Sehr Geehrter Herr Von Sehlen

Sehr Geehrter Herr Von Sehlen

Walter Geltermair

Pappelweg 46 - 56075 Koblenz

Tel.: +49 (0)261/911 870

Fax: +49 (0)261/911 8733

Mobil: +49 (0)178/726 1233


Brief Information


Status: November 2006

E FA – Electronic Hydro Parking Brake System

Preamble: The parking brake described below can be installed as serial-production or subsequently as hydraulic control brake system for all vehicles.

It is independent of the manufacturer and type of control brake system, and it is especially suited for passenger cars or light freight vehicles;

The brake will work on rear and front axle

Also possible with trailer operation and parking on inclined surfaces > 30%

The brake system is comprised of the following components:

  1. Compression unit (pump)
  2. Control unit - hydraulic
  3. Hydraulic unit (piston module)
  4. Control unit (ECU (electronic))
  5. Activation switch
  1. General instructions

1. Compression unit

The compression unit (5) (pump) is comprised of one hydraulic pump with connected hydraulic accumulator (A), which has a capacity for a supply volume (>300 ccm³) and a supply pressure between 120 and 160 bar. The hydraulic accumulator (A) is directly connected to the hydraulic unit (piston module) via the valve (3) of the control unit (EFA Group).

2. Control unit (hydraulic) (EFA Group)

The unit is comprised of two de-energized closed (1)+(2) and two de-energized opened (3)+(4) hydraulic valves. Also belonging in this group (EFA Group) is a hydraulic accumulator (B) as well as a spring-loaded shutoff valve (AS).

2.1 Function:

By means of a time and pressure-defined opening of the valve (1) [activation of the parking brake] the pistons (10)+(11) in the cylinders (8)+(9) are pressurised via the connection (E1) of the hydraulic valve unit (valve module).

The hydraulic accumulator (B) is simultaneously applied with pressure and provided with volume delivery via the valve (4) and the spring-loaded shutoff valve (AS). This pressure is also present at the valve (2).

When the valve (2) is opened [deactivation of the parking brake], both de-energized open valves (3)+(4) are closed, and the pressure in the hydraulic unit (piston module) is relieved via the connection (E1) into the supply tank (T). At the same time, the pressure is maintained in the hydraulic accumulator (B) by the spring loaded shutoff valve (AS). The pistons in the shutoff valve (AS) lock automatically . The hydraulic accumulator (B) serves for pressure and fluid equalization by means of thermodynamics.


3. Hydraulic unit (piston module)

The module is comprised of two cylinders (8)+(9) each with a piston (10)+(11). It is divided into two circuits and is corresponding with the service brake circuits, as configured black/white or X-split.

The cylinders are each fitted with three sealing o- rings (N1)+(N2)+(N3).

The unit is equipped with 2 pressure inlets (E1)coming from valve1+(E2) coming from Accumulator A and 2 pressure outlets going to the ABS Group (A1)+(A2). The connections (MC1) + (MC2) are arranged in the primary and secondary systems of the master brake cylinder.

In a de-activated condition, both the connections (MC1)+(A1), as well as the connection (MC2)+(A2) are independent connected. Additionally, (MC1)+(A1) and (MC2)+A2) are both independently connected in parallel manner via a non-return valve (R1)+(R2).

3.1 Function (depressurized)

When the module is in a depressurised condition, the pistons are held in end-position by compression springs. Via the connections (MC1)+(MC2), the fluid is able to flow unhindered from the master brake cylinder through the in this position open sealing ring (N3) to the outlets (A1)+(A2), connected to the ABS module. All functions of the service brake are ensured in this way.

The sealing ring (N2) separates the service brake from the parking brake, so that no mixture of the fluids for these may occur. In this position, the O-ring (N1) seals the pistons. The pressure on (E2) from the hydraulic accumulator (A),(full pressure) therefore, has no influence upon the pistons.

3.2. Function (under pressure)

When the module is under pressure, both pistons are simultaneously pushed against the spring load. The connections (MC1)+(MC2) are closed off when the piston is enveloped by the sealing O-ring (N3).

Through the continuing piston travel, pressure to the brake wheel cylinders is built up via the ABS module, until the parking brake’s operating pressure (approximately

50 bar) – determined by the electronic control unit – has been reached.

4. Control unit ECU (electronic)

The ECU controls two redundantly operating processors of differing families (Annex: EFA Control Unit), and is thereby in accordance with guidelines for automotive control units.

The control unit is connected with the vehicle via CAN Bus, K-line or flex rate, and at the same time the data from the pressure sensors (PS1)+(PS2)+(PS3) is monitored and processed in the system.

During de-activation or activation of the parking brake, the required corresponding valves (1), (2), (3) or (4) are selected.

By means of a tri axial angle sensor, it is possible to obtain the current vehicle position (inclined or level) for the calculation of a variable energised pressure.

By means of the variable control of the energised pressure it is possible to hold a vehicle with loaded trailer at incline > 30%.

In addition, the control unit is connected with the brake light and the activation switch (S1).

By means of the monitoring of the CAN Bus, K-line or flex rate of the vehicle, comfort functions such as the hill hold feature, driver’s seat occupancy, monitoring of seat belt, open doors, open engine bay or boot, as well as emergency-brake function can be calculated and implemented.

5. Activation switch (S1)

The parking brake is activated or de-activated via the activation switch (S1), which is installed in the passenger compartment.

The hand-brake stick, cable systems or special brake callipers suited for parking brakes are no longer necessary and have been dispensed with completely.

At speeds > 8 km/h and with simultaneously drawn switch (S1), the set energised pressure is applied to all wheels by the piston module, until the desired vehicle deceleration has been reached. When the speed remains > 8 km/h, with a simultaneous release of the switch (S1), then the brake process is immediately interrupted, and driving of the vehicle may continue.

When the speed is less than 8 km/h, the vehicle brakes until reaching standstill via one-time operation of the switch (S1), and the parking brake is activated.

In both cases, the control functions of ABS and ESP take effect, provided that the systems are in full working order. In this way, wheel locking is eliminated, and even in difficult circumstances, such as µ-split, the vehicle will definitely come to a halt.

General safety criteria for the EFA parking brake

Failure of a brake circuit

In the event of a brake circuit failure of an activated parking brake, or during its activation, the piston (10) or (11) of the defective service brake circuit moves into end position, because counter-pressure is no longer present on the wheel end.

The piston simultaneously transverses the defective service brake circuit on its way to the sealing ring (N1). This process opens the inlet (E2), which is directly pressurised with the supply pressure (Hydraulic accumulator A) via the voltage-free open valve (3), and the total supply pressure is channelled into the piston module.

By this means, the still intact brake circuit is pressurised by mixed pressure from the supply pressure (Hydraulic accumulator A) and the energised hydraulic accumulator (B). The braking process of the vehicle is guaranteed by the increased mixed pressure, even in the event of a brake circuit failure.


The system is subject to the laws of thermodynamics.

Due to temperature changes during braking time, the volume that changes for the fluid trapped between the working pistons (10)+(11) and brake callipers may reach up to 10%.

This change in volume is equalised to the normal range (temperature changes of between approximately 50° and 90° K), via the hydraulic accumulator ( B) connected to this circuit.

In the event of extreme cooling, a piston process occurs in the same manner as with brake-circuit failure, because of the volume change of the volume contained by the pistons (10)+(11)and the callipers

As already described in the above paragraph, following the transversal of the sealing ring (N1), the total supply pressure from accumulator A for mixed pressure is channelled into the piston module, thereby replacing the lost volume by thermodynamic means.

The processes described above are purely mechanical and thermal in nature, and no electricity is required; the operation occurs automatically and voltage-free.

Driver’s wish privilege

As described in 3.2, the connections (MC1) + (MC2) to the master brake cylinder are closed off when the parking brake is operated


When required, the motorist at all times has the possibility to correct the energised pressure of the parking brake by using the brake pedal. This is made possible by the non-return valve (R1) (R2), described in 3.0.

Comfort possibilities

The possibilities for the customers’ desired comfort features have previously been described under >Control Unit (Electronic) <.

The query of the seat belt, driver’s seat occupancy, open engine bay and boot, parking on a hill (angle sensor) is carried out by the electronic control unit, via the customer-specific CAN bus, K-line or flex rate.

Material used

We refer here to the hydraulic diagram and performance data provided for you in the annex.

With regard to the electronic control unit, we refer to the circuit block diagram and performance data, which is included in the annex.

The pressure sensors used are pressure sensors (PS1, PS2, PS3) from the automotive branch.(ABS)

The electro-hydraulic valves (1, 2, 3 and 4) are also from the automotive branch.

Previous test procedures

Up to this point in time, the following test procedures have been carried out:

Multiple testing of valves (EFA Group) with valve block, 220,000 load changes

Test of valves for impermeability : 90 days

Multiple working tests of the piston module, more than 220,000 load changes

Vehicle testing

Mercedes A 160

Version 1

Presentation of the vehicle at Daimler Chrysler, (Ing. Dieter Jurkschat)

TÜV Bayern – Technical Inspection Authority of Bavaria (Ing. Dieter Reiser)

and at Brembo/Italy. (Automotive Testing Engineer - Serge Tempestini)

Duration: Approximately 9 months

Lamborghini Murciélago

Versions 2 and 3 (differing in the use of a newer generation of electronic control unit)

Automotive testing approximately 10000 Kilometers

Beginning November 2005, testing at the Audi development department, Ingolstadt (Anton Hünnerkopf, Technical Director at Lamborghini) until November 2006

Renault Mascott, Light freight vehicle 6.5 tonnes

Version 2, 3 and the current version 4 (2 and 3 differ in their electronic control units. The current version 4 has been additionally equipped with a new piston module and a new valve block.)

Automotive testing approximately 20,000 kilometres

Presentation and evaluation at BWB Koblenz,

(Dipl. Ing Bernhard Jansen, Team Leader)

Herr Gernot Schwingeler, technical government representative,

Dipl. Ing. Paul Schneider, DaimlerChrysler HPC 162

Peter Leis, Head of Operations Krauss-Maffei Wegmann)

Presentation at the Bundeswehr Automotive Testing Centre in Trier

(Martin Gemmel, technical government representative for brake systems)

Presentation at the manufacturer of special vehicles based upon T5 (Volkswagen)

(Dr. rer. Nat. Dipl. Phys. Bernd Georgi, Technology Centre Manager VW,

Peter Seikel, Managing Director, Special Vehicle Development Auto Seikel)

Presentation at the DaimlerChrysler Dieter Jurkschat

Beginning April 2006 in Italy at the firm “Brembo” until November 2006 long time automotive testing on hill hold

Dipl. Ing Serge Tempestini

Presentation at a meeting with Krauss Maffei Wegmann Munich

to build in the brake system in to a Unimog truck of Daimler Chrysler

(Dipl. Ing Project Manager Raiko Trostorf, Dipl. Ing. Maximilian Hiebl,

Peter Leis, Head of Operations)

Evaluations (enclosed)

Test diagrams for the test-bed runs,

Vehicle pressure reading and temperature curves

The current developmental status is protected by a patent registration.

The patents are registered for the European Community, USA, Mexico, Brazil, Korea, and Japan.

Should you be in need of further information, we may be contacted at the following

e-mail address:


We will make the greatest effort to provide you with all of the information you require.

Status: November 2006

Legend :

1 inlet valve ( activations valve powerless closed)

2 outlet valve (deactivation valve powerless closed)

3 supply pressure valve ( powerless open)

4 Accumulator B for thermodynamic valve (powerless open)

5 Supply pressure pump


7 cylinder group

8 cylinder circuit 1

9 cylinder circuit 2

10 piston circuit 1

11 piston circuit 2

E1 inlet fluid parking brake

E2 inlet fluid supply pressure Acc A

A Accumulator supply pressure

B Accumulator thermodynamic

MC1 from master cylinder circuit 1

MC2 from master cylinder circuit 2

A1 outlet to ABS group circuit 1

A2outlet to ABS group circuit 2

N1O-ring rear position

N2O-ring middle position

N3O-ring front position shut off MC1 or MC2 by moving piston

R1chek valve MC1 to A1

R2chek valve MC2 to A2

ASspring loaded shut off valve

PS1pressure sensor circuit 1

PS2pressure sensor EFA group

PS3pressure sensor supply pressure

S1activations switch