Vehicle Electric Drive Hydraulic Cooling and Lubrication Switching
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Solution Overview
Problem
Existing electric drives for vehicles face challenges in efficiently combining cooling and lubrication of electric machines and transmissions, with passive splash lubrication leading to churning losses at high speeds and inadequate cooling at low speeds, compromising efficiency.
Innovation Solution
A hydraulic circuit with a mode control valve that switches between low speed mode for stator cooling and high speed mode for transmission lubrication, using a bidirectional pump and directional valves to optimize fluid distribution based on operating conditions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If passive splash lubrication is used for the transmission, then the device complexity is reduced, but churning losses increase under high-speed operation
Solution Approach 1:
The patent implements a dynamic lubrication system that switches between passive splash lubrication at low speeds and active hydraulic lubrication at high speeds. The control unit activates the pump and opens the lubrication valve when rotational speed exceeds a threshold, dynamically adapting the lubrication method to operating conditions to minimize churning losses while maintaining simplicity at low speeds.
Solution Approach 2:
The system changes the lubrication parameter (from passive to active) based on rotational speed. The control unit monitors speed and adjusts the lubrication mode accordingly, using the pump and valve to regulate fluid delivery to the transmission only when high-speed operation requires it, thereby reducing energy losses during high-speed operation.
2Temperature
If active cooling is provided to the electric machine, then temperature control is improved, but device complexity increases
Solution Approach 1:
The hydraulic circuit serves multiple functions: it provides active cooling to the electric machine stator when needed, and active lubrication to the transmission when needed. The same pump, control unit, and fluid circuit are used for both cooling and lubrication purposes, reducing overall system complexity compared to having separate dedicated systems for each function.
Solution Approach 2:
The cooling and lubrication are provided periodically based on operational requirements. The control unit activates the pump and opens appropriate valves only when temperature or speed thresholds are exceeded, rather than continuously operating the system, thereby simplifying the effective system operation while maintaining adequate temperature control.
3Device complexity
If a single hydraulic circuit is used for both cooling and lubrication, then device complexity is reduced, but the ability to optimize both functions simultaneously is compromised
Solution Approach 1:
The single hydraulic circuit is segmented into separate controllable branches: one leading to the electric machine stator for cooling, and another leading to the transmission for lubrication. The control unit independently manages each branch through separate valve control, allowing simultaneous or independent optimization of both cooling and lubrication functions despite using a shared pump and fluid reservoir.
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 solution provides optimized cooling and lubrication for both electric machines and transmissions, reducing losses and enhancing performance across varying speed modes.
Implementation Method 1
a pump for circulating the fluid
Implementation Method 2
a mode control valve for directing a fluid flow from the pump to either the hydraulic stator path or the hydraulic transmission path
Implementation Method 3
a hydraulic stator path for supplying the fluid to the stator
Implementation Method 4
a hydraulic transmission path for supplying the fluid to the transmission
Data Source
AI summary
An electric drive for a vehicle comprises a housing, an electric machine with a stator connected to the housing and including stator end-windings, a rotor rotatable relative to the stator, and a driveshaft connected to the rotor and rotatably supported in the housing about an axis of rotation, a transmission to transmit a rotary movement from the driveshaft to drive a driveline of the vehicle, and a hydraulic circuit for circulating a fluid.