Brake Booster Spindle Nut Axial Shifting Mechanism
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Solution Overview
Problem
Conventional brake boosters lack an effective emergency mode that allows for mechanical braking without assistance when the drive motor cannot provide sufficient torque, and there is no straightforward method to test the functionality of this emergency mode.
Innovation Solution
The spindle nut features an external tooth set engaging with an internal tooth set of an annular drive gear, allowing axial shifting while maintaining rotational entrainment, enabling mechanical braking force transfer to the brake master cylinder. This is achieved through tooth flanks with oblique or divergent profiles that generate axial forces, preventing self-locking and ensuring axial shiftability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the drive motor is used to provide braking assistance, then braking power is improved, but the system loses the capability for mechanical emergency braking when the motor fails
Solution Approach 1:
The tooth flanks are designed to change their functional state dynamically: under normal conditions they engage to prevent self-locking and enable axial shifting, while under emergency conditions (motor failure) the same tooth flanks allow pure mechanical force transmission. This dynamic adaptability resolves the contradiction between powered assistance and mechanical emergency capability
Solution Approach 2:
The oblique angle of the tooth flanks changes the force transmission parameters between circumferential and axial directions. This parameter change allows the system to switch between motor-assisted operation and pure mechanical emergency braking, maintaining both braking power and emergency adaptability
2Adaptability or versatility
If the spindle nut is made axially shiftable relative to the drive gear, then emergency mechanical braking is enabled, but the risk of damaging the linkage increases
Solution Approach 1:
The oblique tooth flanks act as a protective mechanism that prevents self-locking and reduces impact forces during axial shifting. This beforehand design feature cushions the linkage against damaging forces while enabling emergency mechanical braking, resolving the contradiction between adaptability and damage risk
3Ease of manufacture
If conventional axial tooth flanks are used, then manufacturing is simplified, but self-locking occurs preventing axial shifting
Solution Approach 1:
The tooth flanks are designed with a slight obliquity parameter deviation from the conventional axial configuration. This small parameter change prevents self-locking and enables axial shifting while maintaining manufacturing simplicity, resolving the contradiction between ease of manufacture and ease of operation
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
This design allows for reliable mechanical braking without damaging the linkage or brake booster, and includes a travel sensor to test the emergency function's availability, providing a compact and functional brake boosting device.
Implementation Method 1
at least one first tooth flank of at least one tooth, which extends in a first axial portion in its longitudinal extent in a direction leading toward an oppositely located tooth flank, tooth flanks of the teeth of the internal tooth set and of the external tooth set extend axially. The spindle nut is thus axially shiftable with reference to the annular drive gear... the first tooth flank of at least one tooth extends, in a first axial portion, divergently from the axial extent of the other tooth flanks, the tooth set has on the first axial portion a region in which the encounter between mutually oppositely located tooth flanks not only transfers a force in a circumferential direction, i.e., a torque, but moreover also generates an axial force acting on the spindle nut
Implementation Method 2
the linkage having a rotatable spindle nut having an internal thread and a nonrotatable, axially displaceable spindle rod having an external thread, the threads interengaging in order to convert a rotational motion of the drive motor into a translational motion of the spindle rod
Data Source
AI summary
A brake booster for a brake master cylinder including a drive motor connected via a linkage to a pressure piston for the brake master cylinder, the linkage having a rotatable spindle nut having an internal thread and a nonrotatable, axially displaceable spindle rod having an external thread, the threads interengaging to convert a rotational motion of the drive motor into a translational motion of the spindle rod in order to displace the pressure piston. The spindle nut has an external tooth set that is in engagement with an internal tooth set of a annular drive gear of the linkage. The spindle nut is axially displaceable with respect to the annular drive gear. Except for a first tooth flank of a tooth, which extends in a first axial portion in its longitudinal extent toward an oppositely located tooth flank, tooth flanks of the internal and external tooth sets extend axially.