XJ40 ( XJ81 ) 1986 - 1994

Teves ABS with yaw control

 
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Old 06-29-2018, 08:26 PM
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Question Teves ABS with yaw control

I picked up a 1994 XJ12 brochure and was looking through the specifications, and one that grabbed my attention was:

Teves computerized 4-wheel anti-lock brake system (ABS) with yaw control.
Looking up the usage of "yaw control" in the context of the Teves ABS system, it seems that may be the equivalent or similar to what is usually called electronic stability control (ESC):

https://en.wikipedia.org/wiki/Electr...bility_control

As far as I know, there is no traction control on the XJ40, which is also normally part of an ESC type function.

Any idea if the XJ40 Teves ABS system incorporated any sort of ESC type of function referencing the "yaw control" or what they mean by "yaw control" at all?

.
 
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Old 06-29-2018, 11:58 PM
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Hi Al,

I don't remember ever hearing about yaw control in an XJ40/XJ81, so that is very interesting. I've seen yaw control in later Jaguars. For example, in the X350 the ABS module contains a lateral accelerometer to sense lateral rotation. I believe "yaw control" can be accomplished based only on wheel speed sensor signals, so perhaps that was part of your car's ABS control module's programming.

The article at the link below seems to indicate that "yaw control" was a mechanical element of the suspension design, but you wouldn't think Jaguar would mention this in the context of the ABS system:

https://auto.howstuffworks.com/1938-...ar-sedans8.htm

I'll be curious to know if other members can illuminate us!

Cheers,

Don
 

Last edited by Don B; 06-30-2018 at 10:13 AM.
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Old 06-30-2018, 08:03 PM
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Default yaw wikipedia road vehicule

Road vehiclesEdit

Studying the stability of a road vehicle requires a reasonable approximation to the equations of motion.


Dynamics of a road vehicleThe diagram illustrates a four-wheel vehicle, in which the front axle is located a metres ahead of the centre of gravity and the rear axle is b metres towards the rear from the center of gravity. The body of the car is pointing in a direction (theta) while it is travelling in a direction (psi). In general, these are not the same. The tyre treads at the region of contact point in the direction of travel, but the hubs are aligned with the vehicle body, with the steering held central. The tyres distort as they rotate to accommodate this mis-alignment, and generate side forces as a consequence.

From directional stability study, denoting the angular velocity , the equations of motion are:The coefficient of will be called the 'damping' by analogy with a mass-spring-damper which has a similar equation of motion. By the same analogy, the coefficient of will be called the 'stiffness', as its function is to return the system to zero deflection, in the same manner as a spring.

The form of the solution depends only on the signs of the damping and stiffness terms. The four possible solution types are presented in the figure.



The only satisfactory solution requires both stiffness and damping to be positive. If the centre of gravity is ahead of the centre of the wheelbase (, this will always be positive, and the vehicle will be stable at all speeds. However, if it lies further aft, the term has the potential of becoming negative above a speed given by:Above this speed, the vehicle will be directionally (yaw) unstable. Corrections for relative effect of front and rear tyres and steering forces are available in the main article.
 
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Old 07-01-2018, 08:39 AM
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Thanks, yes there is a Teves system that includes traction and stability control, but just curious if or how the XJ40 Teves system claimed to provide yaw control as noted in the sales brochure.

For example, most traction or ESC systems have a way to manually disable them, usually via a dashboard button, but neither is available on the XJ40.

Perhaps it is a non-defeatable system, or maybe a brochure misprint? Or...?
 
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Old 07-02-2018, 04:07 PM
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Originally Posted by al_roethlisberger View Post
Perhaps it is a non-defeatable system, or maybe a brochure misprint? Or...?
It may have been a non-defeatable feature, or it may also have been a capability of the Teves system that was ultimately not implemented by Jaguar. I'm going to keep an eye out for any additional info whenever I'm reading the service documentation. I'm glad you found that reference - it may lead to increasing our knowledge of the system operation.

Cheers,

Don

 
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Old 07-03-2018, 07:09 AM
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I guess one thing that may help would be to identify which version of Teves series/model ABS system was fitted to the XJ40.

For example, the excerpt below suggests some Teves systems had traction control in the early 1990s:

https://books.google.com/books?id=hR...%20yaw&f=false

.
 
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Old 07-03-2018, 09:04 AM
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I don't know if you've seen the Power Hydraulic System manual that I am attaching, but you may find it interesting reading.The 1990 XJ40 Model Year Update, which is too large a file to attach to a post, states that the Teves system is the "same one used in the 1989 XJ-S." According to Kirby Palm's "Experience in a Book" for XJ-S owners, the system used in the 1989 XJ-S was the Teves Mk III, and it offers a good summary of the system:

Experience in a Book - Help for the Jaguar XJ-S Owner by Kirby Palm

The brake system DTC Summaries for the X300 indicates that those models used the Teves Mk IV system.

Cheers,

Don
 
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Last edited by Don B; 07-03-2018 at 09:08 AM.
 
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