GB2579612A

GB2579612A - Linear actuator assembly

Info

Publication number: GB2579612A
Application number: GB1819910.9A
Authority: GB
Inventors: Chirosca Costel; Salavastru Cristian
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: 2018-12-06
Filing date: 2018-12-06
Publication date: 2020-07-01
Also published as: GB201819910D0

Abstract

A linear actuator (LAC) for a hydraulic electronic control unit (HECU) of a vehicle, the linear actuator being supplied with braking fluid from a reservoir 300 through a hydraulic route 1 by means of refill valves 211, 212 and outlet valves 221, 222. The actuator comprises: a first piston 11 with a first working surface S1 that builds up a first pressure p1 within a first chamber and a second piston 12 with two working surfaces: second surface S21 and third surface S22, with surface S22 building up a second pressure p2 within a second chamber which is different to the first pressure (e.g. higher pressure). The chambers may be defined by separate housings 101, 102 and communicate via the hydraulic route 1, or by a single common housing (110; fig. 2) with a travel limiter (111; fig. 2). The first surface S1 may have equal area to the second surface S21. The linear actuator is for a “one box” design of HECU and is scalable for different vehicle sizes, i.e. to output both low volume low pressure and high volume high pressure brake fluid.

Description

Linear Actuator Assembly The present invention refers to a linear actuator assembly for automotive braking.

Continental has developed a Hydraulic Electronic Control Unit (HECU) designed as "one box". HECU is supplied with brake fluid from a reservoir and contains an Electronic Control Unit (ECU) provided with at least one printed board circuit (PCB), a valve support which ensures hydraulical connections with a Pedal Feel Simulator (PFS) and a plurality of electro-mechanical valves, as well as an electrical motor with a shaft, used to generate the hydraulic pressure needed for braking. The rotation movement of the electrical motor shaft is transformed in linear movement by means of a Ball-Screw Drive (BSD) and transmitted to a piston placed in a housing; said hydraulical pressure is built up due to the piston movement; the Ball-Screw Drive (BSD), the piston and the piston housing are parts of an assembly known as Linear Actuator (LAC).

HECU is adapted to vehicles of different sizes (small, medium or large), therefore such a linear actuator must fulfil two main conditions depending on vehicle size, namely: 1) the volume of brake liquid the linear actuator may distribute at one complete stroke, and 2) the maximum pressure the linear actuator may create. As an order of magnitude, for a medium-size vehicle, the linear actuator must have a volume of ca. 16 cm= and must create a maximum pressure of ca. 190 bars; for a large-size vehicle, the volume is about 19 cm3 and the pressure is maximum 220 bars.

However, currently there is no scalability between the volume of said linear actuator and the diameter (surface) of its piston.

That is, for large-size vehicles, the stroke increases, resulting in a longer piston housing, which would imply further modifications in terms of shape of ECU's housing or cover, for example, or getting a hole on the printed circuit board (PCB), which is not always possible, nor desirable. Additionally, by reference to the ball-screw drive dimensions, two scenarios are possible: - First scenario: a "one-size-for-all" linear actuator, which means an oversized ball-screw drive for small and medium vehicles, but fit for large vehicles; - Second scenario: each vehicle size has a different ball-screw drive adapted to the respective size.

Any of these scenarios implies disadvantages such as different working stations, material consumption, operations etc. For these reasons, there is a need to ensure the linear actuator's scalability for different vehicle sizes, without affecting the rest of HECU components.

Amain object of the present invention is to redesign the linear actuator's piston and the afferent piston housing.

According to the invention, this object is achieved by the subject-matters of the independent claim.

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

The subject-matter of the present invention is a linear actuator, 30 comprising: -a first piston with a first working surface that builds up a first pressure within a first chamber; -a second piston with two working surfaces, namely a second surface of the second piston and a third surface of the second piston, wherein said third surface builds up a second pressure within a second 5 chamber, the second pressure being different than the first pressure.

This is particularly advantageous since the scalability is ensured, by adapting the needed volume of braking fluid and the 10 required pressure to the type and size of vehicle.

Further special features and advantages of the present invention can be taken from the following description of advantageous embodiments by way of the accompanying drawings.

Fig. 1 is a schematic view of a first embodiment of a linear actuator according to invention.

Fig. 2 is a schematic view of a second embodiment of a linear 20 actuator according to invention.

Referring to Fig. 1, that depicts a first embodiment of a linear actuator LAC by means of the hydraulic scheme and forces involved in the braking process. Said linear actuator LAC is supplied with braking fluid from a reservoir 300 through a hydraulic route 1 by means of refill valves 211, 212 and outlet valves 221, 222. Said linear actuator LAC push with an axial force F_,N, generated by the electrical motor (not figured) a first piston 11 with a first working surface Si that builds up a first pressure p_ within a first chamber; said first chamber is delimited by a first housing 101 of a volume corresponding to the volume of brake fluid needed for braking. When first pressure pi is reached, the brake fluid pushes a second piston 12 with two working surfaces S2-and S22, namely a second surface S21 of the second piston and a third surface S22 of the second piston. Second surface S2± of second piston 11 is equal to the first surface St of first piston 12, so that under equal pressure, equal forces act on the respective surfaces 521, Si. On the other side of second piston 12, third surface S22 builds up a second pressure p2 within a second chamber, that is delimited by a second housing 102. Also, second piston 12 is fitted within second chamber by means of a spring 13. First housing 101 and second housing 102 are independent one from another and communicate through hydraulic route 1.

The linear actuator according to the first embodiment of invention operates as follows: when the first piston 12 with the first surface St is pushed by the axial force FLAc generated by an electrical motor (not figured) through a ball-screw drive (also not figurated), it slides within the first chamber and builds up the first pressure pi under which the brake fluid is pushed through the correspondent outlet valve 221 towards the vehicle's braking callipers (not figured). When first pressure psis reached, the brake fluid goes through hydraulic route 1 in the second chamber and here it pushes the second piston 12 with an equal force Fpt= plSt= p1S2t. Spring 13 of an elastic force Fc is accordingly dimensioned as to be defeated by the force Fpt at a specific pressure value. Therefore, second piston 12 is pushed with a resulting force (distributed on third surface S22 smaller than first surface S2L), which builds up the second pressure p2. Since second pressure p2 (up to 220 bars for large vehicles) is higher than first pressure pt, it closes outlet valve 221 and open outlet valve 222, through which the brake fluid is pushed towards the vehicle's braking callipers as well.

Meanwhile, the brake fluid has been supplied from reservoir 300 to the first chamber through the afferent refill valve 211, until first piston 11 is pushed back on initial position; second piston is pushed back on initial position under the effect of elastic force F, and brake fluid is supplied from reservoir 300 also in the second chamber as well.

By choosing the first embodiment, it is possible to adopt 5 different mutual arrangements between the two said independent chambers, not necessarily co-axial, depending on the available space within the "one-box" design of HECU.

Referring now to Fig. 2, which illustrates a second embodiment of the invention, namely a linear actuator with a different housing arrangement. Instead of two separate, independent housings 101 and 102, there is a single, common housing 100. Within this common housing 100, the first chamber extends from first surface Si of first piston 11 to second surface S2eof second piston 12, without intermediary housing walls, but a travel limiter 111 integrated in common housing 100. By this particular arrangement, said two chambers actually communicate directly to each other.

According to the second embodiment of invention, the linear actuator operates as follows: when the first piston 12 with the first surface Si is pushed by an axial force F,,c generated by the electrical motor (not figured) through the ball-screw drive (also not figurated), it slides within the first chamber and builds up the first pressure pi under which the brake fluid is pushed through the correspondent outlet valve 221 towards the vehicle's braking callipers (not figured). When first pressure p_ is reached, the brake fluid pushes the second piston 12 with an equal force F31= pie_ = p1S2_. Spring 13 of an elastic force Fe is accordingly dimensioned as to be defeated by the force Fp_ at a specific pressure value. Therefore, second piston 12 is pushed with a resulting force F02 (distributed on third surface S2, smaller than first surface Sr), which builds up the second pressure pi. Since second pressure pi is higher than first pressure pi, it closes outlet valve 221 and open outlet valve 222, through which the brake fluid is pushed towards the vehicle's braking callipers as well. Meanwhile, the brake fluid is supplied from reservoir 300 to the first chamber through the afferent refill valve 211, until first piston 11 is pushed back on initial position; second piston is pushed back on initial position under the effect of elastic force Fe, and brake fluid is supplied from reservoir 300 also in the second chamber as well.

Second embodiment of the inventive linear actuator allows economic benefits (less material consumption, less parts, less manufacturing operations).

No matter the implemented embodiment of the inventive linear 15 actuator, parameters such the first chamber volume and the ratio between piston surfaces S-/S22 vary depending on vehicle size.

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 signs 1 Hydraulic route 11 First Piston 12 Second piston 13 Spring Common Housing 101 First Housing 102 Second Housing 111 Travel Limiter 211, 212 Refill Valves 221, 222 Outlet Valves 300 LAC Si S22 Pi P2 F. F31 F32 Reservoir Linear Actuator First Surface of first piston Second Surface of second piston Third Surface of second piston First Pressure Second Pressure Axial Force Elastic Force Force generated by first pressure Force generated by second pressure

Claims

Patent claims 1. Linear actuator for a hydraulic electronic control unit of a vehicle, said linear actuator being supplied with braking fluid 5 from a reservoir by means of refill and outlet valves through a hydraulic route, characterized by that it comprises: - a first piston with a first working surface that builds up a first pressure within a first chamber; - a second piston with two working surfaces, namely a second 10 surface of the second piston and a third surface of the second piston, wherein said third surface builds up a second pressure within a second chamber, said first pressure being different than said second pressure.
2. Linear actuator according to claim 1, wherein said first chamber is delimited by a first housing and said second chamber is delimited by a second housing, said first and second housings are independent one from another and communicate through the hydraulic route.
3. Linear actuator according to claim 1, wherein said first chamber and said second chamber are delimited by a common housing provided with a travel limiter, said first housing and said second 25 housing communicate directly.
4. Linear actuator according to claim 1, wherein said first surface of the first piston and said second surface of the second piston have equal areas.
5. Linear actuator according to claim 1, wherein said first surface of said first piston is larger than said third surface of said second piston, and the ratio between respective surfaces varies depending on vehicle size.
6. Linear actuator according to claim 1, wherein said first chamber volume varies depending on vehicle size.
7. Linear actuator according to claim 1, wherein said second pressure varies depending on vehicle size.