafts. It amplifies the small torque from the steer motor into the large torque differential needed for steering, while the main propulsion motors handle the bulk of the power delivery. This mediator enables small steer motors to control large propulsion systems.
2Device complexity
If the propulsion cross-shaft is mounted outside the motor or motor mounted outside the propulsion shaft, then the drive configuration is achieved, but package size increases and idler gears are required, increasing complexity
Solution Approach 1:
The invention merges the propulsion motor and cross-shaft into a single integrated unit. The motor shaft directly becomes the cross-shaft, eliminating the need for separate mounting arrangements and idler gears. This consolidation reduces the number of components and simplifies the overall drive configuration.
Solution Approach 2:
The motor shaft serves multiple functions simultaneously: it acts as both the propulsion motor output shaft and the propulsion cross-shaft that drives the differential mechanism. This multi-functionality eliminates the need for separate components and reduces package size.
3Ease of operation
If the controlled differential causes the two half shafts to run at different speeds during steering, then steering is achieved, but high speed operation causes increased parasitic losses and bearing stress
Solution Approach 1:
The invention uses a dynamically controllable differential mechanism where the steer motor actively adjusts the speed differential between half shafts based on steering requirements. At high speeds, the system can minimize unnecessary speed differences, reducing parasitic losses while maintaining steering capability when needed.
Solution Approach 2:
The system dynamically changes operational parameters by adjusting the steer motor output to minimize the speed differential between half shafts during high-speed straight-line operation, thereby reducing parasitic losses. During steering, the parameter changes to create the necessary speed differential for directional control.
4Device complexity
If a hollow motor shaft is used to pass the cross-shaft through, then integration is achieved, but motor bearing diameter increases making high speed motors difficult
Solution Approach 1:
The invention merges the motor shaft and cross-shaft functions into a single solid shaft design. The motor shaft directly serves as the cross-shaft that drives the differential, eliminating the need for hollow construction and large bearing diameters. This integration is achieved through functional consolidation rather than physical nesting.
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
A drive configuration for a skid steered vehicle comprising drive members (6A) which engage a track or wheel located at each side of the vehicle. At least one propulsion motor (1) is in operable communication with the drive members (6A), and at least one steer motor (9A) is in driveable communication with a controlled differential (8) positioned between, and connecting, a pair of primary shafts (7A). The ends of the primary shafts (7A) remote from the controlled differential (8) form an output of the transmission and are in driveable communication with the drive members (6A). The at least one propulsion motor (1) is provided on a secondary shaft (7A, 7B) remote from the primary shafts (7A).