Vehicle Differential Low-Range Epicyclic Layout for Starting Torque
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Solution Overview
Problem
Current motor vehicle transmission designs face a trade-off between achieving a short first gear ratio for easy starting in heavy conditions and reducing fuel consumption, as an excessively short first gear ratio leads to suboptimal engine conditions when shifting to higher gears, impacting driveability and fuel efficiency, especially in off-road use.
Innovation Solution
A motor-vehicle differential incorporating a first and second epicyclic unit with an engagement device that allows for a dual operating mode, enabling a low-range gear selection through the second epicyclic unit, which decouples the gearbox from starting conditions, allowing for longer gear ratios and smoother transitions between gears, thereby optimizing fuel efficiency without compromising starting performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a short first gear ratio is adopted to enable easy starting in heavy load conditions, then starting performance is improved, but fuel consumption increases due to suboptimal engine operating conditions when shifting to higher gears
Solution Approach 1:
The transmission system is segmented into two independent paths: a conventional forward gear path (1st-5th gears) and a low range path (L1-L2 gears) accessible via a dedicated low range device. This segmentation allows the forward gears to be optimized for fuel efficiency with longer ratios, while the low range path provides short ratios for starting performance without compromising the other function.
Solution Approach 2:
The low range device acts as an intermediary mechanism between the conventional transmission and the differential. It includes a low range input shaft, low range synchronizer, and low range gears that mediate the power flow to provide additional gear reduction specifically for starting conditions, allowing the main transmission to maintain fuel-efficient ratios.
2Force
If a short first gear ratio is adopted, then starting performance is improved, but driveability deteriorates due to excessively marked speed step when shifting to second gear
Solution Approach 1:
The transmission is divided into separate forward gear operations and low range operations. The forward gears (1st-5th) form one segment optimized for smooth progression and driveability, while the low range (L1-L2) forms another segment for heavy load starting. This prevents the need for extreme first gear ratios that would cause harsh shifts.
Solution Approach 2:
The system dynamically selects between conventional forward gears and low range gears based on operating conditions. The low range device can be engaged or disengaged as needed, allowing the transmission to adapt its gear ratios to the specific driving situation, providing smooth transitions during normal operation and high torque when needed.
3Use of energy by moving object
If longer gear ratios are adopted to reduce fuel consumption, then fuel efficiency is improved, but starting performance deteriorates in burdensome conditions
Solution Approach 1:
The transmission system separates the function of fuel-efficient cruising (handled by forward gears with longer ratios) from the function of heavy load starting (handled by low range gears with short ratios). The low range device provides the necessary gear reduction for starting without requiring the forward gears to have excessively short ratios.
Solution Approach 2:
The low range device serves multiple functions: it provides additional gear reduction for starting performance, enables the main transmission to use fuel-efficient ratios, and maintains smooth driveability. This multi-functional addition resolves the contradiction between fuel efficiency and starting performance.
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
Enables effective starting in burdensome conditions while reducing fuel consumption by allowing longer gear ratios and smoother gear transitions, decoupling the gearbox from starting constraints and allowing for efficient engine operation across all gears, including the first gear and reverse.
Implementation Method 1
The first epicyclic unit (2) includes a first sun gear (8), a second sun gear (10), and a first planetary unit (12), which meshes with the sun gears (8 and 10)
Data Source
Figure 1
Figure 2
AI summary
Described herein is a motor-vehicle differential (1) comprising a first epicyclic unit (2), the first epicyclic unit including: - a first sun gear (8), which is rotatable about a first axis of rotation (X1) and can be connected to a first output shaft (S1); - a second sun gear (10) coaxial to the first sun gear, which is rotatable about the first axis of rotation and can be connected to a second output shaft (S2); and - a first planetary unit (12), meshing with said first sun gear (8) and said second sun gear (10), said first planetary unit (12) being carried by a planet carrier (14), which is rotatable about the first axis of rotation (X1). The differential (1) includes a second epicyclic unit (4) and an engagement device (6) operatively connected to said second epicyclic unit (4). By means of the engagement device, it is possible to select a normal gear range and a low gear range.