Jens Falkenstein

Two-speed transmissions can improve battery electric vehicle (BEV) drivetrain efficiency. However, the additional losses caused by shifting actuators offset these efficiency gains. Particularly hydraulic actuated wet-running multi-plate clutches, which enable powershifts, typically require rotary feedthroughs. Commonly used rectangular sealing rings (RSR) demand continuous hydraulic power due to leakage and cause friction torque. This leads to high RSR temperatures, especially at high angular velocities of electric machines. This article introduces a two-speed BEV transmission concept using wet-running multi-plate clutches actuated via a rotating 5/3-way valve that can shut off, i.e., lock up the actuating pressure directly in the rotating system. Consequently, the rotary feedthrough is depressurized and contactless gap seals are usable. This reduces supply pressure requirements and minimizes hydraulic and friction losses while retaining powershift capability. Component-level tests evaluate leakage, pressure shut off, actuator dynamics and power consumption. Results show that actuating pressure in a shut-off clutch is maintained for longer than 60 min and electrical actuator power consumption is less than 20 W. During overlapping gearshifts, gap seal leakage is less than 1 L/min at 10 bar and sufficient pressure dynamics are achieved. These findings confirm the feasibility of the proposed actuator for multi-plate clutches in two-speed BEV transmissions.

For the investigation of new types of internal gear pumps under realistic conditions, a test bench is presented that enables dynamic load emulation via the pressure with simultaneous dynamic speed control of the pump. For pressure control, a hydraulic half-bridge with separate control edges is used on both sides of the pump and a pressure control is presented. An error-based adaptive controller is used for pressure control and tested experimentally. It is shown that the error-based adaptive controller has a better performance compared to a simple PID control.

In the case of electric vehicle drives, faults in the drive system or in the traction inverter, which controls the vehicle drive unit, could lead to abrupt and unpredictable motion as well as acceleration of the vehicle. In terms of functional safety, the typically existing, permanent mechanical connection of the drive machine with the drive wheels poses a high safety risk. In particular, unintended motion of the vehicle from a standstill is especially critical due to the high risk of injury to traffic participants. To reduce this risk, appropriate monitoring algorithms can be applied for the rapid detection of faulty operation. A corresponding algorithm for fault detection in the electric drive of a vehicle is presented in this paper. In addition to the description of the algorithms, various driving maneuvers of an electric single-wheel drivetrain are simulated in fault-free and faulty operation on a hardware-in-the-loop test bench. The focus here is on the consideration of driving-off operations.

Electric vehicle drivetrains are considered a way to reduce greenhouse gas emissions from road traffic. The use of electric drives in automotive vehicles offers advantages, such as the potential to recover energy during braking (regenerative braking). The limitation of the maximum air gap torque of the vehicle drive machine by several factors requires a temporary standalone or simultaneous use of the conventional vehicle wheel brake. In several studies, it is shown that during braking operations, the drive machine and the vehicle wheel brake can induce torsional oscillations in the drivetrain, which have a negative influence on the driving comfort and lead to a high mechanical load. To reduce these oscillations, the simultaneous use of an active anti-jerk control is necessary. Due to the problem of oscillation excitations caused by a brake intervention, the used drivability function (integrated prefilter, anti-jerk control) is investigated and optimized with regard to brake blending maneuvers and the effectiveness for damping torsional oscillations. Therefore, the dynamics of the drivetrain are adapted to the dynamics of the braking system using the prefilter, which leads to precise fulfilment of the driver’s braking desire, even during dynamic brake blending maneuvers. All investigations are carried out with a hardware-in-the-loop test bench to create reproducible results.

The drivetrain of electric vehicles differs significantly from vehicles with combustion engines. Current concepts of electric vehicle drivetrains usually have a low damping. Typically, there is no clutch to separate the inertial mass of the electric drive machine from the rest of the vehicle drivetrain. External (road unevenness, potholes, etc.) and internal excitation (torque changes of the electric machine, brake interferences, etc.) cause jerk oscillation and sometimes high component stress. These excitations can be reduced by suitable drivability functions, to which a reference filter can also be assigned. A common approach known from conventional drivetrains is to limit the gradient of the demand torque of the drive machine or the driver′s desired torque in order to influence the torque build-up of the drive machine and to reduce the excitation of jerk oscillations. A second approach is the use of a prefilter. The prefilter uses the inverse dynamics of the drivetrain to influence the demand torque of the drive machine. In this paper, the influence of a prefilter based on the inverse dynamics of electric vehicle drivetrains to reduce oscillations is investigated. In addition, an anti-jerk control enhances the drivability function afterwards. All investigations are made on a hardware-in-the-loop test bench to create reproducible results.