GB2600486A

GB2600486A - Linear actuator with axial end stop

Info

Publication number: GB2600486A
Application number: GB2017379.5A
Authority: GB
Inventors: Andrei Vadeanu Victor; Petre Victor; Pavel Ovidiu; Alin Pascal Ionut
Original assignee: Continental Teves AG and Co OHG; Continental Automotive Romania SRL
Current assignee: Continental Teves AG and Co OHG; Continental Automotive Romania SRL
Priority date: 2020-11-03
Filing date: 2020-11-03
Publication date: 2022-05-04
Anticipated expiration: 2040-11-03
Also published as: GB2600486B; GB202017379D0

Abstract

A linear actuator 1 for an electrical-hydraulic braking system of a vehicle. The actuator comprises a ball screw drive 2 including a spindle 3, a piston 4, a profiled pipe 5 and a nut 6. A brushless DC motor 8 turns the spindle 3 via a torque transmitting coupling 9. The spindle 3 includes a v-groove (v-shaped groove g; fig. 3) and a retainer washer 10 is locked in the groove. The washer may be an elastic conical washer with three to six elastic legs (11; fig. 2) and a flat end face (f; fig. 2). Also claimed is a locking procedure for the linear actuator comprising powering the motor in a refill direction with a torque value determined based on the size of the nut and washer. This procedure may be done when the vehicle is parked and engine shut off after a zero-point detection. The washer may provide an axial end stop for the nut 6, which is able to hold the nut 6 in place on the spindle 4 against the force from the motor 8, meaning the zero-point does not have to be recalculated when the vehicle is restarted.

Description

Linear actuator with axial end stop The invention relates to a linear actuator for a braking system of a vehicle, namely a linear actuator with an axial end stop.

Electrical-Hydraulic Braking Systems used in the automotive industry are powered by a linear actuator (LAC) that comprises a ball screw drive (BSD) provided with a spindle, a profiled pipe, a nut and a piston. The profiled pipe is rigidly mounted on the nut and is blocked for rotation by a torque support. The piston is mounted at the tip of the profiled pipe. A brushless DC motor turns the spindle; consequently, the rota-tional movement of the motor is converted into linear motion by means of the nut, profiled pipe and piston. The piston creates the hydraulic pressure needed to brake the vehicle. Basically, such a linear actuator is an electrically driven piston-pump.

Currently, the transmission of the torque from the motor to the spindle is done thru a torque transmitting coupling (hexagon coupling, tolerance ring, etc.). On the spindle, between the nut and the torque transmitting coupling, a buffer assembly is required. This buffer assembly has the following main functions: - stopping the nut when it drives in refill direction with high speed and cushioning the impact at the end of the stroke; - stopping the nut during the zero-point detection.

The zero-point detection is a way of re-determining the position of the nut. In the prior art buffer assembly, a cushioning element -namely a rubber ring -is placed between two steel components. Basically, the spindle is driven in refill direction by the brushless DC motor (approx. 1 Nm torque), the nut moves towards the buffer assembly and compresses it at contact. The system now knows that this is the zero-position and memorizes it.

This zero-point detection must be done each time when the vehicle engine is started (ignition on), because there is no way of guaranteeing that the positions of the nut, profiled pipe and piston remained the same during ignition off period. Vibration, thermal dilation and contraction of the brake fluid can alter the position of components. Moreover, the zero-point detection must be done very fast. The vehicle driver must not notice this procedure is done between the moment he starts the engine and the moment he begins to drive. This means that the speed of the nut driving in refill direction must be very high.

Or, a shortcoming related to this is that, due to the very high speed needed, the nut is at risk of not stopping with high precision and slamming the buffer assembly with high force. This strong impact may damage the components of the ball screw drive. The prior art buffer assembly must be very robust to resist the strong impact, and this means a high number of components and high costs involved. Another issue is that, over time, the rubber used for the cushioning element is aging and its elastic properties weaken, negatively influencing the buffer assembly performances.

For these reasons, the technical problem to be solved is to configure the zero-point detection at ignition off (when the driver shuts down the vehicle engine) instead of ignition on.

Therefore, the object of the invention is to solve the shortcomings and deficiencies of the mentioned prior art and to provide a locking function for the linear actuator.

This objective is achieved according to the invention by means of the technical characteristics mentioned in the independent claim, namely a linear actuator with axial end stop.

Further advantageous embodiments are the subject matter of the dependent claims.

The subject-matter of the present invention is a linear actuator with axial end stop, comprising: -a ball screw drive provided with a spindle, a piston, a profiled pipe and a nut; - a brushless DC motor that turns the spindle, and - a torque transmitting coupling that transmits the torque from the motor to the spindle, and wherein the spindle of the ball screw drive is provided with a V-groove and a retainer washer is locked in the V-groove.

The main advantages of using a linear actuator with axial end stop according to invention are the following: -adds a novel function, namely locking the ball screw drive between ignition off and ignition on; - eliminates the time constraints related to the zero-point detection at engine starting; - reduces the costs and the number of components involved in zero-point detection; - reduces system degradation over time; - enhance the robustness of the buffer assembly.

Further special features and advantages of the present inven30 tion can be taken from the following description of an advantageous embodiment by way of the accompanying drawings.

Fig. 1 is a sectional view of a linear actuator with axial end stop, according to invention; Fig. 2 is a view of a retainer washer, component part of the linear actuator from Fig. 1; Fig. 3 shows a view of a modified spindle, component of the linear actuator from Fig. 1; Fig. 4 presents the steps of assembling the retaining washer from Fig. 2 on the modified spindle from Fig. 3, namely: Fig. 4a shows the direction of pushing the retaining washer over the spindle; Fig. 4b shows the assembled washer; Fig. 5 depicts a ball screw drive, component of the inventive linear actuator.

Referring now to Fig. 1, it is illustrated an exemplary embodiment of invention, namely a linear actuator 1 that comprises a ball screw drive 2 provided with a spindle 3, a piston 4, a profiled pipe 5, and a nut 6. Profiled pipe 5 is rigidly mounted on the nut 6 and is blocked for rotation by a torque support 7. A brushless DC motor 8 turns the spindle 3 and a torque transmitting coupling 9 transmits the torque from the motor 8 to the spindle 3. Instead of a buffer assembly there is provided a retainer washer 10.

Fig. 2 shows a view of the retaining washer 10, namely an elastic conical washer with three to six elastic legs 11 and 25 a flat face f; the retainer washer is made of steel.

Fig. 3 shows a spindle 3 modified by machining a V groove g near the end closer to torque transmitting coupling 9. Elastic legs 11 fix the retaining washer 10 on the spindle 3.

Fig. 4 shows the steps of assembling the retaining washer 10 on the ball screw drive 2, by simply pushing the retaining washer over the spindle 3 in the direction shown in Fig. 4a. Retaining washer 10 slides over the spindle 3 until it locks in the V-groove g. The assembled washer is depicted in Fig. 4b and consists into the axial end stop of the inventive linear actuator.

Fig. 5 depicts the ball screw drive 2 configured according to invention. Retaining washer 10 mounted on spindle 3 acts as a stopper for the nut 6 in refill direction. Retaining washer 10 also acts as a buffer for the nut 6, and the buffering effect is much stiffer than in the prior art buffer assembly.

The zero-point detection is done at ignition off. This means that it can be done in a longer period (with lower speed) because this does not affect the driver or the driving ability of the vehicle. Due of the low speed of the zero-point detec-tion, the stiff buffering effect of the retaining washer is acceptable, since there is no risk of damaging the ball screw drive components.

To ensure that the nut 6 of the newly configured ball screw drive 2 will not move during the ignition off period (i. e. the period when the vehicle is parked, and the engine is shut off) a locking procedure is performed. The locking is done after the end of the zero-point detection at ignition off by powering the brushless DC motor 8 in refill direction with a determined torque value. The exact torque value must be determined experimentally, and it depends on the size of nut and retaining washer, respectively. The force that keeps the ball screw drive locked is the friction force between the nut 6 and the flat face f of the retaining washer 10, indicated in Fig. 5. Elastic legs 11 of the retaining washer 10 elastically deform maintaining the axial force between the retaining washer 10 and the nut 6.

At ignition on, the zero-point detection is not needed anymore, since it was done at ignition off and memorized, and the ball screw drive was locked during the whole ignition off period. In conclusion, because the nut has no possibility to move during ignition off period, the memorized position during zero-point detection at ignition off is the same at ignition on.

At ignition on, the brushless DC motor 8 must power the ball screw drive 2 in the pressure build-up direction for a short time with a torque able to unlock the nut 6 from the retaining washer 10. The actual unlocking torque depends on the size of the nut and retaining washer, respectively, and should be determined individually for each application.

However, while certain embodiments of the present invention have been described in detail, those familiar with the art to which this invention relates will recognize various alternative designs and embodiments for practicing the invention as defined by the following claims.

List of reference numbers 1 -Linear Actuator LAC 2 -Ball Screw Drive 3 -Spindle 4 -Piston -Profiled pipe 6 -Nut 7 -Torque support 8 -Brushless DC motor BLDC 9 -Torque transmitting coupling -Retaining washer 11 -Elastic leg f -Flat face g -v groove

Claims

Patent claims 1. A linear actuator of an electrical-hydraulic braking system 5 of a vehicle, comprising: - a ball screw drive provided with a spindle, a piston, a profiled pipe and a nut; - a brushless DC motor that turns the spindle, and - a torque transmitting coupling that transmits the torque 10 from the motor to the spindle, wherein the spindle of the ball screw drive is provided with a V-groove and a retainer washer is locked in the V-groove.
2. Linear actuator according to claim 1, wherein the retaining washer is an elastic conical washer with three to six elastic legs and a flat face.
3. Linear actuator according to claim 1, wherein the V-groove 20 is placed on the spindle end closer to torque transmitting coupling.
4. Locking procedure of a linear actuator according to claims 1 -3, comprising the step of powering the brushless DC motor in refill direction with a determined torque value, the determined torque value depending on the size of the nut and the retaining washer.
5. Locking procedure according to claim 4, which is done when 30 the vehicle is parked and the engine is shut off, after a zero-point detection.