Variable Stiffness Differential via Fluid Actuator
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Solution Overview
Problem
Conventional differentials struggle to manage torque distribution effectively in varying terrain conditions, leading to loss of traction and poor handling, especially when one wheel loses grip, as they equally distribute torque between wheels, limiting power to both wheels when one is on a low-friction surface.
Innovation Solution
A differential gear system with a carrier housing bevel gears and a pinion gear, where an actuator reciprocates between fluid reservoirs to dampen relative rotation between bevel gears, increasing stiffness in response to wheel slip, allowing for variable torque distribution and the option to lock the differential for improved traction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If an open differential equally distributes torque between wheels, then good handling and control for on-road driving is maintained, but loss of traction occurs when one wheel is on a low-friction surface
Solution Approach 1:
The differential system dynamically adjusts its characteristics between open and locked states based on operating conditions. The actuator reciprocates between first and second positions to vary the stiffness of the differential gear, allowing it to adapt from allowing wheel speed differences (open) to forcing synchronized rotation (locked) to resolve the contradiction between handling and traction.
Solution Approach 2:
The system changes the stiffness parameter of the differential gear continuously between a first stiffness value (open differential) and a second stiffness value (locked differential). This parameter change is achieved through the actuator's reciprocating motion which varies the engagement force between bevel gears, enabling transition from torque equalization to torque differentiation based on traction needs.
2Reliability
If a straight axle is used to prevent wheel spin on low-friction surfaces, then torque redistribution to the non-spinning wheel is achieved, but the vehicle cannot turn corners without dragging wheels
Solution Approach 1:
The differential gear system dynamically transitions between locked and open states. When locked, it provides straight-axle-like torque redistribution for traction; when open, it allows wheel speed differences for cornering. The actuator controls this dynamic transition based on detected wheel slip conditions, resolving the contradiction between preventing wheel spin and enabling cornering.
Solution Approach 2:
The stiffness parameter of the differential gear is varied between maximum (locked, providing traction) and minimum (open, allowing cornering). This continuous parameter change enables the system to exhibit both straight-axle and differential characteristics as needed, eliminating the need to choose between the two extreme designs.
3Reliability
If limited-slip differentials with clutch systems are used to limit torque distribution variance, then torque is redirected to non-spinning wheels, but device complexity increases
Solution Approach 1:
The patent extracts the torque-limiting function from complex clutch systems and implements it through a simpler actuator mechanism that controls bevel gear engagement. The actuator reciprocates to vary the stiffness of the differential gear, achieving torque redistribution without requiring multi-plate clutches, springs, and complex friction-based limiting mechanisms.
Solution Approach 2:
The invention replaces the mechanical clutch-based torque limiting system with an actuator-controlled gear engagement system. The actuator uses controlled reciprocating motion to vary the meshing force between bevel gears, substituting complex friction-based torque limitation with a more straightforward mechanical engagement control that achieves similar traction improvement with reduced complexity.
4Reliability
If the differential is locked to force synchronous wheel rotation, then traction is improved on low-friction surfaces, but component wear increases due to forced rotation under slip conditions
Solution Approach 1:
The differential gear operates dynamically, transitioning between locked and open states based on real-time wheel slip detection. The actuator controls the degree of locking, allowing synchronous rotation only when traction is needed while permitting speed differences during normal operation. This dynamic operation reduces forced rotation and associated component wear compared to permanently locked differentials.
Solution Approach 2:
The stiffness parameter of the differential gear is continuously adjusted between locked and open states. This parameter change allows the system to minimize the time spent in the locked state, engaging synchronous rotation only when wheel slip is detected. By reducing the duration of forced rotation, component wear is minimized while maintaining traction improvement when needed.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system provides continuous variable stiffness in response to terrain conditions, enhancing traction and reducing the likelihood of wheel slip, while minimizing component wear and maintenance needs, by using fluid dynamics and magnetic fields to adjust viscosity for improved performance.
Implementation Method 1
the actuator reciprocates between a first position and a second position, wherein the reciprocating motion of the actuator is dampened by the movement of fluid between the first and the second reservoirs, thereby impeding the relative rotation of the first and second bevel gears relative to each other
Implementation Method 2
by using fluid dynamics and magnetic fields to adjust viscosity for improved performance
Data Source
AI summary
A continuously variable differential gear comprising: a pair of rotating bevel gears engaged with one another via a pinion gear, each of the bevel gears including a first operating surface; an actuator, opposing ends thereof having a pair of interconnected fluid reservoirs, the actuator comprising a pair of secondary operating surfaces; the pair of rotating gears and the pinion gear being housed within the actuator such that the first operating surfaces of the bevel gears and the secondary operating surfaces of the actuator are cooperatively engaged, wherein relative rotation between the pair of bevel gears imparts a linear motion to the actuator thereby varying the pressure between the pair of interconnected fluid reservoirs to resist the linear motion of the actuator and thereby variably dampen relative motion of the bevel gears to each other.