WO2004031714A1

WO2004031714A1 - Device for controlling and regulating brake torque output from a hydraulic retarder in a motor vehicle

Info

Publication number: WO2004031714A1
Application number: PCT/SE2003/001555
Authority: WO
Inventors: Erik Lauri; Marcus Steen; Svante Karlsson
Original assignee: Volvo Lastvagnar Ab
Priority date: 2002-10-01
Filing date: 2003-10-01
Publication date: 2004-04-15
Also published as: AU2003268804A1; SE0202889D0

Abstract

The invention relates to a device for controlling and regulating the brake torque output from a hydraulic retarder (10, 20, 30) in a motor vehicle, in which the brake torque acts on a retarder output shaft (40) and in which the device comprises an actuator (5) for influencing the brake torque output of the retarder, and a control unit (4) for continuously controlling the actuator (5) on the basis of the required brake torque. A torque sensor (81) is designed to measure the brake torque output of the retarder, the control unit (4) using feedback from the torque sensor (81) to continuously control and regulate the actuator (5) and thereby adjust the brake torque output the required brake torque. A safety function is provided in the vehicle in order to warn the driver if the control unit is incapable of adjusting the brake torque to the required brake torque. The warning is based on information from the torque sensor (81).

Description

TITLE

Device for controlling and regulating brake torque output from a hydraulic retarder in a motor vehicle.

TECHNICAL FIELD

The present invention relates to a device for controlling and regulating brake torque output from a hydraulic retarder in a motor vehicle.

DESCRIPTION OF THE PRIOR ART

An auxiliary brake, a so-called retarder, is a type of brake used in motor vehicles, primarily in heavier vehicles, in order to relieve the service brakes on the vehicle .

A common type of hydraulic retarder comprises a stator which is firmly fixed to the vehicle and a moving part, a rotor, adjoining the stator. The rotor and stator are filled with a hydraulic fluid, for example oil or water, and have a space between them which is also filled with fluid. The brake torque from the retarder is transmitted to the rest of the vehicle by means of a shaft, which is fixed to the rotor so that the rotor is driven by the movement of the shaft. This shaft may be connected to the vehicle prop shaft by gears, for example, so that the brake torque is transmitted from the retarder to the vehicle drive wheels.

The brake torque in this type of retarder can be adjusted in that the pressure of the hydraulic fluid in a storage tank, which is connected to the retarder, is adjusted to a level that causes the rotor and the stator to interact at a torque equal to the desired brake torque. The hydraulic fluid pressure and hence the brake torque from the retarder are regulated by controlling the degree of opening of an actuator, usually a valve, which controls the supply of compressed air to the storage tank. In the storage tank the air pressure and the hydraulic fluid pressure are equal .

A problem in this context is the difficulty of correctly regulating the brake torque to a specific value. In existing hydraulic retarders the brake torque is measured indirectly by measuring the hydraulic fluid pressure or the air pressure in the storage tank. Together with the rotational speed of the retarder this provides a measure of the brake torque of the retarder. The correlation between pressure, rotational speed and brake torque, however, is not a very linear one. Due to tolerances in the manufacture of an efficiently functioning retarder, the actual brake torque may differ by up to +10 % for one and the same hydraulic fluid pressure and rotational speed in different specimens of a retarder. For a typical application in present-day vehicles this corresponds to a spread in the brake torque obtained of approximately 650 Nm for a retarder with a torque rating of 3 250 Nm. This means that two different vehicles equipped with similar retarders will react with different brake torques in response to the same demand. Other factors affecting the brake torque output are temperature variations, wear and changes in the characteristic properties of the hydraulic fluid.

WO 02087940 shows an example of the prior art, in which the brake torque output of the hydraulic retarder is regulated indirectly by measuring the hydraulic fluid pressure .

SUMMARY OF THE INVENTION

There is therefore a need for a device which is capable of regulating the hydraulic fluid pressure more precisely than hitherto, so that the brake torque output in a hydraulic retarder in a motor vehicle approximates as closely as possible to the required brake torque .

The present invention meets this need in that it affords a device for controlling and regulating brake torque output from a hydraulic retarder in a motor vehicle. The device comprises an actuator for influencing the brake torque output of the retarder and a control unit for continuously controlling the actuator on the basis of the required brake torque. The invention is characterized in that a torque sensor is designed to measure the brake torque output of the retarder, the control unit using feedback from the torque sensor to continuously control and regulate the actuator and thereby adjust the brake torque output to the required brake torque.

The invention permits the use of types of measuring element other than those used in the prior art, which gives a more precise measurement than could be obtained through the measuring principles hitherto used in hydraulic retarders.

The invention therefore permits a correct adjustment of the retarder brake torque to the required brake torque by measuring the actual brake torque, thereby making it possible to eliminate the influence of manufacturing tolerances on the brake torque, which results in the same brake performance from one specimen of the retarder to another.

Since the brake torque can be regulated more accurately, the vehicle braking can be regulated more precisely, for example with cruise control on downhill gradients or when jointly controlling multiple different brake elements. The invention also affords scope for rationalization of the retarder manufacturing process by permitting larger tolerances and a simpler mechanical construction. Regulating of the brake torque output of the retarder is therefore no longer a function of tolerances, temperature variations, wear and changes in the characteristic properties of the hydraulic fluid.

In one embodiment the invention also affords the facility for warning the driver of the vehicle that the retarder is not fully functional in instances where mechanical or hydraulic faults on the retarder mean that the required brake torque cannot be achieved.

In a further embodiment of the invention the retarder is controlled according to an emergency control table should the torque sensor signal fail.

DESCRIPTION OF THE DRAWINGS

The invention will be described in more detail below with reference to the drawings attached, in which

Fig. 1 shows the basic construction of a retarder, and Fig. 2 shows the retarder from fig 1 with a control and regulating device according to the invention, and Fig. 3 shows the basic construction of a gearbox in a heavy vehicle, equipped with a retarder and a torque sensor according to the invention, and

Fig. 4 shows the basic correlation between pressure in the storage tank, the rotational speed of the retarder, and the resulting brake torque.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Fig 1 shows in highly schematic form the principle of a hydraulic secondary brake or retarder viewed from above. The retarder comprises a fixed part, a stator, 10, which is fitted to the gearbox, and a moving part, a rotor, 20. The rotor and stator usually consist of so-called blade wheels which face one another. Brake torque can be transmitted to the vehicle from the retarder by means of a shaft 40, which is fixed to the rotor and thus in its movement carries the rotor with it. The shaft 40 meshes via a first gear wheel 50 and a second gear wheel 60 with the prop shaft 70 in the vehicle, and the brake torque can therefore be transmitted to the prop shaft from the retarder.

The movement of the parts in the arrangement in Fig. 1 is illustrated by means of circles containing a cross or a dot: a cross indicates a direction of movement "into the paper", a dot indicates the movement of the corresponding part "out of the paper" . It will be appreciated that the prop shaft 70 in the vehicle will cause the rotor 20 of the retarder to rotate, so that the rotor 20 will be able to exert a brake force on the prop shaft, and hence on the vehicle.

The blade wheels and a space 30 between them can be filled with a greater or lesser quantity of hydraulic fluid, usually oil. The hydraulic fluid constitutes the working medium of the retarder and creates forces between the blade wheels, which generates a brake torque on the shaft 40. More hydraulic fluid in the space 30 gives more brake torque and vice-versa. By varying the pressure in a storage tank 2, which is connected to the retarder via a hydraulic fluid line 3, it is possible to replenish the hydraulic fluid in the space 30. The draining of hydraulic fluid from the space 30 back to the storage tank 2 is done by means of hydraulic fluid lines (not shown) . The kinetic energy that is lost in braking is largely absorbed by the hydraulic fluid. The hydraulic fluid in the retarder therefore has to be cooled. The cooling system is also not shown in the figures . The control unit 4 regulates the quantity of hydraulic fluid in the space 30 in that a greater or lesser quantity of compressed air is forced into the storage tank, the compressed air displacing hydraulic fluid to the space 30. The control unit 4 regulates the quantity of compressed air by means of an actuator 5, which in the example of an embodiment shown consists of a compressed air valve. The actuator 5 is in turn connected to a compressed air source 6. The required brake torque is obtained by means of a brake control set by the driver of the vehicle and/or by means of an input signal from other systems 8 disposed in the vehicle, for example a cruise control unit and/or a so-called "brake blending" system

(a system in which the total brake torque is a blend of brake torque from the service brake and the auxiliary brake and in which the blend is automatically varied as a function of various parameters), etc. In the prior art the control unit 4 receives information on the brake torque output indirectly through feedback to the control unit 4 from the compressed air sensor 9 and information on the rotational speed of the retarder. The rotational speed of the retarder is obtained, for example, by means of a revolutions counter arranged in the vehicle gearbox. According to a table prestored in the control unit 4 a certain air pressure and a certain retarder speed correspond to a certain brake torque. The correlation between rotational speed and brake torque and each of the pressures p₄, p₃, p₂ and p_l7 for a hydraulic retarder is shown in schematic form in Fig. 4. The relationship between the pressures shown in Fig. 4 is p>p₃>P2>Pι- The Y-axis shows the brake torque M and the x-axis shows the rotational speed of the retarder in rpm. The prior art in Fig. 1 is shown greatly simplified.

The object of the present invention is to obtain from the retarder, with greater precision than hitherto, a brake torque which corresponds more accurately to the required brake torque . Fig. 2 shows the retarder from Fig. 1, together with a device according to the invention for improved control and regulation of the brake torque. The device comprises the shaft 40, which is used to transmit brake torque from the retarder to the vehicle, together with a first measuring element 80 and a second measuring element 85. The measuring elements with associated electronics constitute a torque sensor 81. The torque sensor is of a non-contact type known in the art.

When the shaft 40 rotates the rotor 10 in the retarder the shaft will be subjected to a certain deformation, which is proportional to the brake torque. By measuring this deformation the measuring elements according to the invention can obtain a correct value for the braking effect obtained via the retarder.

The exact type of measuring element used is not central to the invention, but it is essential that the measuring principle used allows the shaft 40 to rotate freely. In a preferred embodiment the first measuring element 80, which is located on the shaft, is made of a magnetic material and has been given a certain predefined pattern or design. When the shaft is deformed the pattern of the measuring element will be deformed, which is detected by the second measuring element 85, which in this embodiment is a coil. In the coil an electrical signal is generated which is proportional to the deformation of the magnetic pattern and therefore also proportional to the deformation of the shaft and to the brake torque .

The electrical signal which is generated in the coil and which indicates the magnitude of the brake torque allows the control unit 4 to regulate the brake torque correctly, this being achieved by regulating the hydraulic fluid pressure in the retarder via the actuator 5, which in the example of an embodiment shown is a compressed air valve. Thus the brake torque from the retarder is subject to direct regulation which is independent of tolerances, temperature variations, wear and changes in the characteristic properties of the hydraulic fluid. The control unit 4 therefore does not need to contain the said prestored table in which a certain air pressure and a certain retarder speed correspond to a certain brake torque . The tolerance interval for the constituent components of the retarder can be widened without regulating errors occurring. Wider tolerance intervals make it possible to use less expensive methods of manufacture. The design construction of the retarder can possibly be simplified in that a larger spread may be permitted in the correlation between hydraulic fluid pressure, retarder speed and brake torque in different specimens of the same retarder. Overdimensioning on the grounds that certain specimens of the retarder are expected to register more than a maximum permitted brake torque can be reduced. The vehicles in a fleet of vehicles equipped with the device according to the invention will give a more uniform performance in retarder braking, which is of particular advantage where the drivers change vehicles .

In a preferred embodiment of the invention the torque sensor is used in a safety function to warn the driver of the vehicle, by means of a message or warning light on the vehicle instrument panel, for example, if the retarder for any reason cannot deliver the required brake torque, that is to say if the performance of the retarder no longer conforms to the expected norm. Such reasons might include insufficient hydraulic fluid in the hydraulic fluid system of the retarder or various mechanical/hydraulic failures.

In a further embodiment of the invention the device according to the invention is equipped with an emergency function should the torque sensor 81 for any reason cease to supply brake torque information to the control unit 4. A memory unit arranged in the control unit 4, for example, stores the control signal to the actuator 5 in the form, for example, of various control currents for the actuator 5, or any measured signal related to the brake torque, such as the pressure in the storage tank, together with a retarder speed and corresponding brake torque output in an emergency control table. The emergency control table can be used for emergency control of the retarder if the torque sensor 81 should cease to function. The emergency control table can be updated continuously in normal operation, that is to say when the torque sensor is functioning, or the table alternatively prestored in the control unit .

Fig. 3 shows a schematic sketch of a gearbox in a heavy vehicle, with a retarder and a measuring device according to the invention. The parts shown in Fig. 1 and 2 will be recognized and have been given corresponding reference numbers .

In Fig. 3 the device according to the invention, including the retarder (not shown) , is part of the gearbox. However, the invention is naturally just as applicable regardless of whether the retarder is situated inside or outside the gearbox.

A large number of other non-contact measuring methods can furthermore be used without departing from the scope of the invention, and the number of measuring elements on or connected to the retarder shaft (component) is not limited to one of each. More than two interacting measuring elements may be needed in certain applications in order to achieve the required measuring accuracy. The torque sensor can measure the brake torque output of the retarder on the retarder output shaft (according to the examples of embodiment shown in Fig. 2 and 3) , or the brake torque output of the retarder can be measured, for example, on an intermediate shaft arranged between the retarder output shaft and the prop shaft . It is important that the shaft on which the brake torque is measured should only be subjected to a retarder brake torque load in retarder braking. This arrangement makes it possible to set the retarder brake torque to the required level with great precision.

In an alternative embodiment the hydraulic fluid and hence the retarder working medium may consist mainly of water.

The invention is not limited to the examples of embodiments described above but can be freely modified within the scope of the following claims . The component in or adjacent to the retarder on or adjacent to which the measuring elements are arranged can, in principle, be any component that is deformed in proportion to the retarder brake torque .

Claims

l.A device for controlling and regulating brake torque output from a hydraulic retarder (10, 20, 30) in a motor vehicle, in which the device comprises an actuator (5) for influencing the brake torque output of the retarder and a control unit (4) for continuously controlling the actuator (5) on the basis of the required brake torque, characterized in that a torque sensor (81) is designed to measure the brake torque output of the retarder, the control unit

(4) using feedback from the torque sensor (81) to continuously control and regulate the actuator (5) and thereby adjust the brake torque output to the required brake torque.

2. The device as claimed in claim 1, characterized in that the torque sensor (81) measures the retarder output torque on a shaft (40) that is subject only to a retarder brake torque load.

3. The device as claimed in claim 1, characterized in that the actuator (5) is a valve for controlling of the flow of working medium to and/or the quantity of working medium in the retarder.

4. The device as claimed in claim 1, characterized in that the torque sensor (81) comprises a first measuring element (80) and a second measuring element (85) , the first measuring element (80) being arranged on a shaft (40) in the retarder that is deformed in proportion to the brake torque and the second measuring element (85) being arranged adjacent to said shaft (40) in the retarder, the measuring elements interacting with one another without coming into contact . The device as claimed in claim 4, characterized in that .the first measuring element (80) is arranged on a shaft (40) in the retarder that is deformed in proportion to the brake torque.

The device as claimed in any one of the preceding claims, characterized in that a safety function is provided in the motor vehicle in order to warn the driver of the vehicle if the control unit (4) is incapable of adjusting the brake torque to the required brake torque and that the warning is based on the torque measured by the torque sensor (81) .

The device as claimed in any one of the preceding claims, characterized in that if the control unit

(4) cannot obtain brake torque information from the torque sensor (81) , the control unit (4) is designed to control the brake torque output according to an emergency control table, which contains information on the control signal to the actuator (5) or any measured signal that is related to the brake torque, retarder speed and corresponding brake torque.

The device as claimed in claim 7, characterized in that the control unit (4) continuously updates the emergency control table by means of information on the retarder brake torque from the torque sensor.